LBAW Resonator Reflecting Layer for Parasitic Sideband Suppression
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Solution Overview
Problem
Thin film radio-frequency acoustic wave filters, particularly LBAW filters, face challenges in suppressing parasitic sidebands, which affect their band pass filter characteristics and bandwidth.
Innovation Solution
Incorporating one or more acoustic resonators in parallel with the LBAW filters and optimizing the thickness and geometry of the piezoelectric layer and electrodes, along with a reflecting structure, to control the frequency range and suppress sidebands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If LBAW filters are used for band pass filtering, then small size and mass-production capability are achieved, but parasitic sidebands appear that degrade filter characteristics
Solution Approach 1:
The patent introduces a reflecting structure that converts the harmful parasitic sidebands into beneficial effects by reflecting acoustic waves back into the piezoelectric layer, where they are converted to electrical signals that can be filtered out, thereby improving overall filter performance while maintaining the compact LBAW structure
Solution Approach 2:
The reflecting structure acts as an intermediary element between the piezoelectric layer and the external environment, mediating the acoustic wave propagation by reflecting unwanted sidebands while allowing the main filter function to operate, thus resolving the contradiction between compact size and sideband suppression
2Speed
If the piezoelectric layer thickness and electrode gap are optimized for bandwidth, then the achievable bandwidth is improved, but parasitic sidebands are generated
Solution Approach 1:
The patent optimizes specific parameters including the piezoelectric layer thickness (e.g., 1-10 micrometers), electrode gap dimensions, and reflecting structure thickness to achieve desired bandwidth while suppressing sidebands. By carefully controlling these parameters, the filter achieves wide bandwidth without generating excessive parasitic sidebands
3Reliability
If additional acoustic resonators are added in parallel to suppress sidebands, then filter characteristic is improved, but device complexity increases
Solution Approach 1:
The patent merges the sideband suppression function with the existing LBAW filter structure by integrating a reflecting structure directly beneath the piezoelectric layer. This unified approach achieves sideband suppression without requiring separate parallel resonators, thereby improving filter characteristics while avoiding excessive complexity
4Object-generated harmful factors
If the reflecting structure thickness is increased to suppress sidebands, then sideband suppression is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent identifies an optimal thickness range for the reflecting structure (e.g., 0.5-5 micrometers) that provides effective sideband suppression while remaining manufacturable with standard thin-film deposition techniques. This parameter optimization balances sideband suppression performance with realistic manufacturing precision capabilities
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 improves the band pass response of LBAW filters by reducing parasitic sidebands, allowing for wider bandwidth and simpler fabrication, while operating at higher frequencies with reduced size and complexity.
Implementation Method 1
application of a radio frequency voltage between the first electrode and the counter electrode creates acoustic resonance waves in the piezoelectric layer
Implementation Method 2
The reflecting structure located including at least a first reflecting layer... suppress parasitic sidebands in LBAW filters
Data Source
AI summary
Acoustic wave filter devices are disclosed. In an embodiment, the device includes an acoustic wave resonator and a reflecting layer located below the acoustic wave resonator. The wave resonator includes an input electrode including a first electrode and a counter electrode, a piezoelectric layer sandwiched between the first electrode and the counter electrode, and an output electrode. The piezoelectric layer has a first region covered by the first or the output electrode, and a second region not covered by any of the first and the output electrode. The first region has a second order acoustic thickness-shear resonance (TS2) mode dispersion curve with a first minimum frequency, and the second region has a TS2 mode dispersion curve with a second minimum frequency. The reflecting layer's thickness is such that a difference between the first minimum frequency and the second minimum frequency is less than 2% of a filter center frequency.