Bulk Acoustic Resonator Layers to Suppress Stress-Induced Abnormal Growth
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Solution Overview
Problem
Film bulk acoustic resonators face challenges in achieving high effective electromechanical coupling coefficients while minimizing abnormal growths, which affect the quality factor and frequency characteristics due to residual stress issues in piezoelectric layers.
Innovation Solution
A bulk acoustic resonator configuration with a substrate, a first electrode under compressive stress, a piezoelectric body having multiple layers under different applied stresses, including a compressive piezoelectric layer with a higher c-axis to a-axis lattice constant ratio, and a second electrode, where the compressive piezoelectric layer is lattice matched to the first electrode, reducing abnormal growths and enhancing crystal orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the effective electromechanical coupling coefficient is increased to improve frequency characteristics, then the band width is widened, but abnormal growths occur due to residual stress issues in piezoelectric layers
Solution Approach 1:
The patent applies parameter changes by forming at least one piezoelectric layer under compressive stress to alter the stress state of the piezoelectric body. This stress parameter modification prevents abnormal growths while maintaining high effective electromechanical coupling coefficient, thus resolving the contradiction between improving frequency characteristics and preventing harmful abnormal growths
Solution Approach 2:
The patent uses composite material structure by creating a piezoelectric body with multiple piezoelectric layers having different stress states (at least one under compressive stress). This composite layer structure allows the system to achieve both high coupling coefficient for improved frequency characteristics and stress distribution to prevent abnormal growths
2Reliability
If piezoelectric layers are formed to achieve high coupling coefficient, then frequency characteristics improve, but residual stress causes degradation of quality factor
Solution Approach 1:
The patent applies preliminary anti-action by forming at least one piezoelectric layer under compressive stress before the piezoelectric body is fully assembled. This pre-applied compressive stress counteracts the tensile residual stress that would otherwise develop, preventing quality factor degradation while maintaining high coupling coefficient
Solution Approach 2:
The patent changes the stress parameter of the piezoelectric body by introducing compressive stress during the formation of at least one piezoelectric layer. This parameter modification directly addresses the residual stress issue that degrades quality factor, allowing the system to maintain both high coupling coefficient and high quality factor
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 configuration increases the effective electromechanical coupling coefficient, improves frequency characteristics, and minimizes abnormal growths, leading to enhanced performance in film bulk acoustic resonators.
Implementation Method 1
When electrical energy is applied to the first and second electrodes to induce an electric field in the piezoelectric layer, the electric field may generate a piezoelectric phenomenon in the piezoelectric layer to allow the resonant part to vibrate in a predetermined direction. Resultantly, bulk acoustic waves may be generated in the same direction as the direction in which the resonant part vibrates, thereby generating resonance.
Data Source
AI summary
A bulk acoustic resonator includes a substrate, a first electrode disposed above the substrate, a piezoelectric body disposed on the first electrode and including a plurality of piezoelectric layers each including aluminum nitride with a doping material, and a second electrode disposed on the piezoelectric body, where at least one of the piezoelectric layers is a compressive piezoelectric layer formed under compressive stress.