Curved RF Electrode for Consistent MEMS Capacitance
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Solution Overview
Problem
MEMS devices face challenges in achieving repeatable and consistent capacitance due to inconsistent contact between the movable plate and the dielectric layer, leading to variations in capacitance values between devices.
Innovation Solution
The RF electrode is designed with a convex top surface matching the concave bottom surface of the movable plate, achieved through chemical mechanical polishing and a sacrificial layer process, ensuring intimate contact and consistent capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the movable plate is designed with a flat bottom surface, then the manufacturing process is simple, but the contact with the dielectric layer is inconsistent leading to variable capacitance
Solution Approach 1:
The RF electrode is designed with a convex curved top surface that matches the concave curvature of the movable plate's bottom surface. This curved geometry ensures intimate contact between the movable plate and dielectric layer across the entire contact area, eliminating the inconsistent contact problems associated with flat surfaces and achieving repeatable capacitance values.
Solution Approach 2:
The convex surface of the RF electrode is specifically shaped to match the local contact requirements of the movable plate. By creating a localized curved contact region rather than a uniform flat surface, the design ensures optimal contact quality precisely where the movable plate interacts with the dielectric layer, improving capacitance consistency without unnecessarily complicating the entire electrode structure.
2Manufacturing precision
If chemical mechanical polishing is used to create a convex surface on the RF electrode, then contact quality improves, but the manufacturing process becomes more complex
Solution Approach 1:
A sacrificial layer is introduced as an intermediary element in the fabrication process. This sacrificial layer is deposited over the RF electrode, undergoes reflow to create the desired convex curvature, and is then removed. The sacrificial layer acts as a temporary mediator that enables the formation of the convex RF electrode surface through a controlled process, making the manufacturing more manageable despite the added complexity.
3Reliability
If the movable plate contacts the dielectric layer inconsistently, then device fabrication is simpler, but capacitance repeatability deteriorates
Solution Approach 1:
Both the RF electrode top surface and the movable plate bottom surface are designed with complementary curved geometries (convex and concave respectively). This curved interface ensures that the movable plate makes consistent intimate contact with the dielectric layer across the entire contact area, eliminating the inconsistent contact points that lead to variable capacitance and improving device-to-device repeatability.
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 design results in improved Cmax performance and uniformity across devices, with higher capacitance and reduced variations, by ensuring a domed-to-domed contact between the movable plate and the RF electrode.
Implementation Method 1
chemical mechanical polishing the dielectric layer to expose the one or more electrodes, wherein the chemical mechanical polishing results in a convex upper surface of the one or more electrodes
Data Source
AI summary
The present invention generally relates to a MEMS device and a method of manufacture thereof. The RF electrode, and hence, the dielectric layer thereover, has a curved upper surface that substantially matches the contact area of the bottom surface of the movable plate. As such, the movable plate is able to have good contact with the dielectric layer and thus, good capacitance is achieved.