Journal of Sensor Science and Technology (센서학회지)

The Korean Sensors Society (한국센서학회)
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Capacitive Touch Sensor Pixel Circuit with Single a-InGaZnO Thin Film Transistor

단일 a-InGaZnO 박막 트랜지스터를 이용한 정전용량 터치 화소 센서 회로

  • Kang, In Hye (School of Electronics & Display Engineering, Hoseo Unversity) ;
  • Hwang, Sang Ho (School of Electronics & Display Engineering, Hoseo Unversity) ;
  • Baek, Yeong Jo (School of Electronics & Display Engineering, Hoseo Unversity) ;
  • Moon, Seung Jae (School of Electronics & Display Engineering, Hoseo Unversity) ;
  • Bae, Byung Seong (School of Electronics & Display Engineering, Hoseo Unversity)
  • 강인혜 (호서대학교 전자디스플레이공학부) ;
  • 황상호 (호서대학교 전자디스플레이공학부) ;
  • 백영조 (호서대학교 전자디스플레이공학부) ;
  • 문승재 (호서대학교 전자디스플레이공학부) ;
  • 배병성 (호서대학교 전자디스플레이공학부)
  • Received : 2018.12.27
  • Accepted : 2019.03.29
  • Published : 2019.03.31
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Abstract

The a-InGaZnO (a-IGZO) thin film transistor (TFT) has the advantages of larger mobility than that of amorphous silicon TFTs, acceptable reliability and uniformity over a large area, and low process cost. A capacitive-type touch sensor was studied with an a-IGZO TFT that can be used on the front side of a display due to its transparency. A capacitive sensor detects changes of capacitance between the surface of the finger and the sensor electrode. The capacitance varies according to the distance between the sensor plate and the touching or non-touching of the sensing electrode. A capacitive touch sensor using only one a-IGZO TFT was developed with the reduction of two bus lines, which made it easy to reduce the pixel pitch. The proposed sensor circuit maintained the amplification performance, which was investigated for various drive conditions.

Keywords

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Fig. 1. Capacitive-type touch sensor ; (a) Mutual capacitance type, (b) Self-capacitance type [10].

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Fig. 2. Cross section of top gate a-IGZO TFT pixel sensor.

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Fig. 3. Transfer characteristics of a-IGZO TFT.

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Fig. 7. The measurement result of the proposed circuit.

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Fig. 9. Output characteristics according to the voltages of a readreset line.

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Fig. 10. Output characteristics according to the voltages of scan line and readreset line.

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Fig. 11. Output characteristics according to the pulse widths of scan and readreset line.

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Fig. 4. (a) Reference circuit for the capacitive touch sensor, (b) Proposed circuit for the capacitive touch sensor.

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Fig. 5. Simulation results; (a) the reference circuit, (b) the proposed circuit.

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Fig. 6. (a) Mask design, (b) Microscope image.

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Fig. 8. Output characteristics according to the voltages of a scan line.

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