Pasqualina M. Sarro

Silicon carbide as a new MEMS technology

Silicon carbide (SiC) is a material with very attractive properties for microsystems applications. Its mechanical strength, high thermal conductivity, ability to operate at high temperatures and extreme chemical inertness in several liquid electrolytes, make SiC an attractive candidate for MEMS applications, both as structural material and as coating layer. The recently reported progress in material growth and processing techniques has strengthened the potential of this material for MEMS, especially for applications requiring operation at high temperature or in severe environments. Examples of SiC microsensors and microstructures are given and interesting development in both material characteristics and micromachining processes are discussed.

Thermal sensors based on the seebeck effect

Abstract The thermoelectric effects in metals and semiconductors are reviewed and particular attention is devoted to the Seebeck effect in silicon and its possible exploitation for thermal sensing. For this purpose, an analysis of the performance of integrated silicon thermopiles is presented. Several thermal sensors that measure magnetic, mechanical, radiation and chemical signals, as well as electrical converters, are reviewed. Many of the devices described are fabricated by integrated circuit (IC) technology, which makes them very attractive, since they can be batch-fabricated and on-chip signal conditioning-electronics added.

Process and design considerations for surface micromachined beams for a tuneable interferometer array in silicon

A special surface micromachining process, using oxidized polysilicon sacrificial layer and poly-nitride/poly membranes, has been developed for realizing the monolithic integration of light modulators with silicon devices. The design and processing considerations for developing a compact micromachined silicon Fabry-Perot interferometer are presented. Initial tests have shown that these micromachined membranes represent a compact and effective light modulating method.<<ETX>>

Atomic-scale electron microscopy at ambient pressure

We demonstrate a novel nanoreactor for performing atomic-resolution environmental transmission electron microscopy (ETEM) of nanostructured materials during exposure to gases at ambient pressures and elevated temperatures. The nanoreactor is a microelectromechanical system (MEMS) and is functionalized with a micrometer-sized gas-flow channel, electron-transparent windows and a heating device. It fits into the tip of a dedicated sample holder that can be used in a normal CM microscope of Philips/FEI Company. The nanoreactor performance was demonstrated by ETEM imaging of a Cu/ZnO catalyst for methanol synthesis during exposure to hydrogen. Specifically, the nanoreactor facilitated the direct observation of Cu nanocrystal growth and mobility on a sub-second time scale during heating to 500 degrees C and exposure to 1.2 bar of H(2). For the same gas reaction environment, ETEM images show atomic lattice fringes in the Cu nanocrystals with spacing of 0.18 nm, attesting the spatial resolution limit of the system. The nanoreactor concept opens up new possibilities for in situ studies of nanomaterials and the ways they interact with their ambient working environment in diverse areas, such as heterogeneous catalysis, electrochemistry, nanofabrication, materials science and biology.

FLEXIBLE MIRROR MICROMACHINED IN SILICON

An electrostatically controlled flexible mirror has been fabricated on a silicon chip by means of bulk micromachining. The mirror has a 10.5 mm × 10.5 mm square aperture and consists of a 0.5-µm-thick tensile-stressed silicon-nitride diaphragm coated with a 0.2-µm-thick reflective aluminum layer. The reflecting surface is initially plane with a mean-square deviation of ~λ/8 for λ = 633 nm. The shape of the reflecting surface is controlled electrostatically by an array of integrated actuators. Good initial optical quality and the possibility of electrostatic control of the reflecting surface make the on-chip mirror useful for various electro-optical applications.

Integrated thermopile sensors

Abstract This paper is about integrated silicon thermopiles and their applications in silicon sensors. After a short description of the thermoelectric effect and its use in silicon thermopiles, some attention is devoted to the design of micromachined structures for implementing thermal sensors. The various sensing principles based on thermal effects are discussed next. Finally, an impression is given of some of the recently developed silicon-thermopile sensors which implement these sensing principles.

Technology and applications of micromachined silicon adaptive mirrors

The technology of low-cost high-quality micromachined adaptive mirrors is reported. Adaptive mirrors are fabricated by combining bulk silicon micromachining with standard electronics technologies. Mirrors with tens of control channels, having RMS initial deviation from plane of the order of ?/20 and a range of surface deflection of 10 to 20 ?m with linear frequency response in the range of 50 Hz to 1 kHz, are fabricated on standard PCB substrates. Advanced devices with hundreds of control channels, demanding integration of driver and switching electronics, are currently under development

Microfluidic sensor based on integrated optical hollow waveguides

A simple integrated optical refractometric sensor based on hollow-core antiresonant reflecting optical waveguides is proposed. The sensor uses the antiresonant reflecting guidance mechanism and permits one to measure the refractive index of a liquid filling the core by simply monitoring the transmitted spectrum. The device has been made with standard silicon technology, and the experimental results confirm numerical simulations performed in one- and two-dimensional geometry. The sensor exhibits a linear response over a wide measurement range (1.3330-1.4450) and a resolution of 9 x 10(-4) and requires a small analyte volume.

Spray coating of photoresist for pattern transfer on high topography surfaces

In this paper, a new method of photoresist coating, direct spray coating, is studied. This method is especially suited to coat high topography surfaces for some special applications in microelectromechanical systems, radio frequency components and packaging. The most suitable photoresist type and coating process are found. The influence of several coating parameters on the thickness and uniformity of the photoresist layer is investigated. A model describing the dependence of the thickness on the major parameters is presented. Very promising results are obtained using spray coating for the fabrication of several three-dimensional structures.

Compatibility of zinc oxide with silicon IC processing

Abstract In this paper we present the passivation of zinc oxide by a thin silicon nitride layer. With this passivation, silicon wafers covered with zinc oxide can be further processed without contamination of the process chambers of the subsequent processes, and without damaging the zinc oxide layer. In addition, we review some process technology concerning zinc oxide: the cleaning and etching of zinc oxide and the etching of aluminium on zinc oxide.