MicroLED

microLED, also known as micro-LED, mLED or µLED, is an emerging flat panel display technology. As the name implies, mLED displays consist of arrays of microscopic LEDs forming the individual pixel elements. Compared to the widespread LCD technology, mLED displays offer far greater contrast, much faster response times, and would use less energy.

Along with OLEDs, mLEDs are primarily aimed at small, low-energy devices such as smartwatches and smartphones. OLED and mLED both offer greatly reduced energy requirements compared to conventional LCD systems. Unlike OLED, mLED is based on conventional GaN LED technology, which offers far higher total brightness than OLED products, 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, although the multi-year lifespan of modern OLEDs has mitigated this issue in most roles.

As of 2016, mLED displays have not been mass produced or commercialized.

Early history of microLED

Inorganic semiconductor microLED (µLED) technology [[1]] was first invented in 2000 by the research group of Prof. Hongxing Jiang and Prof. 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.[[2]] Many related potential applications have been identified. Most notably, various on-chip connection schemes of microLED pixel arrays have been employed by III-N Technology, Inc. allowing for the development of single-chip high voltage DC/AC-LEDs [[3]] to address the compatibility issue between the high voltage electrical infrastructure and low voltage operation nature of LEDs and high brightness self-emissive microdisplays.[[4]] The µLED array has also been explored as a light source for optogenetics applications [[5]] and for visible light communications.[[6]] More recently, the technology has evolved into micro-LED displays (or crystal LED displays) which are being pursued by several companies including Sony.[[7]] Early InGaN based µLED arrays and microdisplays were primarily passively driving. The first active driving video-capable self-emissive InGaN µLED 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.[[8]]

References

  1. ↑ 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
  2. ↑ 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
  3. ↑ 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
  4. ↑ 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.
  5. ↑ 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).
  6. ↑ 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
  7. ↑ InfoComm 2016: Sony Unveils New CLEDIS Display Featuring Ultrafine LEDs.
  8. ↑ 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

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