CAREER: Strain-driven phase transitions in 2D van der Waals based devices

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Proposal TitleCAREER: Strain-driven phase transitions in two-dimensional van der Waals based devicesNon-technical AbstractThe conventional focus for advancements in computing have strongly relied on the continued shrinking of the field-effect transistors (FET) that makes up almost all integrated circuits. Since the fundamental physical and economic limits of transistor scaling are now being reached, new types of devices are being explored for added functionality beyond conventional transistor switching. This project explores the use of strain in two dimensionally (2D) bonded materials, such that applied stretching or compression may induce various phase-changes in these systems. Since these phase-changes are not limited to electrically conducting versus non-conducting as in on/off states of conventional transistors, additional functionality may be engineered through other changes in materials properties under strain. This type of strain-induced phase-change device would not operate under the same physical mechanism as conventional transistors, and therefore are not subject to the same limitations. By impacting the building blocks of modern nanoelectronics, there may be large impacts in various aspects of computing technology that are currently limited due to various power, speed, or efficiency limitations of conventional transistors. This project also seeks to use the research framework to promote science, technology, engineering and mathematics (STEM) to traditionally underrepresented communities by connecting with the Eastman School of Music at the University of Rochester. Examples of activities include running summer educational courses in music and electronics to local grade 7-12 students to create unconventional instruments that may be used in live concert performances.Technical AbstractThis project seeks to understand the foundational principles of using device-scale gate-controllable strain in two-dimensional (2D)-bonded materials to create new types of phase change transistors. By exploring a new mechanism of transistor switching using strain, limitations associated with conventional field-effect transistor operations may be overcome. With the wide variety of phases in the two-dimensional materials class close to strain-tunable phase transitions, the opportunity exists to set the basis for a wide variety of gate-controllable exotic states of matter. The device platform used in this project uses dynamic strain applied from ferroelectric oxides in combination with static thin film stress capping layers to demonstrate phase-switching in the Mo1-xWxTe2 class of two-dimensional materials. Using the MoTe2 semimetallic to semiconducting phase transition as a starting point, critical issues are identified that may still limit the implementation of reliable dynamic device scale strain in 2D systems, with the goal of expanding this "straintronic" concept to higher-endurance higher-yield operation as well as adding new phases to control within the Mo1-xWxTe2 class of materials. Additionally, learned foundational concepts from room-temperature operation in single 2D systems allow for the translation of this dynamic strain engineering concept to low temperatures and to van der Waals heterostructures, widely expanding the applicability of dynamic strain engineering in 2D systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.