Microassembly technologies for MEMS

Proceedings of SPIE - The International Society for Optical Engineering

Volumn 3511, Issue , 1998, Pages 2-16

  Cohn, Michael B ^a   Böhringer, Karl F ^a,b   Noworolski, J Mark ^a   Singh, Angad ^a   Keller, Chris G ^c   Goldberg, Ken Y ^a   Howe, Roger T ^a  

^a UNIVERSITY OF CALIFORNIA   (United States)

^b UNIVERSITY OF WASHINGTON   (United States)

^c MEMS Precision Instruments   (United States)

Author keywords

MEMS; Microassembly; Packaging; Parallel assembly; Self assembly; Serial assembly; Wafer to wafer transfer

Indexed keywords

ASSEMBLY; CMOS INTEGRATED CIRCUITS; CRYSTAL MICROSTRUCTURE; ELECTRON TRAPS; ELECTRONICS PACKAGING; ELECTROSTATICS; INTEGRATED CIRCUIT MANUFACTURE; MICROELECTRONIC PROCESSING; MICROMACHINING; SEMICONDUCTING SILICON; SUBSTRATES; WSI CIRCUITS; SILICON WAFERS; MICROSTRUCTURE; SILICON;

ELECTROSTATIC TRAPS; MICROASSEMBLY; PARALLEL ASSEMBLY; SERIAL ASSEMBLY; MICROASSEMBLY STRATEGIES; WAFER-TO-WAFER TRANSFER; SELF ASSEMBLY; MICROASSEMBLY TECHNOLOGIES;

MICROELECTROMECHANICAL DEVICES;

EID: 0032302212     PISSN: 0277786X     EISSN: None     Source Type: Conference Proceeding    
DOI: 10.1117/12.324300     Document Type: Conference Paper

References (107)

1. K. F. Böhringer, K. Goldberg, M. Cohn, R. Howe, and A. Pisano, "Parallel-microassembly with electrostatic force fields," Int. Conf. on Robotics and Automation, Leuven, Belgium, May 1998.
2. Figure after M. B. Cohn, "Self assembly using electrostatic particle traps," Ph.D. Qualifying Exam, Dept. of EECS, Univ. of Calif. at Berkeley, May 1995.
3. S. M. Rodgers and J. J. Sniegowski, "5-level polysilicon surface micromachine technology: application to complex mechanical systems," Solid State Sensor and Actuator Workshop, Hilton Head, S.C., June 1998, pp. 144-149.
4. Pister, K.S.J.; Judy, M.W.; Burgett, S.R.; Fearing, R.S. Microfabricated hinges. Sensors and Actuators A (Physical), vol.A33, (no.3), June 1992, p.249-56.
5. R. S. Fearing, "A survey of sticking effects for micro parts handling," IEEE/RSJ Int. Workshop on Intelligent Robots and Systems, Pittsburgh, Penn., 1995.
6. C. G. Keller and R. T. Howe, "Hexsil tweezers for teleoperated microassembly," IEEE Micro Electro Mechanical Systems Workshop, Nagoya, Japan, Jan. 1997, pp. 72-77.
7. A. E. Quaid and R. L. Hollis. Cooperative 2-dof robots for precision assembly. IEEE Int. Conf. on Robotics and Automation, Minneapolis, Minn., Apr. 1996.
8. W. Zesch. Multi-Degree-of-Freedom Micropositioning Using Stepping Principles. PhD Thesis, Swiss Federal Institute of Technology, Zurich, Switzerland, 1997.
9. G. Danuser, I. Pappas, B. Vögel, W. Zesch, and J. Dual. "Manipulation of microscopic objects with nanometer precision: Potentials and limitations in nano-robot design," submitted to Int. Journal of Robotics Research, 1997.
10. K. S. J. Pister, R. S. Fearing, and R. T. Howe, "A planar air levitated electrostatic actuator system," IEEE Micro Electro Mechanical Systems Workshop, Napa Valley, Calif., Feb. 1990, pp. 67-71.
11. M. W. Judy, Y.-H. Cho, R. T. Howe, and A. P. Pisano, "Self-adjusting microstructures (SAMS)," IEEE Micro Electro Mechanical Systems Workshop, Nara, Japan, Jan.-Feb. 1991, pp. 51-56.
12. K. S. J. Pister, M. W. Judy, S. R. Burgett, and R. S. Fearing, "Microfabricated hinges: 1 mm vertical features with surface micromachining," 6th Int. Conf. on Solid-State Sensors and Actuators, San Francisco, Calif., June 1991.
13. Y. Fukuta, D. Collard, T. Akiyama, E. H. Yang, and H. Fujita, "Microactuated self-assembling of 3D polysilicon structures with reshaping technology," IEEE Micro Electro Mechanical Systems Workshop, Nagoya, Japan, Jan. 1997, pp. 477-481.
14. C. Gonzaléz, R. L. Smith, D. G. Howitt, and S. D. Collins, "MicroJoinery: concept, definition, and application to microsystem development," Sensors and Actuators A (Physical), 66, 315-332 (1998).
15. F. Arai and T. Fukuda, "A new pick up and release method by heating for micromanipulation, IEEE Micro Electro Mechanical Systems Workshop, Nagoya, Japan, Jan. 1997, pp. 383-388.
16. C. Bark, T. Binnenböse, G. Vögele, T. Weisener, and M. Widmann, "Gripping with low viscosity fluids," IEEE Micro Electro Mechanical Systems Workshop, Heidelberg, Germany, Feb. 1998, pp. 301-305.
17. H. H. Langen, "A study on micromachining/assembly," Ph.D. thesis, Univ. of Tokyo, 1994.
18. W.-H. Chu and M. Mehregany, "Microfabricated tweezer with a large gripping force and a large range of motion," Solid State Sensor and Actuator Workshop, Hilton Head, S.C., June 1994, pp. 107-111.
19. C.-J. Kim, R. S. Muller, A. P. Pisano, and M. G. Lim, "Polysilicon microtweezers," Sensors and Actuators A (Physical), 33, 221-227 (1992).
20. C. G. Keller, "Microfabricated silicon high aspect ratio flexures for in-plane motion", Ph.D. Thesis, Dept. of Materials Science and Mineral Engineering, Univ. of Calif. at Berkeley, 1998.
21. I. Shimoyama, "Scaling in microrobotics," IEEE/RSJ Int. Workshop on Intelligent Robots and Systems, Pittsburgh, Penn., 1995, pp. 208-211.
22. R. A. Bowling, "A theoretical review of particle adhesion," in K. L. Mittal, ed., Particles on Surfaces I Detection, Adhesion, and Removal. New York: Plenum, pp. 129-155.
23. E. T. Yablonovitch, J.P. Harbison,; P. Bhat, "Extreme selectivity in the lift-off of epitaxial GaAs films." Applied Physics Letters, 51, 28 Dec. 1987, pp. 2222-4.
24. K. W. Goosen, et al, "GaAs MQW modulators integrated with silicon CMOS," IEEE Photonics Tech. Lett., 7, 360-363 (1995).
25. Camperi-Ginestet, C.; Hargis, M.; Jokerst, N,M.; Allen, M., "Alignable epitaxial liftoff of GaAs materials with selective deposition using polyimide diaphragms," IEEE Photonics Technology Letters, vol.3, no.12 p.1123-6 Dec. 1991.
26. M.B. Cohn, Y.-C. Liang, R.T. Howe, A.P. Pisano, "wafer-to-wafer transfer of microstructures for vacuum packaging," 1996 Solid-State Sensor and Actuator Workshop, Hilton Head Island, SC, USA, June 2-6, 1996.
27. L.S. Goodman, "Geometric optimization of controlled collapse interconnections," IBM J. Res. Devel 13(3): pp. 251-265, 1969.
28. K.W. Marcus, V. Dhuler, D. Roberson, A. Cowen, M. Berry, S. Nangalia, "Smart MEMS: Flip Chip Integration of MEMS and Electronics," SPIE Smart Materials Conference, Feb 1995.
29. A. Singh, D.A. Horsley, M.B. Cohn, A.P. Pisano, R.T. Howe, "Batch Transfer of Microstructures using flip-chip solder bump bonding", Technical Digest, Transducers'97, Chicago, June, 1997.
30. C.G. Keller and M. Ferrari, "Milli-Scale Polysilicon Structures," Solid-State Sensor and Actuator Workshop, Hilton Head SC, pp. 132-137, June 1994.
31. D.A. Horsley, A. Singh, A.P. Pisano, R. Horowitz, "Angular Micropositioners for Disk Drives," Intl. Workshop on Micro Electro Mechanical Systems, Nagoya, Japan, pp. 454-459, 1997.
32. Horsley, D.A.; Cohn, M.B.; Singh, A.; Horowitz, R.; Pisano, A.P. Design and fabrication of an angular microactuator for magnetic disk drives. Journal of Microelectromechanical Systems, vol.7, (no.2) IEEE, June 1998, p.141-8.
33. A. Singh, D.A. Horsley, M.B. Cohn, A.P. Pisano, R.R. Howe, "Batch Transfer of Microstructures using flip-chip solder bonding", in the Journal of Microelectromechanical Systems submitted 5/98.
34. S. Wolf and R. N. Tauber, Silicon Processing for the VLSI Era, Volume 1: Process Technology, Lattice Press, Sunset Beach, CA, 1986, p. 8 ff.
35. J. Darnell, H. Lodish, D. Baltimore, Molecular cell biology / New York: W.H. Freeman, 1986.
36. C. Cantor, The behavior of biological macromolecules / San Francisco: W. H. Freeman, 1980.
37. M. B. Cohn, R. S. Fearing, "Self-Assembly in Microfabrication," Seminar Presented to the Berkeley Sensor and Actuator Center, Nov. 22, 1992.
38. H. Lodish, D. Baltimore, A. Berk, S. Zipursky, P. Matsudaira, J. Darnell, Molecular Cell Biology, Third Edition, / New York: W. H. Freeman, 1995, p. 1322.
39. M. Cohn, C.J. Kim, A.P. Pisano, "Self-Assembling Electrical Networks: An Application of Micromachining Technology," Transducers '91 International Conference on Solid-State Sensors and Actuators, Digest of Technical Papers, San Francisco, June 24-27, 1991 / New York: IEEE, 1991, p. 493.
40. S. Yando, Method and Apparatus for Fabricating an Array of Discrete Elements, U.S. Patent No. 3,439,416, Assigned to GTE Laboratories, Inc., 1969.
41. H. Hitakawa, "Advanced parts orientation system has wide application," Assembly Automation, 8(3), 1988.
42. M. A. Hadley, "Self-orienting fluidic transport (SOFT) assembly of liquid crystal displays," presentation at the Defense Manufacturing Conference, Palm Springs, Calif., Dec, 1-4, 1997.
43. H. J. Yeh, J.S. Smith, "Fluidic self-assembly of microstructures and its application to the integration of GaAs on Si," Proceedings IEEE Micro Electro Mechanical Systems, Oiso, Japan, 25-28 Jan 1994 / New York: IEEE, 1994. p.279-84.
44. A. Ashkin and J.M. Dziedzic, Science 235, 1517 (1987).
45. M. M. Burns, J. M. Fournier, J. A. Golovchenko, "Optical Binding," Physical Review Letters 63:12, p. 1233 ff. (18 Sept 1989).
46. K.V.I.S. Kaler and H.A.Pohl, "Dynamic dielectrophoretic levitation of living individual cells," IEEE Trans. IAS, vol. IA-19, 1983, 1089-1093.
47. T.B. Jones, Electromechanics of Particles / New York: Cambridge University Press, 1995.
48. G.Fuhr, W.M. Arnold, R. Hagedorn, T. Muller, W. Benecke, B. Wagner, and U. Zimmermann, "Levitation, holding, and rotation of cells within traps made by high-frequency fields," Biochim. Biophys. Acta, 1108, 1992, 215-223.
49. M. Washizu, T.B. Jones, and K.V.I.S. Kaler, "High-order DEP effects: Levitation at a field null," Biochim. Biophys. Acta, 1158, 1193a, 40-46.
50. T.B. Jones and J.P. Kraybill, "Active feedback-controlled dielectrophoretic levitation," J. Appl. Phys., 60, 1986, 1247-1252.
51. M.B. Cohn, R. T. Howe, A. P. Pisano, "Self-Assembly of Microsystems Using Non-Contact Electrostatic Traps," Proc. ASME International Mechanical Engineering Congress and Exposition (IMECE), San Francisco, California (November 1995), p. 893-900.
52. Cohn, M.B., "Self Assembly of Microfabricated Devices," US Patent No. 5,355,577, October, 1994.
53. Berggren, K.K.; Bard, A. Wilbur, J.L.; Gillapsy, J.D. Helg, A.G.; McClelland, J.J.; Rolston, S.L.; Phillips, W.D.; Prentiss, M.; Whitesides, G. M. "Microlithography by using neutral metastable atoms and self-assembled monolayers." Science v269, n5228 (Sept 1, 1995):1255.
54. A. Terfort, N. Bowden, and G.M. Whitesides, "Three-dimensional self-assembly of millimetre-scale components." Nature 386, 6621 (March 13, 1997):162.
55. M. Cohn, U.S. Patent No. 5,355,577, issued 10/1994.
56. K.-F. Böhringer, M. Cohn, K. Y. Goldberg, R. Howe, A. Pisano, Electrostatic Self-Assembly Aided by Ultrasonic Vibration, Presented at AVS'97 - American Vacuum Society National Symposium on Micro Electro Mechanical Systems (MEMS), San Jose, CA (October 1997).
57. H. Fujita. Group work of microactuators. In International Advanced Robot Program Workshop on Micromachine Technologies and Systems, pages 24-31, Tokyo, Japan, Oct. 1993.
58. S. Konishi and H. Fujita. A conveyance system using air flow based on the concept of distributed micro motion systems. In Transducers - Digest Int. Conf. on Solid-State Sensors and Actuators, pages 28-31, Pacifico, Yokohama, Japan, June 1993.
59. K.-F. Böhringer, B. R. Donald, R. Mihailovich, and N. MacDonald. A theory of manipulation and control for microfabricated actuator arrays. In Proc. IEEE Workshop on Micro Electro Mechanical Systems (MEMS), pages 102-107, Oiso, Japan, Jan. 1994.
60. C. W. Storment, D. A. Borkholder, V. Westerlind, J. W. Suh, N. I. Maluf, and G. T. A. Kovacs. Flexible, dry-released process for aluminum electrostatic actuators. Journal of Microelectromechanical Systems, 3(3):90-96, Sept. 94.
61. J. W. Suh, S. F. Glander, R. B. Darling, C. W. Storment, and G. T. A. Kovacs. Combined organic thermal and electrostatic omnidirectional ciliary microactuator array for object positioning and inspection. In Proc. Solid State Sensor and Actuator Workshop, Hilton Head, NC, June 1996.
62. C. Liu, T. Tsao, P. Will, Y. Tai, and W. Liu. A micro-machined magnetic actuator array for micro-robotics assembly systems. In Transducers - Digest Int. Conf. on Solid-State Sensors and Actuators, Stockholm, Sweden, June 1995.
63. W. Liu and P. Will. Parts manipulation on an intelligent motion surface. In IEEE/RSJ Int. Workshop on Intelligent Robots & Systems (IROS), Pittsburgh, PA, 1995
64. K.-F. Böhringer, B. R. Donald, N. C. MacDonald, G. T. A. Kovacs, and J. W. Suh. Computational methods for design and control of MEMS micromanipulator arrays. IEEE Computer Science and Engineering, pages 17-29, January-March 1997.
65. M. B. Cohn. Assembly Techniques for Microelectromechanical Systems. Ph.D. thesis, University of California at Berkeley, Department of Electrical Engineering and Computer Sciences, 1997.
66. K.-F. Böhringer, K. Goldberg, M. B. Cohn, R. Howe, and A. Pisano. Parallel microassembly with electrostatic force fields. In Proc. IEEE Int. Conf. on Robotics and Automation (ICRA), Leuven, Belgium, May 1998.
67. J. S. Hwang,. Modern solder technology for competitive electronics / New York: McGraw-Hill, 1996.
68. L.S. Goodman, "Geometric optimization of controlled collapse interconnections," IBM J. Res. Devel 13(3): pp. 251-265, 1969
69. M. M. Schwartz, "Fundamentals of Soldering," in ASM Handbook, 10th Edition, Volume 6: Welding, Brazing, and Soldering / Materials Park, OH; ASM International, 1990, p. 129-30.
70. S. M. Bobbio, N. G. Koopman, S. Nangalia, Fluxless soldering sample pretreating system, U.S. Patent No. 5,499,754, MCNC Corporation, Research Triangle Park, NC. ISSUED: Mar. 19, 1996
71. Y. C. Chen, C. Y. Wang, and C. C. Lee, "Directly deposited lead-indium-gold composite solder," IEEE Transactions on Components, Hybrids, and Manufacturing Technology, vol.16, (no.8), Dec. 1993, p.789-93.
72. T. Nishikawa, M. Ijuin, R. Satoh, Y. Iwata, M. Tamura, M. Shirai, "Fluxless soldering process technology," 1994 Proceedings. 44th Electronic Components and Technology Conference, Washington, DC, USA, 1-4 May 1994 / New York, NY, USA: IEEE, 1994, p.286-92.
73. C. H. Lee, Y. M. Wong, C. Doherty, K.L. Tai, E. Lane, D. D. Bacon, F. Baiocchi, and A. Katz, "Study of Ni as a barrier metal in AuSn Soldering Application for Laser Chip/Submount Assembly, J. Appl. Phys. 72 (8), 10/15/1992, pp. 3808-15.
74. M.A. Hadley, Vertical-cavity surface-emitting laser diodes: design, growth, mode control and integration by fluidic self-assembly, Ph.D. thesis, EECS Dept., UC Berkeley, 1994.
75. G. S. Matijasevic, C. C. Lee, C. Y. Wang, "Au-Sn phase diagram and properties related to its use as a bonding medium," Thin Solid Films, 223 (1993), 276-87.
76. T. Kawanobe, K. Miyamoto, M. Hirano, Proc. 33rd IEEE Electronic Components and Technology Conf., 1983, IEEE, New York, 1983, pp. 221-26.
77. W. H. Ko, J. T. Suminto, G. J. Yeh, in C. D. Fung, P.W. Cheung, W.H. Ko, and D.G. Fleming (eds.) Micromachining and Micropackaging of Transducers, Elsevier, Amsterdam, 1985, pp. 41-61.
78. C.A. Mackay and S.W. Levine, IEEE Trans. Compon., Hybrids, Manuf. Technol., 9 (1986) pp. 195-201.
79. C.H. Lee, Y.M. Wong, C. Doherty, K.L. Tai et al, "Study of Ni as a barrier metal in AuSn soldering application for laser chip / submount assembly," J. Appl. Phys. 72:8 (15 Oct 1992), pp. 3808-15.
80. American Welding Society, Welding handbook, Charlotte Weisman, editor. 7th ed. Miami, Fla.: American Welding Society, 1984.
81. R.R. Tummala, E. J. Rumaszewski, A.G. Klopfenstein, Microelectronics Packaging Handbook. Technology Drivers. Part 1, Chapman & Hill, 1997.
82. H. Yatsuda and T. Eimura, "Flip-chip assembly technique of SAW devices," 1995 International Symposium on Microelectronics, Los Angeles, CA, USA, 24-26 Oct. 1995.) SPIE, 1995, p.365-70.
83. D. Gupta, "Evaluation of alternative processes for Au-Sn-Au flip chip bonding of power devices. 1995 International Symposium on Microelectronics, Los Angeles, CA, USA, 24- Oct. 1995.) SPIE, 1995, p. 371-7.
84. G.K.Fedder, J.C. Chang, R.T. Howe, "Thermal assembly of polysilicon microactuators with narrow-gap electrostatic comb drive," Technical Digest. IEEE Solid-State Sensor and Actuator Workshop, Hilton Head Island, SC, USA, 22-25 June 1992, New York, NY, USA: IEEE, 1992. p.63-8.
85. Bartek, M.; Foerster, J.A.; Wolffenbuttel, R.F. Vacuum sealing of microcavities using metal evaporation. Sensors and Actuators A (Physical), vol.A61, (no.1-3), (Eurosensors X, Leuven, Belgium, 8-11 Sept. 1996.) Elsevier, June 1997. p.364-8.
86. Ajluni, C. Silicon accelerometer targets airbag restraint systems. Electronic Design, vol.43, (no.21), 13 Oct. 1995. p.143-4. (Motorola MMAS40G accelerometer with glass frit hermetic package)
87. K. Ikeda, et al, "Three dimensional micromachining of silicon resonant strain gauge, 7th Sensor Symposium, Tokyo, Japan, May 1988, pp. 193-196.
88. C. H. Mastrangelo and R. S. Muller, Int. Electron Devices Meeting, San Francisco, Calif., Dec. 1989, pp. 503-506.
89. Guckel, H.; Rypstat, C.; Nesnidal, M.; Zook, J.D.; Burns, D.W.; Arch, D.K. Polysilicon resonant microbeam technology for high performance sensor applications. Technical Digest. IEEE Solid-State Sensor and Actuator Workshop, Hilton Head Island, SC, USA, 22-25 June 1992. New York, NY, USA: IEEE, 1992. p. 153-6.
90. Lin, L., McNair, K.J., Howe, R.T., and Pisano, A.P., "Vacuum Encapsulated Lateral Microresonators," Digest of Transducers '93, International Conference on Solid-State Sensors and Actuators, pp. 270-3, 1993.
91. K. S. Leibouitz, A. P. Pisano, and R. T. Howe, "Permeable polysilicon etch-access windows for microshell fabrication," 8th Int. Conf. on Solid-State Sensors and Actuators, Stockholm, Sweden, June 1995, vol. 1, pp. 224-227.
92. Alpha Metals, Advanced Products Division, Jersey City, NJ. Alpha-Bond anisotropically conductive film preliminary data sheet. 10/94.
93. P. H. Singer, "Die bonding and package sealing materials," Trans. on Electron Dev., ED-26, 12, pp. 1896-1905 (1979).
94. Norland Products, Inc., New Brunswick, NJ (908)545-7828.
95. J.B. Lasky, S. R. Stiffler, F.R. White, J. R. Abernathey, "Silicon-on-insulator (SOI) by bonding and etch-back," Technical Digest, 1985 IEEE International Electron Devices Meeting, p. 684, Dec 1985.
96. M. Shimbo, K. Furukawa, K. Fukuda, T. Tanzawa, "Silicon-to-silicon direct bonding method," Journal Of Applied Physics, Vol. 60, No. 8, P. 2987, Oct 1986.
97. M. A. Schmidt, "Silicon wafer bonding for micromechanical devices," Solid-State Sensor and Actuator Workshop, Hilton Head, SC, June 13-16, 1994, pp. 127-131.
98. J. A. Folta, C. E. Hunt, S. N. Farrens, "Low-temperature wafer bonding of surfaces using a reactive sputtered oxide," Journal of the Electrochemical Society, vol. 141, (no.8), Aug. 1994. pp. 2157 - 60.
99. 4 direct bonding," Appl. Phys. Lett., vol. 62, no. 26, pp. 3485-7, 1993.
100. T.J. Brosnihan, J.M. Bustillo, A.P. Pisano, R.T. Howe, "Embedded interconnect and electrical isolation for high-aspect-ratio, SOI inertial instruments." Tranducers 97. 1997 International Conference on Solid-State Sensors and Actuators. Chicago, IL, USA, 16-19 June 1997. New York, NY, USA: IEEE, 1997, p. 637-40 vol. 1.
101. Q.-Y. Tong, U. Gosele, "Semiconductor wafer bonding: recent developments." Materials Chemistry and Physics, vol.37, (no.2), March 1994 p.101-27.
102. Q. Y. Tong, G. Cha, R. Gafiteanu, U. Gosele, "Low Temperature Wafer Direct Bonding," Journal of Microelectromechanical Systems, vol. 3, no. 1 (March 1994), pp. 29-35.
103. Hoogerwerf, A.C., Wise, K.D., "A three-dimensional neural recording array," Transducers '91 1991 International Conference on Solid-State Sensors and Actuators, San Francisco, CA, 24-27 June, 1991, pp. 120-123.
104. B. Shivkumar and C.-J. Kim "Microriveting - A New Wafer Joining Method" IEEE Micro Electro Mechanical Systems Workshop, Nagoya, Japan, Jan. 1997, pp. 197-202.
105. H. Han, L.E. Weiss, M.L. Reed, "Design and Modeling of a Micromechanical Surface Bonding System," Transducers '91, pp. 974-77.
106. R. Prasad, K.-F. Böhringer, N. C. MacDonald, "Design, Fabrication, and Characterization of SCS Latching Snap Fasteners for Micro Assembly," Proc. ASME International Mechanical Engineering Congress and Exposition (IMECE), San Francisco, California (November 1995).
107. M. B. Cohn, Assembly Techniques for Microelectromechanical Systems, Ph.D. Thesis, Department of Electrical Engineering and Computer Science, University of California, Berkeley, 1997.