Fundamentals on Bionanotechnologies - Bionanoelectronics: Bioinquiring and Bioinspired Devices - page 51

a

isotropic
etching

b

anisotropic etching -
dependent on orientation

c anisotropic etching -

independent of orientation

Fig. 1.51 Si etching techniques

There are many other types of lab-on-chips, all performing the following tasks:

• Fluid transport
• Fluid control (valves)
• Fluid mixing
• Fluid separation
• Detection
• Readout
The development of microfluidic technology is related to the development of
microelectromechanical systems (MEMS). Although there are other materials in
which microfluidic devices are made, in what follows, we will briefly describe some
Si MEMS techniques to fabricate them because in this way, the microfluidic devices
can be integrated with electronic devices, which are able to process the information.
The microfluidic devices are fabricated by etching silicon.
Various etching shapes result from different techniques, as shown in Fig. 1.51 .
There are two main categories of etching techniques: wet or chemical etching,
illustrated in Fig. 1.51 a, b, and dry or plasma etching, shown in Fig. 1.51 c. The final
goal is to fabricate high-precision and low-roughness microchannels with control-
lable shapes or other microfluidic devices using the etching process. However, ideal
vertical walls can be realized only with plasma-etching techniques.
There are two basic types of micromachining techniques: bulk micromachining
and surface micromachining. In bulk micromachining, a specific mechanical struc-
ture is fabricated from a wafer by etching the back side of it. A typical example,
of producing a micromechanical membrane, is illustrated in Fig. 1.52 . Such a mem-
brane, with a thickness of 1m and a surface as large as 2 2 cm 2 , can be produced
using chemical or plasma-etching methods. In the case of bulk micromachining,