An amorphous CrGeTe/polyimide double-layer foil with an extraordinarily outstanding strain sensing ability.

To realize a wearable health monitoring system, a piezoresistive material capable of detecting very small mechanical strains is needed. In this study, an amorphous CrGeTe thin film was deposited on a polyimide film by sputtering, and the piezoresistive properties were investigated. In experiments, the CrGeTe/polyimide double-layer foil exhibited an outstanding piezoresistive performance as evidenced by the appearance of self-healing cracks during tensile tests and a remarkably large gauge factor of 60 000 in resistance change measurements. Owing to the self-healing character of cracks, the resistance change is repeatable within a specific strain range. Noteworthily, the double-layer foil is simple to prepare and does not require heat treatment. Furthermore, this double-layer foil was used to fabricate a pressure sensor comprising an extremely simple electrical circuit, and it was deployed on the wrist to monitor the artery pulse signal. As a result, the pressure sensor accurately detected artery pulse waves containing large amounts of information.