Large Diameter Patterned Sapphire Substrates Explained

Rubicon Technology offers large diameter PSS in a range range of shapes including cone, dome and pyramid as well as custom.

Rubicon Technology offers large diameter PSS in a range of shapes including cone, dome and pyramid and range of orientations.

While LED chip manufacturers have been using patterned sapphire substrates (PSS) for years, there’s growing interest in large diameter PSS.  Recently, Rubicon Technology announced the commercial availability of large diameter PSS.  During their latest earnings call, they indicated that they’ve received interest from 7 major LED chip manufacturers for 4- and 6-inch large diameter PSS.  Why the interest from LED chip manufacturers?

First, PSS helps improve epitaxial growth by promoting growth of the GaN in parallel to the substrate surface. This also helps reduce the number of dislocations, called the dislocation density, which can degrade performance of an LED.  Secondly, patterning can help extract as much as 30 percent more light from an LED.  This is particularly advantageous for high brightness LEDs (HB LEDs) that are used in LED lighting applications.

Second, the evolution of patterning large diameter substrates brings economical advantages to LED chip manufacturers, especially those anticipating demand from the LED lighting market.  Large diameter sapphire wafers help LED chip manufacturers cut costs by enabling more throughput for each run of the MOCVD reactor.  This helps chip manufacturers make better use of the reactor “real estate” and decreases the cost per unit of area processed because of the curvature of the larger wafer.  The outer curvature of a 6-inch wafer is less, enabling greater use of the surface area than the tighter curvature of a 2-inch wafer resulting in less edge loss.  Larger diameter wafers also provide post-MOCVD efficiencies.  Depending on the type of MOCVD reactor used, LED chip manufacturers using six-inch wafer platforms may achieve up to 48% greater usable area per reactor run compared with two-inch wafers.  These efficiency gains become very compelling when manufacturers want to ramp up LED chip production to support greater volumes of LEDs for light bulbs.

Finally, LED chip manufacturers have been buying smaller 2-inch and 4-inch PSS from outside suppliers for years.  The next step in the evolution in the market is the migration to large diameter PSS for the reasons we mention above.  While some LED chip manufacturers will have specialized patterning needs and the resources to keep the work in-house, others will not.  Some LED chip manufacturers may not have the expertise and equipment to move to large diameter PSS, so having a ready, trusted supplier will prove handy.

For Further Reading

ClearlySapphire, LED Lighting Spotlight: Patterned Sapphire Substrates

Semiconductor Today, Patterned sapphire for nitride enhancements,

Compound Semiconductor, New Wet Process For LEDs On Patterned Sapphire Boosts Efficiency,

Compound Semiconductor, Rubicon Orders Multiple Profilers For Sapphire Production,, Larger Wafers, Larger Yield – The Numbers Behind Large Diameter Sapphire Wafers and Yield,

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






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LED Lighting Spotlight: Patterned Sapphire Substrates

In the ongoing quest to make LEDs more efficient, LED chip manufacturers have developed patterned sapphire substrates (PSS).  In fact, most high-brightness LEDs are made using PSS. There are very few resources online that explain patterned sapphire substrates. Here’s a brief explanation.

PSS helps extract more light from LEDs.  A lot of light bounces back into the LED when using a polished sapphire substrate.  Researchers discovered that patterning the surface of the substrate by etching nano-scale patterns helps more light, in the form of photons, escape, improving the light generated or extracted by the LED.  It is reported that patterning can improve the extraction of light by as much as 30%.

A second important point is that patterning also improves the epitaxial growth process.  The nano-patterned surface can have a positive effect on the nitride semiconductor growth process by promoting growth of the GaN in parallel to the substrate surface, called lateral growth.  This also helps reduce the number of dislocations, the dislocation density, that can degrade performance.

LED chip manufacturers originally developed PSS.  The patterns are quite proprietary and helped the LED chip companies differentiate themselves.  Today, the sapphire industry has joined in and sapphire wafer manufacturers have begun to put patterns on sapphire wafers in partnership with the LED chip manufacturers. The patterning work is concentrated with smaller wafers in the 2 to 4-inch diameter range, but manufacturers of large diameter wafers like Rubicon Technology are beginning to develop PSS for larger wafers.

Most patterning is based on a proprietary design from the LED chip manufacturer.  The patterns can vary from cones, pyramids and flat tops and can be organized in hexagonal or trigonal patterns.  Some basic design rules based on height and height/pitch ratio have emerged, but so far, no standards exist.  Currently the most popular pattern is a cone shape, but these patterns change frequently.  Here are some sample patterns.

Sample patterns:

Sample patterns for PSS








Sample Pattern for PSS







For Further Reading

Semiconductor Today, Patterned sapphire for nitride enhancements,

Compound Semiconductor, New Wet Process For LEDs On Patterned Sapphire Boosts Efficiency,

Compound Semiconductor, Rubicon Orders Multiple Profilers For Sapphire Production,


US DOE Reports on Efficiency and Environmental Impact of LED Lighting

LED lighting has been hyped as the next best thing in lighting because of its energy efficiency. As Earth Day 2012 approaches, we would like to share the results of a new report from the US DOE, Life-Cycle Assessment of Energy and Environmental Impacts of LED Lighting Products Part I: Review of the Life-Cycle Energy Consumption of Incandescent, Compact Fluorescent, and LED Lamps, February 2012.

Part 1 of the report focuses on a comparison of the energy consumption during the lifecycle of LEDs, CFLs, halogen and Incandescent light bulbs. The lifecycle is defined as the three major lifecycle phases: manufacturing, transportation and use.  The authors of the report took on a lot of work. The report is a comprehensive look at the energy consumption of the three light technologies based on ten existing studies from academia, manufacturers and independent researchers.

The results of the report were not surprising given the buzz about LEDs.  The use phase is the most energy intensive for all — incandescent, CFLs and LED lighting.  Transportation accounted for less than one percent of the lifecycle for all. The real differences occurred during the manufacturing phase with LEDs initially being higher due to the larger “packages” required to meet the equivalent lumens, or the amount of light.  These differences in the manufacturing phase will be eliminated by advances in LEDs over time.  For example, as LED technology improves with increases in yield, wafer size and automation in LED manufacturing, LEDs will become brighter requiring fewer, smaller “packages” to make the same amount of light, lumens.  Even given these initial differences in current LEDs, they all disappeared when totaling everything up throughout the lifecycle.

According to the authors of the report, “the key results of this analysis indicate that the average life-cycle energy consumption of LED lamps and CFLs are similar, at approximately 3,900 MJ per functional unit (20 million lumen-hours). This is about one quarter of the incandescent lamp energy consumption—15,100 MJ per functional unit.”  Further, the authors estimate that, “by 2015, if LED lamps meet their performance targets, their life-cycle energy use is expected to decrease by approximately one half.” This means that as LEDs become more efficient, they’ll outshine CFLs.

This all sounds like very good news for LEDs, but it still is very early. The report is the first report from a larger DOE project to assess the lifecycle environmental and resource costs to manufacture, use and dispose of LED lighting products versus comparable traditional lighting technologies.  Look for more from the DOE.

For Further Reading:, LED Manufacturing,

US DOE, SSL Program,

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


Barriers to Entry 1: China’s Appetite for MOCVD Reactors & How Easy Is It to Make Sapphire?

Questions about the barriers to entry and new market entrants from China have been dogging the LED industry.  A few industry experts have been taking a look at China and what it means to the industry.  Strategies Unlimited analyst Tom Hausken recently wrote a piece for LEDs Magazine about the Chinese LED manufacturing industry. China has been throwing a lot of capital at its nascent LED industry and the world is watching.  Tom’s article put some of the talk about the Chinese LED industry into perspective.

According to Hausken, research on the Chinese LED industry by Strategies Unlimited partner GG-LED shows that the Chinese effort goes far beyond MOCVD equipment.  The report further calls into question whether the Chinese can match world-class competitors.  “The report points out that the real shortage in expertise is not only designing LEDs and operating epitaxy reactors in general research, but particularly in planning and leading enterprises that can match world-class competitors,” wrote Hausken.

According to the report, Chinese investment is overly concentrated in LED epitaxy and chip production due to an outdated perception that the distribution of profit margins in the supply chain were concentrated at the epitaxy and chip layer. 

Only time will tell if the Chinese LED industry can get up to speed and become competitive on the world stage.  Hausken commented, “There is over-investment in LED manufacturing in China, but what will be the impact? At the very least, it makes the market less certain. A glut will accelerate the trend toward cheaper LEDs and LED lighting, which has been a goal of national policy makers. It may hurt chip makers and vendors of fab equipment along the way,if only by spoiling an otherwise rational market.”

Look for Part 2, Barriers to Entry 2 in a future post.

For Further Reading:  LEDs Magazine