Unlike atomic clocks, which rely on the steady resonance of atoms when exposed to a specific frequency, the new chip uses the constant, measurable rotation of molecules — not atoms – when exposed to a certain frequency of electromagnetic radiation to keep time. Such a device, say the researchers, offers the potential of significantly improving the accuracy and performance of navigation on smartphones and other consumer devices.
Today’s electronics use much less accurate internal clocks that rely on the “trilateration” of time signals broadcast from GPS satellites to navigate. Errors can be reduced with corrections from additional satellite signals – if available – but at the expense of performance and speed. When signals drop or weaken, a phone primarily relies on its internal clock and an accelerometer to estimate its location and for local navigation.
The on-chip clock developed by the researchers exposes specific molecules to an exact, ultra-high-frequency that causes them to spin at a rate reliably constant enough that it can serve as a precise timing reference. When the molecular rotations cause maximum energy absorption, a periodic output is clocked — in this case, a second.
In experiments, the molecular clock averaged an error of under one microsecond per hour – comparable to miniature atomic clocks and 10,000 times more stable than the crystal oscillator clocks typically used in smartphones. Because the clock is fully electronic and doesn’t require the bulky, power-hungry components used to insulate and excite the atoms in atomic clocks, it is manufactured with standard low-cost, CMOS integrated circuit technology.
The chip consumes only 66 milliwatts. In comparison, many common smartphone features — such as GPS, Wi-Fi, and LED lighting — can consume hundreds of milliwatts during use.
The chip-scale molecular clock can, say the researchers, also be used for more efficient time-keeping in operations that require location precision but involve little to no GPS signal, such as underwater sensing or battlefield applications. While the U.S. Defense Advanced Research Projects Agency (DARPA) has previously developed chip-scale atomic clocks, the devices cost about $1,000 each.
“Our vision is, in the future, you don’t need to spend a big chunk of money getting atomic clocks in most equipment,” says Ruonan Han, an associate professor in MIT’s Department of Electrical Engineering and Computer Science and co-author of a paper describing the clock. “Rather, you just have a little gas cell that you attach to the corner of a chip in a smartphone, and then the whole thing is running at atomic clock-grade accuracy.”
Looking ahead, the researchers plan to shrink the size of the clock further and reduce its average power consumption to a few milliwatts, while also cutting its error rate by another one or two orders of magnitude. For more, see “An on-chip fully electronic molecular clock based on sub-terahertz rotational spectroscopy.”