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This paper describes a drastic enhancement of the effective coupling factor by mass loading in layered surface acoustic wave (SAW) device structures such as the ScAlN film/Si substrate structure. This phenomenon occurs when the piezoelectric layer exhibits a high acoustic wave velocity. The mass loading decreases the SAW velocity and causes SAW energy confinement close to the top surface where an interdigital transducer is placed. It is shown that this phenomenon is obvious even when an amorphous SiO2 film is deposited on the top surface for temperature compensation. This enhancement was also found in various combinations of electrode, piezoelectric layer, and/or substrate materials. The existence of this phenomenon was verified experimentally using the ScAlN film/Si substrate structure.

We report on a novel MEMS (microelectromechanical system) based on a Fabry–Perot spectrometer with an ultrawide wavelength range (3.2 to 8.4 µm) compared to the previously reported ones (typically 2.8 to 5.8 µm). The wavelength range of a Fabry–Perot spectrometer is known to be increased by increasing the ratio of the refractive indexes of the multilayer mirrors. Thus, a novel mirror structure was proposed, replacing a low‐refractive‐index layer of SiO2 (nL = 1.44) by air (nL = 1) for a wider wavelength range. The proposed device was fabricated by HF sacrificial layer etching of SiO2 between four ultrathin polysilicon films (ca. 320 nm). The following two ideas were adopted to fabricate this delicate structure properly. (1) Electrostatic force was generated only in the outer region surrounding the air mirror so as not to deform the mirror. (2) A supercritical drying process was employed after the sacrificial etching to prevent possible sticking issues. © 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 96(5): 50–57, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10433

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