Low-temperature bonding of photodiodes on glass substrate using Au stud bumps and its application to microsensors with three-dimensional structure

We report successful bonding of photodiodes on glass substrate using Au stud bumps by Au-Au surface-activated bonding at a relatively low bonding temperature of 150degC. A glass substrate with the flip-chip bonded photodiode chips was then vertically stacked on a Si substrate with the bonded laser diode chip using Au-Au surface-activated bonding. Applying this technique, compact and thin optical microsensors with three-dimensional structure (2.8 mm times 2.8 mm times 1 mm thick) were fabricated. The feasibility of measuring velocity was demonstrated using prototype microsensors.