Scientists and engineers have created and used microelectromechanical systems (MEMS) since they mastered the fabrication techniques used to transform lab curiosities into sensors, microphones, security devices, engines, and even electromechanical switches for smartphones.
Researchers at the Sandia Corporation have created machines complete with gears and microscopic transmissions, as shown in the photo below. But like all mechanical components, MEMS devices suffer from a variety of failure mechanisms.
(Photo courtesy of Sandia National Laboratory.)
The US National Institute of Science and Technology (NIST) recently publicized a new direction for MEMS devices by "machining" diamonds -- the hardest substance known. According to NIST, semiconductor makers hope the diamond-etching techniques will let them develop components for long-lasting micro-machines. In the abstract for a research paper, authors Craig McGray, et al., note:
Etching of monocrystalline diamond in oxygen and water vapor at 1100C through small pores in a silicon nitride film produced smooth-walled rectangular cavities. The observed cavities ranged in size from approximately 1μm up to 72μm wide, in each case exhibiting smooth, vertical sidewalls, a flat bottom, and a depth equal to half its width. Cavity boundaries were determined to lie along slow-etching (100) crystallographic planes, suggesting the possibility of a powerful class of techniques for micromachining of diamond.
This image shows the box-like shape of a pit the NIST team etched into a diamond surface and the pit's smooth vertical sidewalls and flat bottom. (Photo courtesy of NIST.)
So far, the NIST researchers have created virtually indestructible nano-rulers, but the etching technology might lead to improvements in MEMS devices because moving parts made of diamond should last much longer than those fabricated from silicon. The inherent cubic-crystal structure of diamonds should also help researchers -- and later, engineers -- create precision structures.
According to NIST, the speed of the etching process depends on the orientation of the diamond crystal. Etching occurs more slowly in the direction of the crystal faces or planes, which can serve as a boundary of sorts where etching would cease as desired. The cavities created at NIST all have smooth vertical sidewalls and a flat bottom.
"We'd like to figure out how to optimize control of this process next," said McGray, "but some of the ways diamond behaved under the conditions we used were unexpected. We plan to explore some of these mysteries while we develop a prototype diamond MEMS device."
I don't relish the idea of having to develop a diamond-etching process with 1100C water vapor formed from hydrogen and oxygen in a reaction chamber, but additional research might uncover other etching and manipulation techniques that lead to diamond-based MEMS. The NIST paper and announcement made no mention of creating structures on the diamond surface, but perhaps deposition of diamond or diamond-like materials could lead to layers of complicated mechanical movements. And even a diamond substrate might improve reliability of present MEMS structures.
Great article. It's neat to see something like this that is relatively new. So new, it appears the engineers are really saying, "Cool...so what does it do?" I enjoy hearing about technology that is so recently developed that engineers aren't really sure what to do with it. I think this is where a technology like this can grow into something that is much bigger than the discovering engineers believe.
As the technique is good at making rectangular things, I suggest the creation of a machine tool in microminiature size. Such a tool needs a programmable motion X-Y Table. One design that might fit the bill is a very miniaturized version of US Patent #4,676,492,1985. The general geometry enables rectilinear motion in X-Y, transfer of vertical loads directly to substrate (there are no piled up stages), and the drives for the miniaturised system can be electrostatic or any other suitable prime movers. Electromagnetic would probably be too bulky.
To keep the product in place upon the X-Y table while being machined or processed, magnetics could be used, or quantum grabbing if the system can be cooled to about -200 C. The same quantum grabbing can also be used as prime mover.
Do any MEMS devices use a lubricant (solid or liquid)? This could be a big deciding factor on how different materials will work together or with themselves. Dissimilar materials might last longer if they run against each other. For instance, at the macro sizes, 2 pieces of stainless or aluminum rubbing together easily causes galling.
From what the NIST people said, it seems more likely they will use diamonds to form the "block" on an engine, for example, rather than the pistons, cams, and gears. Some of the photos on the Sandia Labs Web site show what can happen as silicon "bearings" and "axles" wear. Lots of wear and tear that leads to catastrophic failure. Diamond might make a better substrate rather than a wholesale replacement for silicon in every MEMS device.
For anyone interested in Minecraft, find the Minecraft site at: http://www.minecraft.net/. --Jon
Thanks for a great article, Jon. I'm certain the good folks at NIST are characterizing their new MEMS materials, but I'm concerned that at least at the macroscopic level, building a complex machine out of diamond wouldn't fair very well. The extreme hardness of diamond would be similar to making gears and shafts out of cast iron -- a very hard material that is too brittle to withstand the stresses involved with machines.
However, I'm intrigued with the creation of square objects with diamond. This reminds me of the very popular "Minecraft" game that permits players to create entire cities complete with complex machinery out of square blocks. When NIST perfects the square diamond MEMS fabrication technique, there will be an army of teenage engineers standing by to create.
Not to worry, Beth. The NIST researchers used synthetic diamonds produced at microscopic sizes, so you might still have a shot at a new ring or pendant. NIST won't try to corner the market for mined dimaonds and I doubt it would pay to carve such diamonds into small slices for future MEMS devices. When I worked at DuPont in 1969, a chemist in the nextlab worked on methods to separate synthetic diamonds by size. Because the diamonds were tiny, he tried several techniques to suspend diamonds of different weights at individual levels, or "bands," in a fluid with a variety of flow rates. I don't know how the research turned out.
DuPont's interest in diamonds stemmed from a desire to use explosives in new ways. In this case, to create shock waves that turned graphite into tiny industrial diamonds, not gemstones. DuPont made explosives and I worked in the Explosives Department in the Gibbstown, NJ lab, now long gone. Thankfully the diamond "blasts" occurred at a testing ground away from our labs. --Jon
Are there any practical uses for this type of micromachine yet, or at least fundamental ideas? Also, I didn't catch what is being used to power them. I'm sure that's another whole topic.
@Beth - They are probably using industrial diamonds such as those used in saws. You'll still be able to get your jewelry! :)
Interesting post, Jon. I know I'm probably looking at this a bit differently than most of the Design News audience, but machining diamonds to make some sort of machine? That seems like a waste, not to mention, wouldn't the cost factor be an issue given how expensive these gems are?
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