MEMS Resonator Suspension Layout for Stable Frequency and Low Loss
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Solution Overview
Problem
MEMS resonators have low rejection of external stresses such as temperature and humidity variations, leading to frequency instability and higher power consumption due to energy dissipation towards the substrate.
Innovation Solution
The MEMS resonator design features a suspension structure with centrally arranged anchoring elements and closely attached stator and rotor electrodes, minimizing deformation and energy dissipation, and incorporating interdigitated electrodes for enhanced capacitive coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If MEMS resonators are designed with standard integrated circuit manufacturing processes, then size containment and cost reduction are achieved, but rejection of external stresses such as temperature and humidity variations deteriorates
Solution Approach 1:
The resonator structure is segmented into multiple components: a resonant structure with moving arms, a suspension structure with suspension arms, and a substrate. This segmentation allows each component to be optimized for its specific function while collectively improving external stress rejection through the decoupling of the resonant structure from the substrate.
Solution Approach 2:
The suspension structure acts as an intermediary element between the resonant structure and the substrate. The suspension arms mechanically couple the resonant structure to the substrate while providing isolation from external stresses, thereby mediating between the need for substrate support and the need for stress rejection.
2Ease of manufacture
If MEMS resonators use standard integrated circuit manufacturing processes, then production cost is reduced, but frequency stability deteriorates due to low external stress rejection
Solution Approach 1:
The resonator is divided into distinct functional segments (resonant structure, suspension structure, substrate) that can be manufactured using standard integrated circuit processes. This segmentation enables cost-effective manufacturing while allowing each segment to be optimized for its specific role in maintaining frequency stability.
Solution Approach 2:
The suspension structure serves as an intermediary that protects the resonant structure from substrate-induced stress variations, thereby maintaining frequency stability. This intermediary layer allows the resonator to achieve reliable frequency performance without requiring complex manufacturing processes.
3Device complexity
If the resonant structure is directly attached to the substrate, then structural simplicity is achieved, but energy dissipation increases leading to higher power consumption
Solution Approach 1:
The direct attachment is segmented into an indirect attachment through suspension arms. This segmentation introduces an additional structural element that, while increasing device complexity, significantly reduces energy dissipation by isolating the resonant structure from the substrate, thereby lowering power consumption.
Solution Approach 2:
The suspension structure acts as an intermediary mechanical connection between the resonant structure and substrate. This intermediary coupling reduces energy dissipation pathways to the substrate while maintaining structural support, resulting in lower power consumption despite increased structural complexity.
4Manufacturing precision
If stator and rotor electrodes are positioned at a distance from each other, then manufacturing tolerance is easier to achieve, but capacitive coupling efficiency deteriorates
Solution Approach 1:
The electrode arrangement transitions from a planar configuration to a three-dimensional interdigitated structure. This dimensional change allows electrodes to be positioned closer in multiple directions, improving capacitive coupling efficiency while maintaining manufacturability through the structured interdigitated pattern.
Solution Approach 2:
The electrode structures are implemented as thin film layers that can be precisely deposited using standard semiconductor manufacturing techniques. This thin film approach enables close spacing of stator and rotor electrodes while maintaining manufacturing tolerance through controlled deposition processes.
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 achieves improved frequency stability and reduced power consumption by minimizing external interference effects and energy losses, resulting in a higher quality factor and better electrical performance.
Implementation Method 1
micromechanical structures made by micromachining techniques, which are caused to vibrate at their natural resonance frequency as a result of external stimuli in the form of suitable DC (continuous) electrical bias and AC (alternating) actuation signals
Implementation Method 2
The moving mass, together with a fixed electrode structure coupled to it, forms a capacitor, and the resonant vibration of the moving mass causes a variation in the capacitance of this capacitor, which is converted into an output signal at the desired operating frequency
Implementation Method 3
The resonant moving structure is suspended above the substrate by a suspension structure, comprising a suspension arm and an attachment arrangement consisting of a number of attachments arranged in the window defined by the resonant moving structure
Data Source
Figure 1~2
Figure 3~4A
Figure 4B~5
AI summary
A MEMS resonator (10) is equipped with a substrate (13); a moving structure (12) suspended above the substrate in a horizontal plane (xy) formed by a first (x) and a second (y) axis, having a first (12a) and a second (12b) arm, parallel to one another and extending along the second axis, coupled at their respective ends by a first (14a) and a second (14b) transverse joining element, forming an internal window (15); a first electrode structure (20), positioned outside the window, capacitively coupled to the moving structure; a second electrode structure (21), positioned inside the window, one of the first and second electrode structures causing an oscillatory movement of the flexing arms in opposite directions along the first horizontal axis at a resonance frequency, and the other of the first and second electrode structures having a function of detecting the oscillation; a suspension structure (16) having a suspension arm (17) in the window; and an attachment arrangement (18), coupled to the suspension element centrally in the window, near the second electrode structure.