MEMS Mirror Thermal Control for LiDAR Frequency Stability
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Solution Overview
Problem
LiDAR systems face challenges in maintaining resonant frequency stability of MEMS micro-mirrors due to temperature changes caused by mismatched coefficients of thermal expansion between materials, leading to stress and desynchronization of micro-mirror arrays.
Innovation Solution
The implementation of a micro-electromechanical system (MEMS) apparatus with a thermoelectric cooler, heating resistors, additional pins, and widened vias to control temperature and minimize stress, ensuring synchronous operation of micro-mirrors across the array by adjusting resonant frequency and reducing thermal expansion mismatches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the MEMS mirror structure operates at resonant frequency for large scanning angles, then the scanning angle is improved, but the resonant frequency shifts when surrounding temperature changes
Solution Approach 1:
The patent changes the physical parameters of the support structure by introducing a compensation structure with adjustable stiffness. This allows the system to adapt to temperature changes by modifying the mechanical properties of the support, thereby maintaining resonant frequency stability while preserving large scanning angles
Solution Approach 2:
The compensation structure acts as an intermediary between the fixed support and the movable mirror. It mediates the thermal expansion effects and stress changes, isolating the mirror's resonant frequency from temperature-induced variations in the surrounding structure
2Temperature
If temperature changes occur, then stress develops at material interfaces due to CTE mismatch, but this stress causes resonant frequency shift and micro-mirror bowing
Solution Approach 1:
The patent explicitly addresses thermal expansion by designing a compensation structure that accounts for differential thermal expansion between materials. The structure is configured to expand or contract in response to temperature changes, compensating for the CTE mismatch between the micro-mirror substrate and surrounding structures
Solution Approach 2:
The compensation structure is positioned specifically at the support region where thermal stress is most critical. By providing localized compensation at this key location, the patent maintains the overall flatness of the micro-mirror without requiring uniform changes throughout the entire structure
3Measurement precision
If the micro-mirror array operates synchronously at resonant frequency, then the light steering precision is improved, but temperature variations cause desynchronization
Solution Approach 1:
By modifying the stiffness parameters of the compensation structure, the system maintains consistent resonant frequency characteristics across temperature variations. This ensures that all micro-mirrors in the array remain synchronized, preserving light steering precision under varying thermal conditions
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 effectively stabilizes the resonant frequency of MEMS micro-mirror arrays across varying temperatures, maintaining synchronization and reducing light divergence, thereby enhancing the accuracy and reliability of LiDAR systems in autonomous vehicles.
Implementation Method 1
mismatch in CTE (coefficient of thermal expansion) of the various materials. The tension changes within the torsion springs coupled to the suspended micro-mirror. This results in a shift of the micro-mirror's resonant frequency
Implementation Method 2
The implementation of a micro-electromechanical system (MEMS) apparatus with a thermoelectric cooler, heating resistors, additional pins, and widened vias to control temperature
Implementation Method 3
The resonant frequency can be controlled by the design of the MEMS mirror structure and the supporting torsion springs that support them. By operating at the resonant frequency, the mirror can more easily be rotated
Implementation Method 4
a micro-mirror assembly can be a micro-electro-mechanical system (MEMS)-type structure that may be used for a light detection and ranging (LiDAR) system
Data Source
AI summary
A micro-electromechanical system (MEMS) apparatus has an array of micro-mirrors and a control circuit for rotating the micro-mirrors synchronously at a resonant frequency. The MEMS apparatus includes elements with different Coefficients of Thermal Expansion (CTE) for a die substrate coupled to the array of micro-mirrors, a die attach layer, a chip package coupled to the die substrate and a printed circuit board coupled to the chip package. The apparatus provides mechanisms for reducing changes in the resonant frequency due to changes in temperature causing stresses due to a mismatch between the CTE of the different elements. A thermoelectric cooler is used, along with the optional addition of heating resistors, additional pins to distribute stress, and the widened vias allowing room for the pins to bend and relieve stress on the chip package.