2019 Fiscal Year Annual Research Report
Single-nanometer-scale graphene tunnel field effect transistors for ultra-low-power nano electronics
| Project/Area Number |
18F18365
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| Research Institution | Japan Advanced Institute of Science and Technology |
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Principal Investigator |
水田 博 北陸先端科学技術大学院大学, 先端科学技術研究科, 教授 (90372458)
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| Co-Investigator(Kenkyū-buntansha) |
HAMMAM AHMED 北陸先端科学技術大学院大学, 先端科学技術研究科, 外国人特別研究員
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| Project Period (FY) |
2018-11-09 – 2021-03-31
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| Keywords | グラフェン / トンネルトランジスタ / ナノイオンビーム / サブサーマルスイッチング |
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| Outline of Annual Research Achievements |
To fabricate a suspended sub-10 nm Graphene Nanoribbons (GNRs), we first fabricated sub-100 nm-wide GNRs width) using EBL-RIE technique. Motorized HF wet etching process followed by supercritical point drying was developed to remove a supporting SiO2 layer. The helium ion beam milling (HIBM) process was then conducted with ion beam current of 1 pA and dose of of 1.1E18 ions/cm2, and an extremely thin GNR of around 6 nm in width was fabricated successfully. Electrical characteristics were measured using a cryogenic probestation, as a function of temperature ranging from 4.2 K to room temperature. We observed for the 6-nm thin GNR device the nonlinear current-voltage characteristics at room temperature with transport gap opening, Eg, of approximately 0.41 eV. This is in clear contrast that a wide GNR device before HIBM showed linear characteristics with zero transport gap. Simulation was also conducted using ab initio simulation package ATK for different degree of edge roughness to understand the device characteristics, and the experimentally observed Eg variation was justified successfully.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
In order to investigate the physical mechanism behind the observed transport gap opening, multiple single-nanometer GNRs were fabricated and the temperature dependence of Eg was measured for those devices. A finite variation of Eg ranging from 160 to 800 meV was observed at room temperature. The ab-initio simulation was then conducted to evaluate the Eg for various possible edge structures (mixture of zig-zag and armchair edge structures), and the experimentally observed Eg variation was justified successfully. These in-depth analyses are beyond the original research plan.
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| Strategy for Future Research Activity |
The GNR-TFETs are fabricated by using single-nanometer suspended GNRs covered with h-BN, two local bottom gates and one top control gate, and ALD Al2O3 dielectric for encapsulation. On the same graphene, multiple GNR channels are fabricated in different directions which enables us to compare the impacts of various mixture of arm-chair and zigzag edge states. Temperature dependence of SS is measured, and the achieved bandgaps Eg are extracted and analyzed in comparison with the simulation results on the Eg - T dependence obtained for different edge states.EBL resist and CR chemicals are purchased. The ATK licenses fee for ab initio simulation and travelling costs are budgeted for the HIM experiment at AIST and conference trips to JSAP and SSDM.
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