Soitec Strikes Deal with Qualcomm for 5G RF Filters

Having established its leadership in the silicon on insulator (SOI) market, Soitec is now aiming for a similar dominance in piezoelectric on insulator (POI) substrates to address the huge growth in RF filters needed for 5G applications. Soitec announced a business agreement with Qualcomm Technologies to supply high volume POI wafers for RF filters in 4G and 5G smartphone radio frequency (RF) front-end modules.

In an interview with EE Times, Bernard Aspar, executive vice-president of global business at Soitec, said, “This is our first major business agreement disclosed beyond SOI. The POI based on our Smart Cut technology brings a new generation of substrate to the market, and while this is the first customer we have been able to publicly disclose, we already have a few customers using or evaluating our POI. Our ambition for our POI is to become a standard for RF filters for both 4G and 5G.”

He said that Soitec had been collaborating with Qualcomm for several years and was already a supplier of SOI technology to the company. The new agreement aims to bring POI wafer production to high volume manufacturing for use in Qualcomm Technologies’ RF filters that go ino smartphone RF front-end modules.

Aspar said that with a 50% increase in the RF filters required for 5G over 4G, the ability to deliver precision RF filters at low cost will be critical for the RF front-end modules. “The size of the market for POI wafers is going to be bigger than one million wafers per year in 2023-24. We see filters as a strategic part of the market opportunity hence it is a focus for us.  To build high-performance front-end modules, you need high performance filters.” In order to meet demand, Soitec will have a capacity of 500,000 wafers per year when it reaches full capacity, which, according to Aspar will be within 3-4 years.

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SAW on POI
Its POI technology has been key to enabling Qualcomm’s ultraSAW RF filter products announced earlier this year, which claim to significantly improve RF performance and outperform other filter technologies in bands up to 2.7 GHz. Radio frequency (RF) filters isolate radio signals from the different spectrum bands that phones use to receive and transmit information.

By achieving as much as 1 decibel (dB) improvement in insertion loss, Qualcomm said its ultraSAW filters offer a higher performance solution compared to competing bulk-acoustic (BAW) filters in the sub-2.7 GHz frequency range. It is integrating the ultraSAW technology across the Qualcomm product line including PA modules (PAMiD), front-end modules (FEMiD), diversity modules (DRx), Wi-Fi extractors, GNSS extractors and RF multiplexers.

The senior vice president and general manager for RFFE (RF front-end) at Qualcomm Germany RFFE, Christian Block, said, “This agreement with Soitec is key to ensure the supply of high-performance POI substrates from Soitec, and to securely support the demand from our OEM customers for high-performance Qualcomm ultraSAW RF filter products. The combination of Soitec Smart Cut based piezoelectric-on-insulator substrates and Qualcomm Technologies’ filter design and system expertise leads to high-yield multiplexers with multiple filter functions per die.”

Using Soitec’s proprietary Smart Cut technology in 150 mm, the foundation of its POI is a high resistivity silicon substrate, complemented by a buried oxide layer and a very thin and uniform layer of a mono-crystal piezo material on top. These POI engineered substrates enable the design of filters with large bandwidth, very low temperature sensitivity and low insertion loss with a simple device manufacturing technology. They also enable multiple filters to be integrated on the same die while meeting high frequency requirements. This helps meet the need of the latest generation of 4G/5G surface acoustic wave (SAW) filters offering performance with built-in temperature compensation.

Aspar explained the benefits of POI and also its Smart Cut technology. He said POI technology helps avoid frequency shifts due to temperature variations, and the use of high resistivity silicon reduces signal loss. “Confining the acoustic energy in the thin piezoelectric layer results in much better control of the acoustic wave propagating in the piezo material. Compared to a SAW filter on bulk material, a SAW filter on POI has lower loss and better efficiency. It also enables high frequencies and wider filters.”

He then describes Soitec’s POI technology differentiator. “With Smart Cut, we can achieve better uniformity with around + 50nm range. Hence, we have better control of the filter frequency within the wafer. Also, because we peel off a thin layer, we are able to refresh the donor wafer and use it several times.” Aspar continued, “This is compatible with different materials and scalable to larger diameter wafers. SAW on POI is an excellent alternative to BAW and TC-SAW.” Soitec has a roadmap to go to bigger wafers, as Aspar explained, “Our technology is fully scalable to 200mm, but availability of bulk piezoelectric material is limiting us.”

Aspar said Qualcomm chose Soitec’s POI technology because of its track record. “Soitec has demonstrated capacity to ramp to high volumes, and we already created a standard with SOI.” In addition, he said Qualcomm had experience in working with Soitec as the U.S. company was already using its SOI.