All-organic active matrix OLED display

Lisong Zhou, Sungkyu Park, Bo Bai, Jie Sun, Sheng Chu Wu, Thomas Nelson Jackson, Shelby Nelson, Diane Freeman, Yongtaek Hong

Research output: Chapter in Book/Report/Conference proceedingConference contribution

1 Citation (Scopus)

Abstract

There has been great deal of interest in and research on organic light-emitting diodes (OLEDs) because of the possibility of thinner, lighter, faster and more power efficient displays. Several active matrix OLED displays have been demonstrated on both glass and polymeric substrates. To date, most active matrix OLED displays have used polysilicon or amorphous silicon thin film transistors (TFTs) as the active elements. Pentacene organic thin film transistors (OTFTs), with performance comparable to those of a-Si:H, are of interest because of the possibility of reduced processing cost compared to a-Si:H and perhaps also roll-to-roll manufacturing. A small (8×8 pixel) pentacene TFT driven OLED display has been demonstrated [1], however a range of issues including dielectric integrity, device passivation techniques, and TFT uniformity, still need to be addressed. We report here on 48 × 48 pixels pentacene TFT driven active-matrix OLED displays on glass substrate. To our best knowledge these are the largest pentacene TFT driven displays. The displays reported here used a simple two transistor per pixel drive scheme (figure 1) with a pixel pitch of 500 μm and an aperture ratio of 0.54. The drive and select transistors had a W/L ratio of 10 (200 μm/20 μm) and 1 (20 μm/20 μm), respectively and the storage capacitor is 1.2pF. Figure 2 shows a cross section of the pixel, including select OTFT, storage capacitor, drive OTFT and OLED. The substrate is 0.7mm glass coated with 85nm ITO film. First, the ITO is patterned by photolithography and wet etching. A 50nm chrome gate layer was then deposited by sputtering and patterned by wet etching. A 300nm thick ion-beam sputtered SiO 2, was used as the gate dielectric and patterned by lift-off. A 100nm platinum source-drain layer was deposited by sputtering and patterned by lift-off. After vapor treatment in octadecyltrichlorosilane a 50nm pentacene layer was thermally evaporated at 60°C at a rate of 0.1-0.5Å/s. To pattern the pentacene active layer photo-sensitized polyvinyl alcohol (PVA) water-based photoresist was used to mask the active region and field pentacene was removed by oxygen plasma etching. Because residual water trapped in the PVA can reduce OLED lifetime the patterned OTFTs were encapsulated by a 1μm thick parylene layer deposited at room temperature and patterned by photolithography and RIE dry etching. The OLED stack was then deposited onto the OTFT backplane through a shadow mask by thermal evaporation. The OLED organic layers were: 75 nm 4,4′-bis[N-(1-napthyl)-N-Phenyl-amino] biphenyl (α-NPD) as the hole transport layer, and 75 nm tris (8-hydroxyquinoline) aluminum (Alq 3) as the electron transport layer. Next, a 220 nm magnesium/silver cathode was deposited through shadow mask. Finally, the OLED display area was encapsulated with glass sealed by UV cured epoxy. Figure 3 shows the typical characteristics of the drive OTFT on the backplane, from which, the saturation mobility, threshold voltage, on/off ratio and sub-threshold slope can be extracted as 0.6cm 2/V-s, 12.6 V, > 10 7, and 2.5V/Dec, respectively. Since OLEDs are current driven light-emitting devices, i.e., the brightness is proportional to the current, OTFT uniformity is critical to the OLED display. Figure 4 shows the results for a 105 OTFT uniformity test array (W/L=200/20μm). The array yield is 94% with an average threshold voltage of 13.7 V and a standard deviation of 0.78 V, and an average field-effect mobility of 0.584 cm 2/V-s and a standard deviation of 0.017 cm 2/V-s. Figure 5 shows a pentacene OTFT driven OLED pixel and figure 6 shows a 48 × 48 array driven with all the pixels in the on (V SELECT= 0V and V DATA = 0V) and off (V SELECT = 40V, V DATA = 30V) state, at V DD = 20V, V CA = -10V. Although the defect density is large basic display function is demonstrated. These results suggest that that pentacene OTFT backplanes are viable candidates for active-matrix OLED displays.

Original languageEnglish (US)
Title of host publication63rd Device Research Conference Digest, DRC'05
Pages137-138
Number of pages2
DOIs
StatePublished - Dec 1 2005
Event63rd Device Research Conference, DRC'05 - Santa Clara, CA, United States
Duration: Jun 20 2005Jun 22 2005

Publication series

NameDevice Research Conference - Conference Digest, DRC
Volume2005
ISSN (Print)1548-3770

Other

Other63rd Device Research Conference, DRC'05
CountryUnited States
CitySanta Clara, CA
Period6/20/056/22/05

Fingerprint

Organic light emitting diodes (OLED)
Thin film transistors
Display devices
Pixels
Capacitor storage
Masks
Glass
Wet etching
Polyvinyl alcohols
Photolithography
Threshold voltage
Sputtering
Transistors
Substrates
Dry etching
Thermal evaporation
Plasma etching
Defect density
Gate dielectrics
Reactive ion etching

All Science Journal Classification (ASJC) codes

  • Engineering(all)

Cite this

Zhou, L., Park, S., Bai, B., Sun, J., Wu, S. C., Jackson, T. N., ... Hong, Y. (2005). All-organic active matrix OLED display. In 63rd Device Research Conference Digest, DRC'05 (pp. 137-138). [1553092] (Device Research Conference - Conference Digest, DRC; Vol. 2005). https://doi.org/10.1109/DRC.2005.1553092
Zhou, Lisong ; Park, Sungkyu ; Bai, Bo ; Sun, Jie ; Wu, Sheng Chu ; Jackson, Thomas Nelson ; Nelson, Shelby ; Freeman, Diane ; Hong, Yongtaek. / All-organic active matrix OLED display. 63rd Device Research Conference Digest, DRC'05. 2005. pp. 137-138 (Device Research Conference - Conference Digest, DRC).
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title = "All-organic active matrix OLED display",
abstract = "There has been great deal of interest in and research on organic light-emitting diodes (OLEDs) because of the possibility of thinner, lighter, faster and more power efficient displays. Several active matrix OLED displays have been demonstrated on both glass and polymeric substrates. To date, most active matrix OLED displays have used polysilicon or amorphous silicon thin film transistors (TFTs) as the active elements. Pentacene organic thin film transistors (OTFTs), with performance comparable to those of a-Si:H, are of interest because of the possibility of reduced processing cost compared to a-Si:H and perhaps also roll-to-roll manufacturing. A small (8×8 pixel) pentacene TFT driven OLED display has been demonstrated [1], however a range of issues including dielectric integrity, device passivation techniques, and TFT uniformity, still need to be addressed. We report here on 48 × 48 pixels pentacene TFT driven active-matrix OLED displays on glass substrate. To our best knowledge these are the largest pentacene TFT driven displays. The displays reported here used a simple two transistor per pixel drive scheme (figure 1) with a pixel pitch of 500 μm and an aperture ratio of 0.54. The drive and select transistors had a W/L ratio of 10 (200 μm/20 μm) and 1 (20 μm/20 μm), respectively and the storage capacitor is 1.2pF. Figure 2 shows a cross section of the pixel, including select OTFT, storage capacitor, drive OTFT and OLED. The substrate is 0.7mm glass coated with 85nm ITO film. First, the ITO is patterned by photolithography and wet etching. A 50nm chrome gate layer was then deposited by sputtering and patterned by wet etching. A 300nm thick ion-beam sputtered SiO 2, was used as the gate dielectric and patterned by lift-off. A 100nm platinum source-drain layer was deposited by sputtering and patterned by lift-off. After vapor treatment in octadecyltrichlorosilane a 50nm pentacene layer was thermally evaporated at 60°C at a rate of 0.1-0.5{\AA}/s. To pattern the pentacene active layer photo-sensitized polyvinyl alcohol (PVA) water-based photoresist was used to mask the active region and field pentacene was removed by oxygen plasma etching. Because residual water trapped in the PVA can reduce OLED lifetime the patterned OTFTs were encapsulated by a 1μm thick parylene layer deposited at room temperature and patterned by photolithography and RIE dry etching. The OLED stack was then deposited onto the OTFT backplane through a shadow mask by thermal evaporation. The OLED organic layers were: 75 nm 4,4′-bis[N-(1-napthyl)-N-Phenyl-amino] biphenyl (α-NPD) as the hole transport layer, and 75 nm tris (8-hydroxyquinoline) aluminum (Alq 3) as the electron transport layer. Next, a 220 nm magnesium/silver cathode was deposited through shadow mask. Finally, the OLED display area was encapsulated with glass sealed by UV cured epoxy. Figure 3 shows the typical characteristics of the drive OTFT on the backplane, from which, the saturation mobility, threshold voltage, on/off ratio and sub-threshold slope can be extracted as 0.6cm 2/V-s, 12.6 V, > 10 7, and 2.5V/Dec, respectively. Since OLEDs are current driven light-emitting devices, i.e., the brightness is proportional to the current, OTFT uniformity is critical to the OLED display. Figure 4 shows the results for a 105 OTFT uniformity test array (W/L=200/20μm). The array yield is 94{\%} with an average threshold voltage of 13.7 V and a standard deviation of 0.78 V, and an average field-effect mobility of 0.584 cm 2/V-s and a standard deviation of 0.017 cm 2/V-s. Figure 5 shows a pentacene OTFT driven OLED pixel and figure 6 shows a 48 × 48 array driven with all the pixels in the on (V SELECT= 0V and V DATA = 0V) and off (V SELECT = 40V, V DATA = 30V) state, at V DD = 20V, V CA = -10V. Although the defect density is large basic display function is demonstrated. These results suggest that that pentacene OTFT backplanes are viable candidates for active-matrix OLED displays.",
author = "Lisong Zhou and Sungkyu Park and Bo Bai and Jie Sun and Wu, {Sheng Chu} and Jackson, {Thomas Nelson} and Shelby Nelson and Diane Freeman and Yongtaek Hong",
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Zhou, L, Park, S, Bai, B, Sun, J, Wu, SC, Jackson, TN, Nelson, S, Freeman, D & Hong, Y 2005, All-organic active matrix OLED display. in 63rd Device Research Conference Digest, DRC'05., 1553092, Device Research Conference - Conference Digest, DRC, vol. 2005, pp. 137-138, 63rd Device Research Conference, DRC'05, Santa Clara, CA, United States, 6/20/05. https://doi.org/10.1109/DRC.2005.1553092

All-organic active matrix OLED display. / Zhou, Lisong; Park, Sungkyu; Bai, Bo; Sun, Jie; Wu, Sheng Chu; Jackson, Thomas Nelson; Nelson, Shelby; Freeman, Diane; Hong, Yongtaek.

63rd Device Research Conference Digest, DRC'05. 2005. p. 137-138 1553092 (Device Research Conference - Conference Digest, DRC; Vol. 2005).

Research output: Chapter in Book/Report/Conference proceedingConference contribution

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T1 - All-organic active matrix OLED display

AU - Zhou, Lisong

AU - Park, Sungkyu

AU - Bai, Bo

AU - Sun, Jie

AU - Wu, Sheng Chu

AU - Jackson, Thomas Nelson

AU - Nelson, Shelby

AU - Freeman, Diane

AU - Hong, Yongtaek

PY - 2005/12/1

Y1 - 2005/12/1

N2 - There has been great deal of interest in and research on organic light-emitting diodes (OLEDs) because of the possibility of thinner, lighter, faster and more power efficient displays. Several active matrix OLED displays have been demonstrated on both glass and polymeric substrates. To date, most active matrix OLED displays have used polysilicon or amorphous silicon thin film transistors (TFTs) as the active elements. Pentacene organic thin film transistors (OTFTs), with performance comparable to those of a-Si:H, are of interest because of the possibility of reduced processing cost compared to a-Si:H and perhaps also roll-to-roll manufacturing. A small (8×8 pixel) pentacene TFT driven OLED display has been demonstrated [1], however a range of issues including dielectric integrity, device passivation techniques, and TFT uniformity, still need to be addressed. We report here on 48 × 48 pixels pentacene TFT driven active-matrix OLED displays on glass substrate. To our best knowledge these are the largest pentacene TFT driven displays. The displays reported here used a simple two transistor per pixel drive scheme (figure 1) with a pixel pitch of 500 μm and an aperture ratio of 0.54. The drive and select transistors had a W/L ratio of 10 (200 μm/20 μm) and 1 (20 μm/20 μm), respectively and the storage capacitor is 1.2pF. Figure 2 shows a cross section of the pixel, including select OTFT, storage capacitor, drive OTFT and OLED. The substrate is 0.7mm glass coated with 85nm ITO film. First, the ITO is patterned by photolithography and wet etching. A 50nm chrome gate layer was then deposited by sputtering and patterned by wet etching. A 300nm thick ion-beam sputtered SiO 2, was used as the gate dielectric and patterned by lift-off. A 100nm platinum source-drain layer was deposited by sputtering and patterned by lift-off. After vapor treatment in octadecyltrichlorosilane a 50nm pentacene layer was thermally evaporated at 60°C at a rate of 0.1-0.5Å/s. To pattern the pentacene active layer photo-sensitized polyvinyl alcohol (PVA) water-based photoresist was used to mask the active region and field pentacene was removed by oxygen plasma etching. Because residual water trapped in the PVA can reduce OLED lifetime the patterned OTFTs were encapsulated by a 1μm thick parylene layer deposited at room temperature and patterned by photolithography and RIE dry etching. The OLED stack was then deposited onto the OTFT backplane through a shadow mask by thermal evaporation. The OLED organic layers were: 75 nm 4,4′-bis[N-(1-napthyl)-N-Phenyl-amino] biphenyl (α-NPD) as the hole transport layer, and 75 nm tris (8-hydroxyquinoline) aluminum (Alq 3) as the electron transport layer. Next, a 220 nm magnesium/silver cathode was deposited through shadow mask. Finally, the OLED display area was encapsulated with glass sealed by UV cured epoxy. Figure 3 shows the typical characteristics of the drive OTFT on the backplane, from which, the saturation mobility, threshold voltage, on/off ratio and sub-threshold slope can be extracted as 0.6cm 2/V-s, 12.6 V, > 10 7, and 2.5V/Dec, respectively. Since OLEDs are current driven light-emitting devices, i.e., the brightness is proportional to the current, OTFT uniformity is critical to the OLED display. Figure 4 shows the results for a 105 OTFT uniformity test array (W/L=200/20μm). The array yield is 94% with an average threshold voltage of 13.7 V and a standard deviation of 0.78 V, and an average field-effect mobility of 0.584 cm 2/V-s and a standard deviation of 0.017 cm 2/V-s. Figure 5 shows a pentacene OTFT driven OLED pixel and figure 6 shows a 48 × 48 array driven with all the pixels in the on (V SELECT= 0V and V DATA = 0V) and off (V SELECT = 40V, V DATA = 30V) state, at V DD = 20V, V CA = -10V. Although the defect density is large basic display function is demonstrated. These results suggest that that pentacene OTFT backplanes are viable candidates for active-matrix OLED displays.

AB - There has been great deal of interest in and research on organic light-emitting diodes (OLEDs) because of the possibility of thinner, lighter, faster and more power efficient displays. Several active matrix OLED displays have been demonstrated on both glass and polymeric substrates. To date, most active matrix OLED displays have used polysilicon or amorphous silicon thin film transistors (TFTs) as the active elements. Pentacene organic thin film transistors (OTFTs), with performance comparable to those of a-Si:H, are of interest because of the possibility of reduced processing cost compared to a-Si:H and perhaps also roll-to-roll manufacturing. A small (8×8 pixel) pentacene TFT driven OLED display has been demonstrated [1], however a range of issues including dielectric integrity, device passivation techniques, and TFT uniformity, still need to be addressed. We report here on 48 × 48 pixels pentacene TFT driven active-matrix OLED displays on glass substrate. To our best knowledge these are the largest pentacene TFT driven displays. The displays reported here used a simple two transistor per pixel drive scheme (figure 1) with a pixel pitch of 500 μm and an aperture ratio of 0.54. The drive and select transistors had a W/L ratio of 10 (200 μm/20 μm) and 1 (20 μm/20 μm), respectively and the storage capacitor is 1.2pF. Figure 2 shows a cross section of the pixel, including select OTFT, storage capacitor, drive OTFT and OLED. The substrate is 0.7mm glass coated with 85nm ITO film. First, the ITO is patterned by photolithography and wet etching. A 50nm chrome gate layer was then deposited by sputtering and patterned by wet etching. A 300nm thick ion-beam sputtered SiO 2, was used as the gate dielectric and patterned by lift-off. A 100nm platinum source-drain layer was deposited by sputtering and patterned by lift-off. After vapor treatment in octadecyltrichlorosilane a 50nm pentacene layer was thermally evaporated at 60°C at a rate of 0.1-0.5Å/s. To pattern the pentacene active layer photo-sensitized polyvinyl alcohol (PVA) water-based photoresist was used to mask the active region and field pentacene was removed by oxygen plasma etching. Because residual water trapped in the PVA can reduce OLED lifetime the patterned OTFTs were encapsulated by a 1μm thick parylene layer deposited at room temperature and patterned by photolithography and RIE dry etching. The OLED stack was then deposited onto the OTFT backplane through a shadow mask by thermal evaporation. The OLED organic layers were: 75 nm 4,4′-bis[N-(1-napthyl)-N-Phenyl-amino] biphenyl (α-NPD) as the hole transport layer, and 75 nm tris (8-hydroxyquinoline) aluminum (Alq 3) as the electron transport layer. Next, a 220 nm magnesium/silver cathode was deposited through shadow mask. Finally, the OLED display area was encapsulated with glass sealed by UV cured epoxy. Figure 3 shows the typical characteristics of the drive OTFT on the backplane, from which, the saturation mobility, threshold voltage, on/off ratio and sub-threshold slope can be extracted as 0.6cm 2/V-s, 12.6 V, > 10 7, and 2.5V/Dec, respectively. Since OLEDs are current driven light-emitting devices, i.e., the brightness is proportional to the current, OTFT uniformity is critical to the OLED display. Figure 4 shows the results for a 105 OTFT uniformity test array (W/L=200/20μm). The array yield is 94% with an average threshold voltage of 13.7 V and a standard deviation of 0.78 V, and an average field-effect mobility of 0.584 cm 2/V-s and a standard deviation of 0.017 cm 2/V-s. Figure 5 shows a pentacene OTFT driven OLED pixel and figure 6 shows a 48 × 48 array driven with all the pixels in the on (V SELECT= 0V and V DATA = 0V) and off (V SELECT = 40V, V DATA = 30V) state, at V DD = 20V, V CA = -10V. Although the defect density is large basic display function is demonstrated. These results suggest that that pentacene OTFT backplanes are viable candidates for active-matrix OLED displays.

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Zhou L, Park S, Bai B, Sun J, Wu SC, Jackson TN et al. All-organic active matrix OLED display. In 63rd Device Research Conference Digest, DRC'05. 2005. p. 137-138. 1553092. (Device Research Conference - Conference Digest, DRC). https://doi.org/10.1109/DRC.2005.1553092