Tilted C-Axis Piezoelectric Bulk Layers With Low-Temperature Sputtering
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Solution Overview
Problem
Existing methods for producing bulk acoustic wave resonators with inclined c-axis hexagonal crystal structure piezoelectric materials, such as aluminum nitride (AlN) and zinc oxide (ZnO), face challenges in achieving uniform c-axis tilt angles, leading to variations in acoustic wave propagation characteristics and reduced performance in liquid/viscous media applications.
Innovation Solution
A two-step deposition process is employed, where the initial portion of the bulk layer is deposited at an off-normal angle to establish the desired c-axis tilt, followed by deposition at normal incidence to maintain the tilt, allowing for the production of bulk layers with uniform c-axis orientation and improved shear to longitudinal coupling ratios, without the need for a traditional seed layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high-temperature vapor phase epitaxy processes are used to grow tilted c-axis films, then the desired c-axis tilt can be achieved, but compatibility with microelectronic structures is compromised due to high deposition temperatures
Solution Approach 1:
The patent changes the deposition temperature parameter from high-temperature vapor phase epitaxy to low-temperature magnetron sputtering (below 300°C), enabling compatibility with microelectronic structures while maintaining the ability to produce tilted c-axis films through angular deposition geometry
Solution Approach 2:
The patent replaces the thermal field-based vapor phase epitaxy process with a physical field-based magnetron sputtering process, using plasma-enhanced physical vapor deposition to achieve tilted c-axis orientation without high temperature exposure
2Temperature
If low temperature deposition processes are used to ensure compatibility with microelectronic structures, then device compatibility is improved, but achieving uniform tilted c-axis orientation becomes difficult
Solution Approach 1:
The patent introduces asymmetric deposition geometry by positioning the substrate at a non-normal angle (e.g., 45 degrees) relative to the sputtering target, creating preferential growth directions that induce tilted c-axis orientation in the deposited AlN film while maintaining low deposition temperature
Solution Approach 2:
The patent adds the angular dimension to the deposition process by controlling the substrate tilt angle relative to the incident flux, enabling c-axis orientation control in a third dimension (angle) independent of temperature control
3Ease of manufacture
If standard sandwiched electrode configuration is used with perpendicular polarization axis, then device fabrication is simplified, but shear mode resonance cannot be excited
Solution Approach 1:
The patent creates a composite structure combining the tilted c-axis AlN piezoelectric layer with standard sandwiched electrode configuration, enabling the simple electrode geometry to excite shear mode resonance through the anisotropic piezoelectric properties of the tilted crystal 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 approach results in bulk layers with enhanced mechanical quality factor, reduced acoustic losses, and increased uniformity, enabling consistent performance across multiple resonator chips and improved efficiency in manufacturing.
Implementation Method 1
a first portion of a piezoelectric bulk material layer is deposited onto a substrate at a first angle; and a second portion of the piezoelectric bulk material layer is deposited onto the first portion at a second angle
Data Source
AI summary
A structure includes a substrate including a wafer or a portion thereof; and a piezoelectric bulk material layer comprising a first portion deposited onto the substrate and a second portion deposited onto the first portion, the second portion comprising an outer surface having a surface roughness (Ra) of 4.5 nm or less. Methods for depositing a piezoelectric bulk material layer include depositing a first portion of bulk layer material at a first incidence angle to achieve a predetermined c-axis tilt, and depositing a second portion of the bulk material layer onto the first portion at a second incidence angle that is smaller than the first incidence angle. The second portion has a second c-axis tilt that substantially aligns with the first c-axis tilt.