Enhanced Piezocapacitive Effect in CaCu₃Ti₄O₁₂–Polydimethylsiloxane Composited Sponge for Ultrasensitive Flexible Capacitive Sensor

Highly sensitive flexible piezocapacitive (PC) pressure sensor demonstrates wide applications in wearable electronics. In this paper, we first theoretically proposed an effective strategy to improve the sensitivity of the PC pressure sensor, by constructing a porous dielectric layer composted of inorganics with high dielectric constant (εH) and organics with low dielectric constant (εL). By using CaCu3Ti4O12 (CCTO) nanocrystals with giant ε as the dopant and polydimethylsiloxane (PDMS) with a low ε as the matrix, an ultrasoft CCTO-PDMS dielectric sponge was fabricated, via a simple porogen-assisted process. The CCTO-PDMS composited sponge exhibits an ultralow compression modulus of 6.3 kPa, a highly enhanced sensitivity with the gauge factor of up to 1.66 kPa–1 in a range of 0–640 Pa, and a response time of 33 ms, and the sensitivity outperforms that of pure PDMS and other PC sensors reported recently. This sensitivity enhancement is attributed to the hybridization of two phases of εH/εL in the composites, which provides an effective route to other novel flexible PC sensors. In practical applications, CCTO-PDMS-based PC sensor demonstrates potential applications, such as recording wrist pulse wave with fine accuracy and fidelity, bending and twisting detection, and Moss code simulating. The low-cost fabrication process in conjunction with its superior sensitivity, robustness of the functional versatility, and mechanical flexibility make the CCTO-PDMS-based pressure sensor widely promising for applications in wearable devices, flexible electronics, robotics, etc.