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

• Negative voltage regulators LM2990T-5 were exposed to X and gamma radiation.
• Most devices in X radiation fields failed to operate after absorption of 37–132 Gy.
• All ICs exposed to gamma radiation remained functional after deposition of 500 Gy.
• Primary failure mechanism was the generation of radiation-induced leakage currents.
• NPN transistors in the operational amplifier circuit were critical components.

Negative voltage regulators were examined in the effective 60-keV and 170-keV bremsstrahlung fields, as well as in the field of 60Co 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(SiO2). However, all samples irradiated in the gamma radiation environment remained completely functional, even after deposition of a total dose of 500 Gy(SiO2). 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.