Aluminum Nitride Dielectric Constant

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Aluminum nitride (AlN) is an electrical insulator with a high dielectric constant. It is used in a wide variety of applications in the civil and military fields, including integrated circuit substrates for IGBT control modules, electrostatic chucks for wafer processing, and heat sinks for high-power LEDs. It is also widely used in aerospace, defense weapons and microwave radar applications.

The dielectric constant of sintered AlN ceramic is typically a strong function of frequency and temperature. This is due to the fact that at low frequencies, interfacial polarization effects dominate dielectric loss. At radio frequencies (RF) / microwave and infrared frequencies, however, the loss is dominated by dipolar interactions.

It has been found that a selective combination of the cooling rate and the atmosphere after sintering or heat treatment of a sintered AlN body can change the nitrogen vacancy population “frozen in” the material, which in turn changes the room temperature dielectric loss, dissipation factor and DC resistivity of the material. For example, a high dielectric loss material can be produced by rapidly quenching the sample after the sintering or heat treatment process in a low nitrogen atmosphere.

Conversely, a very low dielectric loss material can be produced by slowly quenching the sample after the sintering process in a pure nitrogen atmosphere. It has also been discovered that the metallization of an aluminum nitride resonator can significantly change the temperature dependence of its permittivity. This discovery has important implications for the development of wireless passive sensors, since their operation is often subject to harsh environmental conditions.