Flexible Ferroelectric Hafnia-Based Synaptic Transistor by Focused-Microwave Annealing

Abstract

Hafnia-based ferroelectric memory devices with excellent ferroelectricity, low power consumption, and fast operation speed have attracted considerable interest with the ever-growing desire for nonvolatile memory in flexible electronics. However, hafnia films are required to perform a high temperature (>500 degrees C) annealing process for crystallization into the ferroelectric orthorhombic phase. It can hinder the integration of hafnia ferroelectric films on flexible substrates including plastic and polymer, which are not endurable at high temperatures above 300 degrees C. Here, we propose the extremely low-temperature (similar to 250 degrees C) process for crystallization of Hf0.5Zr0.5O2 (HZO) thin films by applying a focused-microwave induced annealing method. HZO thin films on a flexible mica substrate exhibits robust remnant polarization (2P(r) similar to 50 mu C/cm(2)), which is negligibly changed under bending tests. In addition, the electrical characteristics of a HZO capacitor on the mica substrate were evaluated, and ferroelectric thin film transistors (Fe-TFTs), using a HZO gate insulator, were fabricated on mica substrates for flexible synapse applications. Symmetric potentiation and depression characteristics are successfully demonstrated in the Fe-TFT memory devices, and the synaptic devices result in high recognition accuracy of 91.44%. The low-temperature annealing method used in this work are promising for forming hafnia-based Fe-TFT memory devices as a building block on a flexible platform.