Discipline: Technology and Engineering
Subcategory: Electrical Engineering
Benjamin Grisafe - University of Notre Dame
Co-Author(s): Rui Zhao and Joshua Robinson, Pennsylvania State University, PA
As CMOS scaling becomes increasingly difficult, novel materials, devices and architectures are required to advance computation capabilities. Materials such as transition metal dichalcogenides (TMDs) have been examined as potential compliments or replacements to silicon due to their unique 2D layered structures, large ON/OFF ratios, thermal stability, carrier mobility and compatibility with CMOS processing. However, TMD materials face several challenges for FET applications such as large contact resistance due to inherent Schottky barrier contacts and the absence of practical doping techniques that reduce ON-state current of the transistor. Furthermore, the absence of dangling bonds in these materials present challenges in the formation of high quality gate dielectrics with excellent interfaces having low interface trap density (Dit). To surpass these challenges while harnessing the advantages of 2D materials, we explore a novel transistor concept known as a Hybrid Phase Transition-FET, wherein we attempt to augment the performance of a conventional 2D MoS2 FET with the insulator-to-metal transition (IMT) in another 2D material 1T-TaS2. Further, we also explore an MoS2 based Hyper-FET using VO2 (having a much larger resistance ratio between the insulating and metallic states) to further illustrate the design and performance considerations for a fully 2D system. Back-gated FETs were fabricated using exfoliated MoS2 and characterized. ON/OFF ratios of ~106 are observed and a minimum subthreshold swing of ~100 mV/dec is achieved when using HfO2 as the back-gate oxide. Simultaneously, the two-terminal measurements of standalone 1T-TaS2 devices were measured. However, as we electrically integrate the 1T-TaS2 with the source of the MoS2 FET, the high trigger current for the IMT prohibits the transition. Therefore, we replace the 1T-TaS2 with VO2, which exhibits lower trigger current enabling us to induce the phase transition in VO2. Our experiments with 1T-TaS2 and VO2 provide useful insight into the desired requirements for 2D phase transition materials including optimization of the electrically induced transition and subsequently towards the realization of an all-2D Hyper-FET.
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Funder Acknowledgement(s): This work was supported by the National Science Foundation Emerging Frontiers in Research and Innovation program under award number 1433307.
Faculty Advisor: Suman Datta, firstname.lastname@example.org
Role: For this work, I performed fabrication of all steps for the samples and devices presented. This was done using the University of Notre Dame cleanroom mainly with electron beam lithography and liftoff metalization. Upon completion of fabrication, I performed all characterization of each device electrically using a semiconductor parameter analyzer.