We survey progress over the past 25 years in the development of microscale devices for pumping fluids. We attempt to provide both a reference for micropump researchers and a resource for those outside the field who wish to identify the best micropump for a particular application. Reciprocating displacement micropumps have been the subject of extensive research in both academia and the private sector and have been produced with a wide range of actuators, valve configurations and materials. Aperiodic displacement micropumps based on mechanisms such as localized phase change have been shown to be suitable for specialized applications. Electroosmotic micropumps exhibit favorable scaling and are promising for a variety of applications requiring high flow rates and pressures. Dynamic micropumps based on electrohydrodynamic and magnetohydrodynamic effects have also been developed. Much progress has been made, but with micropumps suitable for important applications still not available, this remains a fertile area for future research.

https://microfluidics.stanford.edu/Publications/Micropumps_Cooling/Laser%20Review%20of%20Micropumps%20in%20JMM.pdf

A review of micropumps

Two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution in three dimensions and has made possible the development of three-dimensional fluorescence imaging, optical data storage, and lithographic microfabrication. These applications take advantage of the fact that the two-photon absorption probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order λ3 (where λ is the laser wavelength). Any subsequent process, such as fluorescence or a photoinduced chemical reaction, is also localized in this small volume. Although three-dimensional data storage and microfabrication have been illustrated using two-photon-initiated polymerization of resins incorporating conventional ultraviolet-absorbing initiators, such photopolymer systems exhibit low photosensitivity as the initiators have small two-photon absorption cross-sections (δ). Consequently, this approach requires high laser power, and its widespread use remains impractical. Here we report on a class of π;-conjugated compounds that exhibit large δ (as high as 1, 250 × 10−50 cm4 s per photon) and enhanced two-photon sensitivity relative to ultraviolet initiators. Two-photon excitable resins based on these new initiators have been developed and used to demonstrate a scheme for three-dimensional data storage which permits fluorescent and refractive read-out, and the fabrication of three-dimensional micro-optical and micromechanical structures, including photonic-bandgap-type structures.

Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication

This paper presents a review of silicon micromachined accelerometers and gyroscopes. Following a brief introduction to their operating principles and specifications, various device structures, fabrication, technologies, device designs, packaging, and interface electronics issues, along with the present status in the commercialization of micromachined inertial sensors, are discussed. Inertial sensors have seen a steady improvement in their performance, and today, microaccelerometers can resolve accelerations in the micro-g range, while the performance of gyroscopes has improved by a factor of 10/spl times/ every two years during the past eight years. This impressive drive to higher performance, lower cost, greater functionality, higher levels of integration, and higher volume will continue as new fabrication, circuit, and packaging techniques are developed to meet the ever increasing demand for inertial sensors.

/pdf/micromachined-inertial-sensors-esf6197vdc.pdf

Micromachined inertial sensors

Samples of 53 materials that are used or potentially can be used or in the fabrication of microelectromechanical systems and integrated circuits were prepared: single-crystal silicon with two doping levels, polycrystalline silicon with two doping levels, polycrystalline germanium, polycrystalline SiGe, graphite, fused quartz, Pyrex 7740, nine other preparations of silicon dioxide, four preparations of silicon nitride, sapphire, two preparations of aluminum oxide, aluminum, Al/2%Si, titanium, vanadium, niobium, two preparations of tantalum, two preparations of chromium, Cr on Au, molybdenum, tungsten, nickel, palladium, platinum, copper, silver, gold, 10 Ti/90 W, 80 Ni/20 Cr, TiN, four types of photoresist, resist pen, Parylene-C, and spin-on polyimide. Selected samples were etched in 35 different etches: isotropic silicon etchant, potassium hydroxide, 10:1 HF, 5:1 BHF, Pad Etch 4, hot phosphoric acid, Aluminum Etchant Type A, titanium wet etchant, CR-7 chromium etchant, CR-14 chromium etchant, molybdenum etchant, warm hydrogen peroxide, Copper Etchant Type CE-200, Copper Etchant APS 100, dilute aqua regia, AU-5 gold etchant, Nichrome Etchant TFN, hot sulfuric+phosphoric acids, Piranha, Microstrip 2001, acetone, methanol, isopropanol, xenon difluoride, HF+H/sub 2/O vapor, oxygen plasma, two deep reactive ion etch recipes with two different types of wafer clamping, SF/sub 6/ plasma, SF/sub 6/+O/sub 2/ plasma, CF/sub 4/ plasma, CF/sub 4/+O/sub 2/ plasma, and argon ion milling. The etch rates of 620 combinations of these were measured. The etch rates of thermal oxide in different dilutions of HF and BHF are also reported. Sample preparation and information about the etches is given.

/pdf/etch-rates-for-micromachining-processing-part-ii-2gdyzs6x1d.pdf

Etch rates for micromachining processing-Part II

Diffusion in silicon of elements from columns III and V of the Periodic Table is reviewed in theory and experiment. The emphasis is on the interactions of these substitutional dopants with point defects (vacancies and interstitials) as part of their diffusion mechanisms. The goal of this paper is to unify available experimental observations within the framework of a set of physical models that can be utilized in computer simulations to predict diffusion processes in silicon. The authors assess the present state of experimental data for basic parameters such as point-defect diffusivities and equilibrium concentrations and address a number of questions regarding the mechanisms of dopant diffusion. They offer illustrative examples of ways that diffusion may be modeled in one and two dimensions by solving continuity equations for point defects and dopants. Outstanding questions and inadequacies in existing formulations are identified by comparing computer simulations with experimental results. A summary of the progress made in this field in recent years and of directions future research may take is presented.

Point defects and dopant diffusion in silicon

In this study we report on sub-wavelength nanostructuring of sputtered Indium-Tin-Oxide (ITO) films using a high-repetition rate near-infrared Ti:Sapphire laser system based on a 85 MHz, sub-10 fs resonator. Our experiments demonstrate that cuts as small as 20 nm in width can be generated by ablation. ITO nanowires ranging in size down to 50 nm were produced by laser writing at radiant exposure below the ablation threshold followed by etching in hydrochloric acid. The dependence of the minimum structure size on irradiation and material parameters as well as the electrical properties of the nanowires were investigated.

Nanoscale laser writing of Indium-Tin-Oxide nanowires

Anordnung zur Messung von Beschleunigungen, die folgende Merkmale aufweist:
 a) die Anordnung besteht aus wenigstens zwei einzelnen, auf einem gemeinsamen
Substrat angeordneten Einzelsensoren mit jeweils einer
Hauptempfindlichkeitsachse, b) jeder Einzelsensor weist ein freitragendes, mit einem Biegebalken
verbundenes Paddel mit einem Schwerpunkt als seismische Masse
auf, c) jeder Biegebalken weist Mittel zur Messung der Auslenkung der seismischen
Masse auf, d) alle Biegebalken sind parallel zur Oberflache des Substrats angeordnet
und e) die Hauptempfindlichkeitsachsen der jeweiligen Einzelsensoren weisen
jeweils einen Fehlwinkel zur Normalen der Substratoberflache
auf.

Anordnung zur dreiachsigen Messung von Beschleunigungen

A near-infrared 12-fs laser scanning microscope was employed for structuring glass surfaces. A Ti–sapphire laser operated at 85 MHz and emitted light pulses at wavelengths around 800 nm. A focused laser beam with a mean power of less than 27 mW, corresponding to a maximal pulse energy of 318 pJ, was applied for line scanning at and beneath the surfaces of cover slips as well as of a filter glass BG39. Periodic arrangements of dots along the processed lines were produced through digital control of the scanner. Depending on the pulse energy and the scan speed, the diameter of the dots ranged from 550 nm down to 100 nm. For the cover slips, the dots occur as cavities after wet chemical etching. For BG39, which exhibits strong near-infrared absorption, both chains of cavities and bumps can be generated without any etching process. The result shows that structures with a size down to 1/8λ can be generated, probably through nonlinear single-photon processes confined within the focal volume.

Submicron-dot chains at and beneath surfaces of glasses written by a picojoule 12-fs laser scanning microscope

Im vorliegenden Beitrag wird ein neuer Ansatz eines MEMS-basierten (Micro-Electro-Mechanical System) piezoelektrischen Energiewandlers vorgestellt. Dieser MEMS-Generator basiert im Wesentlichen auf einer massebeaufschlagten piezoelektrischen Membran, die in der Lage ist, umgebende mechanische Vibrationen in elektrische Energie zu wandeln. Im Folgenden wird ein entsprechender MEMS-Entwurf präsentiert, wobei im Speziellen auf die Optimierung der geometrischen Anordnung des Bauteils eingegangen wird. Darüber hinaus demonstrieren erste Experimente die Funktionsweise des Energiewandlers. Elektrische Messungen zeigen Abhängigkeiten bezüglich elektrischer Last, Schichtstress in der Membran und Elektrodenstruktur. Der typische Frequenzgang eines piezoelektrischen Mikrogenerators wird ebenso vorgestellt. A new approach of a MEMS (Micro-Electro-Mechanical System) power generator based on a piezoelectric membrane is presented. A MEMS design is introduced taking an optimum membrane thickness and a beneficial electrode structure into account. Experiments demonstrate the functionality of the energy converter. Electrical measurements show dependencies regarding electrical load, residual stress within the diaphragm, and electrode design. The frequency response of the device is also presented.

MEMS-basierter piezoelektrischer Energiewandler (MEMS-based Piezoelectric Energy Converter)

L'invention porte sur un filtre mecanique a particules (214) comportant une membrane (312), laquelle possede un grand nombre de pores (316), au moins une zone partielle, accessible au fluide a filtrer, de la surface de la membrane (312) etant fabriquee en un materiau carbone ayant une structure de type diamant. L'invention porte en outre sur un procede de fabrication d'un tel filtre a particules (214).

Helmut Seidel

Papers

Nanoscale laser writing of Indium-Tin-Oxide nanowires

Anordnung zur dreiachsigen Messung von Beschleunigungen

Submicron-dot chains at and beneath surfaces of glasses written by a picojoule 12-fs laser scanning microscope

MEMS-basierter piezoelektrischer Energiewandler (MEMS-based Piezoelectric Energy Converter)

Filtre à particules, ainsi que son procédé de fabrication