Scalable MoS2 based flexible devices and circuits for wireless communications

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Emerging flexible electronics is one of the most extensively investigated fields in recent years. It is expected to provide human beings with smaller, lighter, and more comfortable electronic devices. Among all the candidates for a suitable active channel material for transistors on flexible substrates, two-dimensional (2D) transition metal dichalcogenide (TMD) layered materials such as molybdenum disulfide (MoS2) are very promising for flexible circuits targeting wireless communications. TMDs show excellent mechanical flexibility due to their inherent thinness while at the same time exhibiting very high mechanical strength, which is critical for the stability of flexible devices and circuits. The charge carrier mobility in semiconducting TMDs is relatively high, which enables performance in the RF regime, and the semiconducting nature of TMDs results in well-behaved transistor characteristics, i.e. high on/off current ratio, steep switching and high output impedance. The scalability of transistor gate lengths has been demonstrated down to less than 10 nm, in particular for MoS2, a material with a large direct band gap of 1.8 eV in single layer form. However, the scalability of TMD materials synthesis so far is not optimized, but large scale deposition of TMDs is under development and has been demonstrated in general using chemical vapor deposition. In this project, the feasibility of fabricating electronic devices and circuits based on the 2D material MoS2 on flexible substrates will be assessed. Direct deposition of MoS2 layers on flexible substrates at low temperatures will be investigated in detail. Metal contacts fabricated on such directly grown materials will be optimized with regard to the metal-MoS2 contact resistance and their stability under strain. Furthermore, the performance of flexible transistors based on MoS2 will be assessed and optimized for different geometries with a targeted frequency response up to the GHz regime. At the circuit level, different logic and analogue circuits based on flexible RF transistors will be designed, simulated, fabricated, optimized and characterized. Any issues that might arise will be identified and addressed by a combination of structural material analysis, DC and RF measurements of devices and circuits, and device and circuit modeling. We target flexible demonstration circuits that can perform at 400 MHz.