GOALI: Negative Capacitance in Epitaxial Oxide Heterostructures

University Of Texas At Austin, Austin TX

Investigators

Abstract

This project is jointly funded by the Electronic and Photonic Materials Program (EPM) and Ceramics Program (CER) in the Division of Materials Research (DMR). Technical Description: This GOALI project explores the fundamental materials science problems of integrating a single-crystalline, single-domain ferroelectric material (with polarization out of plane) onto silicon. A ferroelectric layer in series with a dielectric is predicted to produce negative capacitance, which will lower the sub-threshold slope of a field effect transistor and significantly lower the power dissipated in a transistor. This research project develops the materials and the fundamental understanding necessary to make the predictions a reality. Molecular beam epitaxy is used to grow strontium titanate epitaxially on single-crystal silicon as a buffer layer for the nucleation and growth of single-crystal ferroelectric films, such as barium titanate. The research explores routes to integrate these single- crystal layers on silicon, approaches to achieving out-of-plane polarization in the ferroelectric layer for thicknesses up to 50 nanometers, approaches to achieving a single-domain ferroelectric state, and integration of these layers into transistor devices to harness the negative capacitance state of the heterolayers and realize sub-threshold slopes less than 60 millivolts per decade. The experimental growth studies are guided by ab-initio theory, and materials properties are characterized using in-situ and ex-situ methods. Non-technical Description: Scaling of the complementary metal oxide semiconductor (CMOS) technology is at the heart of Moore's law; it is driven by the desire to produce ever faster field effect transistors. However, the faster the transistor is the more heat it generates in the switching process. New device concepts are required to enable significantly lower power dissipation and to realize the full speed potential for the smaller devices. This research project explores one of the new device concepts of using a ferroelectric/dielectric composite film in place of the dielectric that is currently used in field effect transistors - a concept that is yet to be realized because of the challenges in growing the layers with the proper crystal structure and orientation on the silicon surface that forms the transistor. The research combines an interdisciplinary team and explores growth and properties of barium titanate layers (the ferroelectric) on strontium titanate (the dielectric) on a silicon wafer. The research partners university researchers with a technology leader in advanced device design to broaden the student experience as they are exposed to problem definition that keeps the end goal of developing a viable technology front and center. The outreach activities are aimed at attracting high-school female students to physical sciences and engineering; in collaboration with the physics instructors in local high schools, the students spend summers in research groups at the University of Texas at Austin and participate in real science in a supportive environment.