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

The fact that light carries both linear and angular momentum is well-known to physicists. One application of the linear momentum of light is for optical tweezers, in which the refraction of a laser beam through a particle provides a reaction force that draws the particle towards the centre of the beam. The angular momentum of light can also be transfered to particles, causing them to spin. In fact, the angular momentum of light has two components that act through different mechanisms on various types of particle. This Review covers the creation of such beams and how their unusual intensity, polarization and phase structure has been put to use in the field of optical manipulation.

Tweezers with a twist

Exercise Physiology: Energy, Nutrition and Human Performance

The ability to pattern materials in three dimensions is critical for several technological applications, including composites, microfluidics, photonics, and tissue engineering. Direct-write assembly allows one to design and rapidly fabricate materials in complex 3D shapes without the need for expensive tooling, dies, or lithographic masks. Here, recent advances in direct ink writing are reviewed with an emphasis on the push towards finer feature sizes. Opportunities and challenges associated with direct ink writing are also highlighted.

/pdf/direct-ink-writing-of-3d-functional-materials-3agrqrwm1s.pdf

Direct ink writing of 3D functional materials

Localized fluid flow measurements with an He-Ne laser spectrometer

A low-temperature bonding of vertical-cavity surface-emitting laser (VCSEL) chips on Si substrates was achieved by using plasma activation of Au films. After the surfaces of Au films were cleaned using an Ar radio frequency plasma, bonding was carried out by contact in ambient air with applied static pressure. The experimental results showed that surface morphological change (the reduction of asperity width) as well as removal of adsorbed organic contaminants by plasma treatment significantly improved the quality of joints. At a bonding temperature of 100degC, the die-shear strength exceeded the failure criteria of MIL-STD-883.

Low-Temperature Bonding of Laser Diode Chips on Silicon Substrates Using Plasma Activation of Au Films

Hybrid integration of multiple optical chips in three dimensions is an important technology for realizing highly functional, compact optoelectronic microsystems. In this paper, we report successful 3-D integration of optical chips performed using Au-Au surface-activated bonding (SAB) at a relatively low bonding temperature of 150degC. A glass substrate with the flip-chip-bonded photodiode chips was vertically stacked on a Si substrate with the bonded laser diode chip using Au-Au SAB. By applying this technique, compact and thin optical microsensors (2.8 mm times 2.8 mm times 1 mm thick) were fabricated. The feasibility of measuring velocity was demonstrated using prototype microsensors.

Au–Au Surface-Activated Bonding and Its Application to Optical Microsensors With 3-D Structure

GaAs dry etching using reactive–fast‐atom beam etching to obtain an etched mirrorlike surface is investigated. An etch rate of 0.1–0.6 μm/min is obtained when Cl2 gas is used, which is 50–100 times faster than when Ar gas is used. The etch rate ratio between GaAs and photoresist AZ‐1350J is more than 30. As a result, a trench with a depth of more than 10 μm and a width of less than 2 μm is easily fabricated under the etch conditions of a Cl2 gas pressure of 5–6.5×10−2 Pa, an accelerate voltage of 1.5–1.8 kV, and a substrate temperature of about 100 °C. The radiation damage caused by this etching is very small, and it is similar to that caused by wet chemical etching, in spite of the relatively higher accelerator voltage. The thickness of an induced damage layer is only 150 A. It is found that the radiation damage induced by reactive–fast‐atom beam etching decreased with an increase of the etch rate. It is confirmed that vertical, smooth, damage‐free etching can be easily attained with reactive–fast‐atom b...

Reactive–fast‐atom beam etching of GaAs using Cl2 gas

The feasibility of room-temperature (RT) bonding of vertical-cavity surface-emitting laser (VCSEL) chips on silicon (Si) substrates with Au microbumps was demonstrated by Au–Au surface-activated bonding. The diameter at the top, the height, and the pitch of Au microbumps measured approximately 5, 2, and 10 µm, respectively. Following activation of the Au surfaces with argon radio-frequency plasma, Au–Au bonding was carried out using contact at RT in ambient air. The measured results of light–current–voltage (L–I–V) characteristics indicated no significant degradation of the VCSEL chips after bonding.

https://iopscience.iop.org/article/10.1143/APEX.1.112201/pdf

Room-Temperature Bonding of Vertical-Cavity Surface-Emitting Laser Chips on Si Substrates Using Au Microbumps in Ambient Air

The micro-mirror apparatus of the invention has; a mirror 33 , a plurality of torsion springs 35, 36 for supporting the mirror 33 so as to be tiltable relative to an upper substrate 27 , a lower substrate 21 arranged facing a lower face of the mirror 33 , a convex portion 34 provided on an upper face of the lower substrate 21 and a plurality of lower electrodes 22, 23 formed on an outer face of the convex portion 34 . For the torsion spring 36 , an aspect ratio of height/width in a cross-section perpendicular to a longitudinal direction thereof is at least 1.8.

Renshi Sawada

Papers

Low-Temperature Bonding of Laser Diode Chips on Silicon Substrates Using Plasma Activation of Au Films

Au–Au Surface-Activated Bonding and Its Application to Optical Microsensors With 3-D Structure

Reactive–fast‐atom beam etching of GaAs using Cl2 gas

Room-Temperature Bonding of Vertical-Cavity Surface-Emitting Laser Chips on Si Substrates Using Au Microbumps in Ambient Air

Micro-mirror apparatus and production method therefor