Computer technology is facing a number of bottlenecks that block the increase of speed, energy efficiency, and cost per computation. The bottlenecks can originate form the intrinsic nature of the elementary building block of VLSI circuits, the CMOS transistor, or from the system architecture (for example a well known von Neumann bottleneck). The solutions range from novel devices such as non-volatile memory elements to novel architectures such as oscillatory neural networks.
Resistive switching devices for non-volatile ultra-dense memories
Currently we target two types of non-volatile switching (memory) devices: oxide Resistive Random Access Memories relying on the Valence Change Mechanism and phase change RAM based on Ge2Sb2Te5 and related chalcogenides. We focus on development of new functional materials, identification of the mechanisms involved in resistive switching, advanced metrology, and simulation.
Oxide-based threshold switches
Threshold switch is similar in function to a memory switch. It also has two different states of resistance and switches from high to low resistance if the voltage exceeds the threshold but the switch is volatile and "forgets" its state when the bias is removed. Threshold switches are used as two terminal devices with applications as selection devices in memory arrays and oscillators.
The simplest of threshold switching devices consists of two metallic electrodes with a layer of vanadium dioxide in between (lateral device is shown in the figure). VO2 is one of the strongly correlated electrons oxides which exhibit a metal-insulator transition. At temperatures below 61 oC, VO2 is a leaky insulator and transforms to a metal above. In nanoscale devices, the leakage current at 1-2 V is sufficiently high to generate enough heat and switch the VO2 to a metal effectively shorting the electrodes. What is truly interesting is the possibility of inducing the MIT by application of electric field rather than heat.
Electro-thermal finite element simulation of the current and heat distribution in VO2-based threshold switch.
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