I see in literature a lot of researchers use a small Vds to study pH response on extended gate MOSFETs i.e. in triode or linear region. In linear region Id is dependent on Vgs and Vds. When measuring pH response as a change in Vgs (threshold) , why shouldn't one prefer to operate MOSFET in saturation region and make Id dependent only on Vgs.
More importantly WHY operate in 'that' region for such an application ?
Hung phan ...Study on extended gate field effect transistor with tin oxide sensing membrane on Materials Chemistry and Physics Volume 63, Issue 1, 14 February 2000, Pages 19–23
A very small Vds applied here... there are other papers on extended gate MOSFETs with similar Vds values ( linear region operation)
Not sure if its because the integrated charge per unit area ( baseline charge) with low Vds ( linear region ) is less and when you measure changes at gate the ...delta change / baseline charge is high ...a little analogous to Signal to Noise ratio.
And secondly increasing Vds would generate more heating effects due to increase in the Id current and affect the mobility of the charges in the channel and hence a temperature drift in threshold voltage at the gate. This would definitely reduce the signal to noise ratio of the system.
Any feedback will be highly appreciated !! Thanks guys !!
Dear Nikhil Bhalla sir,
Small Vds is preferred to keep the power dissipation low.
We can use it in linear/saturation region but prefer linear region because in linear region ID is dependent on maximum bias parameters(thats preferred while studying the effect or sensitivity) whereas in saturation region ID is almost independent of drain voltage.
if you are measuring changes in gate voltage....ID independent of VD is better because your changes are now only dependent on VGS....you have now one less variable in saturation!
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