电子器件场效应晶体管.ppt
6.4.3 Effects of real surfaces,alkali metal ions 碱金属离子sodium(Na+)ion 钠离子mobile charge可动电荷trapped charge陷阱电荷interface charge界面电荷fixed charge固定电荷effective positive charge有效正电荷heavily doped poly-silicon重掺杂多晶硅,MOS Structure,Poly-silicon-OS Structure,Ideal MOS capacitance,Real Surface Effects:Work function difference&interface charge,Non-ideal capacitance,(1)work function difference,semiconductor,oxide,n+polysilicon(多晶硅),ms=m-s,n+poly-n Si,n+poly-p Si,Ideal,Non-ideal,(EFm-EFs)=(qs-qm)V=s-m,VG=VFB(平带电压)=-V=m-s=ms,(2)Interface charge,Generally,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,Ideal,Interface charge,Qi,Effects of real surface,6.4.4 Threshold voltage,To achieve the flat band,To accommodate the depletion charge,To induce the inverted region,Qd=-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?,1）flat band voltage,2）threshold voltage,3）depletion mode because VT0,(4)MOS Capacitor(ideal),Capacitance-voltage characteristics(电容电压特性）,Ci,Cs,Because Cs is depending on VG,the overall capacitance becomes voltage dependent.,Ci Cs,To 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 capacitor,High frequency,6.4.5 MOS capacitance-voltage analysis,VTSubstrate Doping Type,C-VG Performance Substrate Doping Type,To measure the doping density 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,To 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 capacitor,Show under flat band condition,(2)To measure the fast interface state Dit,(3)To measure the mobile charge within the oxide Fig.6-22,6.4.6 Time-dependent capacitance measurementsTo measure the generation lifetime,6.4.7 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，从而使阈值电压偏离理想的电压值。n沟道/p-型衬底的阈值电压可正可负，与掺杂浓度有关。由于界面效应，增强型器件可能变为耗尽型。(3)根据C-VG曲线，可以求得掺杂浓度，平带电压，阈值电压，界面快态密度及可移动离子密度。,
