BAW Filter Internal Shielding for Parasitic Capacitance Control
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Solution Overview
Problem
Bulk Acoustic Wave (BAW) filters face performance degradation due to electrostatic interference, particularly parasitic capacitance, which affects filter rejection in high-frequency communication applications.
Innovation Solution
A BAW filter structure with internal electrostatic shielding, featuring a planar electrostatic shield positioned between the substrate and top electrodes of transducers, coupled to a ground node to interrupt parasitic capacitance and reduce its influence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a BAW filter structure is used for high-frequency communication applications, then filtering performance is achieved, but parasitic capacitance causes filter rejection degradation
Solution Approach 1:
A planar electrostatic shield is introduced as an intermediary element between the substrate and top electrodes. This shield acts as a mediator that interrupts the electrical field lines responsible for parasitic capacitance, thereby reducing the harmful capacitive coupling while maintaining the filter's operational integrity
Solution Approach 2:
The harmful parasitic capacitance effect is extracted and isolated by introducing the electrostatic shield. The shield effectively separates and removes the detrimental electrical field interactions from the filter structure, allowing the desired filtering function to operate without degradation
2Speed
If the filter structure operates at high frequencies above 1.5 GHz, then communication application requirements are met, but electrostatic interference increases
Solution Approach 1:
The planar electrostatic shield serves as a frequency-independent intermediary that provides electrostatic shielding across the entire operating frequency range. By positioning the shield between charged elements, it mitigates electrostatic interference effects that would otherwise increase with higher operating frequencies
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
The internal electrostatic shielding significantly improves filtering performance by minimizing parasitic capacitance, leading to enhanced filter rejection and reduced rejection degradation compared to unshielded BAW filters.
Implementation Method 1
The planar electrostatic shield is coupled to a ground node and interrupts an electrical field associated with the parasitic capacitance of the filter to reduce the parasitic capacitance
Implementation Method 2
Each of the plurality of transducers comprises a bottom electrode, a piezoelectric layer over the bottom electrode, and a top electrode over the piezoelectric layer
Data Source
AI summary
Embodiments of the disclosure are directed to a Bulk Acoustic Wave (BAW) filter structure with internal electrostatic shielding. In exemplary aspects disclosed herein, a shielded BAW filter structure includes a substrate, a plurality of transducers over the substrate, and a planar electrostatic shield between the substrate and a top electrode of the plurality of transducers. Each of the plurality of transducers forms a portion of a BAW resonator and resides in a filter including a parasitic capacitance. The planar electrostatic shield is coupled to a ground node and interrupts an electrical field associated with the parasitic capacitance of the filter to reduce the parasitic capacitance. Accordingly, the shielded BAW filter structure reduces the influence of parasitic capacitance providing improved filtering performance compared to an unshielded BAW filter structure.