MEMS Resonator Cover Structure for Vacuum-Sealed Eutectic Bonding
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The diffusion of silicon into the eutectic layer during eutectic bonding in MEMS resonance devices reduces the vacuum degree in the vibration space, leading to degradation of vibration characteristics such as the Q value of the resonator.
Innovation Solution
A resonance device with a first substrate and a second substrate bonded by a bonding part, where the second substrate has a first oxide film with a through hole along the periphery of the vibration space containing a first metal layer, which blocks gases like helium from entering the vibration space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an oxide film is formed on the silicon substrate to suppress silicon diffusion into the eutectic layer, then silicon diffusion is prevented, but gas such as helium can pass through the oxide film and enter the vibration space, reducing the vacuum degree
Solution Approach 1:
The invention uses a composite structure consisting of an oxide film layer and a metal layer. The oxide film suppresses silicon diffusion while the metal layer blocks gas permeation. This composite material approach combines the advantages of both materials to simultaneously prevent silicon diffusion and gas ingress into the vibration space.
Solution Approach 2:
The metal layer is selectively formed only in specific regions where gas permeation is a concern, such as around through-holes or at the bonding interface. This localized application of the metal layer provides targeted protection against gas ingress while maintaining the transparency of the oxide film in other areas.
2Strength
If eutectic bonding is performed to bond the upper substrate to the support frame, then strong bonding is achieved, but silicon diffuses into the eutectic layer causing degradation of vibration characteristics
Solution Approach 1:
The oxide film acts as an intermediary barrier layer between the silicon substrate and the eutectic bonding interface. It prevents direct contact and diffusion between silicon and the eutectic layer while still allowing the bonding process to proceed effectively, thus maintaining both bonding strength and vibration characteristics.
Solution Approach 2:
The combination of oxide film and metal layer creates a composite barrier structure that maintains bonding strength while preventing silicon diffusion. The oxide film provides chemical stability and the metal layer provides mechanical strength and diffusion barrier properties.
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 suppresses the reduction in vacuum degree, maintaining the vibration characteristics of the resonator by preventing gas ingress through the oxide film.
Implementation Method 1
it is known that an oxide film such as a silicon dioxide (SiO2) film allows a gas such as helium to pass therethrough. Therefore, the degree of vacuum of a vibration space of a resonator may be reduced due to entry of helium gas from the oxide film
Implementation Method 2
the piezoelectric resonator and the upper substrate are bonded to each other through eutectic bonding of a first metal layer formed of a metal having aluminum (Al) as a main component and a second metal layer formed of a metal having germanium (Ge) as a main component
Implementation Method 3
a method has been proposed for suppressing diffusion of silicon into the eutectic layer by forming an oxide film such as a silicon dioxide (SiO2) film on the silicon substrate
Data Source
AI summary
A resonance device that includes a MEMS substrate that includes a resonator, a top cover having a silicon oxide film on a surface thereof that faces the MEMS substrate, and a bonding part that bonds the MEMS substrate and the top cover to each other so as to seal a vibration space of the resonator. The silicon oxide film includes a through hole that is formed along at least part of the periphery of the vibration space when the top cover is viewed in a plan view and that penetrates to a surface of the top cover. The through hole includes a first metal layer.