Acoustic Resonator Back-Side Coating for Precise Frequency Tuning
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Solution Overview
Problem
Existing RF filters face challenges in achieving uniform dielectric coatings over interdigital transducers (IDTs) due to shadow casting by metal electrodes, leading to difficulty in controlling spurs and inaccurate resonance frequency adjustments.
Innovation Solution
Applying a uniform dielectric coating on the back-side of piezoelectric plates instead of over the IDT fingers, with the shunt resonator having a greater thickness than the series resonator, allowing for precise resonance frequency tuning and improved control of spurs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dielectric coating is applied over IDT fingers, then resonance frequency adjustment is possible, but coating uniformity deteriorates due to shadow casting by metal electrodes
Solution Approach 1:
The patent applies dielectric coating on the backside of the piezoelectric plate rather than over the IDT fingers. This inversion of the coating location eliminates shadow casting by metal electrodes, achieving uniform coating thickness while maintaining resonance frequency control capability through backside coating thickness variation.
2Measurement precision
If different thickness coatings are applied to different resonators, then resonance frequency tuning is achieved, but manufacturing complexity increases
Solution Approach 1:
The patent segments the dielectric coating into separate layers for different resonator types (series and shunt resonators) on the backside of the piezoelectric plate. Each resonator receives its specific coating thickness independently, enabling precise frequency tuning without requiring complex frontside coating processes.
Solution Approach 2:
The patent moves the dielectric coating process to the backside dimension of the piezoelectric plate, away from the IDT finger region. This dimensional change allows independent thickness control for different resonators without the shadow casting constraints that exist in the planar frontside coating approach.
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 method enables more accurate resonance frequency control and reduced manufacturing complexity, resulting in improved RF filter performance with enhanced frequency selectivity and reduced spurious responses.
Implementation Method 1
at least one piezoelectric plate having opposing first and second surfaces and attached to the substrate
Implementation Method 2
the at least one second dielectric coating layer of the shunt resonator has a greater thickness than a thickness of the at least one second dielectric coating layer of the series resonator
Data Source
AI summary
A filter device is provided that includes a substrate and a piezoelectric plate attached to the substrate. A conductor pattern is formed at a first surface of the piezoelectric plate and includes interdigital transducers of series and shunt resonators that each have interleaved fingers at respective diaphragms of the plate suspended. A first dielectric coating layer is formed over the interleaved fingers of the IDTs and on the first surface of the piezoelectric plate; and a second dielectric coating layer is formed on the second surface of the piezoelectric plate that is opposite the first surface. The second dielectric coating layer of the shunt resonator has a greater thickness than a thickness of the at least one second dielectric coating layer of the series resonator.