Microstructured glass devices

Viscous flow in microstructured glass devices, which is responsible for the rounding of edges and the deformation of walls, occurs during the postcrystallisation of UV-sensitive devices which is performed to improve their mechanical properties (see Sect. 1.2.4). Certain technical provisions are required to prevent the undesired deformation of glass devices. 

To eliminate bubbles and chemical inhomogeneities, a fining and homogenisation step has to be followed. These process steps are described in the following section considering the problems that may occur if a microstructured glass device shall be produced. 

Properties and Selected Applications of Microstructured Glass Devices... 

Considering the electrical, chemical and optical requirements for microstructured glasses, quartz glass should be the most widely used glass for such applications. However, that is not the case. Because of its lack of workability quartz glasses are more commonly used as tools in the production of microcomponents rather than the microstructured device itself. 

The mechanical properties of photostructurable glasses allow the fabrication of spring-like mechanical sensor devices, because of their linear stress-strain behaviour (see also Sect. 11.1.1). However, for such applications it is necessary to detect the distortion of these devices. Real microstructured glass springs or other microstructured glass components could be used... 

Fig. 1.50. Refractive index at A = 635 nm near the surface of microstructured, Na+ exchanged FS 21 glass devices [201]. The exchange temperature was varied between 320 and 400° C and the residence time in the melt was 210 min...

Microstructured glasses are also used in biotechnology, for instance, in separation processes. For this purpose capillary systems are used in medical and biochips. Figure 11.8 shows t3cpical elements and design features of a medical chip. The elements shown were successfully tested as capillary electrophoresis chip [28]. Using this microfabricated device the successful separation of amino acids was demonstrated. It can also be used to separate blood components. 

A chip-type micro reactor array comprises parallel mixer units composed of inverse mixing tees, each followed by a micro channel that it is surrounded by heat exchange micro channels (so called channel-by-channel approach similar to the tube-in-tube concept). Such an integrated device was developed as a stack of microstructured plates made of a special glass, termed Foturan (Figure 4.26). The integrated device was attached to PTFE tubes of various lengths. 

This coupled electrorotation mixer was actually not built as a complete device, but realized as a prototype version with simple microstructures, which were made by sputtering on to glass cover slips [95], By photolithography a small gap was etched in the middle of the coated slip to separate it into two equal halves. The latter are used as two electrodes of equal size. A wedge, freshly cut from the comer of a raw material piece, is placed on the gap as a kind of fixed microstructure to perform as the static dipole object so that an adjacent microsphere can be set into rotation. 

Figure 1.79 Microstructured four-plate glass stack of the interdigital micro mixer (left) and assembled device with steel frame (right) [124] (source IMM).

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