Sakae Matsuzaki

Wafer-level hermetic packaging technology for MEMS using anodically-bondable LTCC wafer

This paper describes a versatile and reliable wafer-level hermetic packaging technology using an anodically-bondable low temperature cofired ceramic (LTCC) wafer, in which electrical feedthroughs and passive components can be embedded. The hermeticity of vacuum-sealed cavities was confirmed after 3000 cycles of heat shock (−40 °C/+150 °C, 30 min/30 min) by diaphragm method. The width of seal rings necessary for hermetic sealing of saw-diced chips is 0.1 mm or less. Electrical connection between MEMS on a Si wafer and feedthroughs in the LTCC wafer was established using Sn-containing metal stack simultaneously with anodic bonding. The developed wafer-level hermetic packaging technology is ready for practical applications.

Adhesive wafer bonding using a molded thick benzocyclobutene layer for wafer-level integration of MEMS and LSI

This paper describes a wafer bonding process using a 50 µm thick benzocyclobutene (BCB) layer which has vias and metal electrodes. The vias were fabricated by molding BCB using a glass mold. During the molding, worm-like voids grew between BCB and the mold due to the shrinkage of polymerizing BCB. They were completely removed by subsequent reflowing in N2. After patterning Al on the reflowed BCB for the electrodes and via connections, bonding with a glass substrate was performed. Voidless bonding without damage in the vias and electrodes was achieved. Through the process, the control of the polymerization degree of BCB is important, and thus the polymerization degree was evaluated by Fourier transform infrared spectroscopy. The developed process is useful for the wafer-bonding-based integration of different devices, e.g. micro electro mechanical systems and large-scale integrated circuits.

Integration and packaging technology of MEMS-on-CMOS tactile sensor for robot application using molded thick BCB layer and backside-grooved electrical connection

This paper describes a novel integration and packaging process for a chip-size-packaged integrated tactile sensor. A MEMS wafer and a CMOS wafer were bonded with a thick (50 µm thick) BCB (benzocyclobutene) layer, which also works as the dielectric layer of sensing electrodes. The large thickness is advantageous to reduce parasitic capacitance to the CMOS circuit. The thick BCB layer was formed on the CMOS wafer and molded with a glass mold to make a flat surface with via holes. For surface mounting, bond pads are located on the backside of the senor chip by drawing electrical feed lines through the chip edge. To make the feed lines in wafer level, tapered grooves were fabricated along the scribe lines by TMAH wet etching, and half dicing was done along the grooves to access electrodes on the BEOL layer. Finally, the tactile senor was completed and preliminarily evaluated.