RF Filter Fabrication with Sacrificial Carrier and BST Tuning
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Solution Overview
Problem
The increasing demand for higher frequency operation in next-generation mobile phones requires smaller, low-power RF filters with high Q factors to manage the growing data traffic, while existing Bulk Acoustic Wave (BAW) filters face challenges in achieving flexible bandwidth and reducing size and power consumption.
Innovation Solution
The method involves fabricating RF filters using single crystal piezoelectric films such as BaxSr(1-x)TiO3, AlN, or AlGaN, with innovative membrane supporting structures and electrode designs, allowing for higher Q factors and reduced size, and utilizing electrostrictive materials like BST for tunability and reduced power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If BAW filters are used to achieve high Q factors and higher frequency operation, then filter performance is improved, but device size and power consumption are not sufficiently reduced
Solution Approach 1:
The patent uses thin film piezoelectric layers (AlN, AlGaN, or BST) deposited on flexible sacrificial carriers that are later removed. This thin-film approach enables high Q factors while reducing device volume compared to traditional bulk acoustic wave filters.
Solution Approach 2:
The patent extracts and removes the sacrificial carrier (such as silicon oxide or silicon nitride layers) after piezoelectric film deposition, leaving only the necessary functional layers. This extraction process reduces overall device size while maintaining the high Q factor performance of the piezoelectric resonators.
2Reliability
If BAW filters are used to achieve high Q factors, then filter performance is improved, but power consumption is not sufficiently reduced
Solution Approach 1:
The patent changes the material parameter by using electrostrictive materials like BST (Barium Strontium Titanate) which offer higher piezoelectric coefficients and lower loss tangents. This material substitution enables achieving high Q factors at lower operating powers, directly addressing the power consumption issue.
Solution Approach 2:
The patent employs composite structures combining multiple thin films including piezoelectric layers, electrode layers, and sacrificial carrier materials. This composite approach optimizes the balance between Q factor performance and power consumption by selecting materials with complementary properties.
3Reliability
If single crystal piezoelectric films are used with innovative membrane structures, then Q factor and frequency performance are improved, but manufacturing complexity increases
Solution Approach 1:
The patent performs preliminary deposition of piezoelectric films on sacrificial carriers before final device assembly. This preliminary action allows for optimized film growth conditions and carrier removal timing, simplifying the overall manufacturing process despite the advanced materials used.
Solution Approach 2:
The patent uses sacrificial carriers (silicon oxide, silicon nitride) as intermediary structures during fabrication. These carriers provide a temporary substrate for piezoelectric film deposition and are removed later, acting as mediators that simplify the manufacturing process while enabling high-performance single crystal films.
4Adaptability or versatility
If electrostrictive materials like BST are used for tunability, then bandwidth flexibility is improved, but device complexity increases
Solution Approach 1:
The patent uses BST (Barium Strontium Titanate) electrostrictive material that allows dynamic tuning of resonator frequency and bandwidth through applied electric fields. This dynamic control provides bandwidth flexibility without requiring multiple discrete filter components, thereby managing device complexity.
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 approach results in RF filters with improved Q factors, reduced size, and lower power consumption, enabling efficient operation at higher frequencies and flexible bandwidth, addressing the limitations of current BAW filters.
Implementation Method 1
These typically include a piezoelectric electromechanical transduction layer which converts mechanical energy into electrical energy
Implementation Method 2
utilizing electrostrictive materials like BST for tunability and reduced power consumption
Data Source
AI summary
A method of fabricating an RF filter comprising an array of resonators comprising the steps of:Obtaining a removable carrier with release layer;Growing a piezoelectric film on a removable carrier;Applying a first electrode to the piezoelectric film;Obtaining a backing membrane on a cover, with or without prefabricated cavities between the backing film and cover;Attaching the backing membrane to the first electrode;Detaching the removable carrier;Measuring and trimming the piezoelectric film as necessary;Selectively etching away the piezoelectric layer to fabricate discrete resonator islands;Etching down through coatings and backing membrane to a silicon dioxide layer between the backing membrane and the cover to form trenches;Applying a passivation layer into the trenches and around the piezoelectric islands;Depositing a second electrode layer over the piezoelectric film islands and surrounding passivation layer;Applying connections for subsequent electrical coupling to an interposer;Selectively removing second electrode material leaving coupled resonator arrays;Creating a gasket around perimeter of the resonator array;Thinning down cover to desired thickness;Optionally fabricating upper cavities between the backing membrane and cover by drilling holes through the cover and then selectively etching away the silicon dioxide;Dicing the wafer into flip chip single unit filter arrays;Obtaining an interposer;Optionally applying a dam to the interposer surface to halt overfill flow;Coupling the flip chip single unit filter array to pads of the interposer by reflow of the solder cap;Encapsulating with polymer underfill/overfill; andSingulating into separate filter modules.