1、CHAPTER6 Fundamentals of the Metal-Oxide-Semiconductor Field-Effect TransistorWhen a drain-to-source voltage, VDS, is applied, electrons flow from the source through the channel to the drain. The current is a function of the amount of charge the inversion layer that, in turn, is a function of the ve
2、rtical electric field. The term field-effect refers to the concept that the current is controlled by an electric field per pendicular to the flow of charge. The basic transistor action is that the voltage across two terminals (gate-to-source) controls the current in the third terminal (drain). This
3、device is called an n-channel MOSFET since the current is due to the flow of electrons in the channel.6.1.2 Modes of OperationOne primary electrical parameter of a MOSFET is the threshold voltage, VT. If the gate-to-source voltage is less than the threshold voltage, the transistor is cut off and all
4、 currents are zero. If the gate-to-source voltage is greater than the threshold voltage, an inversion layer is formed and a drain current can be induced.Figure 6.3 shows the transistor current-voltage characteristics. The drain current is plotted as a function of drain-to-source voltage for various
5、gate voltages. In this case, a threshold voltage of VT = 0.5 V is assumed. If the transistor is biased in the saturation region, VDS VCS - VT, then ideally the drain current is independent of the drain-to-source bias and is given byID = Kn(VGS - VT) 2 (6.1) The conduction parameter Kn is a function
6、of electron mobility, oxide capacitance and the channel width-to-length ratio.6.1.3 Amplification with MOSFETsOne application of a transistor is to amplify a small, time-varying input signal Figure 6.4a shows a circuit that would perform this function If the Input signal is vi=0,Figure 6.4 1 (a) A c
7、ircuit that can a time-varying input signal vi . (b) Loadline and time-varying signals supe nmposed on transistor characteristics.then the transistor is to be biased in the saturation region at the Q-point shown in Fig-ure 6.4b. Writing the voltage law equation around the drain-source loop, we find
8、VDS= VDD - ID RD (6.2) Equation (6.2) is called the load line equation and is superimposed on the transistor characteristics in Figure 6.4b.When a time-varying input signal vi is appIied, the gate-to-source voltagechanges with time. A time-varying drain current is induced that in turn causes a time-
9、varying drain-to-source voltage. A time-varying output sigh al is generated whosemagnitude can be greater than the magnitude of the input signal. Thus, the circuit isan amplifier.We now begin to analyze the MOS capacitor to gain an understanding of theformation of the inversion layer.6.2 THE TWO-TER
10、MINAL MOS CAPACITORObjective:Describe the characteristics of the two-terminal MOS capacitor,Including energy-band diagrams and charge distributions.The heart of the MOSFET is the metal-oxide-semiconductor capacitor. An under-standing of the MOS capacitor is fundamental in understanding the character
11、istics andcharacteristics of the MOSFET. For the reason, we will spend time initially in studying the characteristics of the MOS capacitor. The MOS capacitor is shown in Figure 6.5. The metal may be aluminum or some other type of metal, although in most cases now,6 章 金属氧化物半导体场效应晶体管的原理。 当电源电压 VDS 被应用
12、，通过给排水管道电子从源流量。目前是一个收费的逆温层，反过来，是一个垂直电场作用量的函数。一词场效应是指概念，目前是由每垂直于流动的电荷电场的控制。晶体管的基本动作是，在两个终端（栅源）电压控制在第三终端（漏）电流。这个装置被称为一个 N 沟道 MOSFET ，因为目前的 N 沟道 MOSFET 是由于电子在通道流动。 6.1.2 操作模式一个主要的电气参数的 MOSFET 的阈值电压 VT。如果栅源电压低于阈值电压，晶体管被切断，所有的电流为零。如果栅源电压低于阈值电压大，形成了逆温层和地漏电流可以被诱发。图 6.3 显示了晶体管的电流电压特性。漏电流是绘制为漏源电压为各门电压的功能。在这种
13、情况下，V T= 0.5 V 的阈值电压是假定的。如果晶体管是偏向于饱和区，V DS VCS - VT, 那么理想的漏电流对漏源偏置独立的，给予ID = Kn(VGS - VT) 2导参数 Kn 是电子迁移率，氧化层电容和功能的通道宽度与长度的比例。6.1.3 扩增用 MOSFET晶体管的一个应用是一个小放大，时变图 6.4a 显示输入信号的电路，将输入信号，如果执行这个函数是 vi = 0，图 6.4 图 1（a）的电路，可随时间变化的输入信号六。 （b）负载线路和时间变化的信号苏佩 nmposed 上晶体管的特点。然后，晶体管是要在 Q -如图点饱和区偏颇，如图 6.4b。写作周围的漏源电
14、压回路方程法，我们发现：VDS= VDD - ID RD (6.2) 方程（6.2）被称为负载线方程，是对晶体管叠加特征图6.4b。当一个时变输入信号 vi 是 appIied 的栅源电压随时间变化。随时间变化的漏电流引起的，反过来导致时间不同的漏源电压。时变输出产生的叹息人震级可以比输入信号的幅度更大。因此，电路是放大器。 现在我们开始分析的 MOS 电容获得一种理解形成的逆温层。6.2 双端 MOS 电容器目的：描述了双端 MOS 电容的特性，包括能带图和电荷分布。MOSFET 的核心是金属氧化物半导体电容。一名副站立的MOS 电容的特点是在理解基本和 MOSFET 的特性。至于原因，我们会花时间在研究初期的 MOS 电容的特性。MOS 电容见图6.5。金属铝或可能是一些其他类型的金属，虽然目前在大多数情况下，
