midterm230B_2010ans

midterm230B_2010ans - Calculate the flatband voltage and...

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ECE 230B Midterm (Winter 2010) Assume silicon, room temperature, complete ionization. 1. (20 pts) An abrupt p-n junction with N d = 10 18 cm -3 and N a = 10 17 cm -3 is forward biased at 0.5 V. (a) Draw the band diagram. Label the Fermi levels and indicate where the voltage appears. (b) What are the total depletion layer width and the maximum field in the junction? Solutions: (a) c E E v E f c E E v E f 0.5 V n-type p-type (b) 90 . 0 ln 2 = = i d a bi n N N q kT ψ V 075 . 0 ) 5 . 0 )( ( 2 = - + = d a bi d a si d N qN N N W ε μ m E max = + = si d a d d a N N N W qN ) /( 1.1 × 10 5 V/cm
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2. (20 pts) Consider an MOS device with 20 nm thick gate oxide and uniform p-type substrate doping of 2x10 16 cm - 3 . The gate work function is that of n + Si. (a)
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Unformatted text preview: Calculate the flatband voltage and the threshold voltage for strong inversion. (b) Sketch the high frequency C-V curve and label where the flatband voltage and threshold voltage are. Calculate the capacitance at V g = 1.5 V. Solutions: (a) 38 . ln = = i a B n N q kT ψ V 94 . 2-=--= B g fb q E V V 23 . 41 . 76 . 94 . ) 2 ( 2 2 = + +-= + + = ox B a si B fb t C qN V V ε V. (b) C V V V g t fb At V g = 1.5 V, 22 . ) 2 ( 2 = = = a B si dm d qN W W μ m 8 10 7 . 3 1 1-× = + = si dm ox W C C F/cm 2 ....
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This note was uploaded on 10/09/2010 for the course ECE 230 at UCSD.

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midterm230B_2010ans - Calculate the flatband voltage and...

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