Single Chip 3-Axis Thermal Accelerometer Design
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Solution Overview
Problem
Existing multi-axis thermal accelerometers lack enhanced performance, particularly in terms of reduced temperature coefficients, DC offset, and drift, and fail to provide efficient acceleration sensing in multiple axes on a single chip.
Innovation Solution
The development of single chip 3-axis thermal accelerometers with a substrate, cavity, fluid, bridge structure, and strategically arranged heater and temperature sensing elements, which utilize differential and common mode temperature measurements to detect acceleration in the X, Y, and Z axes, with configurations to minimize DC offset and enhance sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional multi-axis thermal accelerometer devices are used, then basic acceleration sensing is achieved, but temperature coefficients, DC offset, and drift are not reduced
Solution Approach 1:
The device segments the sensing function into separate X-axis and Y-axis thermal acceleration sensors, each with dedicated heater elements and temperature sensing elements arranged in specific geometric patterns. This segmentation allows independent optimization of each axis sensing while maintaining overall system performance and reducing cross-axis interference.
Solution Approach 2:
The patent applies local quality by positioning temperature sensing elements at specific locations relative to heater elements, with certain elements closer to the heater than others. This non-uniform local arrangement creates differential temperature measurements that are sensitive to acceleration while being less sensitive to temperature drift, thereby improving measurement precision while addressing reliability concerns.
2Measurement precision
If conventional multi-axis thermal accelerometer devices are used, then basic acceleration sensing is achieved, but DC offset and drift are not reduced
Solution Approach 1:
The device employs feedback through differential measurement techniques, where temperature sensing elements continuously monitor temperature differences caused by acceleration-induced convection patterns. The system uses these differential signals to compensate for DC offset and drift, as the differential configuration inherently rejects common-mode temperature variations while maintaining sensitivity to acceleration-induced temperature differences.
Solution Approach 2:
The patent utilizes asymmetry in the positioning of temperature sensing elements relative to heater elements, with elements placed at different distances to create asymmetric thermal sensing zones. This asymmetric arrangement generates differential temperature signals that are sensitive to acceleration direction and magnitude while being less susceptible to symmetric drift and offset errors.
3Productivity
If multiple axis sensing is implemented on a single chip, then integration is achieved, but performance enhancement is not fully realized
Solution Approach 1:
The device achieves universality by integrating both X-axis and Y-axis acceleration sensing capabilities into a single chip structure with a unified substrate, cavity, and fluid system. The shared thermal convection environment and common processing electronics enable compact integration while maintaining the measurement precision of individual axis sensors through careful geometric design and differential measurement techniques.
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
These devices offer improved performance with reduced temperature coefficients and DC offset, enabling accurate and sensitive acceleration sensing in multiple axes, addressing the limitations of conventional multi-axis thermal accelerometers.
Implementation Method 1
a heater element suspended over the cavity in the X-Y plane
Implementation Method 2
the first and second temperature sensing elements are disposed along either the X-axis or the Y-axis on opposite sides of and at substantially equal distances from the heater element
Data Source
AI summary
Single chip 3-axis thermal accelerometer devices include a substrate, at least one cavity etched in the substrate, a fluid disposed in the cavity, a bridge structure suspended over an opening of the cavity, and a plurality of heater elements and temperature sensing elements disposed on the bridge structure. The substrate has a substantially planar surface defined by X and Y coordinate axes, and the bridge structure is suspended over the opening of the cavity in the X-Y plane. In one embodiment, the bridge structure is configured to position at least two of the temperature sensing elements out of the X-Y plane. The heater and temperature sensing elements are disposed on the bridge structure in optimized arrangements for providing reduced temperature coefficients and for producing output voltages having reduced DC offset and drift.