Mechanical and Electrical Evaluation of Materials for High Temperature Applications on Low CTE AlN Ceramic Substrates

The demand for high-temperature electronics in aerospace, power systems, and geothermal drilling necessitates materials that withstand 300° C+ and thermal fluctuations from 40° C to 300° C. Aluminum nitride (AIN) is promising due to its high thermal conductivity and low CTE, but surface oxidation remains a challenge, particularly when high-temperature inks require sintering at 850° C. This study explores additive processes for Aerosol Jet printed (AJP) conductors and dielectrics on Digital Light Processing (DLP)-printed and commercial AIN substrates to develop reliable packaging for high-temperature applications. Four candidate conductors were evaluated for fine-line printability (<100 μm), conductivity, and adhesion on different surface oxidation conditions (no oxide/partial oxidation/ full oxidation). A similar adhesion evaluation was conducted on two dielectric materials. X-ray photoelectron spectroscopy (XPS) analysis revealed that three firing cycles at 850° C induce full surface oxidation, and oxidation thickness reached about 670 nm after five cycles. Only one conductor showed good adhesion to the three surface oxidation conditions. This conductor, a thick film gold, was successfully diluted for AJP, achieving a line width of 100 μm. Additionally, one dielectric exhibited high adhesion (>40 MPa) to the three surface oxidation conditions, while the other dielectric exhibited poor adhesion on no oxide surfaces, but adhesion improved with more oxidation. Ultimately, the downselected conductor and dielectric achieved stable adhesion after aging at 300° C for 100 hours. Developing processes and materials for high-temperature AIN ceramics can add a valuable new tool to the toolbox of high-temperature research.