Optical characteristics of GaAs MSM photodetectors flip-chip bonded upon micromirrors using micromachined conductive polymer bumps

Using flip-chip bonding techniques with micromachined conductive polymer bumps and passive alignment techniques with electroplated side alignment pedestal bumps, a prototype MOEMS structure for optical I/O couplers has been designed, fabricated and characterized. A top MOEMS substrate has through holes, contact metal pads, and side alignment pedestals with electroplated copper to align GaAs MSMs. Conductive polymer bumps have been micromachined on contact metal pads of GaAs MSMs using thick photoresist bump-holes as molding patterns. A diced GaAs photodetectors die with micromachined conductive polymer bumps was aligned to the side alignment pedestals within ±5 μm and flip-chip bonded onto the substrate. This conductive polymer flip-chip bonding technique allowed a very low contact resistance (approximately 10 mΩ), a lower bonding temperature (approximately 170 °C), and simple processing steps. The GaAs MSM photodetectors flip-chip mounted on the top of OE-MCM substrate showed a low dark current of about 10 nA and a high responsivity of 0.66 A/W. By using bulk-micromachining, conductive polymer flip-chip bonding, and passive pedestal alignment techniques, a prototype MOEMS structure for optical I/O couplers realized in this work shows high potential to use as a fundamental building block in OE-MCMs.