J. Semicond. > 2013, Volume 34 > Issue 1 > 015009
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SEMICONDUCTOR INTEGRATED CIRCUITS

A new LTPS TFT AC pixel circuit for an AMOLED

Yongwen Zhang and Wenbin Chen

+ Author Affiliations

 Corresponding author: Chen Wenbin, chenwb@uestc.edu.cn

DOI: 10.1088/1674-4926/34/1/015009

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Abstract: This work presents a new voltage programmed pixel circuit for an active-matrix organic light-emitting diode (AMOLED) display. The proposed pixel circuit consists of six low temperature polycrystalline silicon thin-film transistors (LTPS TFTs), one storage capacitor, and one OLED, and is verified by simulation work using HSPICE software. Besides effectively compensating for the threshold voltage variation of the driving TFT and OLED, the proposed pixel circuit offers an AC driving mode for the OLED, which can suppress the degradation of the OLED. Moreover, a high contrast ratio can be achieved by the proposed pixel circuit since the OLED does not emit any light except for the emission period.

Key words: low temperature polycrystalline silicon thin-film transistors, active-matrix OLED, pixel circuit, SPICE simulation, uniformity



[1]
Meng Z G, Kwok H, Wu C Y, et al. Fabrication of a 125 mm poly-Si TFT active-matrix driving color AMOLED. Chinese Journal of Semiconductors, 2006, 27(8):1514 https://www.ncbi.nlm.nih.gov/pubmed/18069874
[2]
Liu X Q, Zhang T, Wang L J, et al. A testing method on a thin film transistor array for active matrix organic emitting diode. Chinese Journal of Semiconductors, 2007, 28(7):1161 http://www.sciencedirect.com/science/article/pii/S1369702104003980
[3]
Nathan A, Chaji G R, Ashtiani S J. Driving schemes for a-Si and LTPS AMOLED displays. IEEE J Display Technol, 2005, 1(2):267 doi: 10.1109/JDT.2005.858913
[4]
Wu W J, Zhou L, Yao R H, et al. A new voltage-programmed pixel circuit for enhancing the uniformity of AMOLED displays. IEEE Electron Device Lett, 2011, 32(7):931 doi: 10.1109/LED.2011.2148152
[5]
Lee J H, Kim J H, Han M K. A new a-Si:H TFT pixel circuit compensating the threshold voltage shift of a-Si:H TFT and OLED for active matrix OLED. IEEE Electron Device Lett, 2005, 26(12):897 doi: 10.1109/LED.2005.859674
[6]
Popovic Z D, Aziz H. Reliability and degradation of small moleculebased organic light-emitting devices (OLEDs). IEEE J Sel Topics Quantum Electron, 2002, 8(2):362 doi: 10.1109/2944.999191
[7]
Lin Y C, Shieh H P D. Improvement of brightness uniformity by AC driving scheme for AMOLED display. IEEE Electron Device Lett, 2004, 25(11):728 doi: 10.1109/LED.2004.837535
[8]
Goh J C, Jang J, Cho K S, et al. A new a-Si:H thin-film transistor pixel circuit for active-matrix organic light-emitting diodes. IEEE Electron Device Lett, 2003, 24(9):583 doi: 10.1109/LED.2003.816590
[9]
Lin C L, Chen Y C. A novel LTPS-TFT pixel circuit compensat-ing for TFT threshold-voltage shift and OLED degradation for AMOLED. IEEE Electron Device Lett, 2007, 28(2):129 doi: 10.1109/LED.2006.889523
[10]
Jung S H, Nam W J, Han M K. A new voltage-modulated AMOLED pixel design compensating for threshold voltage variation in poly-Si TFTs. IEEE Electron Device Lett, 2004, 25(10):690 doi: 10.1109/LED.2004.836028
[11]
Lin C L, Tsai T T. A novel voltage driving method using 3-TFT pixel circuit for AMOLED. IEEE Electron Device Lett, 2007, 28(6):489 doi: 10.1109/LED.2007.896895
[12]
Lee J H, Nam W J, Jung S H, et al. A new current scaling pixel circuit for AMOLED. IEEE Electron Device Lett, 2004, 25(5):280 doi: 10.1109/LED.2004.826567
[13]
Si Y J, Xu Y L, Lang L Q, et al. A new AC driving method for a current-programmed AM-OLED pixel circuit. Chinese Journal of Semiconductors, 2006, 27(9):1562 doi: 10.1889/1.2036281/abstract
[14]
Shur M S, Slade H C, Jacunski M D, et al. SPICE models for amorphous silicon and polysilicon thin film transistors. J Electrochem Soc, 1997, 144(8):2833 doi: 10.1149/1.1837903
[15]
Chen C W, Lin C L, Wu C C. An effective cathode structure for inverted top-emitting organic light-emitting devices. Appl Phys Lett, 2004, 85(13):2469 doi: 10.1063/1.1798392
Fig. 1.  Proposed circuit schematic and control signal timing diagram. (1) Presetting period. (2) Compensation period. (3) Emission period.

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Fig. 2.  OLED model current-voltage characteristics and the experimentally measured results of the inverted top-emitting OLED structure[15] used in this study.

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Fig. 3.  (a) An example of the layout design for the proposed pixel circuit. (b) The equivalent scheme of the proposed pixel circuit for SPICE simulation.

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Fig. 4.  Transient simulation results for the proposed pixel circuit (Δ$V_{\rm data}$ $=$ 4 V, Δ$V_{\rm TH-TFT}$ $=$ 0 V, and Δ$V_{\rm TH-OLED}$ $=$ 0 V).

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Fig. 5.  Voltage stored in $C_{\rm s}$ in the emission period versus Δ$V_{\rm data}$ at different threshold voltage variations of the driving TFT and OLED (Δ$V_{\rm TH-TFT}$ $=$ $\pm$0.3 and 0 V; Δ$V_{\rm TH-OLED}$ $=$ 0 and $+0.3$ V).

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Fig. 6.  Transfer characteristics of the proposed pixel circuit at different threshold voltage variations (Δ$V_{\rm TH-TFT}$ $=$ $\pm$0.3 and 0 V; Δ$V_{\rm TH-OLED}$ $=$ 0 and $+0.3$ V).

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Fig. 7.  Non-uniformity of the OLED current versus the average current in the proposed 6T1C pixel circuit compared with that in the conventional uncompensated 2T1C pixel circuit.

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Table 1.   Values of circuit parameters.
[1]
Meng Z G, Kwok H, Wu C Y, et al. Fabrication of a 125 mm poly-Si TFT active-matrix driving color AMOLED. Chinese Journal of Semiconductors, 2006, 27(8):1514 https://www.ncbi.nlm.nih.gov/pubmed/18069874
[2]
Liu X Q, Zhang T, Wang L J, et al. A testing method on a thin film transistor array for active matrix organic emitting diode. Chinese Journal of Semiconductors, 2007, 28(7):1161 http://www.sciencedirect.com/science/article/pii/S1369702104003980
[3]
Nathan A, Chaji G R, Ashtiani S J. Driving schemes for a-Si and LTPS AMOLED displays. IEEE J Display Technol, 2005, 1(2):267 doi: 10.1109/JDT.2005.858913
[4]
Wu W J, Zhou L, Yao R H, et al. A new voltage-programmed pixel circuit for enhancing the uniformity of AMOLED displays. IEEE Electron Device Lett, 2011, 32(7):931 doi: 10.1109/LED.2011.2148152
[5]
Lee J H, Kim J H, Han M K. A new a-Si:H TFT pixel circuit compensating the threshold voltage shift of a-Si:H TFT and OLED for active matrix OLED. IEEE Electron Device Lett, 2005, 26(12):897 doi: 10.1109/LED.2005.859674
[6]
Popovic Z D, Aziz H. Reliability and degradation of small moleculebased organic light-emitting devices (OLEDs). IEEE J Sel Topics Quantum Electron, 2002, 8(2):362 doi: 10.1109/2944.999191
[7]
Lin Y C, Shieh H P D. Improvement of brightness uniformity by AC driving scheme for AMOLED display. IEEE Electron Device Lett, 2004, 25(11):728 doi: 10.1109/LED.2004.837535
[8]
Goh J C, Jang J, Cho K S, et al. A new a-Si:H thin-film transistor pixel circuit for active-matrix organic light-emitting diodes. IEEE Electron Device Lett, 2003, 24(9):583 doi: 10.1109/LED.2003.816590
[9]
Lin C L, Chen Y C. A novel LTPS-TFT pixel circuit compensat-ing for TFT threshold-voltage shift and OLED degradation for AMOLED. IEEE Electron Device Lett, 2007, 28(2):129 doi: 10.1109/LED.2006.889523
[10]
Jung S H, Nam W J, Han M K. A new voltage-modulated AMOLED pixel design compensating for threshold voltage variation in poly-Si TFTs. IEEE Electron Device Lett, 2004, 25(10):690 doi: 10.1109/LED.2004.836028
[11]
Lin C L, Tsai T T. A novel voltage driving method using 3-TFT pixel circuit for AMOLED. IEEE Electron Device Lett, 2007, 28(6):489 doi: 10.1109/LED.2007.896895
[12]
Lee J H, Nam W J, Jung S H, et al. A new current scaling pixel circuit for AMOLED. IEEE Electron Device Lett, 2004, 25(5):280 doi: 10.1109/LED.2004.826567
[13]
Si Y J, Xu Y L, Lang L Q, et al. A new AC driving method for a current-programmed AM-OLED pixel circuit. Chinese Journal of Semiconductors, 2006, 27(9):1562 doi: 10.1889/1.2036281/abstract
[14]
Shur M S, Slade H C, Jacunski M D, et al. SPICE models for amorphous silicon and polysilicon thin film transistors. J Electrochem Soc, 1997, 144(8):2833 doi: 10.1149/1.1837903
[15]
Chen C W, Lin C L, Wu C C. An effective cathode structure for inverted top-emitting organic light-emitting devices. Appl Phys Lett, 2004, 85(13):2469 doi: 10.1063/1.1798392

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    Received: 20 June 2012 Revised: 24 July 2012 Online: Published: 01 January 2013

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      Article Navigation >  Journal of Semiconductors  > 2013  >  34(1): 015009
      Yongwen Zhang, Wenbin Chen. A new LTPS TFT AC pixel circuit for an AMOLED[J]. Journal of Semiconductors, 2013, 34(1): 015009. doi: 10.1088/1674-4926/34/1/015009 ****Y W Zhang, W B Chen. A new LTPS TFT AC pixel circuit for an AMOLED[J]. J. Semicond., 2013, 34(1): 015009. doi: 10.1088/1674-4926/34/1/015009.
      Citation:
      Yongwen Zhang, Wenbin Chen. A new LTPS TFT AC pixel circuit for an AMOLED[J]. Journal of Semiconductors, 2013, 34(1): 015009. doi: 10.1088/1674-4926/34/1/015009 ****
      Y W Zhang, W B Chen. A new LTPS TFT AC pixel circuit for an AMOLED[J]. J. Semicond., 2013, 34(1): 015009. doi: 10.1088/1674-4926/34/1/015009.
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      A new LTPS TFT AC pixel circuit for an AMOLED

      DOI: 10.1088/1674-4926/34/1/015009

      • School of Optoelectronic Information, University of Electronic Science and Technology of China, Chengdu 610054, China

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      • Corresponding author: Chen Wenbin, chenwb@uestc.edu.cn
      • Received Date: 2012-06-20
      • Revised Date: 2012-07-24
      • Published Date: 2013-01-01

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