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,

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:

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:

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,


Rubicon Ships 400,000th Large Diameter Sapphire Wafer

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

Today, Rubicon Technology, Inc. (NASDAQ:RBCN) announced that they shipped their 400,000th six-inch large sapphire wafer to the LED manufacturing and SoS/RFIC markets. Most of the world’s LED manufacturing takes place using sapphire – just as computer chip makers like Intel and AMD use silicon to make their microprocessors.

The most flashy, if you’ll pardon the pun, market for sapphire wafers is in LEDs, which are used for energy-efficient general lighting and as the source for backlighting in consumer products such as HDTVs, laptops, smart phones and tablets.  A second and significantly growing market for sapphire is its use in Silicon-on-Sapphire (SoS) Radio Frequency Integrated Circuits (RFICs).  SoS RFIC chips deliver high RF performance with low power consumption, a small form factor, and significantly reduced crosstalk in antenna applications that are pervasive in smart phones and other consumer devices.

Why large diameter wafers? Rubicon began developing large diameter sapphire wafers for SoS RFICs in the 2000s.  But the company soon tapped into the larger opportunity in the LED market, especially with LED-based general lighting. And, it’s all about the math.

The market has been dominated by two-inch wafers for years. The surface area of a six-inch wafer is nine times greater than that of a two-inch wafer, and its outer curvature is less, enabling greater use of the surface area, culminating in a reduction in edge loss.  In addition, use of larger wafers enables operational savings that offset the cost of the larger, thicker substrate and can help drive down the total cost of LEDs.  According to Rubicon, and 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.

What does that mean? Larger diameter wafers will help LED manufacturers reduce costs throughout the manufacturing process in order to make LED-based lighting more affordable for consumers and encourage adoption worldwide.

Further Reading

Rubicon Technology, Rubicon Technology Ships 400,000th Large Diameter Sapphire Wafer; Company Continues Market Leadership Supplying Large Diameter Sapphire Wafers to LED and SoS/RFIC Markets,

Alternative Substrates for LEDs – Not Ready for Prime Time

Over the past several months, there has been some industry chatter about alternative substrates for the production of LEDs.  In fact, the dialog has been more heat than light until now if you think about it in terms of a filament in an incandescent light bulb.

Large Diameter Sapphire Wafer (source: Rubicon Technology)

Sapphire substrates have been established for quite some time as the base material for LED chips.  Today, more than 80% of LEDs are based on sapphire substrates with the remainder based on SiC and a few other materials.  But the big question is whether an alternative substrate like silicon or GaN can offer the performance and cost advantages of sapphire.

Last week, market research firm Yole Developpement held a webcast, Alternative Substrates for LED Manufacturing, to examine the alternatives, the technical challenges and the conditions for success.  You can access the archive here.

According to Yole analyst Eric Virey, the principal benefit of using Si as an LED substrate would be the ability to leverage larger 8” wafers and use fully depreciated and highly automated CMOS fabs.  But “the jury is still out,” he said, “regarding a massive industry transition from sapphire to silicon.  At the end of the day, this is a cost game; manufacturing yields are a major cost contributor to LED, and they pose specific challenges to the use of silicon.”

These challenges range from a lattice mismatch and thermal expansion coefficient mismatch, to melt back and blue light absorption. Sapphire outperforms silicon on all of these factors, and each is having a negative impact on LED chip yields from silicon.  Virey commented silicon and/or GaN must meet the performance of sapphire to be successful. To date, that hasn’t happened.

In the meantime, the sapphire substrate manufacturers have made great strides to making large diameter substrates that help LED manufacturers drive down costs and increase yields to support the aggressive cost targets of SSL.  For example, Rubicon Technology has shipped more than 230,000 large diameter sapphire wafers with this number growing.

Where are efforts now? Virey mentioned during the webinar that almost all LED manufacturers are exploring alternative substrates, although most are doing so only as a defensive strategy. Toshiba and Bridgelux have been working with silicon as a substrate. In July, the companies announced Toshiba would begin silicon-based LED production in October 2012, but there has been no further word. Plessey Semiconductors and Lattice Power also announced they would enter production in 2012.

LED Magazine reports that silicon-based substrates are “no sure thing” in their latest SSL Technology Update video blog.  Associate editor Nicole Pelletier said, “A number of companies plan to ride the incumbent sapphire technology. At The LED Show back in August, LED market leader Nichia said it had investigated and dismissed the possibility of using silicon.”

At the conclusion of the webcast, Virey agreed.  “If the technology hurdles are cleared, LED on silicon will be adopted by some LED manufacturers, but not necessarily become the standard.”

For Further Reading

LED Magazine, SSL Technology Update: October 22, 2012,

Yole Developpement Webinar, Alternative Substrates for LED Manufacturing,

Solid State Technology, Beyond sapphire: LED substrates from GaN to ZnO, SiC, and Si,

Solid State Technology, The demise of sapphire wafers?

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.”

Emerging Markets for Sapphire, Part 1 — SoS

SoS improves performance and integration for RF circuits found in smart phones.

While LED is the largest market for sapphire, there are several other emerging markets that take advantage of the physical attributes of sapphire.  We’ll take a look at these emerging markets over the next month or so.   We will begin with Silicon on Sapphire (SoS) for the RFIC market.

SoS is a part of the Silicon on Insulator (SOI) family of CMOS (Complementary metal–oxide–semiconductor) technology for making integrated circuits.  SoS improves performance and integration for RF circuits.  The holy grail of the wireless industry has been finding a better way to optimize power consumption and real estate utilization in mobile phones.  One application for SoS technology is the production of RF chips used in the antenna switch in smart phones.  These SoS chips are significantly smaller and use less power than chips traditionally used for this application.  As a result, chips produced using SoS technology are rapidly gaining market share in the mobile phone industry.

Peregrine Semiconductor is a pioneer in SoS and holds much of the industry’s IP in SoS.  In an interview with EE Times in 2011, Dr. Ronald E. Reedy, Peregrine co-founder said, “SoS is the first and most successful form of SOI focused entirely on improving performance and integration for RF circuits. We saw the emerging need for such a technology when commercial wireless communications started taking off in the early 1990s.”

What makes sapphire so good for SoS? Peregrine summarized it in a paper on the history on SoS. Sapphire and silicon have a unique way of lining up together at an atomic level because of oxygen atoms.  The scientific explanation is that the r-plane of sapphire has oxygen atoms spaced at a distance that is close to the spacing of the atoms in the (100) plane of a silicon crystal.  The spacing delivers unique insulating properties when the silicon is layered on top of the sapphire wafer.  This was discovered by researchers at Boeing in 1963.  Researchers at RCA continued the development of SoS technology into the mid-1970s and continue to process them for space applications.

Technological barriers leading to defects held SoS back from commercial applications until just recently.  Peregrine has been able to overcome these hurdles at just the right time as the wireless industry needs the insulating and power saving benefits of SoS for the latest generations of smart phones.  You’ll find more coverage of the emerging market in posts to come.

For Further Reading:

Electronics Weekly, Peregrine: Single chip phone RF is possible

EE Times, What’s up with silicon on sapphire?,

Peregrine Semiconductor Corporation, The History of Silicon on Sapphire,,


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


The Art of Sapphire – Ensuring High Quality Sapphire Wafers

You might think from the title of this post that we’re talking about gems or jewelry, but we’re not. We’re talking about commercial sapphire – the type that is used to make LEDs. Not all commercial sapphire is high quality. In fact, the quality of the sapphire crystal impacts the quality of the sapphire wafer and the resulting LED. Sapphire producers must go through a qualification process in order for LED manufacturers to select the vendor. What are they looking for? Raja Parvez, President and CEO of Rubicon Technology shared information about what LED manufacturers look for when they come to Rubicon.

Rubicon Technology shared information about what LED manufacturers look for when they come to Rubicon.

Flatness: When a sapphire wafer is not flat it will become like a potato chip during processing. This prevents the wafer from being processed properly. The key tolerance for 6-inch and 8-inch is the flatness across the wafer. Thickness is not standardized yet and can range anywhere from 1-2 mm. The greater thickness also uses a larger amount of sapphire, but we’ll get to that in a later post.

Cleanliness: Surface morphology of the wafer needs to be clean and presents a uniform surface before depositing the epitaxial layer. The particulate count on the polished surface is very important too. A dirty wafer will cause issues when depositing the epitaxial layer. In addition, if impurities have been introduced in crystal development, colorization will be introduced rendering a colored crystal. This has a negative effect on commercial sapphire quality in contrast to gem quality sapphire that depend on impurities for their color such as red (with chromium impurities) for rubies and blue (with titanium and iron impurities) for sapphire. For example, commercial sapphire crystals with impurities result in pink wafers that interfere with LED performance.

Stress: LED manufacturers need stress-free wafers. Sapphire crystals go through temperature cycles of up to 1200ºC. That causes stress that can create cracks in the wafers and reduce yield. Rubicon’s ES2 technology produces almost stress-free crystals. During the crystal growth cycle, 50 percent of the time is taken to grow our crystal, and 50 percent is taken to cool down the crystal. During cooling, stresses are automatically released. Other wafer technologies introduce significant stress, so it’s common to put those wafers through an annealing furnace to reduce stress. This adds operational costs and time to production.