N沟MOS晶(jing)体管

金属-氧化物-半导(dao)体(Metal-Oxide-SemIConductor)构(gou)造的(de)晶体管(guan)简称MOS晶体管(guan)，有(you)P型(xing)MOS管(guan)和(he)N型(xing)MOS管(guan)之分。MOS管(guan)构(gou)成的(de)集成电(dian)路(lu)(lu)称为(wei)MOS集成电(dian)路(lu)(lu)，而PMOS管(guan)和(he)NMOS管(guan)共同构(gou)成的(de)互补型(xing)MOS集成电(dian)路(lu)(lu)即(ji)为(wei)CMOS集成电(dian)路(lu)(lu)。

由p型(xing)(xing)衬底和两(liang)个高(gao)浓度n扩(kuo)散区(qu)构(gou)成的MOS管(guan)(guan)叫作n沟(gou)(gou)道(dao)(dao)(dao)MOS管(guan)(guan)，该(gai)管(guan)(guan)导(dao)通时(shi)在(zai)(zai)两(liang)个高(gao)浓度n扩(kuo)散区(qu)间构(gou)成n型(xing)(xing)导(dao)电(dian)沟(gou)(gou)道(dao)(dao)(dao)。n沟(gou)(gou)道(dao)(dao)(dao)加(jia)强(qiang)型(xing)(xing)MOS管(guan)(guan)必(bi)需在(zai)(zai)栅(zha)极(ji)上施加(jia)正(zheng)向偏压(ya)(ya)，且只要栅(zha)源电(dian)压(ya)(ya)大于阈值(zhi)电(dian)压(ya)(ya)时(shi)才有导(dao)电(dian)沟(gou)(gou)道(dao)(dao)(dao)产生(sheng)的n沟(gou)(gou)道(dao)(dao)(dao)MOS管(guan)(guan)。n沟(gou)(gou)道(dao)(dao)(dao)耗(hao)尽型(xing)(xing)MOS管(guan)(guan)是指(zhi)在(zai)(zai)不(bu)加(jia)栅(zha)压(ya)(ya)（栅(zha)源电(dian)压(ya)(ya)为零）时(shi)，就有导(dao)电(dian)沟(gou)(gou)道(dao)(dao)(dao)产生(sheng)的n沟(gou)(gou)道(dao)(dao)(dao)MOS管(guan)(guan)。

NMOS集(ji)(ji)成(cheng)电(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)是(shi)N沟(gou)道MOS电(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)，NMOS集(ji)(ji)成(cheng)电(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)的输入(ru)阻抗很高(gao)，根本上不需求(qiu)(qiu)吸(xi)收电(dian)(dian)(dian)(dian)(dian)流，因而，CMOS与NMOS集(ji)(ji)成(cheng)电(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)衔(xian)接(jie)时(shi)不用(yong)(yong)思(si)索(suo)电(dian)(dian)(dian)(dian)(dian)流的负载问题。NMOS集(ji)(ji)成(cheng)电(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)大多采用(yong)(yong)单(dan)组(zu)正电(dian)(dian)(dian)(dian)(dian)源供电(dian)(dian)(dian)(dian)(dian)，并(bing)且(qie)以5V为多。CMOS集(ji)(ji)成(cheng)电(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)只需选用(yong)(yong)与NMOS集(ji)(ji)成(cheng)电(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)相同的电(dian)(dian)(dian)(dian)(dian)源，就可与NMOS集(ji)(ji)成(cheng)电(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)直(zhi)(zhi)接(jie)衔(xian)接(jie)。不过，从(cong)NMOS到CMOS直(zhi)(zhi)接(jie)衔(xian)接(jie)时(shi)，由于NMOS输出的高(gao)电(dian)(dian)(dian)(dian)(dian)平(ping)低于CMOS集(ji)(ji)成(cheng)电(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)的输入(ru)高(gao)电(dian)(dian)(dian)(dian)(dian)平(ping)，因此需求(qiu)(qiu)运(yun)用(yong)(yong)一个（电(dian)(dian)(dian)(dian)(dian)位）上拉电(dian)(dian)(dian)(dian)(dian)阻R，R的取值普通选用(yong)(yong)2～100KΩ。

N沟道加强(qiang)型MOS管的构(gou)造

在(zai)一块掺(chan)(chan)杂(za)浓度较低的(de)P型硅衬底(di)上，制(zhi)造两个高掺(chan)(chan)杂(za)浓度的(de)N+区(qu)，并用金(jin)属铝引出两个电极，分别作(zuo)漏(lou)极d和源极s。

然后(hou)在(zai)半导体外(wai)表掩盖一(yi)层很(hen)薄的(de)二氧化硅(SiO2)绝缘层，在(zai)漏——源极间的(de)绝缘层上再(zai)装上一(yi)个铝电极,作为栅(zha)极g。

在(zai)衬(chen)底上也引出(chu)(chu)一个电(dian)极B，这就构成(cheng)了一个N沟(gou)道加(jia)强型MOS管(guan)。MOS管(guan)的源极和衬(chen)底通常(chang)是接(jie)在(zai)一同(tong)的(大多数(shu)管(guan)子在(zai)出(chu)(chu)厂(chang)前已连接(jie)好)。

它的栅极与其它电(dian)极间是绝缘的。

图(tu)(a)、(b)分(fen)别是它的构造表示图(tu)和代表符号。代表符号中的箭头方向(xiang)表示由P(衬底)指向(xiang)N(沟道)。P沟道加强型MOS管的箭头方向(xiang)与上述相反(fan)，如(ru)图(tu)(c)所示。

N沟(gou)道加(jia)强(qiang)型MOS管的工作原理

（1）vGS对iD及(ji)沟道的(de)控(kong)制造用

① vGS=0 的(de)状(zhuang)况(kuang)

从图1(a)能够看出，加(jia)强(qiang)型MOS管的漏极(ji)d和(he)源(yuan)(yuan)极(ji)s之(zhi)间有(you)两个(ge)背(bei)靠(kao)背(bei)的PN结(jie)。当栅(zha)——源(yuan)(yuan)电(dian)压(ya)vGS=0时(shi)，即便加(jia)上漏——源(yuan)(yuan)电(dian)压(ya)vDS，而且不管vDS的极(ji)性如何，总有(you)一个(ge)PN结(jie)处于反偏状(zhuang)态，漏——源(yuan)(yuan)极(ji)间没有(you)导电(dian)沟道，所以(yi)这时(shi)漏极(ji)电(dian)流iD≈0。

② vGS>0 的状况(kuang)

若vGS＞0，则(ze)栅极和(he)衬(chen)(chen)底(di)之间的SiO2绝缘层中便产(chan)生(sheng)一个电(dian)(dian)场(chang)。电(dian)(dian)场(chang)方向垂(chui)直于半(ban)导体外表的由栅极指向衬(chen)(chen)底(di)的电(dian)(dian)场(chang)。这个电(dian)(dian)场(chang)能排(pai)挤空(kong)穴而(er)吸收电(dian)(dian)子。

排(pai)挤空(kong)穴(xue)：使(shi)栅极(ji)左近(jin)的(de)(de)P型衬(chen)底(di)(di)(di)中的(de)(de)空(kong)穴(xue)被排(pai)挤，剩(sheng)下(xia)不能挪(nuo)动的(de)(de)受主离子(负离子)，构成耗尽层。吸收电子：将(jiang) P型衬(chen)底(di)(di)(di)中的(de)(de)电子（少子）被吸收到衬(chen)底(di)(di)(di)外(wai)表(biao)。

（2）导电沟道(dao)的(de)构成：

当vGS数值较小，吸(xi)收(shou)电(dian)(dian)(dian)(dian)子(zi)(zi)的才能(neng)不强(qiang)(qiang)时，漏——源极(ji)之间仍(reng)无导(dao)电(dian)(dian)(dian)(dian)沟道(dao)(dao)呈(cheng)现，如(ru)图1(b)所(suo)(suo)示。vGS增加时，吸(xi)收(shou)到(dao)P衬底外(wai)表层(ceng)的电(dian)(dian)(dian)(dian)子(zi)(zi)就增加，当vGS到(dao)达某一(yi)数值时，这些电(dian)(dian)(dian)(dian)子(zi)(zi)在栅(zha)极(ji)左近的P衬底外(wai)表便构(gou)(gou)成(cheng)一(yi)个N型薄层(ceng)，且与两(liang)个N+区相连通，在漏——源极(ji)间构(gou)(gou)成(cheng)N型导(dao)电(dian)(dian)(dian)(dian)沟道(dao)(dao)，其导(dao)电(dian)(dian)(dian)(dian)类型与P衬底相反(fan)，故又称为反(fan)型层(ceng)，如(ru)图1(c)所(suo)(suo)示。vGS越大(da)，作用于半导(dao)体外(wai)表的电(dian)(dian)(dian)(dian)场就越强(qiang)(qiang)，吸(xi)收(shou)到(dao)P衬底外(wai)表的电(dian)(dian)(dian)(dian)子(zi)(zi)就越多，导(dao)电(dian)(dian)(dian)(dian)沟道(dao)(dao)越厚，沟道(dao)(dao)电(dian)(dian)(dian)(dian)阻越小。

开端(duan)构成(cheng)沟道(dao)时(shi)的栅(zha)——源极电(dian)压称为开启电(dian)压，用VT表示。

上(shang)面讨论(lun)的N沟道(dao)MOS管(guan)在vGS＜VT时(shi)，不能构成(cheng)(cheng)(cheng)导(dao)电沟道(dao)，管(guan)子处(chu)于截止状态。只要当vGS≥VT时(shi)，才(cai)有沟道(dao)构成(cheng)(cheng)(cheng)。这种必需在vGS≥VT时(shi)才(cai)干构成(cheng)(cheng)(cheng)导(dao)电沟道(dao)的MOS管(guan)称(cheng)为加强型MOS管(guan)。沟道(dao)构成(cheng)(cheng)(cheng)以后，在漏——源极间加上(shang)正向电压vDS，就(jiu)有漏极电流产生。

vDS对iD的影响

如图(a)所示，当vGS>VT且为(wei)一(yi)肯定值时(shi)，漏(lou)——源(yuan)电(dian)(dian)压vDS对导电(dian)(dian)沟道及电(dian)(dian)流(liu)iD的影响与结型场效应管(guan)类似。

漏(lou)极(ji)电(dian)流(liu)iD沿沟(gou)(gou)道产生的电(dian)压(ya)降使沟(gou)(gou)道内各点与栅(zha)极(ji)间(jian)的电(dian)压(ya)不(bu)再相(xiang)等，靠近源极(ji)一端的电(dian)压(ya)最大(da)，这里沟(gou)(gou)道最厚，而漏(lou)极(ji)一端电(dian)压(ya)最小，其值为VGD=vGS－vDS，因此这里沟(gou)(gou)道最薄(bo)。但(dan)当(dang)vDS较小（vDS随(sui)着(zhe)vDS的增(zeng)(zeng)(zeng)大(da)，靠(kao)近漏极(ji)(ji)的沟(gou)道越来越薄，当vDS增(zeng)(zeng)(zeng)加到使VGD=vGS－vDS=VT(或vDS=vGS－VT)时，沟(gou)道在漏极(ji)(ji)一端呈现预(yu)夹(jia)断，如(ru)图2(b)所示。再继续增(zeng)(zeng)(zeng)大(da)vDS，夹(jia)断点将向源极(ji)(ji)方向挪动，如(ru)图2(c)所示。由(you)于vDS的增(zeng)(zeng)(zeng)加局部简直(zhi)全(quan)部降落在夹(jia)断区，故iD简直(zhi)不随(sui)vDS增(zeng)(zeng)(zeng)大(da)而(er)增(zeng)(zeng)(zeng)加，管子进(jin)入饱和(he)区，iD简直(zhi)仅由(you)vGS决议(yi)。

N沟道加强(qiang)型(xing)MOS管的特性曲线、电流方程及参数

（1）特性曲(qu)线和电流方(fang)程

1）输出特(te)性曲(qu)线

N沟(gou)道(dao)加强型(xing)MOS管的输出特性(xing)曲(qu)线如图1(a)所示。与结型(xing)场效应管一样,其(qi)输出特性(xing)曲(qu)线也可分为可变(bian)电阻(zu)区(qu)(qu)、饱和(he)区(qu)(qu)、截止区(qu)(qu)和(he)击穿(chuan)区(qu)(qu)几(ji)局部。

2）转移特(te)性(xing)曲(qu)线

转(zhuan)移特(te)性(xing)曲线(xian)如图1(b)所(suo)示,由于场效应(ying)管(guan)作放大(da)器(qi)件运用(yong)时是(shi)工(gong)作在饱(bao)和(he)区(qu)(恒流(liu)区(qu)),此时iD简直(zhi)不(bu)随vDS而变(bian)化,即不(bu)同的(de)vDS所(suo)对应(ying)的(de)转(zhuan)移特(te)性(xing)曲线(xian)简直(zhi)是(shi)重合的(de),所(suo)以(yi)可用(yong)vDS大(da)于某一数(shu)值(vDS＞vGS-VT)后的(de)一条转(zhuan)移特(te)性(xing)曲线(xian)替代(dai)饱(bao)和(he)区(qu)的(de)一切转(zhuan)移特(te)性(xing)曲线(xian)。

3）iD与vGS的近(jin)似关系

与结型(xing)场效应(ying)管相相似。在饱(bao)和区内,iD与vGS的近似关系(xi)式(shi)为(wei)

式中IDO是(shi)vGS=2VT时(shi)的漏极电流iD。

（2）参数

MOS管(guan)的主(zhu)要参数(shu)与结型(xing)场效应管(guan)根本相同，只是加(jia)强型(xing)MOS管(guan)中不用(yong)(yong)夹断电压(ya)VP ，而用(yong)(yong)开启电压(ya)VT表征管(guan)子的特性(xing)。

N沟道耗尽型MOS管的基(ji)本(ben)结构(gou)

（1）构造：

N沟道耗(hao)尽型(xing)MOS管(guan)与N沟道加强型(xing)MOS管(guan)根本(ben)类似。

（2）区别：

耗尽型MOS管(guan)在(zai)vGS=0时，漏——源极间已有导电沟道产生，而加(jia)强型MOS管(guan)要在(zai)vGS≥VT时才呈现导电沟道。

（3）缘由：

制造N沟(gou)道(dao)耗(hao)尽型MOS管(guan)时，在(zai)SiO2绝(jue)缘(yuan)层中掺入(ru)了大量的(de)碱金属正离子(zi)Na+或(huo)K+(制造P沟(gou)道(dao)耗(hao)尽型MOS管(guan)时掺入(ru)负离子(zi))，如图1(a)所示，因而(er)即(ji)便vGS=0时，在(zai)这(zhei)些正离子(zi)产生(sheng)的(de)电场作用下，漏——源(yuan)极间的(de)P型衬底外(wai)表(biao)也能感(gan)应(ying)生(sheng)成(cheng)N沟(gou)道(dao)(称(cheng)为初始沟(gou)道(dao))，只需加上正向电压vDS，就有电流iD。

假(jia)如加(jia)(jia)上正的vGS，栅极与N沟(gou)(gou)道(dao)(dao)(dao)间的电(dian)场将在沟(gou)(gou)道(dao)(dao)(dao)中吸收来更(geng)多的电(dian)子，沟(gou)(gou)道(dao)(dao)(dao)加(jia)(jia)宽，沟(gou)(gou)道(dao)(dao)(dao)电(dian)阻变小，iD增(zeng)大。反之vGS为负时，沟(gou)(gou)道(dao)(dao)(dao)中感(gan)应(ying)的电(dian)子减(jian)少，沟(gou)(gou)道(dao)(dao)(dao)变窄，沟(gou)(gou)道(dao)(dao)(dao)电(dian)阻变大，iD减(jian)小。当(dang)vGS负向增(zeng)加(jia)(jia)到某一数(shu)值时，导电(dian)沟(gou)(gou)道(dao)(dao)(dao)消逝(shi)，iD趋于(yu)零，管子截止，故(gu)称为耗尽型。

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