Scandium-Doped Aluminum Nitride Piezoelectric Layers with C-Axis Orientation Control
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Solution Overview
Problem
Current methods struggle to selectively fabricate rare-earth element doped piezoelectric materials with specific C-axis orientations, such as compression-positive (CP) and compression-negative (CN) polarities, on the same substrate, which is essential for advanced resonator applications like coupled resonator filters and stacked thin film bulk acoustic resonators, due to difficulties in controlling the crystalline orientation during fabrication.
Innovation Solution
A method involving the use of scandium-doped aluminum nitride (AlScN) with specific atomic percentages of scandium, where the piezoelectric layers are grown using a deposition system with controlled gas flows and seed layers to achieve desired orientations, allowing for the formation of both CP and CN piezoelectric layers with enhanced piezoelectric coefficients and electromechanical coupling coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional deposition methods are used to grow piezoelectric layers, then the fabrication process is simple, but the C-axis orientation cannot be selectively controlled to achieve both CP and CN polarities on the same substrate
Solution Approach 1:
A seed layer is introduced as an intermediary between the substrate and the piezoelectric layer. This seed layer has a specific crystal structure that templates and directs the growth of the piezoelectric layer, enabling selective C-axis orientation. The seed layer acts as a mediator that transfers the desired orientation from the substrate to the piezoelectric material, solving the orientation control problem without requiring complex in-situ manipulation during deposition.
Solution Approach 2:
The invention controls the crystallographic orientation by changing parameters such as the composition and structure of the seed layer, deposition temperature, and gas flow conditions. By adjusting these parameters, the growth mechanism is influenced to favor specific C-axis orientations, enabling selective formation of CP and CN polarities on the same substrate while maintaining a relatively simple deposition process.
2Volume of moving object
If the piezoelectric layer thickness is reduced to achieve compact resonators, then the device size is reduced, but the mechanical stability and quality factor deteriorate
Solution Approach 1:
The invention uses composite structures consisting of multiple layers including seed layers, piezoelectric layers with specific orientations, and buffer layers. This composite approach allows thin piezoelectric layers to maintain mechanical stability because the layered composite structure provides structural support and stress distribution, preventing the deterioration of quality factor that would normally occur with reduced thickness.
Solution Approach 2:
Different regions of the resonator structure are assigned different properties: the piezoelectric layer is optimized for thinness to reduce size, while the seed layer and buffer layers are optimized for mechanical strength and structural integrity. This local differentiation of material properties and functions allows the overall device to be compact while maintaining reliability through strategically placed structural support elements.
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
Enables the fabrication of piezoelectric layers with tailored orientations, improving the performance of resonators by enhancing their piezoelectric properties and mechanical stability, thereby facilitating the development of compact and efficient acoustic devices.
Implementation Method 1
the piezoelectric layers are grown using a deposition system with controlled gas flows and seed layers
Implementation Method 2
rare-earth element doped piezoelectric materials either compress or expand upon application of a voltage. By convention, a rare-earth element doped piezoelectric material that compresses when a voltage of a certain polarity is applied is referred to as compression-positive (CP) material
Data Source
AI summary
A method of fabricating a rare-earth element doped piezoelectric material having a first component, a second component and the rare-earth element. The method includes: providing a substrate; initially flowing hydrogen over the substrate; after the initially flowing of the hydrogen over the substrate, flowing the first component to form the rare-earth element doped piezoelectric material over a surface of a target, the target comprising the rare-earth metal in a certain atomic percentage; and sputtering the rare-earth element doped piezoelectric material from the target on the substrate.