CA2626800A1 - Optically- initiated silicon carbide high voltage switch - Google Patents
Optically- initiated silicon carbide high voltage switch Download PDFInfo
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- CA2626800A1 CA2626800A1 CA002626800A CA2626800A CA2626800A1 CA 2626800 A1 CA2626800 A1 CA 2626800A1 CA 002626800 A CA002626800 A CA 002626800A CA 2626800 A CA2626800 A CA 2626800A CA 2626800 A1 CA2626800 A1 CA 2626800A1
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- 229910010271 silicon carbide Inorganic materials 0.000 title description 23
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 title description 22
- 239000000758 substrate Substances 0.000 claims abstract description 92
- 239000000463 material Substances 0.000 claims abstract description 31
- 230000005684 electric field Effects 0.000 claims abstract description 14
- 230000003287 optical effect Effects 0.000 claims description 37
- 239000010410 layer Substances 0.000 claims description 22
- 239000004020 conductor Substances 0.000 claims description 11
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 6
- 229910052581 Si3N4 Inorganic materials 0.000 claims description 6
- 239000002019 doping agent Substances 0.000 claims description 6
- 238000000926 separation method Methods 0.000 claims description 5
- 239000002344 surface layer Substances 0.000 claims description 5
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 claims description 4
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims description 3
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims description 3
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims description 3
- 229910052782 aluminium Inorganic materials 0.000 claims description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 3
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 3
- 229910052796 boron Inorganic materials 0.000 claims description 3
- 239000013078 crystal Substances 0.000 claims description 3
- 239000011810 insulating material Substances 0.000 claims description 3
- 229910052757 nitrogen Inorganic materials 0.000 claims description 3
- 229910052760 oxygen Inorganic materials 0.000 claims description 3
- 239000001301 oxygen Substances 0.000 claims description 3
- 229910052698 phosphorus Inorganic materials 0.000 claims description 3
- 239000011574 phosphorus Substances 0.000 claims description 3
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 claims description 3
- 229910052721 tungsten Inorganic materials 0.000 claims description 3
- 239000010937 tungsten Substances 0.000 claims description 3
- 229910052720 vanadium Inorganic materials 0.000 claims description 3
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 claims description 3
- 229910052725 zinc Inorganic materials 0.000 claims description 3
- 239000011701 zinc Substances 0.000 claims description 3
- 229910001218 Gallium arsenide Inorganic materials 0.000 abstract description 5
- 239000004065 semiconductor Substances 0.000 description 9
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 8
- 238000000034 method Methods 0.000 description 8
- 238000010521 absorption reaction Methods 0.000 description 6
- 239000012212 insulator Substances 0.000 description 6
- JBRZTFJDHDCESZ-UHFFFAOYSA-N AsGa Chemical compound [As]#[Ga] JBRZTFJDHDCESZ-UHFFFAOYSA-N 0.000 description 5
- 239000000356 contaminant Substances 0.000 description 5
- 230000008569 process Effects 0.000 description 5
- 229910052681 coesite Inorganic materials 0.000 description 4
- 238000010276 construction Methods 0.000 description 4
- 229910052906 cristobalite Inorganic materials 0.000 description 4
- 230000001419 dependent effect Effects 0.000 description 4
- 230000005499 meniscus Effects 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- 239000002245 particle Substances 0.000 description 4
- 229910052682 stishovite Inorganic materials 0.000 description 4
- 229910052905 tridymite Inorganic materials 0.000 description 4
- 239000011800 void material Substances 0.000 description 4
- 239000000969 carrier Substances 0.000 description 3
- 230000015556 catabolic process Effects 0.000 description 3
- 238000004140 cleaning Methods 0.000 description 3
- 239000011248 coating agent Substances 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- 235000012239 silicon dioxide Nutrition 0.000 description 3
- 239000000377 silicon dioxide Substances 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 2
- 238000002347 injection Methods 0.000 description 2
- 239000007924 injection Substances 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 238000000623 plasma-assisted chemical vapour deposition Methods 0.000 description 2
- 229910052710 silicon Inorganic materials 0.000 description 2
- 239000010703 silicon Substances 0.000 description 2
- 230000002123 temporal effect Effects 0.000 description 2
- 235000012431 wafers Nutrition 0.000 description 2
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 230000001133 acceleration Effects 0.000 description 1
- 235000011114 ammonium hydroxide Nutrition 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 230000000903 blocking effect Effects 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 229910021419 crystalline silicon Inorganic materials 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000000151 deposition Methods 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 229910001385 heavy metal Inorganic materials 0.000 description 1
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- 238000001465 metallisation Methods 0.000 description 1
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- -1 shown at 90 Chemical compound 0.000 description 1
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Classifications
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/02—Apparatus for electrographic processes using a charge pattern for laying down a uniform charge, e.g. for sensitising; Corona discharge devices
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices 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; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/08—Semiconductor devices 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; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
- H01L31/09—Devices sensitive to infrared, visible or ultraviolet radiation
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
- H05H7/00—Details of devices of the types covered by groups H05H9/00, H05H11/00, H05H13/00
Abstract
An improved photoconductive switch having a SiC or other wide band gap substrate material, such as GaAs and field-grading liners composed of preferably SiN formed on the substrate adjacent the electrode perimeters or adjacent the substrate perimeters for grading the electric fields.
Description
OPTICALLY-INITIATED SILICON CARBIDE HIGH VOLTAGE SWITCH
[0001] The United States Government has rights in this invention pursuant to Contract No. W-7405-ENG-48 between the United States Department of Energy and the University of California for the operation of Lawrence Livermore National Laboratory.
1. REFERENCE TO PRIOR APPLICATIONS
[0001] The United States Government has rights in this invention pursuant to Contract No. W-7405-ENG-48 between the United States Department of Energy and the University of California for the operation of Lawrence Livermore National Laboratory.
1. REFERENCE TO PRIOR APPLICATIONS
[0002] This application claims the benefit of U.S. Provisional Application Nos.
60/730,161, filed October 24, 2005, and U.S. Provisional Application No.
60/798,016, filed May 4, 2006, all of which are incorporated by reference herein.
II. FIELD OF THE INVENTION
60/730,161, filed October 24, 2005, and U.S. Provisional Application No.
60/798,016, filed May 4, 2006, all of which are incorporated by reference herein.
II. FIELD OF THE INVENTION
[0003] The present invention relates to photoconductive switches and more particularly to an optically initiated silicon carbide (SiC) high voltage switch.
III. BACKGROUND OF THE INVENTION
III. BACKGROUND OF THE INVENTION
[0004] Particle accelerators, such as for example dielectric wall accelerators (DWA), are critically dependent upon high voltage, high current, fast closing switches that can be activated with nanosecond precision. Photoconductive switches offer the most potential in terms of handling such high voltages and high currents with minimum inductance, rapid closure, precise temporal control and the possibility of long life.
Photoconductive switching is a technique where optical energy is applied to a semiconductor material, and the optical energy creates carriers within the semiconductor which renders it conductive.
Photoconductive switching is a technique where optical energy is applied to a semiconductor material, and the optical energy creates carriers within the semiconductor which renders it conductive.
[0005] The materials that have been used to date for photoconductive switch applications include Silicon and Gallium Arsenide (GaAs). The difficulty with these materials is that various failure mechanisms occur even at modest parameters.
Further, the optical absorption depth for these materials is low, thus the carriers are forced to flow in a very thin area of the material bulk just below the surface. Thus, the principal issue with photoconductive switching has been short lifetime resulting from overstressing current and voltage conditions.
Further, the optical absorption depth for these materials is low, thus the carriers are forced to flow in a very thin area of the material bulk just below the surface. Thus, the principal issue with photoconductive switching has been short lifetime resulting from overstressing current and voltage conditions.
[0006] Additionally, silicon carbide (SiC) has long been a promising alternative candidate for use as a photoconductive switch material. It is only very recently, however, has this particular material been made commercially available in sizes and purity that merit application as a high voltage switch. SiC material has high dielectric breakdown strength greater than that of most solid materials (- 4MV/cm), has high thermal conductivity (comparable to that of copper), and low optical absorption. Thus with the availability of single crystalline Silicon Carbide, a new class of switches is possible.
[0007] While promising, even SiC is subject to failure due to high electric fields locally produced where the electrodes separate from contact with the photoconductive substrate. Figure 1 shows a photoconductive switch lcnown in the art having a SiC
photoconductive substrate 10 and two opposing electrodes 11 and 12. Figure 2 shows an enlarged view of the box A in Figure 1 showing the meniscus formed at the metal contact between the electrode and substrate surfaces. Figure 3 shows the magnitude of the electric field on the contact surfaces, and illustrating the spike in magnitude at the triple points. Various methods have been employed to reduce and minimize these fields at such "triple points," such as including filling the space between the electrode and substrate with a high permittivity material. This is shown in Figures 4-6.
Similar to Figure 1, Figure 4 shows a SiC substrate 15 and two electrodes 16 and 17.
Additionally, a high permittivity insulator 18 is filled into the space between the separation of the electrodes from the substrate. The meniscus 19 is shown in Figure 5 at the triple point, where the triple point now includes the insulator material 18.
Figure 6, however, shows that there is still a spike, albeit with less magnitude, at the triple point of electrode-substrate separation.
photoconductive substrate 10 and two opposing electrodes 11 and 12. Figure 2 shows an enlarged view of the box A in Figure 1 showing the meniscus formed at the metal contact between the electrode and substrate surfaces. Figure 3 shows the magnitude of the electric field on the contact surfaces, and illustrating the spike in magnitude at the triple points. Various methods have been employed to reduce and minimize these fields at such "triple points," such as including filling the space between the electrode and substrate with a high permittivity material. This is shown in Figures 4-6.
Similar to Figure 1, Figure 4 shows a SiC substrate 15 and two electrodes 16 and 17.
Additionally, a high permittivity insulator 18 is filled into the space between the separation of the electrodes from the substrate. The meniscus 19 is shown in Figure 5 at the triple point, where the triple point now includes the insulator material 18.
Figure 6, however, shows that there is still a spike, albeit with less magnitude, at the triple point of electrode-substrate separation.
[0008] What is needed therefore is a photoconductive switch for high voltage applications such as for particle accelerators, preferably implemented with a SiC
material or other photoconductive materials, such as GaAs, that minimizes or at least reduces the high magnitude electric fields at the points of electrode-substrate separation.
IV. SUMMARY OF THE INVENTION
material or other photoconductive materials, such as GaAs, that minimizes or at least reduces the high magnitude electric fields at the points of electrode-substrate separation.
IV. SUMMARY OF THE INVENTION
[0009] One aspect of the present invention includes a photoconductive switch comprising: a photoconductive substrate composed of a greater-than-1.6 eV wide band gap material, said substrate having two' opposing concavities, and a facet optically connectable to an optical source for receiving optical energy therefrom; and two electrodes having convex surfaces contactedly seated in the two concavities, for applying a potential across the substrate.
[0010] Another aspect of the present invention includes a photoconductive switch comprising: a photoconductive substrate composed of a greater-than-1.6 eV wide band gap material, said substrate having opposing electrode-contacting surfaces and a facet optically connectable to an optical source for receiving optical energy therefrom;
two electrodes electrically connected to the electrode-contacting surfaces of the substrate, for applying a potential across the substrate; and two field-grading liners formed on the substrate surrounding the electrode-contacting surfaces, for grading the electric fields therealong.
V. BRIEF DESCRIPTION OF THE DRAWINGS
two electrodes electrically connected to the electrode-contacting surfaces of the substrate, for applying a potential across the substrate; and two field-grading liners formed on the substrate surrounding the electrode-contacting surfaces, for grading the electric fields therealong.
V. BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The accompanying drawings, which are incorporated into and form a part of the disclosure, are as follows:
[0012] Figure 1 is a side view of SiC photoconductive switch known in the art.
[0013] Figure 2 is an enlarged side view of box A in Figure 1 illustrating the meniscus formed at the triple point.
[0014] Figure 3 is a graph showing the magnitude of the electric field along the interface of the SiC substrate and metal coating.
[0015] Figure 4 is a side view of SiC photoconductive switch known in the art and similar to Figure 1, and having a high permittivity insulator filling the space at the perimeter of the electrodes .
[0016] Figure 5 is an enlarged side view of box B in Figure 4 illustrating the meniscus formed at the triple point, now including the insulator.
[0017] Figure 6 is a graph showing the magnitude of the electric field along the interface of the SiC substrate, metal coating, and high permittivity insulator.
[0018] Figure 7 is a perspective view of a basic photoconductive switch.
[0019] Figure 8 is a schematic view of an illustrative embodiment of the photoconductive switch of the present invention used in a switching system.
[0020] Figure 9 is a cross-sectional view of an upper half of a first exemplary embodiment of the photoconductive switch of the present invention, showing the electrical connection between an upper electrode and the photoconductive substrate.
[0021] Figure 10 is a cross-sectional view of an upper half of a second exemplary embodiment of the photoconductive switch of the present invention.
[0022] Figure 11 is a cross-sectional view of an upper half of a third exemplary embodiment of the photoconductive switch of the present invention.
[0023] Figure 12 is a cross-sectional view of an upper half of a fourth exemplary embodiment of the photoconductive switch of the present invention.
[0024] Figure 13 is a cross-sectional view of an upper half of a fifth exemplary embodiment of the photoconductive switch of the present invention.
[0025] Figure 14 is a cross-sectional view of a plane of a SiC substrate of the photoconductive switch of the present invention.
VI. DETAILED DESCRIPTION
VI. DETAILED DESCRIPTION
[0026] The photoconductive switch of the present invention improves upon the basic photoconductive switch construction and operation shown in Figure 7, with enhancements enabling the switch to handle high voltages and high currents with minimum inductance, rapid closure, precise temporal control and the possibility of long life. As such, the photoconductive switch of the present invention shares much the same construction as a basic photoconductive switch shown in Figure 7 generally having a photoconductive material 21 between two electrodes 22 and 23. Without optical energy injection, i.e. in the dark, the photo-conductive material is an insulator with a large resistance value (much larger than the circuit impedance) and thus the switch essentially blocks current flow. When optical energy is injected and absorbed in the photoconductive material, the switch resistance drops to a small value (much less than the circuit impedance) and the switch conducts current. Thus the basic photoconductive switch is essentially an optically controlled resistance. The availability of relatively small pulsed lasers or other optical sources enable the injection of optical energy in a short pulse so that the switching time between large blocking resistance and small conduction resistance can easily be several nanoseconds.
[0027] There are several physical embodiments or geometries of photoconductive switches one of which is illustrated in Fig. 7, in which the contacts or electrodes are placed in relation to the semiconductor material. The geometry of the switch (electrodes and semiconductor material) is determined by the method in which the optical energy is applied to the switch and the mode of photoconductivity employed in switch operation. The mode of photo-conductivity, intrinsic or extrinsic, is dependent upon the ratio of the photon energy to the band gap energy in the semiconductor. In an intrinsic photo-conductor, the photon energy is greater than the semiconductor band gap energy. In the intrinsic case, the optical absorption depth or the depth, which the optical energy can penetrate, is very small and on the order of tens of microns. In the extrinsic mode, the photon energy is less than the band gap energy of the semiconductor and the optical energy can penetrate to much large depths, dependent upon the active dopant and defect densities in the semiconductor.
[0028] These two modes of photoconductivity are further operated in linear and non-linear switch systems. In a linear photoconductive switch, each absorbed photon produces one electron and one electron vacancy or hole, referred to as an electron-hole pair. The electron and hole density is made sufficient to reduce the switch resistance to the desired conduction value by injecting sufficient optical energy.
Furthermore, the rate at which the switch closes is dependent upon the rate at which the optical energy is injected into the switch volume such that the closure time is approximately equal to the optical pulse width. The current density in a linear photo-switch is determined by the distribution of the optical energy in the switch volume.
Furthermore, the rate at which the switch closes is dependent upon the rate at which the optical energy is injected into the switch volume such that the closure time is approximately equal to the optical pulse width. The current density in a linear photo-switch is determined by the distribution of the optical energy in the switch volume.
[0029] In the present invention, the linear, extrinsic mode of operation is preferred because the optical absorption depth and thus the dimensions of the conducting cross section can be tailored by the controlling the density of interband dopants.
However, the inventions is not limited only to such. The density of interband dopants also determines the maximum density of current carriers (electrons and holes) and thus current density at which conduction is possible (the current density is self limiting if the linear mode of operation). The linear mode of operation requires that each current carrier pair be produced by a photon and does not rely on internal avalanche processes that have shown to produce extremely dense current filaments that damage contacts and bulk materials.
However, the inventions is not limited only to such. The density of interband dopants also determines the maximum density of current carriers (electrons and holes) and thus current density at which conduction is possible (the current density is self limiting if the linear mode of operation). The linear mode of operation requires that each current carrier pair be produced by a photon and does not rely on internal avalanche processes that have shown to produce extremely dense current filaments that damage contacts and bulk materials.
[0030] Preferably, the photoconductive switch of the present invention uses compensated, Semi-Insulating Silicon Carbide (CSI-SiC) as the photoconductive substrate, since it is considered the best material for application in high power photo-conductive switch applications. This is due to the following reasons. First, CSI-SiCs very large dielectric strength (3 MV/m) which permits very thin layers to support large voltages (GaAs can only support - 250 kV/cm). CSI-SiC switches require reduced levels of optical closure energy since the required optical closure energy scales as the thickness of the CSI-SiC material. CSI-SiC's large dark resistance (1011 -1015 Ohm-cm) which perinits low rates of voltage application or charging (maximum GaAs resistivity - 109 Ohm-cm). CSI-SiC's large thermal conductivity which permits high average power operation without thermally induced conduction (GaAs thermal conductivity is only 10 % of SiC). And the compensated nature of CSI-SiC's enables the design of recombination times, optical absorption depths, and thus current densities.
[0031] The substrate is a compensated, semi-insulating material selected from a group consisting of 4h SiC, 6h SiC, and GaN. Preferably having a hexagonal crystal structure and cut in a plane selected from the group consisting of the A-Plane, C-Plane and M-plane. With multiple laminated layers so reduce the length of the micropipes. The semi-insulating SiC is preferably doped with at least one of the following dopants: Boron, Vanadium, Nitrogen, Aluminum, Phosphorus, Oxygen, Tungsten and Zinc. And preferably at least one non-electroded facet of the substrate is coated with a dielectric to produce total internal reflection.
[0032] Figure 8 shows a schematic view of and exemplary embodiment of the photoconductive switch 30 of the present invention, connected to an optical source 37, such as a laser via a optic fiber 38. It includes a photoconductive substrate 31 having two electrodes 32 and 33 (preferably opposing, but not necessary) electrically connected to the substrate. Furthermore, there are field-grading liners 34 and shown formed on the substrate to grade the electric field.
[0033] Figures 9-13 show various embodiments of the electrical connection between the electrodes and an electrode-contacting surface of the substrate (e.g. 63 in Figure 11). Figure 9 shows the electrode-contacting surface being a plane and the liners 42 recessed below the substrate. And liners 42 between the substrate and the electrode perimeter. Figure 10 shows the liners 55, 56 adjacent the substrate perimenter/ends.
Figure 11 shows the electrode-contacting surface having two opposing concavities for seating a convex electrode 62. The electrode-contacting surface 63 is therefore also concave. Figure 12 shows a similar switch construction of Figure 11, also including liner 75 between the electrode perimeter and the substrate. And Figure 13 shows a similar construction as Figure 12 with the liners adjacent the substrate perimeter.
Figure 11 shows the electrode-contacting surface having two opposing concavities for seating a convex electrode 62. The electrode-contacting surface 63 is therefore also concave. Figure 12 shows a similar switch construction of Figure 11, also including liner 75 between the electrode perimeter and the substrate. And Figure 13 shows a similar construction as Figure 12 with the liners adjacent the substrate perimeter.
[0034] The photoconductive switch preferably comprises a photoconductive substrate composed of a greater-than-1.6 eV wide band gap material, said substrate having two opposing concavities, and a facet optically connectable to an optical source for receiving optical energy therefrom; and two electrodes having convex surfaces contactedly seated in the two concavities, for applying a potential across the substrate.
[0035] Furthermore, at least one field-grading liners formed on the substrate surrounding a corresponding one of the electrode-contacting surfaces, for grading the electric fields therealong. The two field-grading liners are adjacent the electrode perimeters. Also, wherein the two field-grading liners form the rims of the two concavities for grading the electric fields at the separations of the electrodes from the substrate. Preferably the field-grading liners are integrally formed on the substrate.
[0036] Preferred material for the field-grading liners are a high permittivity material, or either conductive and semi-conductive materials. Preferably it is composed of silicon nitride. Ehe conductive or semi-conductive material may be formed as a doped sub-surface layer of the substrate, extending into the substrate about 1 micron deep. Optionally, the substrate is a multilayer having at least two photoconductive layers separated by a divider layer, with the divider layer composed of conductive and semi-conductive materials.
[0037] Also the photoconductive substrate composed of a greater-than-1.6 eV
wide band gap material, said substrate having opposing electrode-contacting surfaces and a facet optically connectable to an optical source for receiving optical energy therefrom;
two electrodes electrically connected to the electrode-contacting surfaces of the substrate, for applying a potential across the substrate; and two field-grading liners formed on the substrate surrounding the electrode-contacting surfaces, for grading the electric fields therealong. In the case where the field-grading liners are adjacent the electrode perimeters, the field-grading liners are preferably formed between the substrate and the electrode perimeters. Also, the two field-grading liners are recessed below the level of the electrode-contacting surfaces. Wherein outer surfaces of the field-grading liners are coplanar with the electrode-contacting surfaces to form extensions thereof. Wherein the field-grading liners are adjacent the substrate perimeter.
wide band gap material, said substrate having opposing electrode-contacting surfaces and a facet optically connectable to an optical source for receiving optical energy therefrom;
two electrodes electrically connected to the electrode-contacting surfaces of the substrate, for applying a potential across the substrate; and two field-grading liners formed on the substrate surrounding the electrode-contacting surfaces, for grading the electric fields therealong. In the case where the field-grading liners are adjacent the electrode perimeters, the field-grading liners are preferably formed between the substrate and the electrode perimeters. Also, the two field-grading liners are recessed below the level of the electrode-contacting surfaces. Wherein outer surfaces of the field-grading liners are coplanar with the electrode-contacting surfaces to form extensions thereof. Wherein the field-grading liners are adjacent the substrate perimeter.
[0038] In most substrates, there are imperfection within the structure, such as shown in Figure 14. These imperfections 92 can include voids, fractures, and the like. In a particular plane of SiC such as shown at 90, these voids can also include "micropipes," such as shown at 91. That is long and narrow tubular voids through the full length of the substrate. When high voltage is applied to the substrate, arc breakdown can occur through the full length of the device either by connecting through the voids or completely through the micropipes. It is well known to those skilled in the art that breakdown occurs in a void by the acceleration and collision of charge particles created within the void by ionization. The collisions create ion-electron pairs which further contribute to the process until a full avalanche i.e., arc occurs. It is also well known that the shorter the charge particles can travel, the less energy they receive, and the less likely an avalanche can occur. Thus small void can have less of an effect than a large void. Eliminating all voids is a difficult and expensive process.
[0039] Thus an enhancement for isolating voids and reducing their scale size is shown in Figure 15 of the present invention. In this structure, the substrate is made into a laminated structure, such as three layers 100-102. Micropipes no longer can make a full connection through the entirety of the substrate thickness. Further, the majority of voids can be made smaller.
[0040] Many substrates are very transparent to the optical energy that is used to transition them from the non-conducting to conducting state, as shown in Figure 16.
Optical absorption depths are on the order of 1 cm for approximately 1 micron light.
As a result, in an optically short switch, the majority of the input optical energy is wasted. Substrates can be expensive and thus an optically long switch would be expensive to be efficient. As a result, operating a large array of these switches in perhaps an accelerator, could become prohibitive because of cost. As shown in Figure 17, an exemplary embodiment of the present invention makes the switch into a cavity which contains all the admitted optical energy. This is accomplished by a means, such as a dielectric coating shown in Figure 17, whereby the substrate scale can be made small and optimization of the device size can be focused on the electrical requirements such as current density through the switch.
Optical absorption depths are on the order of 1 cm for approximately 1 micron light.
As a result, in an optically short switch, the majority of the input optical energy is wasted. Substrates can be expensive and thus an optically long switch would be expensive to be efficient. As a result, operating a large array of these switches in perhaps an accelerator, could become prohibitive because of cost. As shown in Figure 17, an exemplary embodiment of the present invention makes the switch into a cavity which contains all the admitted optical energy. This is accomplished by a means, such as a dielectric coating shown in Figure 17, whereby the substrate scale can be made small and optimization of the device size can be focused on the electrical requirements such as current density through the switch.
[0041] An example fabrication process for integrally forming the field-grading liners in a 6H-Sic substrate, for example, is as follows. First RCA clean 6H-SiC
substrates.
Then plasma-enhanced chemical vapor deposition or PECVD growth at 350 C of 0.5 um Silicon Nitride layer over surface of 6H-SiC substrates. High temperature (1200 C) growth of 1 um thick thermal oxide (SiO2) layer over surface Nitride layer.
Reactive ion etch through SiO2 and Si3N4 layers and approximately 1 -2 um into 6H-SiC substrate surface. Reactive ion etch using SF6-02 gas will result in a radiused profile at the edge of the pattern etched through Si02, Si3N4 and into SiC.
Next, contact metal layers are deposited directly over etched pattern such that the high fields at the edge of metalization are pushed into thermal Si02 layer. Thermal oxide layer has a critical field strength three thimes higher than 6H-SiC.
substrates.
Then plasma-enhanced chemical vapor deposition or PECVD growth at 350 C of 0.5 um Silicon Nitride layer over surface of 6H-SiC substrates. High temperature (1200 C) growth of 1 um thick thermal oxide (SiO2) layer over surface Nitride layer.
Reactive ion etch through SiO2 and Si3N4 layers and approximately 1 -2 um into 6H-SiC substrate surface. Reactive ion etch using SF6-02 gas will result in a radiused profile at the edge of the pattern etched through Si02, Si3N4 and into SiC.
Next, contact metal layers are deposited directly over etched pattern such that the high fields at the edge of metalization are pushed into thermal Si02 layer. Thermal oxide layer has a critical field strength three thimes higher than 6H-SiC.
[0042] It is appreciated that RCA clean is the industry standard for removing contaminants from wafers. Contaminants present on the surface of silicon wafers at the start of processing, or accumulated during processing, have to be removed at specific processing steps in order to obtain high performance and high reliability semiconductor devices, and to prevent contamination of process equipment, especially the high temperature oxidation, diffusion, and deposition tubes.
The RCA
cleaning procedure has three major steps used sequentially: First there is organic cleaning involving the removal of insoluble organic contaminants with a 5:1:1 H20:
H202: NH4OH solution. Next there is oxide stripping involving the removal of a thin silicon dioxide layer where metallic contaminants may accumulated as a result of (I), using a diluted H2 0: HF solution. And finally, there is ionic cleaning involving the removal of ionic and heavy metal atomic contaminants using a solution of 6:1:1 H20: H202: HCI.
The RCA
cleaning procedure has three major steps used sequentially: First there is organic cleaning involving the removal of insoluble organic contaminants with a 5:1:1 H20:
H202: NH4OH solution. Next there is oxide stripping involving the removal of a thin silicon dioxide layer where metallic contaminants may accumulated as a result of (I), using a diluted H2 0: HF solution. And finally, there is ionic cleaning involving the removal of ionic and heavy metal atomic contaminants using a solution of 6:1:1 H20: H202: HCI.
[0043] While particular operational sequences, materials, temperatures, parameters, and particular embodiments have been described and or illustrated, such are not intended to be limiting. Modifications and changes may become apparent to those skilled in the art, and it is intended that the invention be limited only by the scope of the appended claims.
Claims (36)
1. A photoconductive switch comprising:
a photoconductive substrate composed of a greater-than-1.6 eV wide band gap material, said substrate having at least one concavity(s), and a facet optically connectable to an optical source for receiving optical energy therefrom; and two electrodes electrically connected to the substrate with at least one of the electrodes having a convex surface contactedly seated in a corresponding one of the at least one concavity(s), for applying a potential across the substrate.
a photoconductive substrate composed of a greater-than-1.6 eV wide band gap material, said substrate having at least one concavity(s), and a facet optically connectable to an optical source for receiving optical energy therefrom; and two electrodes electrically connected to the substrate with at least one of the electrodes having a convex surface contactedly seated in a corresponding one of the at least one concavity(s), for applying a potential across the substrate.
2. The photoconductive switch of claim 1, further comprising two field-grading liners formed on the substrate surrounding the electrode-contacting surfaces, for grading the electric fields therealong.
3. The photoconductive switch of claim 2, wherein the two field-grading liners are adjacent the electrode perimeters.
4. The photoconductive switch of claim 3, wherein the two field-grading liners form the rims of the two concavities for grading the electric fields at the separations of the electrodes from the substrate.
5. The photoconductive switch of claim 2, wherein the field-grading liners are integrally formed on the substrate.
6. The photoconductive switch of claim 2, wherein the field-grading liners are a high permittivity material.
7. The photoconductive switch of claim 2, wherein the field-grading liners are selected from a group consisting of conductive and semi-conductive materials.
8. The photoconductive switch of claim 7, wherein the field-grading liners are composed of silicon nitride.
9. The photoconductive switch of claim 7, wherein the conductive or semi-conductive material is formed as a doped sub-surface layer of the substrate.
10. The photoconductive switch of claim 9, wherein the doped sub-surface conductive or semi-conductive sub-surface layer extends into the substrate about 1 micron deep.
11. The photoconductive switch of claim 1, wherein the substrate is a multilayer having at least two photoconductive layers separated by a divider layer.
12. The photoconductive switch of claim 11, wherein the divider layer is selected from a group consisting of conductive and semi-conductive materials
13. The photoconductive switch of claim 1, wherein the substrate is a compensated, semi-insulating material selected from a group consisting of 4h SiC, 6h SiC, and GaN.
14. The photoconductive switch of claim 13, wherein the substrate is semi-insulating SiC having a hexagonal crystal structure and cut in a plane selected from the group consisting of the A-Plane, C-Plane and M-plane.
15. The photoconductive switch of claim 14, wherein the substrate comprises at least two layers cut in the C-Plane and offset from each other.
16. The photoconductive switch of claim 13, wherein the semi-insulating SiC is doped with at least one of the following dopants: Boron, Vanadium, Nitrogen, Aluminum, Phosphorus, Oxygen, Tungsten and Zinc.
17. The photoconductive switch of claim 1, wherein at least one facet of the substrate is coated with a dielectric to produce total internal reflection.
18. A photoconductive switch comprising:
a photoconductive substrate composed of a greater-than-1.6 eV wide band gap material, said substrate having opposing electrode-contacting surfaces and a facet optically connectable to an optical source for receiving optical energy therefrom;
two electrodes electrically connected to the electrode-contacting surfaces of the substrate, for applying a potential across the substrate; and at least one field-grading liner(s) formed on the substrate surrounding a corresponding one of the electrode-contacting surfaces, for grading the electric fields therealong.
a photoconductive substrate composed of a greater-than-1.6 eV wide band gap material, said substrate having opposing electrode-contacting surfaces and a facet optically connectable to an optical source for receiving optical energy therefrom;
two electrodes electrically connected to the electrode-contacting surfaces of the substrate, for applying a potential across the substrate; and at least one field-grading liner(s) formed on the substrate surrounding a corresponding one of the electrode-contacting surfaces, for grading the electric fields therealong.
19. The photoconductive switch of claim 18, wherein the field-grading liners are adjacent the electrode perimeters.
20. The photoconductive switch of claim 19, wherein the field-grading liners are formed between the substrate and the electrode perimeters.
21. The photoconductive switch of claim 20, wherein the two field-grading liners are recessed below the level of the electrode-contacting surfaces.
22. The photoconductive switch of claim 21, wherein outer surfaces of the field-grading liners are coplanar with the electrode-contacting surfaces to form extensions thereof.
23. The photoconductive switch of claim 18, wherein the field-grading liners are adjacent the substrate perimeter.
24. The photoconductive switch of claim 18, wherein the field-grading liners are integrally formed on the substrate.
25. The photoconductive switch of claim 18, wherein the field-grading liners are a high permittivity material.
26. The photoconductive switch of claim 18, wherein the field-grading liners are selected from a group consisting of conductive and semi-conductive materials.
27. The photoconductive switch of claim 26, wherein the field-grading liners are composed of silicon nitride.
28. The photoconductive switch of claim 26, wherein the conductive or semi-conductive material is formed as a doped sub-surface layer of the substrate.
29. The photoconductive switch of claim 28, wherein the doped sub-surface conductive or semi-conductive sub-surface layer extends into the substrate about 1 micron deep.
30. The photoconductive switch of claim 18, wherein the substrate is a multilayer having at least two photoconductive layers separated by a divider layer.
31. The photoconductive switch of claim 30, wherein the divider layer is selected from a group consisting of conductive and semi-conductive materials
32. The photoconductive switch of claim 18, wherein the substrate is a compensated, semi-insulating material selected from a group consisting of 4h SiC, 6h SiC, and GaN.
33. The photoconductive switch of claim 32, wherein the substrate is semi-insulating SiC having a hexagonal crystal structure and cut in a plane selected from the group consisting of the A-Plane, C-Plane and M-plane.
34. The photoconductive switch of claim 33, wherein the substrate comprises at least two layers cut in the C-Plane and offset from each other.
35. The photoconductive switch of claim 32, wherein the semi-insulating SiC is doped with at least one of the following dopants: Boron, Vanadium, Nitrogen, Aluminum, Phosphorus, Oxygen, Tungsten and Zinc.
36. The photoconductive switch of claim 18, wherein at least one facet of the substrate is coated with a dielectric to produce total internal reflection.
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| US60/730,161 | 2005-10-24 | ||
| US79801606P | 2006-05-04 | 2006-05-04 | |
| US60/798,016 | 2006-05-04 | ||
| PCT/US2006/041814 WO2007120191A2 (en) | 2005-10-24 | 2006-10-24 | Optically- initiated silicon carbide high voltage switch |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2626800A1 true CA2626800A1 (en) | 2007-10-25 |
Family
ID=38609951
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002626800A Abandoned CA2626800A1 (en) | 2005-10-24 | 2006-10-24 | Optically- initiated silicon carbide high voltage switch |
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| EP (1) | EP1941552A2 (en) |
| JP (1) | JP5376951B2 (en) |
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| CN (1) | CN101390223B (en) |
| AU (1) | AU2006342150A1 (en) |
| CA (1) | CA2626800A1 (en) |
| WO (1) | WO2007120191A2 (en) |
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| JP5376951B2 (en) | 2013-12-25 |
| CN101390223A (en) | 2009-03-18 |
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| EP1941552A2 (en) | 2008-07-09 |
| WO2007120191A2 (en) | 2007-10-25 |
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