绝缘栅型场效应管
信(xin)息来源：本站 日期：2017-04-13
在结(jie)(jie)型(xing)场(chang)效(xiao)应(ying)管中，栅(zha)(zha)(zha)极和沟(gou)道间的(de)PN结(jie)(jie)是(shi)反向偏(pian)(pian)置的(de)，所(suo)以输入电阻很大。但PN结(jie)(jie)反偏(pian)(pian)时(shi)总会(hui)有(you)一(yi)(yi)些反向电流存在，这就限制(zhi)了输入电阻的(de)进一(yi)(yi)步提高(gao)。如果在栅(zha)(zha)(zha)极与沟(gou)道间用一(yi)(yi)绝(jue)缘层(ceng)(ceng)隔(ge)开，便制(zhi)成(cheng)了绝(jue)缘栅(zha)(zha)(zha)型(xing)场(chang)效(xiao)应(ying)管，其输入电阻可提高(gao)到。根(gen)据绝(jue)缘层(ceng)(ceng)所(suo)用材料之(zhi)不同(tong)，绝(jue)缘栅(zha)(zha)(zha)场(chang)效(xiao)应(ying)管有(you)多种类型(xing)，目前应(ying)用最广泛的(de)一(yi)(yi)种是(shi)以二氧化硅（SiO2）为绝(jue)缘层(ceng)(ceng)的(de)金属(shu)一(yi)(yi)氧化物一(yi)(yi)半导体(ti)（Meial-Oxide-Semiconductor）场(chang)效(xiao)应(ying)管，简称MOS场(chang)效(xiao)应(ying)管（MOSFET）。它也(ye)有(you)N沟(gou)道和P沟(gou)道两类，每类按结(jie)(jie)构不同(tong)又分为增强型(xing)和耗尽(jin)型(xing)。
一、耗(hao)尽型MOS管
N沟道耗尽型MOS管和N沟道增强型MOS管的(de)结构基本相同(tong)。差(cha)别在于(yu)耗(hao)尽型(xing)MOS管的(de)SiO2绝缘层中(zhong)掺有大量的(de)正离子，故在UGS= 0时，就在两个(ge)N十(shi)区(qu)之间的(de)P型(xing)表面(mian)层中(zhong)感应出大量的(de)电子来，形成一定(ding)宽(kuan)度的(de)导电沟(gou)(gou)道。这(zhei)时，只要UDS＞0就会(hui)产生ID。对于(yu)N沟(gou)(gou)道耗(hao)尽型(xing)MOS管，无论(lun)UGS为正或(huo)负，都(dou)能控制ID的(de)大小(xiao)，并且不出现栅(zha)流。这(zhei)是耗(hao)尽型(xing)MOS管区(qu)别于(yu)增强(qiang)型(xing)MOS管的(de)主要特(te)点。
二、增强型MOS管
1．结(jie)构与符号(hao)
图Z0125是N沟道增强型MOS管的(de)结构示意图和(he)符号。它是在一(yi)块P型(xing)硅(gui)衬底上，扩散两(liang)(liang)(liang)个高浓度掺(chan)杂(za)的(de)N+区，在两(liang)(liang)(liang)个N+区之间的(de)硅(gui)表面上制作(zuo)一(yi)层很薄的(de)二氧化硅(gui)（SiO2）绝缘(yuan)层，然后在SiO2和(he)两(liang)(liang)(liang)个N型(xing)区表面上分别引出(chu)三个电(dian)极(ji)(ji)，称为源极(ji)(ji)s、栅极(ji)(ji)g和(he)漏(lou)极(ji)(ji)d。在其图形符号中，箭头表示漏(lou)极(ji)(ji)电(dian)流的(de)实(shi)际方向。
2．输出特性曲(qu)线
N沟(gou)(gou)道(dao)(dao)(dao)(dao)增(zeng)(zeng)强型MOS管(guan)输(shu)出(chu)特(te)性(xing)曲线(xian)如图(tu)Z0127所示(shi)，它是UGS为不同定值(zhi)时(shi)(shi)，ID 与(yu)UDS之(zhi)间关(guan)系的(de)一(yi)(yi)簇曲线(xian)。由图(tu)可(ke)见(jian)，各条曲线(xian)变化规律基本(ben)相(xiang)同。现以UGS＝5V一(yi)(yi)条曲线(xian)为例来进行分(fen)(fen)析。设UGS＞VT，导(dao)电(dian)(dian)(dian)沟(gou)(gou)道(dao)(dao)(dao)(dao)已形成。当(dang)UDS= 0时(shi)(shi)，沟(gou)(gou)道(dao)(dao)(dao)(dao)里没有电(dian)(dian)(dian)子的(de)定向(xiang)运动(dong)，ID=0；当(dang)UDS＞0且较小时(shi)(shi)，沟(gou)(gou)道(dao)(dao)(dao)(dao)基本(ben)保(bao)持(chi)原状(zhuang)，表(biao)现出(chu)一(yi)(yi)定电(dian)(dian)(dian)阻(zu)，ID随UDS线(xian)性(xing)增(zeng)(zeng)大(da) ；当(dang)UDS较大(da)时(shi)(shi)，由于电(dian)(dian)(dian)阻(zu)沿(yan)沟(gou)(gou)道(dao)(dao)(dao)(dao)递(di)增(zeng)(zeng)，使(shi)UDS沿(yan)沟(gou)(gou)道(dao)(dao)(dao)(dao)的(de)电(dian)(dian)(dian)位从(cong)(cong)(cong)漏(lou)端(duan)到源端(duan)递(di)降(jiang)，所以沿(yan)沟(gou)(gou)道(dao)(dao)(dao)(dao)的(de)各点(dian)上，栅极与(yu)沟(gou)(gou)道(dao)(dao)(dao)(dao)间的(de)电(dian)(dian)(dian)位差沿(yan)沟(gou)(gou)道(dao)(dao)(dao)(dao)从(cong)(cong)(cong)d至(zhi)s极递(di)增(zeng)(zeng)，导(dao)致垂直于P型硅表(biao)面(mian)的(de)电(dian)(dian)(dian)场强度从(cong)(cong)(cong)d至(zhi)s极也递(di)增(zeng)(zeng)，从(cong)(cong)(cong)而形成沟(gou)(gou)道(dao)(dao)(dao)(dao)宽度不均匀，漏(lou)端(duan)最窄(zhai)，源端(duan)最宽如图(tu)Z0126所示(shi)。随着(zhe)UDS的(de)增(zeng)(zeng)加，漏(lou)端(duan)沟(gou)(gou)道(dao)(dao)(dao)(dao)变得更(geng)窄(zhai)，电(dian)(dian)(dian)阻(zu)相(xiang)应变大(da)，ID上升变慢 ；当(dang)UDS继续增(zeng)(zeng)大(da)到UDS=UGS- VT时(shi)(shi)，近漏(lou)端(duan)的(de)沟(gou)(gou)道(dao)(dao)(dao)(dao)开始(shi)消失，漏(lou)端(duan)一(yi)(yi)点(dian)处被夹(jia)(jia)断(duan)；如果UDS再(zai)增(zeng)(zeng)加，将出(chu)现夹(jia)(jia)断(duan)区。这时(shi)(shi)，UDS增(zeng)(zeng)加的(de)部(bu)分(fen)(fen)基本(ben)上降(jiang)在夹(jia)(jia)断(duan)区上，使(shi)夹(jia)(jia)断(duan)部(bu)分(fen)(fen)的(de)耗尽层变得更(geng)厚(hou)，而未夹(jia)(jia)断(duan)的(de)导(dao)电(dian)(dian)(dian)沟(gou)(gou)道(dao)(dao)(dao)(dao)不再(zai)有多(duo)大(da)变化，所以ID将维持(chi)刚出(chu)现夹(jia)(jia)断(duan)时(shi)(shi)的(de)数(shu)值(zhi)，趋于饱和，管(guan)子呈现恒流特(te)性(xing)。
对于不同(tong)的(de)UGS值，沟道深浅也不同(tong)，UGS愈大，沟道愈深。在恒流(liu)区，对于相(xiang)同(tong)的(de)UDS 值，UGS大的(de)ID也较(jiao)大，表现为输出特性曲线上移。
3．工作原理(li)
绝(jue)缘栅(zha)场效应(ying)管(guan)的(de)导(dao)电机(ji)理(li)是，利用UGS 控制"感应(ying)电荷"的(de)多(duo)少来改变导(dao)电沟(gou)道的(de)宽窄(zhai)，从而控制漏(lou)极(ji)电流ID。若UGS＝0时(shi)，源、漏(lou)之(zhi)(zhi)间不存(cun)在导(dao)电沟(gou)道的(de)为(wei)增(zeng)强型MOS管(guan)，UGS＝0 时(shi)，漏(lou)、源之(zhi)(zhi)间存(cun)在导(dao)电沟(gou)道的(de)为(wei)耗尽(jin)型MOS管(guan)。
图Z0125中衬(chen)底为P型(xing)半(ban)(ban)导(dao)体(ti)，在(zai)(zai)(zai)它的(de)(de)(de)上(shang)(shang)面(mian)(mian)是(shi)一层(ceng)(ceng)(ceng)(ceng)SiO2薄(bo)膜、在(zai)(zai)(zai)SiO2薄(bo)膜上(shang)(shang)盖一层(ceng)(ceng)(ceng)(ceng)金属铝，如果(guo)在(zai)(zai)(zai)金属铝层(ceng)(ceng)(ceng)(ceng)和半(ban)(ban)导(dao)体(ti)之间加电(dian)(dian)(dian)(dian)压(ya)(ya)UGS，则(ze)金属铝与(yu)半(ban)(ban)导(dao)体(ti)之间产生一个垂直(zhi)于半(ban)(ban)导(dao)体(ti)表(biao)(biao)面(mian)(mian)的(de)(de)(de)电(dian)(dian)(dian)(dian)场(chang)，在(zai)(zai)(zai)这一电(dian)(dian)(dian)(dian)场(chang)作用下(xia)，P型(xing)硅表(biao)(biao)面(mian)(mian)的(de)(de)(de)多数载流(liu)(liu)子(zi)(zi)(zi)-空穴(xue)受(shou)到(dao)排斥，使(shi)硅片表(biao)(biao)面(mian)(mian)产生一层(ceng)(ceng)(ceng)(ceng)缺乏(fa)载流(liu)(liu)子(zi)(zi)(zi)的(de)(de)(de)薄(bo)层(ceng)(ceng)(ceng)(ceng)。同时(shi)在(zai)(zai)(zai)电(dian)(dian)(dian)(dian)场(chang)作用下(xia)，P型(xing)半(ban)(ban)导(dao)体(ti)中的(de)(de)(de)少(shao)数载流(liu)(liu)子(zi)(zi)(zi)-电(dian)(dian)(dian)(dian)子(zi)(zi)(zi)被(bei)吸引到(dao)半(ban)(ban)导(dao)体(ti)的(de)(de)(de)表(biao)(biao)面(mian)(mian)，并被(bei)空穴(xue)所俘获而形(xing)成(cheng)(cheng)负离(li)(li)子(zi)(zi)(zi)，组成(cheng)(cheng)不可移动的(de)(de)(de)空间电(dian)(dian)(dian)(dian)荷层(ceng)(ceng)(ceng)(ceng)（称耗尽(jin)层(ceng)(ceng)(ceng)(ceng)又叫受(shou)主离(li)(li)子(zi)(zi)(zi)层(ceng)(ceng)(ceng)(ceng)）。UGS愈大，电(dian)(dian)(dian)(dian)场(chang)排斥硅表(biao)(biao)面(mian)(mian)层(ceng)(ceng)(ceng)(ceng)中的(de)(de)(de)空穴(xue)愈多，则(ze)耗尽(jin)层(ceng)(ceng)(ceng)(ceng)愈宽，且UGS愈大，电(dian)(dian)(dian)(dian)场(chang)愈强；当UGS 增大到(dao)某一栅源电(dian)(dian)(dian)(dian)压(ya)(ya)值VT（叫临界电(dian)(dian)(dian)(dian)压(ya)(ya)或开启电(dian)(dian)(dian)(dian)压(ya)(ya)）时(shi)，则(ze)电(dian)(dian)(dian)(dian)场(chang)在(zai)(zai)(zai)排斥半(ban)(ban)导(dao)体(ti)表(biao)(biao)面(mian)(mian)层(ceng)(ceng)(ceng)(ceng)的(de)(de)(de)多数载流(liu)(liu)子(zi)(zi)(zi)-空穴(xue)形(xing)成(cheng)(cheng)耗尽(jin)层(ceng)(ceng)(ceng)(ceng)之后，就会吸引少(shao)数载流(liu)(liu)子(zi)(zi)(zi)-电(dian)(dian)(dian)(dian)子(zi)(zi)(zi)，继而在(zai)(zai)(zai)表(biao)(biao)面(mian)(mian)层(ceng)(ceng)(ceng)(ceng)内形(xing)成(cheng)(cheng)电(dian)(dian)(dian)(dian)子(zi)(zi)(zi)的(de)(de)(de)积(ji)累(lei)，从(cong)而使(shi)原(yuan)来(lai)为空穴(xue)占(zhan)多数的(de)(de)(de)P型(xing)半(ban)(ban)导(dao)体(ti)表(biao)(biao)面(mian)(mian)形(xing)成(cheng)(cheng)了(le)N型(xing)薄(bo)层(ceng)(ceng)(ceng)(ceng)。由于与(yu)P型(xing)衬(chen)底的(de)(de)(de)导(dao)电(dian)(dian)(dian)(dian)类型(xing)相反(fan)，故称为反(fan)型(xing)层(ceng)(ceng)(ceng)(ceng)。在(zai)(zai)(zai)反(fan)型(xing)层(ceng)(ceng)(ceng)(ceng)下(xia)才是(shi)负离(li)(li)子(zi)(zi)(zi)组成(cheng)(cheng)的(de)(de)(de)耗尽(jin)层(ceng)(ceng)(ceng)(ceng)。这一N型(xing)电(dian)(dian)(dian)(dian)子(zi)(zi)(zi)层(ceng)(ceng)(ceng)(ceng)，把原(yuan)来(lai)被(bei)PN结高阻层(ceng)(ceng)(ceng)(ceng)隔开的(de)(de)(de)源区和漏区连接起来(lai)，形(xing)成(cheng)(cheng)导(dao)电(dian)(dian)(dian)(dian)沟道(dao)。
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