Lecture 24 - MOS Non-idealities

Lecture 24 - MOS Non-idealities - MOS Non-idealities...

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1 MOS Non-idealities Objectives: To understand common non-idealities that affect MOS-based devices. Questions to be answered Questions to be answered: • How does the difference in work-function between the metal and semiconductor affect device characteristics? • How do various charges in the oxide and at the oxide-semiconductor interface affect device EE360 – Lecture 24 characteristics? • How can we have conduction through the oxide layer? Equilibrium Band Diagram: Ideal Structure Ideal case: • Metal and semiconductor work functions are equal • Only charges that can exist are those in the semiconductor and those at the metal surface (no charges are present in and those at the metal surface (no charges are present in the oxides or fixed at the interfaces). • No carrier transport through the insulator (d.c. current = 0) EE360 – Lecture 24 From Pierret
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2 Equilibrium Band Diagram: Real Structures Al p-Si SiO 2 • Real structure: (Al – SiO 2 –S i) Φ m ≠ Φ s p-Si SiO 2 Separate Band Diagrams Eq. MOS Band Diagram EE360 – Lecture 24 From Pierret pg. 646 From Pierret pg. 646 Note: Device is in depletion with no applied bias. Metal-Semiconductor Work Function Difference Metal-Semi Work function difference (in volts): φ ms = (1/q)( Φ m - Φ s ) Relate V G to S : • Some common work- function differences: Biasing regions: just shift gate voltage, V G , by V G = (V G –V G-ideal ) = ms i.e. Ideal p-bulk MOS is in accumulation for V <0 Non ideal p bulk MOS is in 0 2 s A GSo Sm s Os K qN Vx KK φφ ε =+ + EE360 – Lecture 24 V G < 0.
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This note was uploaded on 04/20/2008 for the course EE 360 taught by Professor Hastings during the Spring '08 term at Kentucky.

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Lecture 24 - MOS Non-idealities - MOS Non-idealities...

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