Calibration of Electrometers with Sub-PPM Accuracy

We performed calibrations of different commercial picoammeters using the `Ultrastable Low-noise Current Amplifier' (ULCA) operated in current source mode as calibrator in the current range between 1 fA and 1 μA. The results allow the comprehensive characterization of the devices under test regarding noise, settling and burden voltage behavior as well as stability of the gain factor, and confirm the superior performance of the ULCA for use as small current calibrator standard.