All-Polydimethylsiloxane-Based Highly Flexible and Stable Capacitive Pressure Sensors with Engineered Interfaces for Conformable Electronic Skin

Rapid development of flexible pressure sensors is indispensable in electronic skin to have the sensing capability to static and dynamic pressures. Besides high sensitivity and low hysteresis, the high flexibility and stability of these sensors are of paramount importance owing to the application requirement of conformable pressure mapping and rugged structure. Here, we describe a novel approach for highly flexible capacitive pressure sensors with engineered stable interfaces employing PDMS-based substrates and a micropyramidal dielectric layer, Au electrodes, and molecular adhesive. The sensor/matrix stack consists of five interfaces with strong interfacial adhesion achieved using MPTMS molecular adhesive and a partially cured PDMS lamination layer. A highly flexible capacitive pressure sensor capable of a wide pressure sensing range (up to 550 kPa) is developed with a high sensitivity (46.6 MPa^-1 in ≤1 kPa), capability to sense pressure as low as 27 Pa, low hysteresis (4.05%), and high stability for large pressures (11,400 cycles @ 250 kPa). The sensor is successfully demonstrated for arterial pulse signal acquisition and performing a press task when attached on the forefinger. A flexible pressure sensor matrix of 4 × 4 pixels is developed. It can be flexed or crumpled; hence, it is conformably attached on a planar surface and a non-planar 3D-printed surface for single-point and multipoint pressure sensing. The sensor exhibited a maximum shear strain of 2.27 N before breakage. These highly flexible pressure sensor and matrix are also compared with a semi-flexible IO-PET electrode-based pressure sensor and matrix to clearly bring out the flexibility and stability advantages. The proposed process is simple and scalable and offers a conformably stable pressure sensor matrix for electronic skin development.