MOSFET Threshold Voltage: Definition, Extraction, and Applications

Transcription

1 MOSFET Threshold Volage: efnon, Exracon, and Applcaons M. B. Machado, O. F. Sebel, M. C. Schneder, and C. Galup-Monoro Federal Unversy of Sana Caarna Brazl

2 Conens 1 Classcal and curren-based hreshold defnon 2 The g ds /I procedure 3 Comparson of he dfferen curren-based exracon mehods 4 Applcaons 5 - Conclusons 2

3 Classcal hreshold volage (V T ) defnon Classcal (surface poenal based) defnon of hreshold: 2 S F V C Where : S - surface poenal for V G =V T F - Ferm poenal n he subsrae V C - channel poenal In prncple he drec deermnaon of he hreshold volage s possble 1) calculae he sauraon dran curren I Th for 2) njec I Th no he ranssor and measure V G = V T rawbacks 2 V - geomercal (W, L) and echnologcal parameers ( mobly, oxde hckness,.. ) are needed o calculae I Th - he ranssor operaes n he sauraon regon where several secondary effecs are relevan S F C 3

4 Curren-based Threshold defnon. Threshold volage s defned as he gae volage a whch he condon I drf = I dff holds. 130 nm (ox=2.2nm ), W/L= 720 nm /180 nm V G = V T V S = /2=13mV 4

5 Classcal vs. curren-based defnons Physcal Meanng s Value of a hreshold Value of Q I a hreshold fference n V T relave o he classcal defnon Classcal x Curren based Surface concenraon of elecrons= bulk concenraon of holes rf componen = ffuson componen of dran curren 2 F V 2 F V C ( n 1) C ox 0 C n ln n n 1 C ox n 1 nln n 1 n s he slope facor gven by C' b ( V n 1 C' ) ox where C ox s he oxde capacance per un area C s he depleon capacance per un area b GB 5

6 Ideal hreshold volage exracon procedure No parameers are needed o calculae he hreshold curren The ranssor operaes a low curren levels and n he lnear regon o mnmze seres ressances and shor channel effecs Fxed V GB o avod varaon n he slope facor g ds /I procedure 6

7 The g ds /I procedure rec deermnaon of MOSFET parameers from he I vs V S curve a low V S (lnear regon) V G =0.42V V S = /2=13mV TSMC 0.35 µm, W/L= 12 µm /0.5 µm I g ms V S g md V 7

8 The g ds /I mehodology exracon of V T and I S From ranssor model V P I V g I S ( ) S ms 2IS ( d ) 1 f ( r) 1 f r I S C' OX 2 n 2 W L 1 f ( r) 2 ln 1 f ( r) 1 g I ds g I 1 I ds max di dv 1 S 1 f 2 TSMC 0.35 µm, W/L= 12 µm /0.5 µm 1 r When f = 3 V S = /2 gds I 0.53* and 1 gds I 0.53* 1 V G = V T0! V P =V S V T0 = V G when V P = 0 V P = V S 8 I S = 1.14*I 8

9 Auomac V T -exracor crcu - based on g ds /I procedure Basng condon V S = /2 (lnear regon) f = 3 r = 2.12 From ranssor model f r 0. IS I I 88 S V S = /2 V P V S ( ) 1 f ( r) 2 ln 1 f ( r) 1 V P = 0 Auomac V T -exracor crcu V G = V T0 9

10 g ds /I x g m /I mehods g ds /I g m /I g I ds gm 1 g I n I 1 ds f 2 1 r TSMC 0.35 µm, W/L= 125, BSIM3v3 g ds /I s ndependen of slope facor (n). 10

11 Consan curren (CC) mehod For a sauraed ranssor based wh I =3*I S, we have V G =V T for V S =0. From ranssor model V P V S ( ) 1 f ( r) 2 ln 1 f ( r) 1 For V P V G V n T f = 3 V S = 0 V P =0 and V G =V T The CC mehod was used n a prevous V T -exracor crcu for rackng he V T varaon as a funcon of a specfc parameer, e.g. emperaure or onzng radaon. 11

12 Measured V T values vs. L mask for dfferen exracon mehods Mehod g m /I g ds /I CC Operang regon Lnear Lnear Sauraon TSMC 0.18 µm, W/L= 100 These mehods presen smlar behavors, especally for g m /I and g ds /I mehods. 12

13 Applcaons The hreshold volage s a fundamenal elecrcal parameer ha can be used n: echnology characerzaon agng evaluaon machng assessmen emperaure and radaon sensors 13

14 Example of applcaon: Machng assesmen TSMC 0.35 µm, W/L= 12 µm /0.5 µm V T average values: g m /I CC 629mV 611.5mV Relave sandard devaon g m /I 0.59% CC 0.55% Boh mehods presen smlar behavor and almos he same relave sandard devaon. 14

15 Example of applcaon: V T varaon vs. emperaure TSMC 0.35 µm, W/L= 12 µm /0.5 µm In hs example, he CC mehod s used for rackng he V T varaon as a funcon of a specfc parameer (emperaure). 15

16 Conclusons A new procedure for he drec deermnaon of he hreshold volage wh mnmum nfluence of second order effecs s nroduced The hreshold volage s deermned a a consan gae-osubsrae volage, a a low dran-o-source volage and wh ranssor operaon n he weak and moderae nverson regons. Under hese operang condons he effecs of seres ressances, mobly and slope facor varaons, and channel lengh modulaon are praccally neglgble, allowng a drec deermnaon of he hreshold volage. The curren-based exracon n weak-moderae nverson allows he desgn of low power V T -exracor crcus. 16