Junctionless Poly-GeSn Ferroelectric Thin-Film Transistors with Improved Reliability by Interface Engineering for Neuromorphic Computing

Abstract

Ferroelectric HfZrO x (Fe-HZO) with a larger remnant polarization (P r) is achieved by using a poly-GeSn film as a channel material as compared with a poly-Ge film because of the lower thermal expansion that induces higher stress. Then two-stage interface engineering of junctionless poly-GeSn (Sn of ∼5.1%) ferroelectric thin-film transistors (Fe-TFTs) based on HZO was employed to improve the reliability characteristics. With stage I of NH3 plasma treatment on poly-GeSn and subsequent stage II of Ta2O5 interfacial layer growth, the interfacial quality between Fe-HZO and the poly-GeSn channel is greatly improved, which in turn enhances the reliability performance in terms of negligible P r degradation up to 106 cycles (±2.7 MV/1 ms) and 96% P r after a 10 year retention at 85 °C. Furthermore, to emulate the synapse plasticity of the human brain for neuromorphic computing, besides manifesting the capability of short-term plasticity, the devices also exhibit long-term plasticity with the characteristics of analog conductance (G) states of 80 levels (>6 bit), small linearity for potentiation and depression of −0.83 and 0.62, high symmetry, and moderate G max/G min of 9.6. By employing deep neural network, the neuromorphic system with poly-GeSn Fe-TFT synaptic devices achieves 91.4% pattern recognition accuracy. In addition, the learning algorithm of spike-timing-dependent plasticity based on spiking neural network is demonstrated as well. The results are promising for on-chip training, making it possible to implement neuromorphic computing by monolithic 3D ICs based on poly-GeSn Fe-TFTs.

Emerging Materials for Neuromorphic Devices and Systems

“…The transistor showed linear weight update characteristics with 64 states and dynamic range of 14.4. A HfZrO x -based ferroelectric transistor with a poly-GeSn channel was also proposed as a synaptic transistor ( Figure 5 E) ( Chou et al., 2020 ). In this device, NH 3 plasma treatment of poly-GeSn and the interfacial layer was used to improve the endurance and retention characteristics.…”

“… (F and G) (F) Potentiation and (G) depression characteristics of devices using HfZrO x . Reproduced with permission ( Chou et al, 2020 ). Copyright 2020, American Chemical Society.…”

“…Two-terminal devices such as memristors, ferroelectric tunnel junctions (FTJs), and phase change memories (PCMs) have been researched as artificial synapses ( Jang et al., 2019a ; Li et al., 2020a ; Kuzum et al., 2012a ). Also, three-terminal devices including electrochemical transistors, ferroelectric transistors, and charge-trapping transistors have been researched as artificial synapses ( Nikam et al., 2019 ; Chou et al., 2020 ; Kim et al., 2020a ). Neural networks require emulation of the function of neurons; these functions have been achieved using memristors, PCMs, threshold switching devices, and ferroelectric transistors ( Hua et al., 2019 ; Tuma et al., 2016 ; Mulaosmanovic et al., 2018a ).…”

Bio‐Inspired Photoelectric Artificial Synapse based on Two‐Dimensional Ti3C2Tx MXenes Floating Gate

“…One of the leading directions is utilizing the brain‐inspired parallel computing systems based on artificial synapses, i.e., artificial neural systems. [ 1,6–11 ] Just like the information transmission between the two neurons in the biological neural network, the artificial synapse provides an effective approach for data‐processing depends on biomimetic synaptic processes, which could realize a specific logic function through one individual component. [ 1,12–14 ] Through transforming presynaptic stimuli into postsynaptic responses, an artificial synaptic device could mimic the perception, learning, and memory functions of synapses in the human brain.…”

Interface Modification in Three‐Terminal Organic Memory and Synaptic Device

“…Recently, Chou et al. [ 142 ] studied the three‐terminal ferroelectric memory device and adopted it in synaptic applications based on the ferroelectric material of HfZrO x (Fe‐HZO) and the semiconductor material of poly‐GeSn. First, the interface between Fe‐HZO and poly‐GeSn was treated by NH 3 plasma and was improved since the dangling bonds and trap states coming from the N/H radicals were passivated.…”