Practice Exams All EEE 3350

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Practice exams for college semiconductor devices courses. EEL-3350 from UCF University of Central Florida Dr. Malocha

Transcript of Practice Exams All EEE 3350

1 10/21/2012

Figure 1 -VCE

EEE 3350 Sample Exam 3

Closed book 1 help sheet allowed

1. For a given NPN, the BJT gain will be the greatest if

a) IEp/IEn=.01 b) IEp/IEn=.1 c) IEp/IEn=10 =10 d) IEp/IEn=100 =.1 e) Ln/Lp=.1

2. For a given NPN BJT, the gain will be the greatest if

a) WB/Lp=10 b) WB/Lp=.1 c) WB/Ln=10 d) WB/Ln=.1 e) Ln/Lp=.1

3. For a PNP BJT, the device is at the onset of saturation when:

a) VCB >0V b) VCB <0V c) VCB =0V d) VEB =0V e) VEB <0V

4. For a PNP with all parameters equal except Na=2*Nd, the emitter injection efficiency is

= a) ¼ b) 1/3 c) ½ d) 2/3 e) 3/2

5. Breakdown voltage on a BJT in the active mode occurs at

a) EB junction b)BC junction c) EC junction

6. For a BJT the base transport factor is .95, if WB doubles, the new base transport factor is

a) .8 b) .90 c) .94 d) .96 e) .98

7. For a NPN, if VEB= -.7 V, VCB changes from 0 V to -.3 V, the magnitude of the collector current will :

a) increase b) decrease c) same

8. For a NPN transistor, if τn increases while keeping all other parameters constant, the current gain will:

a) increase b) decrease c) remain the same

9. Given a NPN and a PNP transistor with identical respective parameters and Na=Nd, except the hole

mobility is twice the electron mobility in the base; PNPNPN / a) >1 b) 1 c) <1

10. From the Fig. 1, α of the transistor, is calculated as a) .95 ) .97 c) .99 d) .995 e) .999

11. From the Fig. 1, at -VCE = .25V and IB=30uA, the device is in which mode:

a) active b) saturation c) cutoff d) inverted

12. For an NPN transistor, which of the following voltages

are correct for cutoff:

a) VEB + VCB + b) VEB + VCB - c) VEB - VCB - d) VEB – VCB+

13. The ratio of the base transport factor (BTF), for active

versus inverted mode is a) 0 b) 1 c) <1 d) >1 e) >10

14. Given a symmetrical P+NP

+ BJT, for VEB =.6 V and VCB=0V, IB = 1uA, then for VEB =.6 V and

VCB=.6V, IB = a) -1 uA, b) 0 uA c) 1 uA d) 2 uA e) .5 uA

IC

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(For Questions 16, 17, 18): A NPN transistor has the following parameters:

ND+= 10

19/cm

3 NA=10

16/cm

3 ND=10

16/cm

3 WB=5um WE=1um

Lp= 50 um Ln=25um un=1000 cm2/V-sec up=500 cm

2/V-sec.

15. The base transport factor is a) .96 b) .97 c) .98 d) .99 e). 995

16. The emitter injection efficiency is a) .96 b) .97 c) .98 d) .99 e). 997

17. The current gain is approximately a) 33 b) 44 c) 55 d) 66 e) 77

Given the band diagram (for 20-23):

18. The BJT device is a) NPN b) PNP

19. If all electron and hole parameters are equal and WE=WB, based on the band diagram, the emitter

injection efficiency is a) .95 b) .97 c) .98 d) .995

20. The applied voltage to the EB from the

battery to turn fully on is

a) .7V b) .6V c) -.7V d) -.6 V

21. The magnitude of the built-in electric

field is larger on which junction

a) EB junction b) BC junction c) EC junction

Given the schematic, above, of excess carriers

in the base for a BJT:

22. With the figure, as drawn, the device is in

a) Active b) Saturation c) Inverted d) Cutoff

23. For a given emitter current, the base current is maximum if |ΔnE/ΔnC| is

a) <1 b) >1 c) =1 d) =0 e) =∞

24. In general, at the onset of saturation, |ΔnE/ΔnC| is

a) <1 b) >1 c) =1 d) =0 e) =∞

25. For a given transistor, αN=.9, αN=10*αI, and IES=2*ICS, in cutoff, |IB/IES|=

a) .56 b) .66 c) .76 d) .86 e) .96

Solutions: 1) a 2)d 3)c 4)d 5)b 6)a 7)b 8)a 9)c 10)d 11)b 12)a 13)b 14)d 15)c 16)e 17)b 18)a

19)c 20)c 21)b 22)b 23)c 24)e 25)a

Scale: X is horizontal axis and is relative units

Y is vertical = .1eV/div

Eg=1eV ni=1.0*1010

/cm3

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-type

DG

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BJT, MOS &FET 1. If I increase the doping in an n-channel MOSFET, will the magnitude of the threshold voltage increase or decrease:

a. Increase b. Decrease c. Same 2. If I increase the oxide thickness in an n-channel MOSFET, will the magnitude of the threshold voltage increase or

decrease: a. Increase b. Decrease c. Same

3. If I have trapped sodium ions at the Si-SiO2 interface in an n-channel MOSFET, will the magnitude of the threshold voltage increase or decrease:

a. Increase b. Decrease c. Same Probs. 4-9: Given an ideal MOS flatband capacitor structure in which the semiconductor is n-type, the voltages applied to the metal gate ,VG, are given below, you are to determine i) the mode of operation, ii) whether the surface charges under the gate are mobile or immobile(ions), and iii) whether the intrinsic energy level at the surface interface bends up or down, respectively. (remember that –2<-1<0, etc.)

4. VG>0: Mode: a. Accumulation____ b. Depletion______ c. Inversion_______ 5. VG>0: Charges: a. Mobile_________ b. Immobile___________ 6. VG>0: Surface Intrinsic Level Bends: a. Up________ b. Down__________ 7. VG<VT: Mode: a. Accumulation____ b. Depletion______ c. Inversion_______ 8. VG<VT: Charges: a. Mobile_________ b. Immobile___________ 9. VG<VT: Surface Intrinsic Level Bends: a. Up________ b. Down__________

Probs:10-14: A poly-Si gate MOS transistor is fabricated on a n-type Si substrate with ND = 5x1015 cm-3. The thickness of the gate oxide yields CSiO2=3.5x10-8 F/cm2 and the surface charge density at the Si-SiO2 interface is 5x1010 cm -2. The poly-Si is doped p-type at 1019/cm3. eVSi 15.4=χ EgSi=1.12eV

10. The substrate bulk potential, =Bφ a)-.56 b) -.33 c) +.33 d) +.56 volt.

11. The substrate work function, =Φ S a) –5.04 b) -4.38 c) 4.38 d) 5.04 volt.

12. The poly-Si bulk potential, =polyφ a) -.53 b) -.38 c).38 d) .53 volt.

13. The poly-Si work function, =ΦM a) -5.24 b) –4.18 c) 4.18 d) 5.24 volt. 14. The voltage due to the Si-SiO2 interface charge, Vi = a)-2.3 b) –0.23 c) 0.23 d) 2.3 volt 15. Given the following MOS information: n-type Si substrate,

VMS 5.−=Φ , |QD/CSiO2|=.25V, |Qi/Ci|=.15V, and VB 3.|| =φ : Threshold voltage VT= a) -1.5 b) –1.2 c) -.6 d) .2 volt 16. Given the MOSFET I-V characteristics to the right : the transconductance = a) 1 b) 2 c) 3 d) 4 mSiemens Probs 17-21:Given the following MOSFET with partial information completed (the MOS is flatband case) in the figure: 17. The device is a) NMOS b) PMOS c) CMOS 18. To create a channel, VGs is a) positive b) negative c) zero 19. For current flow, VDS is a) positive b) negative c) zero 20. Pinch-off occurs near the a) drain side b) source side c) at the gate metal-oxide interface 21. IDS saturates when a) VDS=VGS b) IDS=IGS c) VDS=VG-VT d) VGS=VGD-VT

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Probs. 22-26: Given the MOS band diagram, no applied external voltage, Ninterface=0, and ni=1x1010/cm3: 22. The MOS structure is which case: a) flatband b) non-flatband 23. The metal semiconductor work function difference =

a) .1 b) .2 c) .3 d) .4 volt. 24. The semiconductor doping density~

a) 4.8x1010 b) 4.8x1015 c) 4.8x1016 d) 4.8x1017 /cm3 25. The MOS structure is in

a) accumulation b) depletion c) inversion d) constipation

26. The ratio of carriers in the bulk to the surface concentration is S

φ~

a) 100 b) 2200 c) .01 d) .005 Probs.27-29: Given the equivalent circuit model and IEo=Ico=10-12 A, IE=1mA, 90.,99. == IN αα 27. Collector current, Ic = a) .9 b) .98 c) .99 d) 1.11 mA. 28. Base current, IB = a) .01 b) .02 c) 0.1 d) 10-9 mA. 29. Current gain, =β a) 9 b) 99 c) 199 d) 1.11 Probs. 30-33: Given the BJT band diagram: 30. The BJT is an a) PNP b) NPN 31. The BJT is in which mode:

a) active b) saturation c) cutoff d) inverted 32. The ratio of the doping density in the base to the collector is

NB/NC = a) 0.5 b) .666 c) 1.0 d) 1.5 e) 2.0 33. Assuming the base transport factor =1, the inverted current gain,

=Iβ a) 0.25 b) 0.5 c) 1.0 d) 2.0 e) 3.0 34. From the excess carrier density in the base, the applied voltages are:

a) VEB + & VCB + b)VEB - & VCB + c) VEB - & VCB=0 d) VEB + & VCB =0 e) VEB - & VCB -

0.1eV/div