Radiation Effects In High Voltage SOI LDMOS Power Devices

SOI LDMOS power devices have broad application in space power integrated circuits because their gate,source and drain are on the same surface which is easy to integrate and has the advantages of fast switching speed and little parasitic effects.In addition,as a power switch,it is the core device of high-voltage power integrated circuits.Total ionizing dose(TID)radiation and single event radiation on its static and transient electrical characteristics in typical SOI high-voltage LDMOS devices are studied in this dissertation combined with theoretical analysis and TCAD physical simulation.The results reveal that the TID radiation induced changing principles in gate control and blocking characteristics and single event radiation induced changing principles in transient current.Moreover,the principles of these changing are verified by radiation experiment.In addition,based on the process design and layout design,a radiationhardened method is proposed to enhance the radiation resistance.SOI LDMOS power devices simulations and test methods are studied.Besides,simulation methods and test systems are built.The structure and electrical characteristics of TID radiation and single event radiation experimental samples are introduced.The TCAD simulations and experimental methods of TID radiation and single event radiation of the device samples are studied combined with the TID effects and single event effects.The TCAD simulation methods of devices are built based on the Sentaurus TCAD simulation software.The test systems of TID radiation and single event burnout(SEB)are built combined with the space radiation environment parameters.The device transfer characteristics and output characteristics are studied according to TID radiation effects on gate control ability of SOI LDMOS power devices.Radiation experiments are studied based on the built transfer characteristics and output characteristics radiation test systems for SOI LDMOS.The influence principles of TID radiation on transfer characteristics and output characteristics are obtained and the degradation principles are revealed.Threshold voltage radiation hardened by process(RHBP)is proposed.Compared with the un-hardened devices,the threshold voltage of hardened devices are reduced from 26.3% to 3% for irradiation experiment with TID=100krad(Si).Based on radiation hardened technology of layout design,the terminal structure is designed to block the current path from the source to the drain through the field area combined with the verification of EMMI experiment and TID radiation experiment.The terminal structure design can reduce the leakage current caused by TID by four orders of magnitude.The results also suggest that TID can improve self-heating effects in SOI LDMOS.The breakdown voltage degradation mechanisms and hardened techniques are studied according to TID radiation effects on blocking characteristics of SOI LDMOS power devices.TID radiation on breakdown voltage variation is predicted based on the built simulation models by introducing the oxide trap charges to simulate TID radiation damage.The influence principles of TID on breakdown voltage are obtained based on the built radiation test system of breakdown voltage for SOI LDMOS power devices.The degradation mechanisms are revealed.Ionizing radiation produces a large amount of positive trap charges in the thick oxide and field oxide in the drift region and the same amount of negative trap charges are caused in the body which modulates the potential field distribution in the body and makes the breakdown voltage degrade.The variations in breakdown voltage caused by TID radiation are studied under different experimental biases,drift region lengths,and doping distributions.The results show that the breakdown voltage degradation of OFF bias is 500% more than the one of ON bias,the breakdown voltage degradation of shorter drift region length is 40.2% more than the one of longer drift region length and the breakdown voltage degradation of linearly doping in the drift region is 16.7% more than the one of uniform doping.The variations of the surface electric field in the drift region is the main reason for the variations in breakdown voltage is proposed by theory,simulation and experiment to verify TID on breakdown voltage degradation principles.Using the relations between the variations in breakdown voltage and the surface electric field in the drift region to optimize the surface field in the drift region can make the breakdown voltage change non-monotonically with accumulated dose.Therefore,a high TID resistance is achieved.Radiation hardening technology of TID radiation for the breakdown voltage of SOI LDMOS is developed according to this study.The radiation resistance of the device is improved by decreasing the thickness of the field oxide,decreasing the radiation-induced trapped charge density in the field oxide and weakening the modulation effect on the potential field distribution in the body.Compared with the un-hardened devices,the breakdown voltage degradation of thin field oxide layer structure devices decreases from 32% to 10.6% after irradiation with TID =100krad(Si)at OFF bias.The breakdown voltage of the device has a good radiation hardened effect.The physical mechanisms of single-event burnout(SEB)effects are studied according to the influence of single-event radiation on the transient effects for SOI LDMOS power devices.The sensitive position of SOI LDMOS single event burnout is determined by the pulsed laser experiment and it is the P-well region near the drift region.The relations between SEB and bias conditions,laser energy and laser injection position are revealed.The relations between SEB and electric field is proposed.The SEB sensitive point is physically explained by the analysis of the potential field distribution in the body.This sensitive region covers the peak region of the electric field.Therefore,more electron hole pairs are generated,which makes the parasitic bipolar transistor of the internal structure of the device easier to turn on.As a result,the device becomes more prone to SEB.The relation between SEB and bias conditions and laser energy is quantitatively analyzed.The mechanism of instantaneous current peak and recovery time change is revealed and the guidance for the radiation hardening design of SOI LDMOS SEB is provided.