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In this work, the root cause of the increase in dark current occurring over time at high temperature in hermetic packages, such as those used in optoelectronic devices, was investigated. It was observed that hermetic Receiver Optical Subassembly (ROSA) devices show continuously increasing dark current when stressed and monitored at 85°C over an extended period of time, reaching, in some cases, values greater than 500nA. However, this increase in leakage current was recoverable once the package seal is broken, and this behavior was found to be very repeatable. Photodetectors from two different suppliers were tested and found to have dark current which is dependent on the fabrication process, as the photodetector (PD) from supplier 1 (PD1) showed three times higher leakage than the photodetector from supplier 2 (PD2). The main difference between the two photodetectors is that the polyimide layer in PD1 in significantly greater than in PD2. It was also observed that 48 hour pre-seal baking at 120°C keeps the dark current constant at much lower levels, but does not stop it completely from rising over time.

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