A CMOS-compatible device for fluid density measurements fabricated by sacrificial aluminium etching

We report a miniaturized CMOS-compatible resonant sensor to measure the den sity of fluids, The device is fabricated using a standard CMOS process foll owed by simple postprocessing combining both sacrificial aluminium etching and bulk silicon micromachining. The size of the active part of the sensor is only 250 x 250 mu m(2). This makes the device suitable for batch fabrica tion or as a component of a larger CMOS-compatible fluid handling system. T he volume of the probed liquid is only 11 pl. A measurement setup that comp letely eliminates electrical crosstalk between the thermomechanical excitat ion and the piezoresistive detection is reported. The quality factor at atm ospheric pressure is typically 215. The measured frequency shift of 6 kHz ( g cm(-3)) of the device agrees well with finite element simulations and ana lytical approximations. (C) 1999 Elsevier Science S.A. All rights reserved.