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Electrical Performance of Co-Fired Alumina Substrates at High Temperatures
Keywords: Co-fired alumina, electric performance, high temperature
Polycrystalline alumina (Al2O3) substrates have been proposed as packaging substrate materials for 500C silicon carbide (SiC) electronics because of their superior stability and acceptable electrical properties demonstrated at high temperatures. A 96% Al2O3 based prototype packaging system with Au thick-film metallization successfully facilitated long term testing of high temperature SiC electronic devices for over 10,000 hours at 500C. However, the 96% Al2O3 chip-level packages of this prototype system were not fabricated via a commercial co-fire process which is more suitable for large scale commercial production. The co-fired alumina materials adopted by the packaging industry today usually contain several percent of glass constituents to provide adhesion and hermetic sealing at interfaces formed during a co-firing process at temperatures usually much lower than the regular sintering temperature for alumina. In order to answer the question if co-fired alumina substrates can provide reasonable high temperature electrical performance comparable to those of regular 96% alumina sintered at 2700C, this paper reports the electric performance of selected co-fired alumina (polycrystalline aluminum oxide with glass constituents) substrates from room temperature to 550C at frequencies of 120 Hz, 1KHz, 10KHz, 100 KHz, and 1MHz. Parallel-plate capacitive devices with dielectrics of various co-fired alumina and precious metal electrodes were used for measurement of the dielectric properties of these alumina materials in the temperature and frequency ranges. The capacitance and parallel conductance of a capacitive device were directly measured by an AC impedance meter, and the dielectric constant and dielectric loss of the dielectric were calculated from the capacitance and conductance measurement results. The temperature and frequency dependent dielectric constant, dielectric conductivity, and quality factor, or dissipation factor, of selected commercial co-fired alumina substrates will be presented and compared to those of 96% alumina. Metallization schemes for co-fired alumina for high temperature applications will be discussed to address packaging needs for low power 500C SiC electronics.
Liang-Yu Chen, Senior scientist
Ohio Aerospace Institute/NASA Glenn Research Center
Cleveland, OH

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