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Fred Cawthorne
 
 

Current Projects

 

(This page is very outdated - stay tuned for updates or see the newsletter at physics.trevecca.edu)

I am currently working with a group of five Trevecca Physics and Engineering students to build a Scanning SQUID Microscope (SSM).  Much of this work is supported through a collaboration with Neocera, LLC., a company that makes a commercial SSM that is used in the semiconductor industry.  The Neocera system licenses technology developed at the University of Maryland.

 

Here is a picture of the SSM in the Physics Research Lab in the Greathouse Science Building

 

 The SSM uses a very sensitive magnetic field detector called a SQUID (Superconducting Quantum Interference Device).  This device is made using superconductors that must be cooled to cryogenic temperatures (below 80K or about -200 degrees Celsius). 

The SQUID is mounted to the end of a sapphire rod (clear, cone-shaped rod at the bottom of the lower right picture below). Because it must be cooled to very low temperatures (less than the temperature where oxygen liquifies), the cooled components must be contained in a vacuum chamber.  A thin diamond window separates the SQUID from the room-temperature sample being scanned.

The SQUID can be seen slightly to the right of center in the picture below.  The square opening in the center of the SQUID is about 30 microns across, smaller than the diameter of a human hair.  You would see this view of the SQUID if you aimed a microscope straight up from beneath the cold finger assembly shown above.

 

Here is a close-up showing the window and vacuum assembly (the window is at the bottom of the brown cone).  The top of the scanning stages can be seen to the lower right.

A computer controls an X-Y-Z stage that scans the sample under the SQUID. 

 

When an electrical current is passed through a wire, the wire produces a magnetic field.  The SQUID can be used to measure the Z component of the magnetic field from current carrying wires, and a magnetic image can be generated.

 

A magnetic inversion algorithm can then be used to calculate a map of the currents that produced the magnetic field.  This allows the SSM to "see through" solid material and determine the location of defects (short circuits) in circuits.  Below is an example of images produced by a defect that was located inside a Multi-Chip Module (MCM). (images courtesy of Neocera, LLC)

The SQUID microscope can also be used to image static magnetic fields such as those produced by the magnetic ink in a dollar bill or even a laser-printed Trevecca logo.  This false-color image is from a Trevecca logo that was printed out, magnetized, then scanned with the SQUID microscope. 

 

 

 
   
 
 
 
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