Tunable flexible capacitive pressure sensors using arrangement of polydimethylsiloxane micro-pyramids for bio-signal monitoring

Recently, microstructured PDMS based pressure sensors are explored as a potential candidate in bio-signal monitoring and electronic-skin applications. Here, we have fabricated capacitive pressure sensors with micro-pyramidal PDMS dielectric thin films, and studied the influence of surface coverage and arrangement of these structures on the sensitivity of pressure sensor devices. Pressure sensor with periodically arranged pyramids (surface coverage: 36.7%) exhibited sensitivity of 0.16 kPa-1 in <1 kPa and 0.04 kPa-1 in 0.75-2.5 kPa pressure range, whereas the pressure sensor with diagonally arranged pyramids (surface coverage: 45.2%) exhibited sensitivity of 0.1 kPa-1 in <1 kPa and 0.05 kPa-1 in 0.75-2.5 kPa pressure range respectively. Despite having large surface coverage, pressure sensor with the diagonally arranged pyramids exhibited high sensitivity (0.05 kPa-1) in 1-2.5 kPa pressure range than the periodically arranged pyramids owing to the large displacement and increase in effective permittivity of diagonally arranged pyramids. Simulation studies on the developed pressure sensor structures using Ansys and Opera also confirmed the relatively large displacement and ΔC/Co in diagonally arranged pyramids compared to periodically arranged pyramids having slightly low surface coverage. Experimental results and simulations demonstrate that the sensitivity of these kinds of pressure sensors can also be tuned by arrangement of pyramids. Also, the developed flexible capacitive pressure sensor is demonstrated for in-vivo, real-time pulse wave form recording.