Effect of Characterization Temperature on the Radiation Induced Degradation of Optocouplers

This study examines the radiation-induced effects on commercial 4N49 optocouplers by measuring their response at different temperatures. The devices under test (DUTs) are subjected to a series of total doses. At each accumulated dose, the devices are characterized at several temperatures between -25 °C and 100 °C. The results demonstrate that irradiation has no negative effects on the light-emitting diode (LED). The current gain of the phototransistor decreases significantly after irradiation. For a constant base current, the gain degradation increases with increasing temperature. The current transfer ratio (CTR) of the optocoupler decreases after irradiation, which is dominated by the gain degradation of the phototransistor. Temperature dependence of the radiation-induced parametric degradation varies with the total ionizing dose (TID) and the forward current of the LED. Specifically, an unusual increase in the photoresponse is observed at extremely low LED forward current and high temperature, which originates from the increased reverse leakage current of the collector-base (CB) junction of the phototransistor.