US RE39261 E1
A solid state laser beam scanning system having a single crystal silicon deflection and scanning mirror integrated with a laser diode. By combining the techniques of deep reactive ion etching of silicon with solder bump bonding techniques, completed and tested laser diodes are integrated with silicon substrates supporting micro-electro-mechanical systems layers.
1. An integrated laser beam scanning structure comprising:
a wafer having a recess on a side;
a layer having a first region and a second region, said layer being attached to said side of said wafer having said recess;
a deflecting mirror fashioned from said first region of said layer;
a torsional mirror fashioned from said second region of said layer, said torsional mirror having a first side; and
a semiconductor light emitter mounted in said recess whereby a light beam emitted from said semiconductor light emitter is deflected by said deflecting mirror onto said first side of said torsional mirror.
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11. A method for making an integrated laser beam scanner comprising the steps of:
providing a wafer having a recess on a side;
attaching a layer having a first region and a second region to said side of said wafer having said recess;
fashioning a deflecting mirror from said first region of said layer;
fashioning a torsional mirror from said second region of said layer, said torsional mirror having a first side; and
mounting a semiconductor light emitter in said recess such that a light beam emitted from said semiconductor light emitter is deflected by said deflecting mirror onto said first side of said torsional mirror.
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21. A MEMS formation method including:
providing a SOI wafer including a single crystal silicon layer attached to an insulator layer;
forming at least one first MEMS component by paterning the single crystal silicon layer;
depositing at least one layer of polysilicon on the patterned single crystal silicon; and
forming at least one second MEMS component by patterning the polysilicon.
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26. A MEMS formation method including:
providing a SOI wafer including a single crystal silicon layer attached to an insulated layer;
forming at least one first MEMS component by patterning the single crystal silicon layer;
depositing at least one layer of polysilicon on the patterned single crystal silicon; wherein forming at least one first MEMS component includes forming a deflecting mirror, and forming at least one second MEMS component by patterning the polysilicon, the at least one second MEMS component including a hinge retaining the deflecting mirror.
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28. A MEMS device comprising:
at least one single crystal silicon component bonded to an insulator that rests on a handle wafer; and
a polysilicon hinge derived from a layer of polysilicon applied over the at least one single crystalline component.
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31. A MEMS device comprising:
at least one single crystal silicon component bonded to an insulator that rests on a handle wafer; and
at least one polysilicon component derived from a layer of polysilicon applied over the at least one single crystalline silicon component;
a recess in the handle wafer aligned with the at least one single crystal silicon component; and
a semiconductor light emitter mounted in the recess to emit a light beam at the single crystal silicon component.
32. The MEMS device of
The present invention is related to “METHOD AND APPARATUS FOR AN INTEGRATED LASER BEAM SCANNER USING A CARRIER SUBSTRATE” by Floyd, Sun and Kubby (Attorney Docket No. D/98707), Ser. No. 09/203,442, filed on the same day and assigned to the same assignee which is hereby incorporated by reference in its entirety.
The present invention relates generally to the field of laser beam scanning systems, and more particularly to micro-electro-mechanical systems (MEMS) for laser beam scanning. Miniature laser beam scanning systems are important for applications such as barcode scanning, machine vision and, most importantly, xerographic printing. The use of MEMS to replace standard raster output scanning (ROS) in xerographic print engines allows simplification of printing systems by eliminating macroscopic mechanical components and replacing them with large arrays of scanning elements. Advanced computation and control algorithms are used in managing the large arrays of scanning elements.
Such MEMS based printing systems are entirely solid state, reducing complexity, and allowing increased functionality, including compensation of errors or failures in the scanner elements. An important step in constructing solid state scanning systems is integrating the semiconductor light emitter directly with MEMS actuators to gain the desired optical system simplification. Integrated scanners, which have lasers and scanning mirrors in the same structure, have been demonstrated using manual placement of laser chips onto MEMS wafers with micromachined alignment parts and adhesives by L. Y. Lin et al in Applied Physics Letters, 66, p. 2946, 1995 and by M. J. Daneman et al in Photonics Technology Letters, 8(3), p. 396, 1996. However, current techniques do not allow wafer-scale integration of the light-emitter and MEMS device.
In accordance with the present invention a laser beam scanner consisting of a single crystal silicon (SCS) deflection and scanning mirror is integrated with a laser diode or light emitting diode. By combining methods of deep reactive ion etching (deep RIE) of silicon with solder bump bonding methods, completed and tested laser diodes are integrated with silicon (Si) or silicon on insulator (SOI) substrates supporting MEMS layers. Details of creating a torsional mirror and actuating it magnetically or electrostatically are detailed in U.S. Pat. No. 5,629,790 by Neukermans and Slater which is incorporated herein by reference in its entirety.
Using solder bump bonding methods, completed and tested laser diodes are bonded to silicon MEMS built using a typical surface and bulk micromachining processes. Because of the deep RIE recesses, the laser diode solder bumps can be passively aligned to those on the host substrate. In addition, the deep RIE recesses allow nearly coplanar laser chip and Si surfaces to be made. The use of the SCS layer of an SOI wafer, rather than the polysilicon film provides for the introduction of very flat and smooth mirrors and high reliability torsion bars. The device is easily scalable to arrays of lasers and scanning mirrors on a single wafer.
Integration of the scanner and light source eliminates the need for external, manual positioning of light sources and scanning mirrors. Simplified and more cost effective post-processing steps such as interconnect metallization can be realized because the use of an etched recess results in nearly planar surfaces. In addition, pick and place technologies commonly used for multi-chip module assembly can be adapted for wafer scale assembly and bonding of light sources to the carrier substrate. With such commercial systems, bare die can be placed with accuracy better than ±30 μm.
Thus, the present invention allows the integration of completed and tested light emitting devices directly with the MEMS actuators to gain the desired simplification of the optical system needed to realize solid state scanning systems.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained and understood by referring to the following detailed description and the accompanying drawings in which like reference numerals denote like elements as between the various drawings. The drawings, briefly described below, are not to scale.
An embodiment in accordance with this invention is shown in
Electrical contact to laser 105 can be made in a variety of ways. Contact can be made by planar surface metallization, by wire bonding to the laser, through the polysilicon layer with solder bumps or some combination of each. Using solder bump bonding methods, completed and tested lasers 105 are bonded to layer phosphorus-doped glass (PSG) layer 119 in recess 135. Deep RIE etching may be used to define recess 135 in the MEMS surface layers 130 and Si substrate 115 for subsequent laser chip 105 placement. Because of deep RIE recess 135, laser diode solder bumps 110 can be passively aligned to wettable metal bonding pads 111 on substrate 115. In addition, deep RIE recess 135 allows for nearly coplanar laser chip 105 and Si surfaces. This allows simplification of the subsequent metallization steps and laser chip 105 does not interfere with the space used for the optical path. The use of SCS layer 130 of SOI wafer 100 for the mirror material, rather than polysilicon film provides for the introduction of very flat and smooth mirrors 140 and 150 and high reliability torsion bars 170. The device is easily scalable to arrays of lasers and scanning mirrors. The reflective surface of deflecting mirror 140 and torsional mirror 150 is typically coated with aluminum 430 (see FIGS. 4e-4m).
Polysilicon hinge 155 is micromachined from a deposited polysilicon layer and attaches deflecting mirror 140 to SOI substrate 115. Polysilicon hinge 155 allows deflecting mirror 140 to rotate clockwise about an axis perpendicular to the plane of
Steps for fabricating deflecting mirror, supporting latch and VCSEL in accordance with this invention are shown in
Linear arrays of lasers can be bonded in a similar way; the extent of the array being perpendicular to the cross section shown in
While the invention has been described in conjunction with specific embodiments, it is evident to those skilled in the art that many alternatives, modifications, and variations will be apparent in light of the foregoing description. Accordingly, the invention is intended to embrace all other such alternatives, modifications, and variations that fall within the spirit and scope of the appended claims.