n mos transistor on resistance

[Eman kamel]

for nmos transistor
the on resistance Ron is given by the equation

Rtransistor =Lg0/(Width* mu *COX*(VDD-VT0))

i use the following values
Lg0 17.5 nm -> .0175 micro meter
width 140 micro meter
this make w/l =8000 which i think very reasonable
VDD 1 volt
VT0 0.18 volt

from my model i found COX 3.137727e-14 farad per Micro meter ^2 which i think reasonable
i use the mobility of electron mu 1500e8
these all give me Ron=.32 ohm

i think Ron is in the range of hundreds of ohms, i found this in literature
so i do not know what is wrong with my calculation
what do u think?

 

[analogLow]

I think you are definitely "in the ball park". Your W is pretty large so less than an ohm is for sure possible (depending on your cmos process). Probably the best way to see the resistance though is using the simulator (i.e. measure current Ids and voltage Vds). Also, you need to think about the type of application that the nmos is used in. 1 ohm or less might be required when the transistor is on (i.e. saturation)? Or do you use the transistor as a linear resistor (i.e. linear region)? Anyways, your resistance is reasonable.
.analogLow

 

[Eman kamel]

thanks for your help :-D
i have another questions
i calculate the interconnect resistance by unit length for 45 nm technology
by the equation

Rinterconnect = Resistivity/(Thickness * Width)
i am using Metal Resistivity value 1.688e-2 ohm.micro meter
Thickness = 0.280 micro meter
Width =140 micrometer
i got R interconnect 0.0004 ohm/micro meter, while i found it in litreature to be in range of .04 ohm /micro meter
what do you think make this difference??
thanks in advance
Eman

I think you are definitely "in the ball park". Your W is pretty large so less than an ohm is for sure possible (depending on your cmos process). Probably the best way to see the resistance though is using the simulator (i.e. measure current Ids and voltage Vds). Also, you need to think about the type of application that the nmos is used in. 1 ohm or less might be required when the transistor is on (i.e. saturation)? Or do you use the transistor as a linear resistor (i.e. linear region)? Anyways, your resistance is reasonable.
.analogLow