New THz on-wafer measurement facility enables FBH to measure frequencies up to 500 GHz

Current semiconductor device technologies enable operational frequencies in the submm-wave frequency range and exhibit transit frequencies approaching 1000 GHz. At Ferdinand-Braun-Institut (FBH), an InP DHBT process has been established with transit frequencies beyond 400 GHz. However, characterization facilities for frequencies beyond 110 GHz are not readily available so far. This is challenging because verification and accuracy assessment techniques still need to be developed due to lack of appropriate calibration techniques, operator dependence, and missing mechanical accuracy and repeatability of the on-wafer equipment.

Now, FBH has made a large leap forward in establishing submm-wave on-wafer characterization facilities. A semi-automatic on-wafer characterization system from Rohde & Schwarz has been purchased. It is based on a vector network analyzer operating up to 500 GHz, with nearly full frequency coverage and requiring a minimum operator interaction. The effort is funded through the EFRE project "Anwendungszentrum Höchstfrequenztechnologien".

Care has been taken to lower RF power during measurements without compromise on the dynamic range of the instrument and measurement speed in order to avoid large-signal excitation of the small high-frequency devices during S-parameter measurements. Also, the issue of prober-positioning accuracy and its impact on the calibration and accuracy was considered. The FBH system features a raised chuck in order to minimize RF losses at the high frequencies, with a motorized chuck and manipulators, together with a vision system for pattern recognition.

The measurement setup offers all what is needed to develop the calibration standards and calibration techniques required for on-wafer characterization in the frequency range beyond 110 GHz, which are not available today. A major issue with calibration at high frequencies is the elimination of the higher-order modes in the calibration substrate and the positioning accuracy and repeatability of the RF probes. These issues will be addressed as the next step together with measurement campaigns on submm-wave transistor devices.

FBH research: 25.07.2011