ABSTRACT
The ideas presented in Section 4.3 also apply to thin-film resistors. The value of a resistor is determined by the sheet resistivity and the length-to-width ratio (aspect ratio). Usually, the substrate is coated completely with resistive material and then conductive material. The conductors and resistors are then etched back using appropriate photoetching techniques. Because of the accuracy obtained in photoprocessing, very fine line widths can easily be achieved. Typical line widths can be as low as 1 to 2 mil. The film deposition and uniformity can be controlled to about ±10%, giving as processed resistors with tolerances of about 10 to 151. Most thin-film resistors can be brought into about ±5% tolerances with heating at elevated temperatures; this is caused by annealing or by oxidation of the surface metal. This heating at elevated temperatures also helps produce very stable resistors.
