Energy-efficient, fully flexible, high-performance tactile sensor based on piezotronic effect: Piezoelectric signal amplified with organic field-effect transistors

Fully flexible piezoelectric tactile sensors with low power consumption and high sensitivity play an important role in artificial intelligence, advanced manufacturing, and smart wearable devices. Herein, we constructed a high-performance, energy-efficient, and fully flexible piezoelectric tactile sensor based on piezotronic effect through the integration of piezoelectric materials with the mechanical-to-electrical conversion function of β polyvinylidene fluoride (PVDF) nanorod arrays and the signal amplification function of organic field-effect transistor (OFET) devices. PVDF nanorod arrays, which considerably improve the piezoelectric properties of materials, transform the external mechanical force into piezoelectric voltage to drive the OFET. Further, the piezoelectric voltage can be effectively amplified using an OFET to improve the sensitivity of the tactile sensor. Enabled by the unique structure of sensing devices and well-defined active materials, the fabricated tactile sensor exhibited excellent pressure sensitivity, detection limit, and response time of 5.17 kPa⁻1, 175 Pa, and 150 ms, respectively. In addition, using a sophisticated fabrication process, we demonstrated a flexible integrated tactile sensor array with a 3 × 3 cell on a polyethylene terephthalate (PET) substrate to detect the bending angle of the user's wrist on which the fabricated device was mounted. This study uses piezotronic transistors to convert pressure into electrical signals without applying a gate voltage, which can substantially simplify circuit models and sensor distribution; additionally, the fabricated device provides technical support for flexible electronic skin (e-skin).