Gate-Stack Engineered IGZO-based Multi-bit OTP FeTFT with Lifelong Retention for Inference Engine Applications

This paper reports back-end-of-line (BEoL) compatible indium gallium zinc oxide (IGZO) based multibit one-time programmable (OTP) ferroelectric thin-film transistors (FeTFT) with lifelong retention capability. The maximum temperature of the entire fabrication process was limited to 350oC. The gate-stack engineering by varying the thickness ratio of hafnium zirconium oxide (HZO) and IGZO layer fomented data-retention capability over ten years and OTP property. Further, we have evaluated the performance of IGZO-based OTP FeTFT as synaptic devices for an inference engine. The system-level simulation revealed inference accuracy loss of only 1.5% after ten years without re-training for Modified National Institute of Standards and Technology (MNIST) hand-written digits in a multi-layer perceptron (MLP) neural network with a baseline of 97%. The proposed inference engine also showed superior energy efficiency and cell area of 95.33 TOPS/W (binary) and 8F2, respectively.