Ultrathin Top Layer Height to Enhance the Performance of Soft Liquid Metal Embedded Pressure Sensor

Soft piezoresistive pressure sensors with liquid metal electrodes are made of elastomeric, viscoelastic materials. Due to this viscoelastic nature, the applied load is partially transferred to the microchannels, resulting in low signals and low sensitivity in the 0-50 kPa range. In this study, the effect of top layer height from the microchannel has been studied mainly through signal response, the sensing zone shift, the sensitivity, and the hysteresis of the sensors. These properties have been tested under dynamic, static, and repetitive load conditions in the 0-50 kPa range. The sensors with overall thicknesses of 2 mm, 1 mm, and 0.5 mm and top layer heights of 800 μm, 300 μm, and 100 μm, respectively, have been fabricated. The design pattern of the microchannels is identical for all the sensors and is inspired by human fingertip ridges. The sensor with a top layer thickness of just 100 μm has shown a reduction in the low sensitivity region from 0-40 kPa to 0-15 kPa, which is a shift of 62.5%, with sensitivity improvement of around 1200%. In the improvement zone (15-40 kPa), the sensitivity has jumped from 0.004 kPa<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> to 0.05 kPa<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup>. In the very low range (0-1000 Pa), the thinnest sensor outperformed the other sensors regarding response and sensitivity, with a detection limit of 32 Pa. However, the sensor with a top layer thickness of 300 μm showed better performance in terms of accuracy of 5.4% and precision of 0.003, along with the hysteresis, which became prominent.