CMOS Current Amplifier for AFM Impedance Sensing on Chip with ZeptoFarad Resolution

A new sensing configuration based on the direct use of the metal input pad of a dedicated CMOS amplifier as a conductive substrate electrode for nanoscale high-performance electrical measurement with a standard conductive AFM is proposed and experimentally validated. Combining the state-of-the-art performance of an integrated current preamplifier (5MHz bandwidth, 14fA/sqrt(Hz) noise at 1MHz) with pad and setup optimization, it has been possible to straightforwardly achieve 14zF total capacitive rms resolution (0.5V applied at 1MHz with 1s averaging time) that corresponds to 75pm resolution in tracking the piezo vertical movement (allowing the detection of 6nm steps of the cantilever with a SNR of ∼40dB).