Out-of-plane accelerometer pillar stiffening
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Solution Overview
Problem
Out-of-plane accelerometers face challenges with high raw bias and bias stability due to assembly stress, temperature changes, and aging effects, which are not adequately addressed by existing decoupling frames and manufacturing methods.
Innovation Solution
The design incorporates a seismic mass acting as a capacitor plate, with a pillar extending between two capacitor plates, supported by elastic beams anchored to the pillar, and a decoupling frame with a limited surface area for mounting, which reduces bias sensitivity and improves stability through stiffening and stress decoupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a decoupling frame with stacked wafer layers is used to reduce assembly stress, then the initial raw bias is reduced, but the structure becomes more complex and difficult to mount on a package
Solution Approach 1:
The accelerometer is divided into separate functional modules: a sensor box containing the capacitive sensing elements and a seismic mass, and a separate decoupling frame. This segmentation allows each module to be optimized independently - the sensor box for sensing precision and the decoupling frame for stress management and mounting ease.
Solution Approach 2:
The decoupling frame acts as an intermediary element between the sensor box and the package substrate. It provides a compliant mounting interface that decouples assembly stresses from the sensitive sensor box while maintaining mechanical support, thereby reducing raw bias without complicating the mounting process.
2Measurement precision
If the decoupling frame is made thin to bend under stress without transmitting it to the sensor box, then assembly stress is reduced, but the surface area for mounting becomes very small making mounting cumbersome
Solution Approach 1:
The decoupling frame exhibits local quality variations: it has thin, compliant regions that bend to absorb assembly stress and protect the sensor box, while simultaneously providing sufficient mounting surface area in strategic locations for easy attachment to the package substrate. This localized differentiation of mechanical properties resolves the contradiction between stress decoupling and mounting ease.
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 configuration significantly reduces raw bias and improves bias stability by minimizing die attach stress and enhancing the sensor box's stiffness, allowing for more accurate acceleration detection over time.
Implementation Method 1
The mass displacement is sensed through capacitive detection. Two capacitor plates are arranged in parallel configuration above and below the seismic mass.
Implementation Method 2
The seismic mass is supported by elastic beams anchored to a frame. This structure absorbs stress and reduces bias instability.
Data Source
AI summary
Accelerometer including a seismic mass in a plane and a first capacitor plate and a second capacitor plate arranged parallel to the plane. The seismic mass is arranged in between the first capacitor plate and the second capacitor plate. The first capacitor plate and the second capacitor plate are configured to detect movements of the seismic mass out of the plane. A pillar extending from the first capacitor plate to the second capacitor plate through a cut-out in the seismic mass for stiffening the accelerometer.