2004 Fiscal Year Final Research Report Summary
Organic Semiconductor Memory using Electronic Function of Photochromic Molecules
| Project/Area Number |
15350111
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Functional materials/Devices
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| Research Institution | Osaka Kyoiku University |
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Principal Investigator |
TSUJIOKA Tsuyoshi Osaka Kyoiku University, Department of Education, Professor, 教育学部, 教授 (30346225)
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| Co-Investigator(Kenkyū-buntansha) |
TANI Keita Osaka Kyoiku University, Department of Education, Associate Professor, 教育学部, 助教授 (60207165)
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| Project Period (FY) |
2003 – 2004
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| Keywords | Photochromic / Memory / Organic Semiconductor / Electronic Function / Carrier / Isomerization / Deposition selectivity |
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| Research Abstract |
Photochromic diarylethenes are well known materials which have thermal stability for both isomerization state and a fatigue resistance. In this study a novel principle of organic memory device using a photochromic molecule was studied. Such a memory device is based on a reversible isomerization reaction of a photochromic bistable molecule by an electric carrier injection. This is achieved by a carrier (hole and electron) encounter excitation of the molecule of a diarylethene derivative. The electron on lowest unoccupied molecular orbital level and the hole on highest occupied molecular orbital level of the molecule produce the excited state identical to that produced by photo excitation, so the molecule is transformed into another isomerization form. For the case of diarylethene derivatives, the ionization potential Ip of the molecule is changed according to its isomerization form. The closed-ring form (colored form) has Ip of 5.7 eV and the open-ring form (uncolored form) has above 6.2eV. The information readout is achieved by detecting the electric current through the molecule affected by the difference of Ip.
A new nonsymmetrical bipolar diarylethene with a triphenylamine group and an oxadiazole group, which exhibited electron donor and acceptor characteristics, respectively, were designed. The thin film sample was used in the experiment to confirm the "writing" and "reading" principles. The memory device was consisted of an anode, a hole injection layer, a hole transport layer, a photochromic layer and cathode. Reversible electric current decrease was observed and, therefore, the isomerization reaction by carrier injection was successfully demonstrated.
For the memory devices with an electron transport layer the information writing speed was considerably improved. This was attributed the effective electron injection and transport from the cathode. Development of the bipolar diarylethene derivative is required to achieve higher speed memory devices.
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