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This paper starts with a short review on interferometric methods for optical analysis of resonant structures. Three important types of resonant sensor elements are then discussed: a piezoelectrically driven beam as the strain sensitive element of a bulk micromachined force-sensor, electrothermally driven/piezoresistively detected single and triple beams as the sensing elements of a bulk micromachined resonant accelerometer, and an electrostatically driven capacitively detected torsional resonator in surface micromachining technology, the key element of a (pseudo-) vibrating gyroscope. We present optical and electrical measurements and discuss the importance of crosstalk in the electric pickup signal. The dynamic behaviour of the resonant accelerometer in closed-loop undamping circuitry is analyzed by external excitation on a shaker table.

Thick poly-SiGe layers, deposited by plasma-enhanced chemical vapor deposition (PECVD), are very promising structural layers for use in microaccelerometers, microgyroscopes or for thin-film encapsulation, especially for applications where the thermal budget is limited. In this work it is shown for the first time that these layers are an attractive alternative to low-pressure CVD (LPCVD) poly-Si or poly-SiGe because of their high growth rate (100-200 nm/min) and low deposition temperature (520 C-590 C). The combination of both of these features is impossible to achieve with either LPCVD SiGe (2-30 nm/min growth rate) or LPCVD poly-Si (annealing temperature higher than 900 C to achieve structural layer having low tensile stress). Additional advantages are that no nucleation layer is needed (deposition directly on SiO 2 is possible) and that the as-deposited layers are polycrystalline. No stress or dopant activation anneal of the structural layer is needed since in situ phosphorus doping gives an as-deposited tensile stress down to 20 MPa, and a resistivity of 10 m-cm to 30 m-cm. With in situ boron doping, resistivities down to 0.6 m-cm are possible. The use of these films as an encapsulation layer above an accelerometer is shown.[958]

We report a new surface micromachining technology to fabricate monocrystalline silicon membranes covering a vacuum cavity for applications like piezoresistive pressure sensors. The main process steps are: (i) local anodic etching of layered porous silicon with different porosities, (ii) tbermal rearrTgement of the porous silicon, and (iii) epitaxial growth of the silicon membrane layer. In contrast to conventional bulk micromachining the new technology has the benefit of a considerable freedom in the design of monocrystalline silicon membranes. The membrane geometry is only determined by the porous region. Further, the new fabrication method is fully CMOS compatible. In fact, except for anodic etching, all process steps are part of a standard mixed signal IC production line. Various aspects of the used key process steps are discussed, particularly with regard to the oxygen and fluorine desorption during the porous silicon annealing. A piezoresistive pressure sensor with integrated ASIC based on the new fabrication method is demonstrated.

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