Flexible capacitive pressure sensors using microdome like structured polydimethylsiloxane dielectric layers

The development of reproducible flexible capacitive pressure sensors with tunable sensitivity is vital for electronic-skin applications. Herein, we propose an improved fabrication process of flexible capacitive pressure sensors by completely eliminating the lamination layer step without compromising on sensor performance. For this, a facile isotropic etching process is also developed for silicon mold with inverted microdome like structures. Flexible capacitive pressure sensors having a ~81 µm thick microdome like structured PDMS dielectric layer, and with and without a lamination layer are fabricated. Sensor having no lamination layer is outperformed the sensor with a lamination layer in a wide pressure range (<500 kPa), exhibited stable relative capacitance (ΔC/Co) up to 1000 cycles, and able to sense low pressure (~55 Pa). The developed sensors are also used for in-vivo arterial pulse waveform monitoring when properly attached on wrist. The single lap shear adhesion test of sensors indicates that the sensor having no lamination layer exhibited maximum shear stress of ~2.7 N (before breakage) compared to the sensor with lamination layer (~1.9 N). The COMSOL simulations also support our experimental findings with large ΔC/Co in the case of sensor having no lamination layer. This study presents a novel process for facile preparation of microdome like structures and improved adhesion between different layers of flexible capacitive pressure sensors, which is important for reproducible pressure sensors.