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How to measure Leffective in the lab?

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sharas

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measuring length lab activity

Hi,
I am trying to measure Leff. I read in one book that you should operate the mosfet in the triode region and measure for differen drawn channel length Vds/Ids. After plotting that (Ron as afunction of L), the straight line will cross the L axis at L=ΔL (because Ron=[(Lnom-ΔL)/µ*Cox*W*(Vgs-vt)].

The only wrong assumption here, as I understand, is that Vt has the same value for all channel length. Hey, what about the short channel effect????:cry:

If anyone has a better idea or knows how the spice guys extract ΔL, I will be very happy to hear.

Thanks.
 

how to reduce channel length

Leff in lab?
Do you mean in term of fabrication?

Leff is result of drawn length that had been reduce to to process like over etch.
 

what is l-effective

Yes, among other reaons. How do I measure the real channel length on silicon?
 

sharas said:
Hi,
I am trying to measure Leff. I read in one book that you should operate the mosfet in the triode region and measure for differen drawn channel length Vds/Ids. After plotting that (Ron as afunction of L), the straight line will cross the L axis at L=ΔL (because Ron=[(Lnom-ΔL)/µ*Cox*W*(Vgs-vt)].

The only wrong assumption here, as I understand, is that Vt has the same value for all channel length. Hey, what about the short channel effect????:cry:

If anyone has a better idea or knows how the spice guys extract ΔL, I will be very happy to hear.

Thanks.
Click to expand...

Another method to get the effective channel length is measuring the capacitance between the gate and the body or the tunneling current between the gate and the body. Of course, you need to draw a transistor in very large W to minimize any error occuring in the W term.

Hope this help
Scottie
 

    S

    sharas

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Thanks, Scottieman.


Do you mean that The capacitance measured is equal to Cox*W*Leffective?
 

sharas said:
Thanks, Scottieman.


Do you mean that The capacitance measured is equal to Cox*W*Leffective?
Click to expand...

You are correct :)

Still, some precaution need to have, especially in very short-channel technology (e.g. L < 0.1um)

The thin gate oxide may introduce a huge amount of leakage current, making coventional CV measurment not accuracy enough. That is also the reason why people propose to measure the gate current instead the gate capacitance for Leff extraction.

Enjoy
Scottie
 

    S

    sharas

    Points: 2
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