Multifunctional Crystalline InGaSnO Phototransistor Exhibiting Photosensing and Photosynaptic Behavior Using Oxygen Vacancy Engineering

A multifunctional optoelectronic device implementing photodetector, photosynapse, and photomemory is of increasing attention for neuromorphic system. This enables multiple devices to be replaced with a single device, which simplifies the structure of complex, highly integrated electronics. Here, a multifunctional c‐axis‐aligned crystalline indium gallium tin oxide thin‐film transistor (TFT) optoelectronic device is demonstrated. The photodetecting and photosynaptic behaviors could be demonstrated by tuning of gate pulse. The device shows a high responsivity of 1.1 × 106 A W−1 to blue light (467 nm) and cutoff frequency (f−3dB) of 2400 Hz exhibiting high frequency switching using a gate reset pulse. It is possible to implement photosynaptic behavior using persistent photoconductivity effect by applying a gate bias to make the TFT depletion mode. When potentiation and depression of synaptic weight are implemented with light pulse and gate voltage pulse, respectively, 64‐state potentiation‐depression curves are demonstrated with excellent nonlinearity of 1.13 and 2.03, respectively. When an artificial neural network is constructed with this device for the Modified National Institute of Standards and Technology training pattern recognition simulation, it shows a high pattern recognition accuracy of 90.4%. A multifunctional c‐axis‐aligned crystalline indium gallium tin oxide (CAAC‐IGTO) optoelectronic device is demonstrated. Crystallization of a‐IGTO increases the oxygen vacancies, leading the significant increase in photoresponse. The fast reset process with a reset pulse is realized by the migration of positively charged oxygen vacancies in the CAAC‐IGTO layer. In addition, photosynaptic characteristics can be implemented using persistent photoconductivity effect.