Stress-Memorized HZO for High-Performance Ferroelectric Field-Effect Memtransistor

A ferroelectric field-effect transistor (FeFET), capable of logic and memory functionalities in a single device, is a promising three-terminal memtransistor that enables high-performance in-memory computing for non Von Neumann architectures. Among all HfO2-based ferroelectric materials, HfZrO2 (HZO) has attracted the most attention due to the low process temperature of <= 500 degrees C; however, it has relatively weak polarization. Many prior works claimed that the way to improve HZO-based FeFET characteristics is to enhance HZO ferroelectric properties, while they did not account for the fundamental compromise on dielectric breakdown strength (BDS), transistor ON/OFF current (ION/IOFF) ratio, and memory window (MW) due to the enhanced polarization. In this work, we propose an approach for controlling the ferroelectric orthorhombic phase (O phase) and the corresponding polarization in optimal value by engineering both the surface morphology and stress of HZO layer by a thermal expansion mismatch with a TiN/W stacked capping layer, to improve the BDS, ION/IOFF ratio, and MW. Through electrode surface optimization and stress memorization we achieved an 18% HZO ferroelectricity increase with a high BDS value of <= 4.8 MV/cm. Our optimized FeFET shows good electrical characteristics and supports operation in an identical pulse programming (IPP) mode, showing good potentiation and depression nonlinearity (-0.84 and -2.04) with an asymmetry factor of 1.2. A simulation based on the proposed FeFET array demonstrates the high potential of application in an artificial neural network (ANN).