This paper reports theoretical analysis and experimental results on a new class of rectangular plate and ring-shaped contour-mode piezoelectric aluminum nitride radio-frequency microelectromechanical systems resonators that span a frequency range from 19 to 656 MHz showing high-quality factors in air (Qmax=4300 at 229.9 MHz), low motional resistance (ranging from 50 to 700 Omega), and center frequencies that are lithographically defined. These resonators achieve the lowest value of motional resistance ever reported for contour-mode resonators and combine it with high Q factors, therefore enabling the fabrication of arrays of high-performance microresonators with different frequencies on a single chip. Uncompensated temperature coefficients of frequency of approximately -25 ppm/degC were also recorded for these resonators. Initial discussions on mass loading mechanisms induced by metal electrodes and energy loss phenomenon are provided

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Piezoelectric Aluminum Nitride Vibrating Contour-Mode MEMS Resonators

Since FBAR (free-standing bulk acoustic resonator) and solidly mounted resonator SMR-BAW devices came onto the scene as serious competition to the entrenched SAW technology (for cell phone applications), there has been much speculation and discussion as to which of these two "disruptive" technologies is the superior one. The one fundamental difference between SMR-BAWs and FBARs, is the means by which the acoustic energy is trapped. For FBAR the air/crystal interface on both faces of the resonator ensures that the main mode of interest (the thickness extensional mode, TE1) is appropriately trapped In the SMR-BAW, Bragg reflectors underneath the resonator, effectively trap this mode. This addition of a Bragg reflector will degrade the effective coupling coefficient as well as creating additional Q loss mechanisms. The science of improving Q must focus on the edges of the resonator for FBAR, while for SMR devices, both the edges and the vertical design of the Bragg reflector must be optimized. That said, compared to conventional SAW technology, both BAW and FBAR provide temperature stability, power handling capability, good ESD (electro-static discharge), and -most important-high Q's. One of the key drivers for the success (in terms of high Q and coupling coefficients) of both BAW and FBAR was the exploitation of AlN as the piezoelectric material and high acoustic impedance, electrode materials such as molybdenum, tungsten or ruthenium. These are the technology differentiators that create the inherent superiority of BAW/FBAR over both the conventional SAW technology and the newer and enhanced flavors of SAW. The need for large coupling coefficients and high Q's becomes an important value proposition as one considers the proliferation of new bands and services.

11E-2 Review and Comparison of Bulk Acoustic Wave FBAR, SMR Technology

In this article, we will provide an overview of BAW filter technology by discussing comparison between BAW and SAW RF filter technologies, working principles of BAW resonator and filter, BAW resonator key performance parameters, comparison between free-standing bulk acoustic resonator (FBAR) and solidly mounted resonator (SMR) technologies, status of BAW resonator design and models, BAW filter manufacturing challenges, and future BAW technology improvement directions.

Bulk acoustic wave RF technology

An acoustic resonator comprises a first electrode a second electrode and a piezoelectric layer disposed between the first and second electrodes. The acoustic resonator further comprises a reflective element disposed beneath the first electrode, the second electrode and the piezoelectric layer. An overlap of the reflective element, the first electrode, the second electrode and the piezoelectric layer comprises an active area of the acoustic resonator. The acoustic resonator also comprises a bridge adjacent to a termination of the active area of the acoustic resonator.

Acoustic resonator structure comprising a bridge

An acoustic resonator comprises a first electrode and second electrode comprising a plurality of sides. At least one of the sides of the second electrode comprises a cantilevered portion. A piezoelectric layer is disposed between the first and second electrodes. An electrical filter comprises an acoustic resonator.

Acoustic resonator structure having an electrode with a cantilevered portion

A bulk acoustic wave (BAW) resonator structure includes a first electrode disposed over a substrate, a piezoelectric layer disposed over the first electrode and a second electrode disposed over the first piezoelectric layer. The piezoelectric layer is formed of a piezoelectric material doped with multiple rare earth elements for improving piezoelectric properties of the piezoelectric layer.

Bulk acoustic wave resonator having piezoelectric layer with multiple dopants

A bulk acoustic wave (BAW) resonator structure comprises a first electrode disposed over a substrate, a piezoelectric layer disposed over the first electrode, a second electrode disposed over the first piezoelectric layer, and a guard ring structure formed around a perimeter of an active region corresponding to an overlap of the first electrode, the first piezoelectric layer, and the second electrode.

Acoustic resonator having guard ring

A film bulk acoustic resonator (FBAR) structure includes a first electrode disposed over a substrate, a piezoelectric layer disposed over the first electrode, and a second electrode disposed over the first piezoelectric layer. A bridge is disposed between the first electrode and the piezoelectric layer.

Chris Feng

Papers

Acoustic resonator structure comprising a bridge

Acoustic resonator structure having an electrode with a cantilevered portion

Bulk acoustic wave resonator having piezoelectric layer with multiple dopants

Acoustic resonator having guard ring

Film bulk acoustic resonator comprising a bridge