Coupled Ion-Gel Channel-Width Gating and Piezotronic Interface Gating in ZnO Nanowire Devices

The piezotronic effect has been extensively investigated and applied to the third generation of semiconductors. However, there currently is no effective method compatible with microelectronics techniques to harness the piezotronic effect. In this work, a facile and low-energy-consuming method to couple the channel-width gating effect with piezotronic devices is developed by precisely patterning ion-gel electrolyte on ZnO NW. The ultrahigh capacitance of ion gel resulting from electrical double layers allows efficient modulation of the charge carrier density in ZnO NW at low gate voltage (2 V) to compensate for the piezotronic effect. The obtained output current variation under negative gate voltage (420%, i.e., enhanced piezotronic effect) is two times higher than that under zero or positive gate biases (200%). Through quantifying the reverse-biased Schottky barrier height and charge carrier density, it is found that the applied negative gate voltage depletes free electrons in ZnO NW and alleviates the screening effect on piezoelectric polarization charges, leading to enhanced piezotronic effect. Based on this, an ion-gel-gated piezotronic strain sensor is fabricated with enhanced gauge factor and tunable logic devices. It is believed that the coupled ion-gel and piezotronic gating effect is of great significance to the design of sophisticated and practical piezotronic devices.