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Main points of this exam paper are: Two Level, Resistor, Patterns, Separately, Starting Material, Lightly, Doped
Typology: Exams
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(Total: 50 points)
The CAD layout for a two-level resistor is shown above; the patterns are shown separately below.
Process Flow
(a) [4 pts.] Find the numerical value of the sheet resistance of the implanted layer formed in step 2, given that the hole mobility in this layer is up = 150 cm^2 /(Vs)
(b) [5 pts.] Accurately sketch the fabricated structure along the cross section A - A' for this CAD layout and process flow. Use the horizontal line below as the silicon surface. The vertical scale should be followed in sketching the deposited layers. Use the "dot" fill pattern from Mask 2 for polysilicon layer and the "slash' fill pattern from Mask 5 for metal layers.
Question #1 Multi-layer Resistor Layout [18 points] 2
(a) [3 pts.] Given that the edge of the depletion region on the n-side of the junction is located at xno = .4 um in thermal equilibrium (Vd = 0 V), plot the thermal equilibrium charge density p 0 (x) on the graph below.
(b) [3 pts.] Find the numerical value of the depletion capacitance in thermal equilibrium Cjo in fF (1 fF = 10 -15^ F).
Question #2 pn Junction Electrostatics [17 points] 4
(c) [4 pts.] For VD = -12 V, the edge of the depletion region on the n-side of the junction is located at xn = 1.5 um. Plot the charge density p(x) for this reverse bias on the graph below.
(d) [4 pts.] Plot the electric field E(x) that corresponds to the charge density in part (c) on the graph below. Your plot should have the numerical values for the field at x = 0 and the locations of the edges of the depletion region.
Question #2 pn Junction Electrostatics [17 points] 5
The electric field E 0 (x) in thermal equilibrium for an MOS capacitor is plotted above. The gate is made of an unknown metal and the substrate is uniformly doped silicon.
(a) [4 pts.] What type (n or p) is the substrate? Justify your answer.
(b) [4 pts.] What is the doping concentration in the substrate?
(c) [4 pts.] What is the numerical value of the voltage drop Vox,o in thermal equilibrium? Hint : the electric field plot is all that you need!
Question #3 MOS Electrostatics [15 points] 7
(d) [3 pts.] What is the potential phig of the unknown gate material?
Question #3 MOS Electrostatics [15 points] 8
