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121B_1_EE121B_Mid-Term_soln

# 121B_1_EE121B_Mid-Term_soln - University of California Los...

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Unformatted text preview: University of California, Los Angeles / Prof. Chui Midterm Exam, p.1 EE 121B Principles of Semiconductor Device Design Winter 2008 Midterm Exam Feb 7‘“, 2008, 2-3z30pm Nam, ,gésﬂ WM Student ID# : Signature FORMAT: — TIME ALLOTTED: 90 MINUTES - CLOSED BOOK — ONE PAGE OF LETTER SIZE SHEET OF NOTES AND SCIENTIFIC POCKET CALCULATOR ALLOWED INSTRUCTIONS: - USE THE FOLLOWING PHYSICAL CONSTANTS AND GENERAL ASSUMPTIONS IF NECESSARY - SHOW ALL WORK AS CLEARLY AS POSSIBLE TO MAXIMIZE OPPORTUNITY FOR PARTIAL CERDIT - USE COMMON SENSE TO INTERPRET THE QUESTIONS, OR ASK IF YOU ARE NOT SURE — INSERT YOUR ONE PAGE NOTES INTO THE EXAM BOOKLET WHEN YOU TURN IN YOUR EXAM Physical constants: 1. Electronic charge = 1.60 X 10'19 C II. Vacuum Permittivity = 8.85 x1044 F/cm III. Boltzmann constant = 8.62 x 10'5 eV/K IV. Planck constant = 6.63 x 10'34 J-s V. Electron mass in vacuum = 9.10 X 10‘31 kg General assumptions in all problems unless speciﬁcally stated otherwise: 1. Temperature = 300 K II. Semiconductor = Silicon a. Intrinsic carrier concentration z 1 X 1010 cm' b. Permittivity = 11.8 3 University of California, Los Angeles / Prof. Chui Midterm Exam, p.2 t—Wb—i itte Base "Dolng(o')'* 7 7' 7 7 W ' N 7 5101 77 W 10 N ' ' " 10 ’ Minority Carrier Diffusion Length (pm) 5.91 16.1 88.1 Minority Carrier Mobility (cm /V-s) 270 400 1,500 Inter Metallurgical Junction Distance (pm) 2 1) For the PNP BJT shown in Fig. 1, a) Sketch the energy band diagrams (showing EC, By, E) at equilibrium and under forward active bias (4 pt.) 1 ' University of California, Los Angeles / Prof. Chui Midterm Exam, p.3 0) Estimate in common emitter mode (V1313 = 0.7 V, and VCB = —10.0 V): (6 pt.) i) Unity gain cutoff frequency ,. it. 2 k; M ~ ‘ - J 3mm 7,: a a? -MM ‘ pp:%up = rwwmﬁ “Vac: ffekw : MW we of {27’3“ :17 “”3“” ‘3“ 3 Wing: ig-[VIEEW‘U A445 :3 "2’4“" ! P Kwé ‘M A if; <9 XFC v" 5 M ””Mumim/m ”MM“ T 11? “as XML?” (/72) 60': “7546!"? 'IXFC: [ILL/“M 5 ii) Current gain Lipt- ii %ﬁ45’ (The? tf‘7/J‘M it“ a. 72’th e : [~0::v [C .2 39 d) Sketch the minority carrier proﬁles in the base for the following modes of operation: (4 pt.) i) Forward active ii) Reverse active iii) Saturation iv) Cutoff f a P0 0 00}, fmw M ei Mt VJ? \ /‘ A K c 0011 6 M93 University of California, Los Angeles / Prof. Chui Midterm Exam, p.4 2) For an NPN BJT, a) Fill in the table below on whether the quantities at the leftmost column will increase (T), decrease (Jr), or remain unchanged (0) when the device parameters on the top row are changed. Assume the terminal biases are kept the same throughout. (7 pt.) 21‘ “795 .— 33140174 V¢071~L b) Explain how the Early Effect would limit the performance of a circuit when BJT is used as an ampliﬁer. (’4 pt.) c) Name 3 design parameters with explanation to reduce the Early Effect (6 pt.) \$)N37‘ (>1)Nc\l’ 3) war k‘WWmMs (ms/T5530 WWW } MMWW C 0;:9; . WW University of California, Los Angeles / Prof. Chui ’ Midterm Exam, p.5 3) Given the Gummel plot of a BJT, a) Sketch the corresponding log(,8) vs. log(IC) (4 pt.) logﬂ) log(ﬂ) my 0.1 0.4 10'8 10'6 104 10‘2 b) Re-sketch the Gummel plot for the following conditions and indicate any change in f,. Brieﬂy explain your answers. (6 pt.) i) Base doping increases -- If we Wer-{M TM TN lama L‘s wWAw-LJLJ t6 SWR M +144. SW " 3W. :6 ‘1‘ 6% He’l‘ * Tc Ts [me/rail. waﬁJﬁ) logﬂ) ii) Operating temperature increases loga) ‘ 5W ‘3‘ 16’? “‘ T’T; W“ cum. I v-s‘ T W’ﬁMWp ': TTJ Hg?) I'm? 3a lakcﬁ-T -- If“? 5416-W‘30-f- ‘HMLC—E 3wd>tM ks M) (£1 T’T, “JUL ’tn 1‘ Cf»- MM) M P. °‘ T-%‘ =9 "thir . '1 " 29% ‘9 3364/ ...
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