Time to Industrialize Chip-scale Atomic Clocks

Barely the size of a matchbox, the new generation of chip-scale atomic clocks (CSACs) developed by Tianjin Huaxin Technology Co. is ready to enable precise timekeeping for deep-sea oil exploration, commercial satellites, and smart power grids.

The "time magic box" has a volume of just 8 cm^3 and power consumption of 0.15 watts, yet can still keep time autonomously without satellite signals, drifting less than one second every 10,000 years. In 2023, China activated its first — and currently only — CSAC production line, breaking the previous foreign monopoly on this critical technology, after a 13-year uphill battle against seemingly impossible physics and engineering odds.

Taming temperature and signal

The journey to produce CSACs began with deceptive simplicity. "We were optimistic at first," recalls Liu Ruiyuan, general manager of Huaxin. "The principles were known." However, their first prototype was a failure, as it could not detect the ultra-weak optical signal needed to lock onto atomic transition frequencies. They had built a "dead clock."

The problem was environmental noise. The critical signal only produced a few thousandths of the power of the laser's intensity and can be completely drowned out by tiny temperature fluctuations. To solve this, the team developed a microfluidic temperature control chip, pushing precision from 0.1°C to an extraordinary 0.001°C. This finally allowed the signal to emerge from the environmental noise.

Unfortunately, the signal remained unstable.

For four years and through hundreds of trials, the team focused on the atomic vapor cell — the "heart" of the device. The type and ratio of buffer gases inside this cell were the key. After endless experimentation, a stable signal finally appeared on a monitor. The atomic clock was "alive." This phase demonstrated that mastering quantum physics is only the first step; conquering micro-system integration and materials science is where true innovation begins.

Engineering the perfect vacuum

Moving a lab prototype to a reliable product required solving vacuum packaging. The entire physics package must be sealed inside a 1 cm^3 ceramic cavity, with an extremely low leak rate needed to maintain a 10-year lifespan.

A leak just 10 times larger would double power consumption and cripple performance.

Initial attempts using standard welding furnaces failed to achieve the necessary vacuum. "Each unit is expensive, and we could only make one or two a week, most ending up as scrap," said Liu, pointing to a pile of failed units. After six months of inconsistent results, the team abandoned off-the-shelf tools and co-developed a custom vacuum welder with a motion mechanism. This meant conquering three major challenges: precision alignment under extreme heat, controlling solder splash, and optimizing heating curves.

The R&D team worked in harsh conditions — a vacant factory in Daxing, Beijing, with summer temperatures over 40°C and winter cold so severe it numbed their hands. A single weld required 20+ hours of continuous monitoring, with teams working in shifts to adjust parameters. In July 2020, after four years of effort, the reliable vacuum seal was finally achieved, turning an experimental possibility into an engineering reality ready for production.

Building a production line

Despite a working product, manual production was unsustainable. Ten technicians using tweezers under microscopes could produce only 200-300 units per year, far short of the thousands needed for national projects. "A major advantage of CSACs is mass production," said Liang Xiaopeng, chairman of Huaxin. "We had to build a line."

With no domestic reference to follow, the team designed everything from scratch. The smallest physical part is just 0.2 mm (two hair-widths), requiring micron-level precision systems. Many automation equipment vendors were unable to help due to the difficulty of the task. Moreover, to automate the manual process, materials and workflows had to be completely redesigned.

To overcome these challenges, Huaxin collaborated with the Institute of Physics at the Chinese Academy of Sciences, leveraging their semiconductor equipment and micronano processing capabilities. Through iterative testing, they locked in optimal process parameters.

By continuously refining equipment and processes, the team pushed the production yield above 98 percent. In the summer of 2023, China's first CSAC production line, with an annual capacity of 30,000 units, went into operation in Tianjin's Binhai High-Tech Zone.

"This component has driven an entire industry," said Liang. The availability of domestic CSACs has enabled more precise node-based seismic exploration and is expanding into commercial satellites and smart grids.

The next goal is to expand capacity to 100,000 or even one million units annually, while collaborating with top research institutes to develop even more advanced products. The quiet "tick" of this tiny clock marks not just the passage of time, but the heartbeat of Chinese innovation — a decisive shift from "Made in China" to "Created in China."

Source: Science and Technology Daily