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A thin film resistor is an electronic component that impedes the flow of electricity, made by vacuum deposition methods. It has a thin layer of resistive material and can be trimmed for accuracy. They are used in demanding applications such as high frequency communications and computing.
A thin film resistor is a resistor, a common electronic component, made by vacuum deposition methods by placing a resistive material on a substrate. It differs from thick film resistors not in material or function but in manufacturing. This rather technical definition is better understood in parts.
A resistor refers to an element in the architecture of electronics that impedes the flow of electricity. An increase in the resistance value will require an increase in the applied voltage to maintain a constant electric current. Mathematically, it is the R value in Ohm’s law, which relates current (I) and voltage (V) – shown by the formula V=I/R – or in another version, expresses the relationship between power (P ) and voltage – as in the formula P=V2/R. By enabling changes to voltage or current, resistance is part of the “language” of electronics that allows mathematical expressions to be evaluated electronically.
There are two main vacuum deposition methods used in the fabrication of a thin film resistor. The material to be used as a resistor, called resistive material, is vaporized by applying electrical heat and then condensed onto a surface. Secondly, in sputtering, the ions of a gaseous plasma impact and excite the molecules of the resistive material. These molecules are expelled from the material and onto a substrate.
The first method can be visualized as spray paint – a direct application of material. The second can be thought of as the spray of a wheel running through a mud puddle, an indirect application of material. In both cases, the layer of resist material is so thin that it is only a few atoms or molecules deep. By conducting the process under vacuum, a uniform layer is obtained and contaminants or unwanted chemical reactions are avoided.
The materials from which the resistors are made include compounds of tantalum, bismuth and ruthenium, as well as chromium, nickel and lead. There are thousands of possible compounds, including new organic blends. A thin film resistor is more expensive than other types, but also has tighter tolerances. These resistors are typically used in more demanding applications such as high frequency communications and computing.
Like their thick film cousins, thin film resistors can be trimmed to increase the accuracy of their evaluation. Resistors are trimmed by depositing slightly excess of the required material. Then computer-controlled lasers etch the material until the desired resistance value is reached. The laser cutting refinement of an already accurate thin-film resistor is an indication of the very tight tolerances required by today’s small, fast, powerful, and less heat-producing electronic devices.
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