Monolithic FBAR Filter Topology With On-Chip Trimming Inductor
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Solution Overview
Problem
Conventional monolithic RF filters using film bulk acoustic resonators (FBARs) require large trimming inductors that cannot be fabricated on the same substrate, necessitating separate fabrication and wire bonding, increasing costs and size due to the need for a printed circuit board and introducing parasitic elements that affect performance.
Innovation Solution
A filter topology where a pair of shunt resonators share a common electrode connected to ground through a small trimming inductor, allowing all components to be fabricated on a single chip with integrated circuit processes, eliminating the need for wire bonding and a separate printed circuit board.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If trimming inductors are fabricated separately on a printed circuit board, then the filter can achieve desired bandwidth and attenuation characteristics, but the overall size increases and parasitic elements are introduced
Solution Approach 1:
The patent integrates the trimming inductors directly onto the FBAR chip substrate, merging previously separate components (FBARs and trimming inductors) into a single integrated structure. This eliminates the need for separate printed circuit boards and wire bonding, reducing overall filter size while maintaining performance through direct integration of all filter components on one chip.
2Reliability
If trimming inductors are fabricated separately with wire bonding, then the desired inductance value can be achieved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent combines the fabrication of FBARs and trimming inductors into a single monolithic manufacturing process on the same substrate. This integration eliminates multiple fabrication steps, wire bonding operations, and assembly procedures, significantly reducing manufacturing complexity and cost while achieving the desired inductance values directly on-chip.
3Reliability
If trimming inductors are made large to achieve desired inductance, then the filter performance is optimized, but the inductor cannot be fabricated on the FBAR substrate
Solution Approach 1:
The patent transitions from planar inductor designs to three-dimensional spiral inductor configurations that can be fabricated within the limited substrate area. By utilizing vertical stacking and spiral patterns, the design achieves the required inductance values (e.g., 2 nH) within the compact FBAR chip footprint, enabling direct on-chip integration without requiring oversized components.
4Adaptability or versatility
If discrete trimming inductors are used with wire bonding, then bandwidth and attenuation can be tuned, but parasitic elements affect filter performance
Solution Approach 1:
The patent integrates trimming inductors directly with the FBAR resonators on the same substrate, eliminating wire bonds and external connections that introduce parasitic elements. The direct integration reduces parasitic inductance and capacitance, improving Q-factor and filter performance while maintaining the ability to tune bandwidth and attenuation characteristics through the trimming inductors.
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 the fabrication of a monolithic RF filter with reduced manufacturing steps and costs, improved performance by eliminating parasitic elements, and a smaller form factor.
Implementation Method 1
An FBAR device essentially comprises a piezoelectric layer, such as zinc oxide or aluminum nitride, sandwiched between two electrodes
Implementation Method 2
Each FBAR exhibits fundamental resonance at a frequency that is dependent upon the thickness of the layers of the FBAR
Data Source
AI summary
A filter formed of film bulk acoustic resonators has a topology that enables a trimming inductor to be fabricated on the same substrate as the resonator arrays. The entire filter can be fabricated on a single chip, utilizing only integrated circuit processes. In an exemplary embodiment, a pair of shunt resonators each have one electrode connected to series-connected resonators. The other electrodes of the two shunt resonators are connected in common to one another. The trimming inductor is connected between the common electrode and ground potential. A third shunt resonator is connected between the series-connected resonators and ground potential.