Terahertz Diode Arrays and Differential Probes based on Heterogeneous Integration and Silicon Micromachining

Abstract

Due to the technological needs of the radio astronomy and remote sensing scientific communities, as well as emerging applications in the areas of imaging, security, and broadband communications, terahertz and submillimeter-wave electronics continues to be an area of growth and increasing interest for academic researchers, government laboratories, and industry. The recent establishment of a commercial infrastructure for test and measurement instrumentation in this spectral region has fueled this growth and the emergence of CMOS as a submillimeter-wave technology has greatly expanded access to this spectral region by providing circuit designers with a platform for realizing terahertz circuits without need for specialized fabrication facilities or processes. The continued emergence of new terahertz devices has created a need for improved approaches to packaging, integration, and measurement tools for diagnostics and characterization in this portion of the spectrum. This paper focuses on progress in two parallel efforts aimed at addressing these needs: (1) the development of a direct-contact probe technology for on-wafer measurement of differential scattering-parameters in the WR-5.1 (140—220 GHz) and WR-3.4 (220—330 GHz) frequency bands, and (2) the development of processing technologies for realizing highly-integrated submillimeter-wave diode-based quasi-optical arrays, including phase modulators and sideband generators, that are based on heterogeneous integration of III-V semiconductors onto thin silicon membranes as a support substrate. The foundation for these efforts is micromachining and processing of silicon, allowing the fabrication of mechanically-robust and low-loss membrane carriers that can support and interconnect terahertz devices as well as directly interface them to surrounding circuitry. Examples of heterogeneous integration onto silicon as an approach to packaging and interfacing terahertz components that are detailed in this paper include development of differential micromachined wafer probes for in situ measurements of devices and circuits in the 140—330 GHz region. The probe design concept includes an integrated on-chip balun and matching network for terminating common-mode signals that may be generated by the DUT. The design methodology and initial measurement results for this probe will be presented. In addition, an example of heterogeneous integration/packaging of a submillimeter-wave frequency sideband generator array for phase modulation at 1.6 THz will be discussed. The sideband generator design incorporates 100 planar varactor diodes integrated into an array of bowtie antennas on a common substrate. Performance of the array as a phase shifter is described and the application of a new quasi-vertical diode fabrication process that consists of transfer of GaAs epitaxy to thin silicon support substrates will be discussed as an approach for implementing optimized arrays in the terahertz frequency range.