Micron lawsuit claims Chinese memory maker YMTC poached its engineers, then sued it using its own stolen tech

Micron this month filed a lawsuit against China's 3D NAND champion YMTC, accusing it of poaching its leading engineers, illegally obtaining its NAND memory know-how from them, and then using that information to build its own non-volatile memory as well as its patent portfolio. The Boise, Idaho-based company further alleges that YMTC uses patents granted to its former employees to accuse Micron of patent infringements in various jurisdictions.

We are all used to cut-throat competition on the memory market as leading producers of DRAM and NAND try to win market share from each other and maintain profitability at the same time. These companies have broad cross-licensing agreements to neutralize direct patent wars that can result in devastating injunctions that could paralyze fab operations and eventually lead to assured mutual destruction. However, this does not seem to be the case for emerging competitors from China, ChangXin Memory Technologies (CXMT) and Yangtze Memory Technologies Co. (YMTC), both established in 2016, which are increasingly attacking Micron in various courts, perhaps making pre-emptive strikes to avoid the destiny of their Chinese counterpart, Fujian Jinhua.

Using Micron's 3D NAND know-how against Micron

In its lawsuit against YMTC, Micron asserts that Yangtze Memory's patent campaign against Micron largely relies on patents that were granted to former Micron employees. Furthermore, Micron alleges that former employees brought its 3D NAND know-how to YMTC and subsequently developed patents covering related or overlapping technologies, which essentially means that Yangtze Memory has built its patent portfolio using Micron's intellectual property, which is why Micron claims that YMTC patents belong to Micron and therefore cannot be used against it.

"For example, these individuals include Daesik Song, Wenxi Zhou, and Hua Tan," Micron's lawsuit reads. "Each of these employees owed Micron contractual obligations to keep trade secrets confidential, had access to certain of the Micron Trade Secrets further described below while employed at Micron, and on information and belief, each joined YMTC shortly after leaving Micron. Each of these employees also regularly accessed one or more of the Trade Secrets that were located on servers in Boise by accessing Micron's highly confidential technical materials relating to its test and/or production nodes."

Micron's allegations in the new complaint go well beyond simple claims that its former employees brought manufacturing expertise to YMTC, something that happens often. The company alleges that YMTC systematically obtained confidential 3D NAND and memory technology from former Micron engineers and incorporated that knowledge into its manufacturing processes starting from its 64-layer 3D NAND, memory products, and, most importantly, its patent portfolio. Micron says it began to uncover the alleged scheme after YMTC sued it for patent infringement in California in November 2023, when it noticed that several patents asserted against it named former Micron engineers as inventors.

In its complaint, Micron identifies a number of its former employees who subsequently became inventors on YMTC patents, including Hongbin Zhu, Jun Liu, Yushi Hu, Qian Tao, Changhyun Lee, Daesik Song, Wenxi Zhou, and Hua Tan. According to Micron, these engineers had access to different classes of confidential technology that covered a broad range of 3D NAND-related know-how, including high-aspect-ratio etching, replacement gate processing, multi-deck connections, pillar shaping and cleaning, and memory I/O circuitry, among others.

Patent records independently confirm an important part of Micron's allegations: several former Micron engineers later became inventors in YMTC patents that YMTC eventually used against Micron. In general, this does not prove any misappropriation: engineers routinely change employers and continue to invent in their areas of expertise, but Micron alleges that some of these patents cover inventions conceived or developed while their inventors still worked for Micron, which is why it is asking courts to transfer ownership of these patents from YMTC to Micron.

One of the clearest examples involves Hongbin Zhu, who left Micron in September 2017 and subsequently became an inventor in numerous YMTC patent applications. One family originates from the international patent application PCT/CN2018/101482, filed on August 21, 2018, and includes three patents. Micron's complaint alleges that these patents relate to technology Zhu 'learned of, worked on, and/or conceived while at Micron' and asks the court to transfer their ownership from YMTC to Micron. The same family also includes two additional patents that YMTC asserted against Micron in its California infringement lawsuit. Micron has already challenged ownership of these two patents in that litigation and claimed that Zhu invented the underlying technology while employed by Micron and had assigned his rights to the company.

Daesik Song provides another connection between Micron's allegations and YMTC's patent enforcement campaign. Song previously worked at Micron on memory I/O technology and later became an inventor on a patent titled 'Double Data Rate Circuit and Data Generation Method Implementing Precise Duty Cycle Control.' YMTC asserted the '851 patent against Micron in the Eastern District of Texas, yet Micron now alleges that it is actually the rightful owner of the patent because Song's invention-assignment agreement transferred inventions conceived during his Micron employment to Micron. The company is therefore asking the Idaho court to transfer legal title to the '851 patent from YMTC to Micron.

The Song connection also extends beyond the United States. In Europe, YMTC owns European patent EP 3 909 047, which covers the same invention as the '851 patent, and uses it against Micron in its UPC in Düsseldorf and U.K. litigations. Thus, YMTC is enforcing different members of the same invention family against Micron in Texas, the UPC, and the U.K. while Micron alleges that the U.S. patent from that family actually belongs to Micron. That does not automatically mean Micron owns the EP '047 since the U.S. and Europe are different jurisdictions, but it demonstrates how Micron's ownership allegations intersect with YMTC's international patent campaign.

There are additional connections. Former Micron engineers Yushi Hu and Qian Tao are named as inventors on two patents that YMTC asserted in California, while Jun Liu, Qian Tao, and Yushi Hu are all inventors on another patent asserted against Micron there. Changhyun Lee is an inventor on US 11,468,957, also part of YMTC's California case. Meanwhile, Wenxi Zhou appears on a YMTC patent family that covers barrier layers for word-line contacts, including US 12,094,767.

The European cases provide a somewhat narrower connection. Of the three European patents YMTC is asserting through the UPC and UK proceedings, EP 3 909 047 is directly relevant because it names former Micron engineer Daesik Song. The other two — EP 3 850 660, which names Qinxiang Wei, Jianhua Sun, and Ji Xia, and EP 4 236 650, which names Zilong Chen and Xiang Fu — do not name any of the former Micron engineers identified in Micron's complaint. Meanwhile, YMTC has also filed eight patent cases against Micron in China, three in Beijing and five in Shanghai, although we have not found a reliable public list of the eight Chinese patents involved, so it is not yet possible to determine whether they include Chinese patents of YMTC's inventions in the U.S. and Europe.

To sum up, the list of patents and YMTC engineers reveal a much more complicated dispute than an ordinary patent fight between two memory manufacturers. In less than a decade, YMTC has built an international patent portfolio and is attempting to enforce it against Micron across the United States, China, Germany, the UPC, and the U.K. Several of the patents used in that campaign are assigned to engineers who previously worked for Micron. Furthermore, Micron now alleges that at least some of those inventions were conceived while at Micron or using its trade secrets, so at least in some cases these patents belong to Micron, according to the company's complaint.

In short, Micron's main allegation is not that YMTC obtained its manufacturing know-how through former employees, but that some of this know-how was ultimately converted into YMTC intellectual property that YMTC later used to sue Micron itself. Hence, if Micron proves to the courts that YMTC's inventions are in fact Micron's inventions, then the whole Yangtze Memory campaign falls apart. However, the decision by the Munich I Regional Court looks rather alarming for Micron, as the company has so far failed to persuade the court that it not only did not infringe any YMTC patents, but that the very patents in question were obtained illegally.

All-out war

YMTC sued Micron in the Northern District of California in early November 2023, alleging that Micron's 3D NAND infringed eight U.S. patents. In early 2024, YMTC brought three additional patent cases against Micron in Beijing, then followed up with another California lawsuit in July that asserted another 11 U.S. patents against Micron’s 3D NAND and DDR5 products. In September 2024, YMTC expanded its Chinese campaign with five more patent cases in Shanghai. The dispute became global on October 6, 2025, when YMTC simultaneously launched another wave of litigation, asserting eight patents in the Eastern District of Texas, three patents in the U.K., three European patents before the Unified Patent Court in Düsseldorf, and five patents before the Munich Regional Court.

By then, what had begun as an eight-patent U.S. dispute had evolved into a multi-jurisdictional patent war covering dozens of patents and some of Micron's most important NAND products. Hence, Micron had to start responding. On October 18, 2024, the company filed a counterclaim alleging that it is the true owner of the US 10,879,254 and US 11,581,322 patents (more on this later). Then, almost two years after YMTC first sued Micron, the company filed the case on October 7, 2025, asking the U.S. District Court for the Northern District of California to issue a declaratory judgment of non-infringement concerning YMTC patents, which essentially means that Micron asked the court to rule that its patents did not infringe certain YMTC patents. These actions were barely a defense from YMTC's all-out patent war.

However, having spent nearly three years primarily defending itself and challenging YMTC's patents, Micron decided to respond more vigorously, which it did in its lawsuit filed with the Boise, Idaho, court on September 15. In the new lawsuit, Micron alleges that YMTC systematically obtained Micron's 3D NAND manufacturing know-how through former Micron engineers and then incorporated that information into both YMTC's manufacturing processes (64-layer, 128-layer, 232-layer, and subsequent nodes) and its patent portfolio. The alleged trade secrets cover multiple aspects of contemporary 3D NAND production, including high-aspect-ratio etching, replacement gate processing, multi-deck connections, pillar formation, and other manufacturing techniques.

Micron claims that its former employees who had access to this information later worked on similar technologies at YMTC and became inventors in YMTC patent applications. More importantly, some of these patents or their family members were subsequently used by YMTC against Micron, which essentially means that YMTC used patents granted to Micron's former employees against Micron itself. In many cases, YMTC allegedly poached Micron engineers who had previously developed and patented certain technologies at Micron, then tasked them with working on similar technologies and filing new YMTC patents covering essentially the same technical solutions. As a result, Micron now claims that several of the underlying inventions actually belong to it.

Back in Europe, Micron launched its own patent offensive against YMTC and companies that sell products which allegedly use the disputed technologies. In July, Micron sued YMTC in the Munich Regional Court, where it named Apacer, Lexar, and Ultron as co-defendants. In addition, it took a separate U.K. High Court action targeting YMTC alongside its partners Apacer, Lexar, and TeamGroup (note that TeamGroup is one of the SSD makers that from time to time uses different memory and even controllers on the same SSD models).

The German ruling

Before we proceed with a rather unprecedented decision of the Munich I Regional court, let us explain the difference between the patent and utility model as neither the U.S. nor the U.K., nor Canada, support the utility model system.

A patent protects major technical inventions across process technologies, tools, and materials for up to 20 years, but it requires a rigorous step-by-step patent office examination that typically takes years and significant expense to obtain. By contrast, a utility model protects incremental, practical mechanical or structural improvements to physical products for a shorter duration (usually 5 to 10 years). It is granted rapidly within months and at a fraction of the cost because it involves a lower inventive threshold and skips substantive examination prior to registration. While most patent offices register utility models without checking whether the idea is actually new, the validity of a utility model remains uncertain until enforcement. This is where YMTC prevailed to a degree that nobody expected.

In fact, YMTC has so far failed to gain any substantial court victory in the U.S., but it scored its first major victories in its German litigation against Micron in September, when the Munich I Regional Court ruled that Micron infringed two YMTC German utility models and granted injunctions against the company. The two utility models — DE 20 2020 006 166 U1 and DE 20 2021 004 551 U1 — cover 3D NAND-related to staircase structures and barrier layers for word-line contacts, respectively. The injunctions prohibit Micron from offering and selling products that infringe the two utility models in Germany. Meanwhile, the court has adjourned decisions on three infringement actions: it did not reject the other three, but simply has not resolved them.

Normally, this would not be a problem for Micron's clients, as unlike injunctions by the U.S. ITC, these rulings in the European Union typically have no effect on downstream entities, so Dell, Lenovo, and other PC OEMs can continue selling PCs containing violating hardware. However, it is possible that this particular decision could affect Micron's downstream partners, effectively prohibiting them from selling systems with Micron's 3D NAND inside. As a result, the injunctions could disrupt sales of PCs, SSDs, servers, and other products containing the affected Micron NAND in Germany.

Micron has appealed the decisions and is challenging the validity of the rights, so the September rulings represent first-instance victories for YMTC rather than the end of the dispute. Three other Munich cases brought by YMTC — including one that involves a European patent — have not yet produced infringement decisions. Yet, the existing decision shows that courts can side with Yangtze Memory and rule that Micron uses YMTC's intellectual property illegally.

Normally, this would be a 'local' problem for Micron. However, it is important to mention that some of the technologies and patent families involved in the European litigation overlap with those asserted in the United States. Several of them name former Micron engineers as inventors.

In fact, both German utility models on which YMTC just won injunctions appear to belong to patent families that involve former Micron engineer Wenxi Zhou, with corresponding U.S. patents being used by YMTC against Micron in Texas. This becomes particularly important in light of Micron's new allegations that former employees brought its 3D NAND know-how to YMTC and subsequently developed patents covering related technologies. If YMTC can win a litigation in Germany, can it also prevail elsewhere using the same patent families?

Summary

The conflict between Micron and YMTC emerged amid the escalating U.S. – China semiconductor confrontation. In October 2022, the U.S. imposed sweeping restrictions on exports of advanced semiconductor manufacturing equipment and technology to China, and in December 2022, the U.S. Department of Commerce added YMTC to its Entity List, which severely restricted the company's access to American fab tools. China responded with pressure on Micron: in May 2023, the Cyberspace Administration of China concluded that Micron had failed a cybersecurity review and prohibited operators of critical information infrastructure from purchasing affected Micron products.

The commercial conflict between the two memory makers eventually moved into the courts, with YMTC accusing Micron of patent infringement and Micron largely defending itself rather than launching a comparable patent offensive of its own. Micron’s new complaint in Boise, Idaho, may explain this strategy: the American memory maker not only seeks to defend itself against YMTC's infringement claims, but also alleges that some of the patents YMTC is using against it incorporate Micron’s confidential technology or actually belong to Micron itself. But while Micron can potentially prevail in the U.S. and perhaps in Europe and the U.K., China represents a different challenge, as the legal battle between the two memory makers may well be considered a part of the broader geopolitical confrontation between the U.S. and China.

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