Varying Substrate Depth for Accelerometer Sensitivity
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Solution Overview
Problem
The existing methods for forming semiconductor devices do not effectively allow for varying substrate depths, which limits the sensitivity and design flexibility of accelerometer springs, particularly for Z-axis accelerometers, as the stiffness and sensitivity of these devices are heavily dependent on substrate thickness.
Innovation Solution
A semiconductor device is fabricated with a non-uniform substrate thickness by etching a cavity and fusion bonding it to a carrier substrate, allowing for the formation of X-axis and Y-axis accelerometer springs at thicker regions and a Z-axis spring at a thinner region over the cavity, optimizing sensitivity and design flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the substrate thickness is kept uniform across the entire device, then the manufacturing process is simpler, but the sensitivity and design flexibility of accelerometer springs are limited
Solution Approach 1:
The patent applies local quality by creating a cavity in the substrate at specific locations to form localized thin regions. This allows different parts of the substrate to have different thicknesses - the cavity region provides enhanced sensitivity for Z-axis accelerometers while other regions maintain standard thickness for X and Y-axis accelerometers. This resolves the contradiction by enabling design flexibility and sensitivity optimization without requiring the entire substrate to be complex or non-uniform.
2Measurement precision
If the substrate thickness is varied to optimize Z-axis accelerometer sensitivity, then the mechanical sensitivity improves, but the manufacturing process becomes more complex
Solution Approach 1:
The patent segments the substrate into distinct regions: thin regions over the cavity for Z-axis accelerometers and thicker regions for X and Y-axis accelerometers. This segmentation is achieved through a systematic manufacturing process that etches cavities at defined locations and forms accelerometer springs in specific zones. The segmentation enables optimized sensitivity for each axis without requiring entirely different manufacturing approaches, as the same general process steps are used throughout the device.
3Measurement precision
If the substrate is thinned over the cavity region, then the Z-axis accelerometer sensitivity is enhanced, but the structural strength of the substrate is reduced
Solution Approach 1:
The cavity-induced thinning is applied locally only at specific regions of the substrate where Z-axis accelerometers are positioned. The majority of the substrate maintains its full thickness, preserving overall structural strength. This localized thinning approach allows the Z-axis accelerometer to benefit from enhanced sensitivity while the rest of the substrate continues to provide mechanical support and strength.
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 approach enables the creation of accelerometer springs with similar sensitivities across axes, reducing design restraints and enhancing the mechanical sensitivity of Z-axis accelerometers by varying the substrate thickness selectively.
Implementation Method 1
a cavity is etched at a selected side of the semiconductor substrate
Implementation Method 2
the selected side is then fusion bonded to another substrate
Implementation Method 3
the side of the semiconductor substrate opposite to the selected side is ground to a defined thickness
Data Source
AI summary
A method for forming a semiconductor device includes providing a substrate having a first major surface and a second major surface, removing a first portion of the substrate to form a cavity at the first major surface of the substrate, bonding the first major surface of the substrate to a carrier substrate after forming the cavity, and reducing a thickness of the substrate. The method further includes forming a first accelerometer device at the second major surface such that at least a portion of the first accelerometer device is over the cavity and forming a second accelerometer device at the second major surface such that the second accelerometer device is not disposed over the cavity.