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We studied the improvement in the performance of back-channel-etched oxide TFT with a top gate (TG) by Ar/O2 plasma treatment. The generation of oxide nanoparticles in the offset region of amorphous InGaZnO was observed from TEM image upon Ar/O2 plasma treatment. This results in the reduction of resistivity in the offset region and performance improvement of dual-gate oxide TFTs. The field-effect mobility increases from 7.7 to 22.5 cm2/V $\cdot $ s, and the ${V}_{\text {TH}}$ shift by positive bias temperature stress (PBTS) decreases from 0.7 to 0.3 V. Performance improvement was observed only in structure, where the TG is exposed in air. The performance improvement of the TFTs results in the operation frequency of the ring oscillator (RO) made of the dual-gate TFTs increasing from 17.75 to 113.4 kHz.

We present a coplanar amorphous InGaZnO (a-IGZO) synaptic thin film transistor (TFT) with counterclockwise hysteresis using an aluminum oxide (Al2O3)/SiO2 gate insulator (GI). The excitatory postsynaptic current (EPSC), paired-pulse facilitation (PPF), short-term plasticity (STP), and long-term plasticity, which are biological synaptic characteristics, are demonstrated by positive charge trapping in the Al2O3 layer. Long retention time can be possible by surface charge in the SiO2, a charge-blocking layer. As a result, multi-level channel conductance can be modulated with positive and negative gate pulses. These results prove synaptic a-InGaZnO TFT with Al2O3/SiO2 stack GI for high-density neuromorphic devices.