Fluorine-Doped Silicon Oxide Layers for Temperature-Stable Acoustic Waves
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing acoustic wave devices, particularly those using silicon oxide films doped with boron as temperature compensation layers, fail to sufficiently improve the temperature dependence of frequency.
Innovation Solution
The use of fluorine-doped silicon oxide films as temperature compensation layers, which increase the peak wave number and decrease the half-value width of the Si-O stretching vibration, thereby improving the temperature frequency coefficient (TCF) of acoustic wave devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a SAW device is used, then the device can be miniaturized and integrated, but the Q factor is limited to less than 100 due to acoustic energy loss at the air-substrate interface
Solution Approach 1:
The patent converts the harmful acoustic energy loss at the air-substrate interface into a beneficial reflected wave by introducing a reflector structure. The reflector captures the acoustic energy that would otherwise be lost and redirects it back to the resonator, transforming the harmful boundary condition into a useful feedback mechanism that enhances resonance and increases the Q factor.
Solution Approach 2:
The patent implements a nested structure where the acoustic wave is trapped between the resonator and the reflector, creating an acoustic cavity. The acoustic energy is confined and repeatedly reflected within this nested configuration, allowing the energy to be retained and reused multiple times, thereby increasing the quality factor without requiring a larger device footprint.
2Ease of operation
If acoustic energy is allowed to escape at the air-substrate interface, then the device operation is simplified, but energy loss increases and Q factor decreases
Solution Approach 1:
Instead of preventing acoustic energy escape through complex encapsulation, the patent allows the energy to escape but immediately recaptures it using the reflector. This approach maintains operational simplicity while converting the energy loss into a useful reflected wave that enhances device performance.
3Area of stationary object
If the acoustic wave is confined to a small area, then device integration is improved, but acoustic energy loss at boundaries increases
Solution Approach 1:
The patent creates an acoustic cavity by nesting the resonator between the substrate and the reflector. This nested configuration effectively traps the acoustic wave within a compact volume, preventing energy loss at the boundaries by reflecting the waves back into the confined space rather than allowing them to escape.
Solution Approach 2:
The patent transforms the boundary condition from a harmful energy loss mechanism into a beneficial reflection mechanism. The reflector converts the acoustic energy that would be lost at the air-substrate interface into useful reflected energy that remains confined within the small device area, simultaneously achieving compact integration and energy retention.
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 fluorine-doped silicon oxide films significantly enhance the temperature frequency coefficient, reducing frequency variation with temperature and minimizing acoustic wave attenuation, thus improving the performance of acoustic wave devices.
Implementation Method 1
increase the peak wave number and decrease the half-value width of the Si-O stretching vibration
Implementation Method 2
a piezoelectric substrate, an interdigital electrode that is arranged on the piezoelectric substrate and excites an acoustic wave
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The present invention provides an acoustic wave device including: a piezoelectric substrate 20 or a piezoelectric film 34, electrodes 22, 32, and 36 located on the piezoelectric substrate 20 or located so as to sandwich the piezoelectric film 34, and silicon oxide films 26, and 38 located so as to cover the comb-shaped electrode 22 on the piezoelectric substrate 20 or located in a region in which the lower electrode 32 and the upper electrode 36, which sandwich the piezoelectric film 34, face each other, and is doped with an element or molecule displacing O in a Si-O bond.