《半导体器件物理》4.pptVIP

OUTLINE The Power MOSFET Currents in Linear Region Operation Regions Acting as a resistor. Linear Region (VDVDsat) Pinch-off Point The thickness of inversion xi (y=L) =0 Current in Saturation Region A MOSFET can be divided into many capacitor fragments VC decrease in this direction ………… vc Source Side Pinch off Drain Side Vc=0 means no charges induced Electron current flow Saturation Region (VDVDsat) ID=constant L L’ The upper characteristics can be derived under the following ideal conditions: The gate structure corresponds to an ideal MOS diode. Only drift current considered. Carrier mobility in the inversion layer is constant. Doping in the channel is uniform. Reverse-leakage current is negligibly. The gradual channel approximation. Idealized drain characteristics of MOS diode nMOST的输出特性曲线 从另一方面来看，沟道漏端 VDS=VDsat=VGS-VT时，Qn(L)=0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VDSVDsat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。 沟道漏端夹断的nMOST 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 L，那么在VDVDsat情形下，未夹断区的纵向及横向电场和电荷分布基本上与VD＝VDsat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。 ion implantation into the channel region Varying the oxide thickness The VT of the field oxide is typically an order of magnitude larger than that of the thin gate side. Substrate bias The Subthreshold Region VgVt Physics of Semiconductor Devices MOSFET AND RELATED DEVICE The MOS Diode MOSFET Fundamentals MOSFET Scaling COMS and BiCOMS MOSFET on Insulator MOS Memory Structure SiO2 metal semiconductor SiO2 semiconductor d Ohmic contact The MOS Diode is of paramount important in semiconductor device physics because the device extremel