Question

need help with vlsi design

good hand writing please

thank you

What is the difference between the depletion mode and the enhancement mode? What do we understand by threshold voltage for the enhancement mode nMOS transistor, will it be positive or negative? Support your answer with a logical reason. (15 points)

Answer 1

If you like please upvote.

Answers:

The differences between the depletion mode mode and enhancement are the following: i) Enhancement mode In an enhancement MOSFET , the channel doesn't exist initially. It will exist only when we give greater than threshold voltage For example, in on n-channel MOSFET, the substrate is made of p-type material and consider the source to be at a reference at ground potential of ovolts. For a gate to source voltage of o volts, there is no channel in the p type substrate. Once the voltage Starts to increase holes are pushed away. from the region near the gate due to the increa- sine positive potential and hence a region of excess electrons exists there - Thés Region of excess elections for forms the channel for the MOSFET. Due to this n-channel reason, it is called MOSFET. e Gate - Drain Sounce 14. SiO2 layer + + + top type substrate Induced n-Channel

i) Depletion Mode In depletion type, everything is the same except only that the channel is already implanted in the substrate through diffusion. Hence & a current con flow between be the source and drain even at vore = 0 volt since charge carrichs are already present and there is no need to apply a bias voltage to create a region of excess carriers near the gate region Sounce & I Drain N + Nt -tube substrate mo For example above shown - Channel depletion type MOSFET the channel has already been implanted into the substrate by diffusion and this is how the device looks without any bias So basically channel already exists. We have to apply some voltage to collapse the Channel so as to stop current flow between source and drain. Default State is ON ine current flows without oppleine voltage. The threshold voltage is the minimum gate to source voltage that is needed to create a Conducting path between the source and drain terminals. for the nos transistor in on enhancement mode will be positive the eshold voltages.

The logic is that the positive voltage attracts free- floating electrons within the body towards the gate forming a conductive communal Channel.