6.4.3 Effects of real surfaces alkali metal ions 碱金属离子碱金属离子sodium(Na+) ion 钠离子钠离子mobile charge可动电荷可动电荷trapped charge陷阱电荷陷阱电荷interface charge界面电荷界面电荷fixed charge固定电荷固定电荷effective positive charge有效正电荷有效正电荷heavily doped poly-silicon重掺杂多晶硅重掺杂多晶硅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 chargeQiEffects of real surface 6.4.4 Threshold voltageTo 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?1）flat band voltage2）threshold voltage3）depletion mode because VT0(4) MOS Capacitor (ideal)Capacitance-voltage characteristics(电容电压特性）CiCsBecause Cs is depending on VG, the overall capacitance becomes voltage dependent.Ci CsTo 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 frequency6.4.5 MOS capacitance-voltage analysisVTSubstrate Doping TypeC-VG Performance Substrate Doping TypeTo measure the doping density of substrateTo measure the interface state To measure the mobile charge within the oxide(1) To measure the width of oxide layer, doping density of substrate, VFB and VT Fig.6-16To 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 capacitorShow under flat band condition(2)To measure the fast interface state Dit(3)To measure the mobile charge within the oxide Fig.6-226.4.6 Time-dependent capacitance measurementsTo measure the generation lifetime6.4.7 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-型衬底的阈值电压可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。型器件可能变为耗尽型。(3)根据根据C-VG曲线，可以求得掺杂浓度，平带电压，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。阈值电压，界面快态密度及可移动离子密度。