This paper presents a short review of the microwave acoustics area, where exciting material innovations and performance advancements have been made in the past decade. The ever-growing demand for more sophisticated passive signal processing functions on-chip has fueled these developments. As a result, microwave acoustic devices have maintained performance leadership in mobile applications. By evaluating three fundamental parameters, namely electromechanical coupling ( k 2), quality factors, and frequency scalability, of microwave acoustics, this paper aims to, extensively but not exhaustively, capture the rationales behind approaches achieving higher performance microsystems. Outlooks for different material systems and addressing their underlying challenges are also offered in hopes of establishing a balanced roadmap for future microwave acoustics development.

Microwave Acoustic Devices: Recent Advances and Outlook

This work presents a new class of microelectromechanical system (MEMS) resonator toward 60 GHz for the fifth-generation (5G) wireless communications. The wide range of the operating frequencies is achieved by resorting to different orders of the antisymmetric Lamb wave modes in a 400-nm-thick Z-cut lithium niobate thin film. The resonance of 55 GHz demonstrated in this work marks the highest operating frequency for piezoelectric electromechanical devices. The fabricated device shows an extracted mechanical $Q$ of 340 and an $f\times Q$ product of $1.87\times 10^{13}$ in a footprint of $2 \times 10^{-3}$ mm2. The performance has shown the strong potential of LiNbO3 antisymmetric mode devices for front-end applications in 5G high-band.

/pdf/10-60-ghz-electromechanical-resonators-using-thin-film-426lh8rzpr.pdf

10–60-GHz Electromechanical Resonators Using Thin-Film Lithium Niobate

This paper presents a new class of micro-electro-mechanical system (MEMS) C-band filters for 5G front-ends. The filter is comprised of resonators based on the first-order asymmetric Lamb wave (A1) mode in thin-film lithium niobate. Two filters have been demonstrated at 4.5 GHz with sharp roll-off, flat in-band group delay, and spurious-free response over a wide frequency range. The first design shows a 3-dB fractional bandwidth (FBW) of 10%, an insertion loss (IL) of 1.7 dB, an out-of-band (OoB) rejection of −13 dB, and a compact footprint of 0.36 mm2, while the second design shows a 3-dB FBW of 8.5%, an IL of 2.7 dB, an OoB rejection of −25 dB, and a footprint of 0.9 mm2. The demonstrations herein mark the largest FBW achieved for acoustic-only filters at 5G frequencies. [2019-0083]

4.5 GHz Lithium Niobate MEMS Filters With 10% Fractional Bandwidth for 5G Front-Ends

Commercial markets desire integrated multifrequency band-select duplexer and diplexer filters with a wide fractional bandwidth and steep roll-off to satisfy the ever-increasing demand for spectrum. In this paper, we discuss the fabrication and design of lithium niobate (LN) thin-film S0 Lamb-wave resonators on a piezoelectric-on-piezoelectric platform. Filters using these resonators have the potential to fulfill all the above requirements. In particular, we demonstrated one-port high-order S0 Lamb-wave resonators with resonant frequencies from $\sim 400$ MHz to $\sim 1$ GHz on a black rotated y-136 cut LN thin film. The effective electromechanical coupling factor ( $k_{eff}^{2}$ ) ranges from 7% to 12%, while the measured quality factor ranges from 600 to 3300. The highest $k_{eff}^{2} \times Q$ achieved on this chip is 194, significantly surpassing contour mode resonators manufactured in other technologies. [2014-0280]

Design and Fabrication of S 0 Lamb-Wave Thin-Film Lithium Niobate Micromechanical Resonators

In a free ZY-LiNbO3 400nm thick platelet, narrow electrodes (500nm wide) placed periodically with a pitch of few micrometers can eXcite standing Bulk Acoustic shear wave Resonances (XBARs), by means of lateral electric field parallel to crystalline Y- axis. The resonance frequency of around 4.8GHz and 13.6GHz are suitable for development of RF filters. The XBARs 3rd, 5th and even 9th harmonics were observed up to 38 GHz.

Laterally excited bulk wave resonators (XBARs) based on thin Lithium Niobate platelet for 5GHz and 13 GHz filters

This paper focuses on the technical differentiation of film bulk acoustic resonator (FBAR) technology from other mechanical resonator technologies for timing applications. The paper will touch on a recent modification of FBARs, the zero-drift resonator (ZDR), that is temperature compensated. One technology differentiator is the size of the chip-scale packaged resonator. Another is that the silicon lid is perfectly suitable for placement of integrated circuits and this is currently being done. Many factors (wide tuning range, high Q, high frequency, small size, integrated circuitry) are being used to differentiate potential products for the time and frequency markets.

Positioning FBAR technology in the frequency and timing domain

We present a fourth-design generation Free Running Oscillator and Voltage Controlled Oscillator using integrated bipolar circuitry in the lid wafer with a temperature-compensated FBAR resonator in the base wafer. The goal is to produce a high frequency, low-noise oscillator. Because there are ~15,000 oscillators per wafer, we can develop very sensitive testing procedures to study the oscillator behavior. For example, we have determined our frequency measurement accuracy and precision to be ~ 0.2 parts-per-million (1 σ), and our phase sensitivity floor to be less than -180 dBc/Hz. Measurements on package hermeticity, suggest that the oscillators behave with the same level of integrity as our standard FBAR filters.

Sub-10 fs jitter S-band oscillators and VCOs in a 1×1×0.23 mm3 chip scale package

Quartz crystals have dominated the timing market for the last 70 years. FBAR technology is poised to replace quartz for many high frequency applications. Integration of the ultra-small form factor of the microcap’d FBAR into the SoC BGA packages currently in the market will make these applications earn the moniker, "Crystal-less". To replace crystals for non-GPS applications, the FBAR must demonstrate superb aging properties, repeatable and well-behaved temperature stability, immunity to mechanical stress, high frequency with +/- 500 ppm accuracy and small size. We will present data showing that we have met all five properties described above. Furthermore, we have integrated 3 resonators into an all-silicon 0.5 X 0.5 X 0.2 mm3 package targeting the 3 BLE advertising frequencies: 2402MHz, 2426 MHz and 2480 MHz.

Triple Ultra-Stable, Zero-Drift Resonators in a Single Package for BLE

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Papers

Positioning FBAR technology in the frequency and timing domain

Sub-10 fs jitter S-band oscillators and VCOs in a 1×1×0.23 mm3 chip scale package

Triple Ultra-Stable, Zero-Drift Resonators in a Single Package for BLE