Mechanisms And Key Radiation Hardness Techniques For Displacement Damage Effects Of MOS-controlled Thyristor

The silicon-based MOS controlled thyristor is a high power device.Due to the short turn-on delay,low on-state resistance and high current rise rate,the MCT is a natural high voltage switch for exploding foil igniter.The anode-short?AS-MCT?is a new generation of MCT,which is distinguished from conventional MCT by an anode-short structure and develops a normally-off characteristic.The normally-off capability can simplify the driver circuit in exploding foil igniter,and then,facilitate the reliability and compactness of missile microelectronic system.As the AS-MCT is a composite structure of MOS and several BJTs,its devices physics are complicated.The concomitant?-rays inevitably exit in neutron source,and then,the AS-MCT suffers from both the displacement and ionization damage following neutron exposures.The damage of AS-MCT switch can bring about that of pulse discharging characteristics of exploding foil igniter.Thereafter,the functional failure of exploding foil igniter may occur.The application of AS-MCT in military equipment effectuates its import embargo.Just a couple of works focus on the devices physics and radiation effects of AS-MCT up to now.These situations hamper the independent design and fabrication of AS-MCT,and block the study on its radiation effect and radiation hardness techniques.For the first time,this work presents the studies on the device physics and radiation effects of AS-MCT,and degradations of capacitor pulse discharging circuit characteristics induced by the radiation damage on its AS-MCT switch.Moreover,the radiation reinforcement techniques for AS-MCT are briefly discussed.This work can benefit the follow-up study on radiation effects of AS-MCT following higher flux neutron exposures,and the design of such devices.This work mainly contains four parts.1.This work presents the analysis of AS-MCT device structure,and identifies six simplified equivalent circuits for AS-MCT under specific bias conditions.These circuits contain reverse diode,open base BJT,MOS,JFET,IGBT and thyristor.Then,the transfer,forward conductive,forward blocking,reverse and pulse discharging characteristics of AS-MCT are studied with TCAD simulations.2.The displacement damage?DD?effects of AS-MCT are studied,and the mechanisms behind the DD are proposed.The studies cover irradiation experiments,device damage effects,electrical parameter damage models and circuit damage effects.The XND1 AS-MCTs examined in this work have a breakdown voltage of 1800 V and current level of 60 A.The samples were irradiated by CFBR-II fission neutron reactor.The neutron flux on samples ranges from 3.1×10⁹ cm^-2 to 5×10¹³ cm^-2.Then,this work presents,from the prospective of simplified equivalent circuits,the DD-induced effects on AS-MCT characteristics,which contain transfer,forward conductive and forward blocking characteristics.The BJTs are key components of an AS-MCT.The current gain of BJT is a critical parameter to describe the DD damages on AS-MCT.This work models the influence of self-build electrical field in graded-doped BJT on the DD effects of current gain.Thereafter,a general degradation model is proposed to describe the current gain degradation of both graded and uniform doped BJTs induced by DD.The trigger current,forward blocking leakage current and forward breakdown voltage are critical parameters of AS-MCT.Based on the current gain degradation model,the degradations of the three critical parameters from DD are analytically modeled.Our models provide an excellent fit to the experimental data of the XND1 AS-MCT subjected to fission neutrons.With the experiment data and equivalent leakage current resistance method,this work reports the study on the degradations of capacitor pulse discharging circuit characteristics induced by the DD in its AS-MCT switch,which contain the changes in charging time,and the decreases in both capacitor voltage and peak surging current.3.The ionization damage effects of AS-MCT are studied,and the mechanisms behind the ionization damage are proposed.The studies cover irradiation experiments,device damage effects and circuit damage effects.The XND1 AS-MCTs are irradiated by Co-60 source.The accumulated dose on the samples was up to 9160 Gy?Si O₂?.Then,this work proposes,from the prospective of simplified equivalent circuits,the?-induced effects on AS-MCT characteristics,which contain transfer,forward conductive and forward blocking characteristics.With the experiment data and equivalent leakage current resistance method,this work reports the study on the degradations of capacitor pulse discharging circuit characteristics induced by the ionization damage in its AS-MCT switch,which contain the changes in charging time,and the decreases in both capacitor voltage and peak surging current.4.This work discusses the radiation hardness techniques for AS-MCT.With the degradation model of current gain,this work proposes a DD-hardened AS-MCT structure by introducing a field-stop layer.The field-stop layer can suppress the depletion of N-base,which realizes the thinning of N-base and results in the decrease of carrier transit time in such region.Thereafter,the measure can alleviate the DD-defect-related recombination of carrier,and enhance the DD tolerance ability of trigger characteristic.The XND1 AS-MCT represents the highest level of technology available.The trigger current of field-stop AS-MCT exhibits better DD tolerance by a factor of 1.7 compared with that of XND1.Moreover,this work proposes an ionization-damage-hardened AS-MCT structure by the introduction of uniform doped channel and“Si₃N₄/Si O₂”double gate insulator.The measures can suppress the depletion of channel and the production of ionization defect.The variable lateral doping technique is adopted to form the uniform doped channel.Then,the leakage current in proposed structre exhibits better ionization damage tolerance by a factor of 7 compared with that in XND1.The work can benefit the further design and radiation hardness research of AS-MCT.The author hopes that this work could prompt the independent design and application of AS-MCT.