MEMS Adjustable Capacitor With Movable Plate for High-Q RF Tuning
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Solution Overview
Problem
Conventional adjustable capacitors for radio frequency circuits face challenges such as low voltage withstand, large volume, limited adjustable range, high cost, and inefficiencies in achieving arbitrarily adjustable capacitance values with high Q values, especially in high-power applications.
Innovation Solution
A MEMS structure-based adjustable capacitor design featuring a movable plate that adjusts capacitance by varying electrostatic attraction forces using adjustable electrodes and dielectric isolation, allowing for continuous and step-wise capacitance adjustment with high voltage and current withstand capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a varactor diode is used to achieve adjustable capacitance, then the capacitance value can be adjusted by bias voltage, but the voltage withstand value is low and it cannot meet high-power requirements
Solution Approach 1:
The patent replaces the electrical field-based varactor diode with a MEMS mechanical structure where a movable plate physically adjusts capacitance through electrostatic attraction and release, enabling high voltage withstand while maintaining adjustability
Solution Approach 2:
The patent changes the adjustment mechanism from electrical parameter (bias voltage in varactor) to mechanical parameter (plate position), allowing the capacitor to withstand high voltages while still achieving continuous capacitance adjustment through controlled plate movement
2Device complexity
If a mechanical variable capacitor is used to adjust capacitance, then the structure is simple, but the volume is large and real-time adjustment cannot be achieved
Solution Approach 1:
The patent transitions from traditional lateral plate movement to vertical plate movement along the electrostatic attraction direction, enabling compact three-dimensional integration and reducing overall device volume while maintaining mechanical adjustment capability
Solution Approach 2:
The patent introduces a movable plate that can dynamically change position through electrostatic attraction and release, enabling real-time capacitance adjustment without complex mechanical structures or large volumes
3Adaptability or versatility
If multiple groups of capacitors with switches are used to achieve adjustable range, then different capacitance combinations can be obtained, but the cost is high and additional losses affect efficiency
Solution Approach 1:
The patent uses a single movable plate that can continuously change position to achieve continuous capacitance adjustment across a wide range, eliminating the need for multiple discrete capacitors and switches while maintaining high adaptability
Solution Approach 2:
The patent achieves wide adjustable range by continuously varying the plate position parameter rather than switching between discrete capacitor combinations, reducing device complexity and eliminating switch-related losses
4Volume of moving object
If a dielectric switch-type MEMS capacitor is used, then the structure is compact, but high direct current bias causes electrostatic attraction that brings about difficulties to turning on the switch
Solution Approach 1:
The patent inverts the traditional switching mechanism by using electrostatic release (removing attraction) to turn the switch on and electrostatic attraction to turn it off, solving the problem of high DC bias preventing switch activation
Solution Approach 2:
The patent employs a spring mechanism that automatically returns the movable plate to its initial position after electrostatic attraction releases, enabling automatic reset without additional actuation and simplifying the switching operation
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 MEMS structure-based adjustable capacitor achieves high Q values, programmable capacitance, and adaptability to different environments with reduced parasitic capacitance and mechanical vibration effects, while maintaining a compact and cost-effective design.
Implementation Method 1
the lower electrode A1 is constantly applied with a working voltage, the working voltage generates an electrostatic attraction force on the movable electrode B1
Implementation Method 2
an electrostatic attraction force of the adjustment electrodes C2 on the adjustment electrodes B2 is adjusted by controlling an adjustable voltage applied to the adjustment electrodes C2
Data Source
AI summary
An MEMS structure-based adjustable capacitor is provided, comprising: a lower plate A, a movable plate B, an upper plate C, a fixed apparatus D and one or more connecting conductors E; a lower end of the fixed apparatus D is fixedly connected to the lower plate A, an upper end of the fixed apparatus D is fixedly connected to the upper plate C, a structure B4 is provided at a middle part of movable plate B, and the movable plate B is able to move up and down along the fixed apparatus D; the lower plate A is provided with a lower electrode A1, and the movable plate B is provided with a movable electrode B1 and adjustment electrodes B2; the lower electrode A1 and the movable electrode B1 constitute a unit capacitor; and the upper plate C is provided with an upper electrode C1 and adjustment electrodes C2.