EEE 334 Lab 4: MOS Characterizations 2026|2027
Solved (Arizona State University
Q1. Define threshold voltage V_T.
A: Voltage at which inversion layer forms
Rationale: Channel begins conducting when V_{GS}\geq V_T.
Q2. Typical V_T for NMOS in lab setup?
A: ≈ 1.2 V
Rationale: Extracted from transfer curve intercept.
Q3. Equation for drain current in saturation?
A: I_D=k_n(V_{GS}-V_T)^2
Rationale: Square-law model.
Q4. What does k_n represent?
A: Transconductance parameter
Rationale: Relates device geometry and mobility.
Q5. How to find k_n experimentally?
A: Slope of \sqrt{I_D} vs. V_{GS}
Rationale: Linear fit method.
Q6. Why does I_D increase quadratically?
A: Square-law dependence
Rationale: MOSFET physics in saturation.
Q7. Define linear region condition.
A: V_{DS}<V_{GS}-V_T
Rationale: Channel not pinched off.
Q8. Equation for I_D in linear region?
A: I_D=k_n[(V_{GS}-V_T)V_{DS}-\frac{V_{DS}^2}{2}]
Rationale: Derived from gradual channel approximation.
Q9. What is transconductance g_m?
A: Derivative of I_D wrt V_{GS}
Rationale: g_m=\frac{dI_D}{dV_{GS}}.
Q10. Typical g_m value in lab?
A: ≈ 2.5 mA/V
Rationale: From slope of I_D vs. V_{GS}.
, Q11. Why is g_m important?
A: Amplifier gain measure
Rationale: Determines voltage gain.
Q12. How to extract V_T graphically?
A: Extrapolate linear portion of \sqrt{I_D} vs. V_{GS}
Rationale: Standard method.
Q13. What causes threshold voltage shift?
A: Oxide charges, body bias
Rationale: Device physics.
Q14. Why is body effect relevant?
A: Raises V_T with substrate bias
Rationale: Increases depletion region.
Q15. Equation for body effect?
A: V_T=V_{T0}+\gamma (\sqrt{V_{SB}+2\phi _F}-\sqrt{2\phi _F})
Rationale: Standard MOSFET relation.
Q16. What is channel-length modulation?
A: Increase in I_D with V_{DS}
Rationale: Similar to Early effect in BJTs.
Q17. Equation including channel-length modulation?
A: I_D=k_n(V_{GS}-V_T)^2(1+\lambda V_{DS})
Rationale: Adds \lambda term.
Q18. Typical \lambda value in lab?
A: ≈ 0.02 V{}^{-1}
Rationale: Extracted from slope of I_D vs. V_{DS}.
Q19. Why does MOSFET act as voltage-controlled current source?
A: I_D depends on V_{GS}
Rationale: Gate voltage modulates channel.
Q20. What limits MOSFET current?
A: Carrier velocity saturation
Rationale: At high fields.
Q21. Why is MOSFET preferred over BJT in VLSI?
A: Low power, scalability
Rationale: CMOS technology advantage.
Solved (Arizona State University
Q1. Define threshold voltage V_T.
A: Voltage at which inversion layer forms
Rationale: Channel begins conducting when V_{GS}\geq V_T.
Q2. Typical V_T for NMOS in lab setup?
A: ≈ 1.2 V
Rationale: Extracted from transfer curve intercept.
Q3. Equation for drain current in saturation?
A: I_D=k_n(V_{GS}-V_T)^2
Rationale: Square-law model.
Q4. What does k_n represent?
A: Transconductance parameter
Rationale: Relates device geometry and mobility.
Q5. How to find k_n experimentally?
A: Slope of \sqrt{I_D} vs. V_{GS}
Rationale: Linear fit method.
Q6. Why does I_D increase quadratically?
A: Square-law dependence
Rationale: MOSFET physics in saturation.
Q7. Define linear region condition.
A: V_{DS}<V_{GS}-V_T
Rationale: Channel not pinched off.
Q8. Equation for I_D in linear region?
A: I_D=k_n[(V_{GS}-V_T)V_{DS}-\frac{V_{DS}^2}{2}]
Rationale: Derived from gradual channel approximation.
Q9. What is transconductance g_m?
A: Derivative of I_D wrt V_{GS}
Rationale: g_m=\frac{dI_D}{dV_{GS}}.
Q10. Typical g_m value in lab?
A: ≈ 2.5 mA/V
Rationale: From slope of I_D vs. V_{GS}.
, Q11. Why is g_m important?
A: Amplifier gain measure
Rationale: Determines voltage gain.
Q12. How to extract V_T graphically?
A: Extrapolate linear portion of \sqrt{I_D} vs. V_{GS}
Rationale: Standard method.
Q13. What causes threshold voltage shift?
A: Oxide charges, body bias
Rationale: Device physics.
Q14. Why is body effect relevant?
A: Raises V_T with substrate bias
Rationale: Increases depletion region.
Q15. Equation for body effect?
A: V_T=V_{T0}+\gamma (\sqrt{V_{SB}+2\phi _F}-\sqrt{2\phi _F})
Rationale: Standard MOSFET relation.
Q16. What is channel-length modulation?
A: Increase in I_D with V_{DS}
Rationale: Similar to Early effect in BJTs.
Q17. Equation including channel-length modulation?
A: I_D=k_n(V_{GS}-V_T)^2(1+\lambda V_{DS})
Rationale: Adds \lambda term.
Q18. Typical \lambda value in lab?
A: ≈ 0.02 V{}^{-1}
Rationale: Extracted from slope of I_D vs. V_{DS}.
Q19. Why does MOSFET act as voltage-controlled current source?
A: I_D depends on V_{GS}
Rationale: Gate voltage modulates channel.
Q20. What limits MOSFET current?
A: Carrier velocity saturation
Rationale: At high fields.
Q21. Why is MOSFET preferred over BJT in VLSI?
A: Low power, scalability
Rationale: CMOS technology advantage.
