《半导体器件物理》

1、MOSFET AND RELATED DEVICE,2020/6/27,1,Physics of Semiconductor Devices,OUTLINE,The Power MOSFET,The MOS Diode,MOSFET Fundamentals,MOSFET Scaling,COMS and BiCOMS,MOSFET on Insulator,MOS Memory Structure,2020/6/27,2,Physics of Semiconductor Devices,SiO2,metal,semiconductor,SiO2,semiconductor,d,Ohmic c

2、ontact,The MOS Diode is of paramount important in semiconductor device physics because the device extremely useful in the study of semiconductor surfaces.,2020/6/27,3,Physics of Semiconductor Devices,The Ideal MOS Diode,2020/6/27,4,Physics of Semiconductor Devices,An ideal MOS diode is defined as fo

3、llows:,At zero applied bias,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.,There is no carrier transport through the oxide under the direct current dc)-biasing con

4、ditions, or the resistivity of the oxide is infinite.,2020/6/27,5,Physics of Semiconductor Devices,Operation Modes,2020/6/27,6,Physics of Semiconductor Devices,Energy Band Diagrams And Charge Distribution,Accumulation :,2020/6/27,7,Physics of Semiconductor Devices,Accumulation:,Qm,QS,-d,x,Charge Dis

5、tribution,x,E(X),Electric Field,An accumulation of holes near the oxide-semiconductor interface.,2020/6/27,8,Physics of Semiconductor Devices,Depletion:,EF,Vg0,EF,Ev,Ec,Ei,Charge Distribution,Electric Field,2020/6/27,9,Physics of Semiconductor Devices,Strong Inversion:,2020/6/27,10,Physics of Semico

6、nductor Devices,Strong Inversion:,x,wm,Qm,-d,Qn,Qsc,Charge Distribution,Electric Field,x,E(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 surfa

7、ce depletion-layer with reaches a maximum, Wm.,2020/6/27,11,Physics of Semiconductor Devices,The Surface Depletion Region,is the band bending with boundary conditions,in the bulk and,EF,Ei,Semiconductor surface,EC,Ev,Eg,Oxide,x,P-type silicon,2020/6/27,12,Physics of Semiconductor Devices,At the surf

8、ace the densities are:,In the MOS diode, the following regions of surface potential can be distinguished:,Accumulation of holes (bands bend upward),Flat band condition,Depletion of hole (bands bend downward),Midgap with ns=np=ni (intrinsic concentration),Inversion (bands bend downward),2020/6/27,13,

9、Physics of Semiconductor Devices,The potential,as a function of distance can be obtained,by using the one-dimensional Poissons equation:,After using the depletion approximation that we employed in the study of p-n junctions.,The surface potential,is:,2020/6/27,14,Physics of Semiconductor Devices,The

10、 criterion of the onset of strong inversion:,The maximum width of the surface depletion region:,and,2020/6/27,15,Physics of Semiconductor Devices,Surface Charge vs. Surface Potential,2020/6/27,16,Physics of Semiconductor Devices,The relationship between Wm and the impurity concentration for silicon

11、and gallium arsenide, where NB is equal to NA for P-type and ND for n-type semiconductor.,2020/6/27,17,Physics of Semiconductor Devices,Capacitance in a MOS capacitor,Small signal capacitance,MOS capacitance is defined as small signal capacitance and is measured by applying a small ac voltage on the

12、 top of a dc bias,2020/6/27,18,Physics of Semiconductor Devices,C-V Curves,2020/6/27,19,Physics of Semiconductor Devices,Frequency Effect,The frequency of ac signal play an important role in the capacitance of a MOS Capacitor (after Grove, et al.),2020/6/27,20,Physics of Semiconductor Devices,Ideal

13、MOS Curves,Qm,Depletion region,EF,EC,Ei,QS,Neutrals region,Band diagram,(p-type substrate),Charge distribution,2020/6/27,21,Physics of Semiconductor Devices,-d,0,w,x,Electric-field Distribution,-d,v0,v,w,x,0,Potential Distribution,The applied voltage will appear partly across the oxide and partly cr

14、oss the semiconductor.,2020/6/27,22,Physics of Semiconductor Devices,Capacitance at Low Frequency,Low frequency or quasi-static,Majority and minority carrier can respond with ac signal and reach at equilibrium condition,P-type subst rate,Accumulation,2020/6/27,23,Physics of Semiconductor Devices,Dep

15、letion,W,2020/6/27,24,Physics of Semiconductor Devices,Inversion,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 capacitance,2020/6/27,25,Physics of Semicond

16、uctor Devices,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

17、 with the measurement signal.,The incremental charges appears at the edge of the depletion region in high measurement frequency.,2020/6/27,26,Physics of Semiconductor Devices,MOSFET Fundamentals,2020/6/27,27,Physics of Semiconductor Devices,Structure of MOSFET,2020/6/27,28,Physics of Semiconductor D

18、evices,Types of MOSFET,2020/6/27,29,Physics of Semiconductor Devices,Non-equilibrium Condition,2020/6/27,30,Physics of Semiconductor Devices,Linear Region & Saturation Region,2020/6/27,31,Physics of Semiconductor Devices,2020/6/27,32,Physics of Semiconductor Devices,Currents in Linear Region,2020/6/

19、27,33,Physics of Semiconductor Devices,Operation Regions,Acting as a resistor.,Linear Region (VDVDsat时的漏极电流饱和现象。这需要从几个方面来加以说明。,首先VDS超过VDsat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y=L，则有,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VGS-VT不变。,2020/6/27,43,Physics of Semiconductor Devices,沟道漏端夹断的nMOST,2020/6/27,44,Physics of Sem

20、iconductor Devices,其次，当VDVDsat时，超过VDsat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（y方向）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N+P单边突变结，结上压降增大时空间电荷区主要向P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 扩大，有效沟道长度L缩短。,对于长沟道MOST，如果在所考虑的VDS范围内始终是 VDsat情形下，未夹断区的纵向及横向电场和电荷分布基本上与V

21、DVDsat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 VDVDsat未夹断区压降始终等于VGS-VT，所以漏极电流恒定不变，这就是电流饱和。,2020/6/27,45,Physics of Semiconductor Devices,ion implantation into the channel region,2020/6/27,46,Physics of Semiconductor Devices,Varying the oxide thickness,The VT of the field oxide is typically an order of magnitude

22、larger than that of the thin gate side.,2020/6/27,47,Physics of Semiconductor Devices,Substrate bias,2020/6/27,48,Physics of Semiconductor Devices,The Subthreshold Region,VgVt,2020/6/27,49,Physics of Semiconductor Devices,The drain current is dominated by diffusion,2020/6/27,50,Physics of Semiconduc

23、tor Devices,Subthreshold swings, S,Except for a slight dependence on bulk doping concentration through Cdn, S is rather insensitive to device parameters.,2020/6/27,51,Physics of Semiconductor Devices,Voltage Transfer Characteristic,Symmetry Design Concept,Noise Margin,2020/6/27,52,Physics of Semicon

24、ductor Devices,Dynamic Operation,2020/6/27,53,Physics of Semiconductor Devices,Power Dissipation,Power dissipation:,Dynamic and static,Dynamic power consumption,For an inverter,Power supply: VDD,Load capacitance: C,Dynamic Power,Power:,Energy stored in c:,Energy dissipated by Qp:,Energy in C will be

25、 consumed by QN in discharge period,2020/6/27,54,Physics of Semiconductor Devices,2020/6/27,55,Physics of Semiconductor Devices,DIBL leads to a substantial increase in electron injection from the source to the drain.,Subthreshold current,2020/6/27,56,Physics of Semiconductor Devices,long channel,short channel,2020/6/27,57,Physics of Semiconductor Devices,CMOS And BiCMOS,The CMOS Inverter,Advantages:,low power consumption,good noise immunit