Metal‐Oxide Heterojunction Optoelectronic Synapse and Multilevel Memory Devices Enabled by Broad Spectral Photocarrier Modulation

Abstract Broad spectral response and high photoelectric conversion efficiency are key milestones for realizing multifunctional, low‐power optoelectronic devices such as artificial synapse and reconfigurable memory devices. Nevertheless, the wide bandgap and narrow spectral response of metal‐oxide semiconductors are problematic for efficient metal‐oxide optoelectronic devices such as photonic synapse and optical memory devices. Here, a simple titania (TiO 2 )/indium‐gallium‐zinc‐oxide (IGZO) heterojunction structure is proposed for efficient multifunctional optoelectronic devices, enabling widen spectral response range and high photoresponsivity. By overlaying a TiO 2 film on IGZO, the light absorption range extends to red light, along with enhanced photoresponsivity in the full visible light region. By implementing the TiO 2 /IGZO heterojunction structure, various synaptic behaviors are successfully emulated such as short‐term memory/long‐term memory and paired pulse facilitation. Also, the TiO 2 /IGZO synaptic transistor exhibits a recognition rate up to 90.3% in recognizing handwritten digit images. Moreover, by regulating the photocarrier dynamics and retention behavior using gate‐bias modulation, a reconfigurable multilevel (≥8 states) memory is demonstrated using visible light.