This work reports the Lamb wave resonator based on Al _0.7 Sc _0.3 N thin films using magnetron sputtering with a single alloy target. The resonator fabrication process based on high Sc doping concentration is discussed. Al _0.7 Sc _0.3 N thin films with a 1.2° (0002) rocking curve were obtained with improved crystalline quality and reduced abnormal orientation grains (AOGs). The etching process has been optimized to achieve an etch rate of 127 nm/min and a profile angle of 72°. The dispersion properties of Lamb waves and the influence of different electrode metals on the coupling coefficient in Al _0.7 Sc _0.3 N thin films were simulated. Al _0.7 Sc _0.3 N Lamb wave resonators operating at approximately 300 MHz and 600 MHz were fabricated. A high electromechanical coupling coefficient ( k _t ² ) of 7.74% is reported, with the loaded quality factor of 1119, respectively. A high Figure-of-Merit (FOM) of 86.6 has been achieved for AlScN film based Lamb wave resonators below 1 GHz. The application potential of high scandium concentration (>25%) in resonators and filters is demonstrated.

Doped AlN thin films, especially high Sc-ratio AlScN film, have been reported to significantly improve the piezoelectric properties and draw attention for high performance resonators, transducers and integrated ferroelectric applications. However, many demonstrated devices were limited by poor film stress control, abnormal oriented grains and lack of a good etching profile. Compared to costly single alloy target, co-sputtered AlScN films can benefit customized doping concentrations and provide a unique solution for high Sc-ratio AlScN film quality and device studies. In this work, the optimized co-sputtering deposition and ICP etching processes of 500 nm AlScN thin film were developed and released AlScN Lamb-wave resonators were demonstrated. The influence of stress control by changing N ₂ process gas on the crystalline orientation, abnormal orientation grains, film roughness and piezoelectric property of AlScN thin films were discussed in detail. The AlScN film with a high Sc content requires a lower deposition pressure to obtain good crystalline quality. Al _0.85 Sc _0.15 N thin films with FWHM of 1.75°, an average stress of −14.5 MPa and a stress range of 156 MPa were obtained. 130 nm/min etching rate and 77° sidewall profile were achieved by optimized ICP etching of Al _0.78 Sc _0.22 N film. Lamb-wave resonators were fabricated based on both Al _0.78 Sc _0.22 N and Al _0.85 Sc _0.15 N thin films, achieving a quality factor of over 1000 at resonant frequency of approximately 300 MHz. The electromechanical coupling coefficients were improved by 152% and 80% compared to pure AlN devices.[2021-0210]

reports novel aluminum scandium nitride (Al _0.7 Sc _0.3 N) thin film acoustic delay lines (ADLs). Low loss ADLs are implemented on sputtered Al _0.7 Sc _0.3 N thin film using cross-field excited single-phase unidirectional transducers (SPUDT), which generate S0 mode Lamb wave between two ports. ADLs are fabricated with up to 300 $\mu \text{m}$ flat delay gap by optimized low stress Al _0.7 Sc _0.3 N thin film. A large electromechanical coupling factor ( $K^{ {2}}$ ) of 7.8% provided by approximately 1 $\mu \text{m}$ Al _0.7 Sc _0.3 N thin film allows for an overall improvement. Compared to implemented aluminum nitride (AlN) thin film counterparts, Al _0.7 Sc _0.3 N ADLs achieve remarkably lower insertion loss (IL), wide fractional bandwidth (FBW), and better impedance matching, featuring a minimum IL of 2.27 dB and a 3-dB FBW of 7.1% at approximately 780 MHz. The increase in relative permittivity due to Sc doping reduces the imaginary part of the matched network by 40%. For fundamental symmetric (S0) Lamb waves, a high group velocity of 8532 m/s, a propagation loss of 0.07 dB/ $ {\lambda }$ , and a propagation quality factor (Q) of 338 are extracted. Upon further development, scandium (Sc) doped AlScN thin films could enable CMOS-compatible piezoelectric acoustic platform for signal processing, sensing, and computing applications.

In the past decade, aluminum scandium nitride (AlScN) with a high Sc content has shown ferroelectric properties, which provides a new option for CMOS-process-compatible ferroelectric memory, sensors and actuators, as well as tunable devices. In this paper, the ferroelectric properties of $A{l}_{0.7}S{c}_{0.3}N$ grown on different metals were studied. The effect of metal and abnormal orientation grains (AOGs) on ferroelectric properties was observed. A coercive field of approximately 3 MV/cm and a large remanent polarization of more than 100 μC/cm² were exhibited on the Pt surface. The $A{l}_{0.7}S{c}_{0.3}N$ thin film grown on the Mo metal surface exhibited a large leakage current. We analyzed the leakage current of $A{l}_{0.7}S{c}_{0.3}N$ during polarization with the polarization frequency, and found that the $A{l}_{0.7}S{c}_{0.3}N$ films grown on either Pt or Mo surfaces have large leakage currents at frequencies below 5 kHz. The leakage current decreases significantly as the frequency approaches 10 kHz. The positive up negative down (PUND) measurement was used to obtain the remanent polarization of the films, and it was found that the remanent polarization values were not the same in the positive and negative directions, indicating that the electrode material has an effect on the ferroelectric properties.

This paper presents the lamb wave contour mode resonators (CMR) based on 22% Aluminum Scandium Nitride (AlScN) thin film with λ of 12-36 μm, and operating in S0 mode. We report the design, fabrication, and characterization of 500 nm-thick AlScN CMRs, which take advantage of optimized stress control of co-sputtered AlScN thin films and vertical ICP etching profile. The experimental results are compared to theoretical predictions by finite element analysis. All Al0.78Sc0.22N devices show excellent agreement with simulations in piezoelectric coupling using modified AlScN film parameters. The best Al0.78Sc0.22N contour mode resonator has achieved an electromechanical coupling coefficient (kt2) of 5.24% and loaded quality factor (Q) of 1219 with an operating frequency at approximately 300 MHz, which exhibits a high figure of merit (FoM) of 63.88 in piezoelectric Microelectromechanical System (MEMS) lamb wave contour mode resonator. This paper also presents the co-sputtering characteristics of the AlScN thin films under N2 gas to achieve low stress and high quality piezoelectric materials, and the etching optimization of high concentration Sc doping AlN thin films under Cl2/BCl3/Ar chemistry to obtain record profile angle of 77°, high selectivity of 1:1 with SiO2 hard mask.

This work presents the laterally vibrating Lamb wave resonators (LVRs) based on a 30% aluminum scandium nitride (Al_0.7Sc_0.3N) thin film with three interdigited transducer pairs operating in the S₀ mode. In order to reduce the anchor loss, perfect matched layer-based finite element analysis simulations are utilized to design and optimize the device. Thanks to the high quality AlScN using magnetron sputtering with a single alloy target, vertical etching profile, and designed device structure, 1-μm-thick Al_0.7Sc_0.3N-based LVRs with high performance are fabricated. The resonator equivalent electric parameters are extracted utilizing the modified Butterworth–Van Dyke model. The best Al_0.7Sc_0.3N LVR achieves an electromechanical coupling coefficient (k_t²) of 9.7% and a loaded quality factor (Q_r) of 1141.5 operating at approximately 305 MHz. The same resonator shows a motional quality factor (Q_m) of 1507.2, resulting in a high figure-of-merit (FoM = k_t² · Q_m) of 146.2. A 1.8 MHz tuning range is measured for an Al_0.7Sc_0.3N LVR by applying DC voltage in the range of −40 to 40 V due to the ferroelectric property of high Sc doping in Al_0.7Sc_0.3N. With the high FoM, Q_r, Q_m, and low motional resistance (R_m), the Al_0.7Sc_0.3N-based LVRs show strong potential in applications of radio frequency communications and piezoelectric transducers.