Acoustic Resonator Filter Layout for Temperature-Stable Bandwidth
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Solution Overview
Problem
Existing acoustic resonator filters face challenges in maintaining performance stability and temperature robustness, particularly in varying temperature conditions, due to sensitivity issues related to resonance frequency changes.
Innovation Solution
The design incorporates a series acoustic resonator connected in series with two shunt acoustic resonators, where at least one shunt resonator has a higher resonance frequency and includes a SiO2 layer to reduce temperature coefficient of frequency (TCF) sensitivity, along with inductors and capacitors connected between shunt resonators and ground to optimize bandwidth and insertion loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If acoustic resonators are used to achieve small size and good performance, then the filter size is reduced and performance is improved, but temperature sensitivity increases causing resonance frequency instability
Solution Approach 1:
The patent applies parameter changes by introducing a SiO2 layer with specific physical properties (low TCF of -20 to +20 ppm/°C) into the acoustic resonator structure. This changes the thermal parameter of the resonator system, reducing the temperature coefficient of frequency from typical values (e.g., +30 to -30 ppm/°C for AlN) to a much smaller range, thereby stabilizing resonance frequency across temperature variations while maintaining the compact size
Solution Approach 2:
The patent uses composite materials by combining AlN (or other piezoelectric materials) with SiO2 layer in the acoustic resonator structure. The SiO2 layer acts as a temperature compensation material with different thermal expansion and TCF characteristics, creating a composite structure that maintains mechanical resonance properties while compensating for temperature-induced frequency drift
2Reliability
If shunt acoustic resonators are added to improve temperature stability, then temperature robustness is improved, but device complexity increases
Solution Approach 1:
The patent applies local quality by strategically placing SiO2 layers specifically in the shunt acoustic resonators rather than uniformly across all resonators. This localized modification targets the specific resonators that need temperature compensation, achieving temperature stability while minimizing the overall structural complexity and material usage
3Speed
If multiple shunt resonators with different resonance frequencies are used to broaden bandwidth, then bandwidth is improved, but insertion loss increases
Solution Approach 1:
The patent applies dynamics by configuring shunt acoustic resonators with specific resonance frequencies (e.g., first shunt resonator at 3.52 GHz, second shunt resonator at 3.48 GHz) that are dynamically positioned to create transmission zeros at band edges. This dynamic frequency placement optimizes the passband shape, achieving broadband performance with controlled insertion loss through precise resonant frequency tuning
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 achieves a stable performance with reduced temperature sensitivity, maintaining a bandwidth difference of less than 20 MHz across -40°C to +95°C and achieving insertion loss of less than 2.27 dB at 3.5 GHz and 2.33 dB at 3.6 GHz, while minimizing energy loss.
Implementation Method 1
a piezoelectric layer disposed between the respective first and second electrodes
Implementation Method 2
at least one series acoustic resonator electrically connected between a first port and a second port in series, through which a radio frequency (RF) signal passes
Data Source
AI summary
An acoustic resonator filter includes at least one series acoustic resonator electrically connected between a first port and a second port in series, through which a radio frequency (RF) signal passes; at least one second shunt acoustic resonator electrically shunt-connected between the at least one series acoustic resonator and a ground; and at least one first shunt acoustic resonator electrically shunt-connected between the at least one series acoustic resonator and a ground and having a resonance frequency higher than a resonance frequency of the at least one second shunt acoustic resonator. At least one shunt acoustic resonator, among the at least one first shunt acoustic resonator and the at least one second shunt acoustic resonator has a temperature coefficient of frequency (TCF) corresponding to resonance frequency sensitivity more insensitive than resonance frequency sensitivity according to a change in temperature of the at least one series acoustic resonator filter.