Soft Capacitive Pressure Sensor With Enhanced Sensitivity Assisted by ZnO NW Interlayers and Airgap

Yogeenth Kumaresan,Sihang Ma,Oliver Ozioko,Ravinder Dahiya

doi:10.1109/jsen.2022.3143030

Abstract

Highly sensitive capacitive pressure sensors with wide detection range are needed for applications such as human-machine interfaces, electronic skin in robotics, and health monitoring. However, it is challenging to achieve high sensitivity and wide detection range at the same time. Herein, we present an innovative approach to obtain a highly sensitive capacitive pressure sensor by introducing a zinc oxide nanowire (ZnO NW) interlayer at the polydimethylsiloxane (PDMS)/electrodes interface in the conventional metal-insulator-metal architecture. The ZnO NW interlayer significantly enhanced the performance with ~7 times higher sensitivity (from 0.81%kPa −1 to 5.6452%kPa −1 at a low-pressure range (0-10 kPa)) with respect to conventional capacitive sensors having PDMS only as the dielectric. The improvement in sensitivity is attributed to the enhanced charge separation and electric dipole generation due to the displacement of Zn + and O − under applied pressure. Further, the orientation of ZnO NWs and their placement between the electrodes were investigated which includes either vertical or horizontal NWs near the electrodes, placing a third ZnO NW interlayer in the middle of dielectric PDMS and introducing an air gap between the ZnO NWs/electrode. Among various combinations, the introduction of air gap between the electrode and ZnO NW interlayer revealed a significant improvement in the device performance with ~50 times enhancement at a low-pressure range (0-10 kPa) and more than 200 times increase at a high-pressure range (10-200 kPa), in comparison with the conventional PDMS-based pressure sensor.

Highlights

HUMAN skin can detect external stimuli such as pressure, strain, chemicals and temperature etc. because of the presence of various receptors at different depths and positions within the skin [1,2,3]
To address the existing challenges, we present a novel design of capacitive pressure sensor by introducing zinc oxide nanowire (ZnO NW) interlayers and an air gap between PDMS/electrodes interfaces to enhance the sensitivity and working pressure range
To evaluate the sensor performance in terms of the influence of ZnO NWs interlayers between the electrode and PDMS, both samples were subjected to different pressure ranges varied from 0 to 200 kPa and their relative change in capacitance were measured as shown in Fig. 3a and 3d

Summary

Introduction

HUMAN skin can detect external stimuli such as pressure, strain, chemicals and temperature etc. because of the presence of various receptors at different depths and positions within the skin [1,2,3]. The structure of a typical capacitive sensor includes a dielectric material sandwiched between the two parallel metal conducting plates [17]. Capacitive sensors have rigid dielectric material, but in the case of e-Skin elastomeric materials such as Ecoflex, polydimethylsiloxane (PDMS), and polyurethane (PU) are commonly used [18,19,20] as they enable soft touch. They have good thermal and chemical stability, biocompatibility, and mechanical properties. Several methods are adopted for the fabrication of high-performance capacitive pressure sensors using these elastomeric dielectric materials. These methods have either used microstructured pyramids, pillars or wrinkles

Methods

Results

Conclusion