Boosting the Visible Light Optoelectronic Synaptic Characteristics of Solution-Processed IGZO Transistors via Vertically Diffused Cd Dopants

Inspired by the human visual system, optoelectronic synaptic transistors have recently received a great deal of attention as promising candidates for next-generation neuromorphic computing systems. For the low-cost, mass production of optoelectronic synaptic devices, it is essential to fabricate devices through a solution process. Furthermore, there should be no compromise on electrical characteristics for improving photoresponse characteristics in high-performance optoelectronic synaptic devices. To obtain both highly enhanced photoresponse characteristics and electrical characteristics, we introduce an indium gallium zinc oxide (IGZO)-based optoelectronic synaptic transistor by doping cadmium (Cd) using a vertical diffusion process. The Cd-doped IGZO transistor showed a remarkable increase in optoelectronic characteristics with a field effect mobility of 8.18 cm 2 V –1 s –1 and on/off current ratio of 1 × 10 8, owing to the increased film density and small effective electron mass of the Cd dopant. Furthermore, the amount of oxygen vacancies of the IGZO film was remarkably increased by doping Cd, which make the IGZO stimulated by incident visible light wavelength. Therefore, we successfully demonstrated the fundamental synaptic properties of the device, including excitatory postsynaptic current (EPSC), paired-pulse facilitation (PPF), and short-term plasticity (STP) to long-term plasticity (LTP) conversion. Our findings offer a promising approach for advancing the development of visible light optoelectronic synaptic transistors for next-generation neuromorphic computing systems.