Planar Resistors

The planar design of the new ac-dc transfer resistor allows it to conduct the Joule heat generated in the resistive layer through the substrate to outside heat sinks so that the temperature of the resistive layer remains low .Substrate.      Aluminum nitride (AlN) ceramic was chosen as the substrate because of its high thermal conductivity of 140 Wm^-1K^-1. This value is eight times the thermal conductivity of Al₂O₃. The substrate is 5 mm thick and 100 mm x 100 mm square. It was not possible to achieve a polished surface on the AlN, as is required for the deposition of a thin-film resistor, owing to holes in the surface of the same size as the resistor path. Therefore, a polished Al₂O₃ substrate 0.4 mm thick was used for the deposition of the resistor, and glued onto the AlN substrate. Along both sides, black aluminum heat sinks are attached to the AlN substrate to increase the heat transfer to the ambient. Computer simulation of the temperature distribution, assuming 10 W power dissipation in the resistor, shows a rise of the resistor temperature of 4 K over ambient.

Resistor.      For the construction of a resistor with a low TC and good long-term stability, we took advantage of the experience acquired in the design of heaters of planar multijunction thermal converters. An NiCrSi-alloy thin film was sputtered onto the substrate with a thickness of 500 nm. The resistive layer is protected by a sputtered SiO₂ layer. Initially, such resistor has a TC of -35

Planar Resistor
AC-DC Transfer, Sampling and Ratio Techniques