Research on improving the sensitivity of a flexible transparent tactile sensor with coplanar electrodes using stress concentration effect of nanograting

Abstract

Pressures sensor has been used for a variety of application such as microphone, health care, electronic skin and humanoid robot. Humanoid robot act on behalf of the person in diverse environments like natural disasters, precision surgery and home. In recently, tactile sensor of humanoid robot is one of the next-generation application of pressure sensor. The first requirement of tactile sensor is wide sensing pressure range because it used to diverse environment. Additional requirements of tactile sensor are transparency and flexibility because of using human artificial skin and installed on curved surface.

Conventionally, in order to recognize pressure, many researchers use capacitive tactile sensor due to advantage of power consumption and sensible dynamic/static pressure. For wide pressure range sensible capacitive tactile sensor, it broads the measurement range using a high spring constant between electrode. However, this have low sensitivity because of low deflection. To increase sensitivity of wide pressure range sensible tactile sensor, floating electrode was inserted between vertical electrodes. In that case, many electrode layers reduce transparency. Therefore, capacitive tactile sensor of vertical electrode type remains the challenge to improve the sensitivity with a wide pressure range, transparency, flexibility.

In this thesis, to solve the transparency problem, we use coplanar electrode instead of vertical electrode. However, coplanar electrodes have low sensitivity because of fixed electrode gap. For this reason, by using the nanograting as stress concentration structure, change of dielectric constant is increased. As a results, the sensitivity of the transparent flexible tactile sensor was improved

To fabricate real sample, the silicon nanograting of 400nm pitch imprint on polyethylene terephthalate(PET)/ polyurethane-acrylate (PUA) for concentration stress. After that, deposited interdigitated electrode covered SU-8 as dielectric material is reached a transmittance of 73.5%.

Average stress on the simulation of tactile sensor used nanograting 1.56 times greater than tactile sensor used flat substrate. On experiment results, sensitivity of nanograting 1.6 times greater than flat substrate. Additionally, for increasing change of dielectric constant, 0.2wt% gold nanoparticles are dispersed in SU-8. Consequently, maximum sensitivity reached 0.0096kPa-1. It shows that using coplanar electrode on nanograting as stress concentrated structure improves sensitivity and transparent.