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lec11 - 6.012 Electronic Devices and Circuits Lecture 11...

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6.012 - Electronic Devices and Circuits Lecture 11 - The MOS Capacitor - Outline Announcements Handout - Lecture Outline and Summary Exams - Will be returned in recitation next Wed. Qualitative description - MOS in thermal equilibrium Definition of structure: metal/silicon dioxide/p-type Si (Example: n-MOS) Electrostatic potential of metal relative to silicon: f m Zero bias condition: Si surface depleted if f m > f p-Si (typical situation) Negative bias on metal: depletion to flat-band to accumulation Positive bias on metal: depletion to threshold to inversion Quantitative modeling - MOS in thermal equilibrium, v BC = 0 Depletion approximation applied to the MOS capacitor 1. Flat-band voltage, V FB 2. Accumulation layer sheet charge density, q A * 3. Maximum depletion region width, X DT 4. Threshold voltage, V T 5. Inversion layer sheet charge density, q N * MOS with bias applied to the adjacent n + -region Implication for depletion region width Impact on threshold voltage Clif Fonstad, 10/03 Lecture 11 - Slide 1
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Another view of bipolar transistor operation: Changing the potential energy barrier between emitter and collector with the B-E voltage The p-type base region places a potential energy barrier for electrons, q f b , between the n- type emitter and collector regions. Clif Fonstad, 10/03 Electrons can only flow from the emitter to the collector when this potential barrier, q f b , is reduced by appling a forward bias on the base- emitter junction. [It is reduced to q( f b - v BE ).] When the collector is biased
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