VLSI与电子器件教学资料：Chapter 6 Field Effect Transistor.pptVIP

Chapter 6 : Field Effect Transistor(FET)(场效应管） Source /源 gate /栅 drain /漏 channel /沟道 reverse bias /反向偏置 forward bias /正向偏置 pinch-off /夹断 saturation /饱和 Chapter 6 : Field Effect Transistor(FET) Bipolar Transistor(双极晶体管） Field –Effect Transistor（场效应管） 6.2.1 Pinch-off and saturation Fig.6-4 . It should be noticed that channel resistivityρis taken as a constant (i.e. electron mobility is a constant, since ρ =1/(nqμ). ) in eqs. above. This assumption may be invalid at high fields and electron velocity is saturated. For instance, a FET with a very short channel . Another departure from the ideal model is that ID will increase beyond pinch-off for short channel devices. It results from the effective channel length decrease as the drain voltage is increased(G0=2aZ/ ρL). By using GaAs instead of Si, a higher electron mobility is available ,and furthermore GaAs can be operated at higher temperature( and therefore higher power levels). Since no diffusion are involved, close geometrical tolerance can be achieved and MESFET can be made very small. This is important at high frequencies. Another important short-channel effect is the reduction in effective channel length after pinch-off as the drain voltage is increased., leading to a slope in the saturated I-V characteristics. * * coordinate system/坐标系 differential element/微分单元 resistivity/电阻率 conductivity/电导率 gradual channel/缓变沟道 abrupt junction/突变结 assume/假定 Modern life Field –Effect Transistor（场效应管）high input impedance Digital circuits, memory devices and microprocessor Chapter 6 : Field Effect Transistor(FET) 6.1 Transistor operation The feature of a resistor = a constant for the resistor The feature of p-n junction: The I-V characteristics: It conducts current in only one direction : Resistance is not a constant for the diode. It depends upon the applied voltage. 6.1.1 The load line iD=f(vD) How to find iD and vD ? (1)Two terminal device (2) Three- terminal device iD=f(vD, vG ) VG=0.5V; ID