Field-effect transistor having a semiconductor layer made of an organic compound

• US 5,705,826 A
• Filed: 06/27/1995
• Issued: 01/06/1998
• Est. Priority Date: 06/28/1994
• Status: Expired due to Term

• Current Assignee: Panasonic Liquid Crystal Display Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Hitachi, Ltd.
• Inventors: Aratani, Sukekazu, Kondo, Katsumi, Ohara, Shuichi
• Primary Examiner(s): TRAN, MINH LOAN
• Application Number:
  US08/495,700
• Time in Patent Office: 924 Days
• Field of Search: 257/40, 257/347, 257/642, 257/59, 257/72, 359/59
• US Class Current: 257/40
• CPC Class Codes: H10K 10/46 Field-effect transistors, e.g. organic thin-film transistors [OTFT] H10K10/43 takes precedence
• CPC Class Codes: H10K 10/464 Lateral top-gate IGFETs comprising only a single gate
• CPC Class Codes: H10K 10/466 Lateral bottom-gate IGFETs comprising only a single gate
• CPC Class Codes: H10K 10/468 characterised by the gate dielectrics
• CPC Class Codes: H10K 85/111 comprising aromatic, heteroaromatic, or aryl chains, e.g. polyaniline, polyphenylene or polyphenylene vinylene
• CPC Class Codes: H10K 85/113 Heteroaromatic compounds comprising sulfur or selene, e.g. polythiophene
• CPC Class Codes: H10K 85/114 Poly-phenylenevinylene; Derivatives thereof

Abstract

A field-effect transistor using a conjugated oligomer having an ionization potential of 4.8 eV or above in the semiconductor layer thereof works stably and has a long life-time and can be used in a liquid crystal display device as a switching element to give excellent contrast and good performances.

Claims

1. A field-effect transistor having a semiconductor layer, wherein the semiconductor layer includes a conjugated oligomer having an ionization potential of at least 4.8 eV.

2. A field-effect transistor according to claim 1, wherein said semiconductor layer has a hole mobility of at least 0.2 cm² /Vs.

3. A field-effect transistor according to claim 1, wherein said conjugated oligomer has 9 to 12 recurring units.

4. A process for operating a liquid crystal display device, the liquid crystal display device including a switching element, the process including the steps of turning the switching element off and on, the switching element being constituted by the field-effect transistor according to claim 1.

5. A field-effect transistor according to claim 1, wherein the conjugated oligomer has an ionization potential in a range of 4.8-6.0 eV.

6. A field-effect transistor according to claim 5, wherein the conjugated oligomer has a hole mobility in a range of 0.2-10 cm² /Vs.

10. A field-effect transistor according to any one of claim 1 to 9, wherein said semiconductor layer is provided overlying a plastic substrate.

11. A liquid crystal display device having a switching element, wherein the switching element is constituted by the field-effect transistor according to claim 10.

13. A liquid crystal display device having a switching element, wherein the switching element is constituted by the field-effect transistor according to any one of claims 1 to 9.

14. A field-effect transistor according to any one of claims 1 to 9, wherein said semiconductor layer is provided overlying an insulating substrate.

15. A field-effect transistor according to claim 14, further comprising source and drain electrodes, spaced apart from each other, each contacting the semiconductor layer, and a gate electrode adjacent a portion of the semiconductor layer between the source and drain electrodes.

16. A field-effect transistor according to claim 15, wherein the gate electrode is adjacent said portion of the semiconductor layer, with a gate insulating film provided between the gate electrode and said portion of the semiconductor layer.

17. A field-effect transistor according to any one of claims 1 to 9, further comprising source and drain electrodes, spaced apart from each other, each contacting the semiconductor layer, and a gate electrode adjacent a portion of the semiconductor layer between the source and drain electrodes.

18. A liquid crystal display device, comprising:

a pair of substrates;

a liquid crystal layer interposed between said pair of substrates; and

a plurality of field-effect transistors provided on one of said pair of substrates and being switching elements of the liquid crystal display device, wherein each of the plurality of field-effect transistors is constituted by the field-effect transistor according to any one of claims 1 to 6.

7. A field-effect transistor having a semiconductor layer, wherein the semiconductor layer includes a conjugated oligomer having an ionization potential of at least 4.8 eV and represented by the following formula:

##STR12## wherein X represents S, Se or Te;

n is an integer of 6 to 12; and

R₁ and R₂ each independently represents a hydrogen atom or a substituent group, provided that, when X represents S, R₁ and R₂ cannot both be hydrogen atoms, and R₁ and R₂ cannot both be methyl groups, and R₁ and R₂ cannot both be ethyl groups.

12. A liquid crystal display device, comprising:

a pair of substrates;

a liquid crystal layer interposed between said pair of substrates; and

a plurality of field-effect transistors provided on one of said pair of substrates and being switching elements of the liquid crystal display device, wherein each of the plurality of field-effect transistors is constituted by the field-effect transistor according to claim 7.

8. A field-effect transistor having a semiconductor layer, wherein the semiconductor layer includes a conjugated oligomer having an ionization potential of at least 4.8 eV and represented by the following formula:

##STR13## wherein n is an integer of 6 to 12;

R₃ is a hydrogen atom, a halogen atom, a cyano group, a nitro group, an unsubstituted or substituted ester group, an unsubstituted or substituted acyl group, an unsubstituted or substituted alkyl group, an unsubstituted or substituted alkoxy group, an unsubstituted or substituted alkylthio group, an unsubstituted or substituted allyl group, or an unsubstituted or substituted alkenyl group; and

R₄ is a halogen atom, a cyano group, a nitro group, an unsubstituted or substituted ester group, an unsubstituted or substituted acyl group, an alkyl group substituted with one or more electron attractive groups, an alkoxy group substituted with one or more electron attractive groups, an alkylthio group substituted with one or more electron attractive groups, an aryl group substituted with one or more electron attractive groups, or an alkenyl group substituted with one or more electron attractive groups.

9. A field-effect transistor having a semiconductor layer, wherein the semiconductor layer includes a conjugated oligomer having an ionization potential of at least 4.8 eV and represented by the following formula:

##STR14## wherein n is an integer of 6 to 12; and

R₅ and R₆ are independently a hydrogen atom, a halogen atom, a cyano group, a nitro group, an unsubstituted or substituted ester group, an unsubstituted or substituted acyl group, an unsubstituted or substituted alkyl group, an unsubstituted or substituted alkoxy group, an unsubstituted or substituted alkylthio group, an unsubstituted or substituted allyl group, or an unsubstituted or substituted alkenyl group.