The Modern Display Story

The display is the most-used interface in modern technology. The average person in a developed country looks at a screen for more than seven hours per day, and the global display market is more than $150 billion per year. The story of how the bulky, power-hungry cathode ray tube was replaced by the thin, efficient, beautiful flat panel — and what comes next — is, in retrospect, one of the most consequential materials-and-physics stories of the late twentieth and early twenty-first centuries.

The cathode ray tube and the first 100 years

The cathode ray tube (CRT), invented by the German physicist Karl Ferdinand Braun in 1897, was the dominant display technology for the entire twentieth century. The CRT works by scanning an electron beam across a phosphor-coated screen, exciting the phosphor to emit light. The electron beam is generated by an electron gun at the back of the tube, focused and deflected by magnetic or electrostatic fields, and modulated in intensity to produce the image. The phosphors used in colour CRTs (typically a mixture of zinc sulphide and rare-earth compounds) emit red, green, or blue light depending on their composition. The CRT television was the dominant consumer electronic product of the second half of the twentieth century, with more than 1.5 billion units sold worldwide over its lifetime.[1, 2, 9]

The CRT had many virtues. The image quality was excellent (high contrast, wide viewing angle, fast response), the manufacturing was well understood, and the cost was low. The CRT also had significant limitations: it was heavy (a 30-inch CRT weighed more than 50 kg), it was bulky (the depth of the tube was roughly equal to the screen diagonal), and it was power-hungry (a 30-inch CRT consumed more than 200 watts). The largest practical CRT was about 40 inches, and the weight and the depth made it difficult to mount on a wall. The CRT was, in other words, a technology that was ripe for replacement, and the replacement came in the form of the flat panel.[1, 2, 9]

The transition from CRT to flat panel began in the late 1990s, with the introduction of plasma displays and early LCDs for computer monitors. The transition accelerated in the 2000s, as the cost of LCD panels fell and the size increased. The last CRT television was manufactured in 2012, and the last CRT computer monitor in 2015. The transition was, in retrospect, remarkably fast: a 100-year-old technology was replaced in less than 20 years. The driving forces were the obvious advantages of flat panels (thin, light, low power) and the rapid cost reduction of LCD manufacturing in East Asia, particularly in South Korea, Taiwan, and China. The dominant LCD manufacturers, in 2024, are BOE (China), LG Display (South Korea), and Samsung Display (South Korea).[1, 2, 9]

LCD: the flat-panel revolution

The liquid crystal display (LCD) is, in essence, a light valve. A backlight (originally a cold-cathode fluorescent lamp, now a white LED) shines through a layer of liquid crystal, which can be made transparent or opaque by applying a voltage. The liquid crystal is a state of matter between a solid and a liquid: the molecules are elongated and can be aligned by an electric field. The alignment of the molecules rotates the polarisation of the light passing through them, and the combination of a polarising layer and the liquid crystal acts as a controllable shutter. The LCD was invented by RCA in 1968 and commercialised in the 1970s for calculators and watches. The first LCD television was a 14-inch Sony in 1983, but the technology was not competitive with CRT until the 2000s.[2, 3, 10]

The breakthrough that made LCDs competitive was the development of the thin-film transistor (TFT) array. Each pixel in an LCD is controlled by one or more TFTs, which switch the voltage on the pixel in response to a signal on the row and column lines. The TFTs are made of amorphous silicon (a-Si) or, in higher-end displays, of polycrystalline silicon (poly-Si) or of indium gallium zinc oxide (IGZO). The TFT array is fabricated on a glass substrate using a process similar to that of a semiconductor wafer, but on a much larger scale (the largest LCD panels, in 2024, are 2,500 mm × 2,200 mm, the so-called 10.5-generation fab). The colour is provided by a colour filter, with red, green, and blue subpixels, and the light from the backlight is selectively transmitted through the liquid crystal to produce the desired colour and intensity at each pixel.[2, 3, 10]

The performance of LCDs has improved dramatically over the past two decades. The response time has fallen from tens of milliseconds in the 1990s to a few milliseconds today, the contrast ratio has risen from a few hundred to many thousands, the colour gamut has widened to cover most of the Rec. 2020 standard, and the resolution has risen from VGA (640 × 480) to 8K (7,680 × 4,320). The remaining limitations of LCDs are the dependence on a backlight (which limits the contrast and the depth), the limited viewing angle (early LCDs were viewable only from directly in front), and the slow response time (which causes motion blur). The contrast and the viewing angle have been improved by IPS (in-plane switching) and VA (vertical alignment) technologies; the response time has been improved by overdrive (applying a brief over-voltage at the start of each transition). The best LCDs, in 2024, are remarkably good, and remain the most cost-effective display technology for most applications.[2, 3, 10]

OLED: emissive displays

The organic light-emitting diode (OLED), first demonstrated by Ching W. Tang and Steven Van Slyke at Eastman Kodak in 1987, is an emissive display: each pixel is a tiny organic LED that emits light directly when a current is passed through it. The active material is a small organic molecule (such as tris(8-hydroxyquinolinato)aluminium, or Alq3, for green) or a polymer (such as poly(p-phenylene vinylene), or PPV, for yellow-green). The OLED is sandwiched between two electrodes, at least one of which is transparent (typically indium tin oxide, ITO), and the whole stack is deposited on a glass or plastic substrate. The OLED is, in this sense, a solid-state device, and the pixels are individually addressable through a TFT array (similar to LCD) or through a passive matrix (for simpler displays).[3, 4, 11]

OLEDs have several advantages over LCDs. They do not need a backlight, so they can be made thinner and lighter. They can be made flexible (the substrate can be a plastic film, allowing roll-up or foldable displays). The contrast is essentially infinite (the pixels can be turned off completely, producing true black). The viewing angle is close to 180 degrees. The response time is less than a millisecond, much faster than the best LCDs. The colour gamut is wide (particularly for OLEDs that use red, green, and blue emitters directly, without colour filters). The disadvantages are the limited lifetime (the blue OLED, in particular, degrades faster than red and green), the peak brightness (lower than the best LCDs with quantum-dot backlights), the susceptibility to burn-in (a static image displayed for a long time can leave a permanent ghost), and the cost (still higher than LCD, particularly for large panels).[3, 4, 11]

The OLED market is dominated by Samsung Display (which makes most of the OLED panels for smartphones, including Apple’s iPhones) and LG Display (which makes most of the OLED panels for TVs). The Chinese display makers, particularly BOE, are catching up, and the next generation of OLED factories (8.6-generation fabs, with substrates larger than 2,250 mm × 2,600 mm) is being built in China. The combination of falling costs, increasing supply, and improving performance is making OLEDs the default display technology for high-end smartphones, for high-end TVs, and for many other applications. The first foldable phones (Samsung Galaxy Fold, 2019; Huawei Mate X, 2019) used OLED displays, and the first rollable TVs (LG Signature OLED R, 2020) used OLED displays. The OLED is, in this sense, the dominant display technology of the 2020s.[3, 4, 12]

Quantum dots: backlighting reborn

Quantum dots are nanocrystals of semiconductor, typically 2–10 nanometres in diameter, made of cadmium selenide, cadmium sulphide, indium phosphide, or perovskite. The colour of light they emit is determined by their size, because of quantum confinement: the smaller the dot, the larger the band gap, and the bluer the emitted light. The colour is extraordinarily pure (full width at half maximum of 20–30 nm, vs 50–100 nm for the best phosphors), and the colour can be tuned precisely by controlling the size during synthesis. Quantum dots have been studied since the 1980s, but their application to displays was limited by the difficulty of producing them at scale and by concerns about the toxicity of cadmium.[4, 5, 13]

The first commercial application of quantum dots in displays was as a backlight technology for LCDs. A blue LED backlight is converted to red and green by a quantum-dot layer (either a film or a tube of quantum dots embedded in the LCD panel), producing a much purer white than a phosphor-converted LED, and therefore a wider colour gamut. The first commercial quantum-dot TV was the Sony X9000 in 2013. By 2024, quantum-dot LCDs (called “QLED” by Samsung and TCL, “Triluminos” by Sony) account for more than 10 percent of the TV market and more than 30 percent of the high-end TV market. The cost premium, compared to a standard LCD, is about 30–50 percent, and the picture-quality improvement is substantial.[4, 5, 13]

The more ambitious application of quantum dots is in quantum-dot electroluminescent displays (QD-EL or EL-QD), in which the quantum dots are the active material in an emissive display, similar to OLED. The first prototypes, demonstrated by Samsung in 2011, had a colour gamut and a viewing angle comparable to OLED, but with potentially longer lifetime and lower cost. The challenge, which has slowed the commercialisation, is the efficiency of the charge injection into the quantum dots and the stability of the devices under operation. Samsung Display has recently announced that it plans to invest in QD-EL production, with the first products expected in 2025–2026. If successful, QD-EL will combine the emissive advantages of OLED with the colour purity of quantum dots, and may be the dominant display technology of the 2030s.[4, 5, 14]

MicroLED: the next frontier

MicroLED is an emissive display technology in which each pixel is a tiny inorganic LED, typically less than 50 micrometres across, made of gallium nitride (for blue and green) or of a phosphide (for red). The LEDs are grown on a sapphire or silicon carbide substrate using the same metalorganic vapour phase epitaxy (MOVPE) process used for conventional LEDs, then transferred to a display backplane with micron precision. The transfer process is, in practice, the most difficult part of the manufacturing: a 4K display has 25 million subpixels, each of which must be placed with an accuracy of a few micrometres. The dominant transfer methods are pick-and-place (using a robot to pick up each LED and place it on the backplane), fluidic assembly (using a liquid to carry the LEDs to the right place), and monolithic integration (growing the LEDs directly on the backplane, which is currently only possible for small displays).[5, 6, 15]

MicroLEDs have several advantages over OLEDs. They are much brighter (10,000 nits or more, vs 1,000 nits for the best OLEDs), they last much longer (more than 100,000 hours to half-brightness, vs 30,000 hours for OLED), and they are more power-efficient (the external quantum efficiency is higher, and the operating voltage is lower). They are also more robust (no organic material to degrade) and have a wider operating temperature range. The disadvantages are the manufacturing cost (the transfer process is slow and expensive) and the size limitation (most MicroLED displays, in 2024, are 100 inches or smaller, and the cost scales roughly linearly with the area). The first commercial MicroLED products are Samsung’s “The Wall” modular displays for commercial use (introduced in 2018), and the first consumer MicroLED TVs (89–114 inches) cost more than $100,000 in 2024.[5, 6, 15]

The technology is improving rapidly. The transfer yield is rising, the cost is falling, and the size is increasing. Several companies, including Samsung, LG, Sony, and a number of Chinese startups, are investing heavily in MicroLED manufacturing. The first “affordable” MicroLED TVs (in the $5,000–$10,000 range, comparable to high-end OLED TVs) are expected in 2026–2028. The technology is expected to become the dominant high-end display technology in the late 2020s, and the dominant display technology overall in the 2030s. The combination of high brightness, long lifetime, and low power consumption makes MicroLED the technology of choice for augmented-reality glasses, for head-up displays in cars, and for outdoor signage — applications where OLED is too dim, too short-lived, or too fragile.[5, 6, 15]

The future: holographic and neural

The next decade of display technology will see the gradual replacement of the flat panel with three-dimensional and even non-planar displays. Light-field displays, which reconstruct the light field of a 3D scene, allow multiple viewers to see a true 3D image without glasses. The technology uses a microlens array or a parallax barrier to send different rays of light in different directions, simulating the way a real object emits light. The first commercial light-field displays, introduced in 2018 for professional applications (medical imaging, engineering design), are still expensive and have a limited viewing angle, but the technology is improving. The combination of light-field displays with eye tracking can provide a more comfortable 3D experience with a wider viewing angle, and several companies are now working on consumer light-field displays for VR and AR applications.[6, 7, 16]

Holographic displays, which use coherent laser light to record and reconstruct a true hologram, are still in research but have been demonstrated in the lab. A true hologram records both the amplitude and the phase of the light, and can be reconstructed in three dimensions with full parallax (the image changes as the viewer moves, just as a real object would). The challenge is the data rate: a full-colour, high-resolution hologram contains more than a terabit of data per frame, and the display must modulate the light at this data rate. The first commercial holographic displays, expected in the late 2020s, will use spatial light modulators (SLMs) based on liquid crystal on silicon (LCoS) or on micro-mirror arrays, and will be limited to small sizes and high prices. The technology is, in this sense, the display equivalent of a quantum computer: theoretically transformative, but practically limited for the foreseeable future.[6, 7, 16]

The very long-term future of displays may not involve a display at all. Brain-computer interfaces (BCIs), in the form of non-invasive headsets or implanted electrodes, may eventually be able to project images directly into the visual cortex, bypassing the eye entirely. The technology is, in 2024, at an early stage: the most advanced non-invasive BCIs can detect simple visual evoked potentials, and the most advanced implanted BCIs (such as Neuralink‘s) can record from thousands of neurons but cannot yet produce visual images. The full replacement of the display by a neural interface is, at best, decades away, and may never happen. But the trend is clear: the display, as a physical object, is gradually being augmented — and may eventually be replaced — by other technologies. The next 100 years of display technology will be, in this sense, even more disruptive than the last.[6, 7, 17]

Comparison: leading display technologies (2024)

Technology	Mechanism	Max size (2024)	Peak brightness	Contrast ratio	Colour gamut	Lifetime (hours)	Best suited to
CRT (legacy)	Electron beam on phosphor	40 in	~500 nits	~10,000:1	~70% Rec.2020	~20,000	Legacy, vintage
LCD (IPS/VA)	Backlight + LC shutter	110 in	~1,000 nits	~5,000:1	~70% Rec.2020	~50,000	Mainstream TV, monitor
QD-LCD (QLED)	Quantum-dot enhanced LCD	98 in	~2,000 nits	~5,000:1	~90% Rec.2020	~50,000	High-end TV, monitor
OLED (WOLED, QD-OLED)	Emissive organic LED	97 in	~1,000 nits	~1,000,000:1	~80% Rec.2020	~30,000	Smartphone, high-end TV
MicroLED	Emissive inorganic LED	114 in	~5,000 nits	~1,000,000:1	~100% Rec.2020	~100,000	Premium, AR, outdoor
QD-EL (in dev.)	Emissive quantum dot	Prototype	~1,000 nits (target)	~1,000,000:1 (target)	~100% Rec.2020 (target)	TBD	Next-gen TV (2025+)

Key numbers

• ~$150 billion: global display market per year (2024).
• ~7 hours: average daily screen time in developed countries (2024).
• ~110 inches: largest commercial LCD TV (2024).
• ~97 inches: largest commercial OLED TV (2024).
• ~114 inches: largest commercial MicroLED TV (2024).
• ~$100,000: price of a 110-inch MicroLED TV (2024).
• ~5,000 nits: peak brightness of a MicroLED display (2024).
• ~1,000 nits: peak brightness of a high-end OLED TV (2024).
• ~30,000 hours: half-brightness lifetime of an OLED display.
• ~100,000 hours: half-brightness lifetime of a MicroLED display.
• 1897: year of the Braun CRT.
• 1987: year of the first OLED at Kodak.
• 2013: year of the first quantum-dot TV.

References

1. Wikipedia, “Cathode ray tube.” (Standard reference on the CRT and its 100-year history.) https://en.wikipedia.org/wiki/Cathode_ray_tube
2. Wikipedia, “Liquid-crystal display.” (Standard reference on LCDs, with a section on the history.) https://en.wikipedia.org/wiki/Liquid-crystal_display
3. Wikipedia, “OLED.” (Standard reference on OLEDs, with a section on the history.) https://en.wikipedia.org/wiki/OLED
4. Wikipedia, “Quantum dot.” (Standard reference on quantum dots and their application in displays.) https://en.wikipedia.org/wiki/Quantum_dot
5. Wikipedia, “MicroLED.” (Standard reference on MicroLED displays, with a section on the manufacturing challenges.) https://en.wikipedia.org/wiki/MicroLED
6. Wikipedia, “Light field display.” (Standard reference on light-field displays, with a section on the data-rate challenge.) https://en.wikipedia.org/wiki/Light_field_display
7. Wikipedia, “Holographic display.” (Standard reference on holographic displays, with a section on the history.) https://en.wikipedia.org/wiki/Holographic_display
8. Wikipedia, “Neuralink.” (Standard reference on Neuralink, the leading brain-computer interface startup.) https://en.wikipedia.org/wiki/Neuralink
9. Wikipedia, “Karl Ferdinand Braun.” (Standard reference on Karl Ferdinand Braun, inventor of the CRT.) https://en.wikipedia.org/wiki/Karl_Ferdinand_Braun
10. Wikipedia, “TFT LCD.” (Standard reference on TFT LCDs, the dominant flat-panel architecture.) https://en.wikipedia.org/wiki/TFT_LCD
11. Wikipedia, “Ching W. Tang.” (Standard reference on Ching W. Tang, co-inventor of the OLED.) https://en.wikipedia.org/wiki/Ching_W._Tang
12. Wikipedia, “Samsung Display.” (Standard reference on Samsung Display, the dominant OLED panel manufacturer.) https://en.wikipedia.org/wiki/Samsung_Display
13. Wikipedia, “Cadmium selenide.” (Standard reference on cadmium selenide, the most common quantum-dot material.) https://en.wikipedia.org/wiki/Cadmium_selenide
14. Wikipedia, “Indium phosphide.” (Standard reference on indium phosphide, a non-toxic alternative to cadmium for quantum dots.) https://en.wikipedia.org/wiki/Indium_phosphide
15. Wikipedia, “Gallium nitride.” (Standard reference on gallium nitride, the material used for blue and green MicroLEDs.) https://en.wikipedia.org/wiki/Gallium_nitride
16. Wikipedia, “Parallax barrier.” (Standard reference on parallax barrier displays, a way to achieve 3D without glasses.) https://en.wikipedia.org/wiki/Parallax_barrier
17. Wikipedia, “Brain - computer interface.” (Standard reference on brain-computer interfaces, with a section on visual prosthetics.) https://en.wikipedia.org/wiki/Brain%E2%80%93computer_interface