Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Physical deformation
Reexamination Certificate
2000-08-01
2003-06-17
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Physical deformation
C257S254000, C257S417000, C257S419000
Reexamination Certificate
active
06580138
ABSTRACT:
TECHNICAL FIELD
The present invention relates to micro electro-mechanical (MEM) tunneling sensors and switches using dual wafers which are bonded together and in which a cantilevered member is released a substrate by etching.
BACKGROUND OF THE INVENTION
The present invention provides a new process of fabricating a single crystal silicon MEM tunneling devices using low-cost bulk micromachining techniques while providing the advantages of surface micromachining. The prior art, in terms of surface micromachining, uses e-beam evaporated metal that is patterned on a silicon dioxide (SiO
2
) layer to form the control, self-test, and tip electrodes of a tunneling MEM switch or sensor. A cantilevered beam is then formed over the electrodes using a sacrificial resist layer, a plating seed layer, a resist mold, and metal electroplating. Finally, the sacrificial layer is removed using a series of chemical etchants. The prior art for bulk micromachining has utilized either mechanical pins and/or epoxy for the assembly of multi-Si wafer stacks, a multi-Si wafer stack using metal-to-metal bonding and an active sandwiched membrane of silicon nitride and metal, or a dissolved wafer process on quartz substrates (Si-on-quartz) using anodic bonding. None of these bulk micromachining processes allow one to fabricate a single crystal Si cantilever (with no deposited layers over broad areas on the beam which can produce thermally mismatched expansion coefficients) above a set of tunneling electrodes on a Si substrate and also electrically connect the cantilever to pads located on the substrate and at the same time affording good structural stability. The fabrication techniques described herein provide these capabilities in addition to providing a low temperature process so that CMOS circuitry can be fabricated in the Si substrate before the MEMS switches and/or sensors are added. Finally, the use of single crystal Si for the cantilever provides for improved process reproductibility for controlling the stress and device geometry. A protrusion is formed on at least one of the substrates to provide better mechanical stability to the resulting switch or sensor.
Tunneling switches and sensors may be used in various military, navigation, automotive, and space applications. Space applications include satellite stabilization in which MEM switch and sensor technology can significantly reduce the cost, power, and weight of the presently used gyro systems. Automotive air bag deployment, ride control, and anti-lock brake systems provide other applications for MEM switches and sensors. Military applications include high dynamic range accelerometers and low drift gyros.
MEM switches and sensors are rather similar to each other. The differences between MEM switches and MEM sensors will be clear in the detailed disclosure of the invention.
BRIEF DESCRIPTION OF THE INVENTION
Generally speaking, the present invention provides a method of making a micro electro-mechanical switch or sensor wherein a cantilevered beam structure and a mating structure are defined on a first substrate or wafer and at least one contact structure and a mating structure are defined on a second substrate or wafer. The first substrate includes an insulator layer, preferably of SiO
2
, on which a layer of silicon is formed. The cantilevered member is formed from the layer of silicon using photolithographic techniques. The mating structure on the second substrate or wafer is preferably of a complementary shape to the mating structures on the first substrate or wafer. A bonding or eutectic layer is provided on at least one of the mating structures and the mating structure are moved into a confronting relationship with each other. Pressure is then applied between the two substrates and heat may also be applied so as to cause a bond to occur between the two mating structures at the bonding or eutectic layer. Next the first substrate or wafer is removed and then the insulator layer is removed to free the cantilevered beam structure for movement relative to the second substrate or wafer. The bonding or eutectic layer also provides a convenient electrical path to the cantilevered beam for making a circuit with the contact formed on the cantilevered beam.
In another aspect, the present invention provides an assembly or assemblies for making a single crystal silicon MEM switch or sensor therefrom. A first substrate or wafer is provided upon which is defined an insulating surface. A beam structure and a mating structure are formed on the insulating surface. A second substrate or wafer is provided upon which is defined at least one contact structure and a mating structure, the mating structure on the second substrate or wafer being of a complementary shape to the mating structure on the first substrate or wafer. At least one of the two mating structures includes a silicon protrusion extending from the wafer on which the corresponding unit is fabricated. A pressure and heat sensitive bonding layer is disposed on at least one of the mating structures for bonding the mating structure defined on the first substrate or wafer with the mating structure on the second substrate in response to the application of pressure and heat therebetween.
REFERENCES:
patent: 5015850 (1991-05-01), Zdeblick et al.
patent: 5210714 (1993-05-01), Pohl et al.
patent: 5226321 (1993-07-01), Varnham et al.
patent: 5265470 (1993-11-01), Kaiser et al.
patent: 5313835 (1994-05-01), Dunn
patent: 5354985 (1994-10-01), Quate
patent: 5475318 (1995-12-01), Marcus et al.
patent: 5659195 (1997-08-01), Kaiser et al.
patent: 5665253 (1997-09-01), Kubena et al.
patent: 5666190 (1997-09-01), Quate et al.
patent: 5747804 (1998-05-01), Williams et al.
patent: 5883387 (1999-03-01), Matsuyama et al.
patent: 5894090 (1999-04-01), Tang et al.
patent: 5929497 (1999-07-01), Chavan et al.
patent: 5994750 (1999-11-01), Yagi
patent: 6075585 (2000-06-01), Minne et al.
patent: 6091125 (2000-07-01), Zavracky
patent: 6092423 (2000-07-01), Beardmore
patent: 6174820 (2001-01-01), Habermehl et al.
patent: 6211532 (2001-04-01), Yagi
patent: 6229190 (2001-05-01), Bryzek et al.
patent: 6296779 (2001-10-01), Clark et al.
patent: 6337027 (2002-01-01), Humphrey
patent: 43 05 033 (1993-10-01), None
patent: 0 619 495 (1994-10-01), None
patent: 04-369418 (1992-12-01), None
patent: 08-203417 (1996-08-01), None
patent: 97/10698 (1997-03-01), None
Grade, J., et al., “Wafer-Scale Processing, Assembly, and Testing of Tunneling Infrared Detectors,” International Conference on Solid-State Sensors and Actuators, Chicago, Illinois (Jun. 16-19, 1997).
Grétillat, F., et al., “Improved Design of a Silicon Mircomachined Gyroscope with Piezoresistive Detection and Electromagnetic Excitation,”IEEE Journal of Microelectromechanical Systems, vol. 8, No. 3, pp 243-250 (Sep. 1999).
Kenny, T.W., et al., “Micromachined Silicon Tunnel Sensor for Motion Detection,”Appl. Phys. Lett., vol. 58, No. 1, pp 100-102 (Jan. 1991).
Yeh, C., et al., “A Low-Voltage Bulk-Silicon Tunneling-Based Microaccelerometer,”IEEE, pp 23.1.1-23.1.4 (1995).
Abstract of JP 04-369418,Patent Abstracts of Japan, vol. 017, No. 250, May 18, 1993.
Abstract of JP 08-203417,Patent Abstracts of Japan, vol. 1996, No. 12, Dec. 26, 1996.
Kubena, R.L., et al., “A New Miniaturized Surface Micromachined Tunneling Accelerometer,”IEEE Electron Device Letters, vol. 17, No. 6, pp. 306-308 (Jun. 1996).
Kubena, R.L., et al., “New miniaturized tunneling-based gyro for inertial measurement applications,” 43rdJournal of Vacuum Science&Technology B(Microelectronics and Nanometer Structures, vol. 17, No. 6, pp. 2948-2952 (Nov./Dec. 1999).
Liu, C-H, et al., “Characterization of a High-Sensitivity Micromachined Tunneling Accelerometer with Micro-g Resolution,”Journal of Microelectromechanical Systems, vol. 7, No. 2, pp. 235-243 (Jun. 1998).
Motamedi, M.E., et al., “Tunneling Tip Engine for Microsensors Applications,”Materials and Device Characterization in Micromachining II—Proceedings of the SPIE, Santa Clara, California, vol. 3875, pp. 192-199 (Sep. 1999).
Cheng, Y.T. and Khalil Najafi, “Localize
Chang David T.
Kubena Randall L.
HRL Laboratories LLC
Ladas & Parry
Lee Eddie
Richards N. Drew
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