AMOLED

AMOLED (active-matrix organic light-emitting diode) is a display technology for use in mobile devices and televisions. OLED describes a specific type of thin-film display technology in which organic compounds form the electroluminescent material, and active matrix refers to the technology behind the addressing of pixels.

As of 2011, AMOLED technology is used in mobile phones, media players and digital cameras,[1] and continues to make progress toward low-power, low-cost and large-size (for example, 40-inch) applications.[2][3][4]

Contents

Design

An AMOLED display consists of an active matrix of OLED pixels that generate light upon electrical activation that have been deposited or integrated onto a thin film transistor (TFT) array, which functions as a series of switches to control the current flowing to each individual pixel.[5]

Typically, this continuous current flow is controlled by at least two TFTs at each pixel, one to start and stop the charging of a storage capacitor and the second to provide a voltage source at the level needed to create a constant current to the pixel and eliminating the need for the very high currents required for passive matrix OLED operation.[6]

TFT backplane technology is crucial in the fabrication of AMOLED displays. Two primary TFT backplane technologies, namely polycrystalline silicon (poly-Si) and amorphous silicon (a-Si), are used today in AMOLEDs. These technologies offer the potential for fabricating the active matrix backplanes at low temperatures (below 150°C) directly onto flexible plastic substrates for producing flexible AMOLED displays.[7]

Future development

Manufacturers have developed in-cell touch panels, integrating the production of capacitive sensor arrays in the AMOLED module fabrication process. In-cell sensor AMOLED fabricators include AU Optronics and Samsung. Samsung has marketed their version of this technology as Super AMOLED. Clear Black Display or CBD is an AMOLED display with a polarized filter on top. Researchers at DuPont used computational fluid dynamics (CFD) software to optimize coating processes for a new solution-coated AMOLED display technology that is cost and performance competitive with existing commercial vapor deposition technology. Using custom modeling and analytical approaches, they developed short- and long-range film-thickness control and uniformity that is commercially viable at large glass sizes.[8]

Comparison to other technologies

AMOLED displays provide higher refresh rates than their passive-matrix OLED counterparts, improving response time often to under a millisecond, and they consume significantly less power.[9] This advantage makes active-matrix OLEDs well suited for portable electronics, where power consumption is critical to battery life.

The amount of power the display consumes varies significantly depending on the color and brightness shown. As an example, one commercial QVGA OLED display consumes 3 watts while showing black text on a white background, but only 0.7 watts showing white text on a black background.[10] Because the black pixels actually turn off, AMOLED also has contrast ratios that are significantly better than LCD.

AMOLED displays may be difficult to view in direct sunlight compared to LCDs because of their reduced maximum brightness.[11] Samsung's Super AMOLED technology addresses this issue by reducing the size of gaps between layers of the screen.[12][13]. Additionally, PenTile technology is sometimes used, rearranging the subpixels for each color and in the case of PenTile RGBW, adding a white subpixel, which lets through more light, thereby increasing brightness, albeit while introducing graininess.

The organic materials used in AMOLED displays are prone to degradation over a period of time. However, technology has been developed to compensate for material degradation.[14][15]

Current demand for AMOLED screens is high and, due to supply shortages of the Samsung-produced displays, certain models of HTC smartphones have been changed to use next-generation LCD displays from the Samsung and Sony joint-venture SLCD in the future.[16] Construction of new production facilities in 2011 will increase the production of AMOLED screens to cope with demand.[17]

Uses

Commercial devices using AMOLED include:

Phones
Portable music players
Games consoles
Music production hardware
Digital cameras

References

  1. ^ Lee, Hyunkoo; Park, Insun; Kwak, Jeonghun; Yoon, Do Y.; Kallmann, Changhee Lee (2010). "Improvement of electron injection in inverted bottom-emission blue phosphorescent organic light emitting diodes using zinc oxide nanoparticles". Applied Physics Letters 96: 153306. doi:10.1063/1.3400224. 
  2. ^ Kim, Yang Wan; Kwak, Won Kyu; Lee, Jae Yong; Choi, Wong Sik; Lee, Ki Yong; Kim, Sung Chul; Yoo, Eui Jin (2009). "40 Inch FHD AM-OLED Display with IR Drop Compensation Pixel Circuit". SID Symposium Digest of Technical Papers 40: 85. doi:10.1889/1.3256930. 
  3. ^ Lee, Myung Ho; Seop, Song Myoung; Kim, Jong Soo; Hwang, Jung Ho; Shin, Hye Jin; Cho, Sang Kyun; Min, Kyoung Wook; Kwak, Won Kyu et al. (2009). "Development of 31-Inch Full-HD AMOLED TV Using LTPS-TFT and RGB FMM". SID Symposium Digest of Technical Papers 40: 802. doi:10.1889/1.3256911. 
  4. ^ Hamer, John W.; Arnold, Andrew D.; Boroson, Michael L.; Itoh, Masahiro; Hatwar, Tukaram K.; Helber, Margaret J.; Miwa, Koichi; Levey, Charles I. et al. (2008). "System design for a wide-color-gamut TV-sized AMOLED display". Journal of the Society for Information Display 16: 3. doi:10.1889/1.2835033. 
  5. ^ "Introduction to OLED Displays — Design Guide for Active Matrix OLED (AMOLED) Displays". 4D Systems. 2008-05-22. http://data.4dsystems.com.au/downloads/micro-OLED/Docs/4D_AMOLED_Presentation.pdf. Retrieved 2010-09-06. 
  6. ^ Lin, Chih-Lung; Chen, Yung-Chih. "A Novel LTPS-TFT Pixel Circuit Compensating for TFT Threshold-Voltage Shift and OLED Degradation for AMOLED". IEEE Electron Device Letters 28: 129. doi:10.1109/LED.2006.889523. 
  7. ^ Sarma, Kalluri R.; Chanley, Charles; Dodd, Sonia R.; Roush, Jared; Schmidt, John; Srdanov, Gordana; Stevenson, Matthew; Wessel, Ralf et al. (2003). "Active-matrix OLED using 150°C a-Si TFT backplane built on flexible plastic substrate (Proceedings Paper)". SPIE Proceedings 5080: 180. doi:10.1117/12.497638.  [1]
  8. ^ Reid Chesterfield, Andrew Johnson, Charlie Lang, Matthew Stainer, and Jonathan Ziebarth, "Solution-Coating Technology for AMOLED Displays", Information Display Magazine, January 2011.
  9. ^ Suyko, Alan. "Oleds Ready For The Mainstream." Electronics News (2009): 20. Associates Programs Source Plus. Web. 9 Dec. 2011.
  10. ^ Mian Dong; Choi, Y.-S.K; Lin Zhong (July 2009). "Power modeling of graphical user interfaces on OLED displays". Design Automation Conference, 2009. DAC '09. 46th ACM/IEEE (IEEE): 652–657. 
  11. ^ How Super AMOLED displays work
  12. ^ "What Are The Benefits Of Using The Super AMOLED Display In My SGH-t959 (Vibrant) Phone?". Samsung. 2010-07-15. http://ars.samsung.com/customer/usa/jsp/faqs/faqs_view_us.jsp?SITE_ID=22&PG_ID=2&PROD_SUB_ID=557&PROD_ID=560&AT_ID=290435. Retrieved 2010-09-07. 
  13. ^ "Big is beautiful". The Age. 2010-08-12. http://digihub.theage.com.au/node/1799. Retrieved 2010-09-07. 
  14. ^ Ashtiani, Shahin J.; Reza Chaji, G.; Nathan, Arokia. "AMOLED Pixel Circuit With Electronic Compensation of Luminance Degradation". Journal of Display Technology 38: 36. doi:10.1109/JDT.2006.890711. 
  15. ^ US 7352345, Chun-huai Li, "Driving apparatus and method for light emitting diode display", issued 2008-04-01 
  16. ^ "HTC ditches Samsung AMOLED display for Sony's Super LCDs". International Business Times. 2010-07-26. http://www.ibtimes.com/articles/38429/20100726/htc-ditches-samsung-amoled-display-for-sony-s-super-lcds.htm. Retrieved 2011-01-01. 
  17. ^ "Samsung Mobile Display to Boost 2011 Production". Wall Street Journal. 2010-09-06. http://online.wsj.com/article/SB10001424052748703713504575475553352680096.html. Retrieved 2011-01-01. 
  18. ^ http://www.samsung.com/uk/consumer/mobile-devices/smartphones/android/GT-I9250TSAXEU
  19. ^ http://www.samsung.com/uk/consumer/mobile-devices/smartphones/android/GT-I9250TSAXEU

External links