High thermal conductivity, insulation and wave transmission boron nitride film material for 5G communication equipment

Introduction: With the improvement of the performance and functionality of electronic devices, the heat generated by each device increases, and it is important to effectively dissipate, dissipate, and cool the heat. For high-performance mobile products such as 5G smart phones and AR/VR devices, the use of high-performance ICs and the highly integrated design that seeks to reduce weight limit the installation space of heat dissipation components. Therefore, TIM materials such as high thermal conductive gaskets and thermal conductive gel are used to better heat dissipation.

What is boron nitride?

Boron nitride is a crystal composed of nitrogen and boron atoms. The chemical composition is 43.6% boron and 56.4% nitrogen, with four different variants: hexagonal boron nitride (HBN), rhombohedral boron nitride (RBN), cubic boron nitride (CBN), and wurtzite boron nitride (WBN).

Boron nitride was introduced over 100 years ago, with its earliest application being hexagonal boron nitride as a high-temperature lubricant. Its structure and properties are very similar to graphite, and it is also pure white, hence it is commonly known as "white graphite".

Boron nitride (BN) ceramics were discovered as early as 1842. Extensive research on BN materials has been conducted abroad since World War II, and it was not until 1955 that the BN hot pressing method was developed. The American Diamond Company and United Carbon Company were the first to enter production, producing over 10 tons by 1960.

In 1957, R.H. Wentrof was the first to successfully develop CBN. In 1969, General Electric sold it as Borazon, and in 1973, the United States announced the production of CBN cutting tools.

In 1975, Japan imported technology from the United States and also prepared CBN cutting tools.

In 1979, pulsed plasma technology was successfully used for the first time to prepare brittle BN thin films at low temperature and low pressure.

In the late 1990s, people were able to prepare c-BN thin films using various physical vapor deposition (PVD) and chemical vapor deposition (CVD) methods.

From a domestic perspective in China, development has made rapid progress. Research on BN powder began in 1963, was successfully developed in 1966, and was put into production and applied in China's industry and cutting-edge technology in 1967.

Material characteristics:

CBN is usually a black, brown, or dark red crystal with a sphalerite structure and good thermal conductivity. Hardness second only to diamond, it is a superhard material commonly used as a tool material and abrasive.

Boron nitride has chemical resistance and is not corroded by inorganic acids and water. The boron nitrogen bond is broken in hot concentrated alkali. Oxidation begins in the air above 1200 ℃. Decomposition begins at around 2700 ℃ under vacuum. Slightly soluble in hot acid, insoluble in cold water, with a relative density of 2.29. The compressive strength is 170MPa. The maximum operating temperature under oxidizing atmosphere is 900 ℃, while it can reach 2800 ℃ under non reactive reducing atmosphere, but the lubrication performance is poor at room temperature. Most of the properties of boron nitride are superior to carbon materials. For hexagonal boron nitride: low friction coefficient, good high-temperature stability, good thermal shock resistance, high strength, high thermal conductivity, low expansion coefficient, high electrical resistivity, corrosion resistance, microwave or infrared transparency.

Material structure:

Boron nitride hexagonal crystal system, most commonly graphite lattice, also has amorphous variants. In addition to the hexagonal crystal form, boron nitride has other crystal forms, including rhombohedral boron nitride (r-BN), cubic boron nitride (c-BN), and wurtzite type boron nitride (w-BN). People have even discovered two-dimensional boron nitride crystals that resemble graphite thin.

The commonly produced boron nitride has a graphite type structure, commonly known as white graphite. Another type is diamond type, which is similar to the principle of graphite transforming into diamond. Graphite type boron nitride can be transformed into diamond type boron nitride at high temperature (1800 ℃) and high pressure (8000Mpa) [5-18GPa]. It is a new type of high-temperature resistant superhard material used for making drill bits, grinding tools, and cutting tools.

Application areas:

1. Mold release agents for metal forming and lubricants for metal drawing.

2. Special electrolytic and resistive materials in high temperature conditions.

3. High temperature solid lubricants, extrusion anti-wear additives, additives for producing ceramic composite materials, refractory materials and antioxidant additives, especially for applications that resist molten metal corrosion, thermal enhancement additives, and high-temperature resistant insulation materials.

4. Heat sealing desiccants for transistors and additives for polymers such as plastic resins.

5. Pressed into various shapes of boron nitride products, which can be used as high-temperature, high-voltage, insulation, and heat dissipation components.

6. Thermal shielding materials in aerospace.

7. With the participation of a catalyst, it can be converted into cubic boron nitride that is as hard as diamond through high-temperature and high-pressure treatment.

8. Structural materials of atomic reactors.

9. Jet nozzles for aircraft and rocket engines.

10. Insulators for high-voltage, high-frequency electrical and plasma arcs.

11. Packaging materials that prevent neutron radiation.

12. A superhard material processed from boron nitride, which can be used to make high-speed cutting tools and drill bits for geological exploration and oil drilling.

13. Separation rings used in metallurgy for continuous cast steel, flow slots for amorphous iron, and release agents for continuous cast aluminum.

14. Make evaporation boats for various capacitor film aluminum plating, cathode ray tube aluminum plating, display aluminum plating, etc.

15. Various fresh-keeping aluminum plated packaging bags, etc.

16. Various laser anti-counterfeiting aluminum plating, trademark hot stamping materials, various cigarette labels, beer labels, packaging boxes, cigarette packaging boxes aluminum plating, and so on.

17. Cosmetics are used as fillers for lipstick, which are non-toxic, lubricating, and glossy.

Future prospects:

Due to the high hardness of steel materials, a large amount of heat is generated during processing. Diamond tools are prone to decomposition at high temperatures and are easily reactive with transition metals. On the other hand, c-BN materials have good thermal stability and are not easily reactive with iron-based metals or alloys, making them widely used in precision machining and grinding of steel products. In addition to excellent wear resistance, c-BN also has extremely good heat resistance. It can cut heat-resistant steels, ferroalloys, quenched steels, etc. at relatively high cutting temperatures, and can also cut high hardness cold hard rolling rolls, carburizing and quenching materials, as well as Si Al alloys that have severe tool wear. In fact, cutting tools and grinding tools made from sintered c-BN crystals (synthesized under high temperature and high pressure) have been applied in high-speed precision machining of various hard alloy materials.

C-BN, as a wide bandgap (6.4 eV) semiconductor material, has high thermal conductivity, high resistivity, high mobility, low dielectric constant, high breakdown electric field, can achieve dual doping, and has good stability. It is known as the third generation semiconductor material after Si, Ge, and GaAs, along with diamond, SiC, and GaN. Their common feature is wide bandgap, which is suitable for making electronic devices used under extreme conditions. Compared with SiC and GaN, c-BN has more excellent properties with diamond, such as wider bandgap, higher mobility, higher breakdown electric field, lower dielectric constant, and higher thermal conductivity. Obviously, as extreme electronic materials, c-BN is superior to diamond. However, as a semiconductor material, diamond has its fatal weakness, which is that n-type doping of diamond is very difficult (the resistivity of n-type doping can only reach 102 Ω· cm, far from meeting device standards), while c-BN can achieve dual type doping. For example, in high-temperature and high-pressure synthesis and thin film preparation processes, adding Be can obtain P-type semiconductors; Adding S, C, Si, etc. can obtain n-type semiconductors. Therefore, overall, c-BN is the most outstanding third-generation semiconductor material, which can not only be used to prepare electronic devices that work under extreme conditions such as high temperature, high frequency, and high power, but also has broad application prospects in deep ultraviolet luminescence and detectors. In fact, the earliest reported c-BN light-emitting diode made under high temperature and high pressure conditions can operate at a temperature of 650 ℃ and emit visible blue light under forward bias. Spectral measurements show that its shortest wavelength is 215 nm (5.8 eV). C-BN has a thermal expansion coefficient similar to GaAs and Si, high thermal conductivity and low dielectric constant, good insulation performance and chemical stability, making it a heat sink material and insulation coating layer for integrated circuits. In addition, c-BN has a negative electron affinity and can be used as a cold cathode field emission material, with broad application prospects in the field of large-area flat panel displays.

In terms of optical applications, due to the high hardness of c-BN thin films and their high transmittance across the entire wavelength range from ultraviolet (approximately 200 nm) to far-infrared, they are suitable as surface coatings for some optical components, especially for window materials such as zinc selenide (ZnSe) and zinc sulfide (ZnS). In addition, it has good thermal shock resistance and commercial hardness, and is expected to become an ideal window material for high-power lasers and detectors.