Failure Analysis of a Full Wave Phase Sensitive Demodulator Induced by Surface Defect

This paper focus on failure analysis of a full wave phase sensitive demodulator induced by surface defect. A phase sensitive demodulator fails, inducing a big AC signal after the post-amplifier. According to the failure analysis, the failure reason of the phase sensitive demodulator is the surface defect in the interface of the Si and the SiO2. The surface defect decreases the current of the operational amplifier of the phase sensitive demodulator, making the signal suppression of the low frequency noise worse. The failure reappearance is performed by adding a parallel resistance between the power supply and the base of the triode of the operational amplifier. Moreover, three improvement measurements that include electrical test, cleaning and process are proposed, solving the failure phenomenon of the full wave phase sensitive demodulator.