References:

[1] Deng, G. W. et al., Charge number dependence of the dephasing rates of a graphene double quantum dot in a circuit QED architecture. Phys. Rev. Lett. 115, 126804 (2015).

[2] Deng, G. W. et al., Coupling two distant double quantum dots with a microwave resonator. Nano Lett. 15, 6620 (2015).

[3] Deng, G. W. et al., Strongly coupled nanotube electromechanical resonators. Nano Lett. 16, 5456 (2016).

[4] Li, S. X. et al., Parametric strong mode-coupling in carbon nanotube mechanical resonators. Nanoscale 8, 14809-14813 (2016).

[5] Luo, G. et al., Coupling graphene nanomechanical motion to a single-electron transistor. Nanoscale 9, 5608-5614 (2017).

[6] Zhu, D. et al., Coherent phonon Rabi oscillations with a high-frequency carbon nanotube phonon cavity. Nano Lett. 17, 915-921 (2017).

[7] Luo, G. et al., Strong indirect coupling between graphene-based mechanical resonators via a phonon cavity. Nature Commun. 9, 383 (2018).

[8] Zhang, Z. Z., et al., Electrotunable artificial molecules based on van der Waals heterostructures. Sci. Adv. 3, e1701699 (2017).

Graphene’s unique properties, including low mass and high stiffness, ultrahigh strength, and high electronic mobility, enable graphene nanoelectromechanical systems (NEMS) very suitable for low power high frequency circuits. Local gate graphene resonant channel transistors (G-RCTs) can reduce parasitic electromagnetic (EM) coupling and thus has good potential in high frequency integrated circuits. To develop the G-RCTs high frequency circuits, a compact model that can predict a G-RCT’s performance and implement into standard circuit simulators is essential.

This paper presents a high-frequency nonlinear equivalent circuit model of G-RCTs including a nonlinear electromechanical model of doubled clamped graphene mechanical resonators. To describe the temperature-dependent modal dispersion, both bias- and temperature-dependent effects are considered. The temperature-dependent built-in strain, the bias-based electrostatic force and the spring restoring force including the nonlinear term upon deformation are used to describe the mechanical motion of the suspended beam. Good agreement between simulated and measured results can be achieved as shown in Fig.1. Moreover, the nonlinear effects including harmonic distortion, third-order intermodulation distortion (IMD), and the hysteresis and nonlinear behavior of G-RCTs are also studied. Fig.2 and Fig.3 are results of mechanical nonlinear characteristics and duffing nonlinear behavior of G-RCTs, respectively. The results in show that the mechanical nonlinearity has strong effects on nonlinear distortion for G-RCTs. The proposed nonlinear equivalent circuit model could be useful for Graphene NEMS in the applications of high frequency integrated circuits.

Atomic layer semiconducting crystals have emerged as a new class of two-dimensional (2D) materials, exhibiting great promises for both fundamental research and technological applications. Their outstanding electromechanical properties make these materials ideal for constructing novel 2D NEMS, providing opportunities for leveraging their unique device properties across multiple information-transduction domains, at scales down to individual atomic layers. One particularly interesting category of 2D NEMS is 2D nanoelectromechanical resonators, which hold potentials for making the next generation RF signal transduction and processing components, with miniaturized size, ultra-low power consumption, and compatibility with transparent and flexible circuits.

Towards future applications in the 5G era, multi-band RF signal handling capability is desired, as the number of bands each mobile device need to have access to significantly increases, and it would be impractical to simply increase the number of RF components that can only function under one RF frequency, as the space required for mounting such components scales with the number of bands. Therefore, ultralow-power tunable and reconfigurable RF devices that can adapt to different frequencies would be one solution to this challenge.

Here we present experimental demonstration of nanomechanical resonators based on layered MoS₂ atomic crystals that have reconfigurable resonant responses. By carefully studying the temperature-dependent frequency response in such MoS₂ resonators[1], we discover clear, repeatable hysteretic behavior as the device temperature is changed[2]. Leveraging this phenomenon, we achieve switchable resonance frequency f_res in such devices by using heating and cooling pulses. Specifically, for an example MoS₂ resonator, during heating pulses, the f_res decreases to ~20MHz. Once the device recovers to room temperature, f_res stabilizes at ~26MHz. During cooling pulses, f_res increases to ~29MHz, and upon reverting to room temperature f_res stays at ~24.5MHz, which is clearly different than the other room temperature state. Our findings suggest that such atomic-layer MoS₂ NEMS resonators could be used towards developing reconfigurable RF components whose frequency response can be switched between different states.

[1] R. Yang, et al., IEEE UFFC, pp 198-201, 2015. [2] Z. Wang, et al., IEEE UFFC, pp 783-786, 2015.

The field of cavity optomechanics deals with a family of systems, each composed of two coupled elements. The first one is a mechanical resonator, commonly having a low damping rate, and the second one is an electromagnetic cavity, which typically is externally driven. Both radiation pressure and bolometric force can give rise to the coupling between the mechanical resonator and the cavity. In recent years a variety of cavity optomechanical systems have been constructed and studied, and phenomena such as mode cooling, self-excited oscillation, and optically induced transparency have been investigated. The first part of the talk will be devoted to some dynamical effects including synchronization and intermittency. In the second part some applications of optomechanical cavities for sensitive sensing will be discussed.