Novel Optical Functionalities in Memristors

Abstract

We present an electronic memristor with expanded optical functionalities enabled by integrating an ultrathin 3 nm cadmium sulfide (CdS) film as a tunnel junction barrier with a La_0.7Sr_0.3MnO₃ (LSMO) bottom electrode. A transparent In₂O₃:SnO₂ (90:10) (ITO) upper electrode provides direct optical access to the junction area. In the dark, the device exhibits non-volatile electrical resistive switching with robust intermediate states. When illuminated with UV light (3.3 eV) between 50 and 150 K, the resistive switching remains unchanged; however, a photovoltaic response emerges, correlating linearly -via the open circuit voltage V_oc- with the resistance of each intermediate state. This behavior enables electro-optical sensing of each state. In contrast, at 10 K, photogenerated carriers enter a high injection regime and modify the device's electrical behavior in the dark, leading to a volatile suppression of the high-resistance states as illumination power reaches 26 mW cm⁻². The equilibrium dark resistance of the memristor states is restored upon removing illumination, with long characteristic recovery times (∼100 s). This slow response can be leveraged in very high-resistance states of 30 GΩ to induce voltage accumulation through low-intensity UV pulses of 0.13 mW cm⁻². Integrating these innovative optoelectronic functionalities, photovoltaic sensing and hybrid electro-optical voltage accumulation, into memristive devices opens exciting possibilities for the development of advanced bioinspired computing architectures.