ZrO2-Buffered AlN Film Structure for Piezoelectric Orientation Control
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Solution Overview
Problem
Existing film structures with c-axis oriented aluminum nitride piezoelectric films face challenges in aligning the polarization direction perpendicular to the substrate and in-plane orientation, which affects dielectric and withstanding voltage characteristics.
Innovation Solution
A film structure is developed with a Si or SOI substrate, a ZrO2 buffer layer, and a c-axis oriented AlN piezoelectric film, where the polarization direction is aligned perpendicularly to the substrate and the orientation direction is aligned in the in-plane direction, using materials like Pt, Mo, W, Ru, or Cu electrodes, and optionally an SRO film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the piezoelectric film is grown with c-axis orientation perpendicular to the substrate, then the polarization direction can be aligned perpendicular to the substrate, but it is difficult to align the orientation direction in the in-plane direction along the substrate surface
Solution Approach 1:
A buffer film is introduced as an intermediary layer between the substrate and the piezoelectric film. The buffer film has a crystal structure that serves as a mediation interface, enabling the piezoelectric film to achieve both perpendicular polarization alignment and in-plane orientation alignment through epitaxial growth, which would be difficult to achieve directly on the substrate
Solution Approach 2:
The invention uses a composite structure consisting of the substrate, buffer film, and piezoelectric film. The buffer film is made from specific materials (such as AlN, GaN, or their mixed crystals) that have crystal structures compatible with both the substrate and the piezoelectric film, enabling dual-directional orientation alignment through the composite layered structure
2Reliability
If the piezoelectric film is oriented with polarization direction perpendicular to the substrate, then the device can achieve advantageous characteristics, but the dielectric constant and withstanding voltage characteristics are not optimized
Solution Approach 1:
The invention changes the crystal orientation parameters of the piezoelectric film by controlling the epitaxial growth process on the buffer film. Specifically, it achieves <11-20> orientation alignment in the in-plane direction while maintaining perpendicular polarization, which optimizes both the dielectric constant and withstanding voltage characteristics along with device performance
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 structure enables improved dielectric and withstanding voltage characteristics, allowing for the formation of electronic devices with enhanced piezoelectric properties and bulk acoustic wave filters or resonators.
Implementation Method 1
a piezoelectric film formed on the buffer film... a polarization direction of the piezoelectric film is preferentially oriented perpendicularly to the substrate
Implementation Method 2
to epitaxially grow the piezoelectric film... an orientation direction of the piezoelectric film is also aligned in an in-plane direction along an upper surface of the substrate
Data Source
AI summary
A film structure (10) includes a Si layer (12a), a ZrO2 layer (12b) which is a buffer film containing ZrO2 and formed on the Si layer (12a), and a piezoelectric film (11) formed on the ZrO2 layer (12b). The Si layer (12a) is an SOI layer in a Si substrate or an SOI substrate including a base made from a Si substrate, an insulating layer on the base, and an SOI layer made from a Si film on the insulating layer. A polarization direction of the piezoelectric film (11) is preferentially oriented perpendicularly to the substrate.