Micromachined Resonant Electrometer

Numerous analytical instruments require a sensor to detect small quantities of electric charge. The techniques of scanning tunneling microscopy and ballistic electron emission microscopy require tiny currents to be sensed, on the order of a few picoamperes.  In a mass spectrometer, the analysis of a sample requires a measurement of the current resulting from ions passing through a mass filter. In a technique known as chargedetection mass spectrometry, used to measure the mass of large molecules such as DNA molecules or virus particles, the resolution of the mass determination is limited in practice by the sensitivity of the charge detector used. A mass spectrometer using a charge detector with a resolution of about 15 electrons could be used by microbiologists to accurately size DNA fragments.  Other applications for a sensitive charge detector include measurement of fields and charging in spacecraft, testing leakage currents in relays and Kelvin probe surface-charge analysis.