Bulk Acoustic Resonator Electrode Recesses for Spurious Noise
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Solution Overview
Problem
Bulk acoustic wave (BAW) filters face challenges with high loss due to dielectric loss, incomplete crystallinity, electrode resistance, and spurious noise, which affect their performance in mobile devices.
Innovation Solution
A bulk acoustic resonator design featuring recess regions on electrodes and a piezoelectric layer with specific depth and width ratios, optimized to reduce spurious noise and improve resonance frequency sharpness, utilizing materials like molybdenum and aluminum nitride, and incorporating protective and seed layers to enhance performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional BAW resonator structure is used, then the device can operate at high frequency, but spurious noise occurs in proximity frequency regions and energy loss increases
Solution Approach 1:
The patent introduces recess regions with specific depth and width ratios at localized positions on the electrode surfaces. These recess regions create local variations in mass distribution and acoustic impedance, which selectively suppress spurious noise modes while preserving the fundamental resonance frequency. The local structural modification targets specific harmful acoustic modes without affecting the overall resonator operation.
Solution Approach 2:
The patent optimizes the depth-to-width ratio of recess regions to satisfy specific mathematical relationships involving natural logarithms and resonance frequency. By adjusting these geometric parameters within defined ranges, the resonator achieves optimal suppression of spurious noise while maintaining high-frequency operation. The parameter optimization creates a balance between fundamental mode performance and spurious mode suppression.
2Ease of manufacture
If a conventional BAW resonator structure is used, then the device can function with standard materials, but dielectric loss and electrode resistance cause energy loss
Solution Approach 1:
The patent introduces recess regions with optimized depth and width ratios that reduce the effective acoustic mass and improve the coupling between electrodes and piezoelectric material. This structural parameter optimization reduces energy loss mechanisms including dielectric loss and electrode resistance by improving the electric field distribution and reducing parasitic effects, achieving lower insertion loss while maintaining manufacturability with standard materials.
3Reliability
If the resonator structure is modified to reduce spurious noise, then the skirt characteristic improves, but the device complexity increases
Solution Approach 1:
The patent implements recess regions with specific geometric parameters on electrode surfaces to improve skirt characteristic and suppress spurious noise. The localized nature of these recess regions allows for targeted improvement of filter performance without requiring complex overall structural changes. The simple geometric modification (depth and width ratios) maintains manufacturing simplicity while achieving reliable spurious noise suppression.
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 design reduces spurious noise, sharpens the resonance frequency, and minimizes energy loss, thereby improving the skirt characteristic and reducing insertion loss in BAW filters.
Implementation Method 1
a piezoelectric layer disposed on an upper surface of the first electrode
Data Source
AI summary
A bulk acoustic resonator includes a first electrode disposed on an upper side of a substrate, a piezoelectric layer disposed on an upper surface of the first electrode, and a second electrode disposed on an upper surface of the piezoelectric layer, wherein an upper surface of at least one of the first electrode and the second electrode has a recess region, wherein a depth of the recess region is D, a width of the recess region is W, and a resonance frequency is F, and ln is a natural logarithm, and wherein [{ln(D*W)}/(−0.59*F)] is [[ln{0.008 (μm)2}]/{−0.59*(3.5 GHz)}] or more and [[ln{0.022 (μm)2}]/{−0.59*(3.5 GHz)}] or less.