WO2006113427A2 - Dual conversion gain imager pixel using schottky and ohmic contacts to the floating diffusion region and methods of fabrication and operation - Google Patents

Dual conversion gain imager pixel using schottky and ohmic contacts to the floating diffusion region and methods of fabrication and operation

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Publication number
WO2006113427A2
WO2006113427A2 PCT/US2006/014054 US2006014054W WO2006113427A2 WO 2006113427 A2 WO2006113427 A2 WO 2006113427A2 US 2006014054 W US2006014054 W US 2006014054W WO 2006113427 A2 WO2006113427 A2 WO 2006113427A2
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WO
WIPO (PCT)
Prior art keywords
diffusion region
charge
conversion gain
pixel
transistor
Prior art date
Application number
PCT/US2006/014054
Other languages
French (fr)
Other versions
WO2006113427A3 (en
Inventor
Inna Patrick
Sungkwon Hong
Jeffrey A. Mckee
Original Assignee
Micron Technology, Inc.
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Filing date
Publication date
Application filed by Micron Technology, Inc. filed Critical Micron Technology, Inc.
Priority to EP06750164A priority Critical patent/EP1872403A2/en
Priority to JP2008506737A priority patent/JP2008537340A/en
Publication of WO2006113427A2 publication Critical patent/WO2006113427A2/en
Publication of WO2006113427A3 publication Critical patent/WO2006113427A3/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14601—Structural or functional details thereof
    • H01L27/14609—Pixel-elements with integrated switching, control, storage or amplification elements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14601—Structural or functional details thereof
    • H01L27/14641—Electronic components shared by two or more pixel-elements, e.g. one amplifier shared by two pixel elements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14643—Photodiode arrays; MOS imagers
    • H01L27/14654—Blooming suppression
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
    • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/86—Types of semiconductor device ; Multistep manufacturing processes therefor controllable only by variation of the electric current supplied, or only the electric potential applied, to one or more of the electrodes carrying the current to be rectified, amplified, oscillated or switched
    • H01L29/861—Diodes
    • H01L29/872—Schottky diodes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/50—Control of the SSIS exposure
    • H04N25/57—Control of the dynamic range
    • H04N25/59—Control of the dynamic range by controlling the amount of charge storable in the pixel, e.g. modification of the charge conversion ratio of the floating node capacitance

Definitions

  • the invention relates generally to imaging devices and more particularly to dual conversion gain imaging devices.
  • Imaging devices including charge coupled devices (CCD) and complementary metal oxide semiconductor (CMOS) imagers, are commonly used in photo-imaging applications.
  • CCD charge coupled devices
  • CMOS complementary metal oxide semiconductor
  • a CMOS imager circuit includes a focal plane array of pixels, each of the pixels including a photosensor, for example, a photogate, photoconductor or a photodiode for accumulating photo-generated charge a portion of the substrate.
  • a photosensor for example, a photogate, photoconductor or a photodiode for accumulating photo-generated charge a portion of the substrate.
  • Each pixel has a charge storage region, formed on or in the substrate, which is connected to the gate of an output transistor that is part of a readout circuit.
  • the charge storage region may be constructed as a floating diffusion region.
  • each pixel may include at least one electronic device such as a transistor for transferring charge from the photosensor to the storage region and one device, also typically a transistor, for resetting the storage region to a predetermined charge level prior to charge transference.
  • the active elements of a pixel perform the necessary functions of: (1) photon to charge conversion; (2) accumulation of image charge; (3) resetting the storage region to a known state; (4) transfer of charge to the storage region accompanied by charge amplification; (5) selection of a pixel for readout; and (6) output and amplification of a signal representing a reset level and pixel charge.
  • Photo charge may be amplified when it moves from the initial charge accumulation region to the storage region.
  • the charge at the storage region is typically converted to a pixel output voltage by a source follower output transistor.
  • CMOS imagers of the type discussed above are generally known as discussed, for example, in U.S. Patent no. 6,140,630, U.S. Patent no. 6,376,868, U.S. Patent no. 6,310,366, U.S. Patent no. 6,326,652, U.S. Patent no. 6,204,524 and U.S. Patent no. 6,333,205, assigned to Micron Technology, Inc., which are hereby incorporated by reference in their entirety.
  • FIG. 1 A typical four transistor (4T) CMOS image pixel 10 is shown in FIG. 1.
  • the pixel 10 includes a photosensor 12 (e.g., photodiode, photogate, etc.), transfer transistor 14, floating diffusion region FD, reset transistor 16, source follower transistor 18 and row select transistor 20.
  • the photosensor 12 is connected to the floating diffusion region FD by the transfer transistor 14 when the transfer transistor 14 is activated by a transfer gate control signal TX.
  • the reset transistor 16 is connected between the floating diffusion region FD and an array pixel supply voltage Vaa_pix.
  • a reset control signal RST is used to activate the reset transistor 16, which resets the floating diffusion region FD to the array pixel supply voltage Vaa_pix level.
  • the source follower transistor 18 has its gate connected to the floating diffusion region FD and is connected between the array pixel supply voltage Vaa_pix and the row select transistor 20.
  • the source follower transistor 18 converts the charge stored at the floating diffusion region FD into electrical output voltage signals Vrst, which is produced when the floating diffusion region FD is reset, and Vsig, which is produced after charge is transferred by transistor 14 from the photosensor 12 to the floating diffusion region FD.
  • the row select transistor 20 is controllable by a row select signal SEL for selectively connecting the source follower transistor 18 and its output voltage signal Vout to a column line 22 of a pixel array.
  • An important performance characteristic of any imager is its dynamic range.
  • a large dynamic range is desirable in applications for sensing low light signals and capturing images with large variations in illuminance or brightness.
  • the dynamic range of an imager can be defined as the ratio of the minimum illuminance the imager detects under saturation to the illuminance the imager detects at a signal-to-noise ratio (SNR) equal to one.
  • SNR signal-to-noise ratio
  • the dynamic range of a scene can also be expressed as the ratio of its highest illumination level to its lowest illumination level.
  • Intrascene dynamic range refers to the range of incident signals that can be accommodated by an imager in a single frame of image data. Examples of scenes that generate high dynamic range incident signals include an indoor room with outdoor window, outdoor mixed shadow and bright sunshine, night time scenes combining artificial lighting and shadows, and in an automotive context, an automobile entering or about to leave a tunnel or shadowed area on a bright day.
  • FIG. 2 illustrates a block diagram of a CMOS imager device 308 having a pixel array 240 with each pixel being constructed as described above or in accordance with other known pixel architectures.
  • Pixel array 240 comprises a plurality of pixels arranged in a predetermined number of columns and rows. The pixels of each row in array 240 are all turned on at the same time by a row select line, and the pixels of each column are selectively output by respective column select lines. A plurality of row and column lines are provided for the entire array 240. The row lines are selectively activated by the row driver 245 in response to row address decoder 255 and the column select lines are selectively activated by the column driver 260 in response to column address decoder 270. Thus, a row and column address is provided for each pixel.
  • the imager 308 is operated by a control circuit 250, which controls address decoders 255, 270 for selecting the appropriate row and column lines for pixel readout, and row and column driver circuitry 245, 260 which apply driving voltages to the drive transistors of the selected row and column lines.
  • the pixel column signals which typically include a pixel reset signal Vrst and a pixel image signal Vsig are read by sample and hold circuitry 261 associated with the column device 260.
  • a differential signal Vrst - Vsig is produced and amplified by a differential amplifier 262.
  • the differential signal is digitized by an analog-to-digital converter 275.
  • the analog-to-digital converter 275 converts the analog differential signals to digital signals that are fed to an image processor 280 to form and output a digital image.
  • the illumination-voltage profile of the conventional pixel 10 (FIG. 1) for the photo-charge converted signal Vsig is typically linear as shown in FIG. 3, which illustrates an illumination versus voltage graph of the prior art pixel 10.
  • the pixel's 10 maximum voltage Vmax may be reached at a relatively low level of illumination Imax, which causes the pixel 10 to be easily saturated.
  • Imax level of illumination
  • the photosensor 12 When the light captured and converted into charge by the photosensor 12 is greater than the capacity of the photosensor 12, excess charge may overflow and be transferred into the substrate and to adjacent pixels, which is undesirable.
  • the present invention in the exemplary embodiments provides an imager with dual conversion gain charge storage and thus, improved dynamic range.
  • a dual conversion gain element e.g., Schottky diode
  • the dual conversion gain element switches in the capacitance of the capacitor, in response to charge stored at the floating diffusion region, to change the conversion gain of the floating diffusion region from a first conversion gain to a second conversion gain.
  • the invention provides in exemplary embodiments an ohmic contact between the gate of a source follower transistor and the floating diffusion region which assists in the readout of the dual conversion gain output signal of a pixel.
  • FIG. 1 is a schematic diagram of a four-transistor (4T) pixel
  • FIG. 2 is a block diagram of an imaging device
  • FIG. 3 illustrates an exemplary luminescence versus voltage graph for the pixel of FIG. 1;
  • FIG. 4 illustrates an exemplary floating diffusion region in accordance with an embodiment of the invention
  • FIG.5 illustrates an exemplary illumination versus voltage graph in accordance with an embodiment of the invention
  • FIG. 6 is a potential diagram illustrating the operation of the FIG. 4 pixel
  • FIG. 7 illustrates an exemplary circuit diagram in accordance with an embodiment of the invention
  • FIG. 8 illustrates an exemplary top-down view of a 4-way shared pixel implementation according to an exemplary embodiment of the invention.
  • FIG. 9 illustrates a processor system incorporating at least one imager device in accordance with an embodiment of the invention.
  • substrate is to be understood as a semiconductor- based material including silicon, silicon-on-insulator (SOI) or silicon-on-sapphire (SOS) technology, doped and undoped semiconductors, epitaxial layers of silicon supported by a base semiconductor foundation, and other semiconductor structures.
  • SOI silicon-on-insulator
  • SOS silicon-on-sapphire
  • doped and undoped semiconductors epitaxial layers of silicon supported by a base semiconductor foundation, and other semiconductor structures.
  • previous process steps may have been utilized to form regions or junctions in the base semiconductor structure or foundation.
  • the semiconductor need not be silicon-based, but could be based on silicon-germanium, germanium, or gallium arsenide.
  • pixel refers to a picture element unit cell containing a photosensor and transistors for converting light radiation to an electrical signal.
  • a representative pixel is illustrated in the figures and description herein and, typically, fabrication of all pixels in an imager array will proceed simultaneously in a similar fashion.
  • FIG.4 illustrates a cross-section of a portion of an exemplary pixel 110 constructed in accordance with an embodiment of the invention.
  • the pixel 110 contains a floating diffusion region 30, which receives charge from a photosensor, illustrated in FIG. 4 as a p-n-p diode, through a transfer transistor 14.
  • a dual conversion gain switch element of the pixel 110 is formed between the floating diffusion region 30 and a capacitor Cl.
  • the dual conversion gain switch element is a Schottky contact 32 which forms a Schottky diode.
  • An ohmic contact 34 is formed between the floating diffusion region 30 and a source follower transistor gate 18.
  • the ohmic contact 34 is formed by an n+ doped region 34 within the n- doped floating diffusion region.
  • the Schottky contact 32 is formed on the n- doped floating diffusion region 30 which is in contact with a p-type layer 26.
  • the contact 32 allows for the realization of a dual conversion gain pixel. That is, as is explained below in more detail, the pixel 110 will have a first conversion gain under a lower level of charge transferred to the floating diffusion region 30 cause by relatively lower levels of incident light and a second conversion gain under higher levels of charge transferred to the floating diffusion region 30 caused by relatively higher levels of incident light.
  • the Schottky contact 32 creates the occurrence of a "knee" in the illumination response (see FIG. 5), where the response and the knee are determined by the barrier height of the Schottky contact 32.
  • FIG. 7 illustrates the equivalent circuit diagram of the pixel 110 of FIG. 4. That is, the pixel 110 includes a photosensor 12 which is connected to the transfer transistor 14. The transfer transistor 14 transfers charge to the floating diffusion region 30. A reset transistor 16 is connected between the floating diffusion region 30 and an array pixel supply voltage Vaa_pix. A reset control signal RST is used to activate the reset transistor 16, which resets the floating diffusion region 30 to the array pixel supply voltage Vaa_pix level.
  • the source follower transistor 18 has its gate connected to the floating diffusion region 30 and is connected between the array pixel supply voltage Vaa_pix and the row select transistor 20.
  • the source follower transistor 18 converts the charge stored at the floating diffusion region 30 into electrical output voltage signals Vrst, which is produced when the floating diffusion region 30 is reset, and Vsig, which is produced after charge is transferred by transistor 14 from the photosensor 12 to the floating diffusion region 30.
  • the row select transistor 20 is controllable by a row select signal SEL for selectively connecting the source follower transistor 18 and its output voltage signal Vout to a column line 22 of a pixel array.
  • the Schottky contact 32 forming a Schottky diode, is connect to the floating diffusion region 30.
  • a low resistance ohmic contact 34 is formed with the floating diffusion region 30, as illustrated in FIG. 4. To form the contact 34, a small n+ region is formed in the floating diffusion region 30 which is doped n- elsewhere. The ohmic contact 34 creates a buffer between the gate of the source follower transistor 18 and the floating diffusion region 30.
  • An exemplary doping level of the ohmic contact 34 is between Ie x 10 14 - 4e x 10 15 atoms per cm 3 and is preferably 2e x 10 15 atoms per cm 3 .
  • the low resistance ohmic contact 34 lowers the gate barrier of the source follower transistor and permits the effects of the Schottky diode 32 to be seen at the output of the source follower transistor 18.
  • the Schottky diode 32 also referred to as a barrier or contact, is formed above the floating diffusion region 30.
  • FIG.4 illustrates that the Schottky diode 32 is formed above the floating diffusion region 30, the diode 32 may alternatively be formed within the floating diffusion region 30.
  • the diode 32 may be formed of either pure a metal or metal silicide layer 32 when contacting the n- silicon layer 30.
  • Exemplary metal silicide materials that may be used for the Schottky diode include tungsten (We), cobalt silicide (CoSk), platinum silicide (PtSi) and titanium silicide (TaSi.).
  • the barrier for each of these silicides is 0.55-0.93V which must be exceed for the diode switch to activate.
  • the material chosen for a particular application depends on the reproducibility and temperature stability of the diode based on the particular material chosen. Additionally, pure metals silver (Ag), aluminum (Al), gold (Au), chromium (Cr), hafnium (Hf), magnesium (Mg), molybdenum (Mo), nickel (Ni), palladium (Pd), platinum (Pt), titanium (Ti) and tungsten (W) may also be used to form Schottky diodes on an n-type silicon.
  • the barrier for these metals is from about 0.5-0.9V.
  • a conductive metal nitride layer (e.g., TiN) is used as the thin barrier layer 38 during contact 32 formation (e.g., Schottky diode formation), as shown in FIG.4.
  • a conductive metal nitride layer e.g., TiN
  • Pt-based Schottky diodes are known to result in a very low barrier and are therefore, easily reproducible diodes.
  • Ti would result in a very low barrier on n-type silicon, however, TiSi formation at a low temperature, employed in conventional silicon processing, raises this barrier. Therefore, any one of a number of materials may be used to implement a very low Schottky diode to n-type silicon, however, the invention, described herein, does not require a very low barrier to n-type silicon.
  • the barrier height may be adjusted by material selection or adjusting the n- doping concentration to result in a desired "knee" for the conversion gain.
  • the Schottky contact 32 electrically allows for the realization of an automatic dual conversion gain pixel.
  • the source follower transistor 18 converts the charge at the floating diffusion region 30 into an electrical output voltage.
  • the ohmic contact 34 which connects the gate of the source follower transistor 18 to the floating diffusion region 30, lowers the barrier potential at the gate of the source follower transistor and allows the source follower transistor 18 to capture the full extent of the voltage swing produced by charges stored at the floating diffusion region 30 and in the capacitor Cl when the Schottky diode 32 couples the capacitor Cl to the floating diffusion region 30.
  • the knee in the illumination versus output voltage produced by the Schottky contact 32 as shown in FIG. 5, can be purposely reflected in the output voltage of the source follower transistor 18 due to the ohmic contact 34.
  • FIG. 5 illustrates an exemplary pixel illumination versus output voltage graph in accordance with the invention.
  • the term knee reflects the fact that the graph creates an angle in the illumination-voltage profile, such that the maximum saturation voltage is reached at a greater level of illumination, point B, than that prior art pixel, point A, as illustrated in FIG. 3.
  • the illumination-voltage profile continues at an angle until the threshold voltage of the diode 32 is met. Once the threshold voltage of the diode is met, the knee is created, point C, and a new illumination- voltage profile angle is created.
  • point B on the chart is the illumination-voltage point at which saturation occurs when realizing the dual conversion gain, whereas the saturation point would be at point A for an implementation not realizing the dual conversion gain aspects of the invention.
  • the target barrier height of the Schottky diode 32 is selected based on where it is determined that the knee response is best based on the particular application.
  • the knee point is the point at which the dual conversion of the proposed dual conversion gain pixel changes from high conversion gain (needed for low signal level), to low conversion gain (needed for high signal level). For example, if the point of saturation is 1.0 V on the floating diffusion region 30, and the knee is desired at 0.4 V, the Schottky diode barrier height is targeted at 0.4V.
  • the knee can be expressed as a fraction of the saturation signal.
  • the current W/TiN/Ti contact process may be used and the intrinsic Schottky diode 32 may be adjusted by implantation.
  • the Schottky diode 32 may be formed of a Ti layer 36 which is in direct contact with the n- floating diffusion region 30, a TiN barrier layer 38 is formed on top of the Ti layer 36 and a W layer 40 formed on top of the TiN layer 38.
  • the intrinsic Schottky diode 32 barrier height is due to the difference in the workfunction and can be further adjusted by adding n- type or p-type doping to silicon in the contact region. Therefore, the final diode 32 barrier height will depend on the material selection and annealing and implantation conditions.
  • FIG. 6 illustrates an exemplary potential energy versus capacitance graph for the pixel 110 of FIG.4.
  • charge is collected in the photodiode PD it reaches it maximum collection point at a pinning voltage Vpin.
  • the transfer transistor is activated, the charge is transferred to the floating diffusion region 30.
  • the amount of charge that the floating diffusion region 30 alone can hold is illustrated by section 2.
  • additional charge may be collected as illustrated by section 1.
  • the above described Schottky diode 32 and ohmic contact may also be implemented in a shared pixel arrangement, as illustrated in FIG. 8.
  • FIG, 8 illustrates a top down view of a 4-way shared pixel implementation.
  • the photosensors 12a, 12b, 12c, 12d each have a corresponding transfer transistor 14a, 14b, 14c, 14d which transfers charge to the floating diffusion region 30.
  • the photosensors 12a, 12b, 12c, 12d share a reset transistor 16, a source follower transistor 18, a row select transistor 20, a floating diffusion region 30 and capacitor Cl.
  • FIG. 8 illustrates a 4-way shared implementation, the Schottky diode 32 and ohmic contact 34 described above may be implemented with other shared pixel or non-shared pixel arrangements.
  • FIG. 9 shows system 300, a typical processor system modified to include an imaging device 200 containing the pixel 110 of the invention.
  • Imaging device 200 is similar to device 308 (FIG. 2) with the exception that the array 240 comprises pixels 110 constructed in accordance with the invention.
  • the processor-based system 300 is exemplary of a system having digital circuits that could include image sensor devices. Without being limiting, such a system could include a computer system, camera system, scanner, machine vision, vehicle navigation, video phone, surveillance system, auto focus system, star tracker system, motion detection system, image stabilization system, and data compression system.
  • System 300 for example a camera system, generally comprises a central processing unit (CPU) 302, such as a microprocessor, that communicates with an input/output (I/O) device 306 over a bus 304.
  • Imaging device 200 also communicates with the CPU 302 over the bus 304.
  • the processor-based system 300 also includes random access memory (RAM) 310, and can include removable memory 315, such as flash memory, which also communicate with the CPU 302 over the bus 304.
  • the imaging device 200 may be combined with a processor, such as a CPU, digital signal processor, or microprocessor, with or without memory storage on a single integrated circuit or on a different chip than the processor.
  • the above described embodiments may be implemented in a manner similar to the imager device illustrated in FIG. 2.
  • the pixel array 240, of FIG.2 may be comprised of the above described pixels 110 having a Schottky diode 32 and ohmic contact 34.
  • a method of fabricating a dual conversion gain pixel comprises the acts of fabricating a photosensitive region within a substrate, forming a first transistor within the substrate for resetting the pixel, providing a floating diffusion region within said substrate, the floating diffusion region having a first capacitance, providing a second transistor between the photosensitive region and the floating diffusion region, the second transistor being controllable to transfer charge from the photosensitive region to the floating diffusion region, forming a capacitive element over the substrate; and forming a Schottky diode within and above the substrate, wherein the diode is connected between the diffusion region and the capacitive element such that when the diode is activated, a capacitance of the capacitive element is added to the first capacitance of the floating diffusion region.

Abstract

An imager with dual conversion gain charge storage, and thus improved dynamic range, comprises a dual conversion gain element (e.g., Schottky diode) coupled between a floating diffusion region and a respective capacitor. The dual conversion gain element switches in the capacitance of the capacitor, in response to charge stored at the floating diffusion region, to change the conversion gain of the floating diffusion region from a first conversion gain to a second conversion gain. An ohmic contact between the gate of a source follower transistor and the floating diffusion region assists in the readout of the dual conversion gain output signal of a pixel.

Description

DUAL CONVERSION GAIN IMAGER PIXEL USING SCHOTTKY AND OHMIC CONTACTS TO THE FLOATING DIFFUSION REGION AND METHODS OF
FABRICATION AND OPERATION
FIELD OF THE INVENTION
[0001] The invention relates generally to imaging devices and more particularly to dual conversion gain imaging devices.
BACKGROUND OF THE INVENTION
[0002] Imaging devices, including charge coupled devices (CCD) and complementary metal oxide semiconductor (CMOS) imagers, are commonly used in photo-imaging applications.
[0003] A CMOS imager circuit includes a focal plane array of pixels, each of the pixels including a photosensor, for example, a photogate, photoconductor or a photodiode for accumulating photo-generated charge a portion of the substrate. Each pixel has a charge storage region, formed on or in the substrate, which is connected to the gate of an output transistor that is part of a readout circuit. The charge storage region may be constructed as a floating diffusion region. In some imager circuits, each pixel may include at least one electronic device such as a transistor for transferring charge from the photosensor to the storage region and one device, also typically a transistor, for resetting the storage region to a predetermined charge level prior to charge transference.
[0004] In a CMOS imager, the active elements of a pixel perform the necessary functions of: (1) photon to charge conversion; (2) accumulation of image charge; (3) resetting the storage region to a known state; (4) transfer of charge to the storage region accompanied by charge amplification; (5) selection of a pixel for readout; and (6) output and amplification of a signal representing a reset level and pixel charge. Photo charge may be amplified when it moves from the initial charge accumulation region to the storage region. The charge at the storage region is typically converted to a pixel output voltage by a source follower output transistor.
[0005] CMOS imagers of the type discussed above are generally known as discussed, for example, in U.S. Patent no. 6,140,630, U.S. Patent no. 6,376,868, U.S. Patent no. 6,310,366, U.S. Patent no. 6,326,652, U.S. Patent no. 6,204,524 and U.S. Patent no. 6,333,205, assigned to Micron Technology, Inc., which are hereby incorporated by reference in their entirety.
[0006] A typical four transistor (4T) CMOS image pixel 10 is shown in FIG. 1. The pixel 10 includes a photosensor 12 (e.g., photodiode, photogate, etc.), transfer transistor 14, floating diffusion region FD, reset transistor 16, source follower transistor 18 and row select transistor 20. The photosensor 12 is connected to the floating diffusion region FD by the transfer transistor 14 when the transfer transistor 14 is activated by a transfer gate control signal TX.
[0007] The reset transistor 16 is connected between the floating diffusion region FD and an array pixel supply voltage Vaa_pix. A reset control signal RST is used to activate the reset transistor 16, which resets the floating diffusion region FD to the array pixel supply voltage Vaa_pix level.
[0008] The source follower transistor 18 has its gate connected to the floating diffusion region FD and is connected between the array pixel supply voltage Vaa_pix and the row select transistor 20. The source follower transistor 18 converts the charge stored at the floating diffusion region FD into electrical output voltage signals Vrst, which is produced when the floating diffusion region FD is reset, and Vsig, which is produced after charge is transferred by transistor 14 from the photosensor 12 to the floating diffusion region FD. The row select transistor 20 is controllable by a row select signal SEL for selectively connecting the source follower transistor 18 and its output voltage signal Vout to a column line 22 of a pixel array.
[0009] An important performance characteristic of any imager is its dynamic range. A large dynamic range is desirable in applications for sensing low light signals and capturing images with large variations in illuminance or brightness. In particular, the dynamic range of an imager can be defined as the ratio of the minimum illuminance the imager detects under saturation to the illuminance the imager detects at a signal-to-noise ratio (SNR) equal to one. The dynamic range of a scene can also be expressed as the ratio of its highest illumination level to its lowest illumination level.
[00010] Intrascene dynamic range refers to the range of incident signals that can be accommodated by an imager in a single frame of image data. Examples of scenes that generate high dynamic range incident signals include an indoor room with outdoor window, outdoor mixed shadow and bright sunshine, night time scenes combining artificial lighting and shadows, and in an automotive context, an automobile entering or about to leave a tunnel or shadowed area on a bright day.
[00011] FIG. 2 illustrates a block diagram of a CMOS imager device 308 having a pixel array 240 with each pixel being constructed as described above or in accordance with other known pixel architectures. Pixel array 240 comprises a plurality of pixels arranged in a predetermined number of columns and rows. The pixels of each row in array 240 are all turned on at the same time by a row select line, and the pixels of each column are selectively output by respective column select lines. A plurality of row and column lines are provided for the entire array 240. The row lines are selectively activated by the row driver 245 in response to row address decoder 255 and the column select lines are selectively activated by the column driver 260 in response to column address decoder 270. Thus, a row and column address is provided for each pixel.
[00012] The imager 308 is operated by a control circuit 250, which controls address decoders 255, 270 for selecting the appropriate row and column lines for pixel readout, and row and column driver circuitry 245, 260 which apply driving voltages to the drive transistors of the selected row and column lines. The pixel column signals, which typically include a pixel reset signal Vrst and a pixel image signal Vsig are read by sample and hold circuitry 261 associated with the column device 260. A differential signal Vrst - Vsig is produced and amplified by a differential amplifier 262. The differential signal is digitized by an analog-to-digital converter 275. The analog-to-digital converter 275 converts the analog differential signals to digital signals that are fed to an image processor 280 to form and output a digital image.
[00013] The illumination-voltage profile of the conventional pixel 10 (FIG. 1) for the photo-charge converted signal Vsig is typically linear as shown in FIG. 3, which illustrates an illumination versus voltage graph of the prior art pixel 10. The pixel's 10 maximum voltage Vmax may be reached at a relatively low level of illumination Imax, which causes the pixel 10 to be easily saturated. When the light captured and converted into charge by the photosensor 12 is greater than the capacity of the photosensor 12, excess charge may overflow and be transferred into the substrate and to adjacent pixels, which is undesirable. Thus, there is a desire and need for an improved saturation response in imager pixels 10 and imagers 308 in general. Improved saturation response will improve the imager's dynamic range. BRIEF SUMMARY OF THE INWNTION
[00014] The present invention in the exemplary embodiments provides an imager with dual conversion gain charge storage and thus, improved dynamic range. A dual conversion gain element (e.g., Schottky diode) is coupled between a floating diffusion region and a respective capacitor. The dual conversion gain element switches in the capacitance of the capacitor, in response to charge stored at the floating diffusion region, to change the conversion gain of the floating diffusion region from a first conversion gain to a second conversion gain.
[00015] In an additional aspect, the invention provides in exemplary embodiments an ohmic contact between the gate of a source follower transistor and the floating diffusion region which assists in the readout of the dual conversion gain output signal of a pixel.
BRIEF DESCRIPTION OF THE DRAWINGS
[00016] These and other features and advantages of the invention will be better understood from the following detailed description, which is provided in connection with the accompanying drawings in which:
[00017] FIG. 1 is a schematic diagram of a four-transistor (4T) pixel;
[00018] FIG. 2 is a block diagram of an imaging device;
[00019] FIG. 3 illustrates an exemplary luminescence versus voltage graph for the pixel of FIG. 1;
[00020] FIG. 4 illustrates an exemplary floating diffusion region in accordance with an embodiment of the invention; [00021] FIG.5 illustrates an exemplary illumination versus voltage graph in accordance with an embodiment of the invention;
[00022] FIG. 6 is a potential diagram illustrating the operation of the FIG. 4 pixel;
[00023] FIG. 7 illustrates an exemplary circuit diagram in accordance with an embodiment of the invention;
[00024] FIG. 8 illustrates an exemplary top-down view of a 4-way shared pixel implementation according to an exemplary embodiment of the invention; and
[00025] FIG. 9 illustrates a processor system incorporating at least one imager device in accordance with an embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[00026] In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized, and that structural, logical and electrical changes may be made without departing from the spirit and scope of the present invention.
[00027] The term "substrate" is to be understood as a semiconductor- based material including silicon, silicon-on-insulator (SOI) or silicon-on-sapphire (SOS) technology, doped and undoped semiconductors, epitaxial layers of silicon supported by a base semiconductor foundation, and other semiconductor structures. Furthermore, when reference is made to a "substrate" in the following description, previous process steps may have been utilized to form regions or junctions in the base semiconductor structure or foundation. In addition, the semiconductor need not be silicon-based, but could be based on silicon-germanium, germanium, or gallium arsenide.
[00028] The term "pixel" refers to a picture element unit cell containing a photosensor and transistors for converting light radiation to an electrical signal. For purposes of illustration, a representative pixel is illustrated in the figures and description herein and, typically, fabrication of all pixels in an imager array will proceed simultaneously in a similar fashion.
[00029] As discussed below, the invention increases the storage capacity of a pixel's floating diffusion region, thereby increasing the dynamic range of the pixel. FIG.4 illustrates a cross-section of a portion of an exemplary pixel 110 constructed in accordance with an embodiment of the invention. The pixel 110 contains a floating diffusion region 30, which receives charge from a photosensor, illustrated in FIG. 4 as a p-n-p diode, through a transfer transistor 14. A dual conversion gain switch element of the pixel 110 is formed between the floating diffusion region 30 and a capacitor Cl. Preferably, the dual conversion gain switch element is a Schottky contact 32 which forms a Schottky diode. An ohmic contact 34 is formed between the floating diffusion region 30 and a source follower transistor gate 18. The ohmic contact 34 is formed by an n+ doped region 34 within the n- doped floating diffusion region. The Schottky contact 32 is formed on the n- doped floating diffusion region 30 which is in contact with a p-type layer 26. The contact 32 allows for the realization of a dual conversion gain pixel. That is, as is explained below in more detail, the pixel 110 will have a first conversion gain under a lower level of charge transferred to the floating diffusion region 30 cause by relatively lower levels of incident light and a second conversion gain under higher levels of charge transferred to the floating diffusion region 30 caused by relatively higher levels of incident light. The Schottky contact 32 creates the occurrence of a "knee" in the illumination response (see FIG. 5), where the response and the knee are determined by the barrier height of the Schottky contact 32.
[00030] The remaining portions of the pixel 110 are similar to that of the pixel illustrated in FIG. 1. FIG. 7 illustrates the equivalent circuit diagram of the pixel 110 of FIG. 4. That is, the pixel 110 includes a photosensor 12 which is connected to the transfer transistor 14. The transfer transistor 14 transfers charge to the floating diffusion region 30. A reset transistor 16 is connected between the floating diffusion region 30 and an array pixel supply voltage Vaa_pix. A reset control signal RST is used to activate the reset transistor 16, which resets the floating diffusion region 30 to the array pixel supply voltage Vaa_pix level.
[00031] The source follower transistor 18 has its gate connected to the floating diffusion region 30 and is connected between the array pixel supply voltage Vaa_pix and the row select transistor 20. The source follower transistor 18 converts the charge stored at the floating diffusion region 30 into electrical output voltage signals Vrst, which is produced when the floating diffusion region 30 is reset, and Vsig, which is produced after charge is transferred by transistor 14 from the photosensor 12 to the floating diffusion region 30. The row select transistor 20 is controllable by a row select signal SEL for selectively connecting the source follower transistor 18 and its output voltage signal Vout to a column line 22 of a pixel array. The Schottky contact 32, forming a Schottky diode, is connect to the floating diffusion region 30. Once a predetermined level of charge collects in the floating diffusion region 30, the Schottky diode 32 automatically connects the capacitor Cl to the floating diffusion region 30, thereby increasing the conversion gain of the floating diffusion region 30. [00032] As mentioned above, a low resistance ohmic contact 34 is formed with the floating diffusion region 30, as illustrated in FIG. 4. To form the contact 34, a small n+ region is formed in the floating diffusion region 30 which is doped n- elsewhere. The ohmic contact 34 creates a buffer between the gate of the source follower transistor 18 and the floating diffusion region 30. An exemplary doping level of the ohmic contact 34 is between Ie x 1014- 4e x 1015 atoms per cm3 and is preferably 2e x 1015 atoms per cm3. The low resistance ohmic contact 34 lowers the gate barrier of the source follower transistor and permits the effects of the Schottky diode 32 to be seen at the output of the source follower transistor 18.
[00033] The Schottky diode 32, also referred to as a barrier or contact, is formed above the floating diffusion region 30. However, although FIG.4 illustrates that the Schottky diode 32 is formed above the floating diffusion region 30, the diode 32 may alternatively be formed within the floating diffusion region 30. The diode 32 may be formed of either pure a metal or metal silicide layer 32 when contacting the n- silicon layer 30. Exemplary metal silicide materials that may be used for the Schottky diode include tungsten (We), cobalt silicide (CoSk), platinum silicide (PtSi) and titanium silicide (TaSi.). The barrier for each of these silicides is 0.55-0.93V which must be exceed for the diode switch to activate. The material chosen for a particular application depends on the reproducibility and temperature stability of the diode based on the particular material chosen. Additionally, pure metals silver (Ag), aluminum (Al), gold (Au), chromium (Cr), hafnium (Hf), magnesium (Mg), molybdenum (Mo), nickel (Ni), palladium (Pd), platinum (Pt), titanium (Ti) and tungsten (W) may also be used to form Schottky diodes on an n-type silicon. The barrier for these metals is from about 0.5-0.9V. Several of the pure metals may also form silicides, as noted above, when the metal reacts with, silicon. Although all of these materials are able to form Schottky diodes 32, several of these metals, including Au and Cu, are known to be contaminates in CMOS technology and therefore may not be as desirable for use in CMOS implementations. The invention described herein does not require a very low barrier to achieve the dual conversion gain aspect of the invention.
[00034] Often, a conductive metal nitride layer (e.g., TiN) is used as the thin barrier layer 38 during contact 32 formation (e.g., Schottky diode formation), as shown in FIG.4. For example, Pt-based Schottky diodes are known to result in a very low barrier and are therefore, easily reproducible diodes. Ti would result in a very low barrier on n-type silicon, however, TiSi formation at a low temperature, employed in conventional silicon processing, raises this barrier. Therefore, any one of a number of materials may be used to implement a very low Schottky diode to n-type silicon, however, the invention, described herein, does not require a very low barrier to n-type silicon. The barrier height may be adjusted by material selection or adjusting the n- doping concentration to result in a desired "knee" for the conversion gain.
[00035] Charge automatically flows through the diode 32 once the charge potential of the floating diffusion region 30 reaches a predetermined threshold potential and is stored in capacitor Cl. The advantage of the Schottky diode 32 is that the step of activating a transistor to connect the floating diffusion region 30 to the capacitor Cl is unnecessary. The predetermined threshold potential is dependant on the diode 32 barrier height. Charge flowing through the diode 32 is stored in the connected capacitor Cl. Capacitor Cl is also connected to the array pixel supply voltage Vaa_pix. The combination of the Schottky diode 32 and capacitor Cl allows for an increased storage capacity of the pixel 110. When the threshold potential of the diode 32 is met and charge flows into the capacitor Cl, the knee in the illumination response is created (see FIG.5).
[00036] Thus, the Schottky contact 32 electrically allows for the realization of an automatic dual conversion gain pixel. The source follower transistor 18 converts the charge at the floating diffusion region 30 into an electrical output voltage. The ohmic contact 34, which connects the gate of the source follower transistor 18 to the floating diffusion region 30, lowers the barrier potential at the gate of the source follower transistor and allows the source follower transistor 18 to capture the full extent of the voltage swing produced by charges stored at the floating diffusion region 30 and in the capacitor Cl when the Schottky diode 32 couples the capacitor Cl to the floating diffusion region 30. Thus, the knee in the illumination versus output voltage produced by the Schottky contact 32, as shown in FIG. 5, can be purposely reflected in the output voltage of the source follower transistor 18 due to the ohmic contact 34.
[00037] FIG. 5 illustrates an exemplary pixel illumination versus output voltage graph in accordance with the invention. The term knee reflects the fact that the graph creates an angle in the illumination-voltage profile, such that the maximum saturation voltage is reached at a greater level of illumination, point B, than that prior art pixel, point A, as illustrated in FIG. 3. For example, in FIG. 5, the illumination-voltage profile continues at an angle until the threshold voltage of the diode 32 is met. Once the threshold voltage of the diode is met, the knee is created, point C, and a new illumination- voltage profile angle is created. As illustrated, point B on the chart is the illumination-voltage point at which saturation occurs when realizing the dual conversion gain, whereas the saturation point would be at point A for an implementation not realizing the dual conversion gain aspects of the invention. [00038] The target barrier height of the Schottky diode 32 is selected based on where it is determined that the knee response is best based on the particular application. The knee point is the point at which the dual conversion of the proposed dual conversion gain pixel changes from high conversion gain (needed for low signal level), to low conversion gain (needed for high signal level). For example, if the point of saturation is 1.0 V on the floating diffusion region 30, and the knee is desired at 0.4 V, the Schottky diode barrier height is targeted at 0.4V. The knee can be expressed as a fraction of the saturation signal.
[00039] From a cost effectiveness point of view, the current W/TiN/Ti contact process may be used and the intrinsic Schottky diode 32 may be adjusted by implantation. For example in FIG. 4, the Schottky diode 32 may be formed of a Ti layer 36 which is in direct contact with the n- floating diffusion region 30, a TiN barrier layer 38 is formed on top of the Ti layer 36 and a W layer 40 formed on top of the TiN layer 38. The intrinsic Schottky diode 32 barrier height is due to the difference in the workfunction and can be further adjusted by adding n- type or p-type doping to silicon in the contact region. Therefore, the final diode 32 barrier height will depend on the material selection and annealing and implantation conditions.
[00040] FIG. 6 illustrates an exemplary potential energy versus capacitance graph for the pixel 110 of FIG.4. As charge is collected in the photodiode PD it reaches it maximum collection point at a pinning voltage Vpin. When the transfer transistor is activated, the charge is transferred to the floating diffusion region 30. The amount of charge that the floating diffusion region 30 alone can hold is illustrated by section 2. With the addition of the Schottky diode 32 and the capacitor Cl, additional charge may be collected as illustrated by section 1. [00041] The above described Schottky diode 32 and ohmic contact may also be implemented in a shared pixel arrangement, as illustrated in FIG. 8. FIG, 8 illustrates a top down view of a 4-way shared pixel implementation. The photosensors 12a, 12b, 12c, 12d each have a corresponding transfer transistor 14a, 14b, 14c, 14d which transfers charge to the floating diffusion region 30. The photosensors 12a, 12b, 12c, 12d share a reset transistor 16, a source follower transistor 18, a row select transistor 20, a floating diffusion region 30 and capacitor Cl. Although FIG. 8 illustrates a 4-way shared implementation, the Schottky diode 32 and ohmic contact 34 described above may be implemented with other shared pixel or non-shared pixel arrangements.
[00042] FIG. 9 shows system 300, a typical processor system modified to include an imaging device 200 containing the pixel 110 of the invention. Imaging device 200 is similar to device 308 (FIG. 2) with the exception that the array 240 comprises pixels 110 constructed in accordance with the invention. The processor-based system 300 is exemplary of a system having digital circuits that could include image sensor devices. Without being limiting, such a system could include a computer system, camera system, scanner, machine vision, vehicle navigation, video phone, surveillance system, auto focus system, star tracker system, motion detection system, image stabilization system, and data compression system.
[00043] System 300, for example a camera system, generally comprises a central processing unit (CPU) 302, such as a microprocessor, that communicates with an input/output (I/O) device 306 over a bus 304. Imaging device 200 also communicates with the CPU 302 over the bus 304. The processor-based system 300 also includes random access memory (RAM) 310, and can include removable memory 315, such as flash memory, which also communicate with the CPU 302 over the bus 304. The imaging device 200 may be combined with a processor, such as a CPU, digital signal processor, or microprocessor, with or without memory storage on a single integrated circuit or on a different chip than the processor.
[00044] The above described embodiments may be implemented in a manner similar to the imager device illustrated in FIG. 2. The pixel array 240, of FIG.2, may be comprised of the above described pixels 110 having a Schottky diode 32 and ohmic contact 34.
[00045] It should be appreciated that other embodiments of the invention include a method of fabricating the circuits of the invention as illustrated in FIG.4. For example, in one exemplary embodiment, a method of fabricating a dual conversion gain pixel comprises the acts of fabricating a photosensitive region within a substrate, forming a first transistor within the substrate for resetting the pixel, providing a floating diffusion region within said substrate, the floating diffusion region having a first capacitance, providing a second transistor between the photosensitive region and the floating diffusion region, the second transistor being controllable to transfer charge from the photosensitive region to the floating diffusion region, forming a capacitive element over the substrate; and forming a Schottky diode within and above the substrate, wherein the diode is connected between the diffusion region and the capacitive element such that when the diode is activated, a capacitance of the capacitive element is added to the first capacitance of the floating diffusion region.
[00046] The processes and devices described above illustrate preferred methods and typical devices of many that could be used and produced. The above description and drawings illustrate embodiments, which achieve the objects, features, and advantages of the present invention. However, it is not intended that the present invention be strictly limited to the above-described and illustrated embodiments. Any modification, though presently unforeseeable, of the present invention that comes within the spirit and scope of the following claims should be considered part of the present invention.

Claims

CLAIMSWhat is claimed as new and desired to be protected by Letters Patent of the United States is:
1. An imager device, comprising:
a photosensor;
a diffusion region having a first capacitance being connected to receive stored charge from said photosensor; and
a circuit having a capacitance for storing charge which is connected to said diffusion region by a Schottky contact, said circuit providing said diffusion region with a second capacitance when activated by said Schottky contact to couple said circuit to said diffusion region.
2. The imager device of claim 1, wherein said diffusion region is an n- region and said Schottky contact includes at least one conductive layer in contact with said n- diffusion region.
3. The imager device of claim 2, further comprising an output transistor having a gate connected to said diffusion region via an ohmic contact.
4. The imager device of claim 1, wherein said Schottky contact couples said circuit to said diffusion region when an amount of charge collected in said diffusion region exceeds a predetermined threshold.
5. The imager device of claim 4, wherein said predetermined charge threshold is correlated to a barrier height of said Schottky contact.
6. The imager device of claim 1, wherein said capacitance of said circuit is provided by a capacitor.
7. The imager device of claim 2, wherein said ohmic contact is formed as a n+ diffusion region within said diffusion region.
8. An imager pixel, comprising:
a photosensor for accumulating charge;
a diffusion region, connected to receive the charge from the photosensor, said diffusion region having an associated first conversion gain; and
a Schottky diode for switchably connecting a capadtive element to said diffusion region to provide said diffusion region with a second associated conversion gain different from said associated first conversion gain.
9. The imager pixel of claim 8, further comprising an ohmic contact connecting a gate of an output transistor to said diffusion region, wherein said transistor converts stored charge into an output signal.
10. The imager pixel of claim 8, wherein said diffusion region is an n- region and said Schottky contact includes at least a conductive layer in contact with said n- diffusion region.
11. The imager pixel of claim 8, wherein said capadtive element is provided by a capacitor.
12. An imager pixel, comprising: a photosensor for accumulating charge;
a first transistor for resetting said pixel;
a second transistor for transferring the charge from the photosensor;
a diffusion region, for receiving the charge from said photosensor through said second transistor, said diffusion region having a first associated conversion gain;
a capacitive element; and
a Schottky contact coupled between said diffusion region and said capacitive element, said Schottky contact switchablly controlling the connection of said capacitive element to said diffusion region such that said diffusion region obtains a second associated conversion gain when the capacitive element is connected to the diffusion region.
13. The imager pixel of claim 12, further comprising a third output transistor having a gate connected to said diffusion region by an ohmic contact.
14. An imager, comprising:
an array of pixel cells formed of a plurality of pixel cells, each pixel comprising:
photosensor for accumulating charge;
a first transistor for resetting said pixel;
a second transistor for transferring the charge from the photosensor; a diffusion region, for receiving the charge from said photosensor through said second transistor, said diffusion region having a first associated conversion gain;
a capacitive element; and
a Schottky contact coupled between said diffusion region and said capacitive element, said Schottky contact switchably controlling the connection of said capacitive element to said diffusion region such that said diffusion region obtains a second conversion gain when the capacitive element is connected to the diffusion region.
15. An imager system, comprising:
a processor; and
an imaging device electrically coupled to said processor, said imaging device comprising a pixel array, at least one pixel of said array comprising:
a photosensor for accumulating charge,
a diffusion region, connected to receive the charge from the photosensor, said diffusion region having a first associated conversion gain, and
a conversion gain altering circuit, including a contact, connected to said diffusion region, said conversion gain altering circuit changing the first associated conversion gain to a second associated conversion gain in response to the amount of charge in the diffusion region.
16. The system of claim 15, wherein said conversion gain altering circuit comprises:
a capacitive element; and
wherein said contact is a Schottky diode controlling when charge is collected in the capacitive element.
17. The system of claim 16, wherein said diffusion region has a first capacitance associated with the first associated conversion gain, said capacitive element has a second capacitance, and a combination of the first and second capacitances is associated with the second associated conversion gain.
18. The system of claim 17, wherein said photosensor has a capacitance greater than the first capacitance and less than the combination of the first and second capacitances.
19. The system of claim 16, wherein said capacitive element is a capacitor.
20. A method of operating an imager device, said method comprising the acts of:
transferring photo-generated charge to a diffusion region;
activating a Schottky diode to change a conversion gain of the diffusion region when the amount of transferred charge exceeds a threshold; and
outputting a signal indicative of the charge in the floating diffusion region.
21. The method according to claim 20, further comprising the act of collecting charge transferred to said diffusion region in a storage element connected to said activated diode.
22. The method according to claim 20, further comprising the act of converting the charge from said diffusion region to an output signal by a circuit connected to said diffusion region by an ohmic contact.
23. A method of operating an imager device, said method comprising:
providing a photosensor;
providing a diffusion region having a first charge storage capacitance;
storing photo-generated charge from the photosensor in the diffusion region; and
changing the storage capacitance of the diffusion region in response to the charge stored in said diffusion region reaching a predetermined value.
24. The method of claim 23, wherein said act of changing causes charge to flow through a Schottky diode to a capacitive element.
25. The method of claim 23, wherein said act of changing is preformed by a
Schottky diode.
26. The method of claim 23 further comprising the act of converting the charge from said diffusion region to an output signal by a transistor having a gate connected to said diffusion region through an ohmic contact.
27. A method of fabricating a dual conversion gain pixel, said method comprising the steps of:
fabricating a photosensitive region;
forming a first transistor within the substrate for resetting the pixel;
providing a diffusion region, the diffusion region having a first associated conversion gain;
providing a second transistor between the photosensitive region and the floating diffusion region, the second transistor for transferring charge collected in the photosensitive region to the diffusion region; and
forming a Schottky for switchably connecting said diffusion region with a capacitive element to provide said diffusion with a second associated conversion gain.
28. The method of claim 27, wherein said diffusion region is an n- region and said
Schottky contact includes least one conductive layer in contact with said n- diffusion region.
PCT/US2006/014054 2005-04-15 2006-04-13 Dual conversion gain imager pixel using schottky and ohmic contacts to the floating diffusion region and methods of fabrication and operation WO2006113427A2 (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8077237B2 (en) 2007-10-16 2011-12-13 Aptina Imaging Corporation Method and apparatus for controlling dual conversion gain signal in imaging devices

Families Citing this family (31)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7498188B2 (en) * 2004-09-02 2009-03-03 Aptina Imaging Corporation Contacts for CMOS imagers and method of formation
US7446357B2 (en) * 2005-05-11 2008-11-04 Micron Technology, Inc. Split trunk pixel layout
US7388271B2 (en) * 2005-07-01 2008-06-17 Texas Instruments Incorporated Schottky diode with minimal vertical current flow
US7638416B2 (en) * 2005-12-13 2009-12-29 Versatilis Llc Methods of making semiconductor-based electronic devices on a wire and articles that can be made using such devices
US7700471B2 (en) * 2005-12-13 2010-04-20 Versatilis Methods of making semiconductor-based electronic devices on a wire and articles that can be made thereby
US20080093633A1 (en) * 2006-10-18 2008-04-24 United Microelectronics Corp. Complementary metal-oxide-semiconductor (cmos) image sensor and fabricating method thereof
US7924333B2 (en) * 2007-08-17 2011-04-12 Aptina Imaging Corporation Method and apparatus providing shared pixel straight gate architecture
JP5068320B2 (en) * 2007-08-21 2012-11-07 シャープ株式会社 Display device
US7989749B2 (en) * 2007-10-05 2011-08-02 Aptina Imaging Corporation Method and apparatus providing shared pixel architecture
US8546765B2 (en) * 2008-06-26 2013-10-01 Trixell High dynamic range X-ray detector with improved signal to noise ratio
JP5257176B2 (en) * 2009-03-18 2013-08-07 ソニー株式会社 Solid-state imaging device, driving method of solid-state imaging device, and electronic apparatus
DE112011100059A5 (en) * 2010-01-28 2012-09-13 Conti Temic Microelectronic Gmbh Highly dynamic image sensor for the detection of modulated light
GB201011640D0 (en) * 2010-07-12 2010-08-25 Univ Sheffield Radiation detection and method
GB201102478D0 (en) * 2011-02-11 2011-03-30 Isdi Ltd Radiation detector and method
KR20130062188A (en) 2011-12-02 2013-06-12 삼성전자주식회사 Image sensor, and image processing device including the same
CN104144305B (en) * 2013-05-10 2017-08-11 江苏思特威电子科技有限公司 Dual conversion gain imaging device and its imaging method
US9570631B2 (en) * 2013-08-19 2017-02-14 Idemitsu Kosan Co., Ltd. Oxide semiconductor substrate and schottky barrier diode
JP6366285B2 (en) * 2014-01-30 2018-08-01 キヤノン株式会社 Solid-state imaging device
US9929204B2 (en) 2014-03-13 2018-03-27 Samsung Electronics Co., Ltd. Unit pixel of image sensor, image sensor including the same and method of manufacturing image sensor
GB2525625B (en) 2014-04-29 2017-05-31 Isdi Ltd Device and method
KR102132211B1 (en) 2014-05-12 2020-07-09 삼성전자주식회사 Repair circuit, fuse circuit and semiconductor memory device including the same
CN104393010B (en) * 2014-12-01 2017-09-05 豪威科技(上海)有限公司 Reduce cmos image sensor of picture delay and preparation method thereof
TWI701819B (en) * 2015-06-09 2020-08-11 日商索尼半導體解決方案公司 Imaging element, driving method and electronic equipment
US9843738B2 (en) 2015-10-01 2017-12-12 Semiconductor Components Industries, Llc High dynamic range imaging pixels with improved readout
US9948875B2 (en) 2015-10-01 2018-04-17 Semiconductor Components Industries, Llc High dynamic range imaging pixels with improved readout
JP6674222B2 (en) * 2015-10-09 2020-04-01 キヤノン株式会社 Radiation imaging apparatus and control method of radiation imaging apparatus
US10110839B2 (en) 2016-05-03 2018-10-23 Semiconductor Components Industries, Llc Dual-photodiode image pixel
EP3719840A4 (en) * 2017-11-30 2021-02-24 Panasonic Intellectual Property Management Co., Ltd. Image capturing device
US10741592B2 (en) 2018-06-07 2020-08-11 Semiconductor Components Industries, Llc Image sensors with multi-photodiode image pixels and vertical transfer gates
CN111403385B (en) * 2020-03-02 2022-10-14 电子科技大学 RC-LIGBT device with embedded Schottky diode
US11658201B2 (en) * 2021-08-25 2023-05-23 Silead Inc. Dual conversion gain image sensor pixels

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0410465A2 (en) * 1989-07-28 1991-01-30 Nec Corporation Solid state image pickup device having photo-shield plate in contact with photo-electric converting region via Schottky barrier
GB2330905A (en) * 1997-11-03 1999-05-05 Hewlett Packard Co Photodiode pixel sensor with switched shunt capacitance
US20040251482A1 (en) * 2003-06-16 2004-12-16 Rhodes Howard E. Method and apparatus for reducing imager floating diffusion leakage
US20040251394A1 (en) * 2003-06-11 2004-12-16 Rhodes Howard E. Dual conversion gain imagers
US20050051701A1 (en) * 2003-09-05 2005-03-10 Hong Sungkwon C. Image sensor having pinned floating diffusion diode

Family Cites Families (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4479139A (en) * 1980-11-10 1984-10-23 Santa Barbara Research Center Charge coupled device open circuit image detector
US5461461A (en) * 1992-01-22 1995-10-24 Ricoh Company, Ltd. Image transferring device and medium separating device for an image forming apparatus
US5557384A (en) * 1992-01-22 1996-09-17 Ricoh Company, Ltd. Image transferring device for image forming equipment
JP3245240B2 (en) * 1992-01-22 2002-01-07 株式会社リコー Transfer device for image forming device
US5659843A (en) * 1992-01-22 1997-08-19 Ricoh Company, Ltd. Image transferring device for image forming equipment
US5680073A (en) * 1993-06-08 1997-10-21 Ramot University Authority For Applied Research & Industrial Development Ltd. Controlled semiconductor capacitors
JPH07248693A (en) * 1994-01-19 1995-09-26 Ricoh Co Ltd Image forming device
US6140630A (en) * 1998-10-14 2000-10-31 Micron Technology, Inc. Vcc pump for CMOS imagers
US6376868B1 (en) * 1999-06-15 2002-04-23 Micron Technology, Inc. Multi-layered gate for a CMOS imager
US6310366B1 (en) * 1999-06-16 2001-10-30 Micron Technology, Inc. Retrograde well structure for a CMOS imager
US6326652B1 (en) * 1999-06-18 2001-12-04 Micron Technology, Inc., CMOS imager with a self-aligned buried contact
US6204524B1 (en) * 1999-07-14 2001-03-20 Micron Technology, Inc. CMOS imager with storage capacitor
US6333205B1 (en) * 1999-08-16 2001-12-25 Micron Technology, Inc. CMOS imager with selectively silicided gates
US6407440B1 (en) * 2000-02-25 2002-06-18 Micron Technology Inc. Pixel cell with high storage capacitance for a CMOS imager
US6730897B2 (en) * 2000-12-29 2004-05-04 Eastman Kodak Company Linearity and dynamic range for complementary metal oxide semiconductor active pixel image sensors
US7079790B2 (en) * 2001-10-26 2006-07-18 Kyocera Corporation Image forming apparatus
US6960796B2 (en) * 2002-11-26 2005-11-01 Micron Technology, Inc. CMOS imager pixel designs with storage capacitor
US7026596B2 (en) * 2003-10-30 2006-04-11 Micron Technology, Inc. High-low sensitivity pixel
JP4242880B2 (en) * 2006-05-17 2009-03-25 日本テキサス・インスツルメンツ株式会社 Solid-state imaging device and operation method thereof

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0410465A2 (en) * 1989-07-28 1991-01-30 Nec Corporation Solid state image pickup device having photo-shield plate in contact with photo-electric converting region via Schottky barrier
GB2330905A (en) * 1997-11-03 1999-05-05 Hewlett Packard Co Photodiode pixel sensor with switched shunt capacitance
US20040251394A1 (en) * 2003-06-11 2004-12-16 Rhodes Howard E. Dual conversion gain imagers
US20040251482A1 (en) * 2003-06-16 2004-12-16 Rhodes Howard E. Method and apparatus for reducing imager floating diffusion leakage
US20050051701A1 (en) * 2003-09-05 2005-03-10 Hong Sungkwon C. Image sensor having pinned floating diffusion diode

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of EP1872403A2 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8077237B2 (en) 2007-10-16 2011-12-13 Aptina Imaging Corporation Method and apparatus for controlling dual conversion gain signal in imaging devices

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US7718459B2 (en) 2010-05-18
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