Composite Substrate Bonding Interface for Low-Spurious Piezoelectric Devices
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Solution Overview
Problem
Conventional piezoelectric devices with composite substrates face issues of spurious noise due to bulk wave reflection at the bonding interface between the piezoelectric and sapphire substrates, which affects their performance and reliability.
Innovation Solution
A composite substrate is created by directly bonding a piezoelectric substrate with a sapphire substrate, where the oxygen-to-aluminum atomic ratio at the bonding surface is less than 1.5, achieved through heat-treating the sapphire substrate in a reducing atmosphere or vacuum, to introduce an oxygen deficiency without compromising bonding strength, and using direct diffusion bonding to enhance the interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If direct bonding is used between piezoelectric substrate and sapphire substrate, then bonding strength and heat resistance are improved, but bulk wave reflection at the bonding interface causes spurious noise
Solution Approach 1:
The patent applies local quality by creating a region with disrupted crystallinity specifically at the bonding interface through hydrogen ion implantation. This localized modification reduces bulk wave reflection and spurious noise only at the critical bonding region without affecting the overall properties of the substrates. The crystallinity disruption is confined to a shallow depth from the bonding surface, allowing the bulk materials to maintain their excellent mechanical and thermal properties.
Solution Approach 2:
The patent changes physical parameters by controlling the implantation conditions of hydrogen ions (energy, dose, angle) to achieve the desired level of crystallinity disruption. By adjusting these parameters, the patent optimizes the balance between reducing spurious noise and maintaining bonding strength. The oxygen-to-aluminum atomic ratio is also controlled as a key parameter to achieve the optimal crystallinity state at the bonding interface.
2Object-generated harmful factors
If hydrogen ion implantation is used to reduce spurious noise, then bulk wave reflection is suppressed, but bonding strength may be compromised
Solution Approach 1:
The patent carefully controls the hydrogen ion implantation parameters (energy, dose, angle) to achieve the optimal balance between noise suppression and bonding strength. By adjusting these parameters, the patent ensures that crystallinity is disrupted enough to reduce spurious noise while maintaining sufficient bonding strength for reliable device operation.
Solution Approach 2:
The patent creates a composite structure at the bonding interface by combining regions with different crystallinity states. The bonding interface region has disrupted crystallinity for noise suppression, while the bulk regions maintain their original excellent properties. This composite approach allows simultaneous achievement of low spurious noise and high bonding strength.
3Object-generated harmful factors
If oxygen deficiency is introduced in the bonding surface region, then bulk wave reflection is reduced, but material stability may be affected
Solution Approach 1:
The patent applies local quality by introducing oxygen deficiency specifically in the bonding surface region through controlled hydrogen ion implantation, while the bulk sapphire substrate maintains its stoichiometric composition and stability. This localized modification ensures that material stability is preserved in the bulk while achieving reduced bulk wave reflection at the interface.
Solution Approach 2:
The patent controls the degree of oxygen deficiency by adjusting hydrogen ion implantation parameters and subsequent heat treatment conditions. By optimizing these parameters, the patent achieves the right balance between reducing bulk wave reflection and maintaining material stability, ensuring the oxygen-to-aluminum atomic ratio remains within acceptable limits for device reliability.
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 effectively reduces bulk wave reflection, improving noise suppression and maintaining high bonding strength between the substrates, thus enhancing the performance and reliability of piezoelectric devices.
Implementation Method 1
a step of heat-treating the sapphire substrate in a reducing atmosphere or in a vacuum
Implementation Method 2
heat-treating the sapphire substrate in a reducing atmosphere or in a vacuum
Implementation Method 3
using direct diffusion bonding to enhance the interface
Data Source
AI summary
A composite substrate of the present disclosure is a composite substrate comprising a piezoelectric substrate and a sapphire substrate which are directly bonded, wherein the ratio of the number of oxygen atoms to the number of aluminum atoms in the bonding surface region including the bonding surface of the sapphire substrate bonded to the piezoelectric substrate is less than 1.5. The piezoelectric device of the present disclosure comprises the composite substrate. A method for manufacturing the composite substrate of the present disclosure comprises a step of preparing a piezoelectric substrate and a sapphire substrate, a step of heat-treating the sapphire substrate in a reducing atmosphere or in a vacuum, and a step of directly bonding the piezoelectric substrate to the sapphire substrate.