Integrated BAW Capacitor Layout for Wideband Low-Loss Filters
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Solution Overview
Problem
Existing bulk acoustic wave (BAW) devices face challenges in achieving a wide bandwidth and maintaining optimal skirt performance and insertion loss, particularly when using resonators with a high electromechanical coupling coefficient (Kt2).
Innovation Solution
The integration of a capacitor with a passivation layer positioned between conductive layers and electrodes in a BAW device, where the capacitor is strategically placed between the resonator and the interconnect structure, utilizes the passivation layer as the insulator to provide additional capacitance and improve electrical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a resonator with high electromechanical coupling coefficient (Kt2) is used to achieve wide bandwidth, then bandwidth is improved, but skirt performance and insertion loss deteriorate
Solution Approach 1:
A capacitor is introduced as an intermediary component between the resonator and the interconnect structure. This capacitor acts as a mediator to compensate for the degraded skirt performance and insertion loss caused by using high Kt2 resonators, thereby resolving the contradiction between wide bandwidth and optimal filter characteristics
Solution Approach 2:
The capacitor modifies the electrical parameters of the filter circuit by providing additional capacitance. This changes the overall impedance and frequency response characteristics, allowing the filter to achieve both wide bandwidth from the high Kt2 resonator and optimal skirt performance through the capacitive compensation
2Reliability
If a capacitor is added to improve electrical characteristics, then performance is improved, but device complexity increases
Solution Approach 1:
The capacitor is merged with the existing interconnect structure by using the passivation layer as the capacitor dielectric. The passivation layer, which is already present to protect the resonator electrodes, is repurposed to form the capacitor insulator, combining two functions into a single integrated structure
Solution Approach 2:
The passivation layer serves multiple functions: it protects the resonator electrodes from environmental damage and simultaneously acts as the dielectric layer for the capacitor. This multi-functionality reduces the need for additional layers and simplifies the overall device structure
3Manufacturing precision
If additional process steps are added to form the capacitor, then manufacturing precision is improved, but manufacturing time and cost increase
Solution Approach 1:
The passivation layer is deposited in advance during the resonator fabrication process, before the final interconnect structure is completed. This preliminary action prepares the capacitor dielectric layer ahead of time, so that when the interconnect conductors are added, the capacitor is automatically formed without requiring separate capacitor fabrication steps
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 configuration enhances the skirt performance and reduces insertion loss while maintaining a compact device size, as the capacitor provides a high quality factor (Q) without increasing the device thickness, and no additional process steps are needed to form the capacitor, minimizing manufacturing costs and time.
Implementation Method 1
A bulk acoustic wave resonator can include a set of metal electrodes deposited on opposite surfaces of a piezoelectric material, generating a bulk acoustic wave within the volume of the piezoelectric material. The interaction between the electrodes and the piezoelectric material results in the formation and propagation of a bulk acoustic wave.
Implementation Method 2
a capacitor including the passivation layer positioned between the conductive layer and the first or second electrode in a first direction
Data Source
AI summary
A bulk acoustic wave device and a capacitor in a bulk acoustic wave device are disclosed. The bulk acoustic wave device can include a resonator, an interconnect structure, and a capacitor. The resonator includes a first electrode, a second electrode, a piezoelectric layer between the first and second electrodes, and a passivation layer over the second electrode such that the second electrode is positioned between the piezoelectric layer and the passivation layer. The interconnect structure includes a conductive layer. The capacitor includes the passivation layer positioned between the conductive layer and the first or second electrode in a first direction. The capacitor, the resonator, and the interconnect structure are positioned in a second direction different from the first direction.