This letter reports an aluminium nitride (AlN)based micromechanical resonator with high-effective coupling coefficient (k ² _eff ) and low insertion loss (IL), which are comparable with those of Film Bulk Acoustic Resonators (FBARs). The in-house-fabricated resonator comprises of lithographically patterned top and bottom molybdenum interdigitated electrode fingers and a layer of 1-μm-thick AlN sandwiched in between. Synergetic inter-mode coupling between the constituent thickness mode and the lateral mode can be realized within a wide frequency range, which can be treated as a subcategory of degenerated cross-sectional Lamé mode, enabling the capability of lithographic tuning of resonant frequency yet not compromising k ² _eff . Measurement results show that the designed 2.3-GHz resonator achieves a k ² _eff of 6.34% and an IL of 0.26 dB upon direct connection to a network with 50-Ω termination, making it a promising candidate for Wireless Local Area Network (WLAN) and high band Long Term Evolution (LTE) band selection filtering applications.

This letter reports the first implementation of a new class of laterally coupled alternating thickness (LCAT) mode resonators operating above 2 GHz, realised by replacing the bottom interdigitated electrodes of the conventional LCAT mode resonator with an electrically floating plate. Besides saving one mask process and relaxing the tight resolution and alignment requirements for defining small features, the flat unpatterned bottom electrode metal is also more favorable for the growth of highly oriented piezoelectric thin film, which results in an improved resonator quality factor (Q). A group of 8% scandium doped aluminium nitride-based modified LCAT mode resonators with frequency difference over 100 MHz by varying the top interdigitated electrode pitches are fabricated achieving coupling coefficient (k _eff ² ) of up to 6.45% and figure of merit of up to 54, making them promising candidates for integrated band selection filter banks.

A high quality factor (Q) and low-impedance aluminum nitride (AIN) on silicon piezoelectric resonator is reported in this paper. The piezoelectric resonator is fabricated based on the AIN-on-cavity-Silicon-on-Insulator (SOI) platform and vacuum encapsulated using the waferlevel chip-scale packaging by aluminum-germanium eutectic bonding approach. The fabricated resonator achieves a loaded Q of 9520 and a motional impedance of 32.64 Ω at its series resonant frequency of 27.19 MHz. Thermal cycles (TC) and highly-accelerated stress test (HAST) are performed to evaluated the packaging reliability of the fabricated devices. No obvious impedance change caused by the TC and HAST is observed. The TC results indicate that the packaged devices have an equivalent life of more than 11.65 years based on the Coffin-Manson model. The piezoelectric resonator-based programmable oscillators demonstrate an overall frequency drift of ± 3 ppm over the temperature range of -20°C to 70°C thanks to the passive and active temperature compensations. With this stable frequency reference, the programmable oscillator produces a 75.01-MHz frequency output. The measured integrated phase jitter is 2.02 ps (rms) from 12 to 10 MHz.

This letter reports a spurious mode free GHz aluminum nitride (AlN) lamb wave resonator (LWR) towards high figure of merit (FOM). One dimensional gourd-shape phononic crystal (PnC) tether with large phononic bandgaps is employed to reduce the acoustic energy dissipation into the substrate. The periodic PnC tethers are based on a 1 μm-thick AlN layer with 0.26 μm-thick Mo layer on top. A clean spectrum over a wide frequency range is obtained from the measurement, which indicates a wide-band suppression of spurious modes. Experimental results demonstrate that the fabricated AlN LWR has an insertion loss of 5.2 dB and a loaded quality factor (Q) of 1893 at 1.02 GHz measured in air. An impressive ratio of the resistance at parallel resonance (R_p) to the resistance at series resonance (R_s) of 49.8 dB is obtained, which is an indication of high FOM for LWR. The high R_p to R_s ratio is one of the most important parameters to design a radio frequency filter with steep roll-off.

An AlN piezoelectric Lamb-wave resonator, which is excited by two dimensional electric field, is reported in this paper. Rhombus-shape electrodes are arranged on AlN thin film in a checkered formation. When out-of-phase alternating currents are applied to adjacent checkers, two dimensional acoustic Lamb waves are excited in the piezoelectric layer along orthogonal directions, achieving high electromechanical coupling coefficient, which is comparable to film bulk acoustic resonators. The electromechanical coupling coefficient of the 285.3 MHz resonator presented in this paper is 5.33%, which is the highest among AlN based Lamb-wave resonators reported in literature. Moreover, the spurious signal within a wide frequency range is significantly suppressed to be 90% lower than that of the resonance mode. By varying the electrode dimension and inter-electrode distance, resonators having different resonant frequencies can be fabricated on a single wafer, making single-chip broadband filters, duplexers, and multiplexers possible.