| 研究課題/領域番号 |
21K04822
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| 研究機関 | 国立研究開発法人産業技術総合研究所 |
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研究代表者 |
Aurelie Spiesser 国立研究開発法人産業技術総合研究所, エレクトロニクス・製造領域, 主任研究員 (90793513)
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| 研究期間 (年度) |
2021-04-01 – 2024-03-31
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| キーワード | Si spintronics / Spin transport / Magnetic tunnel contacts / Thin channel |
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| 研究実績の概要 |
The first step of this project was to characterize the charge transport properties of the thin Si channels obtained commercially. These Si channels have been grown by Chemical Vapor Deposition (CVD) on undoped Si substrates. Phosphorous dopants have been introduced during the CVD growth process with a designed doping concentration of ~ 1 x 10^19 cm-3. We performed Hall and van der Paw measurements on bare substrates (having a square shape and using In contacts). We found that the doping concentration decreases and the resistivity increases as the channel thickness is reduced from 70 to 15 nm.
Subsequently, we deposited magnetic tunnel contact (Fe/MgO) on Si channels using molecular beam epitaxy and monitored the growth of the tunnel barrier and magnetic contacts in-situ using RHEED technique. RHEED patterns indicated epitaxial growth of the magnetic tunnel contact. We then fabricated spin transport devices to study the effect of the reduction of the channel thickness on the magnitude of the spin signals. Unfortunately, the spin signals observed in all the grown samples were very small. Therefore, we could not demonstrate large spin signals in Si channel with reduced channel thicknesses.
We investigated the origin of the small spin signals in these samples and concluded that the etching process during microfabrication was not done appropriately. A new series of samples is currently being grown and device fabrication will follow. We hope to observe large spin signals in these devices with an enhancement of the spin signal as the Si channel thickness is reduced.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
3: やや遅れている
理由
As explained before, we could not observe large spin signals in the thin Si channels because the microfabrication process (specifically the etching process to define the magnetic tunnel contact) was not done appropriately. This step is critical to obtain spin transport devices. Therefore, we designed a new mask that allows us to test whether the etching process is done correctly, before continuing the rest of the microfabrication process. The design and test of the new mask has been done and works as expected. A new series of samples is currently being grown and device fabrication using this new mask will follow.
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| 今後の研究の推進方策 |
From now on, we will fabricate spin transport devices using the new mask (with tests devices for the etching process). We will then perform magneto-transport measurements to study spin transport in these devices having different channel thicknesses. Specifically, we will carry out spin-valve and Hanle measurements in the nonlocal configuration at various temperatures and bias current. The aim is to demonstrate an increase of the spin signal as the channel thickness decreases.
In parallel, we purchased BaO source material and will investigate the epitaxial growth of BaO on Si grown by molecular beam epitaxy. Structural characterization such as RHEED and TEM will be performed to demonstrate epitaxial growth. Then we will use BaO as a tunnel barrier and fabricate spin transport devices with Fe/BaO magnetic tunnel contacts. BaO is better lattice-matched to Si than MgO so we expect that larger spin signals can be achieved in such devices. We will compare the results with that of a conventional device with Fe/MgO tunnel barrier and study the contact resistance area (RA) product vs the tunnel barrier thickness. The goal is to obtain large spin signals and low contact RA in spin transport device with BaO tunnel barrier.
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| 次年度使用額が生じた理由 |
For FY2022, I need to purchase liquid N2 and He for MBE growth and magneto-transport measurements (PPPMS), respectively. Total cost is ~ 100,000 yen. I also need to design a new mask for 2-terminal devices (~ 200,000 yen) and do transmission electron microscope analysis of the samples with BaO tunnel barrier (~200,000 yen per sample). I also plan to buy a new camera to take RHEED pictures during the MBE growth (cost~ 50,000 yen) and replace the computer of the PPMS measurement system (~50,000 yen).
Finally, I intent to attend several international conference (ICMFS in July in Okinawa) and MMM 2022 in Minneapolis in October. This will cost ~ 500,000 yen.
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