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Competing Systems

 Please note that Shb Instruments is the only company that manufactures Hysteresis Loop Tracers for thin film applications.  The instruments below use alternative (and in our opinion) less optimal technology.

Vibrating Sample Magnetometer (VSM)

VSM’s can make the basic BH loop measurements (Bs, Hc), and some have probes to measure R and dR.  They operate by applying a slowly changing DC field to the sample (via a large magnet with concentrating pole pieces), and plotting the BH loop as the DC field slowly changes.

 

 

 

 

 

 

 

 

 

 

 

 

Limitations:

  • They work only on very small pieces of a wafer (perhaps ½” square or less), or specially made small diameter wafers, while the Shb instruments can measure whole wafers up to 12” (300 mm) in diameter.

  • A loop can take up to several minutes to trace out, while the Shb instruments are “real-time”, displaying 10 loops per second.  Therefore VSM measurements take much longer to complete.

  • There is no easy way to get the critical rotational orientation of a sample exactly correct, while on an Shb instrument the operator rotates the sample and watches the loop change in real time.

  • Repeatability of the critical flux measurements (Bs and Br) is poor (<= 3%), due to dependence on sample positioning.  Shb instruments can achieve repeatability of 0.1% or better.

  • They have limited accuracy at low field strengths (low Hc values) due to remanent magnetization of their pole pieces.  The Shb instruments operate at AC, and have no such limitation.

  • They cannot measure magnetostriction at all.

  • Limited R and dR (magnetoresistance) capability

Advantages:

  • Capable of generating very high field strengths (10-20  kOersteds or more).

 

 

The Shb Mesa can achieve fields of  1000-2000 Oersteds while measuring uncut wafers up to 200mm in diameter. Samples other than silicon wafers can also be measured.

LaFouda Automated Magnetostriction Measurement System (no longer in production)

This is a specialized instrument that measures only magnetostriction.

Limitations:

  • Cannot measure an entire wafer – requires a small strip to be cut.

  • Measures only magnetostriction, yet costs as much as a full Shb system

 

Advantages:

  • Better resolution than the Shb systems…but not by much.  

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Current Shb systems achieve essentially the same resolution as the LaFouda (see Technical Note with performance comparison)

Dedicated 4-point probing system

(multiple manufacturers)

Limitations:

  • Measure only resistance and magnetoresistance, not basic BH loop parameters or magnetostriction.

 

Advantages:

  • More flexibility in probe arrangement and orientation.

Kerr Effect Magnetometer (MOKE)

(multiple manufacturers)

 Limitations:

  • Unable to measure thickness of magnetic layer

  • Measures only the top atomic layers of the sample, resulting in uncertain correlation with bulk magnetic properties. Therefore unable to accurately measure total moment (thickness) of many samples.

  • Operation uncertain in the presence of surface (capping) layers on the sample to be measured.

 

 Advantages:

  • Able to map surface of a wafer

     

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