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ECE 875: Electronic Devices. Prof. Virginia Ayres Electrical & Computer Engineering Michigan State University ayresv@msu.edu. Lecture 31, 28 Mar 14. Chp 04: metal-insulator-semiconductor junction: GATES Capacitances: Low frequency voltage sweep: 1 Hz to 1KHz

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ECE 875: Electronic Devices


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    1. ECE 875:Electronic Devices Prof. Virginia Ayres Electrical & Computer Engineering Michigan State University ayresv@msu.edu

    2. Lecture 31, 28 Mar 14 • Chp 04: metal-insulator-semiconductor junction: GATES • Capacitances: Low frequency voltage sweep: 1 Hz to 1KHz • High frequency voltage sweep: > 1Mz • - slow ramp: Pr. 4.06 • - fast ramp VM Ayres, ECE875, S14

    3. C-V curves and Frequencies: • Use Gate voltage: • Sweeping Vgate for example ± 4 Volts over and over to turn the channel OFF and ON: binary logic • Low: 1- 1 kHz • Intermediate: 1 kHz - 1 MHz • High: > 1 MHz • Vgate: Slow ramp • Vgate: Fast ramp ON/OFF cycles per sec “counting” charge per sec applied to gate VM Ayres, ECE875, S14

    4. C-V curves for n-channel in p-substrate: ON OFF Low Intermediate C / Ci High + slow ramp High + fast ramp VM Ayres, ECE875, S14

    5. What looks different in the readout: flat line in Vfor and Cmin shift ON OFF Low C / Ci Cmin High + slow ramp C’min V’min = VT Vmin VM Ayres, ECE875, S14

    6. Low frequency C-V: You know the experimental values in the circles. Therefore it’s easy to get a number for Cdmin Cmin = Ci CDmin CDmin = CminCi Ci + Cmin Ci + CDmin VM Ayres, ECE875, S14

    7. Low frequency C-V: Low: 1- 1 kHz: develop (ON) and later remove (=> OFF) a full inversion layer and a full depletion region VM Ayres, ECE875, S14

    8. High frequency + slow ramp: > 1 MHz: develop and later remove a full depletion region charge qNAWD. But e-’s don’t have time to form a full inversion layer at the surface Fig. 8, (b) VM Ayres, ECE875, S14

    9. High frequency + slow ramp: simpler: C’Dmin = es /WDmax  So total capacitance C’min is: C’min = Ci C’Dmin Ci + C’Dmin VM Ayres, ECE875, S14

    10. Low frequency High frequency, Slow ramp WDmax is bigger Qn smaller VM Ayres, ECE875, S14

    11. High frequency + slow ramp: WDmax From strong inversion up to thermal energy Have been finding WD = WDm at the start of inversion with ys = 2 kT/q ln (NA/ni). But (Qs, ys) can be bigger VM Ayres, ECE875, S14

    12. High frequency + slow ramp: WDmax: VM Ayres, ECE875, S14

    13. Assume that Pr. 4.06  the high frequency- slow ramp condition VM Ayres, ECE875, S14

    14. Low frequency High frequency, Slow ramp High frequency, Fast ramp WDmax is bigger WDmax is biggest Qn layer; no time to form at all Qn smaller Qn biggest VM Ayres, ECE875, S14

    15. High frequency + fast ramp: during ON: No Qn and big WDmax: “driven into deep depletion” VM Ayres, ECE875, S14

    16. CD Qs region ys (@x = 0) Ci across insulator region VM Ayres, ECE875, S14

    17. VM Ayres, ECE875, S14

    18. ys VGate

    19. Iterate Pr. 3.9 until donor concentration ND-nth – ND-(nth+1) = 0.01 x 1016 cm-3