 Welcome myself, Girdhar Jain, Assistant Professor in Electronics and Telecommunication Engineering, Valchan Institute of Technology, Solapur. Now, today I am going to deliver a lecture on short channel effect in eMOSFET. Now, learning outcomes of the session are at the end of the session, students will be able to describe a short channel effect in eMOSFET. So, this is VI characteristics of eMOSFET. So, the figure shown on the left hand side is the circuit used for simulation. Phi gs is varied from 1 to 5 volt and between drain and source, phi ds varied from 0 to 5 volts. So, this is diagram used for simulation. And on the right hand side you can see the characteristics, drain characteristics, ids versus phi ds for different values of phi gs, phi gs 1, 2, 3, 4 and 5. And this dotted line is boundary that is phi gs minus phi t is equal to phi ds. Towards left hand side is the non-saturation or linear region. On the right hand side of the dotted line is saturation region. And for phi gs less than or equal to phi t, that is your cutoff region. So, that part already we have studied. Now, let us understand this short channel effect. Now, if length of channel is large, then the short channel effect is negligible. But if length of channel is small, then this effect is not negligible. So, here you can see the part of construction of each channel MOSFET. So, E MOSFET that is N channel. So, P substrate, then 2 heavily doped N regions N plus N plus 1 is right hand side is drain. This is source and in between drain and source insulating layer of SiO2. And through polysilicon material it is connected to the gate as shown in figure. Now, generally the substrate is connected to the source. And we apply positive voltage between drain and source for N channel E MOSFET. Now, if substrate is connected to the source, then substrate goes to the ground. And positive voltage will be applied between N plus drain N type drain and the P type substrate. So, here a P N junction is formed. And as the N is connected to positive and the substrate P is connected to negative, a P N junction formed between drain and substrate is reverse bias. Now, if V DS is increased, what will happen? The reverse bias voltage will gone increasing and a depletion layer is formed between this P N junction between the drain and substrate as shown in figure. And as V DS is increased, this depletion layer penetrates into the substrate and it penetrates into the channel. Thereby, the effective length of channel is reduced as shown in figure and it is L effective. So, this is a short channel effect. Means, if V DS is increased, the depletion layer which is formed at the drain and substrate is penetrated into the channel and thereby reducing the effective length of channel for the conduction. Then I DS in this saturation region is given by beta V DS minus V T bracket square by 2. And for saturation region, the condition is V DS minus V T greater than 0 and less than V DS. Where beta is mu epsilon upon T O X W by L, where mu is mobility, epsilon is permittivity insulating layer, T O X is the thickness of oxide layer, W is width of channel and L is length of channel. Now, L effective is given by L effective is equal to L minus L short. L short is shown in the previous diagram. This is L short and this L short is given by L short is equal to square root of 2 epsilon Si divided by Q into N A in the bracket V DS minus in the another bracket V DS minus V T bracket close bracket close. So, this is L short. So, epsilon is the permittivity of Si O 2 permittivity of Si then Q into N A in the bracket V DS voltage between drain and source V GS minus V T, V T is threshold voltage. And due to this short channel effect, it is so according to short channel effect, what will happen? Due to increase in V DS, length of channel is reduced. As the length of channel is reduced. So, there is increase in drain current. There is increase in drain current and this is given by the equation I DS is equal to beta by 2 in the bracket V GS minus V T square into another bracket 1 plus lambda into V DS. Original equation is beta by 2 in the bracket V GS minus V T square. That is in saturation region. So, due to short channel effect, the second bracket 1 plus lambda into V DS is added. Where lambda is the channel length modulation factor and its value is given by 0.0 it value is 0.02 V raise to minus 1 2 0.005 V raise to minus 1. So, this is the range of lambda. So, lambda is short channel length modulation factor. Now pause this video and think on the following. Shall we obtain the value of lambda? Knowing the device characteristics, the value of lambda can be obtained as shown in figure. So, figure shows the VI characteristics for the N channel E MOSFET. So, ID versus V DS for different values of V GS. So, here V DS minus V T 2 whole then V DS minus V T 4 whole, 4 whole, 8 whole. So, these are given. And for this, now if you extend these characteristics in the form of dotted line. So, all the dotted line, there are four dotted lines of the four characteristics and they will meet at one point which is minus V A. And this minus V A is equal to minus 1 by lambda. Means you can obtain lambda is equal to 1 by V A, lambda is equal to 1 by V A. So, in this way the value of lambda can be obtained. And once the lambda is obtained, you can estimate for the increase in drain current due to short channel effect. So, in summary, a short channel effect is nothing but due to increase in V DS. The depletion layer formed at between drain and substrate is penetrated into the channel and effective length of channel is reduced. And thereby there is a increase in the drain current with increase in V DS in the saturation region. So, this is a short channel effect. Now, the advantage of the short channel effect that area of MOSFET is reduced. Hence, more number of MOSFETs are fabricated per unit area means large integration. And gain of MOSFET is increased, so more drain current. And the disadvantage is if V DS is increased, then get loses the control over IDS. So, this is a short channel effect. So, these are the references, principle of CMOSVLSI design, NEL, Weste and Kamran Isirjian person education. And secondly is electronic design by Martin Rodden and others. Thank you for watching the video.