Phosphorus-Doped MEMS Resonator for Temperature-Stable Frequency
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Solution Overview
Problem
Microelectromechanical system (MEMS) resonators face challenges in maintaining low variation of resonance frequency over temperature ranges, particularly due to the negative temperature coefficient associated with piezoelectric layers, which complicates achieving thermal stability.
Innovation Solution
A MEMS resonator design incorporating a phosphorus-doped single-crystalline silicon layer with specific doping concentrations and profiles, combined with a piezoelectric layer of controlled thickness, to minimize temperature-induced frequency variations, achieving thermal stability comparable to quartz resonators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a piezoelectric layer is added to excite the resonator element, then the resonator can be excited to resonance mode, but the negative temperature coefficient of the piezoelectric layer causes increased variation of resonance frequency over temperature
Solution Approach 1:
The patent changes the physical parameters of the single-crystalline silicon layer by introducing phosphorus doping with specific concentration profiles. The doping concentration varies with depth (from 1.99×10^20 cm^-3 to 1.20×10^20 cm^-3 or vice versa depending on the embodiment), which modifies the mechanical properties and thermal response of the silicon layer to compensate for the piezoelectric layer's negative temperature coefficient, thereby stabilizing the resonance frequency over temperature ranges from -30°C to 85°C.
Solution Approach 2:
The patent creates a composite structure consisting of a piezoelectric layer combined with a phosphorus-doped single-crystalline silicon layer. This composite material system leverages the piezoelectric effect for resonance excitation while the doped silicon layer provides thermal compensation, achieving both resonance excitation capability and temperature stability that neither material could achieve alone.
2Stability of the object's composition
If phosphorus doping concentration is increased to improve thermal stability, then resonance frequency variation is reduced, but the risk of precipitation and process variations increases
Solution Approach 1:
The patent applies local quality by creating a non-uniform phosphorus doping profile within the single-crystalline silicon layer. The doping concentration varies with depth from the top surface, with higher concentrations near the surface (1.99×10^20 cm^-3 to 2.97×10^20 cm^-3) and lower concentrations deeper in the layer (1.20×10^20 cm^-3 to 1.78×10^20 cm^-3), or vice versa depending on the embodiment. This localized variation optimizes thermal compensation while controlling precipitation risk by avoiding uniformly high doping concentrations throughout the entire layer.
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 design results in a resonance frequency variation within ±30 parts per million over the temperature range of −30°C to 85°C, providing thermal stability and reducing the risk of precipitation and process variations, while allowing for cost-effective mass production.
Implementation Method 1
the resonator element comprises a layer of single-crystalline silicon, wherein the layer of single-crystalline silicon is doped with phosphorus atoms where the concentration ndop of the said phosphorus atoms is (i) within the range from 1.99×1020 cm−3 to 2.97×1020 cm−3 at d/tDEV=0.1 and within the range from 1.20×1020 cm−3 to 1.78×1020 cm−3 at d/tDEV=0.9
Implementation Method 2
the resonator or resonator element further comprises a layer of piezoelectric material for exciting the resonator element to a resonance mode
Data Source
AI summary
A MEMS (microelectromechanical system) resonator (150) comprising a substrate (105), a resonator element (100), and a cavity (110). The resonator element (100) is separated from the substrate (105) by said cavity (110), and the resonator element (100) comprises a layer of single-crystalline silicon (101). The layer of single-crystalline silicon (101) is doped with phosphorus atoms to obtain a specific doping profile.