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

Low frequency excess 1/f noise in the frequency range 1-104 Hz and conductivity are measured and analysed in trimmed and untrimmed bismuth ruthenate thick film resistors (TFRs) with an aspect ratio of 0.04. The excess flicker noise exhibits a 1/f γ spectrum with γ ≈ 1 which scales with the square of the dc current. Although both the temperature coefficient of resistance and the conductivity of the TFRs did not change significantly upon trimming, we observed a substantial increase in the relative noise index C for trimmed TFRs. The Hooge parameter α H for untrimmed TFRs was estimated to be ∼ 1.1 × 10−3. Application of the Hooge model to trimmed TFRs indicated that trimming increases the values of α H. Further, if V is the volume of the TFR, the noise of the trimmed resistors did not exhibit the expected C ∝ 1/V behaviour that is observed for untrimmed TFRs. These observations may be due to a combination of reasons such as laser trimming induced inhomogeneous damage or a possible reduction in the Vandamme e...