Tilted C-Axis Piezoelectric Bulk Layers With Uniform Film Deposition
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Solution Overview
Problem
Existing methods for depositing piezoelectric films with a tilted c-axis orientation face challenges in achieving uniformity and consistency of c-axis tilt angles, leading to variations in acoustic wave propagation characteristics, which hinder the production of high-performance bulk acoustic wave resonators, especially for use in liquid or viscous media.
Innovation Solution
A two-step deposition process is employed, where a first portion of the bulk layer is deposited at an off-normal angle to establish the desired c-axis tilt, followed by a second portion at normal incidence, allowing the bulk layer to adopt the established tilt without the need for a seed layer, thereby ensuring uniform c-axis orientation across large areas.
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 such as metal electrodes or traces 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 atomic layer deposition (below 300°C), enabling compatibility with microelectronic structures while maintaining the ability to produce tilted c-axis films through controlled deposition angles
Solution Approach 2:
The patent replaces the thermal field-based vapor phase epitaxy process with a deposition process that uses controlled deposition angle (off-normal incidence) to achieve c-axis tilt, substituting thermal control with geometric control
2Ease of manufacture
If conventional single-step deposition is used, then the process is simple, but uniform c-axis tilt distribution across large areas cannot be achieved
Solution Approach 1:
The patent segments the deposition process into multiple steps with different deposition angles, where the first step establishes the desired c-axis tilt and subsequent steps maintain uniformity across large substrate areas, resolving the contradiction between process simplicity and tilt uniformity
3Stability of the object's composition
If the c-axis is oriented perpendicular to the film plane, then thermodynamic stability is achieved, but shear mode vibration cannot be excited effectively for liquid media sensing
Solution Approach 1:
The patent introduces asymmetry by tilting the c-axis away from the perpendicular orientation, creating a non-standard crystal orientation that enables shear mode vibration excitation while maintaining controlled stability through the specific tilt angle achieved by off-normal deposition
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 method achieves a uniform c-axis tilt distribution, enhancing the shear-to-longitudinal coupling ratio, reducing surface roughness, and improving mechanical strength, resulting in consistent performance of bulk acoustic wave resonators with reduced acoustic losses and manufacturing efficiency.
Implementation Method 1
a first portion of a piezoelectric bulk material layer is deposited onto a substrate at a first deposition angle; a second portion of the piezoelectric bulk material layer is deposited onto the first portion at a second deposition 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.