A New Approach to Explore the Semiconductor-to-Metal Phase Transition in Two-Dimensional Crystals Using Ionomers

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Non-technical description: As the number of electronic devices continues to increase, so does the need for energy to power these devices; therefore, decreasing computing power requirements could significantly impact global energy consumption. In this study, a novel device concept based on new materials is being explored to replace traditional silicon-based transistors, with the goal of lowering the operating power. Specifically, a new type of polymer electrolyte (i.e., ion conducting polymer) is designed to induce strain in a two-dimensional (2D) semiconductor when an electric field is applied. The 2D semiconductor has a thickness of only one molecule. The strain changes the electrical properties of the 2D semiconductor, which can then be sensed to perform logic operations. The change is predicted to occur at voltages lower than ones used in conventional transistors, and therefore the power required to operate the device is lower. In addition to applications in nanoelectronics, this research advances new materials for phase change devices that respond to electrical, chemical or strain stimuli, with potential application in brain-inspired computing, and artificial synapses. The postdoctoral scholar, graduate and undergraduate students who work on this project benefit from an interdisciplinary project that combines chemistry, polymer science, inorganic materials science and device physics with the goal of engineering low-power transistors. The research component provides educational case studies to be used in the classroom, and interdisciplinary training of postdocs, graduate and undergraduate students. Technical Description: A new approach to strain 2D crystals is being explored using a field-effect transistor (FET) with a suspended MoTe2 channel for which the gate oxide is replaced by a custom-synthesized ionomer (i.e., single-ion conductor). Gate bias induces an electrostatic imbalance in the ionomer that strains the 2D crystal and induces a semiconducting to metallic phase change. The phase change is detected by the current-voltage characteristics of the FET, and is expected to occur at sub-volt gate bias with nanosecond switching times. This approach offers a gate control architecture that is similar to conventional CMOS architecture but with new materials and new physics. The research addresses both a fundamental and a practical challenge for dynamically controlling the phase behavior of 2D crystals. The fundamental challenge is achieving strain in 2D crystals that is sufficiently large to induce the phase transition; here, electrostatic control via ions is used to address this challenge. The practical challenge is building an electronic device that can exploit this phase-change property for low-power transistors, brain-inspired computing, or the development of artificial synapses.