MEMS Sensor Eutectic Bonding with Polycrystalline Silicon Stop
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Solution Overview
Problem
Existing MEMS sensors face challenges in achieving miniaturization and robust bonding between substrates while preventing electrode damage during the bonding process, particularly when using metal bonding techniques.
Innovation Solution
The MEMS sensor employs eutectic bonding between an aluminum layer on the first substrate and a germanium layer on the second substrate, with a polycrystalline silicon layer on the stop member to enhance bonding strength and prevent electrode attachment, using a method that includes forming a cavity, an electrode, and stop member on the substrates, and then bonding them with eutectic bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If metal bonding is used to bond device-side substrate and cover-side substrate, then miniaturization of MEMS sensors is achieved, but electrode damage during bonding process becomes more severe
Solution Approach 1:
A polycrystalline silicon layer is introduced as an intermediary between the electrode and the stop member. This intermediate layer prevents direct contact and potential damage between the electrode and the stop member during the bonding process, while still allowing the stop member to fulfill its function of preventing electrode displacement toward the cover-side substrate.
Solution Approach 2:
The stop member is designed with different surface characteristics: a first surface facing the electrode with a first surface roughness and a second surface facing the cover-side substrate with a second surface roughness. By controlling the surface roughness locally at different interfaces, the bonding strength is enhanced at the metal layer interface while protecting the electrode from damage at the electrode-stop member interface.
2Strength
If bonding strength between substrates is enhanced, then substrate bonding reliability is improved, but electrode attachment to stop member increases causing damage
Solution Approach 1:
The polycrystalline silicon layer serves as a mediator that allows strong bonding at the metal layer interface while preventing direct bonding between the electrode and stop member. This intermediate layer has appropriate surface properties that promote bonding strength where needed while preventing unwanted electrode attachment.
Solution Approach 2:
Different surface roughness values are applied at different locations of the stop member: the first surface has a roughness optimized for preventing electrode attachment, while the second surface has a roughness optimized for enhancing bonding strength with the cover-side substrate. This local differentiation resolves the contradiction between bonding strength and electrode protection.
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 achieves strong and reliable bonding between substrates, enabling miniaturization of MEMS sensors while protecting the electrode from damage, thereby improving the overall performance and durability of the sensor.
Implementation Method 1
The MEMS sensor employs eutectic bonding between an aluminum layer on the first substrate and a germanium layer on the second substrate
Implementation Method 2
a polycrystalline layer is formed on the stop member... the polycrystalline layer is formed between the second substrate and the second metal layer
Data Source
AI summary
The present disclosure provides a MEMS sensor. The MEMS sensor includes a first substrate having a cavity and a second substrate bonded to the first substrate. The first substrate is provided with an electrode movably disposed in the cavity and a sealed member coupling to the second substrate. The second substrate is provided with a stop member for restricting a movement of the electrode toward the second substrate and a sealing member coupling to the sealed member. The sealed member is formed by a first metal layer on the first substrate. The sealing member is formed by a second metal layer on the second substrate. A polycrystalline layer is formed on the stop member. The polycrystalline layer is disposed between the second substrate and the second metal layer.