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

Abstract

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.

Deposition of ultrathin AlN films for high frequency electroacoustic devices

“…As the resonance frequency of the resonator is determined by the thickness of the AlN layer, there is essential interest of using ultrathin 100-200 nm films to extend the current FBAR technology from 1-2 to 5-10 GHz range. 4 AlN-based solidly mounted BAW resonators for 10 GHz applications require AlN films having thickness as low as approximately 160 nm. 5 Thinner AlN layers are also of strong interest for temperature compensated Lamb wave resonators 6 as it has been shown that for thin AlN layers ͑100-200 nm͒ the temperature coefficient of frequency can be compensated over a very wide frequency range enabling temperature compensation of resonators operating at multiple frequencies.…”

Ozone senosr using ZnO based film bulk acoustic resonator

“…Inserting equation (3) and (8) into (7) yields the following: (9) Reaction (6) is the dominant process during ozone sensing, thus (10) Therefore, the calculated power law exponent n, defined as d(logΔf)/d(logPO 3 ) is (11) where m is sufficiently large under usual conditions [17]. Thus n is around -1, which means the relationship between resonant frequency and ozone concentration is hyperbolic, which is in agreement with the experimental results (Fig.…”

“…A resonance condition occurs if the thickness of piezoelectric thin film is equal to an integer multiple of a half of the acoustic wavelength. In recent years, FBARs have been developed to be radio frequency electrical filters [11] as well as high sensitivity mass, ultraviolet and humidity sensors [12][13][14][15].…”

Experiment and theoretical analysis of relative humidity sensor based on film bulk acoustic-wave resonator

“…FBAR has been well developed both as filters [4] and as high sensitivity mass sensors [5] in recent years. The schematic structure of the FBAR RH sensor is shown in Fig.…”