Uncovering the atomic origins of thin film ferroelectricity

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

Non-technical Summary Memory is a key specification in consumer electronics like laptop computers and cell phones. For instance, a hard disk drive stores information as a series of “1”s and “0”s that are physically realized as tiny magnets. Instead of the magnetic materials in hard disk drives, new “ferroelectric” materials might form the basis of next-generation digital storage. In this project the research team uses advanced electron microscopy to probe the relationships between physical structure (where the atoms are) and electronic structure (how they respond to electric fields) in these new materials at the atomic level. Graduate and undergraduate students sponsored by this award will perform microelectronic device fabrication and testing, and become proficient at electron microscopy. These skillsets are directly applicable in the semiconductor industry. Students are being trained not only at the home institution of UCLA, but also at the minority-serving institutions of Norfolk State University and Fort Lewis College via a collaboration with the Partnership for Education and the Advancement of Quantum and nanoSystems (PEAQS), which is part of the NSF-funded Partnership for Research and Education in Materials (PREM). Technical Summary Hafnia (HfO2), when prepared in a very specific, non-equilibrium crystalline state, can exhibit ferroelectricity. Materials such as hafnia specifically are already commonplace in microprocessors, and underlie the emerging technologies of ferroelectric field effect transistors (FeFETs) and ferroelectric random access memory (FRAM). The team fabricates nanoscale, electron-transparent ferroelectric hafnia devices, and cycles the hafnia thermally and electrically in situ. These stimuli bring the hafnia, which is amorphous as deposited, through its various crystalline phases. Imaging the hafnia in each phase with electron beam-induced current (EBIC) imaging and electron energy loss spectroscopy (EELS), the team produces near-atomic resolution structural, electronic, and temperature maps. Correlating these maps with transport data acquired simultaneously provides a complete picture of these live, switchable devices. In particular, differential measurements of electronic properties, both before and after thermal and electrical cycling, enable the team to directly address such open problems as the origin and stability of the ferroelectric phase. Developing techniques for measuring the electrical and thermal properties of such materials contributes to the rational design of compact, low-power, and robust memory elements. 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.