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, http://www.novuslight.com/optical-grade-sapphire-where-quality-matters_N1596.html#sthash.giGipxT1.dpuf

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, http://www.novuslight.com/optical-grade-sapphire-where-quality-matters_N1596.html#sthash.giGipxT1.dpuf

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, http://www.engadget.com/2013/09/10/iphone-5s-fingerprint-sensor/

 

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, http://www.nytimes.com/2011/12/28/business/the-high-cost-of-failing-artificial-hips.html?pagewanted=all

IMS Research/Rubicon Technology, White Paper: Opportunities for Sapphire, Jamie Fox, http://rubicontechnology.com/resources/papers,

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

Commercial Sapphire Spotlight – Vertical Integration in Sapphire

Rubicon Family of Sapphire Boules

Last month, Compound Semiconductor Magazine featured a contributed article about Vertical Integration in sapphire production by Raja M. Parvez, President and CEO of Rubicon Technology.  Rubicon has adopted vertical integration to set itself apart from other sapphire companies.  The article details Rubicon’s approach.

Vertical integration isn’t a new concept. It has been around since the 1800s when US Steel tycoon Andrew Carnegie introduced the vertical integration by owning virtually every part of the steel-making value chain from iron ore through steel mills to physically building the railroads.  Later, in the 1920s, Ford Motor Company decided to make the steel for their cars, popularizing the concept further.

According to Rubicon’s president and CEO Raja Parvez, vertical integration holds the key to Rubicon’s cost structure and reliable supply of high-quality products.  This integrated approach influences every step in the growth of sapphire crystals and their processing into wafers. The company’s end-to-end manufacturing capability, with strong intellectual property at each step of the manufacturing process, produces an advantageous cost structure and provides better control of product quality and delivery schedules. Vertical integration is also central to the company’s ability to grow larger and larger sapphire and be the first to market with large-diameter sapphire wafers for the LED and SoS/RFIC markets.  To date, Rubicon has shipped more than 400,000 6-inch wafers.

To read the full article, visit:   http://content.yudu.com/A2360p/CompSemMar13/resources/index.htm?referrerUrl=http%3A%2F%2Fwww.compoundsemiconductor.net%2Fcsc%2Fmagazine.php

Made in America – Sapphire for the High Growth LED Market

While Google made a splash recently about making the Nexus Q media player in the US, companies all over the US are making key contributions of the economy by manufacturing in America.  One of the key building blocks for LEDs is sapphire.  Much like silicon is used for computer chips, sapphire is the foundation for an LED chip.  Illinois-based Rubicon Technology is one of the world’s leading producers of sapphire ingots, blanks, polished substrates and windows. With more than 80% of the world’s LEDs based on sapphire, Rubicon makes a very important contribution to the market right here in the US.

Rubicon grows large sapphire crystals in sapphire furnaces in its Franklin Park, Batavia and Bensenville, Illinois-crystal growth facilities.  The company makes very large sapphire crystals – bulk crystal ranging in size from 30 kg to 85 kg to 200 kg – that are cored and shipped to a Rubicon finishing facility in Malaysia or to directly to finishing customers throughout Asia to make sapphire wafers that and then made into millions of little LED chips.  These LED chips are found in everything from smartphones, laptops and tablets, HDTVs, big ad displays, street lights, commercial lighting and even new LED light bulbs.

Why manufacture the sapphire crystals in the US?  According to Rubicon, the crystal growth process is a high precision process that uses energy that must be kept constant. Any deviation in the power during the crystal growth process can lead to imperfections in a crystal rendering that crystal unusable.

Based on a decade of Rubicon company experience and decades of semiconductor expertise, Rubicon has custom-built next-generation crystal growth furnaces for their US plants. Rubicon’s innovations have resulted in industry-leading large-diameter sapphire wafers – six inches or more in size versus the commonly made two, three and four inch wafers – that help bring LED chip manufacturers cost efficiencies they can’t achieve with smaller wafers.  To date, Rubicon has shipped 230,000 large diameter wafers.

“No other country in the world has reliable, low cost utilities like the US,” said William Weissman, CFO for Rubicon.  “We specifically have designed our crystal growth facilities around reliable resources for power and water.  The location in the US also allows us to protect our intellectual property inherent in our furnaces and processes in a way that cannot be maintained outside of the country.”

Barriers to Entry 2: Yole Developpement Talks Sapphire, New Market Entrants Unlikely to Match Yields of Industry Leaders

In Part 2 in our Barriers to Entry posts (Part 1 is here), we’re focusing on a recent report from the industry experts at Yole Developpement.  Yole analysts have been keeping a keen eye on worldwide capacity for sapphire crystal growth.  According to Yole’s Eric Virey, more than 50 companies have announced their intention to enter the sapphire growth market, with more than 40 located in China.  While the capacity plans announced by all of the new companies collectively would add up to triple world demand, Yole believes it is “a situation unlikely to actually materialize.”

Why?  These new market players have little or no prior experience in sapphire crystal growth and wafer manufacturing.  And, while there are some “turn-key” solutions to lower the barrier to entry, “reaching and sustaining high quality and high yields in sapphire crystal growth still requires significant expertise.”  Indeed the learning curve is steep to reach yield levels on par with established Tier 1 manufacturers.

Yole’s report also said that margins in 2010 were favorable to new entrants allowing them to achieve comfortable margins “despite low yields and sub-par technology.”  However, with 2 inch pricing at historic lows, Yole calculates that they will lose money at the current market prices while “established vendors with higher yields, large volumes, and a more favorable product mix, including large-diameter wafers, can achieve production cost <$5 that will allow them to maintain positive margins and weather the storm.”

For Further Reading: Yole Developpement web site