Piezo-Gated Thin Film Transistor—A Novel Device to Develop a Unique Multi-Axial Smart Strain Sensor and the Synergistic Interaction of Piezo-Gating Effect and Thermoelectric Effect

The piezo-gating effect plays a pivotal role to develop piezotronic devices exclusively based on carrier modulation inside the piezoelectric semiconducting material. In earlier studies, the piezotronic devices were extensively developed based on the Schottky barrier height modulation at the interface with the electrode. Therefore, we have created an ohmic junction-based piezo-gated thin film transistor (PGTFT) using ZnO as a model material to eliminate the Schottky barrier height modulation and show the dual mode (depletion and accumulation) function of a PGTFT device for the first time. To obtain the dual mode operation, two configurations of the PGTFTs with Top and Bottom electrode subjected to the compressive force shows the opposite trends in I-V signals, which was further validated by analytical modeling and simulation data. This technique further evaluates and distinguishes the piezoresistive effect from the piezo-gating effect for the first time.Furthermore, utilizing this phenomenon we have developed a double-sided four-electrode-based flexible PGTFT, allowing to not only detect the total amount of strains but also distinguish between bending force (upward/downward) and normal force (tensile/compressive). Thus, we were able to first develop such a smart strain sensor using the piezo-gating effect to capture more information in one single device. Foremost, we also combine the piezo-gating effect with the thermoelectric effect to investigate the carrier dynamics of such effects and obtain a synergistic effect where the thermoelectric power factor was largely enhanced via incorporation of the piezo-gating effect. To examine such behavior, we have used the same PGTFT configuration and exerted a thermal gradient to the source and drain electrode interfaces to initiate the hot electron/hole flow and modulate that via strain-induced piezo-potential inside the channel.