Virtual Labs

1. What operating region of the MOSFET corresponds to the *maximum* measured capacitance on the Cg vs. Vg plot?

a: Depletion Explanation

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b: Accumulation Explanation

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c: Saturation Explanation

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d: Subthreshold Explanation

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2. In a *high-frequency* C-V plot, the capacitance value is at its minimum during which region(s)?

a: Only in the Depletion region Explanation

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b: Depletion and Strong Inversion regions Explanation

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c: Accumulation and Flat-band regions Explanation

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d: Only in the Accumulation region Explanation

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3. The SPICE parameter `TOX` (Oxide Thickness) is primarily extracted from which value on the C-V plot?

a: The voltage at the minimum capacitance Explanation

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b: The maximum capacitance value (in accumulation) Explanation

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c: The slope of the curve in depletion Explanation

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d: The flat-band voltage Explanation

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4. How would a *thinner* gate oxide (a smaller `TOX` value) visually affect the Cg vs. Vg plot?

a: It would *decrease* the maximum capacitance. Explanation

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b: It would *increase* the maximum capacitance. Explanation

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c: It would *increase* the minimum capacitance. Explanation

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d: It would not change the capacitance values. Explanation

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5. What does the SPICE parameter `VFB` (Flat-Band Voltage) represent?

a: The gate voltage where the channel first forms (threshold). Explanation

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b: The gate voltage required to break down the oxide. Explanation

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c: The gate voltage where the semiconductor energy bands are flat. Explanation

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d: The gate voltage where the device is in deep accumulation. Explanation

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6. A 'stretch-out' (a less steep slope) in the depletion region of a measured C-V curve is a strong indicator of what?

a: A very thick gate oxide Explanation

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b: A very low substrate doping Explanation

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c: A high density of interface traps (like `NFS`) Explanation

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d: Polysilicon depletion Explanation

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7. What is the main difference between a *low-frequency* C-V plot and a *high-frequency* C-V plot?

a: The capacitance in accumulation is high for LF, low for HF. Explanation

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b: The capacitance in inversion is high for LF, but low for HF. Explanation

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c: The capacitance in inversion is low for LF, but high for HF. Explanation

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d: There is no difference. Explanation

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8. The substrate doping (`NSUB`) is a key parameter in LEVEL 2/3. How is it primarily extracted from the C-V plot?

a: From the maximum capacitance value in accumulation. Explanation

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b: From the minimum capacitance value (in depletion/inversion). Explanation

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c: From the flat-band voltage. Explanation

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d: From the slope in accumulation. Explanation

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9. In advanced models (like LEVEL 6/BSIM), what is 'polysilicon depletion'?

a: A 'stretch-out' of the C-V curve due to interface traps. Explanation

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b: The formation of a depletion region *in the polysilicon gate itself*, which reduces the total capacitance. Explanation

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c: The minority carriers in the channel failing to respond to the AC signal. Explanation

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d: The complete removal of the polysilicon gate during fabrication. Explanation

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10. How do quantum mechanical (QM) effects (modeled in LEVEL 6) impact the C-V curve in strong inversion?

a: They push charge *away* from the oxide, effectively *increasing* the oxide thickness and *lowering* the capacitance. Explanation

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b: They pull charge *closer* to the oxide, effectively *decreasing* the oxide thickness and *raising* the capacitance. Explanation

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c: They trap charge at the interface, which 'stretches out' the C-V curve. Explanation

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d: They allow charge to tunnel through the oxide, which increases gate current. Explanation

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Extraction of MOSFET LEVEL (1,2,3 and 6) SPICE parameters related to gate voltage Capacitance (Cg vs. Vg)