A CMOS-compatible device for fluid density measurements

We report a miniaturized CMOS-compatible resonant sensor to measure the density of fluids. The device is fabricated using a standard CMOS process followed by simple postprocessing combining both sacrificial aluminium etching and bulk silicon micromachining. The size of the active part of the sensor is only 250×250 μm². This makes the device suitable for batch fabrication or as a component of a larger CMOS-compatible fluid handling system. The volume of the probed liquid is only 1.1×10^-11 l. A measurement setup that completely eliminates capacitive crosstalk between the thermomechanical excitation and the piezoresistive detection is reported. The quality factor at atmospheric pressure is typically 215. The measured frequency shift of 6 kHz/gcm^-3 of the device agrees well with finite element simulations and analytical approximations