BAW Resonator Film Stack for Stable Temperature Compensation
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Solution Overview
Problem
Piezoelectric thin film resonators face deterioration in characteristics due to oxidation and moisture absorption of silicon oxide films used as temperature compensation, leading to changes in resonant frequency and quality factors during high-temperature reliability tests.
Innovation Solution
Incorporating a non-oxygen-containing insulating film between the silicon oxide film and electrodes, and an additional film with higher acoustic impedance than the silicon oxide film, to prevent oxidation and moisture absorption, thereby maintaining the resonator's characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a silicon oxide film is used as a temperature compensation film, then temperature compensation is improved, but oxidation and moisture absorption cause deterioration of resonator characteristics
Solution Approach 1:
A non-oxygen-containing insulating film is introduced as an intermediary layer between the silicon oxide temperature compensation film and the electrodes. This mediator prevents direct contact between the silicon oxide film and electrodes, blocking oxidation of electrodes and preventing moisture absorption by the silicon oxide film, thereby maintaining resonator characteristics while preserving temperature compensation functionality
Solution Approach 2:
The patent creates a composite structure combining silicon oxide film (for temperature compensation) with non-oxygen-containing insulating film (for protection). This composite material system allows the silicon oxide film to perform its temperature compensation function while the insulating film layer protects it from harmful environmental factors, resolving the contradiction between temperature compensation performance and reliability
2Temperature
If the silicon oxide film contacts the electrodes, then temperature compensation is achieved, but oxidation of electrodes occurs through oxygen diffusion
Solution Approach 1:
The non-oxygen-containing insulating film serves as a mediator that physically separates the silicon oxide film from the electrodes. This intermediary layer blocks oxygen diffusion from the silicon oxide film to the electrodes, preventing oxidation while allowing the silicon oxide film to maintain its temperature compensation function
Solution Approach 2:
The non-oxygen-containing insulating film creates an inert environment between the silicon oxide film and electrodes. By eliminating oxygen contact in this intermediate layer, the patent prevents oxidation reactions while preserving the temperature compensation capabilities of the silicon oxide film
3Temperature
If the silicon oxide film is exposed to moisture, then temperature compensation function is maintained, but hygroscopic properties cause film quality degradation
Solution Approach 1:
The non-oxygen-containing insulating film acts as a protective intermediary that shields the silicon oxide film from moisture exposure. This mediator layer prevents water molecules from reaching and being absorbed by the hygroscopic silicon oxide film, maintaining film quality while allowing temperature compensation to continue
Solution Approach 2:
The patent uses a thin non-oxygen-containing insulating film as a protective shell over the silicon oxide film. This thin film barrier effectively prevents moisture penetration while maintaining the overall device structure and allowing the silicon oxide film to perform its temperature compensation function without direct moisture exposure
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 solution effectively reduces the deterioration of resonator characteristics by preventing oxidation and moisture absorption, improving temperature compensation and resonance performance.
Implementation Method 1
the lower electrode and the upper electrode are oxidized by oxygen contained in the silicon oxide film
Implementation Method 2
an additional film located at an opposite side of the silicon oxide film from the non-oxygen-containing insulating film and made of a material different from a material of the silicon oxide film
Implementation Method 3
Piezoelectric thin film resonators using Bulk Acoustic Wave (BAW)
Data Source
AI summary
An acoustic wave device includes: a substrate; a piezoelectric film located on the substrate; a lower electrode and an upper electrode facing each other across at least a part of the piezoelectric film; a silicon oxide film located at an opposite side of at least one of the lower electrode and the upper electrode from the piezoelectric film; a first insulating film that is located between the at least one of the lower electrode and the upper electrode and the silicon oxide film and includes a non-oxygen-containing material; and an additional film located at an opposite side of the silicon oxide film from the first insulating film and made of a material different from a material of the silicon oxide film and a material of the first insulating film.