THICK-FILM PHOTOSENSORS

The use of photoconductive inks based on CdS and CdSe to form photoresistors using standard thick-film hybrid circuit techniques is described. The properties of photoconductive sensors made using these materials together with electrodes printed using standard silver-palladium conductor inks are reported. The sensors showed a wide dynamic range. Photoresistors with an area of 80 mm(2) had a dark resistance of the order of 1 G Omega falling to as low as 75 Omega in bright sunlight, for a sensor formed from a mixture of CdS and CdSe. Response times varied from 2.5 ms for CdSe at high illumination to 2 s for CdS at low illumination. It is shown that the best overall performance is obtained from films formed from a 1:1 mixture of CdS and CdSe. Screen-printed photoconductive array sensors and a potentiometric position sensor are described.