电子器件场效应晶体管

1、电子器件场效应晶体管MOS Structure Poly-silicon-OS StructureIdeal MOS capacitanceReal Surface Effects:Work function difference&interface chargeNon-ideal capacitance(1)work function difference semiconductoroxiden+ polysilicon(多晶硅)ms=m-sn+ poly-n Sin+ poly-p SiIdealNon-ideal(EFm-EFs)= (qs-qm) V=s-mVG=VFB(平带电压平带电

2、压)= -V= m - s= ms (2) Interface chargeGenerally, there are four types of charges in a practical MOS structure.Mobile ionic charge Qm可动离子电荷Oxide trapped charge Qot氧化物陷阱电荷Oxide fixed charge Qf氧化物固定电荷Interface trap charge Qit界面陷阱电荷IdealInterface chargeQiiiiFBGiiisSSiGCQVVVCQVthatrequiresbandFlatVV0; 0:

3、Effects of real surface iimsFBCQV6.4.4 Threshold voltagecasepracticalCQCQVcasepracticalCQVcaseidealCQVFidiimsTiimsFBFidT22To achieve the flat bandTo accommodate the depletion chargeTo induce the inverted regionQd= -qNaWm (n channel/P-sub)Qd= qNdWm (p channel/N-sub)When is the threshold voltage of p-

4、channel MOSFET greater than 0? How to do?iimsFBCQV28614/109 . 6105)1085. 8 () 9 . 3(cmFdCiiVCQViimsFB01. 10116. 089. 0109 . 6)106 . 1 ()105(89. 0819101）flat band voltagecmcmCcmFVcmCVcmFunitmcmqNWVnNqkTaFsmiaF22352115191410151)()(/)(1 (867.01067.8)101 ()106 .1 ()298.0()1085.8()8 .11(22298.0105 .1101l

5、n0259.0ln2）threshold voltageFidFBTCQVV2VCQVVcmCWqNQFidFBTmad21. 0)288. 0( 2109 . 61039. 101. 12/1039. 1)10867. 0)(101)(106 . 1 (8828415193）depletion mode because VT0(4) MOS Capacitor (ideal)Capacitance-voltage characteristics(电容电压特性）CiCssssiisisisiddQCdCCCCCCCCC111Because Cs is depending on VG, the

6、overall capacitance becomes voltage dependent.Ci Cs2/100112111kTqepnkTqeqLkTQQddQCdCCCCCCCCCskTqskTqDssssssssiisisisiss)(onaccumulatiCCiTo measure the capacitance, we must superpose the small a-c signal to the voltage. That is VG=V+dVG.Here dVG used to measure the capacitance will cause the small ch

7、arge change of the MOS capacitorHigh frequency)(22/1inversionstrongtodepletionWddQCCqNWqNQsssdsssaas)/(frequencyhighinversionstrongafterWCmsd)/(fequencylowinversionstrongafterCCi6.4.5 MOS capacitance-voltage analysisVTSubstrate Doping TypeC-VG Performance Substrate Doping TypeTo measure the doping d

8、ensity of substrateTo measure the interface state To measure the mobile charge within the oxide(1) To measure the width of oxide layer, doping density of substrate, VFB and VT Fig.6-16)log(03177. 0log683. 1388.302/ 12minminmin2minmin10ln2;111/ddCCaaaiasmmsdddiiiiiNNNqnNkTWWCCCCCCddCTo measure the ca

9、pacitance, we must superpose the small a-c signal to the voltage. That is VG=V+dVG.Here dVG used to measure the capacitance will cause the small charge change of the MOS capacitorFasmadFidFBTFBFBdebyeiFBDsdebyedssDNqWqNQCQVVFigseeVCCCCLCCCpqkTL22)166 .(111;02Show under flat band conditionDsdLC (2)To

10、 measure the fast interface state Dit12)(1eVcmCCCCCCCCqDHFiHFiLFiLFiit(3)To measure the mobile charge within the oxide Fig.6-22NoImage)(FBFBimifmsFBimfmsFBVVCQCQVCQQV6.4.7 Current-voltage characteristics of MOS gate oxidesTo understand the leakage current through the oxideFig. 6-24 (Something wrong, see English textbook and page 233(chinese textbook)Summary (1) 实际器件与理想情况存在偏差：实际情况要考实际器件与理想情况存在偏差：实际情况要考虑功函数差及界面电荷效应。虑功函数差及界面电荷效应。 (2)实际情况下存在平带电压，从而使阈值电压偏实际情况下存在平带电压，从而使阈值电压偏离理想的电压值。离理想的电压值。n沟道沟道/p-