A research on optoelectronic coupler storage reliability by accelerated degradation testing

In this paper, the storage failure mode and mechanism of optoelectronic couplers are studied by Accelerated Degradation Testing (ADT) and a series of following analyses. Firstly, the type of optoelectronic coupler to be studied is determined in the paper. Then, an ADT is conducted, which ends after 4176 hours. Then it is found that all the parameters show no degradation except for Current Transfer Ratio (CTR) and the degradation rates of CTR between stress levels follow the Arrhenius law. However, different from the previous research, a phenomenon of phased degradation is discovered in the highest stress level. To determine the degradation causes of the two phases, a series of follow-up analyses is conducted. By excluding the possibility of integrated photosensitive circuit degradation and Light Emitting Diode (LED) contamination, we identify the active layer of LED as the degradation region and ascribe the CTR degradation to an improvement of deep-level defects. To describe the phased degradation, we also establish a phased model. In the first phase, the latent defect sources transform into deep-level defects. In the latter phase, deep-level defects form non-radiative carrier-recombination centers, and the non-radiative carrier-recombination centers increase the amount of deep-level defects in return. For a further verification, a simulation with Atlas is also conducted by injecting different amount of deep-level defects into the active layer of LED and observing the degradation of LED luminance. With the fixed transmission ratio between the luminance and the output current, the degradation trend of CTR is acquired. A good fit between ADT and simulation results is shown, which could verify the correctness of the storage degradation model. The established model can be utilized to assess and improve the storage reliability of AlGaAs/GaAs LED based optoelectronic couplers.