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,

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:

LTE and the Benefits of Silicon-on-Sapphire

Apple’s iPhone 5 is driving LTE use in the US.

LTE, the next generation wireless communications standard, is making headlines as adoption of mobile devices using LTE picks up.  Deloitte expects nearly 200 million subscribers to migrate to LTE devices by the end of 2013.  Silicon-on-sapphire is playing an important role in the development of devices that operate using LTE.  Peregrine Semiconductor’s Rodd Novack outlined the benefits of silicon-on-sapphire in a recent article in Compound Semiconductor Magazine.

According to Novack, LTE brings technological challenges that impact the RF front end (RFFE) components in wireless devices such as power amplifiers, filters, antennas and switches.  Silicon-on-sapphire, a specific type of silicon-on-insulator (SOI) technology, offers RFFE components scalable integration, consistent performance and the benefits of CMOS, the most widely used semiconductor technology. Silicon-on-sapphire wafers consist of the formation of a thin layer of silicon on a sapphire wafer at high temperature.  Novack says that sapphire, a near perfect insulator, eliminates nearly all of the parasitic capacitance and leakage currents.

The main challenge for the RFFE components is higher linearity.  Sapphire, as an insulating substrate, provides better isolation between circuit elements. In contrast, silicon by itself requires a capacitor to be charged and discharged with every cycle, meaning silicon behaves in a non-linear manner.  However, sapphire provides the linearity LTE needs with its insulator properties.

The RF interference is an important issue with LTE as worldwide deployment is scattered among a range of frequency bands from 699 MHz to 2690 MHz.  This is further compounded by multiple radios in today’s handsets.  As a result, users experience slower data rates and increased dropped calls.  LTE’s linearity performance requirements demand increasingly complex antenna switches which silicon-on-sapphire accommodates easily.

Sapphire improves transistor performance as well as enables high isolation between circuit elements allowing digital and analog blocks to sit next to high-power RF signals according to Novack.  It also enables integration of RF, analog, passive and digital circuitry on one die.  This enables smaller and smaller die and fewer external components.  Novack notes that a smaller switch size is “highly valued, because it can lead to a smaller overall RFFE with greater design and layout flexibility, and fewer external components.”  Eventually, it is thought that silicon on sapphire will enable to System on a Chip (SOC) configurations for smart phones and other electronic devices.

Focus on LTE

LTE (Long Term Evolution or 4G) is the next generation in wireless network technology and successor to 3G.  LTE is significant because it will provide significantly faster data rates for both uploading and downloading for mobile devices.

LTE is seen as the next advance in wireless networks as smart phones, tablets and other wireless devices require more bandwidth for faster data and content downloads. Smart phones, like the iPhone 5, are expected to drive the adoption of LTE.

For Further Reading

Compound Semiconductor Magazine, Silicon-On-Sapphire; Rising Value In Next-Generation Wireless Networks,;-rising-value-in-next-generation-wireless-network.html

Deloitte, A strong year for LTE adoption, (link to article and video)

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

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,

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,,