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|A Non-contact Testbed for On-wafer Characterization of Terahertz Devices and ICs|
|Keywords: terahertz metrology, non contact testing, quasioptical coupling|
|Recent advances in novel device topologies that exploit ultrafast quantum mechanical transitions in semiconductor systems (such as tunneling, plasma waves, etc.) are enabling new sensors for the THz band. New devices, such as heterostructure backward diodes (HBDs), 2D electron gas (2DEG) FETs, high electron mobility transistors (HEMTs), metal-insulator-insulator-metal (MIIM) junctions and quantum cascade structures can now be produced with cutoff frequencies well beyond the 1 THz barrier. However, metrology limitations in this frequencies spectrum become a major issue. Currently, high speed devices are characterized by contact probes and measurement is carried out by physically contacting the device on the wafer. At millimeter and sub-millimeter waves, these probes become extremely small and fragile with immediate effect on high acquisition and maintenance costs. Therefore, we developed a contact-less measurement method for characterizing devices that operate in the THz regime. We present a non-contact, on-wafer, broadband device and component testing methodology easily scalable to the sub-millimeter and THz bands. The “non-contact” probe setup is based on radiative coupling of vector network analyzer (VNA) test ports onto the coplanar waveguide environment of integrated devices and circuits. Efficient power coupling is achieved via planar antennas that are monolithically integrated with the device under test and act as readily connected “virtual” probe-tips on the chip under test. Radiation patterns and impedances of this on-chip, butterfly-shaped double slot antennas are optimized using full-wave moment method (MoM) tools specially developed in-house to enable robust and broadband quasi-optical coupling of the VNA ports. Repeatable errors of the non-contact probe setup are calibrated using on-wafer standards to perform accurate S-parameter measurements. In this work, theoretical background and full-wave simulated performances are presented together with experimental validation of the new non-contact probes. Proof-of-concept is demonstrated for the 325-500 GHz and 500-750 GHz bands (using WR 2.2 and WR 1.5 frequency extenders and a standard vector network analyzer as the backend). This non-contact probe setup is accurate, low-cost and is readily scalable down to the mmW band and up to the THz band (0.1-3 THz).|
|Georgios C. Trichopoulos, Assistant Professor
Arizona State University