On-Wafer Calibration, Measurement, and Measurement Verification
Pioneering work at NIST led to the development of accurate multiline thru-reflect-line (TRL) calibrations for on-wafer measurement. The method uses multiple transmission line measurements to improve both the accuracy and bandwidth of the calibration over that of conventional TRL.
The multiline method is implemented in the MultiCal®software suite. The software also determines the complex frequency-dependent characteristic impedance of the transmission lines used in the calibration and allows the user to set the calibration reference impedance to the characteristic impedance of the line, to 50, or to any other real value.
The calibration comparison method assesses the accuracy of a working calibration by comparing it to an accurate reference calibration (usually the multiline TRL calibration). This method has led to an understanding of the systematic errors present in many common on-wafer calibrations.
The calibration comparison method has
also proved to be a valuable tool for the development of working calibrations with accuracy comparable to the multiline TRL calibration. NIST now offers software for LRM calibrations that compensate for imperfect loads and thru lines and off-wafer CPW calibrations that compensate for differences in substrate dielectric constant. Both of these methods have been carefully verified with the calibration comparison method.