An array system of optically pumped atomic magnetometers (OPAMs) that uses potassium vapor cells requires the quantity of potassium enclosed in the cells to be uniform. We describe a tablet-shaped potassium source, which generates a fixed amount of potassium, for fabricating homogeneous vapor cells. The tablet consists of a tiny microstructured plate covered with a layer of raw materials. Two sets of raw materials were chosen: one was a mixture of KCl and BaN6, and the other was KN3. The efficiency of potassium generation depended on the shape and size of the microstructure for each raw material, and a maximum potassium yield of 65% was observed for KN3 tablets. The source tablets containing KCl and BaN6 were used to build vapor cells by a microfabrication technique, and the source tablets containing KN3 were used to introduce potassium into glass cells, which were confirmed to work in highly sensitive OPAMs.