《半導(dǎo)體器件物理》

1、半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices1MOSFET AND RELATED DEVICE半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices2 半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices3SiO2metalsemiconductorSiO2semiconductordOhmic contact The MOS Diode is of paramount important in semiconductor device physics b

2、ecause the device extremely useful in the study of semiconductor surfaces.半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices4The Ideal MOS Diode半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices5An ideal MOS diode is defined as follows: At zero applied bias,02BEmsmmsqqqqqqg The only charges that exist i

3、n the diode under any biasing conditions are those in the semiconductor and those with equal but opposite sign on the metal surface adjacent to the oxide. There is no carrier transport through the oxide under the direct current dc)-biasing conditions, or the resistivity of the oxide is infinite.半導(dǎo)體器

4、件物理2021-7-16Physics of Semiconductor Devices6Operation Modes半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices7Energy Band Diagrams And Charge DistributionAccumulation :半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices8Accumulation:QmQS-dxCharge DistributionkTEEiPFienPxE(X)Electric Field An accumulatio

5、n of holes near the oxide-semiconductor interface.半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices9Depletion:EFVg0EFEvEcEiWqNQAscCharge DistributionE(X)xElectric FieldxwQm-d)(x半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices10Strong Inversion:kTEEipiFenn半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devic

6、es11Strong Inversion:xwmQm-dQnQscmAnscnsWqNQQQQxE(x) Once strong inversion occurs, a very small increase in band bending corresponding to a very small increase in depletion-layer width results in a large increase in the Qn in the inversion layer, so the surface depletion-layer with reaches a maximum

7、, Wm.)(x半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices12The Surface Depletion Region is the band bending with boundary conditions0in the bulk ands)0(EFEiSemiconductor surfaceECEvEgBqsqOxidexP-type silicon)(xq0s半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices13At the surface the densities are:kTqip

8、Bsenn)(kTqipsBenp)( In the MOS diode, the following regions of surface potential can be distinguished:0sAccumulation of holes (bands bend upward)0sFlat band condition0sBDepletion of hole (bands bend downward)BsMidgap with ns=np=ni (intrinsic concentration)BsInversion (bands bend downward)半導(dǎo)體器件物理2021

9、-7-16Physics of Semiconductor Devices14The potentialas a function of distance can be obtainedby using the one-dimensional Poissons equation:ssxdxd)(22After using the depletion approximation that we employed in the study of p-n junctions.21WxsThe surface potentialsis:SAsWqN222半導(dǎo)體器件物理2021-7-16Physics

10、of Semiconductor Devices15The criterion of the onset of strong inversion: iABsnNqkTinvln22)(The maximum width of the surface depletion region:AiAsABsmqNnNkTqNWln2)2(2and)2(2BAsscNqQ半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices16Surface Charge vs. Surface Potential半導(dǎo)體器件物理2021-7-16Physics of Semico

11、nductor Devices17 The relationship between Wm and the impurity concentration for silicon and gallium arsenide, where NB is equal to NA for P-type and ND for n-type semiconductor.半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices18Capacitance in a MOS capacitorSmall signal capacitance MOS capacitance i

12、s defined as small signal capacitance and is measured by applying a small ac voltage on the top of a dc biasdtdVCdtdVdVdQdtdQIGGGGG半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices19C-V Curves半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices20Frequency Effect The frequency of ac signal play an importa

13、nt role in the capacitance of a MOS Capacitor (after Grove, et al.)半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices21Ideal MOS CurvesQm0VDepletion regionxw-d-Qn-qNA)(xsEFECEi0qV0VBqsqjxEFInversion regionEvQSNeutrals region Band diagram(p-type substrate)Charge distribution半導(dǎo)體器件物理2021-7-16Physics of S

14、emiconductor Devices22)(x-d0wx0oxsQElectric-field Distribution-dv0vswx0)(xPotential Distribution The applied voltage will appear partly across the oxide and partly cross the semiconductor.sVV0000CQdVS半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices23Capacitance at Low FrequencyLow frequency or quasi

15、-static Majority and minority carrier can respond with ac signal and reach at equilibrium condition)2exp(kTqQsssgoxsSoxVqkTCddQCC211111oxCVQCSiCoxCQQ半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices24 dsisasisddWqNdQdC2)(soxsaisoxdagCqNCWqNV2)2(12asigoxoxqNVCCCoxCDCQQW半導(dǎo)體器件物理2021-7-16Physics of Semic

16、onductor Devices25 oxCinvCsgoxsSoxVqkTCddQCC211111QQwdm Once the inversion layer forms, the capacitance starts to increase, since csi is now given by the variation of the inversion charge with respect to which is much large than the depletion capacitancess半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Dev

17、ices26 In low frequency, the generation-recombination rates in the surface depletion region are equal to or faster than the voltage variation, then the electron concentration (minority) can follow the alternating current (ac) signal and lead to charge exchange with the inversion layer in step with t

18、he measurement signal. The incremental charges appears at the edge of the depletion region in high measurement frequency.半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices27MOSFET Fundamentals半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices28Structure of MOSFET半導(dǎo)體器件物理2021-7-16Physics of Semiconductor

19、Devices29Types of MOSFET半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices30Non-equilibrium Condition半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices31Linear Region &Saturation Region半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices32半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices33Currents in Lin

20、ear Region半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices34Operation RegionsActing as a resistor.DDVI)(0tanTGntconsVDDDVVCLZVIgGDntconsVGDDVCLZVIgD0tan)(0TGnDVVCLZI半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices35Pinch-off PointThe thickness of inversion xi (y=L) =0半導(dǎo)體器件物理2021-7-16Physics of Semic

21、onductor Devices36Current in Saturation Region半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices37A MOSFET can be divided into many capacitor fragmentsVC decrease in this directionvcSource SidePinch offDrain SideVc=0 means no charges inducedElectron current flow半導(dǎo)體器件物理2021-7-16Physics of Semiconductor

22、 Devices38Saturation Region (VDVDsat)ID=constant202TGnDsatVVLCZI0tantconsVDDDGVIgTGoxntconsVGDmVVdLZVIgDtanL L半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices39 The upper characteristics can be derived under the following ideal conditions: The gate structure corresponds to an ideal MOS diode. Only d

23、rift current considered. Carrier mobility in the inversion layer is constant. Doping in the channel is uniform. Reverse-leakage current is negligibly. The gradual channel approximation.半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices400)()(CyVyQsGs)(22)(yVqNWqNyQBAsmAsc)()()(yQyQyQscsndxxLZgx)(10dRI

24、dVDgLdydR 232300)2()2(23222BBGAsDDBGnVCqNVVVCLZI半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices41 Idealized drain characteristics of MOS diode半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices42nMOST的輸出特性曲線(xiàn)的輸出特性曲線(xiàn)半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices43從另一方面來(lái)看，溝道漏端從另一方面來(lái)看，溝道漏端 LVVVCLQTGSoxn

25、VDS=VDsat=VGS-VT時(shí)，時(shí)，Qn(L)=0這種情況叫做漏端溝道夾斷。這種情況叫做漏端溝道夾斷。 現(xiàn)在一般用溝道漏端夾斷來(lái)解釋長(zhǎng)溝道器件現(xiàn)在一般用溝道漏端夾斷來(lái)解釋長(zhǎng)溝道器件VDSVDsat時(shí)時(shí)的漏極電流飽和現(xiàn)象。這需要從幾個(gè)方面來(lái)加以說(shuō)明。的漏極電流飽和現(xiàn)象。這需要從幾個(gè)方面來(lái)加以說(shuō)明。 首先首先VDS超過(guò)超過(guò)VDsat以后，溝道夾斷點(diǎn)的電勢(shì)始終都等于以后，溝道夾斷點(diǎn)的電勢(shì)始終都等于VGS-VT。設(shè)想夾斷點(diǎn)移動(dòng)到設(shè)想夾斷點(diǎn)移動(dòng)到y(tǒng)=L，則有，則有 0LVVVCLQTGSoxn很容易看的出來(lái)很容易看的出來(lái)TGSVVLV) (由此得出結(jié)論，未夾斷區(qū)的電壓將保持等于由此得出結(jié)論，未夾斷區(qū)

26、的電壓將保持等于VGS-VT不變。不變。半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices44溝道漏端夾斷的溝道漏端夾斷的nMOST半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices45 其次，當(dāng)其次，當(dāng)VDVDsat時(shí)，超過(guò)時(shí)，超過(guò)VDsat的那部分外加電壓，即的那部分外加電壓，即VDS-VDsat，降落在夾斷區(qū)上。夾斷區(qū)是已耗盡空穴的空間電，降落在夾斷區(qū)上。夾斷區(qū)是已耗盡空穴的空間電荷區(qū)，電離受主提供負(fù)電荷，漏區(qū)一側(cè)空間電荷區(qū)中的電離荷區(qū)，電離受主提供負(fù)電荷，漏區(qū)一側(cè)空間電荷區(qū)中的電離施主提供正電荷

27、，它們之間建立沿溝道電流流動(dòng)方向（施主提供正電荷，它們之間建立沿溝道電流流動(dòng)方向（y方方向）的電場(chǎng)和電勢(shì)差，漏區(qū)是高摻雜的，漏區(qū)和夾斷區(qū)沿向）的電場(chǎng)和電勢(shì)差，漏區(qū)是高摻雜的，漏區(qū)和夾斷區(qū)沿y方向看類(lèi)似于一個(gè)方向看類(lèi)似于一個(gè)N+P單邊突變結(jié)，結(jié)上壓降增大時(shí)空間電單邊突變結(jié)，結(jié)上壓降增大時(shí)空間電荷區(qū)主要向荷區(qū)主要向P區(qū)一側(cè)擴(kuò)展。所以當(dāng)夾斷區(qū)上電壓降（區(qū)一側(cè)擴(kuò)展。所以當(dāng)夾斷區(qū)上電壓降（VDS-VDsat）增大時(shí)，夾斷區(qū)長(zhǎng)度增大時(shí)，夾斷區(qū)長(zhǎng)度 擴(kuò)大，有效溝道長(zhǎng)度擴(kuò)大，有效溝道長(zhǎng)度L縮短?？s短。L 對(duì)于長(zhǎng)溝道對(duì)于長(zhǎng)溝道MOST，如果在所考慮的，如果在所考慮的VDS范圍內(nèi)始終是范圍內(nèi)始終是 VDsat情形

28、下，未夾斷區(qū)的縱向及橫向電場(chǎng)和情形下，未夾斷區(qū)的縱向及橫向電場(chǎng)和電荷分布基本上與電荷分布基本上與VDVDsat時(shí)相同，從溝道點(diǎn)到源端之間的時(shí)相同，從溝道點(diǎn)到源端之間的電阻因而也保持不變?？紤]到電阻因而也保持不變?？紤]到 VDVDsat未夾斷區(qū)壓降始終等未夾斷區(qū)壓降始終等于于VGS-VT，所以漏極電流恒定不變，這就是電流飽和。，所以漏極電流恒定不變，這就是電流飽和。L半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices46 ion implantation into the channel region半導(dǎo)體器件物理2021-7-16Physics o

29、f Semiconductor Devices47 Varying the oxide thickness The VT of the field oxide is typically an order of magnitude larger than that of the thin gate side.半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices48 Substrate biasBBSBAsTVCqNV2220半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices49The Subthreshol

30、d Region VgVtmVVVtgds半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices50The drain current is dominated by diffusion半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices51Subthreshold swings, SoxdmgdsCCqkTqmkTdVIdS13 . 23 . 2log110 Except for a slight dependence on bulk doping concentration through Cdn, S

31、is rather insensitive to device parameters.半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices52Voltage Transfer CharacteristicSymmetry Design ConceptNoise MargintptnVVppnnLWkLWkIHOHHVVNMtDDVV2381OLILLVVNMtDDVV2381半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices53Dynamic Operation DDnnPHLVLWkCt7 . 1DDP

32、pPLHVLWkCt7 . 1PLHPHLPttt21半導(dǎo)體器件物理2021-7-16Physics of Semiconductor Devices54Power DissipationPower dissipation:Dynamic and staticDynamic power consumptionFor an inverterPower supply: VDDLoad capacitance: CDynamic PowerPower:2DDDCVfP2DDDCVfP2DDDDDDDDCVQVidtVidtV2DDDDDDDDCVQVidtVidtVEnergy stored in c:200021DDVCVdvcvidtvDD Energy dissipated by Qp:221DDCV Energy