Smooth BAW Resonator Electrodes Through Sacrificial Cap Planarization
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Solution Overview
Problem
Existing methods for producing bulk acoustic wave (BAW) resonator devices face challenges such as initial surface roughness of electrodes, rounding of electrodes, and variations in c-axis tilt angle of AlN films, which affect the uniformity and performance of resonator chips.
Innovation Solution
The method involves generating smooth electrodes by depositing a sacrificial cap on each electrode, followed by a planarization film on the substrate and the sacrificial cap. A first planarization procedure removes portions of the planarization film and the sacrificial cap, preserving surface uniformity, and a second planarization procedure further reduces surface roughness and smooths the electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If standard electrode fabrication methods are used, then manufacturing process is simple, but electrode surface roughness is high and uniformity is poor
Solution Approach 1:
A planarization layer is deposited over the electrodes before the piezoelectric layer, creating a smooth surface in advance. This preliminary planarization action ensures that subsequent layers are deposited on a uniform surface, improving electrode surface uniformity without requiring complex post-fabrication processing.
Solution Approach 2:
The patent introduces a planarization layer as an intermediary between the electrodes and the piezoelectric layer. This intermediate layer mediates the surface roughness issue by providing a smooth interface for piezoelectric material deposition, effectively decoupling the electrode fabrication from the surface uniformity requirement.
2Manufacturing precision
If high temperature processes are used to grow tilted c-axis films, then c-axis tilt control is improved, but compatibility with microelectronic structures is reduced
Solution Approach 1:
The patent changes the temperature parameter from high temperature to low temperature deposition processes. This parameter change enables the growth of tilted c-axis AlN films at temperatures below 300°C, maintaining c-axis tilt control while ensuring compatibility with standard microelectronic structures that cannot withstand high temperatures.
Solution Approach 2:
The patent replaces high-temperature thermal processes with low-temperature deposition techniques. This substitution allows for precise control of c-axis tilt through deposition parameters rather than thermal treatment, preserving both crystal orientation control and compatibility with temperature-sensitive microelectronic components.
3Power
If longitudinal mode vibrations are used, then acoustic wave propagation is strong, but acoustic leakage into liquid media increases
Solution Approach 1:
The patent applies different vibration modes to different regions or aspects of the acoustic wave propagation. By utilizing shear horizontal mode vibrations specifically, the device achieves strong localized acoustic fields in the solid piezoelectric material while minimizing acoustic energy radiation into the surrounding liquid media, effectively creating different acoustic properties in different spatial regions.
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 results in electrode structures with a uniformly smooth surface, reduced short-range frequency variation, improved repeatability of resonator spurious content, and enhanced control over the c-axis angle of crystals in bulk material layers, leading to improved mechanical quality factor and coupling coefficient.
Implementation Method 1
Hexagonal crystal structure piezoelectric materials such as AlN and ZnO are of commercial interest due to their piezoelectric and electroacoustic properties
Implementation Method 2
an acoustic wave may embody either a bulk acoustic wave (BAW) propagating through the interior (or 'bulk') of a piezoelectric material
Data Source
AI summary
Resonator structures are provided, as well as methods and structures for generating smooth electrodes and electrode structures with a uniformly smooth surface.