People are always pursuing brighter, thinner and more energy-saving display methods, and cathode ray tubes can no longer meet people's expectations. So after 70 years of glorious history, the screen of cathode ray tube began to gradually withdraw from the historical stage, giving way to the LCD screen and plasma screen invented in the 1960s in the domestic and commercial markets. Emerging screens are often composed of closely arranged small grids, and finally a mosaic-like picture is spelled out: plasma screens are actually many small fluorescent lamps, while liquid crystal screens are many small capsules filled with liquid.
These technologies are mature now, but people's needs are endless. The development and innovation of microelectronic technology and new materials bring more challenges to the screen, which may blur the concept of the screen: the screen using organic light-emitting diodes (OLEDs) can be curved or transparent; The electronic paper screen represented by EInk is compressing the living space of traditional books; Quantum dot screen may become the standard of home display equipment in a few years; Glasses and even hidden glasses displays make the display ubiquitous-even the idea of directly stimulating the visual nerve to produce light sensation can completely make the screen invisible.
Organic light-emitting diodes may be considered as the stars of tomorrow on the screen. Each display unit is like a hamburger, with electrodes at the top and bottom and a thin layer of luminescent material sandwiched between them. When electrified, the energy released by electrons jumping from high energy level to low energy level will be transmitted in the form of visible light-the same principle as the ubiquitous light-emitting diodes around us. Because of the different materials used, organic light-emitting diodes produce red, green and blue primary color displays, which are combined into various colors. Although this technology was invented in 1975, it has gradually shown great advantages in recent years and has become a hot spot pursued by manufacturers: it does not need backlight, has high luminous efficiency at low voltage, excellent contrast and brightness, is thinner and lighter, and its response speed is much faster than that of LCD screen. In addition to these advantages in display performance, it has other additional advantages: using different substrate materials and different electrodes, people have been able to make flexible displays that can be rolled into a roll-although they can't be folded in half like paper, they can already be wound on pipes with a diameter of several millimeters-and transparent display devices, which makes the concept of "screen" subverted again and again.
When flexible screen and transparent screen are not only props in sci-fi and fantasy movies, our life will be like magic. Windows and mirrors can display pictures and information, and can even be used as lighting equipment. The size of mobile phones and tablets can be made smaller. The screen can bend with the direction of the wall, and any imaginable scenery can be created. Posters can show different contents according to the interests of each audience, and GPS and dashboard can be presented directly on the windshield of the car-these are no longer fantasies.
In fact, we can now buy mobile phones that use organic light-emitting diodes as screens, and more organic light-emitting diode products are also under development. Toshiba has developed a notebook computer with a transparent screen, which can achieve 60% transparency; As for the screen that can be rolled into a roll, it appeared in the technology product exhibition seven or eight years ago. These products did not appear in the market because of the limitation of cost and yield. The packaging of organic light-emitting diode products is still one of the technical difficulties, and in the process of flexible screen processing, small dislocation between multilayer electronic components will produce waste products. These technical problems may be broken through in a few years, but before that, large flexible or transparent OLED screens can only be seen in laboratories and trial-production workshops.
While the OLED screen is trying to enter commercial times, more competitors are eyeing it. Although the Eink e-book technology we see on Kindle or other e-books is extremely energy-saving, the refresh rate is too low to display real colors and can only be used for extremely limited purposes. But a new kind of screen seems to have the possibility of replacing organic light-emitting diodes: quantum dot screen, which has all the advantages of organic light-emitting diodes and can bloom more colors.
The name "quantum dot", which sounds a bit sci-fi, was put forward by physicists at Yale University in the United States, and is usually called "nano-dot" or "zero-dimensional material". Quantum dots are a special kind of nano-materials, which are often tiny particles formed by taking gallium arsenide, cadmium selenide and other semiconductor materials as the core and wrapping another semiconductor material outside. Each quantum dot particle is only a few nanometers to dozens of nanometers in size and contains hundreds to millions of atoms. Because of its small size, the movement of internal electrons in all directions is limited, so the quantum confinement effect is particularly significant, and it can also emit fluorescence of specific colors. After the electrons in quantum dots are irradiated by an external light source, they absorb the energy of photons and jump from a stable low-energy level to an unstable high-energy level. When the stability is restored, the energy will be released in the form of photons with a specific wavelength. This way of exciting fluorescence is similar to other semiconductor molecules; The difference is that the fluorescence color of quantum dots is closely related to their size. Only by adjusting the size of quantum dots can pure light of different colors be obtained.
Similar to organic light-emitting diodes, each color pixel of the quantum dot screen corresponds to a thin film light-emitting diode, and the diode emits light to provide energy for the quantum dots, which excites the quantum dots to emit light with different intensities and colors, and combines them into an image in human eyes. Due to the extremely narrow wavelength range and pure color of quantum dots, the screen of quantum dots is fresher and brighter than other screens. Samsung galaxy released the world's first 4-inch full-color quantum dot display screen in February this year, which has higher color and brightness, but the cost is only half of that of the OLED screen. When this technology becomes more mature, it may have the strength to compete with organic light-emitting diodes.
From the user's point of view, a screen may meet everyone's needs, as long as the screen is placed in the right position-for example, on the human nose. Since Google announced the development of glasses display last year, it seems that all major IT vendors have discovered this new blue ocean together and have joined in it. Nowadays, there are only a handful of IT vendors that have not developed glasses display equipment. Because people realize that the equipment that can occupy people's whole field of vision most of the time every day is actually this 600-year-old transparent film.
Now Google Glass, which has entered the testing stage, adopts projection technology, that is, a small picture is projected directly from the glasses frame to the user's eyes, and the principle is similar to that of home projector. Considering the current technical level, this may be the most suitable choice, but it is not necessarily the only way. In the development team of Google Glass, there is a prominent name: Dick Parviz, a scholar who used to work in the University of Washington in Seattle, made the world's first contact lens display in 2008. At that time, he had realized the functions of displaying patterns on contact lenses, transmitting data and wirelessly supplying power, but this kind of display device which is in close contact with glasses needs to undergo more tests. After all, when the last barrier between our eyes and the world-eyelids-no longer exists, any slight negligence will bring great misfortune. Even so, we can still imagine his role in the Google Glass team; Maybe three or five years later, the screen will be directly attached to our cornea, so that the digital world and the real world overlap.
At that time, the screen will become a very personal tool, and now this kind of screen all over the world may even disappear gradually; After all, we already have a display device that can occupy the whole field of vision. Why should we put more in other places?
With the development of technology, the screen connecting us with the digital world will disappear completely-more precisely, it will become a small device implanted in our bodies. As early as the 1920s, people have discovered that it is natural to directly stimulate the optic nerve with electric current to produce light sensation, and to recreate vision in this way. Just as we have been able to restore the hearing of the hearing impaired through cochlear implantation.
The reason why we can implant the screen into the brain is that our eyes are actually similar to digital cameras. The cornea and lens of the eye are equivalent to the lens, the retina behind the eyeball is the photosensitive device, the optic nerve is equivalent to the line connecting the photosensitive device and the memory card, and the visual cortex behind the brain is the memory card and post-processing software. Stimulating the optic nerve with electric current can make the brain receive visual signals-although the actual process is quite complicated. In this field, people have tried for nearly 40 years, and some artificial implants have appeared on the market to help patients with specific eye diseases get light perception, but they are far from being comparable to the retina that has evolved for hundreds of millions of years. Perhaps within this century, we will see the implanted screen with the same effect as the native retina, and even make the brain confused about which is real and which is virtual.