Wafer-Level MEMS Sensor Stacking for Area Reduction
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Solution Overview
Problem
Current methods for integrating pressure-detection and inertial detection structures in MEMS devices result in large package sizes and compatibility issues due to different manufacturing techniques and operational principles, leading to increased space occupation and thickness.
Innovation Solution
Wafer-level integration of pressure-detection and inertial-detection structures before dicing, where a pressure sensor die is stacked with an inertial sensor die, forming a hermetic environment, and then packaged with an ASIC, reducing the number of substrates and thickness while maintaining independent manufacturing processes for each sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If pressure sensor and inertial sensor are integrated at package level with side-by-side positioning, then functional integration is achieved, but space occupation in horizontal plane increases
Solution Approach 1:
The patent transitions from horizontal side-by-side integration to vertical stacking arrangement, moving the sensors into the third dimension (thickness direction). This dimensional change allows both sensors to occupy overlapping horizontal footprints while being separated vertically, thereby reducing the horizontal area occupation while maintaining functional integration.
Solution Approach 2:
The patent implements a nested configuration where the pressure sensor is positioned within the vertical projection area of the inertial sensor (or vice versa), creating a nested spatial relationship. This nesting allows both sensors to share the same horizontal footprint, minimizing the overall package area while maintaining independent functionality.
2Reliability
If three substrates are stacked for hermetic package, then hermetic environment is provided for inertial detection, but package thickness increases
Solution Approach 1:
The patent merges the hermetic sealing function with the pressure sensing function by making the pressure sensor's sensing membrane form part of the hermetic seal for the inertial sensor. This integration eliminates the need for a separate third substrate dedicated solely to hermetic sealing, thereby reducing package thickness while maintaining the required hermetic environment.
Solution Approach 2:
The pressure sensor substrate serves dual purposes: it provides pressure sensing functionality and simultaneously acts as the hermetic seal for the inertial sensor. This multi-functionality reduces the total number of substrates required from three to two, thereby reducing package thickness without compromising hermeticity.
3Reliability
If different front-end manufacturing technologies are used for inertial and pressure sensors, then each sensor achieves optimal performance, but device complexity and integration difficulty increase
Solution Approach 1:
The patent segments the manufacturing process into independent front-end fabrication stages for each sensor type, allowing different specialized technologies to be used for inertial and pressure sensors. After independent fabrication, the sensors are integrated through back-end processes, thus maintaining performance optimization while managing complexity through process segmentation.
Solution Approach 2:
The patent introduces an intermediary integration layer or process that bridges the different manufacturing technologies used for inertial and pressure sensors. This intermediary approach allows each sensor to be manufactured with its optimal technology while providing a standardized interface for integration, thereby reducing overall system complexity.
Data Source
Figure 1~2
Figure 3A~3C
Figure 3D~3F
AI summary
Described herein is a microelectromechanical sensor device (100), comprising: a stack (1) of a first die (2) that integrates a pressure-detection structure (4) and a second die (6) that integrates an inertial detection structure (8), the first die (2) constituting a cap for the inertial detection structure (8) and being bonded to the second die (6) so as to define a hermetic cavity (28, 34). The first die (2) has a first substrate (20), having a front surface (20a) and a rear surface (20b) that is bonded to said second die (6), a buried cavity (22) being buried and entirely contained in the first substrate (20) and being arranged in a position corresponding to the front surface (20a), from which it is separated by a membrane (24). In particular, the aforesaid buried cavity (22) is distinct and separate from the hermetic cavity (28, 34).