Electrical and Thermal Dynamics of Self-Oscillations in TaO_x-Based Threshold Switching Devices

We present experimental results of relaxation oscillations based on the TaOx threshold switching devices as a function of voltage, load resistance, and the parallel capacitance. Of particular interest are the dynamics of transitions between ON and OFF states of the device which impose an upper limit of the oscillation frequency. The dynamics have been captured by the finite element electrothermal model using only electrical conductivity vs temperature and thermally activated conductivities as input data. The model reproduced current and voltage waveforms and allowed for following the changes in current density and temperature distributions within the device during oscillations. Both undergo significant breathing-mode-type changes in each cycle as the current spontaneously constricts during the capacitance discharge/heating stage. The model points out the possible approaches toward achieving higher oscillation frequencies.