D-Band Thin-Film Resistive Line Bolometer as Transfer Standard

A bolometric thin-film-based transfer standard with a novel structure for absolute power detection in D-band (110-170 GHz) is reported. It uses a resonance-type matching technique with thin-film resistive lines. The same line functions as the sensing element. The change in the resistivity of the line under the incident wave is calibrated to measure the absolute RF power in the D-band. This article presents the analysis using equivalent circuit models, the full-wave electromagnetic design, the fabrication, and the comprehensive characterization of the device. The comparison between a single and a folded-line matching structure is performed, showing the wideband capability of the latter. The transfer standard consists of two sensors in one waveguide housing for RF power measurement, as well as for monitoring and calibrating out the ambient temperature variation. It has shown a very good short-term time response with only similar to 0.19% deviation in a given time interval, which is very close to a commercial PM5 sensor with similar to 0.27% deviation. The long-term time response is also impressive, with a deviation of less than 0.6%, similar to a commercial PM5 sensor. The fast response time, good thermal isolation, and ambient compensation ability make it suitable for transfer/working standards, which can be used in ambient temperature environments.