Capacitive microphone with low-stress polysilicon membrane and high-stress polysilicon backplate

Abstract A capacitive single-chip silicon microphone with very low-stress polysilicon membrane was fabricated. A mechanism for stress-releasing due to the high stress of the perforated membrane was introduced. With the achieved stress level of 2 MPa, a microphone with the membrane area of 1 mm 2 can be optimally designed, although the measured components did not show the optimal resolution due to excessive acoustic resistance. With a membrane area of 1 mm 2 , the acoustical sensitivity was 4 mV/Pa (at 1 kHz) and the noise equivalent sound level was 33.5 dB (A), which are adequate values for many applications. The packaged components were tested with a thermal cycle between −40°C and +60°C, and due to low packaging-related stresses, no buckling of the membranes was observed.

[1]  J. Bergqvist,et al.  A silicon condenser microphone using bond and etch-back technology , 1994 .

[2]  Wouter Olthuis,et al.  Improvement of the performance of microphones with a silicon nitride diaphragm and backplate , 1994 .

[3]  A. Erlebach,et al.  Miniature Condenser Microphone With A Thin Silicon Membrane Fabricated On Simox Substrate , 1995, Proceedings of the International Solid-State Sensors and Actuators Conference - TRANSDUCERS '95.

[4]  M. Orpana,et al.  Control of residual stress of polysilicon thin films by heavy doping in surface micromachining , 1991, TRANSDUCERS '91: 1991 International Conference on Solid-State Sensors and Actuators. Digest of Technical Papers.

[5]  Matthias Müllenborn,et al.  A low-voltage silicon condenser microphone for hearing instrument applications , 1999 .

[6]  Silicon capacitive microphones with corrugated diaphragms , 1999 .

[7]  D. W. Burns,et al.  Fine-grained polysilicon films with built-in tensile strain , 1988 .

[8]  Kensall D. Wise,et al.  A high sensitivity polysilicon diaphragm condenser microphone , 1998, Proceedings MEMS 98. IEEE. Eleventh Annual International Workshop on Micro Electro Mechanical Systems. An Investigation of Micro Structures, Sensors, Actuators, Machines and Systems (Cat. No.98CH36176.

[9]  O. Rusanen,et al.  Adhesives as a thermomechanical stress source-comparing silicones to epoxies , 1998, Proceedings of 3rd International Conference on Adhesive Joining and Coating Technology in Electronics Manufacturing 1998 (Cat. No.98EX180).

[10]  Wouter Olthuis,et al.  An integrated silicon capacitive microphone with frequency-modulated digital output , 1998 .

[11]  Robert Aigner,et al.  Silicon micromachined microphone chip at Siemens , 1999 .

[12]  A. W. Mitchell,et al.  Fabrication of a silicon micromachined capacitive microphone using a dry-etch process , 1996 .

[13]  W. Kronast,et al.  Single-chip condenser microphone using porous silicon as sacrificial layer for the air gap , 1998, Proceedings MEMS 98. IEEE. Eleventh Annual International Workshop on Micro Electro Mechanical Systems. An Investigation of Micro Structures, Sensors, Actuators, Machines and Systems (Cat. No.98CH36176.