Scalable MoS2 based flexible devices and circuits for wireless communications

新兴的柔性电子产品是近年来研究最广泛的领域之一。它有望为人类提供更小、更轻、更舒适的电子设备。在用于柔性衬底上的晶体管的合适的有源沟道材料的所有候选者中，二维（2D）过渡金属二硫属化物（TMD）层状材料如二硫化钼（MoS 2）对于以无线通信为目标的柔性电路是非常有前途的。TMD由于其固有的薄度而显示出优异的机械柔性，同时表现出非常高的机械强度，这对于柔性器件和电路的稳定性至关重要。半导体TMD中的电荷载流子迁移率相对较高，这使得能够实现RF机制中的性能，并且TMD的半导体性质导致表现良好的晶体管特性，即高开/关电流比、陡峭的切换和高输出阻抗。晶体管栅极长度的可缩放性已被证明可低至小于10 nm，特别是对于MoS 2，一种单层形式的具有1.8 eV的大直接带隙的材料。然而，到目前为止，TMD材料合成的可扩展性还没有优化，但是TMD的大规模沉积正在开发中，并且通常已经使用化学气相沉积来证明。在这个项目中，将评估在柔性衬底上制造基于2D材料MoS 2的电子器件和电路的可行性。将详细研究在低温下在柔性衬底上直接沉积MoS 2层。在这种直接生长的材料上制造的金属接触将在金属-MoS 2接触电阻和它们在应变下的稳定性方面进行优化。此外，基于MoS 2的柔性晶体管的性能将针对不同的几何形状进行评估和优化，目标频率响应高达GHz范围。在电路层面，基于灵活RF晶体管的不同逻辑和模拟电路将被设计、仿真、制造、优化和表征。任何可能出现的问题都将通过结构材料分析、器件和电路的DC和RF测量以及器件和电路建模来识别和解决。我们的目标是可以在400 MHz下运行的灵活演示电路。

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.