Integration of Glass Layer for Meso and Micro-System Applications

With recent development, multi-functional platform with substrate based on ceramics composite technology, in particular low temperature co-fired ceramic (LTCC) multilayer technology, is gaining advantages over conventional silicon technology. LTCC offers ease of integration for both homogenous and heterogeneous structures and materials. Its intrinsic properties and unique fabrication process makes 3-D meso and micro-system possible. There is, however, among the functionalities, optical access is desirable for most of the micro-electronic devices and micro-systems. Therefore, a process of integrating glass layer is always required. Glass layer could be fabricated directly on a fired ceramics composite substrate or ideally be co-sintered. In this paper, preliminary investigation on direct thermal glass bonding process on a fired LTCC substrate is presented. Bonding interfacial integrity was characterized using nondestructive scanning acoustic microscopy. At a temperature of 720degC for 30 minutes, bonding began to establish over 7 - 8 % of the interfacial area for a glass chip size of 10 mm times 10 mm. At 800degC, the bonded area reached approximately 98%. Glass sagging measurement over a number of open cavities was also conducted. Average sagging of about 42 mum was measured on a Oslash5 mm open cavity. Visible light transmittance for the open cavity after glass bonding was in the range of 89 - 92% which is closed to the reference "as received" glass of 92%. Cross-sectional micrograph at bonding interface showed a continuous metallurgical glass fused bond to the LTCC surface. Destructive shear strength test on glass/LTCC bonding was conducted. Failure was observed in the glass chip with an average shear apparent strength of about 2.5 MPa. Further investigation is required to eliminate edge deformation and to minimize sagging for large cavity.