VPG's New Hermetically Sealed Metrology, Laboratory, and Military Ultra-High-Precision Resistors Feature TCR to ±0.05ppm/°C, Load-Life Stability of 0.005%, and Tolerance to ±0.005%

The VHZ devices feature a TCR of ±0.2ppm/°C typical from -55°C to +125°C, +25°C ref., and ±0.05ppm/°C from 0°C to +60°C, resistance tolerance to ±0.005% (to 0.001% is available), load life stability to ±0.005% (50 ppm) at 70°C for 10,000 hours at 0.15 W, and Power TCR (ΔR due to self-heating) of ±5ppm at rated power of 0.6 W at +70°C and 0.3 W at +125°C.

The new hermetically sealed resistors released today offer an immediate answer to many resistor applications previously thought to be unsolvable, including secondary standards, feedback devices for operational amplifiers, precision voltage dividers, meter multipliers, precision bridge resistors, and decade voltage dividers. The VH102Z offers a resistance range from 10 Ω to 100 kΩ, while the VHZ555 resistor offers a resistance range of 4.99 Ω to 121 kΩ . The VHZ555 is manufactured on the same production line and is subjected to all the same process and lot control requirements imposed on the RNC90Z version, as well as all of the special screening, environmental conditioning, and documentation stipulations outlined in MIL-PRF 55182/9. Vishay Foil resistors are not restricted to standard values, and specific as required values (e.g. 1.2345 kΩ vs. 1 kΩ) can be supplied at no extra cost or impact on delivery time.

The devices' hermetic sealing eliminates the ingress of both oxygen, which degrades resistors over long periods, and moisture, which degrades resistors more quickly. Featuring a hermeticity of 10 ^-7 atmospheric cc/s maximum, the resistors offer a shelf life stability of 2 ppm total for at least six years. The devices are made with glass-to-metal seal enclosures employing Kovar eyelets which allow the copper leads to pass through the enclosure to minimize the thermal EMF from the lead junctions. Rubber fill between the metal housing and resistance element acts both as a mechanical damper and thermal transfer path.

The Bulk Metal precision Z-Foil resistor elements by VPG are virtually insensitive to destabilizing factors. Their element is a solid alloy that displays the desirable bulk properties of its parent material, and thus is inherently stable and noise-free. The alloy and matched substrate form a single entity with balanced temperature characteristics for an unusually low and predictable TCR. Resistance patterns are photoetched to permit trimming of resistance values to very tight tolerances.

The VH102Z and VHZ555 feature electrostatic discharge (ESD) immunity up to at least 25,000 V, a rise time of 1 ns, with effectively no ringing, a thermal stabilization time of <1 s (nominal value achieved within 10 ppm of steady state value), and current noise of <-40 dB. The devices offer a non-inductive (<0.08 μH), non-capacitive design, thermal EMF of 0.1 µV/°C maximum, a maximum working voltage of 300 V, and a voltage coefficient of <0.1 ppm/V, and they feature lead (Pb)-free or tin/lead alloy terminal finishes. For similar hermetically-sealed resistors with 0.001% tolerance, see model VHP100 or the VHA series.

The VHZ series was developed by the Vishay Foil Resistors Company as a new resistor concept, through the use of a proprietary Bulk Metal Z-Foil and new ultra-fine photo-etching techniques created by the company, so that the conductor can be considered a flat wire. Because the metals are not drawn, wound, or mistreated in any way during the manufacturing process, VHZ resistors maintain all of their design, physical, and electrical characteristics. The temperature coefficient of the resistor is carefully controlled through compensation techniques to eliminate the effect of different coefficients of expansions for all materials used in the resistor. With the VHZ devices, only a minimal shift in resistance value will occur during the device's entire lifetime. Most of this shift takes place during the first few hundred hours of operation, and subsequent change is negligible.

While the hermetically-sealed series of Bulk Metal Foil resistors is already more stable than other resistor technologies and more stable than any other foil resistors, this stability can be further improved through a specially selected process of stability enhancements. These enhancements may be achieved through special post-manufacturing operations (PMO testing), including short time overload, accelerated load life, and temperature cycling.

Samples and production quantities of the VHZ series resistors are available now, with lead times of five days for samples, and eight weeks for standard orders.