The same power-hungry AI that is driving the need for more efficient cooling in data centers is heating up smartphones, but smaller form factors have unique challenges.

XMEMs is taking a solid-state approach to cooling with what it calls a “fan on a chip” for ultraportable devices that are increasingly running more demanding applications and AI workloads.

Drawing on its expertise in all-silicon micro speakers, the company’s XMC-2400 µCooling chip is an all-silicon, active micro-cooling fan for ultramobile devices that provides active, fan-based micro-cooling (µCooling) at the chip level.

Measuring only 1 mm thin, the silent, vibration-free, solid-state XMC-2400 µCooling chip can be integrated by manufacturers into smartphones, tablets and other advanced mobile devices.

In a briefing with EE Times, Mike Housholder, VP of marketing and business development for xMEMs, said a single chip can move up to 39 cm³ of air per second with 1,000 Pa of back pressure.

A smartphone is just a broad-based example of a thin edge device that could benefit from xMEMs’ ultra-thin cooling solution, he said. Typically, devices are about 5 mm thick, while the smallest conventional fan is about 3 mm thick. “There is no real active cooling solution that you can implement today in the in the thinner devices, tablets, phones and the ultra thin PCs.”

Instead, everything is passively cooled with heat spreaders and vapor chambers, Housholder added. “They’re just spreading the heat throughout the real estate of the device, but there is no physical means to expel the heat from the device.”

Once heat spreading has been maximized across the real estate of the device, he said, the only thing left to do is throttle back processing, which in turn throttles apps and services with features like a screen brightness dim, while application performance is slowed down.

The need for a better way to cool smartphones comes at a time when major players like Apple and Samsung are adding more AI, while Microsoft has been making announcements in the PC space, Housholder said. Features like computational photography and real-time voice assistants are compounding the problem, especially given the network connectivity they require, while more cores, memory and power mean more heat, he added.

Smartphones are the obvious target for xMEMs’ XMC-2400 µCooling chip, and the company’s initial focus is to bring active cooling to thin devices that could not have accommodated a fan if they wanted to, Housholder said.

The principles of the cooling chip are based on the company’s MEMs speakers that are already on the market. Housholder said a speaker moves air for the purpose of generating sound that the ears can hear using ultrasonic transduction.

He said the ultrasonic transducer for audio was the trigger point to get xMEMs working on ultrasonic transducers for air flow and cooling because it replaces coils, magnet paper and plastic diaphragms with solid state MEMs to essentially create a fan-less fan. “We’ve got MEMS structures that are moving up and down,” he said. “It performs the function of air flow, which you might equate to a fan, but this is very different in terms of how it operates and some of the efficiencies that it delivers.”

Housholder said there are no standards for this new space xMEMs is serving with its new cooling chip, but the company’s semiconductor process can scale to very high volumes with its fab partners, which today include TSMC and Bosch. “This supply chain is already functioning and shipping in high volumes for our audio products,” he said. “We have a fully functional, fully validated supply chain.”

Active cooling for thin devices may be a new space, but research has been going on for at least a decade. Saibal Mukhopadhyay, professor and a fellow of the IEEE at Georgia Tech’s School of Electrical and Computer Engineering, told EE Times in an interview that there was not a lot of interest in cooling mobile devices back in 2014. “Now it’s becoming an important problem.”

He said the main challenge for cooling mobile devices has been lack of space, as well as the cost. Research done so far includes work in 2016 that looked at the feasibility of using Piezoelectric pumps on a Snapdragon processor.

Another approach is using thermoelectrics to cool a specific spot on a chip by integrating thermoelectric devices within the package to electrically control the area that is getting hotter and give it a cooling boost, Mukhopadhyay said.

Other work at Georgia Tech includes investigating phase change materials that act as a thermal capacitor, which will change state as the chip gets hotter, he said. “It will start capturing heat without letting the temperature go up.”

While mobile has different challenges than data centers, Mukhopadhyay said, it is notably different in that a device doe not need to cool when it is sitting idle. “It’s never going to be always busy.”

Cost considerations are different, too, he said, as the mobile market is much more sensitive to price—a cooling solution cannot add too much cost per unit.

That means any cooling solution must account for the on-demand nature of a mobile device, he said, while the goal of the data center is to maximize server use and processing power.

In addition to more compute intensive AI, smartphone and edge devices are increasingly doing more communications with 5G and 6G that require more power and in turn generating more heat. “Both of these factors are playing a role.”

By: DocMemory
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