International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 10, October 2012) 392 Analysis on Effective parameters influencing Channel Length Modulation Index in MOS Abhishek Debroy 1 , Rahul Choudhury 1 ,Tanmana Sadhu 2 1 Department of ECE,NIT Agartala, Tripura 2 Department of ECE,St. Thomas college of Engineering,Kolkata,west Bengal Abstract— We study the phenomenon of Channel length modulation (CLM) in Metal Oxide semiconductors, both PMOS and NMOS and analyze the parameters affecting it. The phenomenon of variation of drain-source current with drain-source voltage is analyzed with respect to channel Length modulation parameter. The governing factor for channel modulation is generally taken as a constant, but detail analysis shows the variation of the channel length modulation parameter in saturation region. The channel length modulation parameter is seen to be varying with thickness of the depletion region, and eventually with drain-source voltage. The Equation governing channel length modulation is first studied with constant parameter and I-V characteristics are plotted. Then the equation is studied with varying channel length modulation parameter and I-V graph is re- plotted. The dependence of output resistance of both PMOS and NMOS on various parameters is also discussed and results are established. The study of output resistance versus drain- source current at constant & varying Channel length modulation index have been shown and conclusions are being drawn. Keywords— channel length modulation,drain-to-source voltage,drain-to-source current,Metal oxide semiconductor field effect transistor,dynamic resistance I. INTRODUCTION Channel length modulation (CLM) is a shortening of the length of the inverted channel region with increase in drain bias for large drain biases. The result of CLM is an increase in current with drain bias and a reduction of output resistance. The channel is first formed by attraction of carriers to the gate, and the current drawn through the channel is nearly a constant independent of drain voltage in saturation mode. However, near the drain, the gate and drain jointly determine the electric field pattern. Instead of flowing in a channel, beyond the pinch-off point the carriers flow in a subsurface pattern made possible because the drain and the gate both control the current. The channel is generally formed due to gate-source voltage (V gs ) and influenced by drain-source (V ds ) which can be seen as it becomes weaker as the drain is approached, leaving a gap of un-inverted silicon between the end of the formed inversion layer and the drain (the pinch-off region).The channel is generally formed effectively over the length of the substrate As the drain voltage increases, its control over the current extends further toward the source, so the un- inverted region expands toward the source, shortening the length of the channel region, the effect called Channel Length Modulation (CLM).The channel length modulation depends upon the drain-source voltage (V ds ).The relationship between both of them are studied and corresponding Source-drain current (I ds ) is noted. The graph between I ds and V ds are plotted at various values of channel length modulation constant. The Effect of channel length modulation is studied for both NMOS and PMOS. Because resistance is proportional to length, shortening the channel decreases its resistance, causing an increase in current with increase in drain bias for a MOSFET operating in saturation. The effect is more pronounced the shorter the source-to-drain separation, the deeper the drain junction, and the thicker the oxide insulator. The Equation governing output resistance to various parameters is also analyzed. The graph between output resistance and I ds is plotted. Then, we go on to study the effect of channel length modulation with varying modulation parameter. We re-plot the graph of I ds versus V ds and Output resistance versus V ds . Finally, we infer the results obtained during both the cases.