Modulated-Pitch IDT Capacitor for Low-Spurious Acoustic Filters
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing acoustic wave filters face challenges in meeting filter specifications for steep skirts and low insertion loss near band edges, particularly in achieving desired electrical characteristics while minimizing resonance and loss.
Innovation Solution
The integration of an interdigital transducer (IDT) capacitor with modulated pitch and high viscosity material, which includes capacitor fingers with varying pitches and no acoustic reflectors, to minimize resonance and improve skirt performance and insertion loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an interdigital transducer capacitor with uniform pitch is used, then the device structure is simple and easy to manufacture, but it generates spurious responses and mechanical resonance that degrade filter performance
Solution Approach 1:
The capacitor fingers are designed with non-uniform pitch where different regions have different pitch values. Specifically, the pitch varies along the length of the capacitor fingers, creating local variations that prevent coherent acoustic wave generation at spurious frequencies while maintaining acceptable manufacturing complexity
Solution Approach 2:
The capacitor structure employs asymmetric pitch distribution where the spacing between adjacent capacitor fingers is intentionally made non-uniform. This asymmetry disrupts the periodicity that would otherwise generate strong acoustic resonance, thereby reducing spurious responses without requiring complete structural complexity
2Object-generated harmful factors
If acoustic reflectors are added to the capacitor to reduce resonance, then spurious responses are reduced, but the device complexity increases
Solution Approach 1:
The patent extracts and removes the acoustic reflector elements from the capacitor structure. By eliminating these additional components that would normally be used to suppress resonance, the design achieves reduced spurious responses through the pitch modulation of the capacitor fingers alone, thereby maintaining lower device complexity
3Object-generated harmful factors
If the capacitor pitch is modulated to reduce spurious responses, then filter skirt performance is improved, but manufacturing precision requirements increase
Solution Approach 1:
The pitch parameter of the capacitor fingers is systematically varied across different regions and orientations. By changing the pitch parameter in a controlled non-uniform pattern, the design improves filter skirt performance through reduced acoustic resonance while the variations remain within manufacturable tolerances
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 solution effectively reduces spurious responses and maintains desired electrical characteristics by dampening mechanical resonance, resulting in improved filter performance with reduced unwanted frequency responses.
Implementation Method 1
The capacitor fingers can be positioned between the high viscosity material and the piezoelectric layer. The high viscosity material can have a higher viscosity than the piezoelectric layer.
Implementation Method 2
an interdigital transducer capacitor in the first region, and an acoustic wave resonator in the second region. The interdigital transducer capacitor including capacitor fingers
Data Source
AI summary
Aspects of this disclosure relate to an interdigital transducer capacitor that includes capacitor fingers with different pitches between pairs of adjacent capacitor fingers. In certain embodiments, the interdigital transducer capacitor and an acoustic wave resonator can be formed of different regions of a piezoelectric layer. Related acoustic wave devices, filters, multiplexers, radio frequency modules, radio frequency systems, wireless communication devices, and methods are disclosed.