MEMS Acoustic Resonator Passivation for Liquid-Phase Functionalization
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Solution Overview
Problem
Acoustic resonator devices face challenges in stable operation in liquid environments due to electrode corrosion and compatibility issues with functionalization materials, leading to degraded performance in biosensing and biochemical sensing applications.
Innovation Solution
A micro-electromechanical system (MEMS) resonator device with a passivation structure comprising a hermeticity layer and an interface layer, including a dielectric material with low water vapor transmission and a hydroxylated oxide or noble metal surface, respectively, to protect electrodes and facilitate chemical binding of functionalization materials, such as self-assembled monolayers (SAMs), is developed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If electrodes are exposed in liquid environments for functionalization, then chemical binding of functionalization materials is enabled, but electrode corrosion occurs leading to degraded performance
Solution Approach 1:
The electrode structure is segmented into multiple functional layers: a reactive metal layer (Al, Al alloy, or Ag) providing electrical functionality, and a separate noble metal layer (Au, Ag, Pt, Pd, Rh, or Ir) providing corrosion resistance. This segmentation allows each layer to perform its specific function independently, resolving the contradiction between reactivity and stability.
Solution Approach 2:
The electrode is constructed as a composite material system combining reactive metal and noble metal layers. The reactive metal provides the necessary electrical properties and cost-effectiveness, while the noble metal layer provides corrosion resistance in liquid environments. This composite structure enables both functionalization capability and long-term reliability.
2Reliability
If hermeticity layer is added to protect electrodes, then corrosion resistance is improved, but chemical binding capability with functionalization materials deteriorates
Solution Approach 1:
Different regions of the electrode structure have different properties: the hermeticity layer (oxide, nitride, or oxynitride material) provides corrosion protection where needed, while the noble metal layer provides chemical binding capability in contact with liquid. This local differentiation of properties resolves the contradiction between protection and functionality.
Solution Approach 2:
The noble metal layer acts as an intermediary between the hermeticity layer and the liquid environment. It provides a surface that is both protected from corrosion by the hermeticity layer and capable of chemical binding with functionalization materials, thus mediating between the conflicting requirements of protection and reactivity.
3Ease of manufacture
If reactive metal electrodes are used, then cost and electrical performance are improved, but compatibility with liquid environments deteriorates
Solution Approach 1:
The electrode uses a composite structure combining reactive metal (Al, Al alloy, or Ag) for cost-effectiveness and electrical performance with a noble metal layer (Au, Ag, Pt, Pd, Rh, or Ir) for corrosion resistance. This composite approach allows the system to benefit from both the low cost and good electrical properties of reactive metals and the environmental stability of noble metals.
Solution Approach 2:
The noble metal layer creates an inert protective environment around the reactive metal electrode, shielding it from corrosive liquid environments. This inert barrier allows the reactive metal to maintain its cost-effectiveness and electrical performance without suffering from corrosion in liquid media.
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 enables stable operation of acoustic resonator devices in liquid environments while maintaining proper chemical binding and functionalization, enhancing their performance and durability for biosensing and biochemical sensing applications.
Implementation Method 1
a hermeticity layer (32) including a dielectric material with a low water vapor transmission rate
Implementation Method 2
an interface layer (34) including a material having a hydroxylated oxide surface or including gold or another noble metal
Implementation Method 3
A SAM may be formed over the interface layer
Data Source
AI summary
A micro-electrical-mechanical system (MEMS) resonator device includes a top side electrode overlaid with a low water permeability hermeticity layer and an interface layer including a material (e.g., gold or a hydroxylated oxide surface) suitable for receiving a self-assembled monolayer (SAM) that may be functionalized with a functionalization (e.g., specific binding) material, with the foregoing layers being designed to have insubstantial impact on sensor performance. Atomic layer deposition may be used for deposition of the hermeticity and/or interface layers. The hermeticity layer protects the electrode material from attack in corrosive liquid environments, and the interface layer facilitates proper chemical binding of the SAM. Sensors and microfluidic devices incorporating MEMS resonator devices are also provided.