The World’s Smallest Vacuum is the Size of a Penny
Miniaturization makes room for a new industry to emerge.
“DARPA has always wanted exotic instrumentation to be made smaller and portable,” explains Wei Yang, an engineer at Honeywell, who was recently challenged to design the world’s smallest vacuum pump.
The initial brief came when DARPA wanted to put a mass spectrometry gas analyzer, a device that is typically the size of a refrigerator, on an aircraft.
“We looked at what DARPA wanted, and it came down to making a really small vacuum pump,” explains Yang. Five years in the making, Honeywell finally responded with the smallest vacuum pump in the world.
A microfabricated, turbomolecular pump, the device operates in the mid-vacuum and high-vacuum range, and works like a turbine in reverse. Although it was originally designed for use in the analyzer, further miniaturization will expand its use to applications in mobile phones and other handheld devices.
“The vacuum is a really important part of modern technology,” says Yang, as it is involved in almost every aspect of technology. “It is behind all major progress in modern history, from the discovery of atoms and molecules, down to DNA and computer chips.”
While all these discoveries required a vacuum in the process, these vacuums were large and in a lab. “They could not be moved, much less installed on a small plane or in a phone,” he adds. “A new industry is born once you move a main frame computer into a person’s home, and once again when you put that same computer into a person’s pocket: Miniaturization is powerful.”
Now, with what they claim to be the smallest vacuum in the world, Honeywell has eliminated what they believe to be the last hurdle to a whole class of valuable instrumentation.
A Turbine Compressor on a Penny
Microfabrication technology has a long standing legacy of Honeywell, beginning in the 1960s when they began the production of silicon based pressure sensors.
“Honeywell first started working on micro instrumentation back in the 1960s – before the phrase MEMS was even coined. We’ve developed a number micro devices over the years, including a silicon-based pressure sensor, un-cooled IR camera, gyroscopes, and other aerospace and sensor products. The micro vacuum pump is the newest in the MEMS arena for us,” explains Mark Hamel, automation and control solutions at Honeywell.
Since then, the company has been making mechanical structures out of silicon on a much smaller scale.
“Our history is why we were able to be successful in making the vacuum pump,” says Yang. With such history, the company employed the same equipment and steps to develop the vacuum as they have with other microelectromechanical systems (MEMS).
The process beings with photolithography to create the basic pattern of the wafer with mask material. Then, the surface is bombarded with ions to create deep trenches. This process, called deep reactive-ion etching (DRIE), is good at creating tall standing sructures, which was needed to create the blades within the vacuum.
The blades on the rotor work like a turbine compressor, and are angled to push gas outward as they spin, creating a vacuum in the center.
“The blades are tilted in a certain orientation that will preferentially hit molecules to move them in the direction you want them to go, which is how a turbo compressor works,” explains Yang. However, instead of relying on just a few blades like most turbo compressors, the company put hundreds of thousands of blades on the area of a penny.
When the blades move in a turbine compressor, it is like a “baseball bat hitting a ball,” says Yang, “but on this scale, it is the blades hitting molecules.” This scale came with an entirely new set of challenges (see side bar).
The Power of Miniaturization
Creating the world’s smallest vacuum pump has opened up a new class of instrumentation. With support from DARPA, the technology is being developed to address the potential threat of terrorist attacks involving explosives, and biological or chemical agents. “These are top government priorities, so they have spent a lot of money on this kind of technology,” says Yang.
Currently, a plane monitoring the air for these agents basically opens up a bottle, and sends the sample away to await results. The process can take weeks. With a miniaturized sensor, a plane could fly over an area, “smell” the air, and send the information back wirelessly.
On land, six-point sensors are located at certain check points to detect these threats. “If you can place these sensors that are able to smell in the hands of everyone with a phone, a terrorist carrying these harmful devices would be in a network of detectors, and it would be much harder for them to implement an attack,” explains Yang. These government applications could become a reality within three years.
The sensors could also be programmed to detect disease, a technology that has traction in the medical field to speed up the process of diagnosing and treating disease. It could even help create a dynamic map of how a disease is spreading. The same principle would apply to pollution, or a chemical spill.
Consumer products are the most challenging, and further research is required including greater miniaturization to make the technology viable for cellphone use. For Honeywell, the current emphasis is on industrial and commercial applications.
The world’s smallest vacuum pump has the potential to spark the same revolution that occurred when we took the phone off the wall and put them into people’s pockets. Miniaturization is powerful, and with it comes the potential to create an entire new industry.
When CFD Isn’t an Option
Computational fluid dynamics (CFD) software is a common tool used throughout the product design process in regards to simulation and testing. However, when performing these tests at the micron level, the engineers at Honeywell found they required a new tool.
“At these dimensions, gas behaves more like particles bounding around, and you see the granularity of gases instead of the continuous fluid,” explains Wei Yang, engineer at Honeywell. To overcome this challenge, Honeywell developed a proprietary simulation software that treats gas as individual particles, as opposed to a fluid.
Developing this software proved to be critical in the development of the vacuum pump and it was one of the most difficult hurdles to overcome.