Scalable Integration of High Sensitivity Strain Sensors Based on Silicon Nanowire Spring Array Directly Grown on Flexible Polyimide Films

The growth and integration of position-controlled, morphology-programmable silicon nanowires (SiNWs), directly upon low-cost polymer substrates instead of postgrowth transferring, is attractive for developing advanced flexible sensors and logics. In this work, a low temperature growth of SiNWs at only 200 °C has been demonstrated, for the first time, upon flexible polyimide (PI) films, via a planar solid-liquid-solid (IPSLS) growth mechanism. The SiNWs with diameter of ∼146 nm can be grown into precise locations on PI as orderly array and with preferred elastic geometry. Strain sensor array, built upon these spring-shape SiNWs integrated on PI, achieves a gauge factor (GF) of ∼90, sustains large stretching strains up to 3.3% (with 1.5 mm radius) and endures over 30,000 cycles. Strain sensors attached to the finger to monitor movements are also successfully demonstrated, showing high sensitivity and superior mechanical reliability, particularly suited for wearable health applications.