Electrical and Mechanical Characterization of Low Temperature Co-fired Ceramics for High Temperature Sensor Applications

To make use of metals with improved conductivity like Ag, AgPd, Au or Cu for metallization pastes in ceramic multilayer technology, Low-Temperature Co-fired Ceramics (LTCC) are densified at temperatures below 900 degrees C. The densification mechanism can be attributed to viscous sintering in combination with the crystallization of the glass matrix. Lifetime prediction and extension of the application range to elevated temperatures strongly depend on the transition range of the remaining amorphous phase as well as on the final crystallization products. Due to the fact that multilayer ceramics based on LTCCs are gaining increasing interest in the manufacturing of highly integrated devices for microelectronic and sensor applications, there is the need to establish a better understanding of their mechanical and electrical behaviour in the elevated temperature regime. In this study, four commercial LTCC substrate materials in addition to a test product in the sintered state, namely DP 951, DP 943, both from DuPont, CT 800 and AHT-01, both from Heraeus, and GC from CeramTec were investigated in respect to the temperature dependence of their mechanical and electrical properties up to temperatures of 950 degrees C. Mechanical characterization included three-point bending tests on single layer substrates. Furthermore, the surface resistivity as a function of temperature up to 500 degrees C was determined under vacuum for DP 951. Next, these results were correlated to the composition of the glasses, determined by inductively coupled plasma (ICP) analysis, as well as the crystallization products apparent in the composites, which were determined by XRD of the sintered substrates and in-situ HT-XRD for DP 951. Results gained from these investigations of the commercial LTCC products were compared to measurements carried out on glass-ceramic composites developed in-house exhibiting improved electrical behaviour and good temperature stability.