A charge-density-wave oscillator based on an integrated tantalum disulfide–boron nitride–graphene device operating at room temperature

Abstract

The charge-density-wave (CDW) phase is a macroscopic quantum state consisting of a periodic modulation of the electronic charge density accompanied by a periodic distortion of the atomic lattice in quasi-1D or layered 2D metallic crystals. Several layered transition metal dichalcogenides, including 1T-TaSe, 1T-TaS and 1T-TiSe exhibit unusually high transition temperatures to different CDW symmetry-reducing phases. These transitions can be affected by the environmental conditions, film thickness and applied electric bias. However, device applications of these intriguing systems at room temperature or their integration with other 2D materials have not been explored. Here, we demonstrate room-temperature current switching driven by a voltage-controlled phase transition between CDW states in films of 1T-TaS less than 10 nm thick. We exploit the transition between the nearly commensurate and the incommensurate CDW phases, which has a transition temperature of 350 K and gives an abrupt change in current accompanied by hysteresis. An integrated graphene transistor provides a voltage-tunable, matched, low-resistance load enabling precise voltage control of the circuit. The 1T-TaS film is capped with hexagonal boron nitride to provide protection from oxidation. The integration of these three disparate 2D materials in a way that exploits the unique properties of each yields a simple, miniaturized, voltage-controlled oscillator suitable for a variety of practical applications.

Recent Advances in Two-Dimensional Materials with Charge Density Waves: Synthesis, Characterization and Applications

“…Electronic applications such as oscillators [37] and nonvolatile memory storage [38,39] have been demonstrated successfully in recent years, based on the charge density wave phase transitions. Although the investigations of bulk CDW materials have been done extensively for decades, as atomically thin materials, their role is simply up to date.…”

Total-Ionizing-Dose Effects on Threshold Switching in $1{T}$ -TaS2 Charge Density Wave Devices

“…At voltages larger than V H , the I-V curve has a slope larger than below threshold, indicating a resistance switch from a high resistive state to a low resistive state. As the voltage is scanned back from 1 V to 0 V, the current switches out of the low resistive state to the high resistive state at V L = 0.89 V. This switching occurs at the electrically driven phase transition between the NC-CDW and IC-CDW phase in 1T -TaS 2 [9]. Since the switching can take place as long as the temperature is below the NC-IC phase transition at 350 K, this operation is stable at RT.…”

“…method [9]. A thin film of 1T -TaS 2 was placed on a Si substrate with a top layer of 300-nm SiO 2 .…”

“…The thickness of 1T -TaS 2 channel layer (H = 20 nm) has been verified by atomic force microscopy. Details of the device fabrication are reported elsewhere [9]. 1T -TaS 2 devices exhibit a pronounced threshold switching as the voltage exceeds certain threshold values, V H for the positive scan and V L for the negative scan.…”

“…Some of us have recently demonstrated a quasi-2D 1T -TaS 2 device, which operates as a voltage controlled oscillator at room temperature (RT). The physical principal of operation of this oscillator is the transition between two charge density wave (CDW) phases controlled by voltage bias [9], [10]. The transition between the nearly commensurate (NC-CDW) phase and incommensurate (IC-CDW) phase reveals itself as an abrupt change in resistivity of the device channel accompanied by hysteresis.…”