Integrated Opto-Synaptic IGZO Transistors for Image Recognition Fabricated at Room Temperature

Abstract

At room temperature, high-κ HfLaO is adopted as the gate dielectric to fabricate amorphous InGaZnO (a-IGZO) optical synaptic thin-film transistors (TFTs), for which plasma treatments are conducted on the HfLaO dielectric in O₂ and a-IGZO in Ar, respectively, namely, OPT/APT-TFTs. Consequently, high-performance a-IGZO TFTs are obtained with a high carrier mobility of 20.8 cm²/V·s, a high I_on/I_off ratio of 3.2 × 10⁶, and a small subthreshold swing (SS) of 0.25 V/dec. As compared to the pristine TFTs, the photocurrent of the OPT/APT-TFTs under a 365 nm ultraviolet (UV) light is significantly raised three times up to 1.4 μA. Meanwhile, the current decay percentage after irradiation removal is reduced from 98% down to 36% within 60 s, indicating an enhanced persistent-photoconductivity (PPC) effect. Accordingly, various optical synaptic plasticities are obtained based on which a simulated neuronal network with a high 93.22% accuracy is achieved to recognize MNIST handwritten digits. Moreover, both neurotransmitter and neuromodulator behaviors are concurrently emulated in a single device through exploiting the native three-terminal structure of the TFT. Importantly, an artificial visual nervous system is successfully constructed by integrating the a-IGZO optoelectronic TFTs for image recognition.