# Regd: MOS Transistor basics help

Discussion in 'Electronic Basics' started by Kranthi Q, Oct 15, 2004.

1. ### Kranthi QGuest

Hi

I need some help in understanding the difference between -

Gate Length

Gate width

Channel Length

Channel Width

Channel Depth

Depletion Layer Width

Depeltion Layer length

for a MOS transistor. WHich of these quantities are equal and how are
they efected by threshold voltage and gate voltage. I am confused as
to especially w.r.t depth and width.

Help is appreciated.

Kranthi.

2. ### peterkenGuest

All of your parameters refer to the physical dimensions of the fet at
silicon level, they are defined at the manufacturing process
All of them refer to what they stand for, seen in a 3-D manner.
Width = how wide is it
Length = how long is it
Depth = what's the thickness of the given layer
Look at the parameters as a lying down rectangle with a specific thickness

None is affected by threshold voltage and gate voltage, in fact it's the
other way around, the physical dimensions at silicon level affect these
parameters.

None of them you can have any influence on, whatever you try, since it's a
mechanical fact

Hi

I need some help in understanding the difference between -

Gate Length

Gate width

Channel Length

Channel Width

Channel Depth

Depletion Layer Width

Depeltion Layer length

for a MOS transistor.
Which of these quantities are equal and how are they efected by threshold
voltage and gate voltage.
I am confused as to especially w.r.t depth and width.

Help is appreciated.

Kranthi.

3. ### Kranthi QGuest

But aren't channel and depletion layer formed because of difference
between gate and source?? I understand that for gate the length and
width are physical dimensions but what about channel L, W and D. I
want what effects the change of L, W and D.

Thanx.

Kranthi.

4. ### peterkenGuest

as i said, channels are formed during construction

(see drawing with fixed font)

_________
/ gate /
/ /
------------------
\______/

channel
______
/ gate\
------------------

They all have PHYSICAL dimensions.

The ELECTRICAL (virtual) width of the channel is formed by a voltage applied
to gate, thereby forming an electric field in the channel, thereby
reducing(depletion) or allowing (enhancement) the current through the
channel itself, it has nothing to do with the given dimensions in the
datasheets.
It's all basic fet-stuff ya know.

But aren't channel and depletion layer formed because of difference
between gate and source?? I understand that for gate the length and
width are physical dimensions but what about channel L, W and D. I
want what effects the change of L, W and D.

Thanx.

Kranthi.

5. ### Kranthi QGuest

Thanks for your help. But I am in the learning stage of FET basics,
and hence the questions!!

6. ### rayjkingGuest

You are both correct . The difference is one being a simple j-fet and the
other being a vertical power fet.
Ray