A recent district court decision in Sonos v. Google has set forth a novel application of the prosecution laches doctrine to a patent with a post-1995 priority date. Sonos Inc. v. Google LLC, 20-06754 WHA, 2023 WL 6542320 (N.D. Cal. Oct. 6, 2023). If endorsed by the Federal Circuit, this decision could represent a new tool for defendants seeking to invalidate asserted patents, and it could have major implications for patent continuation strategy for U.S. patent owners.

After a $32 million patent infringement jury award for Sonos in the Northern District of California, Judge Alsup found for Google on its post-verdict motions for judgment as a matter of law, concluding that the patents in suit, despite their post-1995 priority date, were equitably unenforceable under the doctrine of prosecution laches.

The invocation of prosecution laches to render post-1995 “targeted continuation” patents unenforceable represents a major potential development in the legal landscape for U.S. patent continuation practice. This decision could restrict the ability of applicants to use long chains of continuation applications to draft new patent claims that cover current market trends. Patent owners and accused infringers alike should monitor further developments in this area, including those arising from any appeal of the Sonos decision.

Patent Term and Prosecution Laches

Before 1995, U.S. patents were entitled to a term of 17 years from the date of issuance. Because patent expiration dates were set based on the patent issuance date, the pre-1995 system created incentives for delay during prosecution, whether by use of continuation practice or by other means, because it allowed patent owners to dramatically extend the period over which their patents were enforceable, sometimes by several decades. The use of “submarine patents” thus proliferated, whereby patent applications were kept pending (often secretly) for years or decades while a related industry or technology developed, only to suddenly “surface” and begin a 17-year enforcement term during which lucrative licenses could be sought in the now-mature industry.

In 1995, several changes to U.S. patent law took effect for patent applications filed thereafter. The changes included a new patent term scheme, setting a term of 20 years from the earliest priority date, rather than 17 years from the date of issuance. This change greatly reduced or eliminated the incentive to dramatically “submarine” a patent application because delays in prosecution now generally led to a shorter overall patent term, with the patent expiration date being set according to the priority date and not the date of issuance.

As a tool to address the remaining pre-1995 families of submarine patent applications, some of which included elaborate family structures spanning dozens of applications and claiming priority back several decades, the courts developed the doctrine of prosecution laches. Prosecution laches is an equitable defense to patent infringement, whereby a valid patent can be deemed equitably unenforceable if the patentee is found to have unreasonably and inexcusably delayed prosecution of the patent application, causing prejudice to the defendant. The Federal Circuit endorsed the patent laches doctrine in seminal case Symbol Techs v. Lemelson, in which patents covering barcode scanner technologies and claiming priority to the 1950s were enforced as late as the 2000s. See Symbol Techs. v. Lemelson Med., 422 F.3d 1378, 1386 (Fed. Cir. 2005). In several other cases, the Federal Circuit affirmed the application of the prosecution laches doctrine to pre-1995 patents benefiting from the 17-years-from-issuance term scheme. See, e.g., Hyatt v. Hirshfeld, 998 F.3d 1347 (Fed. Cir. 2021).

However, with respect to post-1995 applications, the 20-years-from-priority-date patent term scheme has provided a significant disincentive (the shortening of patent term) to delay the presentation of claims during prosecution, and has prevented applicants from cultivating multi-decade families of submarine patent applications. For post-1995 cases, the Federal Circuit has never affirmed application of the doctrine of patent laches.

However, as discussed in further detail below, Judge Alsup’s decision in Sonos v. Google breathes new life into the doctrine, finding that the prosecution laches doctrine can and should apply to post-1995 patent applications.

Targeted Continuation Practice Post-1995

While the introduction of the 20-years-from-issuance patent term removed the term-extension incentive for applicants to submarine their applications, it has not discouraged the use of serial continuation practice during the 20-year term that patentees are afforded.

Using serial continuations, patent applicants will often seek to keep a patent family “alive” by filing continuations just before issuance of a parent case. By keeping a patent family alive (sometimes for 10 or 15 years or longer), applicants are able to craft continuation strategies that account for current market trends and developments, taking into consideration what claims will afford coverage both for their own products and for those of competitors. The latter practice of drafting continuation claims intended to cover a competitor’s product is sometimes referred to as “targeted” continuation practice.

Today, the United States’ permissive continuation filing rules and relatively flexible written description and enablement standards have allowed for serial continuation filings and targeted continuation practice to become commonplace in large U.S. patent portfolios.

In the new Sonos decision, Judge Alsup now makes the case that this practice should, at the least, be significantly curtailed.

Sonos v. Google

Sonos sued Google for infringement of its patents directed to smart speaker technology, alleging that Google’s products infringed their claims covering techniques for creating overlapping groups of speakers in a smart-speaker system. A jury found that Google infringed two of Sonos’s patents, and awarded a verdict of $32 million.

On post-verdict motions for judgment as a matter of law, Google alleged that Sonos’s patents were unenforceable under the doctrine of prosecution laches. To prove prosecution laches on the part of a patentee, a defendant must show two factors: (a) unreasonable and inexcusable delay by the patentee, and (b) prejudice to the defendant.

Judge Alsup agreed with Google, finding that Sonos’s patents “issued after an unreasonable, inexcusable, and prejudicial delay of over thirteen years by the patent holder.”

“Unreasonable and Inexcusable Delay” due to a 13-year continuation chain

In finding an unreasonable and inexcusable delay on Sonos’s part, Judge Alsup points to the approximately 13-year delay from the time of the filing of Sonos’s original provisional application to the time of filing of the targeted continuation claims that would issue as the infringed claims, including five years after Sonos first learned of the Google technology that would eventually infringe Sonos’s as-yet-undrafted claims. Judge Alsup cites various Federal Circuit cases from this century as well as several Supreme Court cases from the early 1900s to support his finding that 13 years is an unreasonable amount of delay.

Sonos was, of course, at all times during the 13-year delay between its original filing and the filing of the continuations at issue, prosecuting other continuations in the patent family. That is to say, Sonos was engaging in the very conventional patent continuation practice of “keeping the family alive” while pursuing one continuation at a time. Judge Alsup reasons, however, that it “would have been a small step for Sonos” to pursue the asserted claims in any of the earlier continuation applications, or to pursue multiple continuations in parallel.

Judge Alsup’s finding of an unreasonable and inexcusable delay may also have been colored by evidence in the record of Sonos’s targeted continuation strategy, which is weighed explicitly as a part of the finding of prejudice against Google. While Judge Alsup acknowledges that “It is also true that a patent applicant is allowed to draft claims to read on competitors’ products and claim a priority date that precedes them,” he states that this right is circumscribed by prosecution laches’ prohibition of unreasonable and inexcusable delay.

Prejudice Against Google due to Google’s Economic Investment in the Infringing Product

In finding that Google was prejudiced by the delay from Sonos’s 13-year continuation chain, Judge Alsup points to Google’s economic investment in developing and bringing to market the infringing product before Sonos presented claims that cover the infringing products. Google’s economic investment in that 13-year period included both Google’s investment before Sonos learned of the Google technology, and Google’s subsequent investment in the five years after Sonos learned of the technology and before Sonos drafted the infringed claims.

Judge Alsup provides the following succinct explanation in the introduction to his order:

“This was not a case of an inventor leading the industry to something new. This was a case of the industry leading with something new and, only then, an inventor coming out of the woodwork to say that he had come up with the idea first — wringing fresh claims to read on a competitor’s products from an ancient application.”

To be clear, this represents a very unfavorable view of targeted continuation practice that, if endorsed by the Federal Circuit, could significantly reshape strategies for U.S. patent invalidity challenges, and for continuation strategies in U.S. patent portfolios going forward.

While Sonos argued that Google was not prejudiced because it could and should have known that Sonos could present future continuation claims using its published live patent families, Judge Alsup rejected this argument, reasoning that Google could not have been expected to “unearth[] the layers of file histories” in what “would have resembled an exercise in archeology.”

Prejudice Against Google Due to Impermissible New Matter

An interesting thread that runs through Judge Alsup’s analysis of prosecution laches in this case is his consideration of Sonos’s inclusion of what he deems to be impermissible “new matter” in the continuation applications at issue.

The facts here are convoluted, but the critical offense by Sonos was an amendment made to the specifications of the continuation applications, ostensibly on the basis of subject matter that was incorporated by reference from an appendix of an underlying provisional application. Judge Alsup concludes that this amendment was in fact not permissible, and that it introduced new matter. In fact, after his prosecution laches analysis, Judge Alsup separately concludes that the amendments made to the specifications moved the priority dates for the issued patents from 2006 to 2019, thereby rendering them invalid as anticipated by the accused Google products.

But, more interesting than the invalidation of the claims is the fact that Judge Alsup seems to have weighed these facts in finding prejudice against Google. Specifically, Judge Alsup states that Sonos’s reliance on new matter (its “machinations during prosecution” constituting “inserting new matter into the specification and masquerading it as subject matter previously disclosed”) meant that Google could never have anticipated that the claims would have been drafted, evidencing prejudice against Google.

Applicability of Prosecution Laches to Post-1995 Patent Applications

The most notable and potentially significant part of the Sonos decision is, of course, the application of prosecution laches to a post-1995 patent filing, in a case where the continuation strategy was not a pre-1995 “submarine” approach, but was instead a conventional post-1995 serial continuation and targeted claims approach.

Judge Alsup acknowledges that the Federal Circuit has never affirmed the application of the prosecution laches doctrine to a post-1995 case, but he reasons that the defense is nonetheless applicable under the circumstances at hand. Judge Alsup points to Supreme Court precedent from 1923 to support his decision, invoking Woodbridge v. United States, 263 U.S. 50 (1923), which itself helped to form the basis for Symbol Techs. v. Lemelson.

In the Woodbridge case, an applicant for a patent directed to improvements in rifled cannon technology requested in 1852 that his patent application be lodged in the patent office’s “secret archives.” Over nine years later, after the outbreak of the U.S. Civil War, the applicant then elected to pursue the patent application, presumably due to a perceived increase in profitability for cannon technology during wartime. In that case, the Supreme Court found that prosecution laches rendered the patent unenforceable due to the applicant’s “purpose of making the term of the monopoly square with the period when the commercial profit from it would be highest.”

Of course, the Woodbridge case differs from the Sonos case in that the Woodbridge patent term was not shortened by delay of the beginning of the term. Nonetheless, Judge Alsup’s reasoning suggests that delaying the presentation of a patent claim post-1995 (for example, to allow competitors to develop products for later targeting) can confer a similar kind of prejudicial commercial advantage as was conferred by delaying the presentation of submarine continuation claims in pre-1995 cases.

On this point, Judge Alsup states:

“True, our patents are not the “submarine patents” of yesteryear, but they likewise issued after many years of lurking beneath the surface, catching competitors off guard. Sonos let the industry develop and only then sought to extract an invention from a much earlier application that would read on an industry trend.”

Practical Implications Going Forward

The Sonos decision is only a single district court case, and it includes multiple unique fact patterns that could limit its applicability going forward. Nonetheless, if the Federal Circuit endorses application of prosecution laches to post-1995 patent applications, it would be a major development that could reshape the manner in which claims are presented, continuation strategies are devised, and invalidity challenges are litigated. If the Sonos theory of post-1995 prosecution laches for targeted continuation applications finds wider application, U.S. continuation practice could be changed in several significant ways:

• Applicants may consider earlier and potentially parallel presentation of continuation claims. In prioritizing earlier filing of continuation applications, applicants may need to weigh the costs of accelerated or parallel patent prosecution against the threat of prosecution laches.
• Applicants may consider prioritizing continuation filings within six years of the earliest priority date. While the Sonos case does not announce any definitive demarcation for how long of a delay may be too long of a delay in serial continuation practice, Judge Alsup alludes in a footnote to “the presumption that a delay of more than six years is unreasonable, inexcusable, and prejudicial.” If the Federal Circuit were to endorse a six-year presumption, then the “six-year” date could become a significant milestone in prosecuting patent families.
• Applicants may consider the potentially diminished viability of targeted continuation claims drafted after the development of a competing product. Even if targeted claims are developed and presented sooner than 13 years after an application’s priority date, the Sonos case suggests that evidence of intentionally trying to target a competitor’s products could weigh unfavorably against a patent. Alternatively, the case could be interpreted to suggest that a lengthy prosecution delay after learning of a competitor’s infringing products could weigh unfavorably against a patent. In the latter case, patent owners developing continuation strategies could be incentivized to file targeted claims sooner after development of a competing product, to minimize potential prejudice from continued investment by the competitor before the patent owners’ continuation claims are filed.
• Applicants may consider documenting considerations that are weighed in determining continuation strategies. For example, Applicants may seek to document how considerations of cost, prosecution workload, and likelihood of success were weighed when filing serial continuations, to attempt to establish a record that continuations were pursued at the earliest reasonable time.
• Freedom-to-operate assessments could provide an increased measure of certainty. Due to the threat of serial and targeted continuation practice, assessing freedom to operate (FTO) has required considering what hypothetical claims might be presented and granted in future continuations for live U.S. patent families. This is certainly a difficult task, and the Sonos case suggests that this burden should be curtailed: “We do not look to the specifications of much earlier related patents to define the scope of a patented invention, and we certainly do not look to an appendix to the specification of a much earlier unpublished provisional application.” If the Sonos case is endorsed by the Federal Circuit, then restrictions on delayed and/or targeted continuation claims could make “live” patent families less of a dynamic FTO threat.

An appeal of the Sonos decision to the Federal Circuit is likely forthcoming, and Morrison & Foerster will continue to monitor any developments in this case.

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