The U.S. Court of Appeals for the Federal Circuit affirmed that
the doctrine of assignor estoppel does not provide a basis for
federal jurisdiction. Semiconductor Energy Labs Co.
v. Nagata, Case No. 12-1245 (Fed. Cir., Feb. 11, 2013)
(Lourie, J.).
In an earlier suit by Semiconductor Energy Labs (SEL) against
Samsung for patent infringement, one of the patent's
co-inventors, Nagata, testified for Samsung that the signatures on
the declarations and assignments in the patent prosecution file
were not his. This raised issues of inequitable conduct and
brought the enforceability of the patent into question. SEL
claims that this resulted in a less advantageous settlement for
SEL. SEL then sued Nagata in district court, claiming that
Nagata's repudiation of the signature was a violation of his
duty under the doctrine of assignor estoppel, which prevents an
assignor from challenging the validity of a patent they have
assigned.
