Multichannel 65 zF rms Resolution CMOS Monolithic Capacitive Sensor for Counting Single Micrometer-Sized Airborne Particles on Chip

The first integrated CMOS monolithic sensor system for on-chip capacitive detection of micrometric airborne particulate matter (PM) is presented. The chip is based on a 32 channel lock-in architecture allowing a dust collection area of 1.15 mm2 where interdigitated differential microelectrodes, fabricated with the top metal and directly exposed to air, allow single particle sensitivity. The preamplifier input capacitance is significantly minimized thanks to the electrode-amplifier proximity and proper partitioning of the sensing area, in order to reduce the noise. Each channel comprises a charge preamplifier with adjustable high-pass filtering for flicker noise shaping, square-wave mixer, gm-C tunable low-pass filter (40-750 Hz), and a 6 bit digital network for automatic compensation of electrodes mismatching with a granularity of 150 aF. Thanks to the capacitive noise of only 65 zF rms with 25 ms temporal resolution, deposition events of single mineral talc particles were recorded down to 1 μm diameter with a signal-to-noise ratio of ≈18 dB. This chip paves the way to pervasive mapping of both indoor and outdoor PM in the 1-30 μm range.