Cost-effective synthesis of aluminum nitride for thermal and light management applications

Efficient thermal management is essential to prevent functional degradation and energy loss in modern electronic devices.

Thermally conductive and electrically insulating ceramic powders—such as alumina, aluminum nitride, and boron nitride—are commonly used as fillers in polymer-based thermal interface materials (TIMs), including thermal gels and sheets, to enhance heat dissipation in electronic circuits. Among these ceramic powders, alumina is widely used because of its low cost and high chemical stability, despite its relatively low thermal conductivity (20–30 W/m·K). In contrast, aluminum nitride and boron nitride powders offer much higher thermal conductivities—approximately 170–220 W/m·K and about 60 W/m·K, respectively—but their commercial use remains limited due to higher production costs.

Aluminum nitride in particular has attracted significant attention as a versatile material thanks to its excellent thermal, electrical, and mechanical properties. Demand for aluminum nitride has thus steadily increased in the electronics industry during the past 40 years.¹

In the context of TIM applications, the recent rapid growth of information and communication technology, electric vehicles, artificial intelligence, and other power electronics has led to increased demand for aluminum nitride powders and substrates. As a result, dedicated research has improved the mechanical and thermal properties of aluminum-nitride-filled gels and sheets, and thermal conductivity now exceeds 10 W/m·K.

These materials are now essential components in 5G base station antenna modules, insulated gate bipolar transistor devices, data center servers, and related applications. In 2024, the global market size for aluminum nitride fillers was estimated at US$78.9 million, with a compound annual growth rate of 6.3%.²

Currently, there are two major industrial processes employed to synthesize aluminum nitride powders:

1. Carbothermal reduction and nitridation of alumina using carbon, under a nitrogen atmosphere at around 1,700°C.
2. Direct nitridation of aluminum metal powders in nitrogen gas under a precisely controlled heating rate between 500°C and 1,300°C.

The resulting aluminum nitride powders are ground, surface-treated to prevent hydrolysis with silane coupling agents or other coatings, and supplied as commercial-grade fine powders with low oxygen content.

An alternative synthesis approach is combustion synthesis.³ This simple and more cost-effective method relies on a highly exothermic reaction between aluminum and nitrogen, which self-propagates after ignition and completes within minutes.

Because combustion synthesis requires no external heating—the temperature at the reaction front can reach nearly 2,000°C due to the heat of formation—the method significantly reduces costs associated with high-temperature furnaces, electricity, and processing times. However, the reaction is extremely difficult to control. A pressurized nitrogen atmosphere is essential to sustain the reaction, but even then, it often results in unreacted or agglomerated products with poor uniformity. Considerable research has been conducted worldwide to optimize this reaction, but industrial applications remain limited.

The authors have studied the combustion synthesis of aluminum nitride for decades,^4–8 and they recently succeeded in producing soft, nonagglomerated aluminum nitride powders. In their process, raw aluminum powders are blended with an appropriate amount of preformed aluminum nitride powder via combustion synthesis to moderate the reaction temperature. This mixture is placed in a graphite tray, and the nitridation is initiated by passing a short current with a few tens of amperes through a carbon heater. The entire reaction occurs in a high-pressure chamber filled with nitrogen gas at less than 1 MPa (Figure 1). The resulting aluminum nitride is pulverized and classified by conventional methods according to application needs.

Figure 1. Schematic illustration of the nitriding combustion reaction of aluminum nitride synthesis in a high-pressure reaction chamber. Credit: Chen and Miyamoto

From powder loading to product retrieval after cooling, the total process time is under two hours. Analysis shows this combustion synthesis method is 30–50% less expensive than the conventional aluminum nitride fabrication processes. Table 1 summarizes and compares the properties of the combustion synthesized aluminum nitride powders to ones produced through the conventional routes.

Table 1. Comparison of commercial aluminum nitride fine powders synthesized by three different methods. All powders have an average particle size of approximately 1 μm, with oxygen contents around 1 wt.%.Credit: Chen and Miyamoto

Considering the advantages and benefits of this new combustion synthesis method, commercial production of aluminum nitride using this method began through a joint startup program with Shanghai Toyo Tanso Co. Ltd., a subsidiary of Toyo Tanso Co. Ltd., a Japan-based global leader in graphite, carbon-based materials, and coated substrates such as silicon carbide- and tantalum carbide-coated graphite. The goal is to expand the use of aluminum nitride synthesized via this cost-effective process in thermal, light, and energy management applications.

For example, spherical aluminum nitride powders are widely used as fillers for TIMs. To produce spherical fillers, fine aluminum nitride powders—mixed with a few percent of yttrium oxide as a sintering aid—are spray-dried and sintered at around 1,800°C. The resulting particles are sieved to sizes ranging from 20–100 μm. Fine aluminum nitride powders (~1 μm) are also suitable for sintering into substrates and structural components, such as electrostatic chucks.

These fine and pure aluminum nitride powders can also be used in the synthesis of red phosphors (e.g., CaAlSiN₃:Eu²⁺) for LEDs—an increasingly vital component in energy-saving lighting technologies. We also produce pure porous aluminum nitride crucibles without any sintering additives. These crucibles are ideal for heat-treating aluminum-nitride-based products in clean environments and offer a cost-effective alternative to boron nitride crucibles with less than half the cost.

While our current production scale is limited and our market remains primarily within China, we aim to expand our distribution worldwide in 2026 by scaling up the process.

Acknowledgments

The authors would like to express their sincere gratitude to their late colleague T. Sakurai for his invaluable contributions to this project. Our deepest condolences for his passing in 2017.