ANN ARBOR, MI - Just how tiny is the world's smallest computer?

According to a team of University of Michigan electrical and computer engineering professors, the new device they created is dwarfed by a grain of rice. It could even be described as the size of a speck of dust.

The team has created a device nearly 10 times smaller than a computer introduced as the world's smallest by IBM in March.

While IBM's 1-by-1 millimeter computer was being revealed, the UM professors were in the process of creating a cousin to their previous tiny computing device, the Michigan Micro Mote.

Measuring in at a mere 0.3 millimeters on each side, the new device also is about 10 times smaller than the previous Michigan Micro Mote, which came in with dimensions of 2-by-2-by-4 millimeters.

David Blaauw, a professor of electrical and computer engineering at UM, said the intent of creating the new computer was to scale it down significantly while maintaining some computational functions.

"With this one, we really wanted to push further on the size and see how far we could reduce it while keeping some level of intelligence and computational capability, which the computer has in there," said Blaauw, who led the development of the new system with fellow UM electrical and computer engineering professors Dennis Sylvester and Jamie Phillips.

The UM device is capable of measuring temperature and could be useful in studying tumors for oncology research.

While it currently holds the record as the world's smallest, Blaauw admitted its capabilities raise questions of what constitutes a "computer."

UM's device can't fit a battery because batteries don't scale well with such small sizes. The device also needs continuous illumination to be able to harvest and operate, meaning it cannot retain programming data if its light source is dropped, similar to the IBM chip.

In other words, if you unplug a desktop computer, its program and data are still there when it boots up after power is restored. These new microdevices, from IBM and now Michigan, lose all prior programming and data as soon as they lose power.

Blaauw likened computers to animals in that they need to be able to eat and store energy, and then eat again, which was the case with the previous Michigan Micro Mote.

"This guy kind of has to graze all of the time," he said of the new record-holder.

"When IBM came out with the news release, we had two reactions," Blaauw added. "One, we have something smaller in the works that we're about to show, and secondly, we weren't quite sure if we should call it a computer or not because of the ability to retain programming and data between times when the system is active."

A computer so tiny can only receive a few nano-amps of energy currents. Blaauw compared that to an inactive cellphone, which uses a milliwatt - about a million times more than the UM chip.

"That (was the) biggest challenge: Can we make the circuits, the processor and the computer survive on such (small) amount of energy and power?" Blaauw said.

Additionally, assembling and packaging a device so small was difficult, Blaauw said. Being the size of a "speck of dust" means the device could only be assembled and moved with a machine. With the previous Michigan Micro Mote, the team was able to protect the computer's circuits against light, while that could not be done with such a small model.

That meant the team had to create a computer that was both low power and able to withstand light exposure. The light from the base station - and from the device's own transmission LED - can induce currents in its tiny circuits.

The computer's size has its advantages, Blaauw noted, with the main function of sensing temperatures. The team created a computer with great accuracy, allowing it to get into small nooks and crannies, while measuring changes in temperature.

The team's longtime collaborator, Gary Luker, a professor of radiology and biomedical engineering, believes the computer could be useful in answering questions about temperature in tumors.

Some studies suggest that tumors run hotter than normal tissue, but the data isn't solid enough for confidence on the issue, Luker said. Temperature may also help in evaluating cancer treatments.

Since the temperature sensor is small and biocompatible, Luker said the device could be implanted it into a mouse and cancer cells grow around it. The temperature sensor could then investigate variations in temperature within a tumor versus normal tissue, determining success or failure of therapy.

"There's interest in understanding how metabolism of tumors change as they're being treated," Blaauw said. "The thought is that if you have some tumor tissue as it becomes malignant or as it's being treated with chemotherapy, that its temperature characteristics change.

"That would be interesting, that's not really known at this point," he added. "That could help for diagnosis at some point down the road. To be able to measure that precisely in a small amount of tissue you would need an extremely small sensor."

The study was presented June 21 at the 2018 Symposia on VLSI Technology and Circuits.