Who can go further on the sapphire substrate VS silicon substrate?

“Working experience and research in the Nakamura research team is very helpful for their future work in the industry. These research experiences are actual and used in the work.” When talking about the experience of the Nakamura research team, Chen Dr. Zhen said.

After leaving the laboratory in Nakamura, Dr. Chen Zhen joined a US LED company and produced prototype LED devices on silicon substrates. "When we saw that the brightness of the first prototype device reached 50% of sapphire, we judged that the technical route of silicon substrate is feasible. Later I learned that China's crystal energy photoelectric is also making silicon substrate LED devices. It has been industrialized as early as 2009. As a technician, I deeply understand the difficulty of long LED materials on silicon substrates, and China has produced such a remarkable technology, and is ahead of other global manufacturers, plus For the pursuit of LED technology, I joined the crystal energy."

Next scrambled technology

From the current use of substrate materials, in addition to CREE using silicon carbide substrates, crystal energy using silicon substrate (Si), the world's most chip manufacturers use sapphire substrates. Several major international companies are also vigorously following up on silicon substrate high-power LED chip technology. For example, Toshiba purchased Puri technology and cut it into silicon substrate. Samsung announced that its next year's technology route and products are silicon substrate chips. Various market signs and technology trends indicate that silicon substrates will be the next competitive technology in the LED field.

When talking about how the silicon substrate can open up a new world in the case of a sapphire substrate monopolizing half of the country, Dr. Chen Zhen is very familiar with introducing the advantages of silicon to reporters. He said that the first is the advantage of the substrate material itself. Silicon substrate materials are characterized by low cost, large size, and electrical conductivity. Silicon substrates are more suitable for large-scale epitaxy than sapphire. When the sapphire substrate technology is changed from 2 inches to 6 inches and 8 inches, the technical barriers are very high, and the production cost is not lowered. Silicon substrates, on the other hand, can be fabricated in large sizes, from 2" to 6" or even larger, to avoid edge effects and greatly increase yield. The silicon integrated circuit industry continues to increase the substrate size, from 8 inches to 10 inches, and even 12 inches. In addition, the advantages of the device structure. The silicon substrate LED is a vertical structure and emits light on one side, so that the spot of the LED of the silicon substrate is good, the direction is easy to control, the current is fast, and it is suitable for driving at a large current. Good thermal conductivity allows for better heat dissipation in the fabricated LED devices.

For the low-power silicon substrate LED chip , one metal wire can be used for packaging, and the electrode occupies less light-emitting area and higher reliability, so it has a relatively large market for small chips that need dense arrangement in digital and display fields. The advantage of the product has entered the Volkswagen and other brands for the backlight of the dashboard.

For high-power silicon substrate LED chips, single-sided light output is easy to control the direction, and the application products have long range and good light quality, which is very suitable for high-end lighting applications that require high-quality light. In car headlights, mobile phone flash, TV backlight High-end portable lighting, high-end indoor lighting and other high-power LED applications have performance advantages. Since the silicon substrate LED chip adopts the stripping method to completely eliminate the stress between the luminescent film and the substrate, and the vertical structure current diffusion is fast, the ability to carry current per unit area is strong, and is suitable for the application of high power LED.

Relieve stress and reduce dislocation density

The biggest technical difficulty compared to silicon substrates and other two substrates, silicon carbide and sapphire, is lattice mismatch and thermal mismatch. "But this is also the attraction and charm of making a GaN LED on a silicon substrate for a technician." Dr. Chen Zhen said with a smile.

The lattice mismatch between silicon and gallium nitride is the largest, several times that of silicon carbide. Large lattice mismatches lead to higher dislocation densities in gallium nitride materials, and it is for this reason that silicon substrates are considered to be an inaccessible technology route for a long time.

In addition, there is a large thermal mismatch between the silicon substrate and gallium nitride. This problem leads to a certain match between the two at high temperature growth, but after the temperature is lowered to room temperature, the thermal expansion coefficient of the two is very different. Causes problems such as cracks.

Faced with these two technical difficulties, the crystal energy team's approach is to use a variety of buffer layers to relieve stress, as well as a variety of complex dislocation filter layers to reduce dislocation density.

Dr. Chen Zhen said that the current efficacy of silicon substrates can be made as good as sapphire. The research level of crystalline silicon substrate LED reached 160lm/W, and the production level reached 145lm/W, which is the highest level in the world.

Breakthrough of international patent barriers

The complete patent protection of silicon substrates is an effective weapon for China's LEDs to face patent risks in the future. Dr. Chen Zhen believes that the silicon substrate LED technology avoids the international patent cofferdam formed by the sapphire substrate and silicon carbide substrate technology route from the source of the substrate, from low-power LED chip technology to high-power LED chip technology. Form a proprietary patent system. Jingneng Optoelectronics has applied for or authorized more than 230 international and domestic patents around the silicon substrate LED technology, including 29 US invention patents and 43 European patents. "This is an effective weapon for us to evade patent litigation by foreign manufacturers." Dr. Chen Zhen said.

At present, the global LED industry has become a three-pronged trend in the United States, Asia, and Europe. The five major manufacturers, such as CREE in the US, Osram in Europe, Philips Lumileds, Nichia, and Toyota Synthes, dominate the global LED market and monopolize GaN. The core technology and patent of base blue LED and white LED. The patents applied by these manufacturers in order to maintain their competitive advantage and maintain their market share cover almost the entire industrial chain including raw materials, equipment, packaging and applications. In addition, R&D and production between manufacturers through patent licensing and cross-licensing not only hinders the emergence of new entrants, but also increases the production costs of enterprises to a certain extent.

As a latecomer to the LED industry, China has a large number of enterprises, but the upstream substrate chip companies account for a small proportion, adding up to no more than 100, and have not obtained core technology, the number of patent applications is small, and the scale of enterprises is small. Insufficient attention has attracted the attention of foreign giants. Once the scale is large, there is no circumvention of patent issues. The patent dispute between Nichia and CREE earlier ended its monopoly. Although many patents are currently expiring, they provide an opportunity for Chinese companies to purchase core patents, but this is not a straw.

Therefore, the development and establishment of a patent system with independent intellectual property rights can not only become the basis for the development of enterprises, but also break the patent barriers for the future development of Chinese enterprises. In this sense, the research and development of silicon substrates is not only a simple technology research and development, but also paving the way for the future development of Chinese LED companies.

It is expected to help transform and upgrade the LED industry

From the production point of view, the large size of the silicon substrate can be used to produce LEDs by the silicon integrated circuit production process developed by humans through years of technology accumulation, thereby greatly improving the degree of automation, and at the same time, the chip is reliable because the participation of personnel is minimized. Sex, consistency and yield will be greatly improved, and labor costs can be reduced, reducing the overall cost of LEDs by 20-30%, which is a revolutionary subversion for the entire LED industry.

In addition, GaN power devices on silicon substrates are also an important application area, and it is expected to open up a new application field beyond traditional power devices. A major feature of the third-generation semiconductor represented by gallium nitride is the wide band gap. This feature makes the device with high breakdown voltage, high current density, high operating temperature, etc., so the performance in high-power, high-temperature power electronic device applications is far superior to traditional silicon and gallium arsenide-based electronic devices. Its application range will include computers, mobile phones, digital cameras, power supplies, motors, UPS, electric vehicles, base stations, power plants, etc. The use of silicon as a substrate for gallium nitride electronic devices has been internationally recognized, primarily because of the unparalleled cost advantages of silicon for other substrate materials.

Speaking of the future of silicon substrates, Dr. Chen Zhen said: "I hope that by introducing silicon substrates, the technology of the LED industry will be fundamentally changed, and GaN LEDs will be upgraded from a semi-automated, labor-intensive industry to modern integrated circuits. The highly automated, high-precision semiconductor industry is quite technologically advanced. It is hoped that the new technology will bring both low cost and high control precision, and eventually form a standard manufacturing industry.