Collaboration And Advanced Substrates

Discussions of semiconductor manufacturing tend to focus on CMOS logic and memory devices, sometimes to the exclusion of everything else. Discussions of silicon-on-insulator wafer markets focus on the needs of high performance logic. Lithography analysts emphasize high density memories.

It’s easy to forget that real systems contain other devices, too. A modern smartphone probably supports Bluetooth, wireless, GPS and several different cellular connectivity standards. It has acoustic filters, accelerometers, and a touch screen. It has, in other words, many components made with process technologies that are not CMOS or memory.

Beyond the importance of these other components to the industry as a whole — wireless connectivity was the industry’s fastest growing segment in 2017 — Soitec CEO Paul Boudre points to RF-SOI growth as a key factor in the company’s improving financial results, and a driver for the recently announced Substrate Innovation Center at Leti. As Soitec CTO Carlos Mazure explained, many customers and potential customers have requirements that don’t fit neatly into the CMOS roadmap, or the FinFET vs. FDSOI dichotomy. For IoT devices, FDSOI chipsets combine low standby power with excellent analog performance. In the automotive sector, soft error rates and heat dissipation are critical. Rather than pursuing extreme scaling, these applications often find a good balance between cost and performance at the 28 nm node.

For RF devices like resonators and filters, key device dimensions depend on the wavelength. Moreover, improved loss characteristics, superior thermal stability, and other improved performance metrics can often be found with piezoelectric materials and other alternatives to silicon and silicon dioxide.

Important materials parameters for these devices include atomic-scale thickness uniformity, high purity, and precise crystallographic orientation, all of which affect frequency response. More than merely a platform, the substrate is an integral part of an RF system. For that reason, Mazure explained, engineered substrates like silicon-on-insulator or piezoelectric-on-insulator wafers must be co-optimized along with the devices. The wafer specifications may change as the design evolves, and the design must allow for the variability that the substrate vendor can deliver.

In this environment, the substrate vendor needs to be able to use industrial tools to fabricate and validate test devices in collaboration with customers and potential customers. The new Substrate Innovation Center at Leti is, Mazure said, unique in the world in offering this combination of capabilities.