MEMS Varactor Composite Beam Tuning Range
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Solution Overview
Problem
Solid-state varactors have limited tuning range, high resistive loss, and high power consumption, while MEMS varactors suffer from a small tuning range due to the 'snap down' effect, restricting their use as continuously tunable devices.
Innovation Solution
The development of MEMS varactors with a composite beam structure having a varying width dimension, including a reduced area portion to control the initial pull-in section, and the use of bumpers to reduce initial capacitance and improve actuation control, enabling a linear response to applied voltage with a tuning range of at least 3.5:1 and up to 10.5:1.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If solid-state varactors are used to achieve tunable capacitance, then capacitance tuning is enabled, but the tuning range is very limited and power consumption is high
Solution Approach 1:
The patent replaces solid-state electronic varactors with a MEMS-based mechanical system. The MEMS varactor uses a movable beam that can be physically positioned to change capacitance, eliminating the need for bias currents and sub-circuits required by solid-state varactors, thereby achieving low power consumption while maintaining capacitance tuning capability
Solution Approach 2:
The patent changes the physical parameters of the MEMS beam, specifically its width dimension, to optimize performance. The beam width is varied along its length to control the pull-in behavior and achieve a linear capacitance response with extended tuning range, while the low operating voltage (below 50V) reduces power consumption compared to solid-state solutions
2Use of energy by moving object
If MEMS varactors are used to avoid power consumption issues, then power consumption is reduced, but the tuning range is small due to the snap down effect
Solution Approach 1:
The patent applies local quality by varying the beam width at different positions along the MEMS beam. The beam has a non-uniform cross-section with different width dimensions at different locations, which controls the electric field distribution and pull-in behavior locally, enabling a linear capacitance response and extending the tuning range beyond what uniform beams can achieve
Solution Approach 2:
The patent utilizes the dynamic pull-in behavior of the MEMS beam to achieve capacitance tuning. By controlling the voltage applied to the beam, the system exploits the nonlinear pull-in effect and the subsequent linear response region to provide a wide, controllable tuning range. The beam transitions from a stable position to a pulled-in state, providing continuous capacitance adjustment
3Ease of manufacture
If conventional MEMS beams are used, then manufacturing is simplified, but the initial capacitance is high and actuation control is poor
Solution Approach 1:
The patent changes the geometric parameters of the MEMS beam, specifically implementing a non-uniform width profile along the beam length. This parameter modification reduces the initial capacitance by decreasing the overlapping area between the beam and fixed electrode, while also improving actuation control by creating a more favorable electric field distribution that enables precise pull-in behavior
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 provides MEMS varactors with improved isolation from the silicon substrate, low leakage current, and the ability to be activated with low currents, overcoming the limitations of solid-state and conventional MEMS varactors by achieving a significantly expanded tuning range and controlled actuation.
Implementation Method 1
the varactor's capacitance is set by a bias current generated by a sub-circuit that consumes a significant amount of steady state power
Implementation Method 2
Varactors are devices whose capacitance varies with applied voltage. Varactors are typically made using MOS capacitors whose depletion region varies with applied voltage
Data Source
AI summary
Micro-Electro-Mechanical System (MEMS) structures, methods of manufacture and design structures are disclosed. The method includes forming at least one fixed electrode on a substrate. The method further includes forming a Micro-Electro-Mechanical System (MEMS) beam with a varying width dimension, as viewed from a top of the MEMS beam, over the at least one fixed electrode.