CONICET | Buscador de Institutos y Recursos Humanos

In this work we present a novel concept consisting on light-controlled metal-oxide-semiconductor memory devices, with optically active Si as bottom electrode. The current through the device depends on the illumination conditions as a result of electron photogeneration in silicon. With this architecture we follow the path towards multifunctional memory devices, in this specific case with light-sensing capabilities included. In detail, we investigate resistive switching in 20 nm-thick amorphous Al2O3 films prepared by atomic layer deposition on p-Si/SiO2 substrates. Pd top metal contacts are deposited by sputtering after photolithography patterning, while Si is used as bottom electrode. The current (I)-voltage (V) curves show a highly reproducible hysteresis when the samples are illuminated with radiation in the ultraviolet (UV)-infrared (IR) range. However, when external illumination is switched off, the samples present a weak non-hysteretic response to applied voltages. We prove that our devices behave as memristors by analyzing the remnant current hysteresis switching loops, HSL. To construct the HSL, we apply voltage pulses of 5 ms following the sequence 0 V, +10 V, -10 V, 0 V, in steps of 0.1 V. After each of these pulse steps we wait 100 ms in short-circuit conditions, then we measure the remnant current (Irem) for a fixed voltage of 6 V. This specific measurement of the remnant current reflects an authentic memristive behavior, since capacitive effects are excluded by the long 100 ms time in short-circuit conditions. From the electrical characterization, the resistive switching can be attributed to electrons from Si combining with traps in the Al2O3 film, thus changing the oxide resistance state. Our system presents interesting applications, for example in codified data storing or in mimicking learning processes for light sensitive bio-systems.

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