BAW Resonator Cavity Structure for Higher Q and Coupling
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Solution Overview
Problem
BAW resonators face challenges with reduced Q value and electromechanical coupling factor due to acoustic impedance mismatch and crystal grain orientation changes, which are exacerbated by the need for higher frequency performance in wireless communication technologies like 5G.
Innovation Solution
The resonance region of the BAW device is suspended relative to a cavity in an intermediate layer or substrate, with a flat piezoelectric layer and carefully positioned electrode layers to enhance acoustic impedance difference and prevent crystal grain orientation changes, using materials like polymers and insulating dielectrics to support the structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the resonance region touches the substrate, then the manufacturing process is simplified, but the acoustic impedance mismatch causes energy loss and reduces Q value
Solution Approach 1:
The patent divides the support structure into multiple segments: the substrate, an intermediate layer, and a cavity structure. This segmentation creates acoustic impedance transitions that prevent energy loss while maintaining manufacturing feasibility through standardized layer deposition processes.
Solution Approach 2:
The patent introduces an intermediate layer as a mediator between the resonance region and the substrate. This intermediate layer has acoustic impedance properties that bridge the gap between the high-impedance piezoelectric layer and the low-impedance substrate, preventing acoustic energy leakage while maintaining a practical manufacturing process.
2Ease of manufacture
If the piezoelectric layer is formed on a non-flat surface, then the device can be manufactured, but crystal grain orientation changes reduce the electromechanical coupling factor
Solution Approach 1:
The patent applies preliminary action by creating a flat surface on the intermediate layer before depositing the piezoelectric layer. This pre-preparation ensures that the piezoelectric layer forms with proper crystal grain orientation and uniform thickness, maintaining high electromechanical coupling factor while enabling manufacturing on complex underlying structures.
Solution Approach 2:
The patent applies local quality by providing a flat surface specifically at the piezoelectric layer interface while allowing the underlying intermediate layer to have the cavity structure. This localized flatness ensures proper piezoelectric properties where needed without sacrificing the acoustic isolation benefits of the cavity structure.
3Loss of energy
If the resonance region is suspended over the cavity, then the Q value increases due to reduced acoustic energy loss, but the device complexity increases
Solution Approach 1:
The patent uses thin film technology to create the intermediate layer and cavity structure, which can be deposited using standard semiconductor manufacturing processes. This approach achieves the suspended resonance region configuration with controlled acoustic impedance without requiring complex mechanical structures, balancing Q value improvement with manufacturing simplicity.
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 increases the Q value and electromechanical coupling factor, improving the performance of BAW filters by reducing energy loss and maintaining crystal grain orientation, thus enhancing filtering capabilities for higher frequency applications.
Implementation Method 1
an acoustic wave is generated by the piezoelectric layer under the alternating voltages with different polarities
Implementation Method 2
the acoustic wave within the resonator propagates in a direction perpendicular to the piezoelectric layer
Implementation Method 3
the acoustic impedance of air is very different from that of metal electrodes, acoustic waves can be totally reflected on an upper surface of an upper metal electrode and a lower surface of a lower metal electrode to form a standing wave
Implementation Method 4
In order to form resonance, the acoustic wave requires total reflection on an upper surface of an upper metal electrode and on a lower surface of a lower metal electrode to form a standing acoustic wave
Data Source
AI summary
The present disclosure provides a bulk acoustic wave resonance device, a bulk acoustic wave filter device and a radio frequency front end device. The bulk acoustic wave resonance device includes: a first layer including a first cavity disposed at a first side of the first layer; a first electrode layer, and a first end of the first electrode layer is in contact with the first layer, and a second end of the first electrode layer is disposed within the first cavity; a second layer disposed at the first side and disposed on the first electrode layer, and the second layer is a flat layer and covers the first cavity; and a second electrode layer disposed at the first side and disposed on the second layer, and a first portion of the first electrode layer overlapping with the second electrode layer is disposed within the first cavity.