Quantum-Mechanical Assessment of Graphene and MoS2 Transistors for Future Radio-Frequency Electronics

• Author / Creator

  Holland, Kyle D

• Due to aggressive device scaling, the performance and cost-effectiveness of field-effect transistors (FETs) have improved exponentially over the last 60 years, a trend known as Moore’s Law. Unfortunately, obstacles have arisen to further scaling, including decreased electrostatic control of the gate from drain-induced barrier lowering. Two major alternatives to planar silicon transistors have been suggested to remedy the electrostatic limitation: the ultra-thin-body silicon-on-insulator (UTB-SOI) transistor and the fin field-effect transistor (FinFET). Furthermore, alternative channel materials have been suggested for future devices, such as carbon-based materials (carbon nanotubes and graphene) and transition-metal dichalcogenides [single-layer molybdenum disulphide (SL MoS2)]. In this work, quantum-mechanical modeling, necessary to capture short-channel and quantum-confinement effects in less-than-20-nm silicon devices and in devices made with new channel materials, is used to investigate the performance potential of graphene transistors, single-layer molybdenum disulphide transistors, and FinFET silicon transistors for RF applications. The first stage of work quantifies the effect of graphene’s lack of a bandgap in limiting its high-frequency performance, an issue recently flagged by Schwierz in Nature as being of critical importance for graphene devices to become commercially viable. We show that although there is a substantial decrease in relevant RF performance metrics due to the lack of a bandgap, the operation of graphene transistors can still exceed industry guidelines. The second stage of work addresses the question of whether devices made from SL MoS2, a material with a bandgap, can match or exceed the potential of gapless graphene for RF applications. We show that the peak performance of graphene is better, but SL MoS2 gains an edge in low-current applications. We place an emphasis on quantifying the necessary improvement of the contact resistances required with SL MoS2, an important limiting factor in current experimental work. Excellent agreement is observed between our simulated results and available experimental results. Ongoing work is being conducted to extend our modeling to examine short-channel FinFETs down to 5-nm channel lengths, in conjunction with industrial collaborators. We show results that illustrate the viability of our chosen approach.

• Subjects / Keywords

  • Graphene
  • FinFET
  • Radio-frequency electronics
  • Field-effect transistor
  • MoS2
  • Molybdenum disulphide

• Graduation date

  Spring 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3348GT93

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.