BAW Resonator Structure for Higher Q and Coupling
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Solution Overview
Problem
BAW resonators face challenges with decreased Q value and electromechanical coupling factor due to acoustic impedance mismatch and crystal grain orientation changes, which affect performance in high-frequency wireless communication.
Innovation Solution
The resonance region is suspended relative to a cavity in an intermediate layer or substrate, and the piezoelectric layer is formed on a flat surface to maintain crystal grain orientation, with electrode layers having adjustable positions and widths to enhance impedance difference and frequency tuning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the resonance region touches the substrate, then the manufacturing process is simpler, but the acoustic impedance mismatch causes energy spread and decreased Q value
Solution Approach 1:
The resonance region is extracted from direct contact with the substrate by suspending it above the substrate surface. This separation prevents acoustic energy from spreading into the substrate, thereby maintaining high Q value while keeping the manufacturing process relatively simple through selective suspension techniques.
Solution Approach 2:
A support structure acts as an intermediary between the resonance region and the substrate. This intermediary element provides mechanical support while acoustically isolating the resonance region from the substrate, preventing energy loss and maintaining high Q value.
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:
A flat support structure is prepared in advance before forming the piezoelectric layer. This preliminary flat surface ensures that when the piezoelectric layer is deposited, the crystal grains maintain proper orientation throughout the layer, achieving high electromechanical coupling factor while enabling manufacturability.
Solution Approach 2:
The support structure provides a uniform flat surface that ensures homogeneous crystal grain orientation across the entire piezoelectric layer. This homogeneity in surface flatness translates to consistent crystal orientation and high electromechanical coupling factor throughout the device.
3Ease of manufacture
If acoustic impedance of substrate is close to piezoelectric layer, then the manufacturing is easier, but energy spreads to non-resonance region causing decreased Q value
Solution Approach 1:
The resonance region is extracted from direct contact with the substrate, physically separating the acoustic pathways. This extraction prevents acoustic energy from coupling into the substrate regardless of impedance matching, thereby eliminating energy loss to non-resonance regions while maintaining manufacturing feasibility.
Solution Approach 2:
The support structure serves as an acoustic intermediary with impedance characteristics that prevent energy transfer from the piezoelectric layer to the substrate. This intermediary blocks the acoustic energy pathway while allowing mechanical support, solving the impedance mismatch problem.
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 performance in high-frequency applications by preventing energy spread and reducing electrical losses.
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 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 cavity disposed at a first side of the first layer; a first electrode layer disposed in the 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 the first electrode layer includes at least two first electrode bars or the second electrode layer includes at least two second electrode bars. The present disclosure can increase the difference between acoustic impedance of a resonance region and a non-resonance region, thereby increasing Q value of the resonance device.