Aluminum scandium nitride thin-film bulk acoustic resonators for 5G wideband applications

Abstract

Bulk acoustic wave (BAW) filters have been extensively used in consumer products for mobile communication systems due to their high performance and standard complementary metal-oxide-semiconductor (CMOS) compatible integration process. However, it is challenging for a traditional aluminum nitride (AlN)-based BAW filter to meet several allocated 5G bands with more than a 5% fractional bandwidth via an acoustic-only approach. In this work, we propose an Al0.8Sc0.2N-based film bulk acoustic wave resonator (FBAR) for the design of radio frequency (RF) filters. By taking advantage of a high-quality Al0.8Sc0.2N thin film, the fabricated resonators demonstrate a large Keff2 of 14.5% and an excellent figure of merit (FOM) up to 62. The temperature coefficient of frequency (TCF) of the proposed resonator is measured to be −19.2 ppm/°C, indicating excellent temperature stability. The fabricated filter has a center frequency of 4.24 GHz, a −3 dB bandwidth of 215 MHz, a small insertion loss (IL) of 1.881 dB, and a rejection >32 dB. This work paves the way for the realization of wideband acoustic filters operating in the 5G band.

Single crystal ferroelectric AlScN nanowires

“…AlScN ferroelectrics show significant promise for use in wideranging device applications, including random-access memory [1][2][3] and acoustic resonators. [4][5][6] Epitaxial growth of AlScN thin films on a wide range of substrates and buffer layers, including Si(111), 7 Al 2 O 3 (0001), 8,9 Al 2 O 3 (0001)/ Mo(110), 10 SiC, 4,11 and GaN(0001) [12][13][14] have been reported. More commonly, columnar polycrystalline AlScN thin films are grown on a variety of textured metallic bottom electrodes deposited onto Si wafers.…”

Observation of Photodielectric Effect in Aluminum Nitride Piezoelectric Films

“…Moreover, the Sc 0.15 Al 0.85 N films exhibited a larger increase in dielectric constant as compared to the original AlN films. The ratio of 15% is an optimal doping level that allows for yielding strong spontaneous polarization and improving the piezoelectric coefficient in AlN films. , …”

Reliable formulas for accurately determining the resonance and antiresonance frequencies of thin film bulk acoustic resonators

“…Compared to experimental data and 3D finite element simulations, our formula can accurately and quickly predict resonant, anti-resonant frequencies, and bandwidth across a wide range of piezoelectric and metallic layer thickness combinations.strength between the metallic and piezoelectric layers in a Film Bulk Acoustic Resonator (FBAR). The selected high acoustic impedance electrodes to fabricate FBAR can improve k eff 2 significantly, such as Molybdenum (Mo)and tungsten (W) [26], or introduce Sc to AlN [10,27,28]. Generally, electrodes with high impedance can generate a consistent stress field in the piezoelectric layer, resulting in a higher value for k .…”

“…and tungsten (W) [26], or introduce Sc to AlN [10,27,28]. Generally, electrodes with high impedance can generate a consistent stress field in the piezoelectric layer, resulting in a higher value for k .…”