 Welcome, myself, Mr. Giridhar Jain, Assistant Professor in Electronics and Telecommunication Engineering, Vulture Institute of Technology, Sholop. Now today, I am going to deliver a lecture on enhancement MOSFET. Now, learning outcomes of this session are, at the end of this session, students will be able to draw construction of eMOSFET and describe its working. Now contents of the session are eMOSFET construction, symbols and working. Now figure shows the n-channel enhancement MOSFET, so this is construction diagram and right hand side is the symbol. Now first, let us understand the construction of n-channel enhancement MOSFET. So, in the construction, the p-type substrate is taken, that is the base material, onto this p-substrate, two heavily doped n-regions are obtained by diffusion, one of this is called as a drain and the another is called as a source. And in between drain and source, whatever is available that we call as a channel, onto this channel, you can see an insulating layer of SiO2 is laid as shown in figure. And above that insulating layer of SiO2, the connection for gate is made using a polycrystalline silicon material. So and there are four terminals for the MOSFET, so one is drain source, this is gate and the fourth one is the substrate. Now actually a physically channel is not provided between drain and source. Now the channel is induced by the application of positive voltage between gate and source and that will provide the path for flow of current from drain to source and on the right hand side you can see the symbol of the n-channel enhancement MOSFET. Now for this n-channel enhancement MOSFET, so in this symbol you can see a dotted line is shown here 1, 2, 3, so dotted line, so that will be that indicates that the channel is induced. It is not a physical channel and upper terminal is drain and generally the substrate is connected to the source and this is your gate. So drain gate and the substrate connected to the source. So this is the electrical symbol used for e MOSFET usually in the circuit. Now pause this video and think on the following question. What will be the change in the construction and symbol for the p-channel MOSFET? So for the p-channel MOSFET the layers that is substrate drain source, so these layers are inter layers are changed and in the symbol this arrow is towards the outwards. So you can see this is a p-channel MOSFET. Now for p-channel MOSFET substrate is n-type, on to n-type substrate the heavily doped p-regions are obtained by diffusion. One of them is drain and another is a source and in between drain and source the channel is formed. So insulating layer of SiO2 over the SiO2 again polysilicon for making the contact to the gate and n-type substrate. So this is the construction of p-channel MOSFET and on the right hand side you can see the symbol for the p-channel e MOSFET. So in this symbol this arrow is pointed in such a way that if the substrate is forward biased so direction of the current is the arrow. So for the n-channel MOSFET you can see the arrow is towards inside and for the p-channel MOSFET the arrow is towards the outside. Now for obtaining the characteristics of n-channel MOSFET this is the connection diagram. Now in this connection diagram you can see a positive voltage is applied between gate and source PGS and drain is made positive with respect to source by applying the positive voltage PDS. So this is PDS, this is PGS. Now due to application of positive voltage between gate and source you can see a negative carriers are induced due to application of positive voltage and this channel is induced provided PGS is greater than threshold voltage and once this channel is induced. Now this channel through this channel the electrons can flow from source to the drain and hence the drain current flows from drain to the source as shown in figure. And on the right hand side you can see the same this is a construction along with connection and the right hand side is the circuit diagram using electrical symbol of the E MOSFET. So this is n-channel E MOSFET connection diagram. So this is the characteristics by keeping PGS constant the drain to source voltage is change from 0 to maximum and the readings are taken for drain current and you can see if VGS is less than threshold voltage the drain current is 0 and this is VGS is equal to 5 volt you can see the characteristics. Then next is for VGS is equal to 10 volt and third one is for VGS equal to 15 volt and this is the DC load line the extreme points are VDD and VDD by RD. So this is the drain characteristics. Now what is the transfer characteristics? Transfer characteristic is nothing but the graph of output versus input. So output for this E MOSFET is the drain current and the input is VGS. So drain current taken on Y axis and VGS taken on X axis that will be the transfer curve or it is also called as transconductance curve. Now for this transfer curve you can see that when VGS is equal to VGS TH that is threshold voltage at that point the drain current is 0 and if VGS exceeds threshold voltage then you can see there is increase in drain current and this relationship is a parabolic curve. So this is VDS on and this is ID on so that are one point is shown. So these are the drain curves or VI characteristics of the drain and the right hand side is the transfer curve. Now for this transconductance curve the drain current depends on VGS and this dependence so this transconductance curve is parabolic or a square law the vertex of parabola is at VGS TH because of this the equation for the parabola is in different is from ID equal to K in the bracket VGS minus VGS TH bracket square where K is a constant that depends on the particular MOSFET, it depends on the MOSFET it can be obtained from the data given in the data sheet of the MOSFET. So this is the mathematical equation describing the transconductance curve or transfer characteristics. So this is the characteristics transfer curve and this is the relation which describe the transfer curve. Now in this way the drain current through each channel MOSFET can be controlled by the gate to source voltage so it is a voltage controlled device. So these are the references electronic principles by Malvino, principles of CMOS VLSI design. Thank you for attending the lecture.