Unveiling the Tradeoff between Device Scale and Surface Nonidealities toward an Optimized Quality Factor at Room Temperature in 2D MoS2 Nanomechanical Resonators

Abstract A high quality (Q) factor is essential for enhancing the performance of resonant nanoelectromechanical systems (NEMS). NEMS resonators based on two-dimensional (2D) materials such as molybdenum disulfide (MoS2) have high frequency tunability, large dynamic range, and high sensitivity, yet the room-temperature Q is typically below 1,000. Here we systematically investigate the size effects on Q by measuring 52 fully-clamped circular MoS2 NEMS resonators with diameters from 1 µm to 8 µm, and optimize the Q by combining the size effect with the strain-modulated dissipation model. We find that the Q first increases and then decreases with diameter, with an optimized room-temperature Q up to 3,105 ± 207 at for a 2-µm-diameter device. Through extensive characterization and analysis using Raman spectroscopy, atomic force microscopy, and scanning electron microscopy, we demonstrate that surface nonidealities such as wrinkles, residues, and bubbles are especially significant for decreasing the Q especially for larger suspended membranes, while resonators with flat and smooth surfaces typically show larger Q factors. To further optimize the Q factor, we measure and model the Q dependence on gate voltage, showing that smaller DC and radio-frequency (RF) driving voltages always lead to a higher Q factor. Such optimization of Q factor delineates a straightforward and promising pathway for designing high-Q 2D NEMS resonators towards ultrasensitive transducers, efficient RF communications, and low-power memory and computing.