Self-packaged Boron Nitride Capacitor for High Temperature Applications

Abstract

In this work, we investigated applicability of boron nitride (BN) and boron oxynitride (BNO) thin films to fabricate multilayer ceramic capacitors (MLCCs) for high temperature and high frequency applications. Advantages of BN include high temperature and chemical resistance, which should result in more compact and reliable devices. Deposited BN layers by a filamentless ion source assisted physical vapor deposition technique show a high thermal stability up to 1000 °C and a very high breakdown voltage of about 600 V/μm. A 15 mm × 15 mm capacitor geometry was picked to create a simpler packaging scheme. Rectangular electrodes are offset and layered to build up the capacitor and a metallization technique is used to produce high temperature oxidation resistant Au/Ti tab electrodes. We have seen consistent results in terms of: stable capacitance values versus frequency from 10 kHz to 2 MHz; near ideal phase angle (low parasitic inductance); and high quality factors values. Laboratory prototype capacitors with operating temperatures (350 °C - 700 °C) far superior to the leading sintering technologies (< 200 °C) were demonstrated. The dissipation factor and the capacitance change within a temperature range of 700 °C are ~ 2% total and ~10 ppm/ °C, respectively. Results on thermal and frequency behavior of single and multilayers self-packaged BN capacitors are presented. We have begun testing the capacitor's performance under actual operating conditions, together with other (R and L) components in a working RLC circuit at elevated temperature, and our preliminary results are reported.