 Hello. Myself Sunil Kalshatti, Assistant Professor, Department of Electronics Engineering, Walsh and Institute of Technology, Solapur. Today, I am going to explain the enhancement type MOSFET from the Industrial Electronics Learning Outcome. At the end of this session, students can describe the construction, working and characteristics of enhancement type MOSFET. Enhancement type MOSFETs are available in two types, n-channel e-MOSFET and p-channel e-MOSFET. Why the name is enhancement type MOSFET? Such type of MOSFETs are operates in only enhancement mode. They never operates in depletion mode. That's why the name is the enhancement type MOSFET. These are the schematic symbols for the n-channel e-MOSFETs, source, gate, drain. These are the three terminals, channel is shown in the above and arrow represents the direction of majority charge carriers from source to drain. Schematic symbols for p-channel e-MOSFET. As compared with n-channel, there is only one difference, direction of arrow, arrow is outward. What is the significance of gap in between the gate and channel? In this MOSFET, the gate is isolated from the channel. In between gate and channel, there is dielectric media, thin layer of oxide layer is there. That's why. The input impedance of MOSFET is very high and it is the significance of gap. Why channel is represented by the broken line in the e-MOSFET? In the depletion MOSFET, channel is present physically, but in e-MOSFET, the channel is present virtually. That's why in the e-channel MOSFET, the channel is represented by the broken line. Direction of n-channel enhancement type MOSFET. This is the construction diagram of e-MOSFET. It is the lightly doped p-type semiconductor material in which two heavily doped n-regions are diffused. That two heavily doped n-regions are represented by the source and gate. The body is represented by the substrate SS. In between gate and body, there is thin layer of oxide layer, SiO2 layer is there. So the input impedance of this MOSFET is very high. Here there is no direct electrical connection in between the gate and body. Working operation of n-channel enhancement type MOSFET. For this mode, VGS is equal to 0. If we set the VGS is equal to 0 and apply the positive voltage in between the drain and source. In the e-MOSFET, there is no connectivity in between the source and drain. So effect of this, there is no movement of charge carriers. So current remains 0. For this mode, the MOSFET operates in cutoff region. Operation with VGS is positive. Apply the positive voltage in between the gate and source and at the same time apply the positive voltage in between the drain and source. Now increase the VGS and VDS simultaneously. Here gate is at positive potential. So the electrons from the P region are attracted towards the gate but they cannot reach up to the gate. They are deposited near the oxide layer. As the VGS increases continuously, so continuously the electrons from the P region are attracted towards the gate and they deposited near the surface of oxide layer. At the specific value of VGS, the sufficient number of electrons are accumulated near the surface. So the channel is formed in between the source and drain. So connectivity is created in between the source and drain. So effect of this, the majority charge carriers electrons are start moving from the source to drain. So effect of this, the current flows from the drain to source. The voltage VGS, at which point the channel is formed, that voltage is called as a three-should voltage. To turn on the subtype of MOSFET, at least we should apply the VGS greater than VT. If VGS is less than VT, the channel is absent, so MOSFET remains off and once the VGS crosses the VT, the current starts flowing from the drain to source. So effect of this, the MOSFET operates in the ohmic region. In this region, the drain current is directly proportional to the VDS and it obeys the ohms law. There is a slight increase in VDS and there is a large change in current and the MOSFET operates in the constant resistance region. Effect of increasing drain to source voltage, when VGS is less than VT, the channel is absent and once the VGS crosses the VT, the channel is formed in between the source and drain. So effect of this, the majority charge carriers flowing from the source to drain and the current starts flowing from the drain to source and further if we increase the VDS, so current starts flowing from the drain to source. In this ohmic region, the current is directly proportional to VDS. So because of this current, the reverse voltage is developed across the channel, across the PN junction. So because of that reverse voltage, the depletion region around the PN junction is encouraged. So because of this increase in depletion region, the effective channel width is reduced. As the channel width is reduced, the rate of change of ID is reduced. At the specific value of VDS, the channel width becomes minimum through which high density charge carriers flows from the drain to source and the MOSFET enters in the pinch of region. The voltage VDS at which point the channel width becomes minimum and the current remains constant and further there will not any increase in current that voltage is called as a pinch of voltage or the saturation region. In this region, pinch of region or in the saturation region, the current remains constant. If you want to use the MOSFET for the voltage amplification, it must operate in the pinch of region or saturation region. It is the drain characteristics of young channel in MOSFET. The characteristics operates in the three different regions, cut-off region, ohmic region and saturation region. In the cut-off region, VDS is less than VT, current remains 0. In the ohmic region, the current is directly proportional to voltage. If you want to use the MOSFET as an close switch, then it must operate in the ohmic region and in the saturation region, the width of channel is minimum and the current remains constant and if you want to use the MOSFET for the amplification purpose, it must operate in the saturation region, which is the transfer characteristics of young channel in MOSFET, so transfer characteristics. It shows the relation between the VGS and ID. As long as VGS is less than threshold voltage, the current remains 0. Once the VGS crosses the threshold voltage, current encourages. As long as VGS is greater than threshold and less than pinch of MOSFET operates in the pinch of region. Once the VGS crosses the pinch of voltage, the MOSFET enters in the saturation region. In this region, the current remains constant, while enhancement type MOSFET is called as a normally off-device. In this MOSFET, when input voltage VGS is 0, then current remains 0. That is why E MOSFET is called as a normally off-device, why power MOSFETs are generally of enhanced SPED type. Up till now, we studied the depletion type MOSFET. In the depletion type MOSFET, when VGS is equal to 0, the current is maximum, but in the enhanced SPED type MOSFET, when VGS is equal to 0, the current remains 0 and MOSFET is in off state. And whenever the VGS crosses the VT, then and then MOSFET conducts. That is why practically, practically power MOSFETs are enhanced SPED type. These are references, thank you.