PZT Ferroelectric Synapse TFT With Multi-Level of Conductance State for Neuromorphic Applications

Dongsu Kim,Goeun Pyo,Hong Soo Choi,Su Jin Heo,Hyuk-Jun Kwon,Jae Eun Jang

doi:10.1109/access.2021.3119607

Abstract

To fundamentally solve the bottleneck of Von Neumann’s computing architecture, a neuromorphic thin-film transistor (NTFT) employing Pb(Zr, Ti)O3 (PZT) was investigated. The indium gallium zinc oxide (IGZO) channel back gate TFT structure was chosen to solve the diffusion of atoms that form a channel layer during the annealing process for crystallization of PZT. A post-deposition process with IGZO after annealing PZT and using an oxide-based material as a channel structure can minimize the diffusion phenomenon of junction materials and oxygen together, which leads to a high and reliable performance of the NTFT. The basic operations of synapses short-term memory (STM) and long-term memory (LTM) were also analyzed to confirm the application of a neuromorphic device. The high dielectric constant and polarization properties of Pb(Zr, Ti)O3 (PZT) allow the power consumption of spike signals used in spike dependent plasticity change to be reduced to 10 pJ. Moreover, a wide dynamic range of $\text{G}_{\mathrm {max}}/\text{G}_{\mathrm {min}} \cong ~1000$ was obtained, and the channel conductance was maintained over 40000 seconds. The optimized pulse achieved multi-level states (>32), which made the learning process efficient. This study verified that the PZT-TFT structure has a high potential and merits for neuromorphic devices.

Highlights

Despite advances in semiconductor devices, when processing big data, the limitation of the bus unit between the memory device and the processing device creates a bottleneck in the Von-Neumann computing architecture
Our study demonstrated that the incremental voltage scheme allowed for a gradual transition of more ferroelectric polarization domain regions, ensuring a wide range of residual polarization states
The manufactured FeFET synaptic device exhibited more than 32 analog states and modulated conductance values using a variable amplitude pulse method with 300ms pulse width over a wide dynamic range of Gmax / Gmin = 1000

Summary

INTRODUCTION

Despite advances in semiconductor devices, when processing big data, the limitation of the bus unit between the memory device and the processing device creates a bottleneck in the Von-Neumann computing architecture. The twoterminal design has some merits, namely high integration density and easy fabrication This structure has difficulty in maintaining reliable operation and uniformity at a large scale. Strontium bismuth tantalate (SBT) and polyvinylidene fluoride (PVDF) show a low residual polarization value and low coercive force value, which are disadvantageous for low power operation [8,9] To solve this problem, hafnium-based ferroelectric materials have recently been studied. Hafnium-based ferroelectric materials have recently been studied Because such materials have relatively low polarizability, they require a very thin film layer to get enough capacitance, which induces a very severe fabrication process margin and a leakage current pathway by a tunneling mechanism. With the optimized process conditions of the PZTIGZO TFT structure, it was possible to learn and process the program efficiently by implementing multiple levels based on a wide weight range

EXPERIMENTAL

RESULTS AND DISCUSSION

CONCLUSION