半导体器件物理.pptx

2024/4/22 周一Physics of Semiconductor Devices1OUTLINE The Power MOSFET The MOS Diode MOSFET Fundamentals MOSFET Scaling COMS and BiCOMS MOSFET on Insulator MOS Memory Structure2024/4/22 周一Physics of Semiconductor Devices2SiO2metalsemiconductorSiO2semiconductordOhmic contact The MOS Diode is of paramount important in semiconductor device physics because the device extremely useful in the study of semiconductor surfaces.2024/4/22 周一Physics of Semiconductor Devices3The Ideal MOS Diode2024/4/22 周一Physics of Semiconductor Devices4An ideal MOS diode is defined as follows:a)At zero applied bias,b)The only charges that exist in 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.c)There is no carrier transport through the oxide under the direct current dc)-biasing conditions,or the resistivity of the oxide is infinite.2024/4/22 周一Physics of Semiconductor Devices5Operation Modes2024/4/22 周一Physics of Semiconductor Devices6Energy Band Diagrams And Charge DistributionAccumulation:2024/4/22 周一Physics of Semiconductor Devices7Accumulation:QmQS-dxCharge DistributionxE(X)Electric Field An accumulation of holes near the oxide-semiconductor interface.2024/4/22 周一Physics of Semiconductor Devices8Depletion:EFVg0EFEvEcEiCharge DistributionE(X)xElectric FieldxwQm-d2024/4/22 周一Physics of Semiconductor Devices9Strong Inversion:2024/4/22 周一Physics of Semiconductor Devices10Strong Inversion:xwmQm-dQnQscCharge DistributionCharge DistributionElectric FieldElectric FieldxE(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,Wm.2024/4/22 周一Physics of Semiconductor Devices11The Surface Depletion Region is the band bending with boundary conditionsin the bulk andEFEiSemiconductor surfaceECEvEgOxidexP-type silicon2024/4/22 周一Physics of Semiconductor Devices12At the surface the densities are:In the MOS diode,the following regions of surface potential can be distinguished:Accumulation of holes(bands bend upward)Flat band conditionDepletion of hole(bands bend downward)Midgap with ns=np=ni(intrinsic concentration)Inversion(bands bend downward)2024/4/22 周一Physics of Semiconductor Devices13The potentialas a function of distance can be obtainedby using the one-dimensional Poissons equation:After using the depletion approximation that we employed in the study of p-n junctions.The surface potentialis:2024/4/22 周一Physics of Semiconductor Devices14The criterion of the onset of strong inversion:The maximum width of the surface depletion region:and2024/4/22 周一Physics of Semiconductor Devices15Surface Charge vs.Surface Potential2024/4/22 周一Physics of Semiconductor Devices16 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.2024/4/22 周一Physics of Semiconductor Devices17Capacitance in a MOS capacitorSmall signal capacitance MOS capacitance is defined as small signal capacitance and is measured by applying a small ac voltage on the top of a dc bias2024/4/22 周一Physics of Semiconductor Devices18C-V Curves2024/4/22 周一Physics of Semiconductor Devices19Frequency Effect The frequency of ac signal play an important role in the capacitance of a MOS Capacitor(after Grove,et al.)2024/4/22 周一Physics of Semiconductor Devices20Ideal MOS CurvesQmDepletion regionxw-d-Qn-qNAEFECEiEFInversion regionEvQSNeutrals region Band diagram(p-type substrate)Charge distribution2024/4/22 周一Physics of Semiconductor Devices21-d0wxElectric-field Distribution-dv0vwx0Potential Distribution The applied voltage will appear partly across the oxide and partly cross the semiconductor.2024/4/22 周一Physics of Semiconductor Devices22Capacitance at Low FrequencyLow frequency or quasi-static Majority and minority carrier can respond with ac signal and reach at equilibrium conditionP-type substP-type substraterateAccumulationAccumulation 2024/4/22 周一Physics of Semiconductor Devices23DepletionDepletion W2024/4/22 周一Physics of Semiconductor Devices24InversionInversion wdm 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 capacitance2024/4/22 周一Physics of Semiconductor Devices25 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 the measurement signal.The incremental charges appears at the edge of the depletion region in high measurement frequency.2024/4/22 周一Physics of Semiconductor Devices26MOSFET Fundamentals2024/4/22 周一Physics of Semiconductor Devices27Structure of MOSFET2024/4/22 周一Physics of Semiconductor Devices28Types of MOSFET2024/4/22 周一Physics of Semiconductor Devices29Non-equilibrium Condition2024/4/22 周一Physics of Semiconductor Devices30Linear Region&Saturation Region2024/4/22 周一Physics of Semiconductor Devices312024/4/22 周一Physics of Semiconductor Devices32Currents in Linear Region2024/4/22 周一Physics of Semiconductor Devices33Operation RegionsActing as a resistor.Linear Region(VLinear Region(VD DVVDsat)ID=constantL L2024/4/22 周一Physics of Semiconductor Devices38 The upper characteristics can be derived under the following ideal conditions:a)The gate structure corresponds to an ideal MOS diode.b)Only drift current considered.c)Carrier mobility in the inversion layer is constant.d)Doping in the channel is uniform.e)Reverse-leakage current is negligibly.f)The gradual channel approximation.2024/4/22 周一Physics of Semiconductor Devices392024/4/22 周一Physics of Semiconductor Devices40 Idealized drain characteristics of MOS diode2024/4/22 周一Physics of Semiconductor Devices41nMOST的输出特性曲线的输出特性曲线2024/4/22 周一Physics of Semiconductor Devices42从另一方面来看，沟道漏端从另一方面来看，沟道漏端VDS=VDsat=VGS-VT时，时，Qn(L)=0这种情况叫做漏端沟道夹断。这种情况叫做漏端沟道夹断。现在一般用沟道漏端夹断来解释长沟道器件现在一般用沟道漏端夹断来解释长沟道器件VDSVDsat时时的漏极电流饱和现象。这需要从几个方面来加以说明。的漏极电流饱和现象。这需要从几个方面来加以说明。首先首先VDS超过超过VDsat以后，沟道夹断点的电势始终都等于以后，沟道夹断点的电势始终都等于VGS-VT。设想夹断点移动到设想夹断点移动到y=L，则有，则有很容易看的出来很容易看的出来由此得出结论，未夹断区的电压将保持等于由此得出结论，未夹断区的电压将保持等于VGS-VT不变。不变。2024/4/22 周一Physics of Semiconductor Devices43沟道漏端夹断的沟道漏端夹断的nMOST2024/4/22 周一Physics of Semiconductor Devices44 其次，当其次，当VDVDsat时，超过时，超过VDsat的那部分外加电压，即的那部分外加电压，即VDS-VDsat，降落在夹断区上。夹断区是已耗尽空穴的空间电，降落在夹断区上。夹断区是已耗尽空穴的空间电荷区，电离受主提供负电荷，漏区一侧空间电荷区中的电离荷区，电离受主提供负电荷，漏区一侧空间电荷区中的电离施主提供正电荷，它们之间建立沿沟道电流流动方向（施主提供正电荷，它们之间建立沿沟道电流流动方向（y方方向）的电场和电势差，漏区是高掺杂的，漏区和夹断区沿向）的电场和电势差，漏区是高掺杂的，漏区和夹断区沿y方向看类似于一个方向看类似于一个N+P单边突变结，结上压降增大时空间电单边突变结，结上压降增大时空间电荷区主要向荷区主要向P区一侧扩展。所以当夹断区上电压降（区一侧扩展。所以当夹断区上电压降（VDS-VDsat）增大时，夹断区长度增大时，夹断区长度 扩大，有效沟道长度扩大，有效沟道长度L缩短。缩短。对于长沟道对于长沟道MOST，如果在所考虑的，如果在所考虑的VDS范围内始终是范围内始终是 VDsat情形下，未夹断区的纵向及横向电场和情形下，未夹断区的纵向及横向电场和电荷分布基本上与电荷分布基本上与VDVDsat时相同，从沟道点到源端之间的时相同，从沟道点到源端之间的电阻因而也保持不变。考虑到电阻因而也保持不变。考虑到 VDVDsat未夹断区压降始终等未夹断区压降始终等于于VGS-VT，所以漏极电流恒定不变，这就是电流饱和。，所以漏极电流恒定不变，这就是电流饱和。2024/4/22 周一Physics of Semiconductor Devices45a)ion implantation into the channel region2024/4/22 周一Physics of Semiconductor Devices46b)Varying the oxide thickness The VT of the field oxide is typically an order of magnitude larger than that of the thin gate side.2024/4/22 周一Physics of Semiconductor Devices47c)Substrate bias2024/4/22 周一Physics of Semiconductor Devices48The Subthreshold Region VgVt2024/4/22 周一Physics of Semiconductor Devices49The drain current is dominated by diffusion2024/4/22 周一Physics of Semiconductor Devices50Subthreshold swings,S Except for a slight dependence on bulk doping concentration through Cdn,S is rather insensitive to device parameters.2024/4/22 周一Physics of Semiconductor Devices51Voltage Transfer CharacteristicSymmetry Design ConceptNoise Margin2024/4/22 周一Physics of Semiconductor Devices52Dynamic Operation 2024/4/22 周一Physics of Semiconductor Devices53Power DissipationPower dissipation:Dynamic and staticDynamic power consumptionFor an inverterPower supply:VDDLoad capacitance:CDynamic PowerPower:Energy stored in c:Energy dissipated by Qp:Energy in C will be consumed by QN in discharge period2024/4/22 周一Physics of Semiconductor Devices542024/4/22 周一Physics of Semiconductor Devices55 DIBL leads to a substantial increase in electron injection from the source to the drain.Subthreshold current2024/4/22 周一Physics of Semiconductor Devices56long channel short channel2024/4/22 周一Physics of Semiconductor Devices57CMOS And BiCMOSThe CMOS InverterAdvantages:low power consumptiongood noise immunityVin=0PMOSFET is onNMOSFET is offVout=VDDVin=VDDPMOSFET is offNMOSFET is onVout=02024/4/22 周一Physics of Semiconductor Devices58 At a fixed Vout,the increase input voltage(Vin)tends to increase In but decrease Ip.2024/4/22 周一Physics of Semiconductor Devices592024/4/22 周一Physics of Semiconductor Devices60Latch-up The cause of latch-up is the action of the parasitic p-n-p-n diode,which consists of a lateral p-n-p and a vertical n-p-n bipolar transistors,in the well structure.2024/4/22 周一Physics of Semiconductor Devices61 Equivalent circuit of the figure on the previous page.2024/4/22 周一Physics of Semiconductor Devices62The methods of avoiding latch-up:a)Reducing the current gains parasitic BJTb)A deeper well structurec)Using a heavily doped substrated)With the trench isolation scheme