Emphasizing that the full claim scope must be enabled, the U.S. Court of Appeals for the Federal Circuit recently affirmed a ruling invalidating a patent for failure to enable the full extent of a claimed open-ended range.  MagSil v. Hitachi Global Storage Techs., Inc., Case No. 11-1221 (Fed. Cir., Aug. 14, 2012) (Rader, C.J.).

The patent-at-issue claimed a read-write sensor for computer hard disk drive storage systems.  In particular, the claims called for a tunneling junction wherein applying a small electromagnetic field causes “a change in the resistance [of the junction] by at least 10 percent at room temperature.”

At the district court, the patentee, MagSil, advocated for a broad construction and the lower court found that the claims cover resistance changes from 10 percent “up to infinity.”  The specification of the patent, however, taught a maximum change in resistance of only 11.8 percent at room temperature.  One of the named inventors testified that before the application was filed, he did not know how to achieve a tunnel junction with greater than 20 percent change in resistance.  Further, a year after the filing of the application the inventors were still unable to achieve even a 20 percent change.  MagSil’s expert testified that a person of ordinary skill in the art could work from the specification and make tunneling junctions with a resistive change between 100 percent and 120 percent without undue experimentation.  Even accepting the accuracy of the expert’s testimony, the district court found the specification did not enable one skilled in the art to practice the full “change of resistance” range.  As a result, the district court found the patent invalid for lack of enablement.

On appeal, the Federal Circuit found that the trial court’s lack of enablement finding fell squarely within the Court’s precedent.  The Court first explained that “[e]nablement serves the dual function in the patent system of ensuring adequate disclosure of the claimed invention and of preventing claims broader than the disclosed invention.”  This not only prevents inadequate disclosure of an invention, but also “overbroad claiming that might otherwise attempt to cover more than was actually invented.”

The Court adopted the broad construction advocated by MagSil and entered by the district court, finding that the range of the “at least 10% resistance change” limitation extended from 10 percent to infinity.  Turning to the specification, the Court noted that reference was made to a 1975 article that predicted an ideal tunnel junction could yield around a 24 percent change in resistance; however, 20 years later, when the application was filed, the specification taught that the highest achieved change was only 11.8 percent.  This was insufficient disclosure to enable a resistance change up to infinity. 

In the end, “[t]he scope of the claims must be less than or equal to the scope of the enablement to ensure that the public knowledge is enriched by the patent specification to a degree at least commensurate with the scope of the claims.”  In attempting to use broad claim language, the patentee risks “losing any claim that cannot be enabled across its full scope of coverage.”  

Practice Note:  Claimed ranges should be carefully drafted to correspond to the range enabled by the specification.  Open-ended ranges, in particular, should be avoided, as they will be closely scrutinized.