Grounded MEMS Cap Structure Without Added Device Thickness
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Solution Overview
Problem
MEMS devices face performance degradation and potential damage due to floating caps, which can lead to undesired electric discharges and electrostatic forces affecting movable masses. Existing solutions either increase device thickness, complicate manufacturing, or are not feasible for devices requiring radiation access.
Innovation Solution
A MEMS device with a cap that is grounded through a conductive region with secondary portions extending laterally, allowing for wire bonding connections to a ground pad without increasing device thickness, thus preventing electric discharges and maintaining device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the cap is covered with a conductive layer during back-end operations and connected to ground through wire bonding, then the cap is properly grounded preventing electric discharges, but the device thickness increases along the Z axis
Solution Approach 1:
The conductive region extends laterally in the XY plane rather than vertically along the Z axis. The secondary portions of the conductive region protrude laterally from the cap to enable wire bonding connections, allowing ground connection without increasing device thickness in the vertical direction.
2Reliability
If a conductive layer is added to cover the cap for grounding, then electrical protection is improved, but radiation access to the MEMS device is blocked due to shielding effect
Solution Approach 1:
The conductive region is segmented into a first portion integrated with the cap and secondary portions that extend laterally. This segmentation allows the grounding function to be achieved through lateral extensions rather than a complete overhead shield, leaving radiation access paths open while maintaining electrical protection.
3Length of moving object
If vertical conductive paths are formed to ground the cap, then device thickness is maintained, but the manufacturing process complexity increases considerably
Solution Approach 1:
Instead of forming vertical conductive paths from the cap downward through the substrate, the solution inverts the approach by extending conductive regions laterally from the cap to the substrate surface. This lateral extension approach simplifies the manufacturing process while achieving the same grounding function and maintaining device thickness.
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
The solution effectively grounds the cap, preventing electric discharges and reducing electrostatic forces on movable masses, while maintaining device thickness and allowing radiation access, thus enhancing the reliability and performance of MEMS devices.
Implementation Method 1
the cap, of semiconductive material, is covered during the so-called 'back-end' operations with a conductive layer, which is connected through a so-called wire bonding to a ground pad placed on an underlying substrate
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
Electronic device including: a MEMS sensor device (20; 120) including a functional structure (45;144,145) which transduces a chemical or physical quantity into a corresponding electrical quantity; a cap (21) including a semiconductive substrate (2); and a bonding dielectric region (19), which mechanically couples the cap (21) to the MEMS sensor device (20;120). The cap (21) further includes a conductive region (10;110), which extends between the semiconductive substrate (2) and the MEMS sensor device (20;120) and includes: a first portion (12;112), which is arranged laterally with respect to the semiconductive substrate (2) and is exposed, so as to be electrically coupleable to a terminal at a reference potential (69,77) by a corresponding wire bonding (58); and a second portion (13;113), which contacts the semiconductive substrate (2).