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New low-stress PECVD poly-SiGe Layers for MEMS

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/spl deg/C-590/spl deg/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/spl deg/C to achieve structural layer having low tensile stress). Additional advantages are that no nucleation layer is needed (deposition directly on SiO/sub 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/spl Omega/-cm to 30 m/spl Omega/-cm. With in situ boron doping, resistivities down to 0.6 m/spl Omega/-cm are possible. The use of these films as an encapsulation layer above an accelerometer is shown.

Experimental characterization of dynamic micromechanical transducers

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.

Piezoelectrical driven resonant force sensor: fabrication and crosstalk

This paper presents a resonant force sensor comprising piezoelectric ZnO thin-film transducers for excitation and detection of resonant beam vibrations. A short description of the processing technique is given, i.e. deposition and passivation of the ZnO layer and separation of beam structures. The electrical behaviour of the sensor was optimized by patterning ZnO areas to minimize electrical crosstalk effects.

A novel concept for long-term pre-storage and release of liquids for pressure-driven lab-on-a-chip devices

On-chip storage of liquids is one of the major challenges of polymer-based lab-on-a-chip (LoC) devices. To ensure long-term storage of even highly volatile reagents in polymer disposal LoC cartridges, robust reagent storage concepts are necessary. Tubular bags, so-called stick packs, are widely used in the packaging industry. They offer sufficient vapor barrier properties for liquid storage. Here we present a polymer multilayer LoC-stack with integrated stick packs for the long-term storage of liquid reagents required for diagnostic applications. The storage concept fulfils two main requirements: firstly, the long-term storage of reagents in stick packs without significant losses or interaction with the surroundings and secondly, the on-demand release of liquids, which is realized by the delamination of a stick pack?s peel seam through pneumatic pressure. Furthermore, effects on the opening behavior of stick packs through accelerated aging were investigated after different storage conditions to proof repeatability. This concept enables on-chip storage of liquid reagents at room temperature and allows the implementation in different pressure driven LoC devices or similar applications. Since liquid storage in stick packs is well-established, emerging fields such as lab-on-a-chip combined with novel reagent release mechanisms should be of great interest for the commercialization of life science products.

Dry Etching for Micromachining Applications

Dry etching processes provide the tools to machine precision high-aspect-ratio structures that form the basic building blocks of microelectromechanical systems. Dry etching processes consist of (1) purely chemical (spontaneous gas phase etching), (2) purely physical (ion beam etching or ion milling), and (3) a combination of both methods (reactive ion or plasma etching) for the controlled removal of desired substrate materials. Although some of the pioneering work in the field was performed as early as the 1970s and 1980s, the area of plasma etching has continued to evolve due to the continuing technological developments in high-density plasma sources, high-throughput vacuum pumps, and process control and instrumentation. Excellent reviews are currently available that provide details in various aspects of the technology and etching process development. This chapter is aimed at providing the reader with a broad understanding of the parameters that influence the results in dry etching techniques and to provide information that is useful to explore dry etching processes for the fabrication of next-generation MEMS devices. Practical recipes suitable for most commonly used plasma reactor configurations are provided and motivated in terms of the influence of the various control parameters and chemicals (gases used). Because process parameters can rarely be transferred directly across equipment or fabrication facilities, it is important to be able to tune the process parameter to specific process flow requirements and constraints. The material presented is not necessarily exhaustive, but focuses instead on practical issues to tackle for the development of dry etching processes suitable for MEMS applications across a broad range of materials.