電子器件場效應(yīng)晶體管ppt課件

1、6.4.3 Effects of real surfaces alkali metal ions 堿金屬離子堿金屬離子sodium(Na+) ion 鈉離子鈉離子mobile charge可動電荷可動電荷trapped charge陷阱電荷陷阱電荷interface charge界面電荷界面電荷fixed charge固定電荷固定電荷effective positive charge有效正電荷有效正電荷heavily doped poly-silicon重摻雜多晶硅重摻雜多晶硅MOS Structure Poly-silicon-OS StructureIdeal MOS capacitanc

2、eReal 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(平帶電壓平帶電壓)= -V= m -s= ms (2) Interface chargeGenerally, there are four ty

3、pes of charges in a practical MOS structure.Mobile ionic charge Qm可動離子電荷Oxide trapped charge Qot氧化物陷阱電荷Oxide fixed charge Qf氧化物固定電荷Interface trap charge Qit界面陷阱電荷IdealInterface chargeQiiiiFBGiiisSSiGCQVVVCQVthatrequiresbandFlatVV0; 0:Effects of real surface iimsFBCQV6.4.4 Threshold voltagecasepracti

4、calCQCQVcasepracticalCQVcaseidealCQVFidiimsTiimsFBFidT22To 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-channel MOSFET greater than 0? How to do?iimsFBCQV28614/109 . 6105

5、)1085. 8 () 9 . 3(cmFdCiiVCQViimsFB01. 10116. 089. 0109 . 6)106 . 1 ()105(89. 0819101flat band voltagecmcmCcmFVcmCVcmFunitmcmqNWVnNqkTaFsmiaF22352115191410151)()(/)(1 (867.01067.8)101 ()106 .1 ()298.0()1085.8()8 .11(22298.0105 .1101ln0259.0ln2threshold voltageFidFBTCQVV2VCQVVcmCWqNQFidFBTmad21. 0)28

6、8. 0( 2109 . 61039. 101. 12/1039. 1)10867. 0)(101)(106 . 1 (8828415193depletion mode because VT0(4) MOS Capacitor (ideal)Capacitance-voltage characteristics(電容電壓特性）CiCssssiisisisiddQCdCCCCCCCCC111Because Cs is depending on VG, the overall capacitance becomes voltage dependent.Ci Cs2/100112111kTqepnk

7、TqeqLkTQQddQCdCCCCCCCCCskTqskTqDssssssssiisisisiss)(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 charge change of the MOS capacitorHigh frequency)(22/1inversionstrongto

8、depletionWddQCCqNWqNQsssdsssaas)/(frequencyhighinversionstrongafterWCmsd)/(fequencylowinversionstrongafterCCi6.4.5 MOS capacitance-voltage analysisVTSubstrate Doping TypeC-VG Performance Substrate Doping TypeTo measure the doping density of substrateTo measure the interface state To measure the mobi

9、le 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 capacitance, we must superpose the small a-c signal to the voltage. Tha

10、t 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 measure the fast interface state Dit12)(1eVcmCCCCCCCCqDHFiHFiLFiLFii

11、t(3)To measure the mobile charge within the oxide Fig.6-22)(FBFBimifmsFBimfmsFBVVCQCQVCQQV6.4.6 Time-dependent capacitance measurementsTo measure the generation lifetime)/(2aiiNCnslope6.4.7 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) 實際器件與理想情況存在偏差：實際情況要考實際器件與理想情況存在偏差：實際情況要考慮功函數(shù)差及界面電荷效應(yīng)。慮功函數(shù)差及界面電荷效應(yīng)。 (2)實際情況下存在平帶電壓，從而使閾值電壓偏實際情況下存在平帶電壓，從而使閾值電壓偏離理想的電壓值。