An abnormal phenomenon due to substrate bias modulation in the integrated PIN photodiode sensor with dielectric isolation

An abnormal phenomenon was found in the integrated PIN photodiode sensors (which is named PIN Photo Integrated Circuits Sensor: PIN-PICS) combined with a bipolar IC in the same substrate. It was observed in the optical device called “2 electric wires type photoelectric sensor”. It occurs at the time to drive the external LED by internal timing generator. This phenomenon was investigated by three methods, that is, the failure analysis the measurement of device parameters and both circuit and device simulations. These results show that the problem was induced from the PIN structure forming PIN-PICS. When the switching noise was altered, the most of this noise was transferred to preamplifier through parasitic capacitance of the PIN photodiode connected with a P⁺tab across a P-layer, and it distorted the output waveform of preamplifier by differential components. Therefore, in order to prevent this phenomenon, it´s necessary to exchange the connection of parasitic capacitance from P⁺tab to substrate. We confirmed that an Au back metallization of 3000 Å thickness, or Au-Si alloy die bonding is the most effective