TEMPERATURE EFFECT ON OXIDIZED SILICON RE FLECTIVITY - EXPERIMENTAL-DETERMINATION OF THE RELATIVE SENSITIVITY - APPLICATION TO TEMPERATURE NONCONTACT MEASUREMENTS ON THE SURFACE OF A GTO THYRISTOR IN COMMUTATION

Temperature effect on the absolute reflectivity of oxidized silicon is experimentally studied in the spectral range 300 nm < lambda < 500 nm . R(lambda) spectra are measured for 25 degrees C < T < 225 degrees C with the precision Delta R/R = 2 x 10(-3). The largest relative variat ions of R are observed near direct interband transition: E(1) = 3.4 eV . In this case, the relative sensitivity R(-1)(dR/dT) reaches the maxi mum value (2.4 +/- 0.4) x 10(-4) K-1 which is about two times higher t han in the case of bare silicon. This result is used to make a tempera ture contactless measurement, by a technique based on reflectometry, a long the gate-cathode junction on the upper face of a 1,200 volts gate turn-off thyristor operating at 400 Hz in the switching mode. The siz e of the optical probe is 20 micrometers, and the smallest temperature variation that can be detected is 10 degrees C. The measurements show a noticeable variation of heating coefficient dT/dE according to the probe's position, dissipated energy E at turn-off being constant (1 mJ < E < 25 mJ). Maximum values of the junction temperature were found a s high as 275 degrees C and 350 degrees C, according to the considered area on the chip.