Soitec Tunes Wafers for RF, Imagers, Photonics

　　A trending narrative in Europe’s microelectronics industry recently is the comeback of French companies, as illustrated in an increased share of French tech designed into Apple’s iPhone X. Local media are almost giddy with the news, touting big wins by STMicroelectronics and Soitec in Apple’s new flagship iPhone model.

　　The good news coincides with both companies’ improved business operations in recent quarters, with rising revenue and net profits.

　　On one hand, to the trained eyes watching from Silicon Valley, this France-centric storyline seems a mite provincial. On the other hand, from outside of Silicon Valley’s own bubble, it’s not so difficult to understand why iPhone X represents a new milestone for France. The French see their technology prowess, backed by decades of foundational R&D by top researchers and engineers, breaking the bounds of an Imaging Valley tucked away near the French Alps and gaining worldwide recognition.

　　Thus far, both STMicroelectronics and Soitec are mum on their recent design wins. However, the latest iPhone X teardown done by Yole Développement in collaboration with its partner, System Plus Consulting, found ST’s NIR sensor inside iPhone X’s TrueDepth module. It was built using silicon-on-insulator (SOI) wafers developed by Soitec.

　　What’s so special about SOI wafers in ST’s NIR sensors? How are they different from other SOI wafers?

　　In recent months, Soitec has also been busy talking up not just RF-SOI and FD-SOI, but Photonics-SOI, Imager-SOI and others. What are they, how are they engineered, and what are they for?

　　Earlier this month in Paris, EE Times sat down with Paul Boudre, Soitec’s CEO, for an interview.

　　Asked about Soitec’s evolving substrate technologies, Boudre first reminded us that Soitec isn’t just a wafer supplier. Its value creation lies in the development of engineered substrates. “Innovation is our core business,” said Boudre. Soitec’s mission is to find “new solutions” demanded by customers, and its customers’ customers. “We engineer new materials, and design to cost” to meet their needs, he explained.

　　Although Soitec won’t talk about ST or Apple, the key to Soitec’s big iPhone win is the specific SOI wafers the company developed for ST’s NIR sensors. Pierre Cambou, activity leader for imaging and sensors at Yole, deduced that SOI has played a critical role in improving the sensitivity of NIR sensors — so that ST can meet Apple’s stringent demands for quality and time to market.

　　Tuned substrates

　　Soitec’s close collaborations with research institutions like CEA-Leti, IMEC and the Université Catholique de Louvain have kept it in the forefront of innovation in SOI-engineered substrates.

　　Soitec takes a toolbox approach. “We build a common platform where those research organizations’ tools and Soitec’s own tools and expertise are combined,” Boudre said. This pays off when developing tailor-made products specific to Soitec’s customers and their customers.

　　There is more to Soitec’s “Smart Cut” and “Smart Stacking” technologies than meets the eye. They are critical in transferring a thin layer of materials to another substrate to produce a range of high-quality, cost-effective wafers. “We look at the resistivity of a given material, thickness of a layer and its uniformity,” said Boudre. “Our job is to model it, run pilots and validate with our customers.”

　　As a result, Soitec has introduced new materials for use in substrates and improved the cost of wafers, while launching a range of new SOI wafers for a variety of applications. They include: RF-SOI, FD-SOI, Power-SOI, Photonics-SOI and Imager-SOI.

　　RF-SOI for front-end modules, 5G

　　RF-SOI, for example, is widely used for front-end module integration in ultra-low power communication.

　　Over the last decade, types of materials and the structure of layers in RF-SOI wafers have evolved, allowing Soitec to develop a tuned substrate that delivers the better RF performance required by a new generation of cellular standards.

　　Historically, GaAs was the mainstream substrate for cellular front-end module switches. Soitec originally entered the smartphone market with silicon on sapphire and high resistivity SOI (HR SOI) substrates.

　　The early use of sapphire in the substrate for RF-SOI wafers — used by Peregrine Semicondcutor’s RF ICs — eventually transitioned to silicon, explained Boudre, to lower the cost. Thanks to Soitec’s collaboration with the Université Catholique de Louvain, the new RF-SOI wafers maintained low RF insertion loss and reduced crosstalk, similar to quartz substrates, Soitec explained. The two parties joined forces to develop a “trap-rich layer” for RF-SOI wafers, which eventually made it possible to combine silicon CMOS circuits on a RF substrate.

　　RF-SOI, now a standard in front-end modules, is “used in 100 percent of smartphones,” according to Soitec. But the company is not standing still.

　　Bourdre said, “Further developments of the technology are taking place to address the next RF requirements.” Think advanced LTE, uplink carrier aggregation, massive MIMO, 5G with mmWave, he noted.

　　For switches, antennas and tuners of 4G and 5G, sub-6GHz front end, Soitec believes that RF-SOI is critical. Cellular operators are pushing supply chains, including system and fabless chip companies. RF-SOI wafer suppliers like Soitec are working on new materials.  Bourdre also mentioned that Soitec is currently working on new engineered substrate using materials such as piezoelectric — to develop “piezoelectric on insulator.” That will be used for SAW filters, Bourdre said.

　　Photonics-SOI for data centers

　　Soitec is also counting on the growth of Photonics-SOI wafers, as demand soars for high-speed optical links in data centers and communication infrastructure.

　　There are clear advantages in leveraging Photonics-SOI. It allows a path for wavelength multiplexing, bringing the optical transceiver closer to the chip (thus lowering propagation loss). Photonics-SOI also provides higher throughput than direct light modulation and enables “100G and 400G transceivers,” according to the company. Perhaps most important is cost. Photonics-SOI wafers allow standard CMOS fabs to produce optical transmitter and receiver chips.

　　Companies such as Intel and Cisco have been actively engaged in Photonics-SOI modeling for their silicon photonics.

　　Imager-SOI for NIR sensors

　　Clearly, Soitec sees a growing opportunity for its Imager-SOI. Without naming any customers, Soitec listed a number of advantages of Imager-SOI. These include the ability to lower NIR illuminator power consumption, better performance through increased signal to noise ratio, and keeping cost down — because of its “lower die size” compared to bulk for the same resolution　　According to Yole’s Cambou, “Apple’s adoption of ST’s NIR sensors marks the debut of SOI in mass production for image sensors.” He added, “Image sensors are characterized by large surface due to the physical size of light. Therefore, this is a great market to be in for a substrate supplier” like Soitec.

　　Evolving business strategy

　　Soitec, founded in 1992, has gone through a few management changes, and in business strategies and target markets. Dorian Terral, a financial analyst at Bryan, Garnier & Co. wrote in a research note a year ago that “although Soitec suffered from a complex history, the arrival of a new management team in 2015 and the work carried out since have clearly renewed the group’s profile.”

　　Boudre asserts that Soitec’s turnaround “is behind us.” While Soitec “can’t afford to try and test everything” for new engineered substrates, he said that his company today is much better equipped to read the market and tune its technologies for bigger opportunities.

　　Boudre explained, “Ten years ago, Soitec was focused on an R&D platform” used in labs. “Today, we are closely working with our customers and our customers’ customers.”

　　To drive design wins, Boudre explained, “We brought in a lot of people capable of talk the talk” with customers in such areas as RF, imagers, power and IoT, and understand what customers’ customers need.

　　For tomorrow, “Soitec plans to be more focused on the development of innovation platforms.” A case in point is Soitec’s plan to closely work with China Mobile. To be an effective player, Soitec needs to be tuned to the 5G decision-making process.

　　Qorvo earlier this year became the first RF supplier to join the China Mobile 5G Innovation Center — an alliance created to develop 5G solutions for China. Soitec is also in the process of joining the alliance.

　　The plan is to “create the innovation platform for 5G together with China Mobile, and to qualify the technology by 2019,” Boudre said.

　　Acknowledging the fast-changing tech industry landscape, the Soitec CEO said, “We want to know what China Mobile wants, what Alibaba is looking for, and what Google is doing.”