【公開日：2025.06.10】【最終更新日：2025.05.13】

課題データ / Project Data

課題番号 / Project Issue Number

24UT0102

利用課題名 / Title

On-Silicon Memristors Based on Single-Crystalline Ferroelectric Thin Films

利用した実施機関 / Support Institute

東京大学 / Tokyo Univ.

機関外・機関内の利用 / External or Internal Use

内部利用（ARIM事業参画者以外）/Internal Use (by non ARIM members)

技術領域 / Technology Area

【横断技術領域 / Cross-Technology Area】（主 / Main）計測・分析/Advanced Characterization（副 / Sub）-

【重要技術領域 / Important Technology Area】（主 / Main）高度なデバイス機能の発現を可能とするマテリアル/Materials allowing high-level device functions to be performed（副 / Sub）次世代ナノスケールマテリアル/Next-generation nanoscale materials

キーワード / Keywords

単結晶薄膜,X線回折/ X-ray diffraction,エリプソメトリ/ Ellipsometry,エレクトロデバイス/ Electronic device

利用者と利用形態 / User and Support Type

利用者名（課題申請者）/ User Name (Project Applicant)

李 海寧

所属名 / Affiliation

東京大学大学院　工学系研究科　電気系工学専攻

共同利用者氏名 / Names of Collaborators in Other Institutes Than Hub and Spoke Institutes

片岡　莉咲,Lee Sangbin,Sarker Md Shamim

ARIM実施機関支援担当者 / Names of Collaborators in The Hub and Spoke Institutes

府川　和弘,飯盛　桂子

利用形態 / Support Type

（主 / Main）機器利用/Equipment Utilization（副 / Sub）,技術補助/Technical Assistance

利用した主な設備 / Equipment Used in This Project

UT-203：粉末X線回折装置
UT-202：高輝度In-plane型X線回折装置
UT-305：環境制御マニュアルプローバステーション

報告書データ / Report

概要（目的・用途・実施内容）/ Abstract (Aim, Use Applications and Contents)

A Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin film is fabricated on SrRuO₃(SRO)/Pt/ZrO₂/Si, and its resistive switching properties are thoroughly investigated. The ZrO₂ thin film serves as a buffer layer for the epitaxial growth of single-crystalline PZT thin films, and spin-coating fabrication is useful for introducing a suitable defect content to achieve effective resistive switching in PZT. The present PZT thin film exhibits improved ferroelectric properties compared with most of the spin-coated or sol-gel prepared PZT films reported previously, with a large saturation polarization of ~43 μC/cm² and coercive filed of ~700 kV/cm. The symmetrically reversed true-remanent hysteresis shows no evident imprint effect and a fully saturated polarization is observed. Intrinsic ferroelectric properties indicate the presence of non-switching components that are conducive to memory applications. Butterfly shaped electrical conduction reveals resistive switching behavior, with abnormal bipolar resistive switching (BRS) at low voltages and normal BRS at high voltages. The abnormal BRS is explained by a microscopic mechanism involving ferroelectric polarization and an induced dipole moment, whereas the normal BRS is studied by fitting different conducting models and is dominated by interfacial barriers and defects. This study presents a progressive strategy for the large-scale production of ferroelectric perovskite thin films, specifically suitable for silicon-based memristors.

実験 / Experimental

PbZr_0.52Ti_0.48O₃ (PZT 52/48) thin films were deposited on the SrRuO₃ (100)/Pt (100)/ZrO₂ (110)/Si (100) heterostructures by high-power radio frequency (RF) sputtering (Equipment No. KT-201). The structural characterizations were conducted using X-ray diffraction (XRD) 2θ/ω scans, φ scans and reciprocal space mapping (RSM) using a four-circle diffractometer with a Ge (220) 2-bounce monochromator (Equipment No. UT-202 and No. UT-203). The electrical characterization was performed using Pt top electrodes deposited by sputtering, with area sizes of 100 × 100 μm² or 200 × 200 μm². Ferroelectric polarization was investigated at room temperature using a ferroelectric property evaluation system FCE-10 (UT-305). The current-voltage (I-V) and capacitance-voltage (C-V) characteristics were measured using a Keithley 4200-SCS semiconductor analyzer (UT-305). For capacitance measurements, a slowly scanning direct current (DC) applied voltage in the range from –5 to +5 V and an alternate current (AC) with a signal amplitude of 30 mV and different frequencies from 10 kHz to 1 MHz were applied across the PZT thin film. For I-V measurements, the sweeping voltage was applied on the top Pt electrode at different maximum voltages but with a constant step 0.1 V from negative to positive and back again.

結果と考察 / Results and Discussion

We applied a strategy to integrate a common ferroelectric material Pb(Zr_0.52Ti_0.48)O₃ onto commercially available Si wafers by employing a ZrO₂ buffer layer. This study includes in-depth investigations of epitaxial growth, layer interfaces, intrinsic ferroelectric properties, abnormal and normal bipolar resistive switching, and the corresponding conduction mechanisms. The effect of the ZrO₂ buffer layer on achieving high quality epitaxial growth of PZT/SRO/Pt/ZrO₂ heterostructures on Si was systematically investigated using XRD, STEM, and SAED measurements. The cube-on-cube epitaxial growth of the PZT, Pt, and ZrO₂ thin films was also characterized as non-rotated. The chemical sharp interfaces within the PZT/SRO/Pt/ZrO₂/Si heterostructures were verified through cross-sectional STEM images and STEM-EDX scanning, where the disordered lattices of ZrO₂ were evidence of narrowing the lattice mismatch. Our measurements on the Pt/PZT/SRO capacitor showed excellent ferroelectric polarization in spin coated PZT thin film at room temperature, with a large coercive filed E_c ≈ 700 kV/cm, which much surpasses that of the PZT thin film grown under identical conditions on the Nb: STO substrate. The true-remanent hysteresis measurement exhibited a symmetrical reversal and well-saturated polarization of ~18 μC/cm², and it also indicated the non-switching components, a necessary feature with potential applications to memory devices. The spin-coated PZT thin film in this study showed improved ferroelectric properties compared to most PZT films prepared by spin-coating or sol-gel methods up to the present. The butterfly shaped electrical conduction exhibited resistive switching behavior, and a microscopic mechanism for the abnormal BRS in the low-voltage region was proposed by combining the ferroelectricity and induced dipole moment. The electron transport properties were studied by fitting the conducting models to various voltage regions, that is, Schottky emission, Schottky lowering effect, and SCLC. This study provides a protocol for the mass production of ferroelectric PZT thin films with symmetrical polarization and resistive switching for use in silicon-based memristor devices.

図・表・数式 / Figures, Tables and Equations

その他・特記事項（参考文献・謝辞等） / Remarks(References and Acknowledgements)

Acknowledgements
This research was supported by the Institute for AI and Beyond of The University of Tokyo, JST, CREST Grant Number JPMJCR22O2, Japan AMED under Grant Number JP22zf0127006, and JSPS KAKENHI Grant Number JP20H05651, JP22K18804, JP23H04099, JP22H01952, JP23KJ0418, and JP23K23220. We are grateful to the Takeda Building and Advanced Research Infrastructure for Materials and Nanotechnology in Japan (ARIM) for access to XRD Smartlab 3 kW and 9 kW and ferroelectric property evaluation system FCE-10 at The University of Tokyo. The authors would also like to express their deep appreciation to Mr. Kazuhiro Fukawa and Ms. Keiko Isagai for their invaluable assistance with XRD.

成果発表・成果利用 / Publication and Patents

論文・プロシーディング（DOIのあるもの） / DOI (Publication and Proceedings)

1. Haining Li, Epitaxial Single‐Crystalline PZT Thin Films on ZrO₂‐Buffered Si Wafers Fabricated Using Spin‐Coating for Mass‐Produced Memristor Devices, Advanced Electronic Materials, 11, (2024).
   DOI: https://doi.org/10.1002/aelm.202400280
   

口頭発表、ポスター発表および、その他の論文 / Oral Presentations etc.

1. Haining Li, T. Kijima, R. Kataoka, H. Yamahara, H. Tabata, M. Seki, “Single-Crystalline PbTiO3-Based Ferroelectric Memristors for Synaptic Plasticity Emulation”, The 85th Japan Society of Applied Physics (JSAP) Autumn Meeting, Niigata, 2024.09.
2. R. Kataoka, Haining Li, T. Kijima, H. Yamahara, H. Tabata, M. Seki, “Fabrication of Ferroelectric Thin Films Using (Hf, Zr)O2 Buffer Layers and Spin-Coating Technique”, The 85th JSAP Autumn Meeting, Niigata, 2024.09.
3. Md S. Sarker, Haining Li, EMK I. Ahamed, H. Yamahara, S. Tang, Z. Liao, T. Iizuka, M. Seki, H. Tabata, “Investigating the Origin of Cluster Spin Glass Behavior in Low Damped Garnet Based Ferrimagnet Towards Neuromorphic Computing”, The 85th JSAP Autumn Meeting, Niigata, 2024.09

特許 / Patents

特許出願件数 / Number of Patent Applications：0件
特許登録件数 / Number of Registered Patents：0件