Micromachined on-wafer probes

Abstract

A micromachined on-wafer probe is designed, fabricated and measured at W-Band as a proof of concept for probes operating at submillimeter wavelengths. A fabrication process is developed to create devices that combine a waveguide probe with a GSG probe tip on a 15 μm silicon substrate. This device is housed in a metal machined waveguide block that provides mechanical support for the probe and connection to a waveguide flange. Load-cell measurements show a DC contact resistance below 0.07 Ω with a force of 1 mN. A two-tier TRL calibration characterizes the operation of the electromagnetic design and an insertion loss of 1.75 dB is achieved; this is comparable with commercial probes operating in the same band.

Terahertz micromachined on-wafer probes: Repeatability and robustness

“…A micromachined on-wafer probe has previously been demonstrated at W-band [5]. This probe is based on a microfabrication process that produces circuits on ultra-thin silicon substrates between 15 µm and 3 µm thick [6].…”

Micromachined On-Water Probes for Characterization of Terahertz Devices and Circuits

“…The research performed at UVa resulted in the development of a new on-wafer probe technology, termed "micromachined probes." In 2010, demonstration of the micromachined probe was first reported as a proof-ofconcept operating in the WR-10 waveguide band (75 -110 GHz), with performance comparable to existing commercial probes [13]. However, in contrast with existing commercial probes, the design of the micromachined probe is more suitable for application at submillimeter-wave frequencies.…”

“…1.3. As noted in [13], the microfabrication process for the probe chips builds on the ultra-thin silicon process originally described in [16] and incorporates metalized vias, patterned frontside and backside metallization, and frontside metal beamleads that extend beyond the edge of the silicon, and a silicon substrate of semi-arbitrary shape. With this process, all of the necessary probe circuitry -the waveguide transition, intermediate transmission line, GSG contacts, and DC bias tee -are lithographically-defined and integrated onto this single chip.…”

“…While electromagnetic simulation demonstrates that a 5 µm silicon substrate is electrically suitable for a WR-1.2 probe, the substrate must also satisfy mechanical requirements given that it forms the probes' contact points which physically touch the on-wafer device. The mechanical design requires: (1) the probe tip be long enough to extend below the bottom of the waveguide block housing with sufficient clearance to contact the on-wafer device and (2) that when the tip is brought into contact with the on-wafer device, the deflection generates sufficient force (> 1mN per tip [13]) to create a low-resistance path between the probe and the on-wafer device. As the probe tip is rigidly fixed to the probe housing at one end, we may consider the probe tip as an end-loaded cantilever beam to evaluate the geometrical effects on the available contact force.…”

“…In 2010, the invention of the micromachined probe by Reck et. al [13] represented an important step toward establishing an on-wafer measurement infrastructure for the terahertz spectrum. The work in this thesis leverages that foundation to extend on-wafer measurement capabilities of micromachined probes to higher frequencies with improved performance and robustness.…”