Novel transducer for potentiometric sensors

Polish Patent:

Dybko A., Chudy M., Wróblewski W., Wojciechowski K., Brzózka Z.

date of application 29.08.2001

The main idea of the transducer design was to make it compatible with a flow-head developed and described in the previous work (see the previous patent). The head is capable of mounting of various types of chemical sensors developed in a back-side configuration. The new transducer was designed in the form of a square (5 by 5 mm, 0.5 mm in thickness) based on a typical printed circuit board (PCB) technology. A typical double-sided layer PCB was used as a basic material. The stages of the transducer development are ordinary processes occurring during the preparation of a double-sided PCB. A special mask was prepared in order to achieve a structure shown in figure.

Schematic cross-section of a new transducer for potentiometric sensors.

After etching of useless copper area, the transducer structure was electrochemically covered with a silver layer (30 um in thickness) and next a silver chloride was fabricated on the top of it. There are many methods of silver chloride fabrication. The quality and homogeneity of this layer is crucial for the work of the whole transducer/sensor. Its thickness should not be too low because the silver must be fully covered with chloride and on the other hand too thick layer can cause errors in the sensor measurements due to improper conversion process. In this work, we have used an electrochemical method of silver chloride developing. It was found that the layer which was created after 10 minutes of electroplating in a 0.1 M solution of KCl with the application of 0.3 V is optimal from the measurement properties of view. In this way, a miniature silver/silver chloride electrode was formed. The active layer was formed in a shape of a circle (diameter of 1 mm), which is surrounded by an o-ring (inner diameter of 2 mm) when mounted in the flow-head. A metallised hole serves here as an ohmic connection between the front and back side of the structure which leads to a so-called back-side contact transducer. When the structure is mounted in the flow-head the o-ring is squeezed and the whole system is sealed, so there is no possibility of any leakage through the hole. An elastic spring contact was used on the back side of the transducer to connect it with the measuring set-up.