MicroLED

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microLED, also known as micro-LED, mLED or µLED, is an emerging flat panel display technology. As the name implies, microLED displays consist of arrays of microscopic LEDs forming the individual pixel elements. When compared to the widespread LCD technology, microLED displays offer better contrast, response times, and energy efficiency.

Along with OLEDs, microLEDs are primarily aimed at small, low-energy devices such as smartwatches and smartphones. OLED and microLED both offer greatly reduced energy requirements compared to conventional LCD systems. Unlike OLED, microLED is based on conventional GaN LED technology, which offers far higher total brightness than OLED produces, as much as 30 times, as well as higher efficiency in terms of lux/W. It also does not suffer from the shorter lifetimes of OLED.

As of 2018, microLED displays have not been mass-produced or commercialized, though Samsung demonstrated a prototype at CES and Apple has begun in-house development of microLED screens of its own.[1][2]

Research[edit]

Inorganic semiconductor microLED (µLED) technology[3] was first invented in 2000 by the research group of Hongxing Jiang and Jingyu Lin of Texas Tech University while they were at Kansas State University. Following their first report of electrical injection microLEDs based on InGaN semiconductors, several groups have quickly engaged in pursuing this concept.[4] Many related potential applications have been identified. Various on-chip connection schemes of microLED pixel arrays have been employed allowing for the development of single-chip high voltage DC/AC-LEDs[5] to address the compatibility issue between the high voltage electrical infrastructure and low voltage operation nature of LEDs and high brightness self-emissive microdisplays.[6]

The microLED array has also been explored as a light source for optogenetics applications[7] and for visible light communications.[8]

Early InGaN based microLED arrays and microdisplays were primarily passively driven. The first actively driven video-capable self-emissive InGaN microLED microdisplay in VGA format (640 x 480 pixels, each 12 microns in size with 15 microns between them) possessing low voltage requirements was realized in 2011 via a hybrid complementary metal-oxide semiconductor (CMOS) and integrated circuit (IC) hybrid assembly.[9]

Commercialization[edit]

microLEDs are considered to have innate potential performance advantages over LCD displays, including lower latency, higher contrast ratio, and greater color saturation, plus intrinsic self-illumination and better efficiency. As of 2016 technological and production barriers have prevented commercialization.[10]

As of 2016 a number of different technologies were under active research for the assembling of individual (pixel, or pixel group) LEDs on a substrate. These include chip bonding of microLED chips onto a substrate, considered to have potential for large displays; wafer production methods using etching to produce an LED array followed by bonding to an IC ; and wafer production methods using an intermediate temporary thin film to transfer the LED array to a substrate.

Sony launched a 55inch "Crystal LED Display" in 2012 with 1920x1080 resolution, as a demonstrator product.[10] Sony announced its CLEDIS (Crystal LED Integrated Structure) brand which used surface mounted LEDs for large display production.[11]

Samsung plans on bringing a 4K microLED TV to market in 2018.[12][13][14] In March 2018, Bloomberg reported Apple to have about 300 engineers devoted to in-house development of microLED screens.[15][2]

References[edit]

  1. ^ "Our first look at Samsung's massive 146-inch 4K MicroLED TV". Engadget. Retrieved 2018-01-08. 
  2. ^ a b "Apple is developing own MicroLED screens: Bloomberg". Reuters. March 18, 2018. Retrieved 2018-03-19 – via Reuters. 
  3. ^ H. X. Jiang, et al "Micro-size LED and detector arrays for mini-displays, hyperbright light emitting diodes, lighting, and UV detector and imaging sensor applications," US patent 6,410,940; "GaN microdisk light emitting diodes," Appl. Phys. Lett. 76, 631 (2000). doi: 10.1063/1.125841; "InGaN/GaN quantum well interconnected microdisk light emitting diodes," Appl. Phys. Lett. 77, 3236 (2000). doi: 10.1063/1.1326479; "III-nitride blue microdisplays," Appl. Phys. Lett. 78, 1303 (2001). doi: 10.1063/1.1351521
  4. ^ I. Ozden, M. Diagne, A.V. Nurmikko, J. Han, and T. Takeuchi, "A matrix addressable 1024 element blue light emitting InGaN QW diode array Phys. Status Solidi. a 188, 139 (2001). DOI: 10.1002/1521-396X(200111)188:1<139::AID-PSSA139>3.0.CO;2-; H.W. Choi, C.W. Jeon, and M.D. Dawson "High-resolution 128 × 96 nitride microdisplay," IEEE Electron Device Lett. 25 277 (2004). DOI: 10.1109/LED.2004.826541
  5. ^ H. X. Jiang, et al, "Light emitting diodes for high AC voltage operating and general lighting," US Patents 6,957,899; 7,210,819; 7,213,942; "Heterogeneous integrated high voltage DC/AC light emitter," US Patent 7,221,044; "Micro-LED based high voltage AC/DC indicator lamp," US Patent 7,535,028; "AC/DC light emitting diodes with integrated protection mechanism," US Patent 7,714,348; "Light emitting diode lamp capable of high AC/DC voltage operation," US Patent 8,272,757
  6. ^ Z. Y. Fan, H. X. Jiang, and J. Y. Lin, "Micro-Emitter Array Based Full-Color Microdisplay," US patent 8,058,663; J. Day, J. Li, D. Lie, Z. Y. Fan, J. Y. Lin, and H. X. Jiang "CMOS IC for micro-emitter based microdisplay," US patent 9,047,818.
  7. ^ M. D. Dawson and M. A. A. Neil, "Micro-pixellated LEDs for science and instrumentation" J Phys D. 41 090301 (2008); V. Poher, N. Grossman, G. T. Kennedy, K. Nikolic, H. X. Zhang, Z. Gong, E. M. Drakakis, E. Gu, M. D. Dawson, P. M. W. French, P. Degenaar, and M. A. Neil, "Micro-LED arrays: a tool for two-dimensional neuron stimulation," J. Phys. D Appl. Phys. 41(9), 094014 (2008).
  8. ^ J. J. D. McKendry et al., "Visible-light communications using a CMOS-controlled micro-light- emitting-diode array," J. Lightw. Technol., 30, 61 (2012). DOI: 10.1109/JLT.2011.2175090
  9. ^ J. Day, J. Li, D.Y.C. Lie, Charles Bradford, J.Y. Lin, and H.X. Jiang, "III-Nitride full-scale high-resolution microdisplays," Appl. Phys. Lett. 99, 031116 (2011). doi:10.1063/1.3615679; J. Y. Lin, J. Day, J. Li, D. Lie, C. Bradford, and H. X. Jiang, "High-resolution group III nitride microdisplays," SPIE Newsroom, Dec. issue (2011). doi: 10.1117/2.1201112.004001
  10. ^ a b Cheng, Skavy (5 Aug 2016), "Overview of Micro-LED History and Current Developments", www.ledinside.com 
  11. ^ InfoComm 2016: Sony Unveils New CLEDIS Display Featuring Ultrafine LEDs.
  12. ^ "Our first look at Samsung's massive 146-inch 4K MicroLED TV". Engadget. Retrieved 2018-02-01. 
  13. ^ Samsung's Micro LED bet will define its future in TVs, 22 Jan 2018 
  14. ^ Samsung presents 146in modular MicroLED TV at CES 2018, 10 Jan 2018 
  15. ^ Apple Is Secretly Developing Its Own Screens for the First Time, 18 Mar 2018 

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