Acoustic Resonator Cap Insulation to Reduce RF Coupling Loss
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Solution Overview
Problem
Conventional electronic devices using bulk acoustic wave resonators suffer from degraded frequency characteristics due to RF signal coupling between substrates, leading to increased pass loss in bandpass filters.
Innovation Solution
The implementation of a thin film of high-resistivity material, such as silicon dioxide or aluminum oxide, on the bottom surface of the cap substrate, and/or using a high-resistivity material for the cap substrate itself, to prevent RF signal coupling and improve frequency characteristics by reducing bypass paths in the electronic device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional electronic device with low-resistivity cap substrate is used, then the device structure is simple and manufacturing is easier, but RF signal coupling occurs between substrates causing increased pass loss
Solution Approach 1:
A thin film of high-resistivity material (such as silicon dioxide or aluminum oxide) is introduced as an intermediary layer between the piezoelectric substrate and the low-resistivity cap substrate. This intermediate layer acts as a barrier that prevents RF signal coupling while maintaining the overall device structure and manufacturing process
Solution Approach 2:
The electrical resistivity parameter of the cap substrate is changed by forming a thin film of high-resistivity material on its bottom surface. This parameter change transforms the substrate from being RF-conductive to RF-insulating, thereby preventing signal coupling and reducing pass loss without changing the mechanical structure
2Reliability
If a thin film of high-resistivity material is formed on the cap substrate, then frequency characteristics are improved by reducing bypass paths, but manufacturing process becomes more complex
Solution Approach 1:
The manufacturing process utilizes existing parameter changes in the fabrication sequence - the high-resistivity material film is formed during the same processing steps when other thin films are deposited, leveraging existing equipment and process parameters to minimize additional manufacturing complexity
Solution Approach 2:
The thin film of high-resistivity material is formed preliminarily during the fabrication process before final assembly. This preliminary action ensures that the RF-blocking property is built into the structure during manufacturing, avoiding the need for post-processing modifications
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 solution effectively reduces pass loss and maintains attenuation levels within the passband, while ensuring minimal degradation outside the passband, thereby enhancing the frequency characteristics of the electronic device.
Implementation Method 1
a thin film of high-resistivity material being formed on at least a portion of the bottom surface of the second substrate to prevent a radio frequency (RF) signal emitted by the electronic circuit from being coupled to the second substrate
Data Source
AI summary
An acoustic resonator that prevents a radio frequency (RF) signal from being coupled to a cap substrate. An electronic device includes a first substrate (device substrate) of piezoelectric material having a top surface on which an electronic circuit including a film bulk acoustic resonator is formed, a second substrate (cap substrate) of low-resistivity material, a bottom surface of which is disposed opposing the top surface of the first substrate, and a side wall disposed between the top surface of the first substrate and the bottom surface of the second substrate. The side wall defines a cavity together with the top surface of the first substrate and the bottom surface of the second substrate, the cavity internally including the electronic circuit. A thin film of high-resistivity material is formed on at least a portion of the bottom surface of the second substrate to prevent an RF signal emitted from the electronic circuit from being coupled to the second substrate.