We propose an insertion force sensor with piezoresistors fabricated by sidewall-doping with rapid thermal diffusion. The sensor consists of a main body, to which a pointed tip is installed, and supporting beams whose sidewalls are made piezoresistive. When an insertion force is applied to the tip and the silicon structure deforms, the change of the strain distribution condition on the piezoresistive sidewall varies the electrical resistance of the sensor, which is in turn transduced into output voltage signal via an outside circuitry. By etching an appropriate pattern onto the wafer, additional exposed surfaces for doping can be created where vertical dope-sites are needed. With rapid thermal diffusion, we are able to fabricate dope-sites which are perpendicular to the surface of the wafer. The displacement sensitivity is 1.03 % per µm. This displacement sensitivity on the insertion direction is as high as that on the vertical direction of reported sensors, which means that our proposal is an effective doping method for sidewall.

References :
Binh Khiem Nguyen, Kazunori Hoshino, Kiyoshi Matsumoto, Isao Shimoyama, “Insertion Force Sensor by Sidewall-Doping with Rapid Thermal Diffusion,” 19th International Conference on Micro Electro Mechanical Systems (MEMS '06), pp. 662-665, Istanbul, Turkey, January 22-26, 2006. [Proceedings]