Transport and Variability Study on Transition Metal Dichalcogenide (MX2) Based Field-Effect Devices: Time-zero Performance

2D materials are very promising alternatives to conventional channel materials such as Si and Ge in extending the logic scaling roadmap. Their atomically thin channels enable excellent electrostatic control and extreme device scaling. Numerous single-device demonstrators have been reported in literature. However, to reach industrial adoption, fundamental understanding of MX2 channel/interface defects and their impact on performance and variability of 2D FETs are needed. Defects form in/around 2D channels due to MX2 growth (e.g., dislocations, islands, grain boundary and point defects) and device fabrication related (e.g., MX2 transfer or interactions with environment) nonidealities. In addition, defects are also present in the gate stack (e.g., intercalated surface contaminants and oxide traps) due to difficulties in ALD oxide nucleation and non-ideal processing. In this PhD, the student will focus on device designs, electrical characterization and analysis of 2D MOS devices to gain fundamental understanding on: 1. Transport: mechanism of mobility degradation in MX2 channels. Impact of MX2 channel/interface/oxide defects (impact of grain boundary, intra-grain point defects, interface and oxide border traps) on time-zero transistor electrical characteristics/performance. Requires low temperature and Hall measurements. 2. Variability and Vt control: statistical study of threshold voltage and sub-threshold swings to investigate the impact of grain size, substrate treatments and gate stacks. In addition, the student will gain deeper insights into the sources of defects and variability by collecting large datasets of electrical characteristics and correlate them with physical characterization like AFM and SEM, and TCAD simulations done by other team members and researchers. The student will work closely with 2D materials process and integration engineers to apply findings and improve the device characteristics over several learning cycles using two different and well-established device fabrication platforms. The first and the main device vehicle is a lab-based fabrication flow which yields high-performance devices with high flexibility in the choice of materials and gate stacks. The second vehicle which can be utilized in the latter part of this PhD is a 300mm fab-based MX2 device platform.