AR HUD currently has three common technologies, namely TFT, DLP and LCoS, and three emerging ones, namely LBS-based MEMS, OLED on silicon i.e. OLEDoS and Micro LED.
Image source: Internet
The purchase price of ordinary HUD is about 1000-1500 RMB, the AR HUD with TFT is about 2000-2500 RMB, and the DLP is 3000-4000 RMB.
HUD core components include PGU image generation unit and free-form reflector, large HUD manufacturers are from the automotive instrumentation field, complete upstream layout, able to produce their own PGU and free-form reflector, free-form reflector production threshold is very high, need 100,000 class clean room and precision optical coating experience. The emergence of AR HUD has led to a rapid increase in the complexity of HUD software, which also takes into account positioning, sensor fusion and ADAS, so the industry has been subdivided, with some HUD companies specializing in software, and some companies from the original optical field entering, specializing in PGU and free-form reflectors, lengthening the industry chain. Software companies are further subdivided, with one part specializing in HMI human-machine interaction design and another part specializing in joint work with instruments and even ADAS systems. Domestic Sunyu was the first to engage in the study of free-form reflectors, and should be the best in China.
The technical route of HUD should actually be the technical route of PGU, but PGU is not the whole of HUD, other parts can also affect the performance and cost of HUD.
Chart source: Public information collation
The biggest disadvantage of TFT is the low resolution, it is impossible to display complex patterns, contrast and brightness is also the lowest, sunlight can not see, other disadvantages are light for the polarized light, can not bring sunglasses, and then there is the projection of the larger the area, the stronger the sunlight backflow, the temperature rises quickly, if not done, a few minutes PGU burned, reduce the amount of incoming light is the most basic solution, but this means that the amount of outgoing light is also less, and the temperature rises quickly. Contrast and brightness performance is worse. The advantage of TFT is low cost and mature technology. TFT-LCD suppliers are mainly Japan Kyocera and JDI, while the domestic Xinli and Tianma.
Image source: Internet
Image source: Internet
The disadvantage of DLP is the need for parallel light sources, the volume is too large, the AR HUD used in the Mercedes-Benz S-Class in order to achieve the best results, the entire system up to 27L, the second generation of the domestic GS8 is 14.5L, only a very large model to allow such a large volume. This with light waveguide can significantly reduce the volume, but compared to other routes, the volume is still slightly higher. Then there is the high cost. The advantage is the high reliability, do not have to worry about sunlight backflow. VID virtual scene distance can be more than 7.5 meters, more suitable for doing two or more images. FOV is also relatively wide.
DLP ARHUD on the Mercedes-Benz S-Class. photo credit: Mercedes-Benz
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LCoS is more active recently, LCoS is not a new technology, as early as the 1990s has appeared, around 2012 to become the best technology for AR glasses, Google for this reason once acquired part of the shares of Taiwan Province of China’s Chikei Optoelectronics, but AR glasses have never been able to open the market, the key reason is that glasses can not be too heavy, therefore, heat dissipation, range has become the death knell of AR glasses. To this day, it can not be solved. Since 2014, LCoS has been silent for a long time, and around 2020, LCoS will come out again.
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In the LCoS structure, the liquid crystal device is fabricated on a monocrystalline silicon substrate to form an image by reflecting light. The liquid crystal body rotates the polarization of light, and fluctuations in the electric field are used to control the amount of rotation of the liquid crystal body, which determines the amount of light that passes through the liquid crystal layer. In other words, the light source “passes through the polarization filter to the device, and the liquid crystal acts as a gate or valve to control the amount of light that reaches the reflective surface. The higher the voltage received by the crystal of a particular pixel, the more light the crystal allows to pass. LCoS can be used not only in the display field, but also has a place in optical communications, which is one of the reasons why Huawei cut in. Reconfigurable all-optical switching (OXC) systems are a core component of modern fiber optic communication networks, supporting the high growth in network capacity over the last decade. Wavelength selective switches (WSS) are the core component of OXC systems, which typically have one input port and n output ports and can switch any wavelength channel received at the input port to any output port. An OXC system typically consists of multiple WSSs paired in a cascade, giving fiber optic network operators the flexibility to schedule individual wavelength channels at the network node, allowing fiber optic communication networks to be reconfigurable at the wavelength level, significantly reducing network transmission and operation costs. Early WSS can be based on pure phase-based LCoS technology, liquid crystal technology or MEMS technology. In recent years, WSS based on LCoS technology has become the mainstream choice in the industry, and WSS systems have extremely high requirements on reflectivity, diffraction efficiency, instantaneous phase jitter and reliability of LCoS devices, and only a few LCoS vendors can support this application. Huawei is the dominant player in optical communication and is naturally familiar with LCoS. LCoS is prone to deformation under strong light irradiation, resulting in uneven picture, while strong light comes and goes 2 times inside the LCoS chip, which is equivalent to halving the thickness of the liquid crystal layer of LCoS, and the strong light effect also reduces the life of the liquid crystal. These problems have improved in recent years, especially the current car replacement cycle has been greatly shortened, unlike the past a car to drive a dozen years or even decades, and now young people want to replace the car in 5 years. The industry’s LCoS suppliers, mainly contains seven companies: Compound Photonics, Raontech, Syndiant (crystal classical), Himax (Chikei Optoelectronics), Ominivision, 4DD (a wholly owned subsidiary of Kopin) and Jasper. but a number of major Japanese manufacturers Sony, Panasonic, Canon, Fuji, and Epson are capable of producing LCoS, but the market is too small for them to see. The first to launch the car AR HUD with LCoS is Qi Jing, Qi Jing in this field of research and development for more than 20 years, the technology accumulated deep, AR glasses field near monopoly, 2021 launched phase modulation LCoS, the main double layer (Plane) display AR HUD, but also can be used for WSS, production capacity of up to 300,000 pieces per month, and plans to increase to 2 million pieces / month. Domestic Howell Technology also launched OP02220 in 2020.
Image source: Internet
OP02220 target market is still mainly AR glasses, LC operating temperature range between 10 ℃ – 70 ℃, high integration, integrated frame cache and drive, is the industry’s first single-chip LCoS display. The domestic market is also more active in South Korea’s RANOTECH, Shanghai Huixinchen Industry and Nanjing Core Vision Yuan Electronics. The most significant advantage of LCoS is high resolution and high contrast ratio. Limited by the complexity of the process, the native resolution of DLP devices has always been stagnant at 2 K. While the native resolution of LCoS devices reach 4 K and 8 K, so the current mainstream high-end laser projection digital cinema system are using LCoS technology. Then there is the small size, LCoS preferred target market is AR glasses, the volume is naturally very small. If with optical waveguide, the volume can be even smaller. Then is the low cost, after all, it is CMOS process, most of the manufacturing process is similar to the chip, the amount of large cost can be made very low. LCoS disadvantages include low brightness, reflective devices naturally lower brightness than the penetrating type, LED as a light source, this disadvantage is more obvious, it is best to use the laser as a light source, but the car grade laser is basically a monopoly of Nichia Chemical, especially green light, the price is very high. The light source is polarized light, can not be used with sunglasses. In addition there are scattered spot problem. Finally, look at the LBS.
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Laser scanning schematic, LBS has been a long time, in 2010 Pioneer had made it into a car HUD, the price is more than 5,000 U.S. dollars. the advantage of LBS is the contrast and brightness is super high, sunlight is also no problem at all, is the best visual effect of HUD, no one. The size is also very small, about the same compared to LCoS, and Microsoft once intended to use LBS in AR glasses. The disadvantage is that it is expensive and difficult to improve the resolution, but it is enough for HUD, Panasonic claims to be able to do 4K, but it is generally 1280*720, the resolution increase will lead to a cost surge. Laser light source heat dissipation is also a problem, but it is easy to solve. More optimistic about LBS manufacturers are Japan’s Panasonic, Pioneer, China Taiwan’s FIC (Popular Computer), Shanghai Fengbao Electronics, Zhejiang Vision Mirror Sensing Technology, the United States MicroVision and Microsoft. In addition to the above-mentioned four, there are two lesser-known, namely OLEDoS (silicon-based OLED) and Micro-LED.
OLEDoS, also known as Micro OLED, is an active organic light emitting diode display device that combines CMOS process and OLED technology, using monocrystalline silicon as the active driving backplane. The silicon-based OLED device structure consists of two parts: the driver backplane and the OLED device. The driver backplane is fabricated using a standard CMOS process to form the pixel circuit, row drive circuit, and other functional circuits required for silicon-based OLED microdisplays. The top metal layer of the CMOS circuit is usually made with highly reflective metal as the anode of the OLED device, and the OLED device part usually includes a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, and a translucent top electrode. A thin film encapsulation layer is fabricated on the top electrode for water and oxygen barrier, followed by spin-coating a transparent laminating adhesive layer and laminating glass for device strength protection. Silicon OLED adopts the mature integrated circuit CMOS process and combines the outstanding advantages of OLED such as fast response, large viewing angle, and low power consumption to realize not only the active addressing matrix of display pixels, but also the drive control circuit of various functions such as SRAM memory TCON, which reduces the external connection of the device, increases the reliability, and realizes light weight with self-illumination, thin thickness, light weight, large viewing angle, and light efficiency. It is especially suitable for near-eye display devices such as AR/VR because it is easy to achieve high PPI (pixel density), easy to carry, and low power consumption. At present, Sony, Panasonic, Samsung, LGD, TCL, BOE are all making efforts in this field, Sony technology is the most excellent, in the leading position, there are already commercial products, Samsung and LGD are in hot pursuit. OLEDoS advantages and disadvantages and LCoS close, but there are still questions about the life of OLEDoS.
Micro LED is theoretically the best display technology. micro LED is LED micro technology, refers to the traditional LED array, miniaturization after addressing the huge amount of transfer to the circuit substrate, forming ultra-small pitch LED, the millimeter level LED length further miniaturized to micron level, in order to achieve ultra-high pixel, ultra-high resolution. micro-LED in the brightness index, performance is significantly higher than OLEDoS, has a greater advantage. Micro-LED pixel pitch is generally less than 10um, with micron-level pitch, each point of pixel can be addressed and controlled and single-point drive luminous. Compared with other LEDs, Micro-LED has the highest luminous efficiency and luminous energy density, and there is still room for improvement. Micro-LED resolution is also easy to reach 4K.
Micro-LED life is also longer, the main drawback is that the technology maturity is very low, especially the full color is very difficult, but in the field of car HUD, the demand for color is very low. Technical maturity, chip substrate, huge transfer, jointing, drive and other aspects are not mature, the yield is very low, the main manufacturers are not strong will, because Samsung, Sony, LG display these giants in the field of OLED are invested in huge amounts of research and development funds, these giants want to OLED technology life as long as possible, to get more profits, Micro-LED is only concerned about, do not want to sincerely do As long as Micro-LED does not threaten the market of OLED, these giants will not sincerely do Micro-LED, and small companies lack experience in mass production, so that from 2015 to now, Micro-LED does not have much substantive progress. HUD is mostly optional, not much standard, manufacturers care most about the cost, the next 5-10 years, I’m afraid TFT is still the mainstream. LCoS is afraid that the transition technology, the big manufacturers began to continue to make efforts in OLEDoS, the next 5 years is likely to replace LCoS, Micro-LED is the ultimate direction, but may have to wait until 10 years later. Difficult to reduce costs, the future is limited to the high-end. The future LBS will challenge the high-end position of DLP, luxury brands may prefer LBS.
