N沟MOS晶体(ti)管

金属-氧化物-半导体(ti)(Metal-Oxide-SemIConductor)构(gou)造的晶体(ti)管(guan)简称MOS晶体(ti)管(guan)，有(you)P型MOS管(guan)和N型MOS管(guan)之分(fen)。MOS管(guan)构(gou)成(cheng)(cheng)的集(ji)(ji)成(cheng)(cheng)电路(lu)(lu)称为(wei)MOS集(ji)(ji)成(cheng)(cheng)电路(lu)(lu)，而PMOS管(guan)和NMOS管(guan)共同构(gou)成(cheng)(cheng)的互补(bu)型MOS集(ji)(ji)成(cheng)(cheng)电路(lu)(lu)即(ji)为(wei)CMOS集(ji)(ji)成(cheng)(cheng)电路(lu)(lu)。

由p型(xing)衬底和两(liang)个高浓度n扩散区(qu)构成的MOS管叫作n沟(gou)(gou)道MOS管，该管导(dao)通时在两(liang)个高浓度n扩散区(qu)间(jian)构成n型(xing)导(dao)电(dian)(dian)(dian)沟(gou)(gou)道。n沟(gou)(gou)道加(jia)强型(xing)MOS管必(bi)需在栅(zha)极上施(shi)加(jia)正(zheng)向偏压(ya)(ya)(ya)，且(qie)只要栅(zha)源(yuan)电(dian)(dian)(dian)压(ya)(ya)(ya)大于阈值电(dian)(dian)(dian)压(ya)(ya)(ya)时才有(you)导(dao)电(dian)(dian)(dian)沟(gou)(gou)道产生的n沟(gou)(gou)道MOS管。n沟(gou)(gou)道耗尽型(xing)MOS管是(shi)指在不加(jia)栅(zha)压(ya)(ya)(ya)（栅(zha)源(yuan)电(dian)(dian)(dian)压(ya)(ya)(ya)为零）时，就有(you)导(dao)电(dian)(dian)(dian)沟(gou)(gou)道产生的n沟(gou)(gou)道MOS管。

NMOS集成(cheng)(cheng)(cheng)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)是(shi)N沟道MOS电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)，NMOS集成(cheng)(cheng)(cheng)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)的输(shu)入阻抗很高(gao)，根本上不(bu)需求吸收电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流，因而，CMOS与(yu)NMOS集成(cheng)(cheng)(cheng)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)衔接(jie)(jie)时不(bu)用(yong)思索电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流的负载问题。NMOS集成(cheng)(cheng)(cheng)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)大(da)多采用(yong)单(dan)组正电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源供电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，并且以(yi)5V为多。CMOS集成(cheng)(cheng)(cheng)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)只需选用(yong)与(yu)NMOS集成(cheng)(cheng)(cheng)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)相同(tong)的电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源，就可与(yu)NMOS集成(cheng)(cheng)(cheng)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)直接(jie)(jie)衔接(jie)(jie)。不(bu)过，从NMOS到CMOS直接(jie)(jie)衔接(jie)(jie)时，由于NMOS输(shu)出的高(gao)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)低于CMOS集成(cheng)(cheng)(cheng)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)的输(shu)入高(gao)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)平(ping)，因此需求运用(yong)一个（电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)位）上拉电(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻R，R的取值普(pu)通(tong)选用(yong)2～100KΩ。

N沟道加强型MOS管的构造(zao)

在一块掺(chan)杂浓(nong)度较低的(de)P型硅衬(chen)底上，制造两(liang)个(ge)(ge)高(gao)掺(chan)杂浓(nong)度的(de)N+区(qu)，并用金属铝引出(chu)两(liang)个(ge)(ge)电极，分别作漏极d和(he)源(yuan)极s。

然(ran)后(hou)在(zai)(zai)半导体外表掩盖(gai)一层很薄的二(er)氧化(hua)硅(SiO2)绝缘层，在(zai)(zai)漏——源极间的绝缘层上再装上一个铝电(dian)极,作为栅极g。

在衬(chen)底上(shang)也引出(chu)一个电极B，这就构成了一个N沟(gou)道(dao)加强型MOS管(guan)。MOS管(guan)的(de)源极和(he)衬(chen)底通常是接(jie)(jie)在一同的(de)(大多数(shu)管(guan)子在出(chu)厂前已连(lian)接(jie)(jie)好)。

它的(de)栅极与其它电(dian)极间是绝缘的(de)。

图(tu)(a)、(b)分别是它(ta)的构造表示(shi)图(tu)和(he)代(dai)表符号(hao)(hao)。代(dai)表符号(hao)(hao)中(zhong)的箭头方向(xiang)表示(shi)由(you)P(衬底)指向(xiang)N(沟道(dao))。P沟道(dao)加强(qiang)型MOS管(guan)的箭头方向(xiang)与上述相反，如图(tu)(c)所示(shi)。

N沟道加(jia)强型MOS管的工作(zuo)原(yuan)理

（1）vGS对(dui)iD及沟(gou)道的控制造用(yong)

① vGS=0 的(de)状(zhuang)况(kuang)

从图1(a)能够看出，加(jia)强(qiang)型(xing)MOS管的(de)(de)漏(lou)极d和源极s之间有两个背(bei)靠背(bei)的(de)(de)PN结。当栅(zha)——源电压vGS=0时，即便加(jia)上漏(lou)——源电压vDS，而(er)且不管vDS的(de)(de)极性(xing)如何，总有一个PN结处于反偏状态，漏(lou)——源极间没有导电沟道，所以这时漏(lou)极电流iD≈0。

② vGS>0 的状(zhuang)况

若(ruo)vGS＞0，则栅极和衬底之间的SiO2绝缘层中便(bian)产生一个(ge)电场。电场方向(xiang)垂(chui)直(zhi)于半导体外表的由栅极指向(xiang)衬底的电场。这个(ge)电场能排挤空穴(xue)而吸收电子。

排挤空穴：使栅(zha)极左近的(de)P型衬底(di)(di)(di)中(zhong)的(de)空穴被(bei)排挤，剩下(xia)不能挪动的(de)受(shou)主离子(负离子)，构成耗(hao)尽层。吸收电(dian)子：将 P型衬底(di)(di)(di)中(zhong)的(de)电(dian)子（少子）被(bei)吸收到衬底(di)(di)(di)外表。

（2）导电(dian)沟道的构成：

当vGS数(shu)(shu)值较(jiao)小(xiao)，吸(xi)收电(dian)子的(de)才能不(bu)强时，漏(lou)——源(yuan)极(ji)之间仍无导(dao)电(dian)沟道(dao)呈现，如图1(b)所示(shi)(shi)。vGS增(zeng)加时，吸(xi)收到(dao)P衬(chen)(chen)底(di)外(wai)表层(ceng)的(de)电(dian)子就增(zeng)加，当vGS到(dao)达某一数(shu)(shu)值时，这些电(dian)子在栅极(ji)左近的(de)P衬(chen)(chen)底(di)外(wai)表便构成(cheng)(cheng)一个(ge)N型(xing)(xing)薄层(ceng)，且与(yu)(yu)两个(ge)N+区(qu)相连通(tong)，在漏(lou)——源(yuan)极(ji)间构成(cheng)(cheng)N型(xing)(xing)导(dao)电(dian)沟道(dao)，其(qi)导(dao)电(dian)类型(xing)(xing)与(yu)(yu)P衬(chen)(chen)底(di)相反，故又称(cheng)为反型(xing)(xing)层(ceng)，如图1(c)所示(shi)(shi)。vGS越大，作(zuo)用于半导(dao)体(ti)外(wai)表的(de)电(dian)场(chang)就越强，吸(xi)收到(dao)P衬(chen)(chen)底(di)外(wai)表的(de)电(dian)子就越多，导(dao)电(dian)沟道(dao)越厚，沟道(dao)电(dian)阻越小(xiao)。

开端构(gou)成沟道时的栅——源极电压称(cheng)为(wei)开启(qi)电压，用VT表示。

上面(mian)讨论(lun)的N沟(gou)道(dao)MOS管在vGS＜VT时，不能构(gou)成导电(dian)(dian)沟(gou)道(dao)，管子(zi)处于截止(zhi)状态。只要(yao)当vGS≥VT时，才有沟(gou)道(dao)构(gou)成。这种必需在vGS≥VT时才干构(gou)成导电(dian)(dian)沟(gou)道(dao)的MOS管称(cheng)为加强(qiang)型MOS管。沟(gou)道(dao)构(gou)成以后，在漏——源极间加上正向电(dian)(dian)压vDS，就(jiu)有漏极电(dian)(dian)流产生(sheng)。

vDS对iD的影(ying)响

如(ru)图(a)所示，当vGS>VT且(qie)为一肯定值(zhi)时，漏——源电压vDS对导电沟道(dao)及电流iD的(de)影响与结(jie)型场效应管类似。

漏极电流iD沿沟道产生的(de)电压(ya)(ya)降使(shi)沟道内各点与栅(zha)极间的(de)电压(ya)(ya)不再相等，靠近源极一端(duan)的(de)电压(ya)(ya)最大，这(zhei)里(li)沟道最厚，而漏极一端(duan)电压(ya)(ya)最小(xiao)，其值为VGD=vGS－vDS，因此这(zhei)里(li)沟道最薄。但当vDS较小(xiao)（vDS随着vDS的(de)增大(da)，靠近漏极(ji)的(de)沟道(dao)越(yue)来越(yue)薄，当vDS增加到使VGD=vGS－vDS=VT(或vDS=vGS－VT)时，沟道(dao)在漏极(ji)一端呈现预夹断，如(ru)图2(b)所示。再继(ji)续增大(da)vDS，夹断点(dian)将向源(yuan)极(ji)方向挪动(dong)，如(ru)图2(c)所示。由于vDS的(de)增加局部简(jian)直(zhi)全部降(jiang)落在夹断区，故iD简(jian)直(zhi)不随vDS增大(da)而增加，管(guan)子进入(ru)饱和区，iD简(jian)直(zhi)仅由vGS决议。

N沟道加强型(xing)MOS管(guan)的特性(xing)曲(qu)线、电流方程及参(can)数(shu)

（1）特性曲线(xian)和电流方(fang)程

1）输出特性(xing)曲线

N沟道加强型MOS管的输出(chu)特性曲线如图1(a)所示。与结型场效应管一样(yang),其(qi)输出(chu)特性曲线也可(ke)分为可(ke)变电阻区(qu)、饱和区(qu)、截止区(qu)和击穿区(qu)几局部(bu)。

2）转(zhuan)移(yi)特性(xing)曲线

转移(yi)(yi)特性曲(qu)线如图1(b)所示,由于场效应(ying)管作放大(da)(da)器(qi)件运用时(shi)是工(gong)作在饱和区(恒流区),此时(shi)iD简直(zhi)不随vDS而变化(hua),即(ji)不同的(de)(de)vDS所对(dui)应(ying)的(de)(de)转移(yi)(yi)特性曲(qu)线简直(zhi)是重(zhong)合的(de)(de),所以可用vDS大(da)(da)于某一数(shu)值(vDS＞vGS-VT)后(hou)的(de)(de)一条转移(yi)(yi)特性曲(qu)线替代饱和区的(de)(de)一切转移(yi)(yi)特性曲(qu)线。

3）iD与vGS的近(jin)似关(guan)系

与(yu)(yu)结型(xing)场(chang)效应管相(xiang)相(xiang)似。在饱和区内(nei),iD与(yu)(yu)vGS的近似关系(xi)式为

式中(zhong)IDO是vGS=2VT时的漏极电流(liu)iD。

（2）参数(shu)

MOS管(guan)(guan)的(de)主要参数与结型场效(xiao)应管(guan)(guan)根本相同，只是加强型MOS管(guan)(guan)中不用夹断电压(ya)VP ，而用开(kai)启电压(ya)VT表征管(guan)(guan)子(zi)的(de)特性(xing)。

N沟道耗尽型MOS管的基本结构

（1）构造：

N沟道耗尽(jin)型MOS管(guan)与N沟道加强型MOS管(guan)根本(ben)类(lei)似。

（2）区别(bie)：

耗尽型MOS管在vGS=0时，漏(lou)——源极间已有导电沟(gou)道产生，而(er)加(jia)强(qiang)型MOS管要在vGS≥VT时才呈现导电沟(gou)道。

（3）缘由：

制造N沟道(dao)耗尽(jin)型MOS管时，在(zai)SiO2绝缘层中掺(chan)入了大量的(de)(de)(de)碱金属(shu)正离(li)子(zi)(zi)Na+或(huo)K+(制造P沟道(dao)耗尽(jin)型MOS管时掺(chan)入负离(li)子(zi)(zi))，如图1(a)所示(shi)，因(yin)而(er)即便(bian)vGS=0时，在(zai)这(zhei)些正离(li)子(zi)(zi)产生的(de)(de)(de)电场作(zuo)用下，漏——源(yuan)极(ji)间的(de)(de)(de)P型衬底外表也能感应生成N沟道(dao)(称为初始沟道(dao))，只需加上正向电压vDS，就(jiu)有(you)电流(liu)iD。

假如加上正的(de)vGS，栅极与N沟(gou)道(dao)间的(de)电场将在沟(gou)道(dao)中吸收来更多的(de)电子(zi)(zi)，沟(gou)道(dao)加宽，沟(gou)道(dao)电阻变小，iD增(zeng)大(da)。反之vGS为负时(shi)，沟(gou)道(dao)中感(gan)应的(de)电子(zi)(zi)减(jian)少，沟(gou)道(dao)变窄(zhai)，沟(gou)道(dao)电阻变大(da)，iD减(jian)小。当(dang)vGS负向增(zeng)加到某一数(shu)值时(shi)，导电沟(gou)道(dao)消(xiao)逝，iD趋于零，管子(zi)(zi)截止，故(gu)称为耗尽型。

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