All-Silicon “Fan-on-a-Chip” Keeps Thin Devices Cool

Most mobile phones and tablets rely on passive cooling, dissipating heat into the body of the device (and, eventually, into your palms). An active cooling fan would help, but conventional fans are too large to fit in smartphones, tablets, and even some laptops.

Microspeaker manufacturer xMEMS thinks it has the solution with the XMC-2400, the world’s first all-silicon fan-on-a-chip. Its design—roughly a millimeter thick and less than a centimeter wide and deep—leans on lessons from xMEMS’ audio products.

“The industry has a stream of technologies that moved from a mechanical device into silicon. From data storage, then to microphone, they made the transition,” says Mike Housholder, vice president at xMEMS. “Now just as we’ve taken the century-old speaker and moved it to silicon, we’re doing the same for the fan.”

How xMEMS used audio expertise to make fans

Speakers and fans might seem unrelated, but they have a common mechanical function: both move air.

The xMEMS XMC-2400 is thin enough to fit in mobile devices. The company says it can be placed “lid-to-lid” on a mobile system-on-chip or integrated elsewhere in a device.XMEMS

Housholder said the XMC-2400 is an “intentional evolution” of the company’s work in all-silicon microspeakers, which are available in earbuds such as the Creative Aurvana Ace and Noble Audio XM-1. “Once we had our ultrasonic transducer that was producing airflow in a new way, we knew an offshoot could be a cooling product.”

The XMC-2400, like xMEMS’ microspeakers, uses piezoelectric materials that change shape when an electrical charge is applied. The fan is a hollow cavity with cantilever vents on the top and a valve on the bottom. Opening the vents with the valve closed creates suction and builds air pressure in the cavity, which is released with the bottom valve.

The volume of air moved each cycle is tiny, but the process repeats hundreds of thousands of times each second to move up to 39 cubic centimeters of air per second. That’s still not a lot: Frore Systems’ AirJet Mini Slim, a solid-state cooling chip, can move 100 cm³ per second. The AirJet is much larger, however, measuring a quarter of a centimeter thick and over four centimeters wide.

Viewing the XMC-2400’s vents in operation with the naked eye isn’t possible, so xMEMS proved its function with a demonstration. The XMC-2400 was placed at one end of a plastic cylinder and a spinner was placed at the other. The fan moved the spinner as expected, first by exhausting air through the cylinder, then by pulling in the opposite direction.

The XMC-2400, like previous xMEMS products, is produced at a chip fab on 8-inch silicon wafers. For the fan, xMEMS’ supply partners are TSMC and Bosch. Housholder said xMEMS is ready to scale up production to “whatever capacity our customers demand.”

“Fan-on-a-chip” can keep on-device AI running

Housholder says the XMC-2400 will appeal to consumer electronics companies looking to improve the cooling of mobile devices without compromising on size, weight, or durability. The company expects to work with partners to integrate the chip in a variety of ways. The simplest example is a “lid-to-lid” mount, with the XMC-2400 placed directly on top of a mobile system-on-chip (SoC) to vent air away. But because the fan can also pull air, it could instead be placed beside and away from the SoC to minimize a device’s overall thickness. In that case, cooling is achieved by pulling air across the SoC.

“Things are getting thinner again,” said Housholder. “Apple started this trend with the new iPad Pro. They spent ample time discussing how it was the thinnest device they’ve ever made...yet thermal management remains one of the biggest barriers to mobile devices.”

The xMEMS XMC-2400 is pictured next to an iPhone. The company hopes the fan will prove small enough to cool mobile devices.xMEMS

Throttling has long caused headaches for device makers. In 2020, Apple agreed to pay US $500 million dollar to settle a class action lawsuit brought by iPhone users unhappy with how their phones reduced performance to keep temperatures in check.

Housholder thinks the problem will be amplified by AI features like Apple Intelligence and Google’s Gemini Nano large language model. These features, unlike prior generative AI tools that operated in the cloud, handle some AI tasks on-device in an effort to reduce latency and reduce concerns about user privacy. But on-device AI asks a lot of a mobile device’s SoC, which results in heat.

If successful, the XMC-2400 could become the first in a line of similar fans. Housholder said xMEMS can combine chips into a fan array for more demanding devices. There’s a practical limit to scale: at some point, a conventional fan is less expensive. Still, multichip MEMS fans could be a fit for thin-and-light laptops similar to a MacBook Air or Microsoft Surface Pro. “We think we can play there and deliver a performance advantage,” said Housholder.