Most UK patent actions are heard in London. This was one of the few cases before the High Court in Northern Ireland - it is not often that patent cases are heard in Belfast.
Siemens of Germany sued a Northern Irish subsidiary of Seagate for patent infringement through manufacture in Northern Ireland of wafers for computer hard drives using Tunnel Magnetoresistance (TMR) technology.
Of interest in this case, is why the court held that the claim (see next page) was limited to Giant Magnetoresistance (GMR) and excluded TMR. The court admitted that the words of the claim did not themselves answer the question.
So what, one might ask, is there in the claim that is so limiting? The Court found three answers:
1. The patent consistently referred to GMR and made reference to anisotropic magnetoresistance (AMR) but made no mention of TMR.
2. Various references in the description to materials and electron scattering were characteristic of GMR and not TMR, and
3. The word "interlayer" in the claim, which might extend to the non-metallic interlayer in TMR as well as the metallic interlayer in GMR (see picture), was said by the expert witness for Seagate (whom the judge described as "the most impressive witness I have ever heard in 36 years in the law") not to be a term of art - she expressed her view that it did not cover TMR devices .
An "interlayer" was held to be merely a layer placed between two other layers. The word was described by the Court as "neutral" and one that would not have led a skilled addressee with the then common general knowledge to conclude that the patent was purporting to cover TMR in the light of the mass of material in the description pointing to GMR.
Evidence was also adduced from corresponding litigation in the United States in which the actual author of the patent, asked whether he saw any mention of anything about TMR in the US equivalent to the patent in suit, replied
"No. It's not involved. I knew about TMR and it's not included in the patent. That was the question, huh?"
Frankly, we do not find these reasons convincing. The Court, persuaded by the relative merits of the witnesses, appears to have read into the claim a limitation that is just not there.
The Court said that the patent sought protection for a stack including an artificial or synthetic antiferromagnetic layer to reduce stray magnetic fields and induce stability in the reference ("bias") layer. We believe the Court should have focussed on whether this feature was present in the alleged infringing product. If the Court believed that the patent monopoly as defined by the claims, extended beyond this technical contribution to the art, and therefore lacked support (under the principles of Biogen v. Medeva), it should have said so, but that doctrine has been severely cut back in view of Generics v Lundbeck. We think the court was right not to go down that path.
The case serves to highlight the crucial influence of expert witnesses on claim construction in the UK.
As to the writer of the patent, it is immaterial what he actually intended by the words of the claim. What matters is what the reader, the person skilled in the art, would have understood the patentee to be using the language of the claim to mean. In Europe, the Protocol on Interpretation of Article 69 EPC requires the Court to combine a fair protection for the patent proprietor with a reasonable degree of legal certainty for third parties, and we would say the Court has incorrectly implied a limitation in the claim which achieves neither of these aspirations.