Considerations for On-Wafer Millimeter-Wave Measurements on Thin Ceramic Substrate

This paper presents an on-wafer millimeter-wave circuit's characterization build on thin ceramic substrate having a high relative permittivity. An RF short circuit, designed with a quarter-wavelength radial stub, is used in load design and launch transition. To improve the design accuracy of electromagnetic (EM) tools, the dielectric constant of the ceramic substrate is extracted using measurements of several pairs of microstrip lines combined with EM simulations. The largest deviation obtained, compared with the mean value over the frequency band, is less than 1%. Thus, a new six-port circuit is designed and characterized using a millimeter-wave probe station. A comparison between the measurement and simulation results, using extracted manufacturer-recommended relative permittivity, is conducted. The six-port $q_{i}$ points' location is close to the simulated and theoretical ones over the frequency band of interest. As demonstrated in this paper, the substrate permittivity extraction has improved the design accuracy of the millimeter-wave circuits. Excellent performance of this circuit in terms of matching, isolation, and amplitude and phase balance is obtained.