Introduction toMetal-Oxide-SemiconductorField Effect .ppt

1、Introduction to Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs) Chapter 7, Anderson and Anderson,MOSFET,History Structure Future Review Threshold Voltage I-V Characteristics Modifications to I-V: Depletion layer correction (Sup. 3) Mobility, Vsat Short Channel Effects Channel Length Mod

2、ulation Channel Quantum Effects MOSFET Scaling and Current Topics (Literature + Sup. 3) Subthreshold Behavior Damage and Temperature (Sup. 3) Spice (Sup. 3) HFET, MESFET, JFET, DRAM, CCD (Some in Sup. 3),MOSFET History (Very Short!),First Patents: 1935 Variable Capacitor Proposed: 1959 Silicon MOS:

3、1960 Clean PMOS, NMOS: Late 1960s, big growth! CCDs: 1970s, Bell Labs Switch to CMOS: 1980s,Structure: n-channel MOSFET (NMOS),IG=0,ID=IS,IS,x,y,(bulk or substrate),MOSFET Future (One Part of),International Technology Roadmap for Semiconductors, 2008 update. Look at size, manufacturing technique.,Fr

4、om Intel,Structure: n-channel MOSFET (NMOS),IG=0,ID=IS,IS,x,y,(bulk or substrate),MOSFET Scaling,ECE G201,Fin (30nm),Gate,BOX,prevents “top” gate,Circuit Symbol (NMOS) enhancement-type: no channel at zero gate voltage,ID= IS,IS,IG= 0,G-Gate D-Drain S-Source B-Substrate or Body,Structure: n-channel M

5、OSFET (NMOS),IG=0,ID=IS,IS,x,y,(bulk or substrate),Energy bands,(“flat band” condition; not equilibrium),(equilibrium),Flatbands! For this choice of materials, VGS0 n+pn+ structure ID 0,VD=Vs,Flatbands VGS VT (Includes VGS=0 here). n+-depletion-n+ structure ID 0,+,VD=Vs,VGS VT n+-n-n+ structure inve

6、rsion,VGSVT,Channel Charge (Qch),Qch,Depletion region charge (QB) is due to uncovered acceptor ions,Ec(y) with VDS=0,(x),Increasing VGS decreases EB,EB,y,0,L,EF EC,Triode Region A voltage-controlled resistor small VDS,G,p,n+,n+,metal,S,D,B,oxide,+,-,+,+,+,- - - - - -,VGS2VGS1,p,n+,n+,metal,S,D,B,oxi

7、de,+,-,+,+,+,- - - - - - - - -,VGS3VGS2,+,ID,VDS,0.1 v,increasing VGS,Increasing VGS puts more charge in the channel, allowing more drain current to flow,cut-off,Saturation Region occurs at large VDS,As the drain voltage increases, the difference in voltage between the drain and the gate becomes sma

8、ller. At some point, the difference is too small to maintain the channel near the drain pinch-off,Saturation Region occurs at large VDS,The saturation region is when the MOSFET experiences pinch-off. Pinch-off occurs when VG - VD is less than VT.,Saturation Region occurs at large VDS,VGS - VDS VGS -

9、 VT,VT,Saturation Region once pinch-off occurs, there is no further increase in drain current,ID,VDS,0.1 v,increasing VGS,triode,saturation,VDSVGS-VT,VDSVGS-VT,Band diagram of triode and saturation,Simplified MOSFET I-V Equations,Cut-off: VGSVT and VDS VT and VDS VGS-VTID = 1/2kn(W/L)(VGS-VT)2where

10、kn= (electron mobility)x(gate capacitance)= mn(eox/tox) electron velocity = mnE and VT depends on the doping concentration and gate material used (more details later),Energy bands,(“flat band” condition; not equilibrium),(equilibrium),VGSVT,Channel Charge (Qch),Qch,Depletion region charge (QB) is due to uncovered acceptor ions,Threshold Voltage Definition,VGS = VT when the carrier concentration in the channel is equal to the carrier concentration in the bulk silicon.Mathematically, this occurs when fs=2ff , where fs is called the surface potential,