In-situ monitoring of opto-coupler degradation during high energy proton irradiation

The degradation under a high energy proton beam of a series of industrial opto-couplers, consisting of GaAs based LEDs and Silicon phototransistors, has been tested by monitoring ex-situ typical parameters, like current-transfer-ratio, receiver photo-current and -voltage, transistor gain and LED current-voltage characteristics. The devices have been irradiated with a 68 MeV proton beam with different fluences between 1e11 p+/cm^2 and 1e13 p+/cm^2. These are typical conditions that are relevant for space missions. In order to distinguish between GaAs emitter degradation and Silicon receiver degradation, the photocurrents of both emitter and receiver diodes have been monitored in-situ during the irradiation. In this way we could verify that the emitter degradation saturates for intermediate irradiation levels of 1e12 p+/cm^2, while the receiver degradation is continuous and for 1e13 p+/cm^2 a photocurrent decrease of about 5 orders of magnitude has been measured. Some beneficial effect of the irradiation in terms of switching speed has been observed, which may be interesting for low-level irradiated devices