FBAR Resonator Thickness Layout for Multi-Band RF Filters
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Solution Overview
Problem
The increasing complexity of RF filters in mobile devices due to multiple operating frequencies requires multiple distinct filters, which is costly and inefficient, especially with the advent of 5G technology, and existing piezoelectric materials like polycrystalline AlN deposited via sputtering have poor quality and difficulty in thickness control.
Innovation Solution
The formation of high-frequency FBAR devices using epitaxially grown piezoelectric elements, where a piezoelectric group III-V material stack is deposited in a trench and overgrown onto STI material, creating distinct thicknesses for multiple resonant frequencies on a single substrate, utilizing a combination of low and high-temperature epitaxial depositions and potentially including sputtered layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple distinct RF filters are used for multiple operating frequencies, then filtering performance is improved, but device complexity and cost increase
Solution Approach 1:
The patent combines multiple resonator structures (first resonator with first piezoelectric layer and second resonator with second piezoelectric layer) onto a single substrate, allowing multiple operating frequencies to be filtered simultaneously or selectively. This merging approach reduces the total number of separate filter devices needed while maintaining the required filtering performance for multiple bands and modes of communication.
Solution Approach 2:
The shared electrode structure serves multiple functions: it acts as a common electrode for both the first and second resonators, provides electrical connection for multiple resonant frequencies, and enables the system to handle multiple operating frequencies within a single integrated filter device, thereby reducing overall device complexity.
2Ease of manufacture
If polycrystalline AlN is deposited via sputtering, then manufacturing process is simple, but film quality and thickness control are poor
Solution Approach 1:
The patent employs low-temperature epitaxial deposition to grow the piezoelectric layers, which provides superior thickness control and film quality compared to conventional sputtering methods. By changing the deposition parameters (temperature and growth method), the invention achieves precise control over the piezoelectric layer thickness, enabling accurate resonant frequency control while maintaining manufacturing feasibility.
3Device complexity
If a single piezoelectric layer is used, then device structure is simple, but multiple resonant frequencies cannot be achieved
Solution Approach 1:
The patent divides the piezoelectric structure into separate first and second piezoelectric layers, each with different thicknesses, deposited on different portions of the substrate. This segmentation allows each layer to resonate at different frequencies, enabling the filter to handle multiple operating frequencies while maintaining a relatively simple integrated structure on a single substrate.
Solution Approach 2:
Different piezoelectric layers are deposited in different regions or portions of the substrate, with each layer having specific thickness characteristics tailored for its intended resonant frequency. This local differentiation of piezoelectric layer properties enables multiple resonant frequencies to be achieved within a single integrated device 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 enables the creation of higher quality RF filters with multiple resonant frequencies on a single substrate, improving filter performance and reducing costs by achieving precise thickness control and enhanced film quality.
Implementation Method 1
a piezoelectric group III-V material stack is deposited in a trench and overgrown onto STI material
Implementation Method 2
potentially including sputtered layers
Implementation Method 3
An FBAR or TFBAR generally includes a piezoelectric material located between two electrodes
Data Source
AI summary
Techniques are disclosed for forming high frequency film bulk acoustic resonator (FBAR) devices having multiple resonator thicknesses on a common substrate. A piezoelectric stack is formed in an STI trench and overgrown onto the STI material. In some cases, the piezoelectric stack can include epitaxially grown AlN. In some cases, the piezoelectric stack can include single crystal (epitaxial) AlN in combination with polycrystalline (e.g., sputtered) AlN. The piezoelectric stack thus forms a central portion having a first resonator thickness and end wings extending from the central portion having a different resonator thickness. Each wing may also have different thicknesses. Thus, multiple resonator thicknesses can be achieved on a common substrate, and hence, multiple resonant frequencies on that same substrate. The end wings can have metal electrodes formed thereon, and the central portion can have a plurality of IDT electrodes patterned thereon.