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

Rapid development of flexible pressure sensors is indispensablein electronic skin to have the sensing capability to static and dynamicpressures. Besides high sensitivity and low hysteresis, the high flexibilityand stability of these sensors are of paramount importance owing tothe application requirement of conformable pressure mapping and ruggedstructure. Here, we describe a novel approach for highly flexiblecapacitive pressure sensors with engineered stable interfaces employingPDMS-based substrates and a micropyramidal dielectric layer, Au electrodes,and molecular adhesive. The sensor/matrix stack consists of five interfaceswith strong interfacial adhesion achieved using MPTMS molecular adhesiveand a partially cured PDMS lamination layer. A highly flexible capacitivepressure sensor capable of a wide pressure sensing range (up to 550kPa) is developed with a high sensitivity (46.6 MPa-1 in & LE;1 kPa), capability to sense pressure as low as 27 Pa,low hysteresis (4.05%), and high stability for large pressures (11,400cycles @ 250 kPa). The sensor is successfully demonstrated for arterialpulse signal acquisition and performing a press task when attachedon the forefinger. A flexible pressure sensor matrix of 4 x 4pixels is developed. It can be flexed or crumpled; hence, it is conformablyattached on a planar surface and a non-planar 3D-printed surface forsingle-point and multipoint pressure sensing. The sensor exhibiteda maximum shear strain of 2.27 N before breakage. These highly flexiblepressure sensor and matrix are also compared with a semi-flexibleIO-PET electrode-based pressure sensor and matrix to clearly bringout the flexibility and stability advantages. The proposed processis simple and scalable and offers a conformably stable pressure sensormatrix for electronic skin development.