Ultra-low thermal expansion coefficient of PZB/β-eucryptite composite glass for MEMS packaging

Abstract

PbO–ZnO–B2O3 (PZB) glass with low-melting temperature has been widely applied in microelectromechanical systems (MEMS) packaging. However, the high thermal expansion coefficient (TEC) of PZB glass usually leads to strict packaging requirements. Here, in order to achieve ideal TEC, we have introduced β-eucryptite into PZB/β-eucryptite composite glass and optimized the composite fabrication process. Firstly, PbO:ZnO:B2O3 in mol ratio of 65:15:20 was selected as glass matrix owing to its low-melting temperature and good wettability. Then, β-eucryptite ceramics with ultra-low TEC were synthesized via a facile solid-state reaction method to optimize subsequent composite TEC value. The combination of corresponding material and device characterizations suggest that the pure phase and regular columnar grains of β-eucryptite ceramic can be obtained by sintering at 1450 °C for three hours, which can result in the lowest negative TEC of α30-300°C = −10.74 × 10−6 K−1. Furthermore, regarding the PZB/β-eucryptite composite glasses, systematic experiments demonstrated that the β-eucryptite introduction can greatly impact the TEC of matrix glass with only negligible effect on the softening point (Ts). Importantly, composite glasses with TEC of α30-300°C = 3.26 × 10−6 K−1, Ts = 380 °C and wetting angle < 30° are ideal for MEMS packaging. This work implements optimized fabrication process to obtain low-melting PZB/β-eucryptite composite glasses with ideal TEC values, which can be envisaged to be applied in advanced MEMS packaging applications.