Design and Simulation of a Novel Biomechanic Piezoresistive Sensor With Silicon Nanowires
IEEE/ASME transactions on mechatronics
This paper presents the design of a novel single square millimeter 3-axial accelerometer for head injury detection of racing car drivers. The main requirements of this application are miniaturization and high-G measurement range. We propose a new miniature accelerometer to be incorporated into an earpiece. Nanowires as nanoscale piezoresistive devices have been chosen as sensing element, due to their high sensitivity and miniaturization achievable. By exploiting the electro-mechanical features
... echanical features of nanowires as nanoscale piezoresistors, the nominal sensor sensitivity is overall boosted by more than 30 times. This approach allows significant higher accuracy and resolution with smaller sensing element in comparison with conventional devices without the need of signal amplification. This achievement opens up new developments in the area of implanted devices where the high-level of miniaturization and sensitivity is essential. Index Terms-Accelerometer, biomedical devices, giant piezoresistance, implantable sensors, silicon nanowires. Toriyama et al.  studied silicon nanowire piezoresistors fabricated by separation of implanted oxygen (SIMOX), thermal diffusion, electron beam (EB) direct writing, and reactive ion etching (RIE). In their study longitudinal and transverse piezoresistive coefficients, π l <110> and π t <110> , were both dependant on the cross sectional area of the nanowires. The π l <110> of the nanowire piezoresistors increased (up to 60%) with a decrease in the cross sectional area, while π t <110> decreased with a increase in the aspect ratio of the cross section. The enhancement behavior of the π l <110> was explained qualitatively using 1-D hole transfer and hole conduction mass shift mechanisms. The reduction in the π t <110> with increase in the aspect ratio of the cross section is explained due to decreased stress transmission from the substrate to the nanowire. The in the specification of approximately 1 KHz (see section E for details). For all cases, under Z-axis and X-or Y-axis acceleration, the design points at higher equivalent stress has been selected as optimal designs. The results of the optimization process are as follows: 1 st mode shape (ω oz ) of 5,277.7 Hz, the maximum equivalent stress (σ eq ) at 250G acceleration in the X or Y-axis are 44.837 MPa and 66.041 MPa in the microscale and nanoscale piezoresistors respectively. In the Z-axis σ eq at 250G acceleration is 66.581 MPa and 99.243 MPa in the microscale and nanoscale piezoresistors respectively. By taking advantage of structure symmetry only the equivalent stress under X-axis acceleration as been analysed. The results for the Y-axis acceleration are equivalent.