Convex BAW Resonator Surfaces for Acoustic Energy Retention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional bulk acoustic wave (BAW) resonators have a low quality factor (Q) due to inefficient retention of acoustic energy, which limits their performance in modern wireless communication devices.
Innovation Solution
The formation of a piezoelectric layer with a convex surface in BAW resonators, using processes compatible with CMOS manufacturing, such as gray-scale lithography, to enhance acoustic energy retention and reduce spurious modes, thereby increasing the Q factor and overall system performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional planar piezoelectric layer is used in BAW resonators, then the device structure is simple and easy to manufacture, but the acoustic energy retention is inefficient resulting in low quality factor
Solution Approach 1:
The piezoelectric layer is formed with a convex surface instead of a conventional planar surface. This curvature modifies the acoustic wave propagation paths and confines the acoustic energy more effectively within the resonator cavity, reducing energy loss and increasing the quality factor by a factor of two or more.
Solution Approach 2:
The convex surface creates localized regions with different acoustic properties. The curvature concentrates acoustic energy in specific areas of the piezoelectric layer, enhancing the interaction between the acoustic waves and the piezoelectric material, thereby improving energy retention without requiring complete structural redesign.
2Reliability
If a convex surface is formed on the piezoelectric layer to improve acoustic energy retention, then the quality factor increases, but the manufacturing process complexity increases
Solution Approach 1:
The mechanical formation of convex surfaces through traditional MEMS processes is replaced by depositing the piezoelectric layer directly in a convex shape using atomic layer deposition (ALD) or chemical vapor deposition (CVD). This substitution eliminates complex mechanical machining or etching steps while achieving the desired convex geometry, thereby maintaining high quality factor without proportionally increasing manufacturing complexity.
Solution Approach 2:
The manufacturing approach changes from post-deposition shaping to controlled deposition parameters. By adjusting deposition conditions (such as precursor flow rates, temperature gradients, or mask patterns during ALD/CVD), the convex surface is formed directly during the deposition process itself, simplifying the overall manufacturing workflow while achieving the required geometric precision for high Q-factor performance.
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 convex surface design increases the Q factor of BAW resonators by a factor of two or more, improving the accuracy and noise level of clock signals in wireless communication systems.
Implementation Method 1
electrodes (e.g., contacts, metal patches, etc.) on top and bottom surfaces of a piezoelectric layer provide voltage bias to excite acoustic waves through piezoelectric (and reverse piezoelectric) effect
Implementation Method 2
The bulk acoustic waves of specific frequencies are generated within the resonant cavity between the top and bottom surfaces of the piezoelectric layer to form a resonance response
Data Source
AI summary
In one example, a method of forming a bulk acoustic wave (BAW) resonator comprises: forming an electrode on at least one of a semiconductor substrate, a sacrificial layer, or an acoustic reflector; and forming a piezoelectric layer on the electrode, the piezoelectric layer having a convex surface.