Advanced Nanofabrication Technologies for Processing Layered Semiconductors and Device Applications

Nanofabrication;2D materials;Multibit memory;Mechanical Engineering;Engineering;Mechanical Engineering

Chen, MikaiLu, Wei ;

University of Michigan

关键词: Nanofabrication;    2D materials;    Multibit memory;    Mechanical Engineering;    Engineering;    Mechanical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/140798/mkchen_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Two-dimensional layered semiconductor materials, such as transition metal dichalcogenides (TMDCs), recently received a great deal of interest due to their excellent electronic, optoelectronic and mechanical properties, as well as large abundance of relevant bulk materials on earth. Especially for semiconductor-related applications, TMDCs can be used for making highly sensitive sensors, high-performance thin-film transistors (TFTs) that are potentially immune to short-channel effects, and ultra-thin flexible photovoltaic (PV) and photodetection devices.However, to utilize layered semiconductors for innovative device applications, we still need to (i) create scalable manufacturing methods with a high throughput for device production, (ii) develop proper material processing technologies to generate stable and reproducible doping effects in 2D semiconductors, therefore enabling diverse optoelectronic and electronic applications, (iii) advance the device physics to leverage the uniquely advantageous electronic, structural, and mechanical properties of TMDCs in device application fields, such as information processing and data storage.The research presented in this dissertation sought to address the challenges mentioned above with a special focus on the following three topics: (1) development of nanoimprint/nanoprint-based processes for producing device structures based on layered semiconductors; (2) invention of a plasma-assisted doping technology for making TMDC-based nanoelectronic devices such as rectifying diodes and ambipolar transistors; (3) fabrication and characterization of TMDC-based memory devices with multi-bit storage capability, simple device structure, and low production cost.The first part of my thesis presents a nanoimprint/nanoprint-based method for fabricating TMDC-based (e.g., MoS2, WSe2) field-effect transistors. The field effect transistors (FETs) made from produced multilayer MoS2 flakes exhibit very consistent performance with high on/off ratios in the range of 105 -107. The characterization data measured from these FETs show that produced MoS2 flakes have a high uniformity of electronic properties.The second part of my thesis presents a novel plasma-assisted doping technology for modulating the electronic properties of layered semiconductor materials such as TMDCs. Taking MoS2 as an exemplary TMDC under study, via plasma doping, we have demonstrated p-type MoS2 transistors that can be complementary to pristine n-type MoS2 transistors, potentially enabling applications in CMOS circuits. Moreover, via applying plasma doping for selected areas, we have created 2D diodes with high rectification degrees and a superior long-term stability at room temperature.The third part of my thesis presents a study on the abnormal charge-trapping and memory characteristics of few-layer WSe2 transistors. In addition, I present an innovative device application of MoS2 in making floating-gate-free, non-volatile, multi-bit memory FETs, which has a unique combination of excellent retention/endurance characterisitcs, simple device structures and extremely low fabrication cost.These presented works provide nanofabrication and material processing solutions for making nanoelectronic devices based on emerging layered semiconductors, which can be generally utilized for making a broad range of functional devices based on various layered materials (e.g., graphene and topological insulators). Especially, the plasma doping method demonstrated in my research holds the potential to be further developed into an industrial material processing technology for precisely tailoring the band structures of TMDCs to achieve desirable characteristics for various device applications. In addition, the obtained device physics knowledge associated with MoS2 and WSe2-based multi-bit charge memory states is anticipated to greatly leverage the unique electronic and structural properties of layered semiconductors for scalable data storage and emerging analog computing applications.