MEMS Switch Capping with Platinum-Group Contacts
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Solution Overview
Problem
MEMS switches with low actuation forces are prone to conductivity degradation due to insulative surface contamination layers, which reduces their effectiveness and lifetime, as they cannot break through these layers effectively.
Innovation Solution
A hermetically capped MEMS switch is fabricated using a platinum-series based material, such as ruthenium, with a conductive passivation layer like ruthenium dioxide, and a gettering system to minimize contamination, ensuring reliable electrical connections and prolonged switch performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If electrostatically actuated MEMS switches use low actuation forces, then energy consumption is reduced, but conductivity is degraded due to insulative surface contamination layers
Solution Approach 1:
The patent changes the material parameter of the contact from conventional metals to platinum-series materials (ruthenium, rhodium, palladium, osmium, or iridium), which have different chemical properties that resist forming insulative oxidation layers. This material substitution allows the contact to maintain conductivity even under low actuation forces where larger switches would normally break through contamination layers.
Solution Approach 2:
The patent employs composite material structures including platinum-series materials combined with conductive oxides (such as ruthenium dioxide) or other conductive coatings. These composite structures provide both mechanical durability and electrical conductivity while resisting the formation of insulative contamination layers, thereby maintaining reliability under low actuation forces.
2Ease of manufacture
If conventional metal contacts are exposed to oxygen and environmental contaminants, then manufacturing is simplified, but insulative surface contamination layers form that reduce conductivity
Solution Approach 1:
The patent creates an inert or controlled atmosphere environment by hermetically sealing the MEMS switch in a package filled with inert gas (such as nitrogen or noble gases) or vacuum. This prevents oxygen and environmental contaminants from reaching the platinum-series contact material, thereby preventing the formation of insulative oxidation layers while maintaining manufacturing simplicity.
Solution Approach 2:
The patent converts the naturally oxidizing property of metals, which normally creates harmful insulative layers, into a beneficial feature by using platinum-series materials that form conductive oxides (particularly ruthenium dioxide) instead of insulative ones. The oxidation process that would normally degrade conductivity now creates a conductive passivation layer that protects the underlying metal.
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 platinum-series based contacts with conductive passivation and gettering system effectively mitigate insulative surface contamination, maintaining conductivity and extending the switch's operational lifetime by preventing the formation of insulative layers.
Implementation Method 1
the contact is oxidized at a first temperature and pressure, and the cap is hermetically sealed at a second, higher temperature and pressure
Implementation Method 2
a hermetically capped MEMS switch that includes a substrate and a platinum-series contact seals a cap to the substrate over the contact in an oxygenated environment
Data Source
Figure 1~2B
Figure 3A~3B
Figure 4
AI summary
A MEMS switch with a platinum-series contact is capped through a process that also passivates the contact by controlling, over time, the amount of oxygen in the environment, pressures and temperatures. Some embodiments passivate a contact in an oxygenated atmosphere at a first temperature and pressure, before hermetically sealing the cap at a higher temperature and pressure. Some embodiments hermetically seal the cap at a temperature below which passivating dioxides will form, thus trapping oxygen within the volume defined by the cap, and later passivate the contact with the trapped oxygen at a higher temperature.