Federal Circuit Upholds BeSang 3D Memory Patent Claims Against Micron and Intel
Photo: Marta Branco / Pexels
Two of the largest chipmakers have lost their appeals against a small patent owner's stacked-memory patent. On 30 October 2026 the US Court of Appeals for the Federal Circuit affirmed two Patent Trial and Appeal Board (PTAB) decisions finding that Micron and Intel had not shown claims 1 and 13 to 17 of BeSang Inc.'s US Patent 7,378,702 to be unpatentable.
The patent
The '702 patent covers a semiconductor memory structure in which vertically oriented DRAM memory cells sit in a "stackable add-on layer" bonded on top of a substrate that already carries electrical devices and interconnect layers. The aim is to reduce the chip area that transistors take up by building upward rather than outward. This 3D approach is now central to the memory industry.
Micron and Intel each filed petitions for inter partes review (IPR) in 2023. The PTAB upheld the challenged claims in final written decisions in November and December 2024. Both companies appealed, and Judge Lourie wrote the court's nonprecedential opinion.
Micron's appeal: a reference that could not be made to work
Micron's main prior art was a reference known as Watanabe, which bonds stacked layers using heat of 900 to 1,000°C. The Board found that a skilled person could not have used that teaching to build the claimed structure. Expert evidence showed that such temperatures would damage or destroy the electronic devices already on the underlying substrate. In patent terms, the reference was not enabled.
The Federal Circuit agreed. It rejected Micron's argument that the Board had quietly read a 650°C temperature limit from the specification into the claims. The court said this was a factual finding about what the prior art could achieve, not a claim construction. It also rejected Micron's "thermal budget" argument that a high temperature might be applied only briefly. The Board had weighed that evidence and was entitled to prefer the expert testimony.
Because Micron's main ground relied only on Watanabe, it failed. A second ground combining Watanabe with a Lee patent failed for the same reason: the same heat problem meant a skilled person had no motivation to combine them. The court also rejected Micron's claim that the Board demanded proof of a specific improvement from the combination.
Intel's appeal
Intel relied on a Park reference. The Board found that Park's adjacent memory cells share a plate and gate electrode, so they are not "separated from each other by dielectric material" as claim 1 requires. Intel argued that the Board had implicitly construed the claim to require electrical separation. The court pointed out that Intel's own petition argued that skilled artisans would want electrical separation, and found no implicit construction. Intel's procedural complaint, that the Board ignored some of its arguments on another limitation, also failed.
Takeaways
- Enablement of prior art is a real barrier. A reference that cannot be carried out as written may fail to anticipate or render a claim obvious, even in a crowded field.
- Expert evidence wins on substantial-evidence review. The court will not reweigh credible testimony the Board relied on.
- "Implicit claim construction" arguments are hard to win when the Board has simply compared the prior art with the claim language.
Sources
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