Vertical BAW Filter Wafer Package for Independent Frequency Trimming
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The fabrication of bulk acoustic wave (BAW) filters and duplexers in consumer electronics faces challenges in achieving precise frequency tuning and compact size due to the complexity and cost of processing, particularly in multi-band applications, where separate frequency trimming of transmitter and receiver filters is not feasible on small substrates, leading to compromises in filter performance and manufacturing yield.
Innovation Solution
An integrated wafer level package is developed, where two wafers are bonded with BAW filters facing each other, surrounded by a seal ring to form a cavity, with external contacts for electrical coupling, allowing independent frequency trimming of each filter before bonding, reducing the footprint and cost by eliminating the need for additional encapsulation and enabling vertical integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If separate frequency trimming of Tx and Rx filters is performed, then filter performance is optimized, but device size and processing complexity increase
Solution Approach 1:
The patent combines Tx and Rx filters into a single integrated package with multiple BAW resonators on one substrate. Each resonator can be independently trimmed via laser processing, allowing separate frequency optimization while sharing common support structures and packaging, thus reducing overall device complexity compared to separate packages.
Solution Approach 2:
The patent transitions from planar side-by-side filter arrangement to a vertically stacked three-dimensional configuration. Multiple BAW resonators are stacked in the vertical dimension, enabling independent frequency control through laser trimming of individual resonator layers while minimizing lateral footprint and reducing packaging complexity.
2Area of stationary object
If multi-band filters are fabricated on a single substrate, then device size is reduced, but manufacturing yield and filter performance deteriorate
Solution Approach 1:
The patent segments the multi-band filter into multiple independent BAW resonator units, each with its own piezoelectric layer stack and electrode structure. Each resonator can be independently designed for specific frequency bands and independently trimmed during manufacturing, allowing high-yield production while maintaining compact integrated packaging.
Solution Approach 2:
The patent applies local quality by giving each BAW resonator within the integrated package distinct piezoelectric layer thicknesses and material compositions tailored to specific frequency requirements. This allows each local region of the device to be optimized for its intended function while maintaining overall manufacturing consistency and yield.
3Manufacturing precision
If frequency tolerance is maintained at 0.1%, then filter performance is ensured, but processing accuracy requirements become excessively stringent
Solution Approach 1:
The patent performs preliminary frequency trimming by depositing a slightly thicker piezoelectric layer than the final required thickness, then removing the excess material through laser processing to achieve the precise target frequency. This preliminary action approach allows for more relaxed initial deposition tolerances while still achieving the stringent 0.1% final frequency tolerance.
Solution Approach 2:
The patent changes the processing parameter approach by using laser trimming to adjust the piezoelectric layer thickness after deposition rather than relying solely on precise control of deposition parameters. This allows frequency tuning through controlled material removal, reducing the stringency requirements for film deposition accuracy while maintaining tight frequency tolerances.
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 significantly reduces the lateral footprint and manufacturing cost of multi-band filters/duplexers, maximizes yield by trimming frequencies independently, and provides a compact, hermetically sealed package that prevents contamination, while allowing for the integration of diverse micro-devices in a single package.
Implementation Method 1
a seal ring disposed between the first wafer and the second wafer such that a hermetic seal is formed surrounding the first BAW filter and the second BAW filter and defining a cavity between the seal ring and the first BAW filter and the second BAW filter
Implementation Method 2
A BAW resonator comprises at least one piezoelectric thin film and at least one pair of a top electrode and a bottom electrode sandwiching the piezoelectric film therebetween
Implementation Method 3
The resonance frequency of a BAW resonator is the frequency for which the mechanical waves propagate in the device. The half wavelength of the propagating waves is equal to the total thickness of the device for a given phase velocity of the mechanical wave in the material
Data Source
AI summary
In one aspect of the present invention, an integrated wafer level package includes a first wafer and a second wafer spaced apart to define a first gap therebetween, a first bulk acoustic wave (BAW) filter disposed on the first wafer and a second BAW filter disposed on the second wafer, where the second BAW filter faces directly the first BAW filter to define a second gap therebetween, a seal ring disposed between the first wafer and the second wafer in the first gap such that a seal is formed surrounding the first BAW filter and the second BAW filter and defining a cavity between the seal ring and the first BAW filter and the second BAW filter, and at least one external contact accessible externally to the wafer level package and electrically coupled to at least one of the first BAW filter and the second BAW filter.