Department of Mechanical Engineering
University of Michigan
Emerging layered transition metal dichalcogenides (TMDCs) have attractive electronic, photonic, structural properties, and versatile chemistry. As two of the most popular TMDCs, MoS2 and WSe2 have emerged as very promising nanoelectronic material candidates for new device applications, such as ultrasensitive biosensors, multi-bit memories, and flexible photovoltaic (PV) devices with high quantum efficiencies. Although a great deal of recent research effort concentrates on the attractive characteristics associated with monolayer MoS2 and WSe2 structures, many important electronic/photonic applications, such as transistor-based memories/sensors, photovoltaics, and power-switching thin-film transistors (TFTs), indeed demand high-quality few-layer or multilayer MoS2 structures with controllable feature thickness as well as consistent device performance. However, there are so far very few research efforts dedicated to produce high-quality multilayer MoS2 and WSe2 device structures with a high uniformity of thicknesses as well as electronic/photonic properties over large areas. Toward ultimately realizing upscalable production of highly uniform multilayer TMDC-based device arrays or large-scale circuits, we developed new nanoimprint/nanoprint-based nanofabrication approaches capable of producing pristine multilayer MoS2 and WSe2 fake arrays with high uniformity of flake thicknesses (i.e., relative thickness error ~ 12%) over cm2-scale areas, and also demonstrated multiple working transistors and electronic biosensors made from as-produced MoS2 flakes, which exhibited very consistent performance (e.g., relative errors of important transistor performance parameters, such as mobility values, ON/OFF currents, subthreshold swings, and threshold voltages < 25%). This work provides new nanofabrication routes for generating pristine TMDC device arrays with well controlled properties, which holds significant potential to be further developed into a continuous high-throughput nanomanufacturing system capable of producing commercially viable electronic products based on emerging layered materials. In this project, we also accidentally found that the field-effect transistors (FETs) made from mechanically-printed few-layer TMDC flakes exhibit very unique charge-retention characteristics, which are attributed to the unique mechanical/structural properties of TMDC layers. More interestingly, such newly identified charge-trapping schemes in TMDC FETs could be further investigated and exploited to produce new multi-bit (or even analog-tunable) memory devices, which could meet current need of novel solid-state memory solutions with the lower cost-per-bit and the better scalability in comparison with the state-of-the-art memory devices as well as new logic devices with multiple levels of excitation states toward future realization of artificial intelligence (AI) capabilities at the hardware level.
Dr. Xiaogan Liang is currently working as a Tenure-Track Assistant Professor at The Mechanical Engineering Department of University of Michigan (UM). Before joining UM, Dr. Liang was a Staff Scientist working at The Molecular Foundry, Lawrence Berkeley National Laboratory. His current research interests are focused on nanomanufacturing, nanoelectronics and optoelectronics based on low-dimensional nanostructures, nanofluidics, and chemical/biological sensing technology. Dr. Liang has coauthored 53 journal publications and 40 conference presentations, has given 21 invited presentations, and has 3 US patents and 8 pending patents. Dr. Liang is the recipient of NSF CAREER Award, and he is the member of Sigma Xi, IEEE, and MRS. Dr. Liang obtained a BS in Physics from Peking University, a MS in Condensed Matter Physics from Institue of Semiconductors, Chinese Academy of Sciences, and a Ph.D. in Electrical Engineering from Princeton University.
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