Different LED technology: Tesla lighting technology decryption

16/06/2022
On December 24, 2021, Tesla launched a major update for car owners. The new UI of the car v11 and the FSD Beta V10.8 version. After the update, the car owners were pleasantly surprised to find that the light show function was added, in which the headlights displayed "TESLA" The pattern is amazing.

Part of the reason is that Tesla has not emphasized this matter in the publicity before, and people are instantly pleasantly surprised when they see this situation; another part of the reason is that whether it is a matrix LED headlight or a laser headlight, it is basically a "light factory". "- Audi's gimmick, due to the high cost and high installation cost, is still far from ordinary consumers, while Tesla's standard configuration in Model 3 and Model Y models starting at 200,000 or 300,000 should be said to be more conscientious. Contrary to the lively display in the circle of friends, Tesla is so low-key that it makes people feel that this is by no means simple.

The author has been engaged in the LED industry for many years. Out of technical curiosity, I have verified relevant public information through multiple parties, hoping to restore the technical route of Tesla's headlight source.
According to public information, Tesla's headlights are manufactured by HELLA, a well-known German spare parts supplier, and the supplier of the light-emitting unit is Samsung Electronics.

"In April 2021, Samsung Semiconductor released a new generation of automotive light source PixCell LED modules, which will be used in automotive smart headlights.
According to Samsung Semiconductor, the newly developed PixCell LED is an ultra-small LED solution suitable for in-vehicle smart headlights, which can realize lighting control through a smaller light-emitting area and light-dark contrast.

In addition, Samsung's products reduce the light-emitting area to 1/16 of that of ordinary smart headlights, making the entire lamp smaller, helping to improve vehicle fuel efficiency, and increasing the design flexibility of headlights. "
From the dismantling analysis released by the domestic research institute-Auto Lamp Research Institute, Tesla does use Samsung Electronics' PixCell LED technology. Therefore, it is necessary to dig a little deeper into the technology.
In order to improve the display effect of PixCell LED and prevent crosstalk between adjacent light sources, a silicon wall partition is set up between each pixel.
From the final display effect, each pixel unit in the PixCell LED achieves a single-sided light-emitting effect. According to past knowledge, the chip segment that can achieve this light-emitting effect is mainly thin-film chips, such as vertical thin-film chips, flip-chip thin-film chip (TFFC) chips, etc.; the package side can also use flip-chip + CSP ( Chip Scale Package) technology, the light around the chip is blocked and reflected by the white wall, so that the side light is reflected to the front, and the effect of single-sided light can also be achieved.

PixCell LED seems to have similarities with CSP technology, but the white wall (high reflective materials such as titanium dioxide) is replaced by a silicon wall, and from the schematic diagram of the promotion, the height of the silicon wall is higher, and the fluorescent film is on the silicon wall. and not covered. This design actually reduces pixel crosstalk and improves pixel resolution.

In order to further understand how the PixCell LED is implemented, we searched many ways and finally found a patent recently disclosed by Samsung:

Published patent number: US17373038

Patent name: LIGHT-EMITTING DEVICES HEADLAMPS FOR VEHICLES AND VEHICLES INCLUDING THE SAME

The patent details the basic design concept of the PixCell LED core light-emitting device:

The basic design idea adopts flip-chip thin-film chip technology (TFFC) and wafer-level packaging (WLP) concepts.
Silicon substrate 1000 forms silicon walls 120 by etching
And made a reflective layer 72 on the sidewall of the silicon wall
The silicon walls are filled with light-transmitting material 74, enabling wafer-level packaging
The electrodes of the actual TFFC are drawn out through the leads. This design goes beyond the design scope of the TFFC and advances the wafer-level packaging technology one step further.
In terms of process flow and final design, Samsung PixCell LED adopts a silicon substrate epitaxy process. The chip structure adopts a TFFC-like structure with a silicon wall, and a white light chip is made by Wafer Level Package (WLP) technology.

Although the patent is not limited to silicon substrates, it is difficult for actual sapphire and silicon carbide substrates to have the effect of selective substrate removal, and silicon substrates are naturally opaque, which is beneficial to prevent adjacent chips from interfering with light.

The content presented in this patent is highly innovative and can expand the vision of developers. For practitioners who have been engaged in the development of thin-film chips for a long time, the implementation of this solution may not be as complicated as imagined, but it is indeed relatively novel. Of course, it should take a lot of energy and investment to reach the car-level and enter the pre-installation market.

Compared with the more mature gallium nitride on sapphire and silicon carbide epitaxy, the GaN-On-Si (gallium nitride on silicon) epitaxy technology used in this scheme has a large lattice mismatch between gallium nitride and silicon, which leads to The quality of the gallium nitride crystal grown by this technical route is poor. The difference in crystal quality will be reflected in reliability and performance to a certain extent. Judging from user feedback, Tesla owners have some problems with burnt headlights after upgrading the light show, and it cannot be ruled out that it may be related to this.

In a sense, Samsung's PixCell LED can be recognized by leading car companies and enter the automotive pre-installation market, which is definitely a milestone event for GaN-On-Si technology based on silicon substrates .

Perhaps Tesla knew in advance that the GaN-On-Si technical solution had certain risks, but it could indeed achieve a smaller light-emitting area and chiaroscuro. Therefore, Tesla's adoption of this technology is in line with its usual technology-driven style of doing things.

In addition to GaN-On-Si technology, PixCell LED combines Wafer Level Package (WLP), Thin Film Flip Chip (TFFC), Drive On Board (DOB) and other technologies, and has evolved and advanced it forward. PixCell LED is the crystallization of Samsung Electronics' cross-innovation in the field of light-emitting chips and semiconductors. Its innovative vision and innovation capabilities are worthy of reference and learning from domestic manufacturers.

Of course, GaN-On-Si technology is not the only way to realize matrix LED headlights. For example, laser lift-off technology is used to realize TFFC chips. Domestic Ganzhao Optoelectronics, Sanan Optoelectronics, and Yimeixinguang have been deeply involved in the field of thin-film chips for many years. , using the mature sapphire laser lift-off technology, there can also be corresponding solutions. And in terms of light efficiency and reliability, thin film chips based on sapphire laser lift-off technology will have more advantages than silicon substrate LED technology.