MEMS Digital Variable Capacitor Plate Design for Linearity
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Solution Overview
Problem
Microelectromechanical system (MEMS) digital variable capacitors (DVCs) face issues with charge build-up in the dielectric layer, leading to decreased efficiency and reliability, as well as non-linear capacitance modulation and limited lifetime due to electrostatic charging when the plate lands on the dielectric layer above the pull-in electrode.
Innovation Solution
The MEMS DVC design incorporates secondary landing contacts and plate bend contacts to ensure consistent contact with the RF plateau, reducing charge build-up and improving linearity, with a stiff plate and flexible legs to manage actuation voltage and prevent secondary landing on the dielectric layer, thereby enhancing reliability and linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the plate is allowed to land on the dielectric layer above the pull-in electrode to achieve maximum capacitance, then the capacitance range is improved, but charge build-up occurs in the dielectric layer leading to decreased efficiency and reliability
Solution Approach 1:
A conductive plateau is introduced as an intermediary structure between the movable plate and the pull-in electrode. The plateau provides a designated landing zone that is electrically conductive, allowing the plate to make contact without charging the insulating dielectric layer. This mediator enables maximum capacitance achievement while preventing charge build-up and maintaining device reliability.
2Adaptability or versatility
If the plate makes contact with the dielectric layer to achieve C max, then the capacitance modulation range is improved, but electrostatic charging occurs leading to limited lifetime
Solution Approach 1:
The conductive plateau serves as a mediator that replaces the dielectric layer as the contact surface. When the plate lands on the conductive plateau, electrostatic charging is prevented because the plateau is electrically conductive and can dissipate charges. This extends device lifetime while maintaining full capacitance modulation range.
3Stability of the object's composition
If the plate is designed to be stiff to maintain position, then the position stability is improved, but the linearity deteriorates due to non-uniform contact with the dielectric layer
Solution Approach 1:
The conductive plateau is designed with specific local geometric properties (area, height, position) that ensure uniform contact with the stiff plate. This local optimization of the contact surface geometry enables both position stability and linear capacitance modulation, as the plate makes consistent contact across the plateau surface throughout its movement range.
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 effectively reduces charge build-up, ensures high linearity, and increases the lifetime of the MEMS DVC by ensuring consistent contact and balanced electrostatic forces, allowing for reliable operation and integration with CMOS controllers.
Implementation Method 1
another electrode applies a voltage to either pull-in the plate or cantilever electrode towards the RF electrode
Implementation Method 2
The farther away from the RF electrode that the plate or cantilever electrode is located, the lower the capacitance of the MEMS DVC
Data Source
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AI summary
The present invention generally relates to a MEMS DVC and a method for fabrication thereof. The MEMS DVC comprises a plate movable from a position spaced a first distance from an RF electrode and a second position spaced a second distance from the RF electrode that is less than the first distance. When in the second position, the plate is spaced from the RF electrode by a dielectric layer that has an RF plateau over the RF electrode. One or more secondary landing contacts and one or more plate bend contacts may be present as well to ensure that the plate obtains a good contact with the RF plateau and a consistent Cmax value can be obtained. On the figure PB contact is the plate bend contact, SL contact is the Second Landing contact and the PD electrode is the Pull Down electrode.