Background and History. Resonator and Filter Topologies. Baw Device Basics. Design and Fabrication of BAW Devices. FBAR Resonators and Filters. Comparison with SAW Devices. Films Deposition for BAW Devices. Characterization of BAW Devices. Monolithic Integration. System-in-Package (SiP) Integration. Index.

RF bulk acoustic wave filters for communications

With the rapid commercialization of fifth generation (5G) technology in the world, the market demand for radio frequency (RF) filters continues to grow Acoustic wave technology has been attracting great attention as one of the effective solutions for achieving high-performance RF filter operations while offering low cost and small device size Compared with surface acoustic wave (SAW) resonators, bulk acoustic wave (BAW) resonators have more potential in fabricating high- quality RF filters because of their lower insertion loss and better selectivity in the middle and high frequency bands above 25 GHz Here, we provide a comprehensive review about BAW resonator researches, including materials, structure designs, and characteristics The basic principles and details of recently proposed BAW resonators are carefully investigated The materials of poly-crystalline aluminum nitride (AlN), single crystal AlN, doped AlN, and electrode are also analyzed and compared Common approaches to enhance the performance of BAW resonators, suppression of spurious mode, low temperature sensitivity, and tuning ability are introduced with discussions and suggestions for further improvement Finally, by looking into the challenges of high frequency, wide bandwidth, miniaturization, and high power level, we provide clues to specific materials, structure designs, and RF integration technologies for BAW resonators

https://www.mdpi.com/2072-666X/11/7/630/pdf

Materials, Design, and Characteristics of Bulk Acoustic Wave Resonator: A Review

Since two decades piezoelectric MEMS resonator research has been making a headway by leaps and bounds in multiple fronts such as micro/nanofabrication techniques, device and system design, monolithic integration, packaging, material engineering, etc. Piezoelectricity based frequency selective resonant tanks are an integral part of radio frequency communication, inertial sensors, infrared sensors, environmental monitoring modules, energy harvesters, etc. To improve the functionality of the aforementioned modules it is cardinal to understand the underlying concepts of resonator design, material selection, and performance enhancement techniques. Here in this review paper, a comprehensive overview of various piezoelectric thin-film material properties along with different commercial microfabrication platforms with CMOS integration facility is presented. The device characteristics greatly depend on the resonator mode shape and thus suitable modes and thin-film material configurations can be chosen depending on the target frequency, application, and power budget requirements. In addition to device modeling, a synopsis of the several acoustic and material engineering approaches to enhance the figure of merit of the resonator has been presented. The future avenues of piezoelectric MEMS cover a wide spectrum of possibilities such as 5G communication, quantum processing, frequency combs, photonics integration, gesture sensors, etc.

Piezoelectric MEMS Resonators: A Review

Microelectromechanical systems (MEMS) have been familiar in the field of microelectronics and device technology since 1965, when Harvey C. Nathanson invented the first MEMS device (known as the resonant gate transistor). Since that time, MEMS have represented a prominent field for academic research, with simplified implementations of several devices such as sensors, transducers, actuators, and accelerometers being fabricated. According to MEMS technology, all devices could be fabricated using standard integrated circuit (IC) techniques, with the device?s lateral dimensions normally ranging from a maximum of 500 nm to submicron ranges.

Paradigm Phase Shift: RF MEMS Phase Shifters: An Overview

Since its first discussions in literature during late `90 s, RF-MEMS technology (i.e. Radio Frequency MicroElectroMechanical-Systems) has been showing uncommon potential in the realisation of high performance and widely reconfigurable RF passives for radio and telecommunication systems. Nonetheless, against the most confident forecasts for successful exploitation of RF-MEMS technology in mass-market applications, with the mobile phone segment first in line, already commencing from the earliest years of the 2000s, first design wins for MEMS-based RF passives have started to be announced just recently. This paper tries to depict and interpret the substantial circumstances that made RF-MEMS technology fail repeatedly, for about one decade, market forecasts. With the graphical support of the hype cycle concept, it will be shown that missed success of RF-MEMS was first caused by intrinsic (i.e. technology-related) factors. Subsequently, extrinsic elements linked to market acceptance and needs of such a technology, not fully weighted since the beginning, caused the second wave of disappointment around RF-MEMS. Quite unexpectedly, the context has changed rather significantly in recent years. The smartphones market segment started to generate a factual need for highly reconfigurable and high performance RF passive networks, and this circumstance is increasing the momentum of RF-MEMS technology that was expected about one decade ago. This work frames the current state of RF-MEMS market exploitation, also providing highlights on further expansion in mobile and telecommunication systems. Eventually, a focused state of the art report is developed around recent RF-MEMS research findings driven by requirements imposed by current market applications.

RF-MEMS: an enabling technology for modern wireless systems bearing a market potential still not fully displayed

This article describes the application of the hierarchical cascading technique (HCT) to the 3-D finite-element method (FEM) analysis of transverse-mode behaviors in surface acoustic-wave (SAW) devices. Mirror cascading is proposed as a speed-up technique for the HCT operation using the general-purpose graphic processing unit (GPGPU). Two methods are implemented for the analysis: one is impedance calculation and the other is the calculation of SAW scattering coefficients at boundaries. It is demonstrated that HCT enables rapid calculation for successive simulation with scanning design parameters. Thus, techniques discussed in this article are quite effective for the optimization of device structures. It is also shown that GPGPU can accelerate HCT calculation dramatically, especially for 3-D cases discussed in this article.

Use of Hierarchical Cascading Technique for FEM Analysis of Transverse-Mode Behaviors in Surface Acoustic-Wave Devices

This paper presented a 4-bit switched-line phase shifter based on the metal-contact SPDT RF MEMS switches. The phase shift module was fabricated on a 20mil RO4350 substrate and mounted with its driver module on an Aluminum platform. This electrically tunable phase shifter is suitable for taking place of mechanical phase shifters used in base station. Measurements indicated a maximum phase shift of 75 degree with a step of 5 degree, a maximum insertion loss of 0.89dB and a minimum return loss of 13.4dB at 2.7GHz. The phase accuracy is within 2 degree at 2.7 GHz.

A 4-bit switched-line phase shifter based on MEMS switches

This paper reports a low phase noise 10 MHz oscillator based on a lateral-extensional mode thin-film piezoelectric-on-silicon (TPoS) resonator. A novel design of interdigital electrodes is introduced to improve both the insertion loss and quality factor of the resonator. The average quality factor gets improved by 43% by this method. The equivalent circuit model of the fundamental lateral-extensional mode is analysed. An oscillator is also designed and manufactured. The whole circuit includes a single common emitter BJT amplifier, LC network filter, a phase shifting unit and a MEMS resonator. Tuning the phase shifter in the feedback circuit, the MEMS resonator works at the best operating point while the phase shifting of the peripheral circuit is 90°. With an operating input power around 0 dBm, the resonator is not driven at its bifurcation point. Little nonlinearity is observed in the output waveform. The phase-noise is measured below −105 dBc/Hz@100 Hz, −135 dBc/Hz@1 kHz offset and the far-from-carrier noise reaches below −150 dBc/Hz.

Study of a 10 MHz MEMS oscillator with a TPoS resonator

In this paper, we propose the use of the hierarchical cascading technique (HCT) for the finite element method (FEM) analysis of bulk acoustic wave (BAW) devices. First, the implementation of this technique is presented for the FEM analysis of BAW devices. It is shown that the traveling-wave excitation sources proposed by the authors are fully compatible with the HCT. Furthermore, a HCT-based absorbing mechanism is also proposed to replace the perfectly matched layer (PML). Finally, it is demonstrated how the technique is much more efficient in terms of memory consumption and execution time than the full FEM analysis.

https://iopscience.iop.org/article/10.7567/JJAP.57.07LC08/pdf

Application of hierarchical cascading technique to finite element method simulation in bulk acoustic wave devices

This paper describes how the hierarchical cascading technique (HCT) expanded capabilities of FEM-based numerical simulation in radio frequency surface and bulk acoustic wave (SAW/BAW) devices. The HCT was originally proposed for speed up and size-reduction of two-dimensional FEM simulation of SAW resonators. The authors' group applied 2D and 3D HCT to attack various problems on SAW/BAW excitation and scattering including those believed to be impossible. The traveling wave excitation source proposed by the author's group fits well with HCT and can be adapted efficiently in these analyses. First basics of HCT and its extensions are explained, and then these techniques are applied to various practical problems as demonstration.

Yulin Huang

Papers

Use of Hierarchical Cascading Technique for FEM Analysis of Transverse-Mode Behaviors in Surface Acoustic-Wave Devices

A 4-bit switched-line phase shifter based on MEMS switches

Study of a 10 MHz MEMS oscillator with a TPoS resonator

Application of hierarchical cascading technique to finite element method simulation in bulk acoustic wave devices

Quantum Leap in Simulation Technologies for Radio Frequency Surface and Bulk Acoustic Wave Devices Gifted by Hierarchical Cascading Technique