On-Wafer Load-Pull for Millimeter-Wave Applications Above 100GHz

There is interest in performing load pull measurements on millimeter-wave power amplifiers above 100 GHz. Losses in the tuner and test fixture make it difficult to present high VSWR impedances to the DUT. Commercial passive tuners are available that achieve VSWRs of 24:1 up to 110 GHz (WR-10). Constructing a load pull system above 110 GHz poses a significant challenge due to the increased loss and lower available powers from amplifiers for active load synthesis. The impedances generated by a passive impedance tuner are limited by intrinsic tuner losses and interconnect losses between the tuning network and DUT. Thus it is necessary to construct the highest achievable VSWRs in the most compact footprint so it can be integrated as close as possible to an on-wafer probe tip.

For the WR-5.1 waveguide band (140-220 GHz), a waveguide based E-H junction tuner has been constructed and measured. Non-contact waveguide sliding shorts were chosen for this purpose due to their high reliability and performance as seen in prior works. It is shown that this topology could be suitable for tuning waveguide based devices, but its performance in an on-wafer load pull application is limited by the practical integration of the waveguide based E-H junction device close to the on-wafer probe transition and its associated loss. VSWRs of 10:1 were measured at the waveguide reference plane on this device.

An alternative tuning structure, the double slug topology implemented using distributed MEMs loaded transmission line, is proposed next. This technique lends itself to being integrated directly on the silicon membrane probe. The double slug tuner creates impedance transformations through the use of two low impedance sections of transmission line separated by lengths of normal impedance transmission line. By selecting the characteristics of an array of MEMs devices loading a section of transmission line, it is possible to design for the suitable coverage of impedances within a certain VSWR.