XBAR Resonator Layout for Lower Thermal Resistance
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Solution Overview
Problem
Existing RF filters, particularly those using acoustic wave resonators, face challenges in handling higher frequencies and wider bandwidths required for future communication networks, with limitations in thermal management affecting their performance.
Innovation Solution
The development of Transversely-Excited Film Bulk Acoustic Resonators (XBARs) with improved thermal management by removing predetermined areas of the bonding oxide layer and piezoelectric layer to reduce thermal resistance, allowing efficient heat conduction from the IDT or busbars to the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a complete bonding oxide layer and piezoelectric layer are present, then electrical insulation and structural integrity are maintained, but thermal resistance increases and thermal efficiency deteriorates
Solution Approach 1:
The bonding oxide layer is segmented into two regions: a first region that remains intact to provide electrical insulation, and a second region that is removed to improve thermal conduction. This segmentation allows the same layer to serve dual purposes of electrical isolation and thermal management in different spatial zones.
Solution Approach 2:
Different regions of the bonding oxide layer are given different properties: the first region maintains full thickness for electrical insulation, while the second region has reduced or zero thickness for thermal conduction. This local differentiation resolves the contradiction by optimizing each region for its primary function.
2Speed
If higher frequency channels are used for future communication networks, then bandwidth and data transmission capability are improved, but thermal management becomes more challenging and output power is limited
Solution Approach 1:
The patent extracts or removes portions of the bonding oxide layer and piezoelectric layer to create thermal conduction paths. This extraction eliminates the thermal barrier created by these layers, enabling efficient heat removal from the IDT and busbars, thereby allowing higher output power in high-frequency channels.
3Temperature
If thermal resistance is reduced by removing bonding oxide and piezoelectric layers, then heat conduction from IDT to substrate is improved, but device complexity and manufacturing steps increase
Solution Approach 1:
The bonding oxide layer is removed in advance during cavity formation, before the piezoelectric layer is deposited. This preliminary action simplifies subsequent processing by eliminating the need for complex selective removal techniques, as the piezoelectric layer can be selectively removed using standard wet etching methods.
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 enhances the thermal efficiency of XBARs, leading to extended operating life and higher output power in high-frequency channels, addressing the thermal barriers in existing technologies.
Implementation Method 1
improved XBAR resonators that efficiently conduct heat from the IDT or busbars to the substrate
Implementation Method 2
An XBAR resonator comprises an interdigital transducer (IDT) formed on a thin floating layer, or diaphragm, of a single-crystal piezoelectric material. The IDT includes a first set of parallel fingers, extending from a first busbar and a second set of parallel fingers extending from a second busbar. The first and second sets of parallel fingers are interleaved. A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm.
Data Source
AI summary
An acoustic resonator device with low thermal impedance has a substrate and a single-crystal piezoelectric plate having a back surface attached to a top surface of the substrate via a bonding oxide (BOX) layer. An interdigital transducer (IDT) formed on the front surface of the plate has interleaved fingers disposed on a diaphragm of the plate that is formed over a cavity in the substrate. The piezoelectric plate and the BOX layer are removed from a least a portion of the surface area of the substrate to provide lower thermal resistance between the IDT and the substrate.