Common Ceramic Substrate Acoustic Waves With Lower Energy Leakage
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Solution Overview
Problem
Existing acoustic wave filters, particularly bulk acoustic wave (BAW) filters, face challenges in achieving high quality factor (Q) values and efficient radio frequency (RF) signal filtering due to issues like energy leakage and substrate resistivity changes.
Innovation Solution
The development of a bulk acoustic wave resonator with a spinel substrate, which includes a ceramic substrate, a piezoelectric layer, electrodes, passivation layers, and a frame structure, addresses these challenges by providing a substrate with high resistivity and mechanical strength, thus enhancing RF performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional substrate is used in BAW filters, then manufacturing is simpler, but energy leakage occurs and quality factor (Q) values are low
Solution Approach 1:
The patent introduces an acoustic mirror as an intermediary layer between the substrate and the piezoelectric layer. This acoustic mirror acts as a mediator that reflects acoustic waves back into the resonator, preventing energy leakage into the substrate. The acoustic mirror consists of alternating layers of high and low acoustic impedance materials, creating a reflective barrier that improves the quality factor by containing acoustic energy within the active region.
Solution Approach 2:
The patent employs composite material structures, specifically the acoustic mirror composed of alternating high and low acoustic impedance layers (such as tungsten and silicon dioxide). This composite structure creates acoustic impedance mismatches that reflect acoustic waves, thereby reducing energy leakage. The frame structure also uses composite materials including metals (ruthenium, molybdenum, tungsten) and ceramics (silicon dioxide, silicon nitride) to provide both mechanical support and acoustic reflection.
2Reliability
If a ceramic substrate with high resistivity is used, then RF performance improves, but manufacturing complexity increases
Solution Approach 1:
The patent segments the substrate function into two distinct parts: the ceramic substrate provides mechanical support and electrical isolation (high resistivity), while the acoustic mirror provides acoustic reflection. This segmentation allows each component to be optimized independently - the ceramic substrate for electrical properties and the acoustic mirror for acoustic properties - simplifying the overall manufacturing approach despite the added layer.
Solution Approach 2:
The ceramic substrate serves multiple functions simultaneously: it provides mechanical support for the entire structure, electrical isolation due to its high resistivity, and a stable platform for the piezoelectric layer. This multi-functionality reduces the need for additional separate components, thereby managing manufacturing complexity while improving RF performance.
3Loss of energy
If acoustic mirrors and frame structures are added, then energy leakage is reduced, but device complexity increases
Solution Approach 1:
The patent merges the acoustic reflection function into the existing device structure by integrating the acoustic mirror at the substrate interface and the frame structure at the resonator perimeter. These structures combine mechanical support, acoustic reflection, and electrical isolation functions into a unified design, reducing the need for separate components and managing complexity while effectively preventing energy leakage.
Solution Approach 2:
The frame structure extends the acoustic reflection concept from the vertical dimension (acoustic mirror at substrate interface) to the horizontal dimension (frame around the resonator perimeter). This two-dimensional approach to acoustic confinement comprehensively prevents energy leakage in all directions, while the frame's integration with existing structures keeps the added complexity manageable.
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 use of a spinel substrate in BAW resonators improves the quality factor (Q) and mechanical strength, reduces energy leakage, and simplifies manufacturing processes, leading to more efficient RF signal filtering and better performance in RF applications.
Implementation Method 1
a piezoelectric layer positioned on the ceramic substrate, first and second electrodes positioned on opposing sides of the piezoelectric layer
Implementation Method 2
an acoustic mirror positioned between the ceramic substrate and the first electrode
Implementation Method 3
a frame structure along an edge of an active region of the bulk acoustic wave resonator
Data Source
AI summary
An acoustic wave component is disclosed. The acoustic wave component can include a bulk acoustic wave resonator and a surface acoustic wave device. The bulk acoustic wave resonator can include a first portion of a ceramic substrate, a first piezoelectric layer positioned on the ceramic substrate, and electrodes positioned on opposing sides of the first piezoelectric layer. The surface acoustic wave device can include a second portion of the ceramic substrate, a second piezoelectric layer positioned on the ceramic substrate, and an interdigital transducer electrode on the second piezoelectric layer.