Effects of Proton Irradiation on Optocouplers with Bipolar and MOSFET Technologies, a Comparison of In-Situ and Ex-Situ Results

The properties of two different types of optocouplers, a conventional bipolar one with phototransistor output stage and a photorelay with power MOS output stage, have been determined before, during, and after irradiation with 68 meV protons with a fluence of up to 1e12 protons/cm2. In-situ measurements of the radiation-induced current of the input LEDs and in the case of the bipolar optocoupler also of the current-transfer-ratio of the device enabled a separate evaluation of input and output device degradation. A moderate degradation of the LED performance is observed for both devices, but in the case of the MOS-based photorelay, the most important overall device parameters are still within the specifications even for the highest irradiation level, while for the coupler with bipolar phototransistor a more than one order of magnitude decrease of the current-transfer-ratio is already observed for moderate fluences. This strong degradation is mainly due to the strong loss of photo-generated charge carriers with increasing fluence.