5 Non-LED Uses of Sapphire

Rubicon Technology may be best known as the worldwide market leader in sapphire for LEDs, but the company’s sapphire is being used in applications far beyond the lighting industry.

From semiconductor equipment components to camera lens covers, there are many intriguing uses for optical and non-wafer sapphire. Here’s a peek at five non-LED usages for Rubicon’s synthetic sapphire.

Rubicon1. Semiconductor Equipment  Components

More than 40 different semiconductor equipment components are made of sapphire. Due to its ability to withstand very high temperatures, extreme environment processing and harsh chemicals like fluorine plasma and many acids, sapphire is ideal for equipment such as plasma tubes, heater plates, lift pins and chamber windows.

2. Medical Component

Sapphire products are used in a variety of medical applications, including dental braces, surgical blades, laser delivery windows, arthroscopy lenses and skull pins. When compared with traditional metal alternatives, medical sapphire components provide advantages of optical transmission, transparency for both aesthetic and performance improvements, high durability and precision, and also can be utilized for procedures requiring active imaging as sapphire does not impact imaging processes like metal.

3. Infrared (IR) Windows

Sapphire windows of optical quality are already being used for military sensing applications on aircrafts and missiles. In fact, sapphire IR windows are now beginning to be used on private, commercial and cargo aircraft to assist with landing in inclement weather.

4. Wafer Carriers

Sapphire is so durable that it is actually used to support other brittle wafers that are being processed, such as gallium arsenide and silicon carbide. These brittle wafers are mounted to sapphire so they do not break or get damaged during transit.

5. Durable Lenses and Windows

One of the largest optical applications for sapphire is in the form of lenses and windows. Due to its hardness and wide range of transmission from UV to Visible to IR wavelengths, sapphire lenses and windows are ideal for use in applications where there is a possibility of impact, scratching, high temperatures, chemical interaction or other harsh conditions. These lenses and windows are used in a wide variety of applications, such as camera lenses, military rifle scopes and as windows for sensors and laser transmission.

We are just scratching the surface when it comes to optical and non-wafer uses for sapphire. As research continues and new applications are discovered, you will see sapphire included in different types of products. Who knows, you may soon be seeing sapphire used for the armored windshields of military vehicles or even in hip replacements!

The challenges of growing the world’s largest sapphire slab

Can optical quality sapphire be grown in a different way to create a large, thick window to protect equipment on the belly of an aircraft?

This is the question that members of the Rubicon Technology design team were asked when the United States Air Force Research Lab (AFRL) called upon them about three years ago to develop a new growth platform that could produce very large polished sapphire infrared (IR) windows.

In the past, these dimensions were met by piecing together several smaller sapphire windows, with less-than-desired performance.

Despite high interest from the defense and aerospace industries, no method for producing sapphire for optical-grade windows of such great size and thickness existed at the time. Sapphire had been limited to smaller sizes and shapes using traditional growth methods. Rubicon studied the problem and agreed that it could be done. In 2012, the Air Force Research Laboratory granted Rubicon a three-year research contract to develop this product.

With several “firsts” already under its belt, such as having been the first to commercialize 6-inch and 8-inch wafers for the LED industry and the first to produce large-diameter patterned sapphire substrates, Rubicon has now successfully become the first to grow a 36 x 18 x 2-inch sapphire slab.

Drawing upon its strong history of scaling up sapphire growth processes, Rubicon successfully produced large sapphire blanks by highly modifying the Horizontal Directional Solidification (HDS) process and developing LANCE. Unlike the ES2 method, which produces high-quality sapphire crystals in the shape of roughly cylindrical boules, the HDS method produces sapphire plates that are advantageous for shaping into large windows.

Scaling up to larger crystal sizes while maintaining crystal quality was, of course, the real test and involved development of a new type of furnace.

Devising how to maintain crystal quality at such a large size proved to be experimental and time-intensive for the designers. By combining multiple platforms, materials and heater types, Rubicon ultimately demonstrated the ability to pull a horizontal boat through a heater surrounded by thermal insulation to achieve the desired thick slab while maintaining its high quality.

Over the past two years, the design team has continued to tweak and perfect the LANCE process, keeping the ultimate goal in mind of producing a sapphire slab with the cut measurements of 36 x 18 x 2 inches. The project is on track to produce optical quality sapphire at this immense size.

Looking to the future, this monolithic sheet is a hugely innovative advance that will provide a large, seamless optical field for military sensing applications and beyond.

For more information on the LANCE project, visit http://www.rubicontechnology.com/research-development/project-lance-very-large-sapphire-windows.

Case Number 88ABW-2015-1571

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