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, http://www.compoundsemiconductor.net/csc/features-details/19736047/Silicon-on-sapphire;-rising-value-in-next-generation-wireless-network.html

Deloitte, A strong year for LTE adoption, http://www.deloitte.com/view/en_GX/global/industries/technology-media-telecommunications/tmt-predictions-2013/tmt-predictions-2013-telecommunications/77ca7f7d2c1eb310VgnVCM2000003356f70aRCRD.htm (link to article and video)

Peregrine Semiconductor, The History of Silicon-on-Sapphire, http://www.psemi.com/articles/History_SOS_73-0020-02.pdf

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 http://www.electronicsweekly.com/Articles/14/02/2012/52966/peregrine-single-chip-phone-rf-is-possible.htm

EE Times, What’s up with silicon on sapphire?, http://www.eetimes.com/design/microwave-rf-design/4216449/What-s-up-with-silicon-on-sapphire-

Peregrine Semiconductor Corporation, The History of Silicon on Sapphire, www.psemi.com/articles/History_SOS_73-0020-02.pdf

Clearlysapphire.com, http://www.clearlysapphire.com/SoS_RFIC.html