Sapphire Demystified

A look at Rubicon Technology's sapphire

A look at Rubicon Technology’s sapphire

There has been so much hype and misinformation about sapphire lately, particularly surrounding sapphire covers or faceplates for smartphones, that we thought we’d review some basic info about commercial sapphire.

  • “Sapphire glass”

There really isn’t any such thing as sapphire “glass.” Sapphire is not a kind of glass; it’s a very hard monocrystalline material. The proper way to reference the clear layer of stuff that may soon cover the screen of your smart phone is as a “sapphire cover” or “sapphire faceplate.” Glass is made of silica or sand, and sapphire is made from aluminum oxide. The two materials have very different physical properties. So, glass isn’t really the right descriptor.

  • Sapphire is unbreakable.

Well, no. That’s not really accurate. A thin piece of sapphire can shatter, similarly to glass or a piece of gorilla glass. Sapphire is the second hardest material on Earth (after the diamond). As such, a thin slice of sapphire will shatter. What is sapphire good at? Sapphire is scratch resistant. That’s one of the main reasons why smartphone vendors are interested in sapphire for applications in lenses and fingerprint scanners.

  • Sapphire is blue.
Sapphires come in a range of colors.

Sapphires come in a range of colors. The purest sapphires are clear.

Yes and No. Sapphire, also called corundum, comes in a range of colors. The purest form of sapphire is clear.  Sapphire is a crystal made from Aluminum Oxide (Al2O3). Natural sapphire forms over thousands of years in the earth, but comes in different colors due to impurities such as minerals or other conditions (like humidity or radiation). Rubies are made of aluminum oxide and are actually sapphires. They are red because the crystal contains impurities in the form of the mineral chromium, making the crystal red. Sapphire gemstones get their blue hue from iron and titanium. Yellow sapphires get their color from a combination of iron and radiation (interesting).  The commercial sapphire that’s now being used in consumer electronics is very pure, so it’s colorless.

  • Sapphire in LEDs and smart phones is from blue sapphire gemstones.

No. The sapphire that is used in LEDs and smartphones is grown in a commercial setting using one of few processes – the Verneuil Method, Kyropoulous Method, Heat Exchanger Method, Czochralski Method and Edge-Defined Film-Fed Growth Method. Each method has its differences, but they produce a single crystal of clear sapphire that is fabricated (cut and polished) into a sapphire substrate used in an LED or into a lens or faceplate for optical uses like smart phones.

 

FIFA World Cup: LEDs Celebrate Soccer

Iconic Christ the Redeemer statue lit up in LEDs to celebrate the FIFA World Cup in Brazil

Iconic Christ the Redeemer statue lit up in LEDs to celebrate the FIFA World Cup in Brazil

While the glitz and glamour of FIFA World Cup soccer remains on the field, others in Brazil are turning to LEDs to celebrate the tournament with light.  Even Brazil’s iconic Christ the Redeemer Statue is taking a role in the FIFA World Cup. The monument will be lit up with the colors of each country’s flag. This is possible due to a recent LED lighting retrofit of the popular tourist destination Rio de Janeiro, Brazil.

Completed in 1931, the famous statue had an LED light retrofit for its 80th birthday in 2011. Lighting company Osram replaced the outdated lighting system with 300 advanced LED projectors (from subsidiary Traxon Technologies).  These high-output spotlights are fitted with a special lens to precisely light the statue in alternating colors and different light intensities.

A special “Lighting Control Engine” aims each LED projector to light a particular part of the statue. The lighting can be programmed and controlled remotely providing energy efficient atmospheric lighting for the monument. The new lighting system saves time and resources for the Archdiocese of Rio de Janeiro.

For Further Reading & Viewing

The Guardian, Rio de Janeiro’s Christ the Redeemer lit up in celebration of the World Cup – video, http://www.theguardian.com/football/video/2014/jun/12/rio-de-janeiro-christ-the-redeemer-lit-up-celebration-world-cup-video

NLB, Christ the Redeemer Monument in Rio de Janeiro Bathed in a New Light, http://www.nlb.org/index.cfm?cdid=10779&pid=10634

NDTV Sports, FIFA World Cup 2014 Opening Ceremony, Highlights: J-Lo, Pitbull Kick Off Biggest Mega-Event in Sao Paulo, http://sports.ndtv.com/fifa-world-cup-2014/news/225479-live-blog-fifa-world-cup-2014-opening-ceremony

ECD Solutions, Brazil’s football stadiums install LED lights ahead of summer tournament, http://www.electricalsolutions.net.au/case_studies/67109-Brazil-39-s-football-stadiums-install-LED-lights-ahead-of-summer-tournament

Schreder, SCHRÉDER, PARTNER FOR LIGHTING THE 2014 FIFA WORLD CUP STADIA IN BRAZIL, http://www.schreder.com/be-en/News/Pages/Schreder-partner-for-lighting-2014-FIFA-World-Cup-Stadia-in-Brazil.aspx

 

 

 

LEDs and the Evolution of Sapphire Quality

Semiconductor Today recently published a new article about sapphire quality, Marked advancement in sapphire crystal quality from improved process control, written by John Ciraldo of Rubicon Technology. The article examines sapphire quality and how sapphire makers strive to keep up with the pace of advances in LED technology. Sapphire is a very important part of LEDs. Sapphire is the substrate, or foundation, for more than 85% of LEDs. And quality starts with that foundation.

According to Ciraldo, sapphire is the most suitable material for a substrate in LEDs because, in addition to its availability, favorable optical properties and relatively low cost of use, it has superior lattice (arrangement of atoms) matching to GaN, the material that is layered on sapphire during epitaxial growth to make an LED. The industry calls it a “lattice mismatch” because the layers don’t line up perfectly due to differences in crystalline structure of the two materials. The mismatch between GaN and sapphire can be further exacerbated by defects in the sapphire crystal such as surface bubbles, dislocations and impurities. The quality of the sapphire and this “mismatch” ultimately impacts the performance of an LED that provides the light source for an LED light bulb.

Ciraldo notes that LED producers continue to push the limits of power and efficiency in their devices making substrate quality an increasingly important consideration. He notes that “as a result, substrate producers need to continue to innovate and find new ways to enhance their material.”

He explains how Rubicon Technology takes a holistic approach to improving the quality of its sapphire using vertical integration throughout crystal growth.  Rubicon controls every aspect of the crystal growth process from the raw material all the way through finishing in order to gain greater consistency and uniformity and has earned a reputation for overall sapphire material quality.

Figure 1: X-ray rocking curve of c-plane sapphire material. The Bragg reflection of the sapphire was  for  the  (0006) reflection which  occurred at a Bragg angle of 21 degrees. The synchrotron  x-ray beam had been preconditioned with a Si(111) x Si(111)  double crystal  monochromator. Intensity recorded via pin-diode.

Figure 1: X-ray rocking curve of c-plane sapphire material. The Bragg reflection of the sapphire was for the (0006) reflection which occurred at a Bragg angle of 21 degrees. The synchrotron x-ray beam had been preconditioned with a Si(111) x Si(111) double crystal monochromator. Intensity recorded via pin-diode.

How do they know they produce quality sapphire? Ciraldo details how Rubicon uses x-ray diffraction (XRD) rocking curves and x-ray topography images to evaluate the quality of sapphire. For research related to the article, Ciraldo partnered with scientists at The Advanced Photon Source at Argonne National Laboratories, Dr. Albert Macrander and Dr. Naresh Kujala, to evaluate sapphire samples from Rubicon and two competitors. This work is supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.

Rocking curve data shows that material from Rubicon exhibits a greater overall intensity with a significantly narrower peak, both of which are indicators of superior crystal quality. In addition, the rocking curve data shows higher symmetry in the Rubicon sample, indicative of a very low stress gradient within the material. Low stress is another very important characteristic of a high quality crystal. X-ray topography measures crystalline quality. The team examined the same samples using X-ray topography.  The images show defects in the lattice structure represented by dark spots and streaks. The Rubicon sample demonstrates fewer defects and streaks.

X-ray topography images of c-plane sapphire. Light and dark spots, such as those that are circled, are artifacts from imaging and developing and are unrelated to crystal structure. Boxed in region is an example of a tangle, or large band of defects.

X-ray topography images of c-plane sapphire. Light and dark spots, such as those that are circled, are artifacts from imaging and developing and are unrelated to crystal structure. Boxed in region is an example of a tangle, or large band of defects.

Ciraldo concludes that, “by exercising more control over the production of our sapphire material through a vertically integrated approach, Rubicon Technology has demonstrated vast improvements in the overall quality of sapphire crystals that make them much more suited to advanced applications, including high-efficiency LEDs.”

 

 

 

For Further Reading

Semiconductor Today, Marked advancement in sapphire crystal quality from improved process control, http://ow.ly/xZcGO

LEDs and Medicine: Diffuse Optical Tomography Uses LEDs to Scan Brain

A look at current DOT testing

A look at current DOT testing

According to a report in BioOptics World, scientists at the Washington School of Medicine in St. Louis, Missouri have developed a new way to study the brain, diffuse optical tomography (DOT), a new non-invasive technique that relies on LEDs rather than magnets or radiation. While still experimental, it offers promise for a new non-invasive test for the human brain.

While it looks primitive now, DOT scans use LED light to measure brain activity. For a DOT scan, a subject wears a cap composed of many light sources and sensors connected to cables. A DOT cap covers two-thirds of the head and involves shining LED lights directly into the head. DOT images show brain processes taking place in multiple regions and brain networks, like those involved in language processing and self-reflection (daydreaming). It also avoids radiation exposure and bulky magnets required by positron emission tomography (PET) and magnetic resonance imaging (MRI) respectively.

DOT works best for patients with electronic implants that can be problematic with MRI testing such as pacemakers, cochlear implants, and deep brain stimulators (used to treat Parkinson’s disease). The magnetic fields in MRI may disrupt either the function or safety of implanted electrical devices while DOT doesn’t impact these types of devices.

How does DOT work? According to author Joseph Culver, Ph.D., associate professor of radiology, DOT can detect the movement of highly oxygenated blood flows to the parts of the brain that are working harder when the neuronal activity of a region in the brain increases. He told BioOptics World that, “It’s roughly akin to spotting the rush of blood to someone’s cheeks when they blush.”  According to the magazine, DOT works by detecting light transmitted through the head and capturing the dynamic changes in the colors of the brain tissue.

DOT has a lot of potential benefits for medicine concerning the brain.  Since DOT technology does not use radiation, doctors could monitor progress of patients using multiple scans performed over time without worry. It could be useful for patients recovering from brain injuries, patients with developmental disorders such as autism, and patients with neurodegenerative disorders such as Parkinson’s.

Currently, a full-scale DOT unit takes up an area slightly larger than a phone booth, but Culver and his team have built versions of the scanner mounted on wheeled carts. The DOT device is designed to be portable, so it could be used at a patient’s bedside in the hospital or at home, in a doctor’s office, or even in the operating room in the future.

For more details about DOT, visit:

BioOptics World, DIFFUSE OPTICAL TOMOGRAPHY ABLE TO SCAN THE BRAIN WITHOUT RADIATION, MAGNETS, http://www.bioopticsworld.com/articles/2014/05/diffuse-optical-tomography-able-to-scan-the-brain-without-radiation-magnets.html

Nature, Mapping distributed brain function and networks with diffuse optical tomography, http://www.nature.com/nphoton/journal/v8/n6/full/nphoton.2014.107.html (registration required)