【公開日：2023.07.28】【最終更新日：2023.05.17】
課題データ / Project Data
課題番号 / Project Issue Number
22BA0041
利用課題名 / Title
イオン輸送を利用して動作するメモリスタ素子の電気特性評価
利用した実施機関 / Support Institute
筑波大学
機関外・機関内の利用 / External or Internal Use
外部利用/External Use
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）-
キーワード / Keywords
Memristor, Synapse, Neuromorphic
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)
NUR Roda Omar
所属名 / Affiliation
物質・材料研究機構
共同利用者氏名 / Names of Collaborators in Other Institutes Than Hub and Spoke Institutes
ARIM実施機関支援担当者 / Names of Collaborators in The Hub and Spoke Institutes
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
報告書データ / Report
概要（目的・用途・実施内容）/ Abstract (Aim, Use Applications and Contents)
This study explored the development of forming-free crossbar array memristors for neuromorphic applications. The resistive switching layer consists of a bilayer structure using ZnO (semiconductor) and HfO2 (insulator). An evaluation of the impacts of metal contacts on the resistive switching behavior was explored. A [4x4] crossbar array was fabricated with 100% yield and its synaptic behavior of long-term potentiation and depression was also evaluated.
実験 / Experimental
Silicon substrate was cleaned with Acetone and IPA using a sonicator. TiN bottom electrode was deposited by DC sputtering (i-Miller CFS-4EP-LL) using a Ti target with Nitrogen gas flow. The resistive switching layer was deposited by RF sputtering of 6nm of ZnO from ZnO target and followed by 4 nm of HfO2 using HfO2 target using O2 and Ar gas flow. Photolithography [Heidelberg DWL66+] process was used to pattern the top electrode. The top electrode was deposited using e-beam evaporation (R-DEC ADS-E86) with Pt and Ti/Pt thin films. Liftoff was done followed by IPA cleaning.
結果と考察 / Results and Discussion
Modern computing systems are based on the Von Neumann architecture where the computing/logic is physically separated from the memory which results in limited processing speeds. Developing neuromorphic computing systems involves developing a new architecture based off the human brain. A Neuromorphic computing system offers advantages such as low power consumption, complex and parallel processing. Memristor devices are two terminal memory devices based on resistive switching. They have been previously demonstrated to mimic synaptic behaviors and are considered to be a promising device for acting as a synapse in a neuromorphic architecture. Traditional memristor devices display digital switching where an abrupt set (low resistance state [LRS]) and reset (high resistance state [HRS]) is observed. For neuromorphic applications, analog switching behavior of gradual conductance modulation is preferred since it mimics neuron’s synaptic plasticity.The device structure and image of the crossbar array can be seen in Fig 1. To switch between digital and analog resistive switching, different top electrodes on HfO2 was evaluated. Fig 2 shows the hysteresis characteristics of the digital memristor (Pt) and the analog memristor (Ti-Pt). A gradual high resistance state modulation was achieved by inserting an interlayer of Ti that functions as an oxygen getter. Fig 3 shows a comparison between the digital and analog memristor during a set (high resistance state to low resistance state switching) and reset (low resistance state to high resistance state switching). A 4x4 crossbar was fabricated with device cell sizes of 2μm x 2μm. All 16 devices worked with 100% yield and showed forming-free switching behavior.To test the synaptic plasticity of the analog memristor, the long-term potentiation (LTP) and long-term depression (LTD) was measured in Fig 4. A constant amplitude pulse train consisting of write pulses (LTP using positive voltages and LTD using negative voltages) was applied. This device showed conductance modulation which demonstrates synaptic capability.
図・表・数式 / Figures, Tables and Equations
Fig 1. Device structure and image of crossbar array
Fig 2. (a)Pt top electrode hysteresis characteristics(b) Ti-Pt top electrode hysteresis characteristics
Fig 3. Digital and Analog resistive switching characteristic
Fig 4. Synaptic Plasticity LTP/LTD
その他・特記事項（参考文献・謝辞等） / Remarks(References and Acknowledgements)
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)
口頭発表、ポスター発表および、その他の論文 / Oral Presentations etc.
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