Advanced thermal sensors for precision AC voltage metrology

Abstract

Abstract-We describe a new generation of thermal sensors for the measurement of ac voltages at frequencies up to 100 MHz. Electronics grade fused silica has been selected as a substrate material because it is significantly more robust than the previous generation of crystalline quartz, yet retains excellent dielectric properties. We report the design and fabrication of the new sensors, including the method of forming thin membranes, and present results for two sensor designs. Our latest devices show a reduction in the RF-DC of more than an order of magnitude over traditional high-frequency thermal sensors. We anticipate that the new sensors will enable significant reductions in the uncertainties in the NIST calibration service for RF-DC thermal converters.

New high-frequency MJTCs of novel design on fused silica substrates

“…The details of the fabrication process have been reported previously [3] and will not be repeated here; however, we have modified the fabrication process to deposit a continuous leg of Ni 90 Cr 10 overlaid with individual legs of Ni 55 Cu 45 . This deposition method has reduced the failures from defective thermocouple banks, and has allowed the reduction in thermocouple resistance from about 20 kΩ to less than 12 kΩ [4].…”

Wideband AC Voltage Standards

“…At frequencies higher than approximately 100 kHz, AC-DC transfer difference increases, mainly due to the adverse influence of the membrane and silicon substrate. For this reason, PMJTCs on quartz substrate [36], fused silica, and fused quartz [44] were developed. Multi-junction hybrid converters were also developed, in which thermocouples were sputtered onto a kapton film stretched on an Al 2 O 3 frame, and a chromium-nickel (Ni75Cr20Al2.5Cu2.5) radiator was deposited onto an aluminum nitride (AlN) substrate [45].…”