Oblique Angle-Engineered IGZO Floating Gates for Light-Assisted Multi-State Memory Devices

In this study, we present a floating gate memory device based on indium–gallium zinc oxide (IGZO), enhanced by applying the oblique angle deposition (OAD) technique. The IGZO floating gate with a nanostructure created using the OAD technique exhibits reduced conductivity. As a result, the IGZO floating gate memory with OAD technique demonstrates a high on/off ratio (∼106) and narrow hysteresis characteristics (0.24 V) in the transfer curve. Additionally, the photoresponse of dinaphtho[2,3 b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) channel, which has a band gap of ∼2.61 eV, enables the light-induced programming and facilitates the charge accumulation in the floating gate. The proposed memory device enables multilevel programming through both photonic (λ = 450 nm) and electrical (VG = +60 V) inputs, either independently or in combination. Under dual-mode operation, a substantial threshold voltage shift (ΔVTH = 23.1 V) is achieved, whereas single-mode inputs yield more moderate shifts of 11.8 V (VG only) and 5.9 V (light only). This dual-mode capability allows for distinct programmable memory states with enhanced control and precision. In contrast, the IGZO floating gate transistor without the OAD technique exhibits a relatively low on/off ratio (∼103), high off-current (∼10–7 A), and broad hysteresis characteristics (>30 V). These results suggest that the IGZO floating gate with the OAD technique applied is appropriate for memory operation.