Lecture24-第六章-理想MOS電容器

1、 Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province Province理想理想MOSMOS電容器電容器

2、Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province ProvinceOutline1. 積累區(qū)（積累區(qū)（

3、VG0）4. 反型區(qū)（反型區(qū)（VG0） Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province Provin

4、ce對于一個理想的對于一個理想的MOS系統(tǒng)，當外加偏壓系統(tǒng)，當外加偏壓VG變化時，金屬極變化時，金屬極板上的電荷板上的電荷QM和半導體表面空間電荷和半導體表面空間電荷QS都要相應發(fā)生變化。都要相應發(fā)生變化。說明，說明，MOS系統(tǒng)有一定的電容效應，所以把它叫做系統(tǒng)有一定的電容效應，所以把它叫做MOS電電容器；但一般說來：容器；但一般說來：QM并不正比于外加偏壓并不正比于外加偏壓VG，需要討論，需要討論微分電容。微分電容。 Micro Electromechanical System Research Center of Engineering and Technology of Micro El

5、ectromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province Province令令C為為MOS系統(tǒng)單位面積的微分電容，則：系統(tǒng)單位面積的微分電容，則：微分電容微分電容C的數值隨外加偏壓的數值隨外加偏壓VG變化，這變化，這個變化規(guī)律稱為個變化規(guī)律稱為MOS系統(tǒng)的電容系統(tǒng)的電容-電壓特電壓特性

6、性S0GVVGMddVQC MSM0MGdddddd1QQVQVC Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province P

7、rovince Province令:C0：絕緣層單位面積上的電容CS：半導體表面空間電荷區(qū)單位面積的電容SSSMS0M0ddddddQQCVQCSCCC1110MSM0MGdddddd1QQVQVC Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research

8、Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province Province兩個電容串聯(lián)后，總電容變小，且其數值主要由較小的一個電兩個電容串聯(lián)后，總電容變小，且其數值主要由較小的一個電容所決定，因為大部分電壓都降落在較小的電容上。容所決定，因為大部分電壓都降落在較小的電容上。C/C0稱為系統(tǒng)的歸一化電容稱為系統(tǒng)的歸一化電容SSCCCCC00SCCCC/1100即有：即有： Micro Electromechanical System Research Center of Engineering and Te

9、chnology of Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province Province00M0000M xQVxVQ電場000M0ddxVQC Micro Electromechanical System Research Center of Enginee

10、ring and Technology of Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province ProvinceSSSSMSddddQQC Micro Electromechanical System Research Center of Engineering

11、 and Technology of Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province Province當當MOS電容器的金屬電極上加有較大的負偏壓時電容器的金屬電極上加有較大的負偏壓時，能帶明顯能帶明顯向上彎曲，在表面造成多數載流子空穴的大量積累；只要表向上彎

12、曲，在表面造成多數載流子空穴的大量積累；只要表面勢面勢 稍有變化，就會引起表面空間電荷稍有變化，就會引起表面空間電荷QS的很大變化；所以，的很大變化；所以，半導體表面電容比較大，可以忽略不計。半導體表面電容比較大，可以忽略不計。MOS系統(tǒng)的電容基系統(tǒng)的電容基本上等于絕緣體電容本上等于絕緣體電容C0。當負偏壓的數值逐漸減小時，空間電荷區(qū)積累的空穴數隨之當負偏壓的數值逐漸減小時，空間電荷區(qū)積累的空穴數隨之減少，且減少，且QS隨隨 的變化逐漸減慢，的變化逐漸減慢，CS變小，它的作用就不能變小，它的作用就不能忽略；將使總電容減小，所以負偏壓的數值愈小，忽略；將使總電容減小，所以負偏壓的數值愈小，Cs愈

13、小，愈小，MOS電容器的總電容電容器的總電容C就愈小。就愈小。SSd00Sd )(xxpxpqQ Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of AnhuiAnhuiA

14、nhui Province Province Province Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Pro

15、vince Province在平帶附近，空間電荷區(qū)中：在平帶附近，空間電荷區(qū)中：由空穴的過?；蚯啡币鸬碾姾擅芏龋河煽昭ǖ倪^?；蚯啡币鸬碾姾擅芏龋涸谄綆Ц浇?，在平帶附近， 。上式進行指數項展開，且只保留前兩項。上式進行指數項展開，且只保留前兩項 T/ )(0)(Vxepxp) 1e ( )()(T/00VqpppqxKTpqVqpx02T0)(VG=0時，時， =0，能帶是平直的，稱為平帶情況能帶是平直的，稱為平帶情況STV Micro Electromechanical System Research Center of Engineering and Technology of Micr

16、o Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province Province則，空間電荷區(qū)內的泊松方程為：則，空間電荷區(qū)內的泊松方程為：式中：式中：其通解為：其通解為：2Ds0222ddLKTpqx2/102sDpqKTLKTpqx02)(s22ddxDD/LxLxBeAeass

17、d2qNx Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province Provinces, 0; 0,xx其邊

18、界條件為：D/sLxeDD/s2Ds/s02)(LxLxeLeKTpqxKTpqx02)(DD/LxLxBeAe電荷密度：電荷密度： Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technol

19、ogy of AnhuiAnhuiAnhui Province Province Province半導體表面單位面積內的總電荷為：半導體表面單位面積內的總電荷為：空間電荷與表空間電荷與表面勢符號相反面勢符號相反平帶情況下半導體表面的小信號電容平帶情況下半導體表面的小信號電容( (微分電容微分電容) )：歸一化平帶電容：歸一化平帶電容：sDs0/s2Ds0Sdd )(DLxeLxxQLxDsSSSddLQC2/1a2sDNqKTL0sD00FB11xLCC2/102sDpqKTL Micro Electromechanical System Research Center of Engineer

20、ing and Technology of Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province Province正比氧化層厚度正比氧化層厚度正比摻雜濃度正比摻雜濃度0sD00FB11xLCC2/1a2sDNqKTL Micro Electromechanical

21、System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province ProvincedsSSSddxQCdaSxqNQ2/1SsaS)2(qNQ可得：可得：SCCC11

22、10s2das2xqN在耗盡區(qū)，由：在耗盡區(qū)，由： Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province

23、Province對于氧化層有：對于氧化層有：SSCCCCC000sd0011xxCC000M0ddxVQCdsSSSddxQCS0GVV0S0CQVS0SGCQVs2aS2dxqN20asG0s0sd21CNqVCCxdaBSxqNQQ Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanic

24、al System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province Province2/1G20sa202/1Gsa2002121VxqNVqNCCCSCCCC/110020asG0s0sd21CNqVCCxdsSSSddxQC000M0ddxVQC耗盡區(qū)歸一化電容為：耗盡區(qū)歸一化電容為： Micro Electromechanical System Research Center of Engineering and Technology of Micro Electrome

25、chanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province Province Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System R

26、esearch Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province Province出現(xiàn)反型層以后的電容出現(xiàn)反型層以后的電容C與測量頻率有很大關系，所謂電容與測量頻率有很大關系，所謂電容C與測量頻率有關，就是與交變信號電壓的頻率有關。與測量頻率有關，就是與交變信號電壓的頻率有關。在測量電容在測量電容C時，在時，在MOS系統(tǒng)上施加有直流偏壓系統(tǒng)

27、上施加有直流偏壓VG，然后然后在在VG之上再加小信號的交變電壓，使電荷之上再加小信號的交變電壓，使電荷QM變化，從而測變化，從而測量電容量電容C。在不同的直流偏壓下測量在不同的直流偏壓下測量C ，便得到便得到C-V關系。關系。測量方法：測量方法： Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromec

28、hanical System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province Province Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Re

29、search Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province Province在出現(xiàn)反型層以后，特別是在接近強反型時，表面電荷由兩部在出現(xiàn)反型層以后，特別是在接近強反型時，表面電荷由兩部分組成：一部分是反型層中的電子電荷分組成：一部分是反型層中的電子電荷QI，它是由少子的增加它是由少子的增加引起的；另一部分是耗盡層下的電離受主電荷引起的；另一部分是耗盡層下的電離受主電荷QB，它是由多它是由多子空穴的喪失引起的：子空穴的喪失引起的：SBSISSSddddddQQQCBISQQQ Micro Ele

30、ctromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province Province如果測量電容的信號頻率較高，耗盡層中電子如果測量電容的

31、信號頻率較高，耗盡層中電子-空穴對的產生和空穴對的產生和復合過程跟不上信號的變化，反型層中的電子電荷復合過程跟不上信號的變化，反型層中的電子電荷QI也就來不也就來不及改變。則有：及改變。則有：則高頻情況下，反型層中的電容為：則高頻情況下，反型層中的電容為：0ddSIQ0sd0011xxCCdsSBSddxQC Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering an

32、d Technology of Micro Electromechanical System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province Province隨著直流偏壓隨著直流偏壓VG的增加，的增加，xd增大，電容增大，電容C按耗盡層的電容變化按耗盡層的電容變化規(guī)律而減小。當表面形成強反型層時，強反型層中的電子電規(guī)律而減小。當表面形成強反型層時，強反型層中的電子電荷隨直流偏壓的增加而增加，對直流偏置電場起屏蔽作用。荷隨直流偏壓的增加而增加，對直流偏置電場起屏蔽作用。于是，耗盡

33、層寬度不再變化，達到極大值于是，耗盡層寬度不再變化，達到極大值xdm，此時，此時，MOS系系統(tǒng)的電容統(tǒng)的電容C就達到最小值就達到最小值Cmin。且不再隨且不再隨VG的增加而變化，如的增加而變化，如圖中虛線所示。圖中虛線所示。 Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical Sys

34、tem Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province Province正比氧化層厚度正比氧化層厚度正比摻雜濃度正比摻雜濃度0sd0011xxCC Micro Electromechanical System Research Center of Engineering and Technology of Micro Electromechanical System Research Center of Engineering and Technology of Micro E

35、lectromechanical System Research Center of Engineering and Technology of AnhuiAnhuiAnhui Province Province ProvinceSISddQC（2）在接近強反型區(qū)，如果測量電容的信號頻率比較低，耗盡）在接近強反型區(qū)，如果測量電容的信號頻率比較低，耗盡層中電子層中電子-空穴對的產生與復合過程能跟得上信號的變化，這時，空穴對的產生與復合過程能跟得上信號的變化，這時，反型層中的電子電荷的變化，屏蔽了信號電場，反型層中的電子電荷的變化，屏蔽了信號電場， 對表面電容的貢獻是主要的，而耗盡層的寬度和電荷對表面電容的貢獻是主要的，而耗盡層的寬度和電荷QB基本上基本上不變：不變：0ddSBQSId/dQ Micro Electromechanical System Research Center of Engineering and Technology of