I posted this in the physics section. I now think this might be more appropriate section for these questions.

I am looking for answers to the following:

  1. What is the order of magnitude of change in electric current when the diameter of the conducting material (that is tens of nano meters) changes by a few (say 1 to 5) nano meters, like in a chip? I am thinking of constant voltage source as that is more commonly used in circuits involving ICs. Is that correct? I am thinking that the change in current would be of the order of tens of nano amperes. Is that correct?

2.What is the easiest way (circuitry) to measure the change in electric current due to change in conducting material? I would like to measure the change NOT necessarily the original current flowing. Is it possible to find a source which has circuit of a pico ammeter that I can use in the circuitry?

Look forward to your thoughts

Thanks in advance

Kind regards

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    \$\begingroup\$ Looks to me like this is a complicated way of asking "how do you measure current?". So the answer to that is: measure the volt drop and use V=IR \$\endgroup\$ – Puffafish Oct 3 '18 at 10:57
  • \$\begingroup\$ In a sense you are right Puffafish, but when you measure very small current in the order of nano amperes or pico amperes, then there are other parameters including a small change in conducting material. \$\endgroup\$ – Shantanu Oct 4 '18 at 2:31

All Voltage sources have an effective series impedance which causes drop in voltage with a rise in current. This is a step load regulation error spec. The load regulation error with a transient, step load or DC load may be different if the rise time and inductance is significant Vdrop=LdI/dt but I doubt this will affect you.

So you could define your worst case load ratio to total loop resistance incl this path to estimate the load voltage regulation error. Identify all series R values in a current loop to estimate this result.

The load is TBD and so is your conductor, so a sensitivity to tolerance variations depends on the initial contribution to this step load error and each individual path.

Once min,max current is defined with tolerances to voltage error, you can define an acceptance criteria for tolerances.

Keithley might be your best source for pA magnitude measurements. Unless you can manage to raise Voltage enough to measure with a current source or high series R gigaohms.

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    \$\begingroup\$ Thanks heaps Tony for your reply... this is very useful and answers my question in full... thanks again! \$\endgroup\$ – Shantanu Oct 4 '18 at 2:26

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