MEMS Piezoresistive Pressure Sensor Based on Flexible PET Thin-Film for Applications in Gaseous-Environments

Abstract

This experimental study presents the operation of pressure sensors made from low-temperature flexible substrates. Design, simulation, fabrication, and characterization are carried out with a number of fabricated flexible pressure devices. Simulations are used to optimize the sensor parameters such as the geometrical shape, electrical potential output, sensitivity and working-range of the sensor, thus predicting the sensing behavior before fabrication. The behaviour of the devices are simulated by using COMSOL Multiphysics. The pressure structure consists of a substrate of polyethylene terephthalate (PET) thin-film used as a diaphragm. A thin layer of indium tin oxide (ITO) on the PET substrate is obtained and used as a first conductive metallic track. Subsequently, nichrome (NiCr 80/20 wt%) alloy material was deposited by electron beaming to generate four piezoresistors with thickness of 50 nm that can be used to detect resistance change using a Wheatstone bridge when the sensor is exposed to different working pressures. Aluminum metallic tracks of 200 nm in thickness are deposited by sputtering in order to connect the four piezoresistors. A working range of pressure is applied from 0 kPa to 130 kPa. Resistivity and sensitivity measured values were <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.37 \times 10^{-3}\, {\Omega }$ </tex-math></inline-formula> -cm and 6.365 mV/kPa respectively. All simulations and experimental results showed that the sensor characteristics are favorable for applications where the pressure is below 130 kPa.