Elastic Wave Resonator Layout for Stable Passband Edge Steepness
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Solution Overview
Problem
Elastic wave apparatuses with existing configurations face challenges in achieving sufficient steepness and attenuation characteristics near the edge of the passband due to variations in capacitance caused by insulating film thickness, leading to degraded filter characteristics.
Innovation Solution
The elastic wave apparatus includes a piezoelectric substrate with a first dielectric film, an IDT electrode, and a capacitor with comb-shaped electrodes directly on the substrate, where the IDT electrode material density is higher than the dielectric film material density, and the elastic wave propagation directions in the resonator and capacitor are orthogonal, reducing the influence of the capacitor's waves on the resonator, thereby improving steepness and out-of-band attenuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an insulating film is provided between the IDT electrode and piezoelectric substrate to adjust electromechanical coupling coefficient and passband width, then the passband width can be adjusted, but the capacitance of the capacitive electrode changes in accordance with the thickness of the insulating film, leading to large variations in filter characteristics
Solution Approach 1:
The patent separates the functions of passband width adjustment and capacitance control into independent elements. The insulating film thickness controls only the electromechanical coupling coefficient and passband width, while the capacitance is controlled by the number of electrode pairs in the capacitive electrode, eliminating the coupling between these parameters and stabilizing filter characteristics
Solution Approach 2:
The patent applies different structural configurations to different parts of the device: the IDT electrode uses an insulating film for coupling coefficient control, while the capacitive electrode uses a variable number of electrode pairs for capacitance control. This localized differentiation allows independent optimization of each function without mutual interference
2Reliability
If the capacitance of the capacitive electrode is adjusted by changing the insulating film thickness, then the electromechanical coupling coefficient can be optimized, but sufficient steepness and attenuation characteristics are not obtained in some cases
Solution Approach 1:
The patent changes the control parameter for capacitance from insulating film thickness to the number of electrode pairs in the capacitive electrode. This parameter change allows independent adjustment of capacitance without affecting the electromechanical coupling coefficient, enabling simultaneous achievement of optimized coupling and sufficient steepness/attenuation characteristics
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 effectively enhances steepness near the passband edge and out-of-band attenuation, stabilizing filter characteristics and improving isolation, as demonstrated by comparative examples showing reduced variations and improved performance.
Implementation Method 1
an IDT electrode provided on the first dielectric film
Implementation Method 2
An elastic wave resonator including the IDT electrode is provided
Implementation Method 3
a capacitor that includes a pair of comb-shaped electrodes provided directly on the piezoelectric substrate and is electrically connected to the IDT electrode
Implementation Method 4
an elastic wave propagation direction in the elastic wave resonator and an elastic wave propagation direction in the capacitor cross each other
Data Source
AI summary
An elastic wave apparatus includes a piezoelectric substrate, a first dielectric film provided on the piezoelectric substrate, an IDT electrode provided on the first dielectric film, and a capacitor that includes a pair of comb-shaped electrodes provided directly on the piezoelectric substrate and is electrically connected to the IDT electrode. An elastic wave resonator including the IDT electrode is provided.