Liquid-Metal-Printed, Modulation-Doped 2D Metal Oxide Transistors

Dartmouth College, Hanover NH

Investigators

Abstract

Liquid Metal Printed Transistors Enhanced with Multilayer 2D Semiconducting Oxide Heterostructures Ultrathin metal oxide semiconductors have exceptional optical, mechanical, and electronic properties that could enable emerging flexible electronics, from resorbable biosensors to low-power displays. Engineering these devices for specific applications requires precise nanoscale control of the transport of electrons for large area devices and systems. However, depositing atomically thin oxides at a large scale while controlling their electrical properties remains technologically challenging. This project overcomes those limitations by leveraging a new form of 2D oxide semiconductors spontaneously formed by native oxidation of liquid gallium and indium to fabricate highly conductive and ultratransparent nanosheets just 2-3 nm thick. The scientific question driving this study is how to precisely control electronic transport in transistors utilizing 2D oxide channels. Our approach involves electrostatic engineering of heterostructures of InOx and GaOx as well as modeling of the density of electronic defects in these channel layers. This work also implements finite element simulations to design low-voltage, high-performance devices that can lead to integration into biomedical sensors, lightweight displays, and other systems that benefit from low-temperature fabrication on flexible polymer substrates. The research plan ties in with planned educational outreach and inclusivity efforts. We build on past efforts, providing engaging research opportunities for a diverse set of undergraduates and graduates while regularly assessing the downstream impact. The planned recorded remote laboratories based on the science of conductivity of liquid metals will deliver content for powering remote learning opportunities for K-12 and undergraduate engineering education. The impact of these activities will be to broaden participation in STEM and strengthen the engineering workforce. The primary goal of this project is to develop a new paradigm of two-dimensional (2D) metal oxide transistors enhanced through quantum modulation doping. Towards this end, this work develops a fundamental understanding of how heterointerfaces can be engineered to enhance electronic transport in channels consisting of heterostructures of quantum confined 2-3 nm thick 2D wide bandgap oxide semiconductors. This strategy can induce 2D electron gas formation and band-like transport characteristics such as temperature-independent mobility. However, the fundamental gap limiting applications of these phenomena is the connection between nanoscale electrostatic interface engineering and electronic transport in oxide semiconductors. A fundamental innovation in this program is to utilize liquid metal printing to fabricate vertically stacked heterostructures channels in which high-mobility, efficient electron transport is produced by the interfacial conduction band energy offset (ΔEc) of 2D InOx and GaOx. Detailed device characterization measurements probe the hypothesis that this modulation doping of 2D heterointerfaces can engineer band-like transport by passivating interface traps and inducing bulk electron accumulation. A complementary goal is to develop TCAD simulations based on density of states data to design electrostatically optimal multilayer architectures, identify the impact of high-k dielectric integration, and design transistors for low-voltage unipolar logic circuits. This combination of experiments and simulations can provide the fundamental device engineering knowledge needed to leverage this scalable fabrication method for various flexible electronics 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.