Development of a Oxygen Sensor for Marine ... - DTU Nanotech

28 CHAPTER 4. SYSTEM DESIGN
until it solidifies. Experiments have been made by M. Dawgul et. al. [36], in
which a membrane has been spin coated on the wafer. The results from this
however were not good, as the membrane often ended up sliding off, or at
best varied greatly in thickness, thereby lacking in regards to the feasibility
of being able to create a preset, uniform membrane thickness.
A logical solution to this has been used by M. Wittkampf et. al [37] where
a second wafer is anodic bonded to the first, with the second wafer having a
hole created with a wet isotropic etch where the exposed part of the sensor is,
there by creating a hole that the membrane liquid can be ’poured’ into. This
is a fairly simple process, however the basic of this design makes it a little
more difficult, as a circular rather than a rectangular hole have to be made.
However it is a problem that can be overcome. In the initial design, the
’O’-ring will be used as a ’container’ for the electrolyte and the membrane.
Also it should be mentioned that a micro electrode have the advantage over
a macro electrode, in that the diffusion occurs in all directions, where as with
the macro it only have diffusion in one direction[38]. Hence at macro scale
the oxygen will be consumed faster at the electrode, and thereby influence
the measurements. (See Figure 4.1)
Figure 4.1: Micro electrodes have diffusion to all directions while Macro only
have to one, why at macro scale setup the oxygen is consumed
faster at the electrode.
4.2 Actual Design
Four ’major’ designs, each with some variant sub design, have been created,
taking into consideration some of the experiences that have already been
made by others[37, 39, 36, 38, 40, 41]. The idea behind the main one as