Out-of-Plane Flexural Micro-Resonator for Low-Power MHz Timing
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Solution Overview
Problem
Existing quartz crystal oscillators (XOs) face challenges in scaling down their size and volume to meet the increasing density of electronic devices, and micro-mechanical resonators like BAW and capacitive MEMS resonators face issues with high power consumption and complex fabrication due to their thickness mode nature and requirement for nanometer-scale gaps.
Innovation Solution
The development of micro-mechanical resonators that operate in out-of-plane flexural modes, with multiple portions extending from a base along different planes, allowing for lower resonant frequencies and reduced power consumption, and enabling multiple frequency operations using a single fabrication process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If quartz crystal oscillators are used to achieve good frequency accuracy and low noise, then timing signal quality is improved, but device area and volume cannot scale down exponentially
Solution Approach 1:
The patent replaces the traditional quartz crystal mechanical resonator with a micro-mechanical resonator that uses flexural modes instead of thickness modes. This substitution allows the resonator to achieve comparable frequency accuracy while enabling significant scaling down of device area, as the flexural mode operation does not depend on thick composite layers.
Solution Approach 2:
The patent changes the operating parameters of the resonator from thickness mode to flexural mode, and from high GHz frequencies to lower MHz frequencies. This parameter change allows the resonator to achieve the desired timing signal quality while occupying much smaller device area, enabling exponential scaling consistent with Moore's law.
2Speed
If BAW resonators operate in GHz range, then high frequency is achieved, but multiple divider stages are required increasing cost and power consumption
Solution Approach 1:
The patent changes the operating frequency parameter from GHz range to MHz range by using flexural modes instead of thickness modes. This parameter change eliminates the need for multiple divider stages, thereby reducing power consumption while still providing the required timing signal frequencies for various applications.
Solution Approach 2:
The patent extracts and eliminates the need for multiple divider stages by directly operating the resonator at the desired MHz frequencies. This removal of unnecessary components reduces both cost and power consumption while maintaining the required frequency output.
3Speed
If BAW resonator thickness is increased to lower resonant frequency, then operating frequency is reduced, but fabrication becomes impractical requiring 1000× film thickness
Solution Approach 1:
The patent replaces the thickness mode mechanical resonance with flexural mode resonance. This substitution allows frequency control through the geometry and stiffness of flexible beams rather than through thickness, making fabrication practical while achieving the desired lower MHz resonant frequencies without requiring impractical increases in film thickness.
Solution Approach 2:
The patent transitions from controlling frequency through the thickness dimension (vertical) to controlling frequency through the lateral dimensions and flexural properties of beams. This dimensional change allows frequency adjustment without increasing film thickness, maintaining ease of manufacture while achieving lower resonant frequencies.
4Speed
If capacitive MEMS resonators use nanometer scale gaps, then resonant frequency is reduced, but fabrication complexity increases
Solution Approach 1:
The patent replaces the capacitive transduction mechanism that relies on nanometer-scale gaps with a piezoelectric transduction mechanism using flexible beams. This substitution eliminates the need for precise nanometer gap control, reducing manufacturing precision requirements while maintaining the ability to operate at lower resonant frequencies.
Solution Approach 2:
The patent introduces piezoelectric material as an intermediary between the mechanical flexural motion and the electrical signal. This intermediary allows for robust frequency operation without requiring precise gap control, as the piezoelectric effect directly converts beam displacement to electrical signal regardless of small variations in gap dimensions.
5Device complexity
If capacitive MEMS resonators operate with lower electromechanical coupling, then device complexity is reduced, but power consumption increases due to higher motional resistance
Solution Approach 1:
The patent uses composite materials including piezoelectric layers combined with flexible beam structures to achieve high electromechanical coupling. This composite approach maintains relatively simple device structure while significantly reducing power consumption through the high coupling efficiency of the piezoelectric material, overcoming the limitation of capacitive MEMS resonators.
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 solution allows for resonant frequencies below a few MHz, reducing the need for multiple divider stages, which in turn decreases cost and power consumption in oscillator circuits, while also enabling compact designs and efficient manufacturing processes.
Implementation Method 1
The first resonator portion is configured to operate in an out-of-plane flexural mode that displaces at least part of the first resonator portion out of the first plane
Implementation Method 2
The second resonator portion is configured to operate in an out-of-plane flexural mode that displaces at least part of the second resonator portion out of the second plane and out-of-phase relative to the first resonator portion
Data Source
AI summary
A micro-mechanical resonator die includes: micro-mechanical resonator die layers; a cavity formed in at least one of the micro-mechanical resonator die layers; and a micro-mechanical resonator suspended in the cavity. The micro-mechanical resonator includes: a base; a first resonator portion extending from the base along a first plane; and a second resonator portion extending from the base along a second plane. The first resonator portion is configured to operate in an out-of-plane flexural mode that displaces at least part of the first resonator portion out of the first plane. The second resonator portion is configured to operate in an out-of-plane flexural mode that displaces at least part of the second resonator portion out of the second plane and out-of-phase relative to the first resonator portion.