Samenvatting

The aim for this thesis is to set up and develop electroplating technique for depositing gold layers. This gold layer will be used as an thermalisation layer in a cryogenically cooled X-ray detector. Key material parameter for the gold layer is a low thermal resistivity at cryogenic temperatures. Since electroplating seemed to be the appropriate deposition technique SRON started up electroplating experiments to deposit gold.
Within this thesis a literature study has been worked out on resistivity at low temperature and on the basic principles of electroplating technique. The experimental part of this thesis comprises the setup and the deposition of gold layers by electroplating. In addition the gold layers were tested and characterized on resistivity at room temperature and at cryogenic (4.2 kelvin) temperature.
The experimental part was an important aspect of this study, particularly establishing a stable setup for the electrodeposition of the gold layers. The plating bath characterization was obtained by conducting an Cyclic Voltammetry. The next characterization was done by determining the amount of bath agitation by mechanically stirring the electrolyte, it was found out that a stirring rate of 500 rpm was sufficient to obtain reproducible depositions. The last characterization was done by assessing the difference between electroplating using current bias or voltage bias. It turned out that current bias showed better reproducibility of the deposited gold layers and their thickness.
With the characterized plating bath defined the plating parameters could be optimized to deposit gold layer with the preferred resistivity values. First the resistivity values of the deposited layers were measured room temperature, then a selection was measured at temperature of 4 Kelvin.
The resistivity at room temperature was found to be around 3 μΩ∙cm which was slightly higher than values demonstrated by other groups. At low temperature we measured resistivity values from 0.3 μΩ∙cm till 0.46 μΩ∙cm. The lowest value was achieved by using electrolyte without the additive ‘brightener’. We assumed that this can be related to larger grain sizes in the microstructure of the gold layer. Compared to other groups the lowest resistivity value we have measured is still a factor of 6 higher than demonstrated by other groups.
Therefore more tests have be done with the electrolyte without brightener. This thesis will also give some suggestions how to proceed a further optimization process.