Custom Magnetic Field Probe Stations - Lake Shore Cryotronics, Inc.

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Custom Magnetic Field Probe Stations

Design Features

Horizontal fields up to 1 Tesla
Vertical fields up to 1 Tesla
Magnet pair and cold stage incorporated into the vacuum chamber eliminate the need for cumbersome external magnets and equipment
4.2 K to 200 K operation (field on); 4.2 K to 325 K operation (field off)
High resolution and stability, 60 A superconducting magnet power supply
High accuracy temperature sensors and control instrumentation
Economical table-top operation
Efficient continuous-transfer refrigeration
Low thermal gradients, sample well shielded, probes cooled
Fast cool down and stabilization
Up to four ultra-stable probes manipulated around 90° axes
Probes up to 22 mm wafers
Probe travel: 51 mm x 25 mm x 16 mm. Retracts easily, even under vacuum
High-resolution microscope includes manipulation system to view whole wafer
CCD camera, light source, 15 inch LCD color monitor included
Easily reconfigured for microwave probing
Frequencies from dc to 67 GHz
In-situ probe planarization (±5º) for microwave probes

Choose one of the products below to customize a system to meet your needs.

		Custom Horizontal Field, 4 Manipulated Stage System
		Custom Vertical Field, 4 Manipulated Stage System

Magnetic field, table-top manipulated probe systems from Desert Cryogenics are comprised of a collection of modular components which can be selected as needed for a given application and reconfigured when needs change.

Refrigeration and Control

The continuous refrigeration system employed by the TT-Prober system is designed from the ground up to provide efficient operation and smooth control. A high-efficiency helium transfer line inserts into a side-bayonet, and the cryogen is exhausted away from the precision mechanics. Vapor-cooled shielding is used extensively to optimize efficiency and to intercept black-body radiation before it reaches the sample. Probes are cooled to prevent heat injection near the device under test. The cold plate incorporates heaters to spread out the control heat, speed thermal response and minimize temperature gradients. The temperature range is available from 4.2 K to 200 K (325 K with field off). Control stability, using the system temperature controller is typically ±0.01 K below 25 K and ±0.05 K above 25 K. A dual-control system to read the probe and wafer temperature is standard.

Sample Holders

Each probe system comes with one grounded sample holder. Additional sample holders are available in grounded, isolated, coaxial, and triaxial configurations at additional cost. Coaxial and triaxial sample holders require a separate triax feed through installation for proper measurement and biasing.

Probes: Model ZN50

The Model ZN50 probe is a 50 -impedance stripline probe, and is shown here. In probe systems built by Desert Cryogenics, probes are cooled to eliminate heat injected at the probe contacts. The ZN50 probes are ideal for a very broad array of applications including: dc biasing, low-frequency transport measurements; low-noise shielded measurements; low-leakage guarded measurements; and high-frequency measurements to 2 GHz (standard) or 5 GHz (HF option). Four available tip radii are ideal for: contacting pads (25, 50, 100, 200 µm tip); contacting large features (10 µm tip); contacting small features (3 µm tip). Tip materials are available in Tungsten (W), Beryllium Copper (BeCu), and Paliney 7, (Au alloy). To specify tip diameter and material, add the diameter in microns to the model number, and then the material abbreviation. I.e.- ZN50-25-BeCu.

Probes with the HF option have an increased bandwidth of 5 GHz. HF probes and probes with a 1 µm tip incorporate a more compliant tungsten wire to minimize tip damage. To specify the HF option, add -HF to the model number. For example, a probe with 3 µm tip diameter and HF option has model number ZN50-03-BeCu-HF.

An SMA jack connects directly to metallization on the alumina blade. This provides optimal performance in the low-frequency microwave range up to 2 GHz. The probe tips are soldered directly to the thick film printing on the signal side of the alumina blade. This can only be soldered reliably one time, therefore the blades are designed to be replaceable as an assembly.

Spare or replacement units, are configured as above, inserting an R after the ZN50, and specifying the radius and tip material as follows in example. I.e.- a ZN50-25-BeCu replacement or spare blade would be a ZNR-BeCu-25. Each tip comes in its own box and is clearly marked, for exchanging tip materials and sizes.

Microwave Probes

Microwave probes are made to Desert Cryogenics' specifications to optimize cryogenic performance. These customized probes have minimal thermal mass in order to reduce the time needed for the probe temperature to stabilize. Soft copper braids are installed to allow the probes to be cooled to minimize heat injected at the device under test. In addition, probes have low-thermal-conductance tips to further reduce heat injection. Probes are available for work to 40 GHz, 50 GHz, and 67 GHz, and with a range of pitches.

Probes: Optical and Custom

In addition to windows and optical access, fibers can be manipulated to transmit or receive light or IR/UV radiation. Custom probes for other applications are available on request.

Cables

The cables offered depend on the application and experimental needs. Simple wires are offered for dc bias. Micro-coax with an SMA connection at the probe end and BNC or triax feedthroughs are offered for shielded or guarded work. Semi-rigid coax with SMA connections at both ends and compression-sealed vacuum feedthroughs are offered for work to 5 GHz with the Z50 probes. A range of semi-rigid cables with microwave connections and compression-sealed vacuum feedthroughs are offered for the microwave probes. The choice of cable and connection depends on the required bandwidth and the trade-off between thermal loss and cable microwave loss.

Stages: The Heart of Manipulation

Manipulation of in-vacuum probes with stages in the ambient environment introduces requirements on the stages not typically met with commercial stages. The loads introduced by the vacuum forces through the edge-welded bellows can be very significant. Desert Cryogenics designs and builds stages optimized for cryogenic probing. The stages for the TT-Prober systems have a travel of 51 mm in the axis of the bellows (X-axis), 25 mm horizontally (Y-axis), and 16 mm to lift and lower the probe (Z-axis). An optional ±5° Theta rotation mechanism allows in-situ planarization of microwave probes. The x-axis stage has a 2-mm pitch and 50-mm knob with tics at each 20 µm, providing 1-µm resolution and swift, effortless adjustment even when loaded by vacuum. The Y- and Z-axis stages have 0.5 mm pitch with positive, zero-backlash micrometer drive (no springs).

Optics Packages

The standard Zoom 70 optics package from Desert Cryogenics does not require the user to lean over the system and peer into eyepieces. A CCD camera on the top of an optimized monoscope sends the image to a high-resolution video monitor which can be viewed from anywhere near the system. The optics can be manipulated to view any part of a 2-inch wafer, and in addition, can be retracted and swung away to allow access to the top of the vacuum shroud. The illumination is coaxial. The standard monoscope has a zoom ratio of 7:1 and an ultimate resolution of 5 µm. A 12.5:1 zoom, or 16:1 zoom upgrade, is available with resolution of up to 4 µm* and 3 µm* respectively.
*field systems with extended chamber heights may vary, decreasing resolution.

Available Vacuum Systems

The available vacuum system package includes an integrated turbo system for fast, hydrocarbon-free pumpdown. A cold cathode gauge, and Pirani gauge, display the level of the vacuum, from atmosphere to 10-6 Torr. Stainless steel flex lines isolate pump vibrations from the system, and an electrical break isolates the pump system electrically from the Faraday cage of the manipulation system. The turbo is robust, and vents itself upon shutdown, making it easier to operate.

Vibration-Isolation Options

In most laboratories the TT-Prober can be placed on a sturdy table without any additional vibration isolation. For laboratories where vibrations are a problem, an available table-top pneumatic isolation system provides isolation with characteristic frequency approximately 3 Hz. The TT-Prober can also be placed on existing isolation tables. Bolt-down hole patterns are provided for bolting to both US and metric tables. Floor mounted vibration isolation stands are also available for the table top units, where no table is available. Pump line vibration isolators, (shipped without cement) are available, complete with additional bellows and hardware for insertion in series into the pump line.