Cryogenic applications require resistors with a structural integrity capable of withstanding extreme temperature cycling without damage or detriment to performance. In addition, the different expansion and contraction rates of composite materials in resistors may induce discontinuities during temperature excursions that are not evident at temperature extremes, making an unreliable resistor appear normal. A resistor used in cryogenic applications must also return to its initial value with no resistance drift.
In the video demonstration, a 10 kΩ VSMP0805 precision foil resistor is taken from a room temperature of +25°C and immersed in a flask of liquid nitrogen with a temperature of −196°C. The resistor is stabilized at −196°C, then removed from the flask and allowed to return to its original 25°C temperature.
Continuous monitoring during the test shows that the resistor not only survived its excursion to −196°C, but also exhibited a TCR of only -5 ppm/°C, experienced no discontinuities, and returned to its starting resistance value when again at room temperature.
In addition to an extensive line of standard products, VFR designs and produces unique customer-oriented products using its Z-Foil technology. Special chip stabilization protocols, including extreme environmental conditions, are added to the production line, and specially developed stress protocols are included in post-manufacturing operations (PMO) to achieve even higher degrees of stability and reliability for extraordinary high/low-temperature applications.
When similar stress extremes are applied to thick film or thin film resistors, particulate shifts in thick film and in sputtered thin film elements, or crystal deformation in evaporated/deposited thin film elements, result in permanent changes in resistance and a reduction in the device”s overall stability. In applications likely to experience cycling through, or extended dwell time at, extreme high or low temperatures, and where stability is the main concern, Bulk Metal Foil and Z-Foil technology assure the best performance and reliability.