Electrical switching and oscillations in vanadium dioxide

Abstract

We have studied electrical switching with S-shaped I-V characteristics in two-terminal MOM devices based on vanadium dioxide thin films. The switching effect is associated with the metal-insulator phase transition. Relaxation oscillations are observed in circuits with VO2-based switches. Dependences of the oscillator critical frequency Fmax, threshold power and voltage, as well as the time of current rise, on the switching structure size are obtained by numerical simulation. The empirical dependence of the threshold voltage on the switching region dimensions and film thickness is found. It is shown that, for the VO2 channel sizes of 10×10 nm, Fmax can reach the value of 300 MHz at a film thickness of ~20 nm. Next, it is shown that oscillatory neural networks can be implemented on the basis of coupled VO2 oscillators. For the weak capacitive coupling, we revealed the dependence of the phase difference upon synchronization on the coupling capacitance value. When the switches are scaled down, the limiting time of synchronization is reduced to Ts ~13 μs, and the number of oscillation periods for the entering to the synchronization mode remains constant, Ns ~ 17. In the case of weak thermal coupling in the synchronization mode, we observe in-phase behavior of oscillators, and there is a certain range of parameters of the supply current, in which the synchronization effect becomes possible. With a decrease in dimensions, a decrease in the thermal coupling action radius is observed, which can vary in the range from 0.5 to 50 μm for structures with characteristic dimensions of 0.1 to 5 μm, respectively. Thermal coupling may have a promising effect for realization of a 3D integrated oscillatory neural network.

Switch Elements with S-Shaped Current-Voltage Characteristic in Models of Neural Oscillators

“…The jump in resistance between these phases can reach several orders of magnitude (10-10 4 ), depending on the structure of the film [55]. Many researchers, including us [56], have demonstrated that the effect of electrical switching occurs due to MIT, when the current passing through the VO 2 structure heats it with Joule heat to a temperature T t . There is a strong dependence of the threshold switching parameters on the ambient temperature T 0 [46].…”

Capacitorless model of a VO2 oscillator

“…One of the technological problems of miniaturization of oscillator circuits is the application of capacitors that occupy a large area of the crystal using standard CMOS technology. For example, with an inter-electrode dielectric thickness of 10 nm, the specific capacitance of the capacitor is ~ 3 fF / μm 2 , and the capacitances with a nominal value of more than 1 pF are needed to generate oscillations on submicron-sized switches [16]. When implementing the capacitor model of the oscillator, nearly 330 μm 2 of the crystal area is required to manufacture the capacitor, while only ~ 1 μm 2 is used to manufacture the switch and the load or current resistors.…”

A Spiking Neural Network Based on the Model of VO2–Neuron

“…In the current study, for the manufacturing of artificial neurons, we propose to use elements with a stable S-shaped I -V characteristic, such as switches based on transition metal oxides with a metal-insulator transition [25][26][27]. Implementations of neuron models on the VO 2 switch are described in References [28][29][30][31][32][33][34].…”