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microLED, also known as micro-LED, mLED or µLED, first invented in 2000 by the research group of Hongxing Jiang and Jingyu Lin of
Texas Tech University Texas Tech University (Texas Tech, Tech, or TTU) is a public research university in Lubbock, Texas. Established on , and called Texas Technological College until 1969, it is the main institution of the five-institution Texas Tech University Sy ...
while they were at
Kansas State University Kansas State University (KSU, Kansas State, or K-State) is a public land-grant research university with its main campus in Manhattan, Kansas, United States. It was opened as the state's land-grant college in 1863 and was the first public inst ...
, is an emerging flat-panel display technology. microLED displays consist of arrays of
microscopic The microscopic scale () is the scale of objects and events smaller than those that can easily be seen by the naked eye, requiring a lens or microscope to see them clearly. In physics, the microscopic scale is sometimes regarded as the scale be ...
LEDs forming the individual
pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a raster image, or the smallest point in an all points addressable display device. In most digital display devices, pixels are the ...
elements. The first high-resolution and video-capable InGaN microLED microdisplay in VGA format was realized in 2009 by Hongxing Jiang and Jingyu Lin and their colleagues at
Texas Tech University Texas Tech University (Texas Tech, Tech, or TTU) is a public research university in Lubbock, Texas. Established on , and called Texas Technological College until 1969, it is the main institution of the five-institution Texas Tech University Sy ...
and III-N Technology, Inc. via active driving of microLED array by a complementary metal-oxide semiconductor (CMOS) IC. Compared to widespread LCD technology, microLED displays offer better contrast, response times, and energy efficiency. MicroLED offers greatly reduced energy requirements when compared to conventional LCD displays while also offering pixel-level light control and a high
contrast ratio The contrast ratio (CR) is a property of a display system, defined as the ratio of the luminance of the brightest shade (white) to that of the darkest shade (black) that the system is capable of producing. A high contrast ratio is a desired aspect ...
. The inorganic nature of microLEDs gives them a longer lifetime advantage over OLEDs and allows them to display brighter images with minimal risk of
screen burn-in Screen burn-in, image burn-in, or ghost image, is a permanent discoloration of areas on an electronic display such as a cathode ray tube (CRT) in an old computer monitor or television set. It is caused by cumulative non-uniform use of the s ...
. The sub-nanosecond response time of µLED has a huge advantage over other display technologies for 3D/AR/VR displays since these devices need more images, more pixels per image, more frames per second and fast response. , microLED displays have not been mass-produced, although
Sony , commonly stylized as SONY, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. As a major technology company, it operates as one of the world's largest manufacturers of consumer and professional ...
,
Samsung The Samsung Group (or simply Samsung) ( ko, 삼성 ) is a South Korean multinational manufacturing conglomerate headquartered in Samsung Town, Seoul, South Korea. It comprises numerous affiliated businesses, most of them united under the ...
, and Konka sell microLED video walls.Sony creates colossal 16K screen in Japan
BBC. April 9, 2019.
LG,
Tianma Tianma ( ', "heavenly horse") was a winged flying horse in Chinese folklore. It was sometimes depicted with chimerical features such as dragon scales and was at times attributed the ability to sweat blood, possibly inspired by the parasite '' Pa ...
, PlayNitride, TCL/ CSoT, Jasper Display
Jade Bird Display
Plessey Semiconductors Ltd, and Ostendo Technologies, Inc. have demonstrated prototypes. Sony already sells microLED displays as a replacement for conventional cinema screens.
BOE BOE, BoE or Boe may refer to: Abbreviations, acronyms or initialisms * Bank of England, the central bank of the United Kingdom * Bank of English, a representative subset of the 4.5 billion words COBUILD corpus * Barrel of oil equivalent, a unit ...
, Epistar, and Leyard have plans for microLED mass production. MicroLED can be made flexible and transparent, just like OLEDs.


Research

Inorganic semiconductor microLED (µLED) technology was first invented in 2000 by the research group of Hongxing Jiang and Jingyu Lin of
Texas Tech University Texas Tech University (Texas Tech, Tech, or TTU) is a public research university in Lubbock, Texas. Established on , and called Texas Technological College until 1969, it is the main institution of the five-institution Texas Tech University Sy ...
while they were at
Kansas State University Kansas State University (KSU, Kansas State, or K-State) is a public land-grant research university with its main campus in Manhattan, Kansas, United States. It was opened as the state's land-grant college in 1863 and was the first public inst ...
. Following their first report of electrical injection microLEDs based on
indium gallium nitride Indium gallium nitride (InGaN, ) is a semiconductor material made of a mix of gallium nitride (GaN) and indium nitride (InN). It is a ternary group III/ group V direct bandgap semiconductor. Its bandgap can be tuned by varying the amount of i ...
(InGaN) semiconductors, several groups have quickly engaged in pursuing this concept. Many related potential applications have been identified. Various on-chip connection schemes of microLED pixel arrays have been employed by AC LED Lighting, LLC (a company funded by Hongxing Jiang and Jingyu Lin) allowing for the development of single-chip high voltage DC/AC-LEDs to address the compatibility issue between the high voltage electrical infrastructure and low voltage operation nature of LEDs and high brightness self-emissive microdisplays. The microLED array has also been explored as a light source for optogenetics applications and for visible light communications. 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 ( pixels, each 12µm in size with 15µm between them) possessing low voltage requirements was patented and realized in 2009 by Hongxing Jiang and Jingyu Lin and their colleagues at III-N Technology, Inc. (a company funded by Hongxing Jiang and Jingyu Lin) and
Texas Tech University Texas Tech University (Texas Tech, Tech, or TTU) is a public research university in Lubbock, Texas. Established on , and called Texas Technological College until 1969, it is the main institution of the five-institution Texas Tech University Sy ...
, via heterogeneous integration between microLED array and CMOS integrated circuit (IC) and the work was also published in the following years. The first microLED products were demonstrated by Sony in 2012. These displays, however, were very expensive. There are several methods to manufacture microLED displays. The flip-chip method manufactures the LED on a conventional sapphire substrate, while the transistor array and solder bumps are deposited on silicon wafers using conventional manufacturing and metallization processes. Mass transfer is used to pick and place several thousand LEDs from one wafer to another at the same time, and the LEDs are bonded to the silicon substrate using reflow ovens. The flip-chip method is used for micro displays used on
virtual reality headset A virtual reality headset (or VR headset) is a head-mounted device that provides virtual reality for the wearer. VR headsets are widely used with VR video games but they are also used in other applications, including simulators and trainers. VR ...
s. The drawbacks include cost, limited pixel size, limited placement accuracy, and the need for cooling to prevent the display from warping and breaking due to thermal mismatch between the LEDs and the silicon. Also, current microLED displays are less efficient than comparable OLED displays. Another microLED manufacturing method involves bonding the LEDs to an IC layer on a silicon substrate and then removing the LED bonding material using conventional semiconductor manufacturing techniques. The current bottleneck in the manufacturing process is the need to individually test every LED and replace faulty ones using an excimer laser lift-off apparatus, which uses a laser to weaken the bond between the LED and its substrate. Faulty LED replacement must be performed using high accuracy pick-and-place machines and the test and repair process takes several hours. The mass transfer process alone can take 18 days, for a smartphone screen with a glass substrate. Special LED manufacturing techniques can be used to increase yield and reduce the amount of faulty LEDs that need to be replaced. Each LED can be as small as 5µm across. LED epitaxy techniques need to be improved to increase LED yields.
Excimer laser An excimer laser, sometimes more correctly called an exciplex laser, is a form of ultraviolet laser which is commonly used in the production of microelectronic devices, semiconductor based integrated circuits or "chips", eye surgery, and microm ...
s are used for several steps: laser lift-off to separate LEDs from their sapphire substrate and to remove faulty LEDs, for manufacturing the LTPS-TFT backplane, and for laser cutting of the finished LEDs. Special mass transfer techniques using
elastomer An elastomer is a polymer with viscoelasticity (i.e. both viscosity and Elasticity (physics), elasticity) and with weak intermolecular forces, generally low Young's modulus and high Deformation (mechanics), failure strain compared with other mate ...
stamps are also being researched. Other companies are exploring the possibility of packaging 3 LEDs: one red, one green and one blue LED into a single package to reduce mass transfer costs.
Quantum dot Quantum dots (QDs) are semiconductor particles a few nanometres in size, having optical and electronic properties that differ from those of larger particles as a result of quantum mechanics. They are a central topic in nanotechnology. When the ...
s are being researched as a way to shrink the size of microLED pixels, while other companies are exploring the use of phosphors and quantum dots to eliminate the need for different-colored LEDs. Sensors can be embedded in microLED displays. Over 130 companies are involved in microLED research and development. MicroLED light panels are also being made, and are an alternative to conventional OLED and LED light panels. Digital
pulse-width modulation Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a method of reducing the average power delivered by an electrical signal, by effectively chopping it up into discrete parts. The average value of voltage (and current) fed ...
is well-suited to driving microLED displays. MicroLEDs experience a color shift as the current magnitude changes. Analog schemes change current to change brightness. With a digital pulse, only one current value is used for the on state. Thus, there is no color shift that occurs as brightness changes. Current microLED display offerings by Samsung and Sony consist of "cabinets" that can be tiled to create a large display of any size, with the display's resolution increasing with size. They also contain mechanisms to protect the display against water and dust. Each cabinet is diagonally with a resolution of .


Commercialization

microLEDs have innate potential performance advantages over LCD displays, including higher brightness, lower latency, higher
contrast ratio The contrast ratio (CR) is a property of a display system, defined as the ratio of the luminance of the brightest shade (white) to that of the darkest shade (black) that the system is capable of producing. A high contrast ratio is a desired aspect ...
, greater color saturation, intrinsic self-illumination, and better efficiency. As of 2016, technological and production barriers have prevented commercialization. As of 2016, a number of different technologies were under active research for the assembling of individual LED pixels 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. Glo and Jasper Display Corporation demonstrated the world's first RGB microLED microdisplay, measuring diagonally, at SID Display Week 2017. Glo transferred their microLEDs to the Jasper Display backplane.
Sony , commonly stylized as SONY, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. As a major technology company, it operates as one of the world's largest manufacturers of consumer and professional ...
launched a "Crystal LED Display" in 2012 with resolution, as a demonstration product. Sony announced its CLEDIS (Crystal LED Integrated Structure) brand which used surface mounted LEDs for large display production. As of August 2019, Sony offers CLEDIS in , and displays. On 12 September 2019, Sony announced Crystal LED availability to consumers ranging from 1080p to 16K displays.
Samsung The Samsung Group (or simply Samsung) ( ko, 삼성 ) is a South Korean multinational manufacturing conglomerate headquartered in Samsung Town, Seoul, South Korea. It comprises numerous affiliated businesses, most of them united under the ...
demonstrated a microLED display called The Wall at CES 2018. In July 2018, Samsung announced plans on bringing a 4K microLED TV to consumer market in 2019. At CES 2019, Samsung demonstrated a 4K microLED display and 6K microLED display. On June 12 at InfoComm 2019, Samsung announced the global launch of The Wall Luxury microLED display configurable from in 2K to in 8K. On October 4, 2019, Samsung announced that The Wall Luxury microLED display shipments had begun. In March 2018, Bloomberg reported
Apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus '' Malus''. The tree originated in Central Asia, where its wild ancest ...
to have about 300 engineers devoted to in-house development of microLED screens. At IFA 2018 in August, LG Display demonstrated a microLED display. At SID's Display Week 2019 in May, Tianma and PlayNitride demonstrated their co-developed microLED display with over 60% transparency. China Star Optoelectronics Technology (CSoT) demonstrated a transparent microLED display with around 45% transparency, also co-developed with PlayNitride. Plessey Semiconductors Ltd demonstrated a monolithic monochrome blue GaN-on-silicon wafer bonded to a Jasper Display CMOS backplane active-matrix microLED display with an 8μm pixel pitch. At SID's Display Week 2019 in May, Jade Bird Display demonstrated their 720p and 1080p microLED microdisplays with 5μm and 2.5μm pitch respectively, achieving luminance in the millions of candelas per square metre. In 2021, Jade Bird Display and
Vuzix Vuzix () is an American multinational technology company headquartered in Rochester, New York. Founded in 1997 by Paul Travers, Vuzix is a supplier of wearable display technology, virtual reality, and augmented reality. Vuzix manufactures and ...
have entered a Joint manufacturing agreement for making microLED based projectors for smart glasses and augmented reality glasses At Touch Taiwan 2019 on September 4, 2019,
AU Optronics AUO Corporation (AUO; ) is a Taiwanese company that specialises in optoelectronic solutions. It was formed in September 2001 by the merger of Acer Display Technology, Inc. (the predecessor of AUO, established in 1996) and Unipac Optoelectronics Cor ...
demonstrated a microLED display and indicated that microLED was 12 years from mass commercialization. At IFA 2019 on September 13, 2019,
TCL Corporation TCL Technology (originally an abbreviation for Telephone Communication Limited) is a Chinese electronics company headquartered in Huizhou, Guangdong Province. It designs, develops, manufactures, and sells consumer products including televis ...
demonstrated their Cinema Wall featuring a 4K microLED display with maximum brightness of 1,500cd/m and contrast ratio produced by their subsidiary China Star Optoelectronics Technology (CSoT).


See also

*
OLED An organic light-emitting diode (OLED or organic LED), also known as organic electroluminescent (organic EL) diode, is a light-emitting diode (LED) in which the emissive electroluminescent layer is a film of organic compound that emits light i ...
*
AMOLED AMOLED (active-matrix organic light-emitting diode, ) is a type of OLED display device technology. OLED describes a specific type of thin-film-display technology in which organic compounds form the electroluminescent material, and active matrix ...
* Mini LED


References

* * *


External links


"The Long View With John Doerr"
John Doerr of KPC&B describes the microLED concept, starts around the 5 minute mark.
Crystal LED
- Sony
LED screens are significantly different from microLED
{{Display technology Display technology Light-emitting diodes