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