Design and optimization of a doubly clamped piezoresistive acceleration sensor with an integrated silicon nanowire piezoresistor

Abstract

Piezoresistive acceleration sensors have found a wide range of applications for the last four decades. However, in recent times, high performance piezoresistive acceleration sensors with lower footprint are in demand, especially in the fields of consumer electronics and biomedical engineering. The design of such sensors remains a challenging task due to the competing requirements of high electrical sensitivity (∆R/R) and resonant frequency (f 0 ) along with low device footprint. In this paper, we elaborate the design and optimization of a highly miniaturized doubly clamped acceleration sensor with an integrated silicon nanowire as a piezoresistor. The diminutive size of the silicon nanowire helps in reducing the device foot print. The design is performed using two methods: (1) electrical approach and (2) mechanical approach. In the electrical approach, the conventional bulk silicon diffused piezoresistors are replaced with a silicon nanowire without changing the dimensions of the original structure. It is shown that compared to the conventional design, a silicon nanowire based sensor exhibits 2.51 times better performance in terms of electrical sensitivity. One of the major constraints with miniaturized high performance acceleration sensors is reduced resonant frequency. Therefore, in the mechanical approach we have devised a geometrical optimization technique to miniaturize the sensor geometry by keeping its resonant frequency constant. Numerical simulations are performed to validate the proposed miniaturized sensor with an integrated silicon nanowire as the piezoresistor. The sensor performance is evaluated with a new performance factor given as $${{\left( {{{\Delta R} \mathord{\left/ {\vphantom {{\Delta R} R}} \right. \kern-0pt} R}} \right)f_{0}^{2} } \mathord{\left/ {\vphantom {{\left( {{{\Delta R} \mathord{\left/ {\vphantom {{\Delta R} R}} \right. \kern-0pt} R}} \right)f_{0}^{2} } {Diesize}}} \right. \kern-0pt} {Diesize}}$$ , which takes into account the electrical sensitivity, the resonant frequency and the die size of the sensor. Results show that the proposed sensor design with an integrated silicon nanowire has 48.2 times better performance factor than a bulk piezoresistor based conventional acceleration sensor.