Design, fabrication and characterization of field-effect transistors based on two-dimensional materials and their circuit applications
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The field of two-dimensional layered materials has witnessed extensive research activities during the past decade, which commenced with the seminal work of isolating graphene from bulk graphite. In addition to providing a rich playground for scientific experiments, graphene has soon become a material of technological interest for many of its fascinating electrical, thermal, mechanical and optical properties. The controllability of carrier density with electric field in graphene, along with very high carrier mobility and saturation velocity, has motivated the use of graphene channel in field-effect devices. Also, the two-dimensional layered materials family has grown very rapidly with the application of the graphene exfoliation technique and many of these elemental and compound materials are considered useful for transistor applications. In this work, various aspects of the use of two-dimensional layered materials for transistor applications were analyzed. Starting with material synthesis, field-effect transistors (FETs) were designed, fabricated and tested for their DC and high frequency performances. Through the detailed electrical and spectroscopic investigations of several processing techniques for enhanced FET performance, numerous insights were obtained into the FET operation and performance bottlenecks. The reduction of charged impurity scattering in graphene FET by Hexamethyldisilazane interaction improved field-effect mobility and reduced residual carrier concentration. This technique was also shown to be promising for other two-dimensional materials based FET. A useful technique for reducing the thickness of black phosphorus flake with oxygen plasma etching was developed. Both back-gated and top-gated FETs were implemented with good performances. Secondary ion mass spectroscopy and x-ray photoelectron spectroscopy revealed vital structural information about layered black phosphorus. Lastly, these exotic materials based FETs were characterized for their high frequency performance, resulting in gigahertz range transit frequency and operated in a variety of important circuit configurations such as frequency multiplier, amplifier, mixer and AM demodulator.