Reliable Accessibility of Intermediate Polarization States in Textured Ferroelectric Al_0.66Sc_0.34N Thin Film

Abstract

Ferroelectric materials are promising candidates for neuromorphic computing synaptic devices due to the nonvolatile multiplicity of spontaneous polarization. To ensure a sufficient memory window, ferroelectric materials with a large coercivity are urgently required for practical applications in highly scaled multi‐bit memory devices. Herein, a remarkable reliability of intermediate ferroelectric polarization states is demonstrated in a textured Al0.66Sc0.34N thin film with a coercive field of 2.4 MV cm−1. Al0.66Sc0.34N thin films are prepared at 300 °C on Pt (111)/Ti/SiO2/Si substrates using a radio frequency reactive sputtering method. Al0.66Sc0.34N thin films exhibit viable ferroelectricity with a large remanent polarization value of >100 µC cm−2. Through the conventional current–voltage characteristics, polarization switching kinetics, and temperature dependence of coercivity, the reproducibility of multiple polarization states with apparent accuracy is attributed to a small critical volume (3.7 × 10−28 m3) and a large activation energy (3.3 × 1027 eV m−3) for nucleation of the ferroelectric domain. This study demonstrates the potential of ferroelectric Al1‐xScxN for synaptic weight elements in neural network hardware.

Ferroelectric Al0.85Sc0.15N and Hf0.5Zr0.5O2 Domain Switching Dynamics

“…Among emerging memory technologies, ferroelectrics are an ideal candidate for realizing NN memory elements because of the intrinsic nonvolatile property of the polarization and the nanosecond programming potential with femtojoule energies per bit. ,,, The breakthrough discoveries of ferroelectricity in fluorite- and wurtzite-structured ferroelectrics open up opportunities for integrating ferroelectric functionalities with scaled logic transistors beyond the 130 nm technology node limit of perovskite-structured ferroelectrics. ,, The capability of ferroelectrics to achieve partial polarization states draws significant attention because this can allow the storage of multiple bits in a single memory element. ,− Multibit storage would result in higher crossbar integration density compared to SRAM, thus facilitating NN models with a large number of parameters at the edge where the chip area is limited. , …”

“…The field-driven configurations of ferroelectric domains and dynamics control the number of achievable partial polarization states and can affect data storage reliability as well as the speed of the state update. ,− Hence, a thorough understanding of the domain switching dynamics involved in the polarization reversal mechanism is required to achieve full control of the multibit capability and understand reliability performances, such as the retention of the intermediate polarization states. In ferroelectrics, polarization reversal relies on the complex interplay between domain nucleation and domain wall motion. ,− Several phenomenological theories have been developed to predict the time-dependent evolution of the switched polarization. − Nonetheless, phenomenological theories do not account explicitly for the correlation between domain dynamics and the crystal structure of the film.…”