David Westberg

Sacrificial aluminum etching for CMOS microstructures

This paper reports recent advances in surface micromachining by sacrificial aluminum etching (SALE). This method is applied to standard CMOS substrates in a single-mask, or even maskless, post-processing scheme. Underetching distances of several hundred microns are feasible. Design issues and technological steps such as protection of contact pads, etching, rinsing, and drying are discussed. The combination of SALE with other micromachining techniques, e.g., silicon bulk micromachining or material deposition is reported. New devices include thermal, capacitive, and mechanical structures for thermal microfluidics, the measurement of pressures and inertial forces, and the evaluation of mechanical thin film properties.

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/spl times/250 /spl mu/m/sup 2/. 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/spl times/10/sup -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/sup -3/ of the device agrees well with finite element simulations and analytical approximations.

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

Abstract 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 11 pl. A measurement setup that completely eliminates electrical 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 (g cm−3) of the device agrees well with finite element simulations and analytical approximations.

A CMOS-compatible fluid density sensor

We report a CMOS-compatible resonant sensor to measure the density of fluids. The device is fabricated using a standard CMOS process followed by simple post-processing consisting of sacrificial aluminium etching and silicon bulk micromachining. The sample volume of liquid probed by the resonating structure is only 11 pl.

Effect of an inhomogeneous insulating film on the capacitance of metal–insulator–semiconductor structures

The capacitance of metal–insulator–semiconductor structures with inhomogeneities in the insulating film is significantly influenced by phenomena not present in the capacitance of corresponding ideal structures. These inhomogeneities may be structural ones like a rough surface topography or compositional ones like inclusions of a different material in the film. In the case of a rough surface, three-dimensional simulations of the accumulation capacitance are compared to measurements on aluminum-polycrystalline diamond-silicon devices. The results show that the surface roughness has to be considered when interpreting the measured data. Also, neglecting the effect of the surface roughness results in erroneous values of the permittivity of the insulating film.