How is the metallization of photodiode pads constructed ?

The pads on Albis photodiode chips are built from a stack of different metals. On the chip front-side we offer two different stacks. The first stack alternative is optimized for wire-bonding. It consists of an adhesion layer followed by 1.3 µm of pure gold. The second alternative is optimized for soldering. Again it consists of an adhesion layer followed by a Platinum layer that acts as solder barrier (aka under-bump metallization). The Platinum layer is covered with 0.1 µm of pure gold to protect the pad from corrosion and secure solder wettabiliy also after extended periods of storage.