UTI shows high-quality sapphire-based AlScN thin films
Quasi-single-crystalline Al0.56Sc0.44N thin films for 5G RFFE BAW/SAW filters and next generation power electronics
Ultratrend Technologies Inc. (UTI), an AlN solution provider based in China, has demonstrated high-quality sapphire-based AlScN thin films with high crystalline quality by innovative technologies at the Power and Compound Semiconductor International Forum 2021, which was organised in conjunction with SEMICON China 2021 on Mar 18-19, 2021 in Kerry Hotel at Shanghai.
AlScN has been so far the most promising new material which could replace conventional Aluminum Nitride (AlN) for 5G RFFE FBAR/SAW filters and next generation power electronics. By introducing high scandium content to AlN, the piezoelectric coefficient and electromechanical coupling factor are significantly improved. However, the instability of the piezoelectric AlScN crystal phase with high atomic Sc-concentration (>40 percent) used to be a problem for the industry because the phase transition usually appears from wurtzite structure to cubic salt structure in the growth process. Therefore, the production of AlScN films is believed to be very challenging.
Fig. 1 above shows sapphire-based Al0.56Sc0.44N thin film demonstrated by UTI
Conventional processes to produce AlScN are magnetron sputtering, MBE and MOCVD. Magnetron sputtering is a dominant technique to grow thin films because a large quantity of thin films can be prepared at relatively low cost. Unfortunately, current quality of these films by this process is insufficient for industrial applications.
The MBE and MOCVD processes could produce relatively higher quality thin films, but the crystalline quality is still need to be improved in order to meet industrial requirements. Meanwhile, the procedures to fabricate AlScN by these two methods are very complicated and the scalability is too low for industrial production.
The researchers at UTI have developed a serial of unique techniques that enable the growth of high-quality AlScN thin films on sapphire with the atomic scandium content up to 44 percent (measured by EDS), and more importantly low cost and scalable as well.
High-resolution X-ray diffraction (HRXRD) rocking curves (omega scan) for the (0002) reflection by third-party inspection revealed that the as-grown 500 nm-thick AlScN films showed full-width at half-maximums (FWHMs) of 88-90 arcsecs, and the peaks reached extraordinarily around 400,000 - 500,000 cps (as illustrated in Fig.2a). The FWHMs of the (10-12) asymmetric reflections are 300 - 350 arcsec. The roughness (Ra) of the as-grown surface was determined to be 4-5 nm by atomic force microscopy (AFM). Excellent uniformity throughout the entire thin films was also observed.
“Many scientists around the world have been spending numerous efforts on the development of high-quality AlScN material, but no one before us was able to synthesise such high-quality films with high scandium content, so it is undoubtedly a very heart-stirring news for various applications, such as high performance 5G FBAR/SAW filters and next generation of power transistors. We are working with several leading fabless partners in China to realize high performance FBAR/SAW resonators that meet the increasing stringent requirements of the industry.”, explained Jason Wu, the founder and CEO of UTI.
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