Evaluation of R-F Noise Measurements for Diode Reliability Improvement by the Elimination of Weak Units

ASTUDY of the noise characteristics of a general purpose silicon diode (type 1 N645) was made to determine whether excessive r-f noise is correlated with high failure rates. The selection of the abnormally high noise diodes was made by monitoring the noise level across the diode as it was excited with an a-c voltage within the diode maximum ratings. Mechanical stress in the form of impacts within the rated value was applied simultaneously to aggravate structural imperfections. Noise measurements at 25 mc were used for the recognition of weaknesses and early failure. The forward and reverse characteristics were obtained for the diodes exhibiting high r-f noise. These were compared with the characteristics of diodes exhibiting normal r-f noise. In the forward direction, no difference was obtained; in the reverse biased condition, the average leakage current of all the noisy diodes was considerably higher than the average of the quiet group. In addition it was noted that the r-f noise level of the diodes was almost inversely proportional to the avalanche breakdown voltage. The diodes were also tested for 1/f noise; 35% of the r-f noisy diodes also exhibited high 1/f noise, whereas only 1.2% of the diodes having normal r-f noise exhibited high I/f noise. The noise spectrum taken on a number of the silicon diodes indicates that the 1/f noise extends into the megacycle region.