Secondary embossing method for the capsulation of high-sensitive flexible piezoresistive sensors

Abstract

Due to the mismatch between thermal expansion and hygroscopic expansion coefficients of polymer packaging materials, the stress and reliability of packaging structure present significant influences on the performance of flexible sensors. In this work, a new capsulation method for polymer-based flexible piezoresistive sensing systems was proposed based on differential-temperature hot embossing. The capsulate mold of the flexible sensing system is designed and the flexible sensor is packaged into a polydimethylsiloxane (PDMS) film to form a “sandwich” structure. The influences of the first embossing pressure and the second embossing time on capsulation result were investigated systematically. The results showed that the optimal parameters for the first embossing pressure and second embossing time were 1.4 MPa and 180 s, respectively. The interlayer peel force of obtained samples under this condition could reach a maximum of 5.7 N. This PDMS bulk bonding method can improve the cracking problem of the sample and provide more effective protection for the flexible sensors, compared with the traditional capsulation methods, this packaging method has little effect on sensor sensitivity (decreased by 0.64 kPa−1). After the packaging is completed, the polymer-based flexible piezoresistive sensor presents a high sensitivity (−5.64 kPa−1), and at the same time, a fast response (92 ms).