Air-Gap FBAR Structure for Bias-Tunable Resonance Frequency
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Solution Overview
Problem
Conventional film bulk acoustic resonators are not frequency-tunable, limiting their ability to adapt to external variables and requiring multiple devices to achieve frequency modification, which hinders miniaturization and efficiency in high-frequency communication applications.
Innovation Solution
A frequency-tunable film bulk acoustic resonator with a multilayer structure of electrodes and piezoelectric layers, featuring an air-gap design that allows resonance frequency tuning via an external bias voltage, enabling dynamic frequency adjustment and miniaturization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional film bulk acoustic resonators are used with fixed frequency, then the device structure is simple, but the frequency cannot be adjusted and multiple devices are needed for frequency modification
Solution Approach 1:
The patent introduces a bias electrode and bias voltage to dynamically adjust the resonance frequency of the bulk acoustic resonator. The bias voltage applied to the piezoelectric film changes its effective thickness and acoustic properties, enabling continuous frequency tuning from fundamental mode to higher overtone modes without changing the physical structure. This transforms a static frequency device into a dynamically adjustable one.
Solution Approach 2:
The patent changes the electrical parameter (bias voltage) to control the acoustic resonance frequency. By applying different voltages to the piezoelectric film, the effective acoustic thickness and wave velocity are modified, thereby tuning the resonance frequency. This allows a single device to achieve multiple frequency points that would otherwise require multiple fixed-frequency resonators.
2Adaptability or versatility
If multiple bulk acoustic resonators are used to achieve frequency modification, then frequency selection is possible, but the device occupies more space and miniaturization is hindered
Solution Approach 1:
The patent makes a single bulk acoustic resonator perform multiple functions by enabling it to operate at different resonance modes (fundamental and overtone modes) through bias voltage control. One resonator structure replaces what would traditionally require multiple resonators for different frequency bands, achieving multi-functionality and frequency selection in a compact form factor.
Solution Approach 2:
The patent combines multiple frequency selection capabilities into a single resonator device. By integrating the bias electrode structure and control mechanism, the device merges the functions of multiple fixed-frequency resonators into one tunable resonator, reducing the overall device area and component count.
3Adaptability or versatility
If mass loading layer is added to tune resonance frequency, then frequency adjustment is possible, but the tuning is disposable and cannot be adjusted after device processing
Solution Approach 1:
The patent implements a controllable feedback mechanism where the bias voltage can be adjusted to tune the resonance frequency after device fabrication. The electrical control system allows real-time frequency adjustment based on operational requirements, unlike disposable mechanical tuning methods. This enables post-processing frequency optimization and adaptation.
Solution Approach 2:
The patent replaces mechanical tuning methods (such as adjusting mass loading layer thickness or area) with an electrical control system. Instead of physically modifying the resonator structure, the frequency is tuned by applying electrical bias voltage to the piezoelectric film, which changes its acoustic properties. This substitution enables non-invasive, reversible, and programmable frequency control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The air-gap type film bulk acoustic resonator can change its resonance frequency in response to bias voltage, achieving the functionality of multiple resonators in a single device, thereby promoting miniaturization and reducing production costs while enhancing communication device performance.
Implementation Method 1
The principle of the film bulk acoustic resonator is to use a piezoelectric effect, which is that when the dielectric medium is deformed by external force along a certain direction, the polarization phenomenon is generated in the dielectric medium, and simultaneously, charges with opposite positive and negative polarities are generated on two opposite surfaces of the dielectric medium.
Implementation Method 2
When the bulk acoustic wave is transmitted to an electrode interface, the acoustic wave is reflected back through an acoustic reflection layer outside the electrode, so that the bulk acoustic wave is limited between the two electrodes to generate oscillation. Since the acoustic impedance of air is approximately zero, there is a very strong ability to reflect acoustic waves at a solid/gas interface composed of the electrode material and air.
Implementation Method 3
When a frequency of the acoustic waves and a thickness of the piezoelectric film satisfy a certain mathematical relationship, a resonance phenomenon occurs, and the principle of the bulk acoustic resonator is that the resonance phenomenon under a specific frequency is used to make frequency selection.
Data Source
AI summary
A frequency-tunable film bulk acoustic resonator and a preparation method therefor are provided. The resonator includes a substrate, an air gap, a sandwiched structure formed by electrodes and piezoelectric layers, and an electrode lead-out layer, wherein the substrate is connected to the sandwiched structure formed by the electrodes and the piezoelectric layers, and a connection face of the substrate and the sandwiched structure formed by the electrodes and the piezoelectric layers is recessed towards inside of the substrate to form the air gap; and the electrode lead-out layer is connected to the sandwiched structure formed by the electrodes and the piezoelectric layers. The sandwiched structure formed by the electrodes and the piezoelectric layers includes a bottom electrode, piezoelectric layers, intermediate electrodes, and a top electrode, wherein the electrodes and the piezoelectric layers are alternately arranged to form the sandwiched structure.