Composite FBAR Filter Module for High Q Factor RF Signals
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Solution Overview
Problem
Current RF filters in mobile phones face challenges in achieving high Q factors and flexible bandwidths to accommodate increasing data traffic and user demands, particularly with the shift to 5G and 4×4 MIMO, which require smaller, low-power resonators that can operate at higher frequencies without increasing phone size or depleting battery power.
Innovation Solution
The development of a Composite FBAR filter module using single crystal piezoelectric films such as BaxSr(1-x)TiO3 (BST), AlN, or AlxGa(1-x)N, with advanced electrode structures and silicon membranes, allows for higher Q factors and coupling coefficients, enabling efficient energy conversion and reduced power consumption, while also potentially eliminating the need for switches in the Front End Module.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If BAW resonators are used to achieve higher Q factors and operating frequencies, then filter performance is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent employs composite FBAR structures combining piezoelectric films (such as AlN or BaxSr1-xTiO3) with silicon membranes and electrode layers. This composite approach achieves high Q factors (2500-5000) and effective coupling coefficients (6-10%) by integrating multiple materials with complementary properties, resolving the contradiction between performance and complexity through material composition rather than structural complication
Solution Approach 2:
The patent modifies key parameters including piezoelectric film thickness (200-2000 nm), silicon membrane thickness (1-10 μm), and operating frequency (2-10 GHz) to optimize the balance between Q factor and coupling coefficient. By tuning these parameters, the design achieves high performance without requiring overly complex device architectures
2Use of energy by moving object
If piezoelectric film thickness is increased to improve coupling coefficient, then energy conversion efficiency is improved, but resonator size increases
Solution Approach 1:
The patent optimizes piezoelectric film thickness within a specific range (200-2000 nm) to achieve the optimal balance between coupling coefficient and resonator size. Thinner films reduce size but limit coupling, while thicker films improve coupling but increase size. The patent identifies the sweet spot in this parameter range that satisfies both requirements for modern mobile phone filters
Solution Approach 2:
The composite FBAR structure with silicon membranes provides mechanical support and stress management that allows thin piezoelectric films to achieve high coupling coefficients without requiring excessive thickness. The silicon membrane acts as a stress-free substrate that enables the piezoelectric layer to maintain its piezoelectric properties at optimized thin dimensions
3Adaptability or versatility
If multiple filters are required for 5G and 4x4 MIMO, then communication capability is improved, but device size increases
Solution Approach 1:
The patent designs FBAR resonators with broad bandwidth capability and high Q factors that can serve multiple frequency bands and communication standards (4G, 5G, Wi-Fi). The high effective coupling coefficient (6-10%) enables a single resonator to effectively handle multiple signals, reducing the total number of filters needed in the mobile phone
Solution Approach 2:
The patent employs array configurations of FBAR resonators that can be selectively activated for different frequency bands and MIMO streams. This segmented approach allows the filter system to handle multiple communication functions while using fewer physical resonators than traditional designs, reducing overall device size
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 solution enhances the quality of RF filters by achieving higher Q factors and coupling coefficients, leading to improved signal transmission, reduced power consumption, and extended battery life in mobile devices, while also simplifying the module architecture and reducing size and cost.
Implementation Method 1
These typically include a piezoelectric electromechanical transduction layer which converts mechanical energy into electrical energy
Implementation Method 2
In Bulk Acoustic Wave Resonators (BAW) the signal is carried through the bulk of the resonator film
Implementation Method 3
The quality of a resonator is given by its Q factor. This is the ratio of the energy stored to the power dissipated. A high Q factor indicates that the filter loses little energy during operation
Data Source
AI summary
A filter package comprising an array of piezoelectric films sandwiched between lower electrodes and an array of upper electrodes covered by an array of silicon membranes with cavities thereover: the lower electrode being coupled to an interposer with a first cavity between the lower electrodes and the interposer; the array of silicon membranes having a known thickness and attached over the upper electrodes with an array of upper cavities, each upper cavity between a silicon membrane of the array and a common silicon cover; each upper cavity aligned with a piezoelectric film, an upper electrode and silicon membrane, the upper cavities having side walls comprising SiO2; the individual piezoelectric films, their upper electrodes and silicon membranes thereover being separated from adjacent piezoelectric films, upper electrodes and silicon membranes by a passivation material.