Inside SkyWater Technology’s Domestic Semiconductor Foundry

Unless you were a resident of Bloomington, Minnesota, SkyWater Technology’s ribbon-cutting for its fab expansion earlier this month probably didn’t make your newsfeed. Many people probably never even heard of SkyWater, as it was only spun out of Cypress Semiconductor several years ago.

SkyWater is a pure-play semiconductor foundry, which means they make chips for other companies. They operate a relatively small 200 mm factory or “fab.” Most of the news these days is about big fabs, like those belonging to companies like TSMC, Intel, Samsung, or GlobalFoundries – facilities that cost more than $10 billion each. The ribbon cutting was for a $170 million facility expansion and some technology upgrades. They currently produce integrated circuits (ICs or “chips”) using 90 nanometer (nm) technology. Okay, IBM and Intel first produced 90 nm chips in 2002, and Taiwan Semiconductor Manufacturing Company (TSMC) introduced them in 2004, and they were using 300 mm diameter wafers at the time. SkyWater is still using 200 mm wafers. Also, SkyWater announced that they were bringing copper interconnects to their chip process. IBM introduced that with some of its first PowerPC microprocessors back around 1997. SkyWater is also moving to a 65 nm process. That’s good, TSMC started offering that around 2005. So the technology upgrades by themselves were not that special.

Maybe the upgrades weren’t that interesting, but what is interesting is what SkyWater is doing with its fab, and who is working with them: 

• Skywater is making qubits for D-Wave’s quantum computer, a project it started when it was still part of Cypress. This is not exactly a high volume product, but then if you have a small specialty fab you can take on customers like D-Wave. SkyWater is sticking with mature technology, avoiding the heavy investments of bleeding edge processes. A surprising number of chips are made today using 65 nm or 90 nm technology, especially radio chips used in phones and wireless devices, devices for the Internet of Things (IoT), and automotive applications. Since it is a mature technology, the manufacturing equipment is likely fully depreciated, and therefore the process can be quite attractive from a cost standpoint. Industry leaders like TSMC and GlobalFoundries produce many chips on 65 and 90 nm processes. SkyWater is also making microfluidic chips for DNA sequencing machines, which are a hot commodity among scientists studying the epidemiology of SARS-CoV-2.

• SkyWater is willing to experiment with processes. As part of the Defense Advanced Research Project Agency (DARPA) Electronics Resurgence Initiative, it is working with a research group from MIT to make carbon nanotube (CNT) transistors on its process line. It has always been critical for the developers of new technologies to demonstrate their viability on commercial production lines, and with so few semiconductor facilities left in the U.S. that have the willingness to do this, the company can play an important role in helping to advance new technologies. Of course, not all new approaches will work, as some skeptics of CNTs that I have talked to point out. But it is critical for U.S. academic and research labs to have access to production facilities for this kind of experimentation. I remember the late Paul Gray, the beloved former president of MIT telling me one of the great regrets he had was not investing in a semiconductor facility for the school at a critical time so that its scientists would have access for research and process innovations. 
• SkyWater is using the copper upgrade to facilitate the stacking of multiple chips in a single package. This is an inexpensive way to increase the amount of circuits in a single chip package while using less advanced silicon processes. I’m a big fan of this kind of 3D packaging approach.
• A big part of the upgrade is to enable the production of radiation-hardened chips. It turns out that there is a fab at the Department of Energy’s Sandia National Labs in New Mexico that has been making these chips using a 350 nm process on 150 mm diameter wafers. That makes SkyWater look super advanced in comparison, as Sandia’s process would have been the latest and greatest in the early 1990s. Processes like 90 nm are actually great for these types of applications – and SkyWater’s version is much less sensitive to radiation than conventional chip processes. At least the Department of Defense (DoD) is upgrading our nuclear arsenal. I haven’t been able to look inside a nuclear warhead for around 25 years (these types of opportunities don’t come around very often), but at that time they were still fashioning solid-state devices to fit in the spaces to replace vacuum tubes. I’m glad these things are solid-state these days.

SkyWater is also the only domestically owned pure-play foundry company, so it is part of DoD’s trusted foundry program to provide a secure source of supply within U.S. borders. The story didn’t receive a lot of news coverage, but sometimes interesting things come in small packages.