Piezoresistance of Silicon Nanowires for Sensing Applications: Optimizing Nanowire Parameters From Electrical and Mechanical Perspectives

P-type silicon nanowires (SiNWs) have attracted significant attention for their potential in miniaturizing sensing devices, attributed to the observed giant piezoresistive (PZR) effects. However, the application of these advantageous PZR properties of SiNWs to microelectromechanical systems (MEMS) has been hindered by unclear noise levels and complicated fabrication methods. Additionally, several previous reports of anomalous PZR effects, such as doping-type inversion in hydrogen fluoride (HF)-treated p-type SiNWs, have introduced further complexities. Consequently, addressing these unclear challenges is necessary to effectively utilize the PZR effects of SiNWs for MEMS sensing applications. In this paper, the primary causes of uncertain noises and resistance levels in HF-treated p-SiNWs and their dependence on surface effects were analyzed to optimize NW parameters. SiNWs were fabricated using a suitable MEMS fabrication method, and their noises with PZR effects were measured and compared. The results indicated that SiNWs with abnormal PZR characteristics were worse in signal-to-noise ratio (SNR) than those with bulk PZR properties attributed to the significant noise increments from the depletion effects. Based on the NW experiment and additional mechanical analyses, suitable SiNW conditions for MEMS sensing unit were optimized and selected. A miniaturized 3-axis accelerometer utilizing the optimized SiNW was developed and tested. The experimental results showed that the developed accelerometer successfully reduced the total area of the sensor structure by 35.4% when compared to commercial capacitive accelerometers while maintaining competitive performance. This result was achieved without relying on the giant or anomalous PZR effects.