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

 

I probably have to incorporate the unit width contact resistance but I am not sure how to do that.

 

Check your units!

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?

 

Check your units!

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?

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

 

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.