场效应管工作原理图

MOS 场效应管也被称为MOS FET， 既Metal Oxide Semiconductor Field Effect Transistor（金属氧化物半导体场效应管）的缩(suo)写(xie)。它一般(ban)有(you)耗(hao)尽型和增强型两种。

场效应管工作原理图-MOS管的结构特点

MOS管(guan)(guan)的(de)(de)内部结构如图所示：其导(dao)通时只有一种(zhong)极性的(de)(de)载流(liu)子(zi)(多子(zi))参与导(dao)电(dian)，是单极型晶体管(guan)(guan)。导(dao)电(dian)机理(li)与小功(gong)率MOS管(guan)(guan)相(xiang)同，但结构上有较大(da)区别，小功(gong)率MOS管(guan)(guan)是横向导(dao)电(dian)器件，功(gong)率MOSFET大(da)都采用垂(chui)直导(dao)电(dian)结构，又称为(wei)VMOSFET，大(da)大(da)提(ti)高了MOSFET器件的(de)(de)耐压和(he)耐电(dian)流(liu)能力(li)。

其主要特(te)点是(shi)(shi)在金属(shu)栅(zha)极与沟(gou)(gou)道(dao)(dao)之间有(you)(you)一(yi)层二氧(yang)化硅绝缘层，因此(ci)具有(you)(you)很高(gao)的输入电(dian)阻，该管导(dao)通时(shi)在两个高(gao)浓(nong)度(du)n扩散区间形成n型(xing)导(dao)电(dian)沟(gou)(gou)道(dao)(dao)。n沟(gou)(gou)道(dao)(dao)增强型(xing)MOS管必(bi)须在栅(zha)极上(shang)施(shi)加(jia)(jia)正向偏压(ya)，且只有(you)(you)栅(zha)源电(dian)压(ya)大(da)于阈值电(dian)压(ya)时(shi)才(cai)有(you)(you)导(dao)电(dian)沟(gou)(gou)道(dao)(dao)产生(sheng)的n沟(gou)(gou)道(dao)(dao)MOS管。n沟(gou)(gou)道(dao)(dao)耗尽型(xing)MOS管是(shi)(shi)指在不加(jia)(jia)栅(zha)压(ya)(栅(zha)源电(dian)压(ya)为零)时(shi)，就有(you)(you)导(dao)电(dian)沟(gou)(gou)道(dao)(dao)产生(sheng)的n沟(gou)(gou)道(dao)(dao)MOS管。

场效应管工作原理图详解

场(chang)(chang)效应(ying)管(guan)(guan)，其(qi)内(nei)部(bu)结构见图5。它可分(fen)为(wei)NPN型(xing)(xing)PNP型(xing)(xing)。NPN型(xing)(xing)通常称为(wei)N沟道(dao)(dao)型(xing)(xing)，PNP型(xing)(xing)也叫P沟道(dao)(dao)型(xing)(xing)。由图可看(kan)出(chu)，对(dui)于N沟道(dao)(dao)的(de)(de)场(chang)(chang)效应(ying)管(guan)(guan)其(qi)源极(ji)和漏极(ji)接(jie)在N型(xing)(xing)半(ban)导体(ti)上(shang)，同样对(dui)于P沟道(dao)(dao)的(de)(de)场(chang)(chang)效应(ying)管(guan)(guan)其(qi)源极(ji)和漏极(ji)则接(jie)在P型(xing)(xing)半(ban)导体(ti)上(shang)。我们知(zhi)道(dao)(dao)一般三(san)极(ji)管(guan)(guan)是(shi)由输(shu)(shu)入(ru)(ru)的(de)(de)电(dian)(dian)流(liu)(liu)控制输(shu)(shu)出(chu)的(de)(de)电(dian)(dian)流(liu)(liu)。但对(dui)于场(chang)(chang)效应(ying)管(guan)(guan)，其(qi)输(shu)(shu)出(chu)电(dian)(dian)流(liu)(liu)是(shi)由输(shu)(shu)入(ru)(ru)的(de)(de)电(dian)(dian)压（或(huo)称电(dian)(dian)场(chang)(chang)）控制，可以认为(wei)输(shu)(shu)入(ru)(ru)电(dian)(dian)流(liu)(liu)极(ji)小或(huo)没有输(shu)(shu)入(ru)(ru)电(dian)(dian)流(liu)(liu)，这使得该器件有很高的(de)(de)输(shu)(shu)入(ru)(ru)阻抗，同时这也是(shi)我们称之为(wei)场(chang)(chang)效应(ying)管(guan)(guan)的(de)(de)原因。

为(wei)解(jie)释(shi)MOS场(chang)效(xiao)应管工作原(yuan)理图，我们(men)(men)先了解(jie)一(yi)下仅含有(you)(you)一(yi)个P—N结的(de)(de)(de)二极(ji)(ji)管的(de)(de)(de)工作过(guo)程。如图6所示，我们(men)(men)知道在(zai)(zai)二极(ji)(ji)管加上正(zheng)(zheng)向(xiang)(xiang)电(dian)(dian)压(ya)（P端(duan)接正(zheng)(zheng)极(ji)(ji)，N端(duan)接负(fu)(fu)(fu)极(ji)(ji)）时(shi)，二极(ji)(ji)管导(dao)(dao)(dao)(dao)(dao)通(tong)，其PN结有(you)(you)电(dian)(dian)流(liu)通(tong)过(guo)。这是因为(wei)在(zai)(zai)P型(xing)半(ban)导(dao)(dao)(dao)(dao)(dao)体(ti)(ti)端(duan)为(wei)正(zheng)(zheng)电(dian)(dian)压(ya)时(shi)，N型(xing)半(ban)导(dao)(dao)(dao)(dao)(dao)体(ti)(ti)内的(de)(de)(de)负(fu)(fu)(fu)电(dian)(dian)子(zi)被吸引而涌向(xiang)(xiang)加有(you)(you)正(zheng)(zheng)电(dian)(dian)压(ya)的(de)(de)(de)P型(xing)半(ban)导(dao)(dao)(dao)(dao)(dao)体(ti)(ti)端(duan)，而P型(xing)半(ban)导(dao)(dao)(dao)(dao)(dao)体(ti)(ti)端(duan)内的(de)(de)(de)正(zheng)(zheng)电(dian)(dian)子(zi)则朝N型(xing)半(ban)导(dao)(dao)(dao)(dao)(dao)体(ti)(ti)端(duan)运动，从而形(xing)成导(dao)(dao)(dao)(dao)(dao)通(tong)电(dian)(dian)流(liu)。同理，当(dang)二极(ji)(ji)管加上反向(xiang)(xiang)电(dian)(dian)压(ya)（P端(duan)接负(fu)(fu)(fu)极(ji)(ji)，N端(duan)接正(zheng)(zheng)极(ji)(ji)）时(shi)，这时(shi)在(zai)(zai)P型(xing)半(ban)导(dao)(dao)(dao)(dao)(dao)体(ti)(ti)端(duan)为(wei)负(fu)(fu)(fu)电(dian)(dian)压(ya)，正(zheng)(zheng)电(dian)(dian)子(zi)被聚集在(zai)(zai)P型(xing)半(ban)导(dao)(dao)(dao)(dao)(dao)体(ti)(ti)端(duan)，负(fu)(fu)(fu)电(dian)(dian)子(zi)则聚集在(zai)(zai)N型(xing)半(ban)导(dao)(dao)(dao)(dao)(dao)体(ti)(ti)端(duan)，电(dian)(dian)子(zi)不移(yi)动，其PN结没有(you)(you)电(dian)(dian)流(liu)通(tong)过(guo)，二极(ji)(ji)管截止。

对于场(chang)效应(ying)(ying)管(guan)（见(jian)图(tu)7），在栅极没有电(dian)压时(shi)，由前面分析可知(zhi)，在源极与漏(lou)极之(zhi)间不会有电(dian)流流过，此时(shi)场(chang)效应(ying)(ying)管(guan)处(chu)与截止状态（图(tu)7a）。当有一个正电(dian)压加在N沟道的MOS

场效应管栅(zha)极上时，由(you)于电(dian)场的(de)(de)(de)(de)作用，此时N型(xing)半导(dao)体(ti)的(de)(de)(de)(de)源极和(he)漏极的(de)(de)(de)(de)负电(dian)子被吸引出来而涌向栅(zha)极，但由(you)于氧化膜(mo)的(de)(de)(de)(de)阻(zu)挡，使(shi)得电(dian)子聚集(ji)在两个N沟(gou)道之(zhi)(zhi)(zhi)间的(de)(de)(de)(de)P型(xing)半导(dao)体(ti)中（见图7b），从而形(xing)成(cheng)电(dian)流(liu)，使(shi)源极和(he)漏极之(zhi)(zhi)(zhi)间导(dao)通。我(wo)们(men)也可以想像为(wei)两个N型(xing)半导(dao)体(ti)之(zhi)(zhi)(zhi)间为(wei)一(yi)条沟(gou)，栅(zha)极电(dian)压的(de)(de)(de)(de)建立相当于为(wei)它们(men)之(zhi)(zhi)(zhi)间搭(da)了一(yi)座桥(qiao)梁，该桥(qiao)的(de)(de)(de)(de)大小由(you)栅(zha)压的(de)(de)(de)(de)大小决定(ding)。图8给出了P沟(gou)道的(de)(de)(de)(de)MOS

场效应管的工作(zuo)过(guo)程，其工作(zuo)原理类似这里不(bu)再重复。

下面简述一(yi)(yi)下用(yong)C-MOS场(chang)(chang)效(xiao)(xiao)应(ying)(ying)管(guan)（增强型(xing)(xing)MOS场(chang)(chang)效(xiao)(xiao)应(ying)(ying)管(guan)）组成的(de)应(ying)(ying)用(yong)电(dian)(dian)(dian)(dian)路的(de)工(gong)作过(guo)程(cheng)（见图9）。电(dian)(dian)(dian)(dian)路将一(yi)(yi)个增强型(xing)(xing)P沟道(dao)MOS场(chang)(chang)效(xiao)(xiao)应(ying)(ying)管(guan)和一(yi)(yi)个增强型(xing)(xing)N沟道(dao)MOS场(chang)(chang)效(xiao)(xiao)应(ying)(ying)管(guan)组合在一(yi)(yi)起使用(yong)。当(dang)输入(ru)(ru)端为低电(dian)(dian)(dian)(dian)平时，P沟道(dao)MOS场(chang)(chang)效(xiao)(xiao)应(ying)(ying)管(guan)导(dao)通(tong)(tong)，输出(chu)端与(yu)电(dian)(dian)(dian)(dian)源正(zheng)极(ji)(ji)接(jie)通(tong)(tong)。当(dang)输入(ru)(ru)端为高电(dian)(dian)(dian)(dian)平时，N沟道(dao)MOS场(chang)(chang)效(xiao)(xiao)应(ying)(ying)管(guan)导(dao)通(tong)(tong)，输出(chu)端与(yu)电(dian)(dian)(dian)(dian)源地接(jie)通(tong)(tong)。在该(gai)电(dian)(dian)(dian)(dian)路中，P沟道(dao)MOS场(chang)(chang)效(xiao)(xiao)应(ying)(ying)管(guan)和N沟道(dao)MOS场(chang)(chang)效(xiao)(xiao)应(ying)(ying)管(guan)总是在相(xiang)(xiang)反的(de)状态下工(gong)作，其相(xiang)(xiang)位输入(ru)(ru)端和输出(chu)端相(xiang)(xiang)反。通(tong)(tong)过(guo)这种(zhong)工(gong)作方式(shi)我们可以获得较大的(de)电(dian)(dian)(dian)(dian)流(liu)输出(chu)。同时由(you)于(yu)漏电(dian)(dian)(dian)(dian)流(liu)的(de)影(ying)响，使得栅压(ya)在还没有到0V，通(tong)(tong)常在栅极(ji)(ji)电(dian)(dian)(dian)(dian)压(ya)小于(yu)1到2V时，MOS场(chang)(chang)效(xiao)(xiao)应(ying)(ying)管(guan)既被(bei)关断(duan)。不同场(chang)(chang)效(xiao)(xiao)应(ying)(ying)管(guan)其关断(duan)电(dian)(dian)(dian)(dian)压(ya)略有不同。也正(zheng)因为如此，

使得该(gai)电路(lu)不会因为两(liang)管(guan)同(tong)时导(dao)通而(er)造成电源短路(lu)。

由以上分(fen)(fen)析我(wo)们可(ke)以画出原理图中(zhong)MOS场效应管电路部分(fen)(fen)的(de)工(gong)作过程（见图10）。工(gong)作原理同前所述(shu)。

场(chang)(chang)效应(ying)晶体(ti)(ti)管(guan)（Field Effect Transistor缩写(FET)）简称(cheng)场(chang)(chang)效应(ying)管(guan)。场(chang)(chang)效应(ying)管(guan)工作原理图一般的晶体(ti)(ti)管(guan)是(shi)由(you)两种(zhong)极(ji)性的载(zai)流子(zi)(zi),即多(duo)数(shu)载(zai)流子(zi)(zi)和(he)反(fan)(fan)极(ji)性的少数(shu)载(zai)流子(zi)(zi)参(can)与(yu)导(dao)(dao)电(dian),因此(ci)称(cheng)为(wei)双极(ji)型(xing)晶体(ti)(ti)管(guan),而FET仅是(shi)由(you)多(duo)数(shu)载(zai)流子(zi)(zi)参(can)与(yu)导(dao)(dao)电(dian),它(ta)与(yu)双极(ji)型(xing)相反(fan)(fan),也称(cheng)为(wei)单极(ji)型(xing)晶体(ti)(ti)管(guan)。它(ta)属于电(dian)压控制型(xing)半(ban)导(dao)(dao)体(ti)(ti)器件，具(ju)有输入电(dian)阻高（108～109Ω）、噪声小、功耗低、动(dong)态(tai)范围大、易于集成、没有二次击穿(chuan)现象、安全工作区域宽(kuan)等优点，现已成为(wei)双极(ji)型(xing)晶体(ti)(ti)管(guan)和(he)功率晶体(ti)(ti)管(guan)的强(qiang)大竞争者(zhe)。

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