Efficiency improvement of a chip-size antenna for wireless microsystems

This work reports on the use of bulk-micromachining technology to increase the efficiency of a folded shorted-patch antenna. This antenna was designed on two stacked wafers (glass bonded on high-resistivity silicon). The analysis was carried out using the HFSS FEM tool. It was shown that bulk-micromachining technology could be used together with HRS to increase the antenna efficiency by ~20 %. Also, it can be used to allow the use of low-resistivity silicon for antenna substrate. Furthermore, bulk-micromachining technology can be used as an option to tune or to select the antenna operating frequency.Fundação para a Ciência e Tecnologia (FCT) -SFRH/BD/4717/2001, POCTI/ESE/38468/2001

Silicon Wet Bulk Micromachining for MEMS

Microelectromechanical systems (MEMS)-based sensors and actuators have become remarkably popular in the past few decades. Rapid advances have taken place in terms of both technologies and techniques of fabrication of MEMS structures. Wet chemical–based silicon bulk micromachining continues to be a widely used technique for the fabrication of microstructures used in MEMS devices. Researchers all over the world have contributed significantly to the advancement of wet chemical–based micromachining, from understanding the etching mechanism to exploring its application to the fabrication of simple to complex MEMS structures. In addition to its various benefits, one of the unique features of wet chemical–based bulk micromachining is the ability to fabricate slanted sidewalls, such as 45° walls as micromirrors, as well as freestanding structures, such as cantilevers and diaphragms. This makes wet bulk micromachining necessary for the fabrication of structures for myriad applications. This book provides a comprehensive understating of wet bulk micromachining for the fabrication of simple to advanced microstructures for various applications in MEMS. It includes introductory to advanced concepts and covers research on basic and advanced topics on wet chemical–based silicon bulk micromachining. The book thus serves as an introductory textbook for undergraduate- and graduate-level students of physics, chemistry, electrical and electronic engineering, materials science, and engineering, as well as a comprehensive reference for researchers working or aspiring to work in the area of MEMS and for engineers working in microfabrication technology

Thermal design issues and performance of microcalorimeter arrays at sub-Kelvin temperatures

We have produced 5/spl times/5 pixel arrays of microcalorimeters using bulk micromachining. Analysis of our data provides the thermal conductivity parameters of Si/sub x/N/sub y/ 1 /spl mu/m thick membranes at 100 mK. Moreover we find that the thermal transport at 100 mK in Si beams, with dimensions 1.25 mm /spl times/ 0.35mm /spl times/ 35/spl mu/m (length /spl times/ height /spl times/ width) is dominated by ballistic phonons with a mean free path of 110 /spl mu/m. These thermal parameters can be used for modelling future 32 /spl times/ 32 pixel arrays. In addition we operated three pixels in a 5 /spl times/ 5 array of microcalorimeters and find that the pixel to pixel reproducibility is very good. When used as an X-ray microcalorimeter individual pixels have a thermal decay time of 200 /spl mu/s is and their energy resolution is between 6 and 7 eV for 5.89 keV X-ray photons

Novel Microelectromechanical Systems Image Reversal Fabrication Process Based on Robust SU-8 Masking Layers

This paper discusses a novel fabrication process that uses a combination of negative and positive photoresists with positive tone photomasks, resulting in masking layers suitable for bulk micromachining high-aspect ratio microelectromechanical systems (MEMS) devices. MicroChem\u27s negative photoresist Nano™ SU-8 and Clariant\u27s image reversal photoresist AZ 5214E are utilized, along with a barrier layer, to effectively convert a positive photomask into a negative image. This technique utilizes standard photolithography chemicals, equipment, and processes, and opens the door for creating complementary MEMS structures without added fabrication delay and cost. Furthermore, the SU-8 masking layer is robust enough to withstand aggressive etch chemistries needed for fabrication research and development, bulk micromachining high-aspect ratio MEMS structures in silicon substrates, etc. This processing technique was successfully demonstrated by translating a positive photomask to an SU-8 layer that was then utilized as an etching mask for a series of trenches that were micromachined into a silicon substrate. In addition, whereas the SU-8 mask would normally be left in place after processing, a technique utilizing Rohm and Haas Microposit™ S1818 as a release layer has been developed so that the SU-8 masking material can be removed post-etching

Design, fabrication and characterization of monolithic embedded parylene microchannels in silicon substrate

This paper presents a novel channel fabrication technology of bulk-micromachined monolithic embedded polymer channels in silicon substrate. The fabrication process favorably obviates the need for sacrifical materials in surface-micromachined channels and wafer-bonding in conventional bulk-micromachined channels. Single-layer-deposited parylene C (poly-para-xylylene C) is selected as a structural material in the microfabricated channels/columns to conduct life science research. High pressure capacity can be obtained in these channels by the assistance of silicon substrate support to meet the needs of high-pressure loading conditions in microfluidic applications. The fabrication technology is completely compatible with further lithographic CMOS/MEMS processes, which enables the fabricated embedded structures to be totally integrated with on-chip micro/nano-sensors/actuators/structures for miniaturized lab-on-a-chip systems. An exemplary process was described to show the feasibility of combining bulk micromachining and surface micromachining techniques in process integration. Embedded channels in versatile cross-section profile designs have been fabricated and characterized to demonstrate their capabilities for various applications. A quasi-hemi-circular-shaped embedded parylene channel has been fabricated and verified to withstand inner pressure loadings higher than 1000 psi without failure for micro-high performance liquid chromatography (µHPLC) analysis. Fabrication of a high-aspect-ratio (internal channel height/internal channel width, greater than 20) quasi-rectangular-shaped embedded parylene channel has also been presented and characterized. Its implementation in a single-mask spiral parylene column longer than 1.1 m in a 3.3 mm × 3.3 mm square size on a chip has been demonstrated for prospective micro-gas chromatography (µGC) and high-density, high-efficiency separations. This proposed monolithic embedded channel technology can be extensively implemented to fabricate microchannels/columns in high-pressure microfludics and high-performance/high-throughput chip-based micro total analysis systems (µTAS)

Silver-based reflective coatings for micromachined optical filters

Silver films of 40 nm thickness, evaporated on a 300 nm thick low-stress silicon nitride layer, are used as high-quality mirrors operating in the visible and near IR spectral range. Application of a silicon nitride membrane under tension, placed within a square Si frame after bulk micromachining, improves the initial mirror flatness. Two parallel mirrors, each with square aperture of up to 2x2 mm2 and an electrostatically controlled spacing, form a tunable Fabry–P´erot optical filter. Investigation of the silver-based reflective coatings, and mirror characterization, including influence of bulk micromachining, are presentedFundação para a Ciência e a Tecnologia FC

Prototype MEMS Capacitive Pressure Sensor Design and Manufacturing.

This paper is intended to describe the design and manufacturing aspects of a simple micromachined capacitive pressure sensor working in the pressure range of 0-1000 mbar. 500 µm thick Borofloat® 33 glass and silicon wafers were used as substrates. The basic transducer structure consists of a rectangular silicon membrane as deformable electrode and a fix aluminum electrode formed on the glass surface. In order to determine the exact geometry of the silicon electrode structure numerical models and simulations were applied. The thin silicon membrane was fabricated by Si bulk micromachining, i.e. anisotropic alkaline etching with electrochemical etch-stop. The two wafers were bonded together at low temperature by anodic bonding. After bonding and dicing the wafers the pressure sensors were characterized mechanically and functionally also. Our results demonstrate the functional behavior of the manufactured sensor structures and provide excellent verification of the preliminary expectations based on theoretical calculations and electro-mechanical simulations

Nanomechanical optical devices fabricated with aligned wafer bonding

This paper reports on a new method for making some types of integrated optical nanomechanical devices. Intensity modulators as well as phase modulators were fabricated using several silicon micromachining techniques, including chemical mechanical polishing and aligned wafer bonding. This new method enables batch fabrication of the nanomechanical optical devices, and enhances their performance