Vibrating Reed Electrometer With Attocoulomb Charge Resolution and Subattoampere Current Resolution

An extremely sensitive vibrating reed electrometer is built, which has attocoulomb charge resolution and subattoampere current resolution within a 1-min measurement. The input leakage current of the setup is typically less than 1 aA with values as low as 0.12 aA, which is less than 1 electron/s. Allan deviation analysis shows that the lowest standard deviation that can be achieved in current measurements is 0.065 aA with a 3-h integration time. Crucial for this extreme sensitivity and low leakage current was the development of an input measurement stage with only vacuum-gap capacitors. The stability and sensitivity of this new electrometer make it suitable for accurate low-frequency characterization of vacuum-gap capacitors as for example used in the electron counting capacitance standard experiment. As a first step toward such a study, the internal vacuum-gap feedback capacitor of the electrometer was measured as a function of applied charge and for different heat treatments resulting in changing surface layers of the capacitor plates.