Two-color Si PIN photodetectors


For contactless (remote) temperature measurement it is convenient to use the so-called two-color photodetectors that measure source radiation intensity at two close wavelengths ("colors") and compare them with standard dependence of blackbody (Planck source). The intensities of the source are determined by measuring currents of two silicon PIN photodiodes in a sandwich configuration. Two almost identical silicon PIN photodiodes are mounted to that purpose one above the other at a close distance of about 100 micrometers so that source radiation impingent to the top one partially absorbs in it, while the unabsorbed part of the ratiation arrives to the bottom diode. This configuration has a large advantage over other methods of remote temperature measurement, because it does not depend on the emissivity of the radiation source which is at that stage still unknown. Also, since the same radiation arrives to both diodes, measurement is independent on obstacles that may be present at the optical path between the radiation source and the detector (dust, smoke, steam) as well as on the movements of the radiation source. Two-color diodes are experimentally investigated in the centre using MEMS (anisotropic etching of silicon, anod bonding between silicon and Pyrex glass, additional etching of silicon after anodic bonding, glass cutting). Diodes are mounted in a sandwich configuration in order to simplify mounting and bonding of contacts.