Anodic Bonding Voltage Pattern for MEMS Optical Sealing
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Solution Overview
Problem
The existing methods for sealing MEMS elements on silicon boards using anodic bonding result in impurities like sodium being precipitated on the glass surface, reducing light transmittance and making it difficult to clean, especially for optical elements.
Innovation Solution
A sealed structure is created by forming a voltage applying pattern around a recessed portion on the silicon board or glass plate, allowing anodic bonding to occur only at the bonding region, preventing impurities from reaching the nonbonding area, and using a metal thin film for efficient bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If anodic bonding is performed by applying high voltage to the entire glass plate surface, then bonding strength is improved, but impurity precipitation on the glass surface increases
Solution Approach 1:
The glass plate surface is segmented into bonding regions and nonbonding regions. The voltage applying pattern is configured to apply high voltage only to the bonding regions (peripheral portions) while excluding the nonbonding regions (central portions). This segmentation allows strong bonding where needed while preventing impurity precipitation in areas where bonding is not required, thus resolving the contradiction between bonding strength and impurity precipitation.
Solution Approach 2:
Different regions of the glass plate are given different properties: bonding regions receive high voltage treatment for strong adhesion, while nonbonding regions are excluded from voltage application to maintain purity and prevent impurity precipitation. This local differentiation of quality allows the system to achieve strong bonding where necessary without the harmful side effect of impurity precipitation in areas where bonding is not needed.
2Illumination intensity
If sodium is removed from the glass surface by cleaning, then light transmittance is improved, but the process becomes complex and transmittance recovery is difficult
Solution Approach 1:
Instead of allowing impurity precipitation and then attempting to remove it through cleaning, the invention takes preliminary action by designing the voltage applying pattern to prevent impurity precipitation in the first place. By excluding nonbonding regions from high voltage application, sodium and other impurities are prevented from migrating to the glass surface in areas where they would interfere with light transmittance, thereby maintaining high transmittance without requiring complex cleaning processes.
3Manufacturing precision
If voltage is applied to the entire glass plate, then bonding coverage is improved, but light transmittance of optical elements is reduced
Solution Approach 1:
The voltage application is segmented into bonding regions (peripheral portions) and nonbonding regions (central portions containing optical elements). The voltage applying pattern is specifically designed to confine high voltage application to the bonding regions while excluding the central regions where optical elements are located. This ensures complete bonding coverage where needed while preserving light transmittance in areas where optical elements require unobstructed light passage.
Solution Approach 2:
Different regions of the glass plate are treated with different voltage application characteristics: peripheral bonding regions receive high voltage for complete bonding coverage, while central nonbonding regions are excluded from voltage application to maintain high light transmittance for optical elements. This local quality differentiation resolves the contradiction between achieving comprehensive bonding coverage and preserving optical performance.
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 method effectively prevents impurity precipitation on nonbonding regions, maintaining light transmittance and simplifying the bonding process by reducing steps and ensuring efficient production.
Implementation Method 1
a wall portion surrounding the recessed portion is anodically bonded to the glass plate or the silicon board by applying a high voltage to the voltage applying pattern
Implementation Method 2
by applying a high voltage in a state of bringing an anode into contact with a lower face (back face) of the silicon board and bringing a cathode into contact with an upper face of the support plate, there poses a problem that in a procedure of softening glass including movable ions by heating the silicon board and simultaneously bonding the silicon board and the glass by an electrostatic attraction force
Data Source
AI summary
According to a sealed structure 60 constituted by anodically bonding a silicon board 20 and a glass plate 40, an upper opening of a recessed portion 22 is sealed in an airtight state by the glass plate 40 by bonding an upper face of a wall portion 26 to the glass plate 40. A voltage applying pattern 70 is formed to surround a light transmitting region to which an optical conversion element 24 is opposed. Further, the voltage applying pattern 70 functions as a cathode pattern applied with a voltage by being brought into contact with a lower face of the cathode plate 50.