Memristive devices prepared by atomic layer deposition

Memristors are a class of new devices hypotesized by L. Chua in 1971, in which the resistance value depends on the past hystory of the device. In the memristor the resistance of the device increases when current flows in one direction, while the resistance decreases when the current flow is reversed. If the supply voltage is removed the memristor retains last resistance value, so it preserves “memory” of its hystory. A memrisors network could theoretically work in a way very similar to neuron synapses, thus enabling the realization of novel kind of advanced devices. Amongst the different ways to realize memristor the deposition of a thin layers of metal oxides is one of the most succesfull ones. Atomic layer deposition (ALD) is a technique for thin film deposition that uses gas pulses, producing one atomic layer at a time. The thickness of the film in principle depends only on the number of deposition cycles, resulting in extremely high uniformity and thickness control. Al2O 3 and TiO 2 less than 100 nm thick were deposited on glass substrates on which Pt bars of micrometer size was deposited as both bottom and top contacts. Good memristive behavior was found in two devices: Al 2 O 3 devices, prepared in the form of a metal-insulator-metal stack of Pt/Al 2 O 3 /Ti and in a more standard Pt/TiO 2 /Pt device.