Data-Driven Analysis of High-Resolution Hyperspectral Image Data Sets through Nanoscale Capacitance–Voltage Measurements to Visualize Ferroelectric Domain Dynamics

Abstract

The key to elucidating various unexplained phenomena regarding ferroelectric materials and discovering new ones as well as improving the properties of these materials is to understand the domain dynamics at the nanoscale. The recently developed local capacitance–voltage (C–V) mapping method allows nanoscale analysis of domain dynamics through dielectric measurements. This method has advantages over conventional methods, such as the ability to simultaneously achieve high speed and high sensitivity in the observation, allowing for high-resolution map data to be acquired quickly. Herein, we present a methodology to analyze hyperspectral image data with the huge amount of information generated by this method using a machine learning approach to extract and visualize the information necessary for understanding domain dynamics. In addition, using this methodology, we focus on the effect of grain boundaries on polarization switching in ferroelectric films. We chose doped HfO2 thin films as the specific target of our measurement. While these materials are expected to be applied to ultralow power consumption nonvolatile memory and neuromorphic devices, a major problem is that their properties change during the application of electric field cycling, known as wake-up and fatigue. In this study, we analyzed doped HfO2 films before wake-up using local C–V mapping. The acquired data sets were then clustered into several regions based on the similarity of their polarization properties using unsupervised learning methods such as k-means and Gaussian mixture models. In addition to the typical butterfly shaped C–V curves that represent normal polarization switching, these clusters contained asymmetric butterfly curves that may be caused by domain pinning or other built-in field-derived effects. Subsequent statistical analysis suggested that, in pristine HfO2 films before wake-up, although defects at grain boundaries have some effect on the polarization switching properties, they are not the main cause of the variation in properties.