Fabrication technologies - Micromixers Fundamentals Design and Fabrication - page 114

4.3 Metallic Microtechnologies .......................................................................................................... 150
4.3.1 Metals as substrate materials......................................................................................150
4.3.2 LIGA.........................................................................................................................151
4.3.3 Micro-electro-discharge machining..............................................................................152
4.3.4 Focused ion beam micromachining .............................................................................152
4.3.5 Powder blasting .........................................................................................................152
4.3.6 Ultrasonic micromachining.........................................................................................153
4.4 Packaging ................................................................................................................................... 153
4.4.1 Anodic bonding .........................................................................................................153
4.4.2 Direct bonding...........................................................................................................154
4.4.3 Adhesive bonding ......................................................................................................155
4.4.4 Eutectic bonding .......................................................................................................155
4.5 Conclusions ................................................................................................................................. 155
References ......................................................................................................................................... 156

Micromixers can be fabricated using microtechnologies that were previously developed for micro-
electromechanical systems (MEMSs). Microdevices have feature sizes ranging from 1 m to 1 mm. In

most cases, these devices are fabricated in a batch process with techniques such as photolithography or
imprinting. In the early development stage, most of these devices were fabricated based on established
technologies from microelectronics where thousands of devices can be fabricated on a single silicon
wafer. Miniaturization increases the functionality significantly and decreases the fabrication cost.
Micromixers can benefit from increasing functionality through the integration of electronic,
mechanical, optical, fluidic, and other technologies in a single device. This functionality may lead to
new applications, especially in life sciences.
Micromixer is one of the many micromachined devices that were reported in the past. With almost
30 years of development, micromachined devices are numerous and cover a wide range of applica-
tions. While in the 1980s and early 1990s, the development of microdevices was focused on physical
sensors such as pressure sensor, accelerometer, and gyroscope, recent development points to research
areas such as radio frequency (RF) MEMS, optical MEMS, and BioMEMS for biochemical and
chemical applications [1] . Most of the microdevices in the past were fabricated either in single-
crystalline silicon with bulk micromachining or in polycrystalline silicon using surface micro-
machining. Silicon has the advantages of established technologies coming from the decades-long
development of microelectronics. However, silicon has poor mechanical and tribological properties,
cannot withstand extremely high operation temperature, and, in some cases, is not biocompatible as
well as chemically compatible. The need of other materials with properties suitable for applications in
the chemical industry or life sciences leads to the development of microtechnologies based on other
materials, such as diamond thin film, silicon carbide, polymer, and metals.

m

4.1 SILICON-BASED MICROTECHNOLOGIES
The history of silicon-based micromachining dates back to the 1960s, when thin silicon membrane was
etched tomake pressure sensors. Bulkmicromachining subsequently has been used for making inkjet print