Solid State Device Fundamentals. MOS Capacitor

Transcription

1 Solid Stte Device Fundmentl MOS pcitor

2 Solid Stte Device Fundmentl Metl-Oxide-Semiconductor cpcitor MOS cpcitor i the centrl prt of emiconductor field effect trnitor. Gte metl Source te d Drin SiO 2 N + SiO 2 N + Si body P-ilicon body MOS cpcitor MOS trnitor

3 N + polyilicon P-Silicon body Solid Stte Device Fundmentl Enery bnd dirm of MOS cpcitor E c E c SiO 2, E c Gte Si ody No bi, = 0 In MOS cpcitor with p-type Si ubtrte, the enery bnd of ilicon bend down t the ide-ilicon interfce.

4 Solid Stte Device Fundmentl Flt-bnd condition nd flt-bnd volte Flt bnd i the condition where the enery bnd (E c nd ) of the ubtrte i flt t the Si SiO 2 interfce c SiO2 =0.95 e E c E 0 q 3.1 e 3.1 e c Si q = c Si + (E c ) =4.05e E c, E 0 i vcuum level E 0 =Ψ i work function E 0 E c i electron ffinity Si/SiO 2 enery brrier for electron i 3.1 e. N + -poly-si 9 e SiO e P-body The bnd i flt t the flt bnd volte : E c

5 Solid Stte Device Fundmentl nd dirm t netive bi of te At netive te volte: < 3.1e E c, E 0 q ccumultion of hole q E c M O S - urfce potentil, bnd bendin - volte cro the ide Since hole concentrtion i hih, the potentil drop in emiconductor Φ i neliible, thu:

6 Solid Stte Device Fundmentl Surfce ccumultion < Q cc ( ) Q / Q / cc

7 Solid Stte Device Fundmentl Poitive bi on te > q te SiO depletion lyer chre, Q dep P-Si body E c, q W dep depletion reion q E c Ev W dep Q 2 qn Q dep qn W dep M O S qn 2

8 Solid Stte Device Fundmentl Surfce depletion qn 2 Thi eqution cn be olved to yield.

9 Solid Stte Device Fundmentl ondition of threhold volte of inverion Threhold (of inverion): n = N, or (E c ) urfce = ( ) bulk, or A=, nd = D E c, t A D q = q t =q E c E i t 2 kt 2 ln q N n i M O S q E 2 ( E f E v ) bulk kt q ln N n i v kt q ln N N v kt q ln N n i

10 Solid Stte Device Fundmentl Inverion threhold volte φ At threhold, t 2 kt 2 ln q N n i qn 2 2 t t threhold 2 qn 2 2

11 Solid Stte Device Fundmentl Threhold olte t (), N + te/p-body T = 20nm t (), P + te/n-body ody Dopin Denity (cm -3 ) t 2 qn ub () for P-body, for N-body ody T = 20nm ody

12 Solid Stte Device Fundmentl Stron inverion > t W dep W dmx 2 2 qn Accumultion of electron > t E c Ev te q SiO E c, Q dep Q inv P- Si ubtrte M O S

13 Solid Stte Device Fundmentl Inverion lyer chre, Q inv [/cm 2 ] t 2 Q inv Q dep Q inv Q inv 2 qn 2 2 ( t ) Q inv > t > t

14 Solid Stte Device Fundmentl Threhold volte nd te dopin type t i enerlly et t mll poitive vlue o tht, t = 0, the trnitor doe not hve n inverion lyer nd current doe not flow between the two N + reion. p-body i normlly pired with n + -te to chieve mll poitive threhold volte. n-body i normlly pired with p + -te to chieve mll netive threhold volte.

15 Solid Stte Device Fundmentl nd bendin nd depletion width veru te volte 2 ccumultion t depletion inverion W dep W dmx W dmx = (2 2 /qn ) 1/2 ( ) 1/2 ccumultion depletion t inverion

16 Solid Stte Device Fundmentl Summry N-type device: N + -polyilicon te over P-body P-type device: P + -polyilicon te over N-body ( Q / ) poly Q / poly

17 Solid Stte Device Fundmentl Summry t 2 kt ln q N ubtrte n i t t qn ub 2 t + for N-type device, for P-type device

18 Solid Stte Device Fundmentl N-type Device (N + -te over P-ubtrte) < <0 E = <0 f N-type Device (N + -te over P-ubtrte) Summry Accumultion Flt-bnd P-type Device (P + -te over N-ubtrte) P-type Device E (P + f -te over N-ubtrte) > >0 = >0 = <0 0> Flt-bnd Depletion = >0 0< Depletion 0> E = t >0 f Threhold 0< = t <0 Threhold = t >0 = t <0 Inverion >>0 E < t