The SM series is a range of high-precision thin film chip resistors engineered specifically for the upper end of the surface-mount resistance range, covering values from 500kΩ to 1GΩ. This resistance window is technically demanding for thin film technology: achieving stable, accurate gigaohm-level resistance values in a compact SMD package requires careful control of the resistive film composition, deposition process, and laser-trimming accuracy. The SM series addresses this challenge with tolerance grades of ±0.1%, ±0.25%, and ±0.5%, and TCR options of ±25, ±50, and ±100 ppm/°C — performance levels that are substantially better than thick film alternatives in the same resistance range and that make the series suitable for precision high-impedance circuit design across a wide operating temperature range.
Power ratings span 1/8W to 2W across the available package sizes, which, given the high resistance values involved, translate to relatively modest operating voltages in continuous-use applications. The thin film construction delivers the low noise characteristics essential in high-impedance analogue circuits, where Johnson–Nyquist thermal noise and current noise from the resistive element directly limit the signal-to-noise performance of the surrounding circuit. Long-term stability under sustained load is a defining requirement for this class of resistor, and the SM series is engineered for extended load life — maintaining resistance within specification over thousands of operating hours, not only on initial measurement.
As a thin film type, the SM series is part of the same RARA precision chip resistor family as the AR series (1Ω to 3MΩ) and the ARN series (aluminium nitride substrate, 50Ω to 30.1kΩ, up to 6W). Where the AR series covers the broad mid-range of resistance values, the SM series extends precision thin film performance into the high-impedance territory occupied in many precision instruments, electrometers, and ionisation detector circuits. The series is qualified in accordance with MIL-STD-202 and JIS-C 5201, covering thermal shock, endurance, damp heat, high-temperature exposure, solderability, and resistance to soldering heat. Components are RoHS compliant and are supplied in tape-and-reel format for automated surface-mount assembly.
Part numbering for the SM series encodes the package size, nominal resistance value, tolerance grade, TCR, and packaging format, enabling complete and unambiguous specification. The three tolerance grades — ±0.1%, ±0.25%, and ±0.5% — and three TCR grades allow the SM series to serve both the tightest-specification precision instrument designs and more cost-sensitive production applications within the high-resistance SMD segment, from a single product family with consistent construction and qualification.
