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EE 434 Lecture 12
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  1. EE 434Lecture 12 Devices in Semiconductor Processes Diodes Capacitors MOS Transistors

  2. Quiz 10 A “10K” resistor has a temperature coefficient of +80ppm/oC If the resistor was measured to be 9.83K at 20oC, what would be the resistor value at 80oC?

  3. And the number is ….

  4. Quiz 10 A “10K” resistor has a temperature coefficient of +80ppm/oC If the resistor was measured to be 9.83K at 20oC, what would be the resistor value at 80oC? Solution

  5. Review from Last Time • Process Flow is a “recipe” for the process • Shows what can and can not be made • Gives insight into performance capabilities and limitations • Back-End Processes • Die attach options (eutectic, preform,conductive epoxy) • Stresses the die • Bonding • Wire bonding • Bump bonding • Packaging • Many packaging options • Package Costs can be large so defective die should be eliminated before packaging

  6. Basic Devices and Device Models • Resistor • Diode • Capacitor • MOSFET • BJT

  7. Diodes (pn junctions) N P Depletion region created that is ionized but void of carriers

  8. pn Junctions N P Physical Boundary Separating n-type and p-type regions If doping levels identical, depletion region extends equally into n-type and p-type regions

  9. pn Junctions N+ P- Physical Boundary Separating n-type and p-type regions Extends farther into p-type region if p-doping lower than n-doping

  10. pn Junctions N- P+ Physical Boundary Separating n-type and p-type regions Extends farther into n-type region if n-doping lower than p-doping

  11. pn Junctions N P I V

  12. pn Junctions I N P V I V Diode Equation: JS= Sat Current Density A= Junction Cross Section Area VT=kT/q n is approximately 1

  13. Basic Devices and Device Models • Resistor • Diode • Capacitor • MOSFET • BJT

  14. Capacitors • Types • Parallel Plate • Fringe • Junction

  15. Parallel Plate Capacitors A2 C A1 cond1 cond2 d insulator A = area of intersection of A1 & A2 One (top) plate intentionally sized smaller to determine C : Dielectric constant

  16. Parallel Plate Capacitors where

  17. Fringe Capacitors C d A is the area where the two plates are parallel Only a single layer is needed to make fringe capacitors

  18. Fringe Capacitors C

  19. Capacitance Junction Capacitor C VD p d d n depletion region • Note: d is voltage dependent • capacitance is voltage dependent • usually parasitic caps • varicaps or varactor diodes exploit • voltage dep. of C Cj0: junction capacitance at VD = 0V B: barrier or built-in potential

  20. Basic Devices and Device Models • Resistor • Diode • Capacitor • MOSFET • BJT

  21. n-Channel MOSFET Poly Gate oxide n-active p-sub

  22. n-Channel MOSFET Gate Drain Source L W LEFF Bulk

  23. n-Channel MOSFET Poly Gate oxide n-active p-sub depletion region (electrically induced)

  24. n-Channel MOSFET Operation and Model VDS ID VGS IG VBS IB Apply small VGS (VDS and VBS assumed to be small) ID=0 IG=0 IB=0 Depletion region electrically induced in channel Termed “cutoff” region of operation

  25. n-Channel MOSFET Operation and Model VDS ID VGS IG VBS IB Increase VGS (VDS and VBS assumed to be small) ID=0 IG=0 IB=0 Depletion region in channel becomes larger

  26. n-Channel MOSFET Operation and Model VDS Critical value of VGS that creates inversion layer termed threshold voltage, VT) ID VGS IG VBS IB (VDS and VBS small) Increase VGS more IDRCH=VDS IG=0 IB=0 Inversion layer forms in channel Inversion layer will support current flow from D to S Channel behaves as thin-film resistor

  27. n-Channel MOSFET Operation and Model VDS ID VGS IG VBS IB (VDS and VBS small) Increase VGS more IDRCH=VDS IG=0 IB=0 Inversion layer in channel thickens RCH will decrease Termed “ohmic” or “triode” region of operation

  28. Triode Region of Operation For VDS small

  29. n-Channel MOSFET Operation and Model VDS ID VGS IG VBS IB (VBS small) Increase VDS ID=? IG=0 IB=0 Inversion layer thins near drain ID no longer linearly dependent upon VDS Still termed “ohmic” or “triode” region of operation

  30. Triode Region of Operation For VDS larger

  31. n-Channel MOSFET Operation and Model VDS ID VGS IG VBS IB (VBS small) Increase VDS even more ID=? IG=0 IB=0 Inversion layer disappears near drain Termed “saturation”region of operation Saturation first occurs when VDS=VGS-VT

  32. Saturation Region of Operation For VDS at saturation

  33. n-Channel MOSFET Operation and Model VDS ID VGS IG VBS IB (VBS small) Increase VDS even more (beyond VGS-VT) ID=? IG=0 IB=0 Nothing much changes !! Termed “saturation”region of operation

  34. Saturation Region of Operation For VDS in Saturation

  35. Model Summary Note: This is the third model we have introduced for the MOSFET