Bulk Acoustic Resonator Frame Structure for Transverse Wave Suppression
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Solution Overview
Problem
Conventional bulk acoustic resonators face challenges in minimizing noise and reducing the impact of transverse modes on the Q factor, which affects the performance of radio frequency devices.
Innovation Solution
A bulk acoustic resonator design that includes a substrate, stacked electrodes and a piezoelectric layer, an acoustic reflection structure, and a frame structure with specific passivation and material layers to enhance acoustic impedance and suppress transverse waves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a frame structure is arranged at the edge of the effective resonance region to suppress transverse waves, then the Q factor is improved, but noise is introduced and the longitudinal mode is compromised
Solution Approach 1:
A passivation layer is introduced as an intermediary between the frame structure and the top electrode. This passivation layer acts as a mediator that prevents direct electrical connection while maintaining the mechanical constraint function of the frame structure, thereby suppressing transverse waves without introducing noise to the longitudinal mode
Solution Approach 2:
The frame structure is segmented into multiple parts with the passivation layer separating the electrical function from the mechanical constraint function. This segmentation allows the frame to suppress transverse waves mechanically while the passivation layer prevents electrical noise from affecting the longitudinal mode
2Speed
If the resonator structure is miniaturized from block to thin-film to optimize high frequency performance, then frequency performance is improved, but acoustic loss increases
Solution Approach 1:
The acoustic impedance of the frame structure is optimized by adjusting material composition and geometric parameters. The frame structure is designed with specific acoustic impedance characteristics that match the thin-film resonator, creating effective acoustic confinement that reduces energy loss while maintaining high frequency performance
Solution Approach 2:
The resonator employs composite material structures including multiple layers with different acoustic properties. The frame structure uses composite materials that provide both mechanical strength for transverse wave suppression and appropriate acoustic impedance for minimizing energy loss in the thin-film configuration
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 proposed design effectively suppresses parasitic transverse waves, reduces acoustic loss, and improves the Q factor by optimizing the acoustic impedance and structural stability of the resonator.
Implementation Method 1
bulk acoustic waves (BAW) propagating in a thickness direction of the piezoelectric layer are excited in the piezoelectric layer due to the reverse piezoelectric effect of the piezoelectric layer
Implementation Method 2
a cavity is arranged between a substrate and the bottom electrode, so that the longitudinal waves are reflected back to a resonance region at an interface between the bottom electrode and the air to eliminate loss of acoustic energy
Implementation Method 3
an acoustic impedance of an effective resonance region corresponding to the frame structure is greater than an acoustic impedance of an effective resonance region that is outside the frame structure
Data Source
AI summary
A bulk acoustic resonator, a method for manufacturing the bulk acoustic resonator, a filter, and an electronic device are provided. A frame structure is arranged at an edge of an effective resonance region configured in the bulk acoustic resonator. An acoustic impedance of the effective resonance region corresponding to the frame structure is greater than an acoustic impedance of the effective resonance region that is outside the frame structure, which effectively suppresses parasitic transverse waves. In addition, as the frame structure includes two passivation layers, it can reduce clutter caused by additional resonance while suppressing the transverse waves. Furthermore, with the structure of the two passivation layers, the stress can be reduced and the structure stability and a Q factor can be improved.