In this work, we present first-order antisymmetric (A1) mode resonators in 128 • Y-cut lithium niobate (LiNbO 3 ) thin films with electromechanical coupling coefficients (k 2 ) as large as 46.4%, exceeding the state-of-the-art. The achievable k 2 of A1 in LiNbO 3 substrates of different orientations is first explored, showing X-axis direction in 128 • Y-cut LiNbO 3 among the optimal combinations. Subsequently, A1 resonators with spurious mode mitigation are designed and fabricated. In addition to the large k 2 , the implemented devices show a maximum quality factor ( Q) of 598 at 3.2 GHz. Upon further optimization, the reported platform can potentially deliver a wideband acoustic-only filtering solution in 5G New Radio.[2020-0003]
This work demonstrates a group of shear horizontal (SH0) mode resonators and filters using lithium niobate (LiNbO 3) thin films on silicon carbide (SiC). The single-crystalline X-cut LiNbO 3 thin films on 4H-SiC substrates have been prepared by ion-slicing and wafer-bonding processes. The fabricated resonator has demonstrated a large effective electromechanical coupling (k 2) of 26.9% and a high-quality factor (Bode-Q) of 1228, hence resulting in a high figure of merit (FoM = k 2 • Bode-Q) of 330 at 2.28 GHz. Additionally, these fabricated resonators show scalable resonances from 1.61 to 3.05 GHz and impedance ratios between 53.2 and 74.7 dB. Filters based on demonstrated resonators have been demonstrated at 2.16 and 2.29 GHz with sharp roll-off and spurious-free responses over a wide frequency range. The filter with a center frequency of 2.29 GHz shows a 3-dB fractional bandwidth of 9.9%, an insertion loss of 1.38 dB, an out-of-band rejection of 41.6 dB, and a footprint of 0.75 mm 2. Besides, the fabricated filters also show a temperature coefficient of frequency of −48.2 ppm/ • C and power handling of 25 dBm. Although the power handling is limited by arc discharge and migration-induced damage of the interdigital electrodes and some ripples in insertion loss and group delay responses are still present due to the transverse spurious modes, the demonstrations still show that acoustic devices on the LiNbO 3-on-SiC platform have great potential for radio-frequency applications.
In this work, we present a new paradigm for enabling gigahertz higher-order Lamb wave acoustic devices using complementarily oriented piezoelectric (COP) thin films. Acoustic characteristics are first theoretically explored with COP lithium niobate (LiNbO 3) thin films, showing their excellent frequency scalability, low loss, and high electromechanical coupling (k 2). Acoustic resonators and delay lines are then designed and implemented, targeting efficient excitation of higher-order Lamb waves with record-breaking low loss. The fabricated resonator shows a 2 nd-order symmetric (S2) resonance at 3.05 GHz with a high quality factor (Q) of 657, and a large k 2 of 21.5% and a 6 th-order symmetric (S6) resonance at 9.05 GHz with a high Q of 636 and a k 2 of 3.71%, both among the highest demonstrated for higher-order Lamb wave devices. The delay lines show an average insertion loss (IL) of 7.5 dB and the lowest reported propagation loss of 0.014 dB/µm at 4.4 GHz for S2. Notable acoustic passbands up to 15.1 GHz are identified. Upon further optimizations, the proposed COP platform can lead to gigahertz low-loss wideband acoustic components.
Microwave photonics, a field that crosscuts microwave/millimeter-wave engineering with optoelectronics, has sparked great interest from research and commercial sectors. This multidisciplinary fusion can achieve ultrawide bandwidth and ultrafast speed that were considered impossible in conventional chip-scale microwave/millimeter-wave systems. Conventional microwave-to-photonic converters, based on resonant acousto-optic modulation, produce highly efficient modulation but sacrifice bandwidth and limit their applicability for most real-world microwave signal-processing applications. In this paper, we build highly efficient and wideband microwave-to-photonic modulators using the acousto-optic effect on suspended lithium niobate thin films. A wideband microwave signal is first piezoelectrically transduced using interdigitated electrodes into Lamb acoustic waves, which directly propagates across an optical waveguide and causes refractive index perturbation through the photoelastic effect. This approach is power-efficient, with phase shifts up to 0.0166 rad / √ mW over a 45 μm modulation length and with a bandwidth up to 140 MHz at a center frequency of 1.9 GHz. Compared to the state-of-the-art, a 9 × more efficient modulation has been achieved by optimizing the acoustic and optical modes and their interactions.
In this work, we present the low-loss acoustic delay lines (ADLs) at 5 GHz, using the first-order antisymmetric (A1) mode in 128 • Y-cut lithium niobate thin films. The ADLs use a single-phase unidirectional transducer (SPUDT) design with a feature size of quarter acoustic wavelength. The design space is analytically explored and experimentally validated. The fabricated miniature A1 ADLs with a feature size of 0.45 µm show a high operating frequency at 5.4 GHz, a minimum insertion loss (IL) of 3 dB, a fractional bandwidth (FBW) of 1.6%, and a small footprint of 0.0074 mm 2. The low IL and high operating frequency have significantly surpassed the state-of-theart performance of ADLs. The propagation characteristics of A1 acoustic waves have also been extracted. The demonstrated designs can lead to low-loss and high-frequency transversal filters for future 5G applications in the sub-6-GHz bands.
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