The competitive fact first: memory bandwidth, not raw capacity, is what gates modern compute, and the IP that widens the memory pipe was being written well before the AI boom made it obvious. US10614859B2, granted April 2020 to Rambus (CPC G11C 5/063), is a stacked-DRAM device and its manufacturing method.
Gloss it once: conventional memory sits beside the processor and talks to it across a relatively narrow, long path. Stacking DRAM dies vertically and connecting them through the silicon shortens that path and multiplies the number of connections, which is the structural recipe behind high-bandwidth memory — the memory class that AI accelerators now consume by the truckload.
“A memory device includes a first dynamic random access memory (DRAM) integrated circuit (IC) chip including first memory core circuitry, and first input/output (I/O) circuitry. A second DRAM IC chip is stacked vertically with the first DRAM IC chip.”— U.S. Patent No. 10,614,859 source
Why this matters for a moat read: Rambus is a licensing-and-IP company, not a high-volume memory maker. Its business model is to hold foundational memory-interface and stacking patents and monetize them through licenses. A 2020 stacked-DRAM grant is therefore not a product announcement — it is inventory in a licensing portfolio that the AI memory cycle later made far more valuable.
The timing is the story. This grant issued in early 2020, before generative AI turned HBM into a sold-out, allocation-controlled product. Reading it now shows you that the bandwidth-through-stacking thesis was already mature and patented — the manufacturing problem, not the idea, was what remained.
The caveat we keep attaching: a patent is a defensive and licensing asset, not proof of shipped product or collected royalties. The grant tells you Rambus held position in stacked-memory IP; it does not by itself quantify the licensing revenue that flowed from it.
For the period investor, the lesson is about where moats are quietly assembled. The companies that owned memory-bandwidth IP before the demand arrived were positioned to extract value when it did. A 2020 stacked-DRAM grant is one brick in that wall.