Fabrication and Testing of Room-Temperature Charge-Density-Wave Devices
Quasi-2D charge-density-wave van der Waals materials demonstrated potential for novel electronic device functionality, which can be achieved at room temperature. This dissertation reports on fabrication and testing of quasi-2D 1T-TaS2 charge-density-wave devices, focusing on the switching mechanisms of such devices. We tested the switching of 1T-TaS2 thin-film charge-density-wave devices, using nanosecond-duration electrical pulsing to construct their time-resolved current-voltage characteristics. The switching action was based upon the nearly-commensurate to incommensurate charge-density-wave phase transition in this material. For sufficiently short pulses, with rise times in the nanosecond range, self-heating of the devices is suppressed, and their current-voltage characteristics are weakly non-linear and free of hysteresis. This changes as the pulse duration is increased to ~200 ns, where the current develops pronounced hysteresis that evolves non-monotonically with the pulse duration. By combining the results of our experiments with a numerical analysis of transient heat diffusion in these devices, we established the thermal origins of their switching. In spite of this thermal character, our modeling suggests that suitable reduction of the size of these devices should allow their operation at GHz frequencies. We found that the charge-density-wave depinning process in 1T-TaS2 devices is not accompanied by an abrupt increase in electric current – in striking contrast to depinning in the “classical” charge-density-wave materials with quasi-1D crystal structure. It was demonstrated that the low-frequency noise spectroscopy and the differential current-voltage characteristics provide unambiguous metrics for the depinning threshold field in quasi-2D materials. It was also established that the depinning of the charge-density waves in quasi-2D materials is of the field-induced nature, and the threshold fields are substantially larger than those in quasi-1D van der Waals materials. The results obtained in this dissertation research are important for the proposed applications of the charge-density-wave devices in electronics.