Sourcing nanoamps and below like a Samurai, or KEI 6221 DC/AC SMU teardown

[voltsandjolts]

10aA source&measurement 

Approximately 62 electrons per second! 

[VintageNut]

10aA source&measurement 

I am scratching my head for an application that requires the measurement of 10aA.

The noise of the Keithley 6430 is around 380 aA p-p. This was an actual measurement. The 6430 is arguably the best bench instrument in existence for sourcing and measuring low currents. 

[Kleinstein]

There are not many measurements that need / care about such small currents. This a regime for speciallized instruments / labs. The Keithley 6430 may be best from Keithley and US general purpose sources. The meters shown are from Soviet time special scientific instruments build mainly for users like national metrology labs and similar. Alone the connectors with saphire isolators make them quite expensive (and also delicate) - a bit more than the teflon isolated triax found in more general purpose ones.
In this area the Soviets were quite good, sparing not much expense in handcrafted systems for special use. The Keithley meters are more the afforable version for every day use in the semiconductor industry.

One use for very low currents and resolving them accurate are electron turnstile systems - kind of trying to count electrons to get the ultimare current reference. This way one can provide small currents with good accuracy, but with the difficulty to transfer to more managable sizes.

[bastl_r]

I am scratching my head for an application that requires the measurement of 10aA.

Maybe Tunnelrastermikroskop.
Sorry, i don't know the english name.
Regards

[Kleinstein]

A tunneling microscope would still use a significant higher current (still low, but more pA or even nA), as they need to be realtively fast to still get a picture with some 100000 and more pixels in a reasonable time. The very low current also implies a rather slow operation and long waiting times from parasitic capacitance and the associated dielectric absorbtion.

[VintageNut]

If I understand correctly, the application is metrology. Specifically, measuring as close to zero as can happen with careful practice.

I have played with similar for resistance. Being able to measure in the 10 to 20 nano ohms region requires exactly the correct instruments and very careful practice.

I still have my ohms labs zero ohm standard. It is fun to try to measure.

[Alex Nikitin]

I am scratching my head for an application that requires the measurement of 10aA.

Mass-spectrometry is one application which I am very familiar with. For example, these guys measure down to aA (the name of their patented amplifier is ATONA  = aA to nA range ),

Cheers

Alex

[VintageNut]

I am scratching my head for an application that requires the measurement of 10aA.

Mass-spectrometry is one application which I am very familiar with. For example, these guys measure down to aA (the name of their patented amplifier is ATONA  = aA to nA range ),

Cheers

Alex

Thanks. That helps. Looks like the instrumentation may be buried in the big iron.

https://www.isotopx.com/product/tims

[MegaVolt]

Mass-spectrometry is one application which I am very familiar with. For example, these guys measure down to aA (the name of their patented amplifier is ATONA  = aA to nA range ),

How do they do it?

[Kleinstein]

I know of one masspectrometer front-end, that use a integrator at the input and photodiode as additional feedback. There the integrator is also directly part of an ADC.

Other very sensitive mass spectrometers use channe-plates as a kind of electron multiplier, a bit similar to a photo mulipliers. The output is than counting pulses, not really measuring the size of the current.