Abstract:
The 3D NAND patent war that has lasted for nearly three years between Micron and Yangtze Memory has escalated again. Micron recently filed a lawsuit against Yangtze Memory in the federal district court in Idaho, accusing the latter of acquiring its 3D NAND manufacturing technology and trade secrets by recruiting former Micron engineers and using these technologies in the construction of its own flash memory products and patent system. Micron further claimed that Yangtze Memory subsequently used some of the patents filed by these former Micron employees to sue Micron for patent infringement in the United States and other countries and regions.
It should be noted that the above contents are currently all accusations made by Micron in the lawsuit documents, and do not mean that the court has determined that Yangtze Memory has indeed committed illegal acts in terms of trade secret misappropriation or patent ownership. Disputes between the parties surrounding these technologies and patents continue in multiple jurisdictions.
Micron stated in the complaint that Yangtze Memory has recruited a number of Micron engineers, including Daesik Song, Wenxi Zhou and Hua Tan. These personnel had access to highly confidential 3D NAND technical information during their previous work at Micron, and according to the contract signed with Micron, they were still obligated to protect trade secrets even after leaving the company.
Micron specifically pointed out that some of the engineers involved joined YMTC soon after leaving the company, but when they left the company, they explained their departure due to personal or family reasons, and did not update their work information in a timely manner on professional social platforms such as LinkedIn. Micron believes this resulted in it not realizing at the time that these individuals had gained access to Yangtze Storage, nor did it immediately suspect that the company's confidential technology might have been taken to a competitor.
According to Micron, these engineers had previously accessed highly confidential technical information on Micron servers in Boise, Idaho, involving test nodes and production nodes. The scope of related technologies is quite wide, including key 3D NAND manufacturing technologies such as high aspect ratio etching, replacement gate process, multi-layer stack connection, memory cell column formation and cleaning, and memory I/O circuits.
Micron alleged that Yangtze Memory then assigned these personnel to similar research and development areas and used their previous technical experience to develop its own products. More importantly, Micron believes that some former employees later became inventors of Yangtze Memory patents, and the technologies involved in these patents overlapped with their previous research and development work at Micron.
Micron believes that the problem is not just that engineers move from one chip company to another, but that some technologies may be converted from Micron's trade secrets to Yangtze Memory's intellectual property during the personnel flow process, and ultimately form a patent portfolio that can be used to initiate patent litigation against Micron.
Micron said it only gradually noticed this problem after Yangtze Memory sued Micron for the first time in November 2023 in California. At that time, Yangtze Memory accused Micron of infringing its 3D NAND-related U.S. patents. When Micron studied the list of inventors of the relevant patents, it found that some of the inventors were engineers who had previously worked at Micron.
The former employees listed by Micron this time include Hongbin Zhu, Jun Liu, Yushi Hu, Qian Tao, Changhyun Lee, Daesik Song, Wenxi Zhou and Hua Tan. Micron believes that the technologies these personnel were exposed to during their tenure covered multiple 3D NAND manufacturing links, and some of them later became the inventors of Yangtze Memory-related patents.
Among them, several US patents related to Hongbin Zhu have attracted particular attention from Micron. Micron believes that some of the Yangtze Memory patents applied for by its former employees are related to the technology they previously developed at Micron, and some of these patents and their patent families were later used by Yangtze Memory in lawsuits against Micron.
However, the fact that a former employee switches jobs from a chip company to a competitor and continues to engage in research and development in a technical field that he is familiar with does not in itself prove theft of trade secrets. The flow of engineers between technology companies is very common, and engineers in the same field are likely to continue working on similar technologies. The real dispute is whether the specific inventions in the relevant patents were formed during Micron's tenure or independently completed after joining Yangtze Memory, and whether confidential technology protected by Micron was used.
If Micron can ultimately prove that some of its patents are actually derived from technological achievements owned by it, then the dispute will no longer be just about whether Yangtze Memory has infringed on Micron’s trade secrets, but may also further involve the ownership of the true rights of the relevant patents. Micron's lawsuit is trying to confirm through the court that some relevant patents actually belong to Micron, thereby weakening the legal basis for Yangtze Memory to use these patents to sue Micron.
This patent war has actually lasted for nearly three years. Yangtze Memory sued Micron in the U.S. District Court for the Northern District of California in November 2023, initially involving 8 U.S. patents, mainly targeting 3D NAND architecture and manufacturing technology. Subsequently, Yangtze Memory filed multiple lawsuits in China and continued to add new patent lawsuits in the United States.
By October 2025, Yangtze Storage has further expanded its front lines to Texas, the United Kingdom, and the European Unified Patent Court and German courts, turning patent disputes originally limited to the United States into global intellectual property disputes covering multiple countries and regions.
Up to now, the two parties have been involved in more than 20 patents and lawsuits, and the cases include not only patent infringement, but also patent invalidity, confirmation of judgments, and other related legal disputes. Micron has also begun to fight back and proposed that the real rights holder of some Yangtze Memory patents should be Micron.
Just before Micron’s latest lawsuit, Yangtze Memory had already made a phased progress in Germany. On September 18, 2026, the First District Court of Munich, Germany ruled that Micron infringed two German utility models related to 3D NAND of Yangtze Memory and issued a ban on related products.
The rights involved are DE 20 2020 006 166 U1 and DE 20 2021 004 551 U1, which involve the ladder structure of 3D NAND and the barrier layer technology related to word line contact. The protection period of these two rights is 10 years, and the court has not yet made a final infringement ruling on three other related cases.
It is worth noting that these two German utility model patent families are related to former Micron engineer Wenxi Zhou, and the corresponding U.S. patents have also been used by Yangtze Memory in litigation against Micron. This is directly linked to Micron’s latest accusation that “former employees brought Micron 3D NAND technology to Yangtze Memory and further participated in related patent research and development.”
However, the German ruling is still only the result of the first instance. Micron has appealed the decision and is challenging the validity of the rights in other judicial proceedings. Therefore, these two German bans do not mean that the global patent dispute between the two parties is over.
Yangtze Memory’s previous lawsuits in the United States have not achieved exactly the same results as this German ruling, and some of the disputed patents have been challenged for invalidity. At the same time, Micron continues to protect its intellectual property rights through counterclaims and confirmation lawsuits.
The industrial background behind this dispute is also very special. 3D NAND is one of the core technologies for modern SSDs, smartphones and enterprise-class storage devices. Manufacturers such as Samsung, SK Hynix, Micron, Kioxia, Western Digital and Yangtze Memory have long maintained their technical barriers through patent authorization, cross-licensing and litigation. Because 3D NAND involves a large number of complex technologies from memory cell structure to etching, stacking, connection and I/O circuits, the patent boundaries between different manufacturers are often very complex.
The strategy adopted by Micron this time is obviously more proactive than the previous method of mainly defending Yangtze Memory patent litigation. In the past three years, Yangtze Memory has continuously used patents to initiate lawsuits against Micron, while Micron has mainly responded through patent invalidation challenges and counterclaims. The direct filing of a lawsuit regarding trade secrets and patent ownership in Idaho, USA, means that Micron has begun to question the formation process of Yangtze Memory's patent portfolio from another angle.
If Micron can prove in court that some of the inventions covered by Yangtze Memory's patents actually belong to Micron, or prove that Yangtze Memory illegally used Micron's trade secrets during the research and development process, the relevant results may also affect other ongoing patent litigation between the two parties. However, if Micron cannot prove that there is improper transfer of these technologies, just because the engineers have worked at Micron is not enough to prove that there are problems with Yangtze Memory's relevant patents.
Therefore, the current dispute actually contains two intertwined issues: on the one hand, whether Yangtze Memory has infringed on Micron’s trade secrets, and who should own some of the patents; on the other hand, whether Micron has infringed on Yangtze Memory’s 3D NAND-related technology that has received legal protection. As the cases in the United States, China, Germany, the United Kingdom and the European Unified Patent Court continue to advance, the intellectual property disputes between the two parties are likely to continue for a long time.
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