MEMS Acceleration Sensor Beam Bonding via Recessed Electrodes
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Solution Overview
Problem
Conventional MEMS devices face issues with electrostatic attraction forces during anodic bonding, leading to deformation and bonding of beams to glass, especially in small chip designs, which affects the accuracy and reliability of capacitance-type acceleration sensors.
Innovation Solution
The introduction of a recess in the movable section and the use of dummy electrodes, along with extended electrodes connected to common potential, reduces the electrostatic attraction force, preventing beams from being bonded to the substrate and enhancing the sensor's resistance to disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If anodic bonding is used to bond electrode substrates to movable body, then bonding strength is improved, but electrostatic attraction force causes beam deformation and bonding to glass
Solution Approach 1:
A recess is formed in the movable body at the bonding interface, acting as an intermediary structure that reduces the bonding area between the movable body and electrode substrate. This recess configuration decreases the electrostatic attraction force during anodic bonding, preventing beam deformation while maintaining sufficient bonding strength through the reduced contact area.
2Volume of moving object
If chip size is reduced for small device, then device miniaturization is achieved, but electrostatic attraction force increases causing beam bonding to glass
Solution Approach 1:
The recess is strategically positioned at the bonding interface between the movable body and electrode substrate, creating a localized structural modification. This local quality change reduces the electrostatic attraction force specifically at the bonding area without affecting the overall device miniaturization, allowing small chip size while preventing beam bonding to glass.
3Strength
If bonding area between movable body and electrode substrate is increased, then bonding strength is improved, but electrostatic attraction force increases causing more beam deformation
Solution Approach 1:
The bonding interface is segmented by forming a recess in the movable body, dividing the bonding area into reduced contact zones. This segmentation decreases the overall bonding area and consequently reduces the electrostatic attraction force, preventing beam deformation while maintaining sufficient bonding strength through the distributed contact points.
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 configuration minimizes beam deformation and bonding to glass, improving the accuracy and reliability of the acceleration sensor by reducing electrostatic attraction forces and maintaining detection sensitivity.
Implementation Method 1
during the anodic bonding, depending on an applied voltage, an electrostatic attraction force is generated between glass and Si. With this electrostatic attraction force, a part of movable section 111 may be attracted to electrode substrate 122a side, and bonded thereto.
Data Source
AI summary
A MEMS device includes a movable section, a frame, a beam, and an electrode substrate. The frame surrounds a surrounding of the movable section. The beam extends from at least a part of the frame, and is connected to the movable section. The electrode substrate includes a fixed electrode, an extended electrode, and a substrate section. The fixed electrode is formed on the electrode substrate in at least a part of a region facing a swing section. The extended electrode is connected to the fixed electrode, and is formed on the electrode substrate in at least a part of a region facing the shaft.