Charged particle detection using a micromechanical electrometer

Abstract

We have developed a MEMS-based electrometer for the detection of small currents from ionized particles in an aerosol particle detection system. We utilize a porous sensing-electrode coupled to a MEMS resonating electrometer. Our electrometer achieved a noise floor below 1 fA rms produced by 10 nm diameter particles within an airflow of 1.0 L/min. At this flow rate, the minimum detectable current (1 fA) corresponds to a minimum measurable particle density of 400 cm-3. We compared and calibrated the MEMS electrometer with two commercial units: a Faraday cup electrometer and a MCPC (Mixing Condensation Particle Counter). The MEMS electrometer achieved an experimental sensitivity of 19.68 μVrms/fA and charge-detection efficiency of 5.476 X 107 V/C.