Novel Solution for High-Temperature Dielectric Application to Encapsulate High-Voltage Power Semiconductor Devices

Traditional semiconductor packaging techniques and materials have been working well for conventional Si devices, which usually operate at temperatures up to 175 °C. As the operating temperature increases, these techniques exhibit failures such as bulk flows, volume shrinkage, brittleness and subsequent cracking, and deterioration of dielectric strength. For the new wide-bandgap power devices, which work at voltages as high as 1200 V and junction temperatures as high as 250 °C, there is currently no known dielectric material to encapsulate and protect the active devices. This paper summarizes novel solutions for high-temperature dielectric materials for encapsulating high-power semiconductor devices without any dielectric breakdown and also without introducing excessive thermal, electrical, and mechanical stresses to the encapsulated devices. Polymer dielectric candidates investigated in this paper include cyanate ester-based resin and silicone-based resin. In addition, conformal coating approaches that include alumina deposited by atomic layer deposition (ALD) technique and tetrahedral amorphous carbon (ta-c) deposited by filtered cathodic vacuum arc technique were evaluated in this paper. Dielectric strength performance of the material combinations with respect to temperatures was evaluated. Among the polymer encapsulants, a silicone resin with silica fillers was determined to be the prospective candidate. Breakdown voltage and leakage current of the silicone-based encapsulant with and without the conformal coating was measured by breakdown tests. It was determined that the ta-c conformal coating deteriorates the dielectric performance of the encapsulant, while the alumina thin film deposited by ALD approach reduces the leakage current of the encapsulation material and also increases the breakdown voltage of the silicone encapsulant. Thus, the combination of alumina thin film deposited by ALD approach along with the silicone encapsulant is recommended for this application, involving high temperature and high voltage.