Advanced thermal sensors for precision AC voltage metrology

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.