Piezoelectric MEMS Resonator Array for Stable Silicon Frequency Control
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Solution Overview
Problem
Silicon-based micromechanical resonators face challenges with actuation requiring high voltages and narrow gaps, temperature drift issues due to silicon's temperature-dependent Young modulus, and difficulties in achieving accurate resonance frequencies and low noise in mass production.
Innovation Solution
A resonator array is designed with laterally arranged piezoelectric transducers that excite resonance modes dependent on the c44 elastic parameter of silicon, allowing for efficient actuation and temperature compensation, and enabling precise frequency control through doped semiconductor layers and accurate resonator geometry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrostatic actuation is used to drive silicon resonators, then resonance can be achieved, but large bias voltages (>20 V) and narrow gaps (2 μm) are required which increase ESD risk and reduce device reliability
Solution Approach 1:
The patent replaces electrostatic actuation with piezoelectric actuation. Instead of using electrostatic fields that require narrow gaps and high voltages, the invention uses piezoelectric films (such as AlN or PZT) deposited on the resonator structure to generate mechanical stress directly through piezoelectric effect, eliminating the need for narrow gaps and reducing ESD risks
Solution Approach 2:
The patent changes the actuation mechanism from electrostatic to piezoelectric, fundamentally altering the physical parameters involved. The piezoelectric actuation allows for larger gaps and lower voltages while maintaining effective resonance driving, thereby improving device reliability without sacrificing actuation effectiveness
2Adaptability or versatility
If piezoelectric film is grown on the resonator structure for actuation, then certain resonance modes can be excited, but Lame mode excitation is problematic in single-crystal silicon plate resonators
Solution Approach 1:
The patent applies piezoelectric films at specific locations and orientations on the silicon resonator structure to enable Lame mode excitation. By strategically positioning the piezoelectric actuation elements and controlling their crystallographic orientation, the invention achieves effective coupling to Lame modes which were previously difficult to excite in single-crystal silicon resonators
3Reliability
If temperature compensation circuitry is added to stabilize resonance frequency, then frequency stability improves, but energy consumption increases and device complexity increases
Solution Approach 1:
The patent uses composite material structures combining silicon resonator elements with piezoelectric films and doped semiconductor layers. These composite structures provide inherent temperature compensation mechanisms where the different thermal expansion coefficients and elastic properties of the combined materials counteract frequency drift, achieving frequency stability without requiring additional active temperature compensation circuitry
Solution Approach 2:
The patent implements self-compensating resonator structures that automatically adjust for temperature variations through their inherent material properties and design. The doped semiconductor layers and piezoelectric components create internal compensation mechanisms that maintain frequency stability passively, eliminating the need for external temperature sensors and control circuits that would consume additional energy
4Reliability
If quartz crystal resonators are used, then accurate and stable frequency is achieved, but production process is separate from silicon-based circuits and integration is difficult
Solution Approach 1:
The patent merges the resonator structure with standard silicon-based semiconductor fabrication processes. By using silicon as the resonator material and applying piezoelectric films through compatible deposition techniques, the invention enables resonators to be manufactured using the same CMOS-compatible processes as digital circuits, allowing for monolithic integration rather than separate quartz crystal assembly
Solution Approach 2:
The patent changes the material parameter from quartz crystal to silicon-based composite structures with piezoelectric films. This material substitution maintains the frequency accuracy and stability characteristics of traditional resonators while enabling compatibility with silicon semiconductor manufacturing processes, thereby facilitating integration with digital circuitry
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 approach reduces the need for high voltages and narrow gaps, minimizes temperature drift, and achieves accurate and stable resonance frequencies, enhancing the reliability and efficiency of silicon-based resonators for various applications.
Implementation Method 1
laterally arranged piezoelectric transducers that excite resonance modes
Implementation Method 2
excite a resonance mode to the resonator elements, the resonance frequency of the resonance mode being dependent essentially only on the c 44 elastic parameter
Data Source
Figure 1a~1b
Figure 2a~3d
Figure 4a~4c
AI summary
The invention relates to a microelectromechanical resonator and a method of manufacturing thereof. The resonator comprises at least two resonator elements (10A, 10B) made from semiconductor material, the resonator elements being arranged laterally with respect to each other as an array, at least one transducer element (12) coupled to said resonator elements (10A, 10B) and capable of exciting a resonance mode to the resonator elements (10A,10B). According to the invention, said at least one transducer element (12) is a piezoelectric transducer element arranged laterally with respect to the at least two resonator elements (10A, 10B) between the at least two resonator elements (10A, 10B) and adapted to excite to the resonator elements (10A, 10B) as said resonance mode a resonance mode whose resonance frequency is dependent essentially only on the C44 elastic parameter of the elastic modulus of the material of the resonator elements. By means of the invention, electrostatic actuation and problems associated therewith can be avoided and accurate resonators can be manufactured.