Abstract
This paper explores the key developments in thin film resistive trimming geometry for use in the fabrication of discrete precision resistors. Firstly an introduction to the laser trimming process is given with respect to well established trim geometries such as the plunge, 'L' and serpentine cuts. The effect of these trim patterns on key electrical properties of resistance tolerance and temperature co-efficient of resistance (TCR) of the thin films is then discussed before the performance of more recent geometries such as the three-contact and random trim approaches are reviewed. In addition to the properties of the standard trim patterns, the concept of the heat affected zone (HAZ) and ablation energy and the effect of introducing a 'fine' trim in areas of low current density to improve device performance are also studied. It is shown how trimming geometry and laser parameters can be systematically controlled to produce thin film resistors of the required properties for varying applications such as high precision, long term stability and high power pulse performance.
Highlights
For thin film resistors it is generally impossible to deposit batches of product with resistance tolerances better than about 10% [1,2,3]
This paper introduced the laser trimming process which can be thought as the most precise and reliable method in order to adjust the resistance value of bar-shaped thin film resistors
It is worth noting that trimming geometries play an important role on the characteristics of the resistors such as stability and tolerance accuracy
Summary
For thin film resistors it is generally impossible to deposit batches of product with resistance tolerances better than about 10% [1,2,3]. This is due to problems in attaining uniform sheet resistance, but mainly due to dimensional variation of the individual resistor elements in the batch, a problem which is amplified as the resistor size decreases [3, 4]. This paper discusses the laser trimming process of thin film resistors with regard to both conventional and well established trim patterns and the influence of their geometry on key electrical performance properties such as resistor tolerance and temperature co-efficient of resistance (TCR).
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