The Effects Of Process Parameters On The Characteristics Of TVS

Lightning, inductive load switching and ESD are sources of transient voltage that can gain entry into sensitive electronic equipment and system, burn off the semiconductor devices and so cause damages to the whole system. Transient voltage suppressor (TVS) is widely applied to protect circuit and system as it can substitute the traditional gas discharge tubes (GDTs),metal oxide varistors (MOVs) and thyristors.In this thesis, electrical characteristic and manufacturing process of TVS are studied. In order to get TVS device with good clamping performance, firstly, the ideal TVS DC characteristic and avalanche breakdown voltage are introduced based on device physics of PN junction. Secondly, the avalanche breakdown voltages under different process parameters were analyzed by using two-steps diffusion method with liquid dopant source. It showed that high resistivity wafers with longer diffusion time and higher diffusion temperature will get higher breakdown voltage TVS. Experiential formula was given out to guide diffusion according to the results. Thirdly, Analysis of surface characteristic and passivation protection shows that surface effect is the main reason for leakage. Thermal oxidation with chlorine, glass passivation and silicon nitride passivation were studied to protect the device. According to the results, leakage can be obviously reduced by oxidation with chlorine and silicon nitride passivation. Finally, it's demonstrated by the analysis that bulk resistance and series resistance will raise the dynamic resistance of device and so affect the capability of clamping. Reduce the dynamic resistance will help to improve the surge capacity of TVS devices.Based on the above studies, failure analysis is performed using EMMI (Emission Microscope) and SEM (Scan Electronic Microscope), mechanical damage in device is the major potential factor which caused the failure.