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The flying lens uses light emitted from plasmons. While this sounds complex, it basically operates sort of like a record arm to make ultra tiny circuits. The end result is circuits possibly as small as 5-nm and a possible replacement for Blu-Ray.  (Source: Liang Pan and Cheng Sun, UC Berkeley)

Patterns on a 4x4 array of lenses created these tiny features, with features 100-nm wide.  (Source: Xiang Zhang Lab, UC Berkeley)
New research from Berkeley could allow circuit shrinks to 5 nm

With the never-ending quest for greater processor power, the hardware industry's sharpest minds and biggest companies are pouring money, time, and effort at the challenge of extending the life of Moore's Law.  Moore's Law, which states that the maximum number of transistors on a given chip area doubles every one and a half years, is close to reaching its limit due to the problems with controlling light at ultra low nanometer resolution.  While Intel, AMD, IBM, and others race to 32 nm and beyond, this wall looms ahead.

Now new research from the University of California Berkeley could buy Moore's Law some more time, and could pave the way for the next generation of ultra-tiny transistors.  It could also pave the way for an optical drive replacement for Blu-ray.  The research was led by Xiang Zhang, UC Berkeley professor of mechanical engineering and David Bogy, UC Berkeley professor of mechanical engineering. Its new approach uses a metal arm similar to that on a record turntable or in a hard drive.  It also utilizes a tiny lens that literally flies above the surface of the chip wafer. 

With the new design, the chip makers were able to form chip designs 80 nm wide, which could easily be made much smaller.  Better yet, the wafer was spun at a rate of 12 meters per second, meaning that production would be very fast.  Professor Zhang explains an overview of the process, stating, "Utilizing this plasmonic nanolithography, we will be able to make current microprocessors more than 10 times smaller, but far more powerful.  This technology could also lead to ultra-high density disks that can hold 10 to 100 times more data than disks today."

The basic concept of photolithography is similar to film development for photography -- light triggers a reaction in a chemical layer.  In photolithography this reaction is typically a hardening.  Caustic baths such as acid can then wash away areas of semiconductor that are not protected by the hardened photolithographic mask.  Through multiple steps a circuit is built, which can contain various metal and semiconductor components.

"With optical lithography, or photolithography, you can instantly project a complex circuit design onto a silicon wafer.  However, the resolution possible with this technique is limited by the fundamental nature of light,” explained Liang Pan, a UC Berkeley graduate student working with Zhang and Bogy, and one of three co-lead authors on the associated paper. “To get a smaller feature size, you must use shorter and shorter light wavelengths, which dramatically increases the cost of manufacturing. Also, light has a diffraction limit restricting how small it can be focused. Currently, the minimum feature size with conventional photolithography is about 35 nanometers, but our technique is capable of a much higher resolution at a relatively low cost."

The new method uses a phenomenon where metal electrons vibrate when exposed to light.  These tiny vibrations are smaller than light's normal wavelength and are known as evanescent waves.  By exploiting these, light can be concentrated into patterns theoretically as small as 5 to 10 nanometers.  The test lens was 100 nm, and used a silver plasmonic lens with a concentric ring pattern.

During photolithography the lens flies above the surface of the substrate.  Similar to flying lenses developed by UC Berkeley's Computer Mechanics Laboratory, the flying lens contacts the surface similar to the needle on a record player arm.  However, unlike a record player the lens is not physically touching -- it uses light instead to "touch" the surface.  The tiny lens uses the same lift mechanics used by aircraft, except on a microscopic scale to stay at a constant 20 nm above the surface.

Professor Zhang added,”The speed and distances we're talking about here are equivalent to a Boeing 747 flying 2 millimeters above the ground.  Moreover, this distance is kept constant, even when the surface is not perfectly flat."

The scan speed is very fast -- approximately 4 to 12 m/s in the testing.  Further, up to 100,000 tiny patterned lenses could be packed into the arm, allowing many parallel writes.

Best of all the new process is extremely cheap compared to conventional methods.  Technologies such as 45-nm lithography equipment are extremely expensive due to complex lens and mirror setups needed to concentrate the light.  With the new method less expensive slightly larger wavelength UV light can be used to excite the plasmonic lens.  With the only price component being the plasmonic lens setup, costs for shrinks would drop dramatically.

Professor Zhang is hoping the technology is put to use in commercial scale production within 3 to 5 years.  He states, "I expect in three to five years we could see industrial implementation of this technology.  This could be used in microelectronics manufacturing or for optical data storage and provide resolution that is 10 to 20 times higher than current Blu-ray technology."

The research will be reported in the December issue of Nature Nanotechnology.

Coauthors on the study are Werayut Srituravanich, a former Ph.D. student in Zhang's lab and currently a lecturer in mechanical engineering at Chulalongkorn University in Thailand, and Yuan Wang, a UC Berkeley graduate student in mechanical engineering, and Cheng Sun, a former graduate student in Zhang's lab and currently an assistant professor in mechanical engineering at Northwestern University.

The research was funded in part by a National Science Foundation Center for Scalable and Integrated Nano-Manufacturing grant.





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