Comparison of excess 1/f noise spectra in trimmed and untrimmed thick filmresistors

Low frequency excess 1/f noise in the frequency range 1-10(4) Hz and conduc tivity are measured and analysed in trimmed and untrimmed bismuth ruthenate thick film resistors (TFRs) with an aspect ratio of 0.04. The excess flick er noise exhibits a 1/f(gamma) spectrum with gamma approximate to 1 which s cales with the square of the de current. Although both the temperature coef ficient of resistance and the conductivity of the TFRs did not change signi ficantly upon trimming, we observed a substantial increase in the relative noise index C for trimmed TFRs. The Hooge parameter alpha(H) for untrimmed TFRs was estimated to be similar to 1.1 x 10(-3) Application of the Hooge m odel to trimmed TFRs indicated that trimming increases the values of alpha( H). Further, if V is the volume of the TFR, the noise of the trimmed resist ors did not exhibit the expected C proportional to 1/V behaviour that is ob served for untrimmed TFRs. These observations may be due to a combination o f reasons such as laser trimming-induced inhomogeneous damage or a possible reduction in the Vandamme effective volume; trimmed TFRs exhibited an effe ctive volume in the range 0.18-0.38.