Can an open-ended claim range be enabled?

Bill Schertler | August 22, 2012

Magsil Corp. and MIT v. Hitachi Global

August 14, 2012

Panel:  Rader, O’Malley, Reyna.  Opinion by Rader.


The U.S. District Court for the District of Delaware granted summary judgment finding claims 1-5, 23, 26 and 28 of appellants’ U.S. Patent No. 5,629,922 (the ‘922 patent) invalid as a matter of law for lack of enablement and therefore non-infringed.  At issue was whether the specification enabled the broad scope of the claimed “open-ended” range of values having a lower threshold, but no upper limit, defined by “a change in the resistance by at least 10% at room temperature”.

Magsil appealed the district court’s decision.  On appeal, the CAFC affirmed the district court’s finding that claims 1-5, 23, 26 and 28 of the ‘922 patent are invalid for lack of enablement.


Technical background of the ‘922 patent

The claims at issue relate to a tri-layer tunnel junction that is incorporated into read-write sensor heads for computer hard disk drive storage systems.  Representative claim 1 is set forth below.

1.  A device forming a junction having a resistance comprising:

a first electrode having a first magnetization direction,

a second electrode having a second magnetization direction, and

an electrical insulator between the first and second electrodes,

wherein applying a small magnitude of electromagnetic energy to the junction reverses at least one of the magnetization directions and causes a change in the resistance by at least 10% at room temperature.

As shown in Fig. 1 of the ‘922 patent reproduced below, the ‘922 patent’s sensor uses a quantum mechanical effect where electric current can pass, or tunnel, from one electrode 10 through a thin insulating barrier layer 14 into a second electrode 12.  The tunnel junction resistance is higher when the magnetization direction of one electrode (e.g., 10) has the opposite direction to that of the other electrode (e.g., 12).  Therefore, the tunnel junction resistance changes with a change in magnetization direction.

An adequate level of change in tunnel resistance is necessary for practical applications; however, past efforts had failed to produce an adequate level of change in tunneling resistance for practical applications.  At room temperature, past efforts had obtained only a 2.7 % change in resistance.  The ‘922 invention achieved a “ten percent change in tunneling resistance with respect to magnetic field (H) variation”; in some cases “as much as 11.8% change was seen.”

The ‘922 patent specification teaches that the increase in change of tunneling resistance is believed to depend on a decrease in surface roughness of the two electrodes and the quality of the intervening insulator between the electrodes.   







The law regarding enablement

35 U.S.C. §112 sets forth the enablement requirement: [t]he specification shall contain a written description of the invention, and the manner and process of making and using it, in such full, clear, concise, and exact terms as to enable any person skilled in the art to which it pertains, or with which it is most nearly connected, to make and use the same.

“To be enabling, the specification of a patent must teach those skilled in the art how to make and use the full scope of the claimed invention without ‘undue experimentation.’” Genentech, Inc. v. Novo Nordisk, A/S, 108 F.3d 1361, 1365 (Fed. Cir. 1997) (quoting In re Wright, 999 F.2d 1557, 1561 (Fed. Cir. 1993)).

“The scope of the claims must be less than or equal to the scope of the enablement to en- sure that the public knowledge is enriched by the patent specification to a degree at least commensurate with the scope of the claims.” Sitrick v. Dreamworks, LLC, 516 F.3d 993, 999 (Fed. Cir. 2008) (quoting Nat’l Recovery Techs., Inc. v. Magnetic Separation Sys., Inc., 166 F.3d 1190, 1195-96 (Fed. Cir. 1999)); see also In re Fisher, 427 F.2d 833, 839 (CCPA 1970) (“[T]he scope of the claims must bear a reasonable correlation to the scope of enablement provided by the specification to persons of ordinary skill in the art.”).

Claim construction

The ‘922 patent application was filed in March 1995 and the patent issued in May 1997.  Magsil filed suit in December 2008 against several defendants alleging their disk drive products infringe the ‘922 patent.  During the time from the filing of the application that issued into the ‘922 patent until Magsil filed suit, the change in tunneling resistance achieved advanced significantly.

During trial, Magsil advocated for a broad construction of the claim language “applying a small magnitude of electromagnetic energy to the junction…causes a change in the resistance by at least 10% at room temperature.”  This broad claim construction was advocated to capture infringement of disk drive products developed after the ‘922 patent issued that produced advances in the change in the tunneling resistance of up to 604% (realized in 2008).

To support the broad claim construction, Magsil relied on expert testimony that the broad claim terminology covers tunnel junctions with resistive changes of 100% to 120%.  One of the inventors testified that a 1000% resistance change falls within the scope of the claims.

The district court gave Magsil its broad construction and found that the asserted claims cover “resistance changes beyond 120% and up to infinity.”

The ‘922 specification and enablement

The CAFC agreed with the district court that the specification does not contain sufficient disclosure to enable an ordinarily skilled artisan to make and use the entire scope of the claimed invention.

The specification – the disclosure available to show the full scope of enablement – teaches that the inventors’ best efforts achieved a maximum change in resistance of only 11.8 % at room temperature.

The CAFC also noted that expert testimony that one of ordinary skill in the art could work from the ‘922 patent to make the tunneling junctions with resistive change between 100% and 120% was counter to the expert’s own testimony that the first tunnel junction with this level of resistive change was not developed until 2006 or 2007.  However, even if the experts’ testimony were given weight, and could somehow overcome the requirement that the enabling disclosure must appear in the specification at the time of filing, the testimony only reaches the lower-end of the claimed scope.  The claims cover resistive changes from 10% up to infinity.

The CAFC concluded that the asserted claims of the ‘922 patent cover resistance changes from 10% up to infinity, while the ’922 patent specification only discloses enough information to achieve a 11.8 % resistance change.  The ‘922 patent specification enables only a marginal advance over the prior art but did not enable at the time of filing a tunnel junction of resistive changes reaching even up to 20%, let alone the more recent achievements above 600%.


The goal of drafting claims that are broad enough to capture infringement of later developed technology should be balanced against the requirement that the full scope of the claimed invention must be enabled.

Full Opinion

Patent At Issue

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