High-voltage pulse stressing of thick-film resistors and noise
Introduction
Several papers were published dealing with different problems of understanding the nature of noise in thick-film resistors [1], [2], [3] but the possibilities that noise measurements can be used for thick-film resistor quality evaluation and evaluation of degradation under stress are insufficiently investigated. A reason for that may be complexity of thick-film resistor microstructure and conduction mechanisms as well as poor understanding of their relationship with noise. On the other hand, different conditions of thick-film resistor application are inducing the need to investigate their behavior under stress, especially high-voltage pulse stress. Several papers dealt with high-voltage pulse trimming of thick-film resistors [4] and behavioral analysis of thick-film surge resistors that are being used in telecom systems as protection under extreme working conditions such as lighting strikes or power cross conditions on external lines [5], [6], although the problem is physically different for surge resistors because of their low ohmic resistances. However, bearing in mind the present miniaturization trend and mass usage in up-to-date very sensitive communication systems, little attention has been paid to the influence of high-voltage pulse stressing on structure and noise performances of conventional thick-film resistors [7], [8]. In this paper the results from a study of high-voltage pulse stressing effects on thick-film resistors are given using resistance measurements as well as measurements of low-frequency noise parameters––resistance noise spectrum and noise index. Experiment––materials, test samples and terms of high-voltage pulse stressing and measurements are described in Section 2, and experimental results and discussion are given in Section 3. Special attention is paid to investigation of correlation between high-voltage damages and low-frequency noise and to possibility of using low-frequency noise for diagnostics of microstructure defects in resistors caused by high-voltage pulse stressing.
Section snippets
Materials and test resistors
Behavioral analysis of thick-film resistors subjected to high-voltage pulse stressing was performed using two groups of thick-film test samples with different resistor geometries (Fig. 1). First group of test samples (Fig. 1a) contains 18 resistors of width w=1 mm and different lengths, while second group of test samples (Fig. 1b) contains 15 resistors with different geometries, both lengths and widths. Test samples were formed on ceramic alumina (96% Al2O3) substrates using conventional
Experimental results and discussion
In order to illustrate performed experiment, typical results obtained by resistance, voltage noise spectrum and noise index measurements for thick-film resistors that were subjected to high-voltage pulse stressing and which degraded but did not fail catastrophically are given in Fig. 3 and Table 1. The results are given for resistors with identical geometries (1 × 2 mm2) and the initial resistance of 16 kΩ from the test-sample group A that were subjected to the impact of 11 pulses with 1500 V
Conclusion
In this paper the results obtained from resistance, noise voltage spectrum and noise index measurements performed on two groups of test resistors based on two commercially available thick-film resistor compositions with different sheet resistances and subjected to high-voltage pulse stressing, are given. Correlation between resistance and low-frequency noise changes and high-voltage pulse stressing is observed. It is shown that low-frequency noise, expressed through noise index or resistance
Acknowledgements
This research was partially supported by the Serbian Ministry of Science and Technology (contract IT.1.04.0062.B).
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