Solid-State Electronics, Vol.141, 40-49, 2018
Thermal coupling and effect of subharmonic synchronization in a system of two VO2 based oscillators
We explore a prototype of an oscillatory neural network (ONN) based on vanadium dioxide switching devices. The model system under study represents two oscillators based on thermally coupled VO2 switches. Numerical simulation shows that the effective action radius R-TC of coupling depends both on the total energy released during switching and on the average power. It is experimentally and numerically proved that the temperature change Delta T commences almost synchronously with the released power peak and T-coupling reveals itself up to a frequency of about 10 kHz. For the studied switching structure configuration, the R-TC value varies over a wide range from 4 to 45 mu m depending on the external circuit capacitance C and resistance R-i, but the variation of R-i, is more promising from the practical viewpoint. In the case of a "weak" coupling, synchronization is accompanied by attraction effect and decrease of the main spectra harmonics width. In the case of a "strong" coupling, the number of effects increases, synchronization can occur on subharmonics resulting in multilevel stable synchronization of two oscillators. An advanced algorithm for synchronization efficiency and subharmonic ratio calculation is proposed. It is shown that of the two oscillators the leading one is that with a higher main frequency, and, in addition, the frequency stabilization effect is observed. Also, in the case of a strong thermal coupling, the limit of the supply current parameters, for which the oscillations exist, expands by similar to 10%. The obtained results have a universal character and open up a new kind of coupling in ONNs, namely, T-coupling, which allows for easy transition from 2D to 3D integration. The effect of subharmonic synchronization hold promise for application in classification and pattern recognition.
Keywords:Vanadium dioxide;Metal-insulator transition;Switching;Oscillatory neural networks;Thermal coupling;Subharmonic synchronization