Biaxial Strained Transfer of Atomically Thin Nano-Electro-Mechanical Membranes

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The next generation of MEMS is NEMS - nano-electro-mechanical systems, and the most promising candidate for NEMS membranes are graphene and 2-dimensional (2-D) materials. 2-D materials exhibit a unique combination of superlative properties such as high stiffness, low bending modulus, high elasticity, low mass per unit area, low thickness and high electrical conductivity. This allows for the development of NEMS membranes that can achieve behaviour that are typically considered conflicting in traditional MEMS devices and membranes, such as both high resonance frequency and high deflection amplitude. A number of 2-D NEMS devices have been demonstrated on the lab scale, including pressure, touch and mass sensors, microphones, self-sustained oscillators, quantum Hall devices, RF front-end filters, switches, photonic modulators and more. These novel NEMS devices will find applications in future robotics, electronics, healthcare, automotive, aerospace and more. The transition from lab-scale devices to large-scale manufacturing of 2-D NEMS has to overcome a number of critical challenges. Some of these challenges, such as minimising nanoscale defects and improving device yield and performance, have been addressed by employing few-layer graphene or graphene-polymer heterostructure membranes. However, there is still one key outstanding challenge in the future manufacturing of novel 2-D NEMS devices. It is well known that 2-D layers possess significant built-in tensile and compressive stresses which are both arbitrarily distributed as well as difficult to control. These arise both from the way that they are grown and the the way that they are transferred from one surface to another during NEMS manufacturing. In the nano-manufacturing of 2-D NEMS devices, it is essential that these built-in stresses are rendered uniformly within each device and across all devices. This will be accomplished in this project by developing a new process that will apply a well-controlled biaxial tensile strain to the 2-D membrane during the transfer from the parent to the target NEMS substrate. Not only will this strain ensure that the suspended membranes are uniform across all devices, the resulting pre-tension will also increase the stiffness of the membrane, and consequently the resonance quality factor of the resulting NEMS device. Furthermore, the static and dynamic sensitivity of the device and its resonance frequency can be tuned by controlling the pre-tension. It is also essential that this applied strain, and the residual strain in the resulting membrane, are monitored in real-time. In this project, we will implement in-situ strain monitoring based on the fact that the strain in 2-D materials can be detected as shifts in their signature Raman spectroscopy peaks.This project will enable the UK to take the lead in wafer-scale and roll-to-roll 2-D NEMS manufacturing, building on the UK's existing strengths in MEMS foundries, printed electronics, 2-D material production, and sensors and actuators. This in turn will strongly reinforce the health of a wide range of other manufacturing sectors including sensors, healthcare, communications, automotive and aerospace. 2-D NEMS will enable various next-generation devices and technologies that will transform our society to be more productive, connected, healthy and resilient.