The Many Sides of Sapphire

Sapphire substrates are used to grow semiconductor compounds, most commonly GaN for LEDs and other applications such as high temperature superconductors. They are also used to grow silicon for manufacturing microwave ICs, high-speed ICs and pressure transducers.

Sapphire is the single crystal form of aluminum oxide (Al2O3), and single crystals are made of identical building blocks, known as unit cells, which repeat themselves continuously and unbroken from edge to edge. This makes the atom arrangement of a sample highly organized and predictable. The crystal structure of sapphire is hexagonal/rhombohedral.

ShapeTo grow different material on sapphire with atom layer-to-layer precision requires atomic level agreement between the substrate and the material. These requirements are only satisfied along specific surfaces known as planes of the sapphire crystal.  Optical properties, hardness and thermal conductivity of sapphire also vary significantly by the orientation.

Based on application specifications, sapphire single crystal structure is divided into multiple planes. The planes most frequently used — c, a, m and r — are shown in the figure with respect to sapphire crystal axis directions. The atomic arrangement in each plane is unique and shown in the figures below with grey atoms representing aluminum and red atoms representing oxygen.









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.


Opportunities for Sapphire – A New Look at Smartphones, Tablets and Even Smartwatches

This week, we’ll take a look at smartphones, tablets and smartwatches and the market opportunity that these consumer devices present for sapphire. Sapphire can be used in a number of ways in them ranging from LEDs for the backlighting display and LEDs for the camera flash to sapphire material for use camera lens covers and home button covers. There’s even speculation that they could be used for front cover plates in smartphones.

Recently, smartwatches and “wearables” have become “fashionable” so we’ll take a look at sapphire in smartwatches too. The infographic in this post points to the number of ways that sapphire could be used in smartphones and tablets.

Opportunities for Sapphire: Smartphones and Tablets

Opportunities for Sapphire: Smartphones and Tablets

Let’s take a closer look at the market for smartphones and tablets.  Backlighting has been a very fertile area for LEDs. The market penetration of LEDs in backlighting displays for mobile phones, tablets, LED camera flash and keyboards is nearly 100 percent. But, let’s look at the numbers.

First, 2013 was a groundbreaking year for smartphones. According to market research firm Gartner, smartphone sales surpassed feature phone sales for the first time with smartphones accounting for 53.6% of overall mobile phone sales for the year.  Overall, Gartner says that 968 million smartphone device units out of a total of 1.8 billion mobiles were sold in 2013. Given that there’s an opportunity to sell sapphire for multiple uses in each smart phone, that’s quite a bit of sapphire. And, even feature phones present an opportunity for sapphire in backlighting, camera flashes and camera lens covers.

In tablets, the opportunity for sapphire is in the same applications, but with a twist. Backlighting is a good opportunity with even more display real estate that larger tablet screens represent.  Many tablets also feature a front facing camera and a back facing camera, doubling the opportunity for camera flashes and protective camera lens covers. According to Gartner, worldwide sales of tablets to end users reached 195.4 million units in 2013. Again, that’s a good opportunity for sapphire.

Wearables like smartwatches are an emerging market and a new opportunity for sapphire. As a traditional cover for watches, sapphire is a natural cover for smartwatches as vendors like Samsung, Omate and the Wellograph Wellness Watch already use sapphire covers in their smart watches. JP Morgan estimates that the smartwatch market size could reach US$26 billion by 2018. This is up from less than US $1 billion in 2013. Once again, that’s a good opportunity for sapphire.

For Further Reading

Tech Crunch, Gartner: Smartphone Sales Finally Beat Out Dumb Phone Sales Globally In 2013, With 968M Units Sold,

Gartner, Gartner Says Worldwide Tablet Sales Grew 68 Percent in 2013, With Android Capturing 62 Percent of the Market,

CNet, Wellograph’s sleek new Sapphire Wellness Watch sparkles with style at CES 2014 (hands-on)

The Smart Watch Review, Apple Might Have Big Plans for Sapphire and its iWatch,

JP Morgan, Smartwatch Market,

Sapphire – Quality Matters, Part 2: Transmission Quality

Recently, Novus Light Today published an article by Dr. Jonathan Levine, Director of Technical Business Development at Rubicon Technology, about sapphire quality.  His article shares a thorough review of the measures of sapphire quality for optical-grade applications.  Last week, we looked at the first two metrics, chemical analysis and X-ray rocking curves.  This week, we’ll look at transmission quality.

Levine writes that the quality of a sapphire is determined by how closely the grown crystal matches the ideal structure with respect to the arrangement of atoms within the lattice, dislocations, defects, and stress.  Root causes for these problems often originate from insufficient purity of the starting material and the growth process itself.

Sapphire exhibits excellent transmission in the ultraviolet (UV) to the mid-infrared (IR) range (~200 – 5000 nm).   According to Levine, conditions within the sapphire growth furnace can induce subtle interactions between the molten sapphire and the growth environment.  These interactions can produce bubbles, dislocations and other stresses that could impact optical performance.   Levine says that carefully controlling the growth environment produces sapphire that maintains excellent transmission at 200 nm through the mid-IR wavelengths.  He illustrates the impact of furnace interactions by comparing Rubicon’s ES-2 sapphire with another commercial sapphire maker’s crystal produced using a different growth method in the figure below.  From the image in the post, you can see a sharp absorption peak at 200 nm for sapphire produced by the commercial maker that is absent in sapphire grown by Rubicon.

Optical transmission of sapphire depicting a sharp absorption peak at 200 nm for sapphire produced by a commercial producer that is absent in sapphire grown by Rubicon.  Inset: Optical transmission for Rubicon sapphire from the visible to mid-IR range approaching 90% due to the high quality of the material.

Optical transmission of sapphire depicting a sharp absorption peak at 200 nm for sapphire produced by a commercial producer that is absent in sapphire grown by Rubicon. Inset: Optical transmission for Rubicon sapphire from the visible to mid-IR range approaching 90% due to the high quality of the material.

For Further Reading

Novus Light Today, Optical-Grade Sapphire, Where Quality Matters,

Sapphire Quality Matters: Part 1

Sapphire is an extremely versatile material with a growing list of applications in a wide range of industries.  Sapphire suits optical applications because of its scratch resistance and its transmission characteristics.  You’ll find sapphire components such as lenses and windows in medical equipment, lasers, satellites, aircraft, flame detectors, smart phones, cameras and watches.  Recent advances in sapphire crystal growth technology and fabrication have improved the performance, purity, and availability of sapphire for all types of applications.

Recently, Novus Light Today published an article by Dr. Jonathan Levine, Director of Technical Business Development at Rubicon Technology, about sapphire quality.  His article gives a thorough review of the measures of sapphire quality for optical applications.  Levine writes that the quality of a sapphire is determined by how closely the grown crystal matches the ideal structure with respect to the arrangement of atoms within the lattice, dislocations, defects, and stress.  Root causes for these problems often originate from insufficient purity of the starting material and the growth process itself.

The effects of these variables in the final product are commonly quantified by three metrics: chemical analysis, X-ray rocking curves, and optical transmission.  Additionally, the observance of bubbles in the crystal provides a baseline from which crystal quality is determined because bubbles serve as scattering centers for any light transmitted through a sapphire optic, thus reducing its performance.

This week, we look at the first two metrics, chemical analysis and X-ray rocking curves.

Powdered aluminum oxide

Powdered aluminum oxide







Purity of the crystal is highly important.  According to Levine, the presence of certain elements can vary drastically between suppliers, and sapphire manufacturers must exercise proper quality control.  For example, titanium (Ti) and chromium (Cr) impurities can result in pink crystals.  In nature, these impurities lead to rubies and other variations of sapphire depending on the impurity.  Levine says trace amounts of these elements must be kept below 1 ppm.  Levine includes a graphic about other elements that can cause issues including silicon (Si), potassium (K), chlorine (Cl), iron (Fe), lithium (Li), and sodium (Na).  The data was collected using glow discharge mass spectroscopy (GDMS).

Typically, a company can buy two types of raw material for crystal growth that can have impurities.  Levine says it can be purified alumina powder and/or Verneuil sapphire.  Rubicon has developed a new in-house purification process that converts the raw powder into densified pellets for crystal growth without an increase in cycle time or decrease in crystal yield. This process enables Rubicon to eliminate impurities in the alumina power that they use to make crystal.

Levine includes another useful metric for analyzing sapphire, rocking curve data obtained via X-ray diffraction.  A rocking curve helps measure various stresses in a crystal.  Levine says the width of the resulting peak is highly sensitive to strain and defects within the crystal.  A narrow peak, indicated by its full width at half maximum (FWHM) measured in arcseconds, signifies a high quality crystal free of low-angle grain boundaries and lattice strain.  A standard narrow rocking curve for Rubicon’s ES2 sapphire windows is shown below.

Sample rocking curve data from Rubicon ES2 sapphire.

Sample rocking curve data from Rubicon ES2 sapphire.









What can introduce a poor rocking curve?  Levine says that high thermal gradients, fast growth rates, and impurities contributed by the surrounding insulation can introduce defects and stress into the crystal that subsequently yield poor results in rocking curve data.  He adds that accurately controlling the temperature gradient and maintaining a stable growth interface throughout the entire process can help make higher quality sapphire.

For Further Reading

Novus Light Today, Optical-Grade Sapphire, Where Quality Matters,

Sapphire Inside: Apple Builds Sapphire Lens into New Home Button, Touch ID

iPhone 5S with the Touch ID includes a sapphire lens

iPhone 5S with the Touch ID includes a sapphire lens on the home button

Today, Apple announced two new models of the iPhone, the iPhone 5S and  the iPhone 5C. One of the biggest news items at the Apple event is that the new iPhone 5S will sport a whole new home button with a fingerprint sensor with a sapphire lens, ringed in stainless steel.

Sapphire, the second hardest material on Earth after the diamond, is scratch resistant, so it should be very well suited for use as a lens. While this is great news for the sapphire community, this is not the only use for sapphire in a smart phone. Many smart phone OEMs already use sapphire for the camera lens cover because of its scratch resistance, but also is used for the LEDs in the backlighting for the screens as well as the silicon-on-sapphire (SOS)-based RFIC chips that power the RF antennas. There are more places for use of sapphire in a smart phone as well since OEMS are looking to use SOS chips for digitally tunable capacitors (DTCs) and power amplifiers. And, don’t forget sapphire’s largest overall market, LEDs, for lighting, displays and more.

Apple claims that Touch ID reads a fingerprint at an entirely new level by scanning sub-epidermal skin layers with 360 degree reading capabilities.  The sensor is part of the home button which is 170 microns thick with a 500 ppi resolution.  Touch ID stores the encrypted fingerprint info securely in a “secure enclave” inside the new A7 chip, the new processor for the iPhone 5S.  The neat thing is that it should be able to store multiple fingers.  The Touch ID will enable you to purchase items on iTunes, the AppStore or iBooks without a password.

You can see where the sapphire is in this photo of the home button from CNet’s live blog of the Apple event:

iPhone 5S graphic illustrates parts of the Touch ID (from CNet)

iPhone 5S graphic illustrates parts of the Touch ID (from CNet) with sapphire








The iPhone 5S (and the 5C) go on pre-sale on September 13th and will be on sale in stores on September 20th.

For Further Reading

Engadget, iPhone 5S fingerprint sensor called Touch ID, recognizes your thumb on the Home button: here’s how it works and what it does,


Alternative Substrates – Dimming the Hype

Two-inch, Four-inch and Six-inch Sapphire Wafers

Two-inch, Four-inch and Six-inch Sapphire Wafers

Today, more than 80% of LEDs are made based on sapphire wafers.   Recently, Lux Research published a report, Dimming the Hype: GaN-on-Si Fails to Outshine Sapphire by 2020, about the state of alternative substrates.  In LED production, sapphire is used as the substrate onto which the chemicals that will become the emitting layer of the LED are deposited as a vapor.  With the LED lighting market expected to grow to $80 billion, Lux Research expects the substrate market to grow to $4 billion in 2020 making it a highly attractive market.  Lux expects sapphire to continue to dominate the substrate market.

“Silicon is already widely used for electronics, and some LED die manufacturers are hoping to take advantage of silicon substrates,” said Pallavi Madakasira, Lux Research Analyst and lead author of the Lux report.  She explained that GaN-on-Si presents technical challenges such as cracking and a lattice mismatch that reduces the performance of LEDs based on the alternative substrate.

In an interview with Compound Semiconductor, Madakasira spoke about LEDs based on silicon substrates.  She doesn’t buy the argument that GaN-on-silicon makers can save on costs.  She says that even if they use fully depreciated CMOS equipment, the process of depositing complex buffer layers onto silicon prior to GaN deposition to overcome GaN and silicon lattice mismatches, adds time and cost to a manufacturing line.

Madakasira also shared performance data in her report with Compound Semiconductor. She notes that alternative substrates haven’t provided the performance of sapphire.  According to Lux, the luminance efficacy of GaN-on-SiC LEDs is 200 Lumens per Watt with GaN-on-sapphire devices coming in at between 150 to 180 Lumens per Watt.

What does this mean?  The Lux report concluded that sapphire will remain highly competitive for the rest of the decade.  GaN-on-silicon, will snare only 10% market share while GaN-on-silicon carbide will grow to 18% of the market.   Where do they fit? Here are Lux’s conclusions:

  • Choice and cost of LEDs will determine adoption. Where GaN-on-sapphire is suited to all applications, GaN-on-bulk GaN will be relegated to niche commercial lighting and GaN-on-Si, with unproven performance, will be better suited to cost-sensitive residential applications.
  • Four-inch wafers will rule (for now), though six-inch wafers start to come into vogue. Four-inch wafers will peak at 62% market share with $2.1 billion in 2017 sales. Later, the LED industry will move towards 6” epiwafers, which will take a 35% share, equivalent to $1.4 billion, in 2020.
  • Technology will advance sapphire substrates. Sapphire substrate manufacturing technology has advanced significantly with specialists such as Rubicon and Monocrystal demonstrating substrates up to 12” in diameter. New methods like hydride vapor phase epitaxy (HVPE) will further improve throughput and cut costs, keeping sapphire highly competitive for the rest of the decade.

For Further Reading

Lux Research, Epi-Wafer Market to Grow to $4 Billion in 2020 as LED Lighting Zooms to $80 Billion,

Compound Semiconductor, Sapphire Substrates to Lead Future LED Markets,

New Applications for Sapphire: Medical (Part 2 of 3)

rod of asclepiusNew industries are finding man-made sapphire a desirable material. The field of medicine is looking at sapphire for its optical transmission range, durability and chemical inertness for bio-compatibility.

Sapphire’s optical properties and durability offer advantages for specific medical laser applications in dermatology, ophthalmology and dentistry. Sapphire is widely used in surgical systems for its laser transmission, high resistance to heat and non-thrombogenic properties (meaning it doesn’t promote clotting).  It is used as a laser window for endoscope lenses, laser hair removal systems and blood cell counters.  In addition, sapphire products are used for surgical tools, implants, braces.  Sapphire microscalpels are transparent blades that make it easier to visualize and illuminate capillary vessels, nerves, cutting zones and cutting depth compared with traditional metal alternatives.

One area that has potential for sapphire is in artificial joint replacements.  Many joint replacements include metal, ceramic, metal-polymer and ceramic polymer endoprosthesis. This is an area that may develop friction and wear over time causing the joint to fail.  Endoprostheses made of metal and ceramics may interact with the body and also degrade from friction over time.  For example, metal-on-metal artificial hips have a lifetime of 15 to 30 years, but have been known to fail earlier.  Sapphire is attractive for endoprostheses for its bio-compatibility since it is chemically inert and won’t react with the body as well as its low friction coefficient, hardness and durability

For Further Reading

The New York Times, The High Cost of Failing Artificial Hips,

IMS Research/Rubicon Technology, White Paper: Opportunities for Sapphire, Jamie Fox,,

Sapphire: Material, Manufacturing, Applications, by E. R. Dobrovinskaya, Leonid A. Lytvynov, V. V. Pishchik. Springer Sciences Business Media, ISBN: 978-1441946737.

How Do They Do It? From Sapphire to LED Infographic

You’ve heard a lot about LEDs, but did you know that a tiny piece of sapphire – the pure, colorless industrial variety, not the blue gemstone – is in more than 80% of LEDs? Sapphire is the foundation for the LED chip, just as silicon is for a computer chip.  Rubicon Technology has put together an infographic that describes the sapphire manufacturing process and where sapphire is found in an LED. The bottom of the infographic features examples of products that feature LEDs for lighting. Click on the infographic below to see it larger.

Infographic for Post






Link to:

New Applications for Sapphire: Aerospace & Defense, Part 1 of 3

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Range of sapphire products available from Rubicon Technology including large optical windows and other shapes for aerospace and defense.

Sapphire’s unique properties make it a perfect material for high-performance applications due to its optical transparency, physical strength, resistance to abrasion and corrosion, temperature durability, chemical inertness, and bio-compatibility. As a result, it is perfectly suited for extreme environments where material durability is just as important as optical clarity.

One extreme use case is in the aerospace and defense industry where there’s a need for rugged windows for targeting pods and missile domes, most notably for the US F-35 fighter jet, that may come in contact with harsh conditions from the harsh, gritty desert with extremely high temperatures to high altitudes with extreme low temperatures.

Market research firm Yole Developpement determined that non-substrate applications for sapphire in the defense, semiconductor and other applications represent 25% of the sapphire industry revenue in a new study.  The market represents a solid growth opportunity for sapphire makers.

While there is opportunity, innovation is needed.  Sapphire traditionally has been limited to smaller shapes and sizes using traditional growth methods.  As sensor technology and applications, in defense and aerospace in particular, have evolved, the size requirements for sapphire windows have grown substantially.  One company that is innovating sapphire crystal growth is Rubicon Technology.

In a recent paper, Rubicon’s Dr. Jonathan Levine, Director of Technical Business Development, detailed how Rubicon successfully produced very large sapphire blanks using a highly modified horizontal directional solidification process. This new method, named the Large‐Area Netshape Crystal Extraction (LANCE) system is currently able to produce crystals of several different orientations. The company plans to produce sapphire windows as large as 36 x 18 x 0.8 inches.

For Further Reading Blog, Opportunities for Sapphire: New Applications & Markets Explained, Blog, How Large Can You Go? Sapphire Windows Grow Up and Across,

Rubicon Technology, Synthesis and characterization of large optical-grade sapphire windows produced from a horizontal growth process,