NewGenerationofHigh–PowerSemiconductorClosingSwitchesforPulsedPowerApplicationsI.IntroductionSolidstatesemiconductorswitchesareveryinvitingtouseatpulsedpowersystemsbecausetheseswitcheshavehighreliability,longlifetime,lowcostsduringusing,andenvironmentalsafetyduetomercuryandleadareabsent.Semiconductorswitchesareabletoworkinanyposition,so,itispossibletodesignsystemsasforstationarylaboratoryusing,andformobileusing.Thereforetheseswitchesarefrequentlyregardedasreplacementofgas-dischargedevices–ignitrons,thyratrons,sparkgapsandvacuumswitchesthatgenerallyusenowinhigh-powerelectrophysicalsystemsincludingpowerlasers.Traditionalthyristors(SCR)aresemiconductorswitchesmostlyusingforpulsedevices.SCRhassmallvalueofforwardvoltagedropatswitch-onstate,ithashighoverloadcapacityforcurrent,andatlastithasrelativelylowcostvalueduetothesimplebipolartechnology.DisadvantageofSCRisobservedatswitchingofcurrentpulseswithveryhighpeakvalueandshortduration.Reasonofthisdisadvantageissufficientlyslowprocessofswitch-onstateexpansionfromtriggeringelectrodetoexternalborderofp-njunctionaftertriggeringpulseapplying.ThisSCRfeatureisdefinedSCRusingintomillisecondrangeofcurrentswitching.ImprovementofSCRpulsecharacteristicscanbereachedbyusingofthedistributedgatedesign.Thisisallowedtodecreasethetimeoftotalswitch-onandgreatlyimproveSCRswitchingcapacity.Thus,ABBcompanyisexpandedthesemiconductorswitchusinguptomicrosecondrangebydesignofspecialpulseasymmetricthyristors(ASCR).ThesedeviceshavedistributinggatestructurelikeaGTO.Thisthyristordesignandforcedtriggeringmodeareobtainedthehighswitchingcapacityofthyristor(=150kA,=50μs,di/dt=18kA/μs,singlepulse).However,inthisdesigngatestructureiscoveredlargeactiveareaofthyristor(morethan50%)thatdecreasetheefficiencyofSiusingandincreasecostofdevice.Si-thyristorsandIGBThavedemonstratedhighswitchingcharacteristicsatrepetitivemode.However,suchdevicesdonotintendforswitchingofhighpulsecurrents(tensofkiloamperesandmore)becauseofwell-knownphysicallimitsareexistedsuchaslowdopingofemitters,shortlifetimeofminoritycarriers,smallsizesofchipsetc.Ourinvestigationhaveobtainedthatswitchesbasedonreverse–switcheddinistorsaremoreperspectivesolid-stateswitchestoswitchsuperhighpowersatmicrosecondandsubmillisecondranges.Reverse–switcheddinistors(RSD)istwo-electrodeanalogueofreverseconductingthyristorwithmonolithicalintegratedfreewheelingdiodeinSi.ThisdiodeisconnectedinparallelandinthebackdirectiontothethyristorpartofRSD.TriggeringofRSDisprovidedbyshortpulseoftriggercurrentatbriefapplyingofreversalvoltagetoRSD.DesignofRSDismadethusthattriggeringcurrentpassesthroughdiodeareasofRSDquasiaxiallyanduniformlyalongtheSistructurearea.Thiscurrentproducestheoncominginjectionofchargecarriersfrombothemitterjunctionstobaseregionsandinitiatestheregenerativeprocessofswitch-onforRSDthyristorareas.SuchmethodoftriggeringforthisspecialdesignofSiplateisprovidedtotalanduniformswitchingofRSDalongallactiveareaintheveryshorttimelikeasdiodeswitch-on.ThefreewheelingdiodeintegratedintotheRSDstructurecouldbeusedasdampingdiodeatfaultmodeinthedischargecircuit.Thisfaultmodesuchasbreakdownofcablelinescanleadtooscillatingcurrentthroughswitch..IthasbeenexperimentallyobtainedinthatsemiconductorswitchesbasedonRSDcanworksuccessfullyinthepulsedpowersystemstodriveflashlampspumpinghigh-powerneodymiumlasers.ItwasshowninthatRSD-switches...
