On-Wafer Contact Probing at Terahertz Frequencies – THz Cryogenic Probe Arm

The THz Cryogenic Probe Arm from Lake Shore Cryotronics is an on-wafer contact probing for cryogenic applications that operates at terahertz frequencies. It opens new measurement possibilities for research and development in next-generation electronics.

Low-Loss THz Waveguide

High-frequency contact measurements need careful consideration to know the transmission of signals to and from the device in test. As frequencies increase above 75 GHz, and into the formerly unattainable THz regime, the signals can decline quickly using the current waveguides over paths as small as a few centimeters.

This issue is usually addressed with room temperature probing solutions, which is done by reducing the path length between the frequency detector modules/extender source and the probe. However, the connecting waveguides can be decreased prior to the bulky modules intruding upon the sample space, complicating arm mobility and limiting options to add extra probes.

In a cryogenic probe station, considerably longer signal paths on the order of 25 cm, are needed to navigate the station’s interior structures and vacuum chamber. Lake Shore’s latest THz cryogenic probe arm with specially developed low-loss THz-frequency wave guarantees superior signal integrity over these longer distances.

Applications

  • Incorporates with network analyzers with appropriate frequency extenders
  • Unites two THz probe arms with typical RF/DC/microwave probe arms for a total of six concurrent contact probes
  • Used for accurate on-wafer contact probing of millimeter wave devices at THz frequencies of 75 GHz and above placed in a Lake Shore cryogenic probe station.

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Components of the THz Cryogenic Probing Arm

Probe Arm

The THz cryogenic probe arm is a high-frequency option intended for Lake Shore probe stations. It can be mounted in arm positions two or five on compatible stations.

The option includes a three-axis micro-manipulated stage which has welded bellows made of stainless steel and comprises of:

  • A DC bias port
  • Feedthrough ports and mounting platform that are configured for use with a third party frequency extender
  • The probe arm and base with built-in theta planarization
  • High frequency waveguide, which is chosen to match the bandwidth of the frequency extender

Only the probe arm is supplied by the Lake Shore. Third parties offer the other needed elements, such as probe and frequency extender.

Frequency Extender

At present, the Lake Shore probe arm supports the MiniVNAX extenders from Virginia Diodes, Inc. VDI extender modules function with the most advanced signal analyzers and vector network from suppliers like Keysight, Rohde & Schwarz and Anritsu.

The VDI modules are provided in a range of frequency bands, where each band requires a slightly varied output coupling configuration. The waveguide topology from Lake Shore must be matched to the extender module’s frequency band.

Probe

The THz cryogenic probe arm assists tailored probes developed by Dominion Microprobes. It is possible to mount these arms in position two or five on suitable stations. The T-Wave™ probes are offered by Lake Shore or Cascade Microtech.

The micro-machined GSG probe has low-insertion loss coupling to the DC and DUT biasing of probed circuits. The probe is cryogenically certified and thermally anchored in order to reduce heat transfer to the DUT. A sensor is affixed to track probe temperature.

Variable Temperature High-Frequency Research

The THz cryogenic probe arm enables fine-tuned S-parameter and additional high frequency measurements that are carried out at very low temperatures and high magnetic fields, which are needed by early-stage researchers. This paves the way for new measurement possibilities for R&D in next-generation electronics, such as quantum computing and radio astronomy.

S-Parameter Measurements

Scattering parameters (S-parameters) illustrate the frequency-dependent electrical behavior of a device, which is voltage signal and steady-state traveling-wave current.

Either a one-port or two-port configuration can be utilized. Based on signal direction, either transmit or receive, the reflection (S11, S22) and transmission (S12, S21) elements are measured individually to offer the entire device profile.

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