Failure of the negative voltage regulator in medium-photon-energy X radiation fields

Abstract Negative voltage regulators were examined in the effective 60-keV and 170-keV bremsstrahlung fields, as well as in the field of 60 Co gamma-radiation. Most devices irradiated in the fields of medium-dose-rate breaking radiation failed to operate after absorption of very small total doses of ionizing radiation, in the range of 37–132 Gy(SiO 2 ). However, all samples irradiated in the gamma radiation environment remained completely functional, even after deposition of a total dose of 500 Gy(SiO 2 ). Devices irradiated with higher input voltages failed after absorption of low total doses, whereas the load current increase mitigated and even prevented circuit failures in X radiation fields. The high radiation sensitivity of the LM2990T-5 voltage regulators operating in the bremsstrahlung fields was a consequence of the dose enhancement on the gold–aluminum connection between the silicon chip and ground contact. Computer model simulations indicated that the primary failure mechanisms were the generation of radiation-induced leakage currents alongside the npn transistors in the operational amplifier circuit. The difference between the voltage regulator responses in various bremsstrahlung environments was affected by the time-dependent effects, leading to the partial recovery of radiation-induced trapped charge.