# Resistance of Thin Film Resistor

Discussion in 'Homework Help' started by smrams28, Apr 2, 2013.

1. ### smrams28 Thread Starter New Member

Mar 29, 2013
13
0
Hi everyone. I am stuck on this problem. Can someone help? I included my work at the bottom but its not right.

The thin film resistor has the following parameters. The film is 0.17 um thick and is doped with donors, Nd = 3.1 x10^17 cm^-3; the electron mobility in the film, mu = 3250 cm^2/(V*s). The resistor length L = 520 um and the width W = 56 um. The unit-width contact resistance is 5 Ohm x mm. What is the resistance of this thin film resistor?

R = (p/t) * (L/W)
R = 1/nqut * (L/W)
= 1/(3.1E17 * 1.6E-19 * 3250 * .17E-4) * (520/56)
= 3388.95

2. ### smrams28 Thread Starter New Member

Mar 29, 2013
13
0
I probably have to incorporate the unit width contact resistance but I am not sure how to do that.

3. ### WBahn Moderator

Mar 31, 2012
18,079
4,917

Edit:

(Actually, the units wasn't your problem, I just couldn't see clearly enough to make out what was and wasn't in the denominator)

The contact resistance goes down with wider contacts, right?

The product of the contact width and the resistance is therefore a constant. Hence

5Ωmm = R*W

and that's for one contact.

At a quick blush that would add a couple hundred ohms. Is that about the amount you are off by?

Last edited: Apr 2, 2013
smrams28 likes this.
4. ### smrams28 Thread Starter New Member

Mar 29, 2013
13
0

Can you explain what role the unit width contact resistance plays in this? I am confused on how to incorporate that into this problem.

5. ### smrams28 Thread Starter New Member

Mar 29, 2013
13
0
I figured it out guys. Thanks

I had to take the unit-width contact resistance and divide that by the width. Then I had to multiply that result by 2 and add it to my initial calculated R value.