https://www.repository.cam.ac.uk/bitstream/1810/264501/1/Fu_et_al-2017-Progress_in_Material_Science-VoR.pdf

Advances in piezoelectric thin films for acoustic biosensors, acoustofluidics and lab-on-chip applications

This invention provides a surface acoustic wave device mounted module which is miniature, light, and highly reliable. The surface acoustic wave device mounted module also has excellent frequency characteristics. The surface acoustic wave device mounted module includes a multilayer substrate which has at least one layer of a shield pattern, input-output electrodes, grounding electrodes, through holes used for connecting electrodes, and a surface acoustic wave element. The surface acoustic wave element has metallic bumps, which are transfer-coated with a conductive resin, on electrode pads and an insulating resin around the surface acoustic wave element. The electrode pads are input-output terminals and grounding terminals formed on the surface acoustic wave element. Continuities between the input-output terminals and the input-output electrodes, and between the grounding terminals and the grounding electrodes are established by the through holes. An electrode pattern is formed on the surface of the multilayer substrate facing and surrounding the surface acoustic wave element. A metallic lid is attached to the electrode pattern by a solder or a conductive resin so that the surface acoustic wave element is sealed in an airtight condition. The electrode pattern is connected to the grounding electrodes by the through holes.

Surface acoustic wave device mounted module

A dielectric substance is laminated on one surface of a piezoelectric substance, and an IDT and reflectors are disposed as electrodes at a boundary between the piezoelectric substance and the dielectric substance, and the thickness of the electrodes is determined so that the acoustic velocity of the Stoneley wave is decreased less than that of a slow transverse wave propagating through the dielectric substance and that of a slow transverse wave propagating through the piezoelectric substance, thereby forming a boundary acoustic wave device.

Boundary acoustic wave device

Today, acoustic filters are the filter technology to meet the requirements with respect to performance dictated by the cellular phone standards and their form factor. Around two billion cellular phones are sold every year, and smart phones are of a very high percentage of approximately two-thirds. Smart phones require a very high number of filter functions ranging from the low double-digit range up to almost triple digit numbers in the near future. In the frequency range up to 1 GHz, surface acoustic wave (SAW) filters are almost exclusively employed, while in the higher frequency range, bulk acoustic wave (BAW) and SAW filters are competing for their shares. Prerequisites for the success of acoustic filters were the availability of high-quality substrates, advanced and highly reproducible fabrication technologies, optimum filter techniques, precise simulation software, and advanced design tools that allow the fast and efficient design according to customer specifications. This paper will try to focus on innovations leading to high volume applications of intermediate frequency (IF) and radio frequency (RF) acoustic filters, e.g., TV IF filters, IF filters for cellular phones, and SAW/BAW RF filters for the RF front-end of cellular phones.

Acoustic Wave Filter Technology–A Review

This paper reports on the design and experimental verification of a new class of thin-film (250 nm) superhigh- frequency laterally-vibrating piezoelectric microelectromechanical (MEMS) resonators suitable for the fabrication of narrow-band MEMS filters operating at frequencies above 3 GHz The device dimensions have been opportunely scaled both in the lateral and vertical dimensions to excite a contour-extensional mode of vibration in nanofeatures of an ultra-thin (250 nm) AlN film In this first demonstration, 2-port resonators vibrating up to 45 GHz have been fabricated on the same die and attained electromechanical coupling, kt 2, in excess of 15% These devices are employed to synthesize the highest frequency MEMS filter (37 GHz) based on AlN contour-mode resonator technology ever reported

/pdf/super-high-frequency-two-port-aln-contour-mode-resonators-4zav670h8q.pdf

Super-high-frequency two-port AlN contour-mode resonators for RF applications

A SAW filter comprising a piezoelectric substrate and at least two filter tracks formed on the substrate, each having at least two IDT electrodes for input and output. The two filter tracks have substantially the same phase within a pass band, while it is substantially inverse-phased outside the pass band. For realizing the above-described conditions, input IDT electrode of one filter track is connected in parallel with input IDT electrode of the other filter track, while output IDT electrode of one filter track is connected in parallel with output IDT electrode of the other filter track. Furthermore, frequency values of said two filter tracks substantially coincide at a point 3dB lower from the peak transfer function value. Thus the above-configured SAW filter of the present invention is smaller in the overall size and offers a broad pass band and a steep attenuation characteristic.

Surface-acoustic-wave filter

The bulk acoustic wave filter composed of piezoelectric thin film resonators has many features superior to those of other small filters such as a surface acoustic wave (SAW) filter and a ceramic filter. As it has no fine structure in its electrode design, it has a high Q factor that leads to low-loss and sharp-cut off characteristics and a high power durability particularly in the high-frequency range. Furthermore, it has the potentiality of integrated devices on a Si substrate. In this paper, we review the recent developments of piezoelectric thin film resonator filters in the world, including our development for mobile communication applications. After describing the feature and history of the piezoelectric thin film resonator filters, our technologies are introduced in focusing on the resonator structures, the piezoelectric thin film and electrode film materials, the cavity structures, the filter structure and its design rules and characteristics, comparing with SAW filters. The competition and coexistence between the piezoelectric thin film resonator filters and the SAW filters are also described. In this paper, we describe the development of a piezoelectric thin film resonator from the standpoint of researchers who have a long experience of SAW filter development.

https://iopscience.iop.org/article/10.1143/JJAP.44.2883/pdf

Development of Piezoelectric Thin Film Resonator and Its Impact on Future Wireless Communication Systems

We have developed an X-band filter utilizing air-gap-type film bulk acoustic resonators (FBARs). The air-gap structure is simple and cost-effective. Results from both simulations and experiments demonstrate that a dome-shaped air gap was formed between the substrate surface and the bottom electrode and that an air-gap-type FBAR structure was possible. The air gap can be formed on the flat substrate using stress control of piezoelectric and metal films without using a thick sacrificial layer. As a result, the fabricated X-band FBAR operated successfully with a keff2 of 6.30%, a resonance Q of 246, and an antiresonance Q of 462. The fabricated filter had a center frequency of 9.07 GHz, a fractional bandwidth of 3.1% and a minimum insertion loss of 1.7 dB.

https://iopscience.iop.org/article/10.1143/JJAP.47.4007/pdf

Development of an X-Band Filter Using Air-Gap-Type Film Bulk Acoustic Resonators

The first 24 and 30 GHz band thin-film bulk acoustic resonator (FBAR) filters are reported in this paper. The filters were configured with air-gap-type FBARs on a flat silicon substrate. They were designed using a Butterworth–Van-Dyke (BVD) equivalent circuit considering the linear relationship between resonant frequency, capacitance ratio, and loss in the FBAR. The measured characteristics corresponded with those of the simulation using the equivalent circuit in the pass-band. The center frequency, fractional bandwidth, minimum insertion loss, and out-of-band suppression were 23.8 GHz, 3.4%, -3.8 dB, and -13 dB in the 24 GHz band filter, and 29.2 GHz, 3.4%, -3.8 dB, and -11 dB in the 30 GHz band filter, respectively.

https://iopscience.iop.org/article/10.1143/JJAP.49.07HD13/pdf

Super-High-Frequency Band Filters Configured with Air-Gap-Type Thin-Film Bulk Acoustic Resonators

In a duplexer, phase matching circuit patterns corresponding to filter chips are formed on a surface layer of a multi-layer ceramic package provided with filter chips having different central frequencies. An end of each of the phase matching circuit patterns is connected to a common terminal pattern.

Yoshio Satoh

Papers

Surface-acoustic-wave filter

Development of Piezoelectric Thin Film Resonator and Its Impact on Future Wireless Communication Systems

Development of an X-Band Filter Using Air-Gap-Type Film Bulk Acoustic Resonators

Super-High-Frequency Band Filters Configured with Air-Gap-Type Thin-Film Bulk Acoustic Resonators

Surface acoustic wave filter duplexer comprising a multi-layer package and phase matching patterns