Tunable Filter Structures With MEMS Cantilever Beam
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Solution Overview
Problem
Existing Thin Film Bulk Acoustic Resonators (FBARs) face challenges in tuning their resonant frequency post-processing due to processing variations and the inability to adjust acoustic resonant characteristics effectively, limiting their application in RF filters and other wireless devices.
Innovation Solution
A tunable filter structure incorporating a micro-electro-mechanical structure (MEMS) cantilever beam that can be actuated to apply a mechanical load on the FBAR, shifting its resonant frequency, allowing for dynamic tuning in situ or post-processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If mass loading is carried out by growing or depositing a thin film material uniformly distributed on one electrode of the resonator, then the resonance frequency can be downshifted, but processing variations cause more or less mass loading material to be deposited, making it difficult to precisely control the resonant frequency
Solution Approach 1:
The patent employs a MEMS cantilever beam that can be dynamically actuated to contact the FBAR electrode, providing adjustable mass loading. The cantilever beam's position and contact force can be controlled to precisely adjust the resonant frequency, overcoming the static and imprecise nature of uniform thin film deposition. This dynamic mechanism allows post-processing tuning and compensates for processing variations.
Solution Approach 2:
The patent changes the mass loading parameter from a fixed uniform thin film to a controllable MEMS structure. By varying the actuation voltage or mechanical position of the MEMS cantilever beam, the effective mass loading on the FBAR can be continuously adjusted, enabling precise control of resonant frequency despite variations in other processing parameters.
2Adaptability or versatility
If the FBAR is built with fixed piezoelectric film thickness, then the device structure is simplified, but it becomes difficult or impossible to tune the resonant frequency after fabrication
Solution Approach 1:
The patent segments the mass loading function from the FBAR structure itself by using a separate, movable MEMS cantilever beam. This allows the FBAR to maintain its simple fixed-thickness piezoelectric film structure while the tuning function is provided by the independent MEMS component. The segmentation enables independent optimization of both the FBAR and the tuning mechanism.
Solution Approach 2:
The MEMS cantilever beam acts as an intermediary between the control system and the FBAR resonator. It transfers the mechanical loading effect to the FBAR electrode without requiring direct integration of complex tuning mechanisms into the FBAR structure itself. This intermediary approach simplifies the overall device architecture while enabling tunability.
3Reliability
If more or less piezoelectric material is deposited for devices in different runs, then processing flexibility is maintained, but the acoustic resonant characteristics vary due to processing variations
Solution Approach 1:
The patent implements a feedback mechanism where the MEMS cantilever beam's actuation is controlled to compensate for variations in FBAR resonant frequency. By measuring the actual resonant frequency and adjusting the MEMS loading accordingly, the system can achieve consistent acoustic resonant characteristics despite variations in piezoelectric film deposition across different manufacturing runs.
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
Enables precise adjustment of the resonant frequency of FBARs, overcoming processing variations and enhancing their performance in RF filters and other applications by allowing for real-time tuning of the acoustic resonant characteristics.
Implementation Method 1
The mass loading effect can be accomplished by depositing or growing a mass of film on the resonator to bring about downshifting of the resonance frequency of the FBAR. The FBAR can be put under a mechanical load so that its resonance frequency can shift.
Implementation Method 2
FBARs utilize the acoustic resonant characteristics of piezoelectric materials, such as AlN or ZnO, to remove unwanted frequencies from being transmitted in a device
Data Source
AI summary
Tunable filter structures, methods of manufacture and design structures are disclosed. The method of forming a filter structure includes forming a piezoelectric resonance filter over a cavity structure. The forming of the piezoelectric resonance filter includes: forming an upper electrode on one side of a piezoelectric material; and forming a lower electrode on an opposing side of the piezoelectric material. The method further includes forming a micro-electro-mechanical structure (MEMS) cantilever beam at a location in which, upon actuation, makes contact with the piezoelectric resonance filter.