Thyristors. Vitezslav Benda Dept. of Electrotechnology Czech Technical University in Prague Czech Republic

Transcription

1 Thyrisors iezslav Beda De. of Elecroechology Czech Techical Uiversiy i rague Czech Reublic

2 Thyrisors - family of swichig devices cosisig of four layers of semicoducor of aleraig doa ye (). Three-ermial hyrisor swiches (riode hyrisors) are he mos imora members of his family. - + J 3 J + J The hree oeraig saes of a hyrisor srucure The aode is egaively biased wih resec o he cahode,, - a high imedace sae called he reverse blockig sae ( R, R ) The aode is osiively biased wih resec o he cahode - a high imedace sae he forward blockig sae ( D, D ) - a low imedace sae he forward coducig sae ( T, T ) T L BR H R T

3 The (Reverse) Blockig Sae + (+ve) reverse blockig sae ) avalache breakdow a jucio J ε rε EBR BR ed D(BO) R(BR) ) breakdow a resul of uch-hrough edw T ε rε w is he hickess of he -regio J 3 J J (a) J 3 J J (-ve) (-ve) Sace-c harge layer Sacecharge layer forward blockig sae The breakdow volage is maximum whe D ε rε E ew The srucure ca be regarded as ha of a rasisor coeced i commo-emier cofiguraio BR (b) (+ve) R(BR) BR ~ γ cosh w R L κ

4 Surface rofiles for High Breakdow olages large-area devices of a circular shae, surface bevellig is ofe used. The surface is mechaically beveled, eched, ad assivaed wih silico rubber For DRM < 35, osiive-egaive or double osiive bevellig are ofe used (a) double egaive bevellig (b) osiive - egaive bevellig For high volages, double osiive bevellig is mosly used (c) double osiive bevellig (d) double osiive bevellig devices of a recagular shae, he guard rig, filed lae ad SOS echiques are used, oo.

5 The Two-Trasisor Model for Thyrisor Swichig C C (a) (b) (c) he case of oe gae ( ) + E E C C C M ( α ) M ( α + ) + M The aode curre is he Thyrisor urs o ( ) if For > E C ( ) - M ( α + α ) Collecor curres of he arial rasisor srucures C C E M α C +α Suosig D << BR, M, ad α + C α ( α + )

6 To decrease emeraure deedece of D(BO), i is ecessary o decrease ijecio efficiecy of he cahode emier by cahode shors R SH J 3 J J + Sace-charge layer (a) (b) Sice J3 SH R SH, his becomes α < J 3 eff α α J 3 + SH The ur-o codiio is ow α +α eff

7 Criical d/d f he blockig volage icreases wih he rae d D /d, he dislaceme curre desiy J q d d ( C ) j D C j + D dc d j D d d has a effec similar o a osiive gae curre, herefore a cahode shor aer is geerally used The dislaceme curre flows radially o a shor wih a desiy r ( r) J π rdr J π ( r r ) q r q The radial oeial gradie is: d ( r) D dr ρ π rw (r -r ) r The volage bewee r ad r, ca be exressed as SH r r d dr dr ρj r w q r F r E F r l r 4 r r F E is a volage causig he direc ijecio from + jucio ha occurs a a criical curre desiy w ρr F J qcri E J q J qcri d d D d d D cri 5 r 5 r

8 The Forward Coducig Sae + + J+ J+ w he wo rasisor model, a leas oe of he arial rasisor srucures mus be sauraed whe he hyrisor is i he o-sae α α + J J < T T + i + The ier layers are flooded wih excess carriers due o high ijecio from boh + ad + emiers (elecro-hole lasma) carrier coceraio -w/ w/ x The o-sae characerisic of a hyrisor is similar o a forward diode characerisic T αkt + e l J w cosh J L a m F oeial J+ w comlicaes he DRM T rade-of J+ w w + w + x

9 α α The ur-o codiio + < J J is valid for curre desiies J T > J M T T + Sace-charge regio J 3 J + + off o The miimum curre desiy J M is i order /cm. J large-area devices, oly a orio T of he oal area + J J J 3 T J T M is ured-o (elecro-hole lasma) Some differeces from a diode-like characerisics ca be observed a lower curres

10 Trasie rocesses durig Tur-O..9 D. D D D d g f Whe a gae imuls is alied, a chage of characerisics ca be observed wih a delay w w d > + D D The delay ime is coeced wih a miimum riggerig charge Q T. Therefore, he d deeds o he gae curre d τ l T The ur-o ime + The fall ime f deeds o he d T /d i he circui g d f T dt d The origial ur-o regio is close o he gae coac ad i sreads due o a laeral velociy The saic o-sae chracerisic is reached for v s l J + B v s J J M

11 Criical di/d high d T /d. he begiig a area is ured-o. Eergy dissiaed i he ur-o area W W d ( ) d ( ) cri For W > W cri he hermal breakdow occurs d T /d < (d T /d) cri large is ecessary a large gae sigal is ecessary for High di/d oeraios The amlifyig gae cosrucio J J 3 + uxiliary cahode J +

12 Trasie rocesses durig Tur-off Turig hyrisor off, is is ecessary o remove charge of excess carriers sored i ier layers (elecro-hole lasma) o resore he sace charge regio a he jucio J (he blockig sae). could be realised by. Tur-off whe he o-sae curre decreases below he holdig curre. Tur-off by circui commuaio 3. Tur-off brough abou by he alicaio of a egaive gae volage. Tur-off by a Decrease of Forward Curre. α α For o-sae curre desiy,j T + < J J The miimum o-sae curre desiy J M ( /cm < J M < /cm ) is a fucio of layer hickess, carrier lifeime ad emier efficiecy ad emeraure (a deedece o he cahode shu desiy rereseed by he geomeric facor F is demosraed i figure) f he o-sae curre decreases, he ured-o area decreases, so ha he curre desiy remais a J M. T T The holdig curre, H, deeds o he rae of decrease of he o-sae curre, he miimum holdig curre H is for very slow decrease of T. f he geomeric facor, F, ca be reduced raidly, by makig emier shors elecroically, i is ossible o ur he hyrisor off icreasig he holdig curre. This ricile is used i he ur-off rocess of he MOS-Corolled Thyrisor

13 Thyrisor Tur-off Usig Circui Commuaio Wih a dc-suly, ur-off requires a auxiliary source ha is able o commuae he aode curre whe i is alied o he hyrisor for a shor ime. The ur-off ime q is he ierval from he isa ha he fallig aode curre crosses zero uil he mome ha he aode volage agai becomes osiive. The excess carrier disribuio i a hyrisor i he o-sae is similar o ha i a forward biased + + diode. Therefore, he reverse recovery akes lace i a similar way. he sorage ime s, a charge Q remais i ier layers of hyrisor srucure. The hyrisor urs off successfully oly if he excess free charge remaiig i he device afer q is less ha some criical value, Q cr. q s + τ eff Q l Q cr τ eff Q l Q Q, deeds o he circui commuaio codiios (di R /d ad R ) The criical charge, Q cri, decreases wih icreasig d D /d a recovery ad emeraure. cr

14 The criical charge Q cri decreases wih boh d D /d ad emeraure shor carrier lifeime is ecessary for obaiig a shor ur-off ime q. From ha follows a comlicaed rade-off bewee DRM, T, ad q

15 Basic iverer circuis SCR C SCR fas reverse blockig hyrisor is ecessary i L v L L The soluio wih aiarallel diodes ivolves he use of assymerical hyrisors wih he T cosrucio (SCR) or wih a iegraed aiarallel diode RCT- Reverse Coducig Thyrisor C Diode Secio s Thyrisor Secio SCR D D SCR D 3 Load + +

16 ae Tur-Off he wo-rasisor aalogy, he aode curre ca be exressed as: α + α α + + ( ) α lyig a egaive gae gurre The maximum available ur off gai offm The off has a maximum whe α is high ad α is low Q Q α α + α Reverse blockig (T) TO large -base hickess ad a low carrier lifeime o kee α low ssymerical (T) TO α decreased by he use of aode shors

17 The maximum allowable egaive gae curre he laeral resisace of he -base layer R he breakdow volage of jucio J 3, (BR), M 4 (BR) R is limied by TQM 4 offm R (BR) 4α (BR) ( α + α ) R The high-ower TO mus be cosruced as a iegraio of may -arallel coeced segmes. The maximum o sae curre TQM deeds o umber of segmes TQM

18 The sored charge eriod a charge of excess carriers from he -base mus be removed Q ew av Q ( w + w ) ( w + w ) o τ gs H av (BR) he sorage ime gs gs Q w τ H τ H off ( w + w ) ( w + w ) w RM off / < offm This meas oeraig he hyrisor a a lower ur-off gai off, he gae sigals should be see gs d / d C s Courses of curre ad volage durig he ur-o rocess deed o he load. For a resisive load.8τ H ε ε rs g f w + w e ( ) D T T.9 T. T s gs gq gf Tail curre Resisive load Effec of subber D s R s To decrease loses durig ur-o, subbers are ofe used

19 Differece i sorage ime of TO segmes wih differe carrier lifeime gs τ H w w + w ll he curre coceraes i he wih he loges carrier lifeime a ossibiliy of desrucio Maximum Miimum carrier lifeime ( s) irradiaio dose ( - cm - )

20 To decrease differeces i he sorage ime gs a higher egaive gae imulse may be alied gs τ H w w + w For >, i is ossible o obai siuaio whe all segmes ur-off a he same ime ad he cahode curre is o coceraed oly for a few segmes i he ed of he ur-off CT - ae Commuaed Thyrisors he case cosrucio wih a arasiic iducace i he gae elecrode below 5 H CT egraed ae Commuaed Thyrisor iegraio of a CT wih a source of gae sigals ivolvig d /d > /µs

21 LTT Ligh Triggerig Thyrisor bsorio deh (micros) he alicaio of ligh (hν > W g ), oical geeraio of elecro-hole airs occurs. The effec of he oical carrier geeraio is similar o ha of he elecro ijecio from he + emier followig he alicaio of a osiive gae volage Wavelegh (micros) Ligh uide + + To obai saisfacory ur-o wih a reasoably low oical ower, while o he oher had high values of he arameers, (d D /d) cri ad (d T /d) cri, are required, he srucure ad layou of he oical gae regio is very imora - + Oical ower desiy r