FBAR Trench Layout for Blocking Transverse Waves
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Solution Overview
Problem
Current film bulk acoustic resonators face challenges in improving the quality factor and performance due to transverse wave propagation in inactive resonance regions, which affects the overall efficiency of RF filters in 5G communication systems.
Innovation Solution
The introduction of a film bulk acoustic resonator design featuring a piezoelectric stacked layer with first and second trenches that block transverse waves, forming an active resonance region and improving acoustic wave loss, while avoiding parasitic resonance by patterning the electrode regions to prevent overlap above the cavity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If transverse waves are allowed to propagate in inactive resonance regions, then the device structure is simpler, but the quality factor decreases due to acoustic wave loss
Solution Approach 1:
The resonator structure is segmented into active resonance region and inactive resonance region by introducing trenches. The trenches divide the piezoelectric stacked layer, confining acoustic waves to the active region and preventing transverse wave propagation into inactive regions, thereby reducing acoustic wave loss and improving quality factor.
Solution Approach 2:
The harmful transverse wave propagation path is extracted and removed by creating trenches that block the wave paths. The trenches physically remove the continuous piezoelectric material that would otherwise allow transverse waves to propagate through inactive resonance regions, eliminating the source of acoustic wave loss.
2Reliability
If electrode regions are overlapped above the cavity, then the manufacturing process is simpler, but parasitic resonance occurs which degrades performance
Solution Approach 1:
The electrode regions are patterned with different local geometries to prevent overlap above the cavity. The first electrode and second electrode are designed with complementary shapes (e.g., interdigitated or offset circular patterns) that maintain electrical functionality while avoiding spatial overlap in the resonance region, thereby eliminating parasitic resonance.
3Reliability
If trenches are introduced to block transverse waves, then acoustic wave loss is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The trench positions are predetermined and pre-planned in the design stage based on the active resonance region boundaries. By carefully selecting trench locations at the interfaces between active and inactive regions, the design anticipates and prevents manufacturing variability from compromising the wave-blocking function, as long as trenches are positioned within specified tolerances.
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
This design enhances the quality factor and performance of the film bulk acoustic resonator by effectively blocking transverse waves and reducing parasitic resonance, thereby improving the efficiency of RF filters for 5G communication systems.
Implementation Method 1
The piezoelectric film layer is used to generate vibration under an alternating electric field; the vibration excites the bulk acoustic wave propagating along the thickness direction of the piezoelectric film layer
Implementation Method 2
at least two trenches, arranged at a junction of the active resonance region and the inactive resonance region to define a range of the active resonance region
Implementation Method 3
such acoustic wave may be reflected back from the interface between the air and each of the two film electrodes, and then be reflected back and forth inside the film layer to form an oscillation. When the acoustic wave propagates in the piezoelectric film layer having exactly an odd multiple of the half wavelength, a standing wave oscillation is formed
Data Source
AI summary
The present disclosure provides a film bulk acoustic resonator and its fabrication method, a filter, and a radio frequency communication system. The film bulk acoustic resonator includes a first substrate and a support layer disposed on the first substrate, where a cavity is formed in the support layer; a piezoelectric stacked layer covering the cavity, where the piezoelectric stacked layer includes an active resonance region and an inactive resonance region surrounding the active resonance region; and at least two trenches, arranged at a junction of the active resonance region and the inactive resonance region to define a range of the active resonance region. The at least two trenches include a first trench and a second trench; the second trench passes through the second electrode layer and the piezoelectric layer; and the first trench passes the first electrode and the piezoelectric layer and is connected to the cavity.