Design of a Flexible Stethoscope Sensor Skin Based on MEMS Technology

Since the first stethoscope based on wood was invented by a Frenchman named Laenec in 1816, medical doctors had collected much more information of patients and saved many lives. In this paper, a novel prototype of stethoscope based on silicon flexible skins and the process flow of fabrication by classical MEMS technology have been proposed. This novel approach enables embedding of the sensors into textiles without compromising the flexibility and wearability of the textiles, and the doctor can study the state of an illness continually in door using wireless communication. A piezoelectric cantilever is designed to consist of materials such as Si₃N₄, Ti/Pt, PZT, Ni-Cr, Au layers that may transform sound energy into volt signal is fabricated on a silicon wafer using micromachining techniques. Using sol-gel techniques, Pb(Zr_x,Ti_{1 - x})O₃, a PZT thin film, which is considered as an excellent piezoelectric material is deposited and pattered on a supporting layer of low-stress silicon nitride. The 500 times 200 times 1 mum³ PZT cantilever beam is patterned using a HF/HCl escharotics system. The backside of the wafer is dry etched with plasma in order to eliminate the stress concentrated, and then each sensor is isolated, namely silicon island. Finally, the wafer is coated with polymer both sides to protect the sensors and make sure the sensor array flexible. In addition, FEA software has been used to obtain modal and harmonic of the piezoelectric micro cantilever and stress of the silicon island simulation results