Manufacturing Silicon-Nanowire Based Piezoresistive Force Sensors with Top-Down Stepwise Controllable Etching Process

Reported giant piezoresistive effect of silicon nanowires (SiNWs) motivates research of SiNWs-based devices, particularly for inertial and force sensors, whose fabrication however remains a challenge. This paper reports a controllable manufacturing process to fabricate a force sensor utilizing $<600 ~\text{nm} \times 600 ~\text{nm}$ SiNWs with a GF of 35 as the sensing element while $10 \mu \mathrm{m}$ thick comb fingers as the actuator and force generator. Different from the previous bottom-up process using epitaxial growth, this work proposes a straightforward top-down process with stepwise controllable etching and only ultraviolet lithography to integrate SiNWs of which minimum diameter is 100nm with the $10 \mu \mathrm{m}$ thick actuator. A fabricated force sensor demonstrates a sensitivity of $508 \text{ppm} / \mu \mathrm{N}$ and linearity of $\pm 1.4 \%$.