Ladder Filter IDT Pitch Tuning for Compact Multi-Band Resonators
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Solution Overview
Problem
There is a need for improved radio frequency filters that can operate at different frequency bands while enhancing manufacturing processes, particularly for applications in communications systems and radar systems, to achieve better system performance in terms of larger cell size, longer battery life, higher data rates, and greater network capacity.
Innovation Solution
A filter device is designed with a substrate and piezoelectric plates having interdigital transducers (IDTs) with varying pitches for resonators, including a series and shunt resonator configuration, where the first resonator has a higher resonance frequency than the second, and dielectric layers are used to coat the diaphragms of these resonators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the thickness of resonators is altered to vary resonance frequencies, then frequency selectivity is improved, but manufacturing complexity and device size increase
Solution Approach 1:
The patent changes the pitch parameter of IDT fingers instead of altering resonator thickness. By varying the center-to-center spacing between adjacent IDT fingers, different resonance frequencies are achieved while maintaining uniform resonator thickness, thus improving frequency selectivity without increasing manufacturing complexity
Solution Approach 2:
The patent creates a universal manufacturing process where a single fabrication sequence can produce resonators with different resonance frequencies by simply adjusting the IDT finger pitch pattern. This multi-functional approach allows the same manufacturing line to produce various frequency filters without reconfiguring equipment or processes
2Adaptability or versatility
If multiple resonators with different resonance frequencies are implemented, then frequency band coverage is improved, but device size increases
Solution Approach 1:
The patent merges multiple resonators with different pitch patterns into a single filter device. By arranging IDTs with varying finger spacings on the same substrate, the device achieves broad frequency band coverage while maintaining a compact footprint, as all resonators share common support structures and cavities
Solution Approach 2:
Instead of varying resonator thickness (vertical dimension) to achieve different frequencies, the patent uses the horizontal dimension by changing IDT finger pitch. This dimensional shift allows frequency differentiation without increasing device height or requiring additional vertical space
3Ease of manufacture
If uniform dielectric coating is applied to all resonators, then manufacturing process is simplified, but frequency tuning flexibility is reduced
Solution Approach 1:
The patent decouples frequency tuning from dielectric thickness by changing the IDT pitch parameter. This allows uniform dielectric coating to be applied to all resonators for manufacturing simplicity, while frequency differentiation is achieved through geometric pitch variation rather than material thickness variation
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 allows for improved frequency selectivity and reduced manufacturing complexity by varying resonance frequencies without altering the thickness of the resonators, leading to smaller device size and enhanced performance in RF filters.
Implementation Method 1
at least one piezoelectric plate supported by the substrate; and a plurality of interdigital transducers (IDTs) of a plurality of resonators that each have a plurality of interleaved fingers at respective diaphragms of the at least one piezoelectric plate
Implementation Method 2
a first resonator of the plurality of resonators includes a first plurality of interleaved fingers having a first pitch, and a second resonator of the plurality of resonators includes a second plurality of interleaved fingers having a second pitch that is different than the first pitch
Data Source
AI summary
A filter device is provided that includes a substrate having a surface and a piezoelectric plate supported by the substrate. A plurality of interdigital transducers (IDTs) for multiple resonators are provided that each have interleaved fingers at respective diaphragms of the piezoelectric plate disposed over one or more cavities. Moreover, a first resonator includes a first plurality of interleaved fingers having a first pitch and a second resonator includes a second plurality of interleaved fingers having a second pitch that is different than the first pitch. This configuration adjusts the resonance frequencies of each resonator. Moreover, a dielectric layer may be uniformly disposed over at least one surface of the respective diaphragms of the piezoelectric plate.