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    Over fifty years after its invention by physicist Dr. Felix Zandman in 1962, Bulk Metal® Foil technology still outperforms all other resistor technologies available today for applications that require precision, stability, and reliability. VFR Bulk Metal Foil products are offered in a variety of resistor configurations and package types to meet the needs of a wide range of applications. Introduced in 2000, Bulk Metal Foil products built on the revolutionary Z Foil Technology deliver an absolute temperature coefficient of resistance (TCR) of ±0.2 ppm/°C (–55°C to +125°C, +25°C ref.), one order of magnitude better than previous foil technologies. The lower the absolute TCR, the better a resistor can maintain its precise value despite ambient temperature variations and self-heating when power is applied. A specific foil alloy with known and controllable properties (Ni/Cr with additives) is cemented to a special ceramic substrate, resulting in a thermo-mechanical balance of forces. A resistive pattern is then photo-etched in the foil. This process uniquely combines the important characteristics of low TCR, long-term stability, non-inductance, ESD insensitivity, low capacitance, fast thermal stabilization, and low noise in one single resistor technology. These capabilities bring high stability and reliability to system performance without any compromise between accuracy, stability, and speed. To acquire a precision resistance value, the Bulk Metal Foil chip is trimmed by selectively removing built-in “shorting bars.” To increase the resistance in known increments, selected areas are cut, producing progressively smaller increases in resistance. In the planar foil, the parallel patterned element design reduces inductance; maximum total inductance of the resistor is 0.08 μH. Capacitance is 0.5 pF maximum. A 1 kΩ resistor has a settling time of less than 1 ns up to 100 MHz. Rise time depends on resistance value, but higher and lower values are only slightly slower than mid-range values. Absence of ringing is especially important in high-speed switching as in, for example, signal conversion. The DC resistance of a 1 kΩ Bulk Metal Foil resistor compared with its AC resistance at 100 MHz can be expressed as follows: AC resistance/DC resistance = 1.001. Foil techniques produce a combination of highly desirable and previously unattainable resistor specifications. By taking advantage of the overall stability and reliability of VFR resistors, designers can significantly reduce circuit errors and greatly improve overall circuit performance. Bulk Metal technology enables customer-oriented products designed to satisfy challenging technical requirements. Customers are invited to contact our Application Engineering Department with nonstandard technical requirements and special applications (email: foil@vpgsensors.com).