VLSI Design - May 2014

Electronics Engineering (Semester 7)

TOTAL MARKS: 100
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks. 1 (a) The segregation co-efficient of oxygen is 0.25. Find the concentration of oxygen in the silicon ingot at a fraction solidified of 0.3. The concentration of oxygen in the silicon at the top of the crystal is 12.5x10¹⁷ atoms/cm³ at fraction solidified of 0.1.(5 marks) 1 (b) Draw the schematic diagram and stick diagram of NMOS depletion inverter (5 marks) 1 (c) Explain what is pass transistor logic ? Calculate the op voltage of the circuit if V_DD = 5V and V_TH = 1.5V(5 marks) 1 (d) Define the threshold voltage with equation and explain the body effect. (5 marks) 1 (e) State the difference between diffusion and ion implementation.(5 marks) 2 (a) With neat cross sectional diagram explain the process of CMOS fabrication using p-well process. Thus give the number of masks required.(10 marks) 2 (b) Consider an Aluminum silicon MOS structure with the following parameters:
N_D=2.5x10¹⁴ /cm³
Q_OX=10¹⁰ q^c/cm³
T_OX=650 A^o
?_ms= -0.35V
N_i=1.45 x 1010/cm³
(10 marks) 3 (a) Draw the circuit diagram of two input NAND gate using CMOS. Draw its stick diagram & layout using ? based design rules.(10 marks) 3 (b) State all types of inverter with their merits and demerits. Give their applications.(10 marks) 4 (a) Determine pull up to pull down ratio (Z_pu/Z_pd) for an NMOS inverter when driven by another inverter.(10 marks) 4 (b) Explain latch up in CMOS in detail. What are the remedies to avoid latch-up.(10 marks) 5 (a) Implement the following using CMOS logic function: F= X. (Y + Z) + XW Design the circuit and draw the stick diagram using Euler?s method. (10 marks) 5 (b) Design 4: 1 multiplexer using MOS transmission logic. Draw the stick diagram of the same.(10 marks) 6 (a) Compare both the scaling methods. Show analytically how power dissipation, maximum operating frequency, current density and saturation current scale in terms of scaling factors.(10 marks) 6 (b) Write the Verilog code for 2 input NAND gate using the module of NAND gate design SR latch and write the Switch level Verilog code for the same.(10 marks) 7 (a) Short channel effect in MOSFET?s.(7 marks) 7 (b) Compare buried and butting contacts.(7 marks) 7 (c) Semicustom and full custom design(7 marks)