Three-Layer XBAR Electrodes for Heat Dissipation and Spurious Mode Control
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Solution Overview
Problem
Existing RF filters are not well-suited for higher frequencies and bandwidths required by future communications networks, particularly in 5G NR and WiFi bands, due to inefficiencies in heat dissipation and spurious acoustic modes in transversely-excited film bulk acoustic resonators (XBARs).
Innovation Solution
The use of a three-layer IDT finger structure with specific metal combinations and geometries in XBARs to reduce spurious modes and improve thermal and electrical conductivity, enhancing heat dissipation through the IDT fingers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional single-layer IDT fingers are used in XBARs, then the structure is simple and easy to manufacture, but thermal conductivity is insufficient and spurious acoustic modes occur at higher frequencies
Solution Approach 1:
The IDT fingers are constructed as composite structures with multiple metal layers (e.g., aluminum, copper, tungsten, molybdenum, or gold layers) deposited in sequence. Each layer contributes different properties: some layers provide high electrical conductivity, others provide high thermal conductivity, and the combination suppresses spurious acoustic modes through optimized acoustic impedance matching. This composite approach enables the IDT to handle higher frequencies and dissipate heat more effectively while maintaining structural integrity.
Solution Approach 2:
The invention transitions from a single-layer IDT structure to a multi-layer structure, adding the vertical dimension of layering to the traditional planar IDT design. This dimensional evolution allows independent optimization of electrical and thermal properties in different layers, enabling simultaneous improvement of electrical conductivity, thermal conductivity, and acoustic mode suppression without compromising manufacturing feasibility.
2Temperature
If thicker IDT fingers are used to improve thermal conductivity, then heat dissipation improves, but viscous losses increase and device size increases
Solution Approach 1:
The IDT finger structure is segmented into multiple thin layers rather than using a single thick layer. This segmentation allows each layer to be optimized for specific functions: thinner individual layers reduce viscous losses and acoustic impedance mismatch, while the stacked configuration of multiple layers collectively provides enhanced thermal conductivity and heat dissipation capacity. The segmented approach also reduces overall device footprint compared to a single thick finger structure.
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 minimizes viscous losses and spurious acoustic modes, enabling high piezoelectric coupling and efficient heat removal, suitable for high-frequency and wide-bandwidth applications.
Implementation Method 1
improve thermal and electrical conductivity, enhancing heat dissipation through the IDT fingers
Implementation Method 2
high piezoelectric coupling
Data Source
AI summary
A bulk acoustic resonator device and filter device including the same is provided. The resonator includes a substrate; a piezoelectric layer attached to the substrate; and an interdigital transducer having interleaved fingers on the piezoelectric layer. The interleaved fingers include a first layer proximate the piezoelectric layer, a second layer over the first layer, and a third layer over the second layer such that the second layer is between the first and third layers. Adjacent layers of the first, second and third layers are comprised of different metals. Moreover, a primary shear acoustic mode is excited in the piezoelectric layer and is a bulk shear mode where acoustic energy propagates in a direction predominantly orthogonal to the surface of the piezoelectric layer and predominantly orthogonal to a direction of an electric field created by the interleaved fingers of the IDT that is predominantly lateral in the piezoelectric layer.