MEMS Sensor Abutment Structure for Mechanical Robustness
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Solution Overview
Problem
Micromechanical sensor devices, particularly those with thin polysilicon layers, face mechanical robustness issues due to high risk of breakage under large overloads, as existing designs lack effective abutment mechanisms to absorb mechanical stress without increasing complexity or space requirements.
Innovation Solution
A micromechanical sensor device with a bonding structure that uses a polysilicon layer as a spacer and a bonding layer, such as germanium or metal, between the MEMS and ASIC elements to create a defined spacing and abutment point on the ASIC wafer, preventing direct contact with the sensitive polysilicon layers and thus enhancing mechanical robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a thin polysilicon layer (1-3 μm) is used for the MEMS structure, then the device complexity and material usage are reduced, but the mechanical robustness deteriorates with high risk of breakage under large overloads
Solution Approach 1:
A robust abutment element is introduced as an intermediary component between the thin polysilicon MEMS structure and the substrate. This abutment element has high mechanical strength and serves as a mediator that absorbs overload forces, preventing direct stress transmission to the fragile polysilicon layers while maintaining the thin-layer design benefits
Solution Approach 2:
The abutment element is pre-positioned beneath the polysilicon layers to provide beforehand cushioning against mechanical overloads. When drop tests or large accelerations occur, the abutment element absorbs the mechanical energy first, protecting the thin polysilicon structure from breakage before the stress can reach critical levels
2Strength
If a robust abutment structure is added to protect the MEMS structure, then the mechanical robustness is improved, but the device complexity and space requirements increase
Solution Approach 1:
The abutment element is merged with existing substrate structures or manufacturing processes. The robust abutment is integrated into the substrate architecture or formed using the same polysilicon deposition and release processes already used for the MEMS structure, avoiding additional complex fabrication steps
Solution Approach 2:
The abutment element serves multiple functions: it provides mechanical protection against overloads, maintains the electrical potential of the MEMS structure during abutment events, and can be formed using the same material layers already present in the device. This multi-functionality reduces the need for separate protective structures
3Volume of moving object
If the gap between the MEMS structure and substrate is reduced, then the device volume is reduced, but the mechanical robustness deteriorates as the Z-abutment becomes ineffective
Solution Approach 1:
The abutment element acts as an intermediary that enables effective mechanical support at reduced gaps. By positioning this robust element closer to the MEMS structure, it can provide protection even when the overall device volume and gaps are minimized, maintaining effectiveness in compact designs
Data Source
AI summary
A micromechanical sensor device includes: a MEMS element; an ASIC element; a bonding structure provided between the MEMS element and the ASIC element; a layer assemblage having insulating layers and functional layers disposed alternatingly on one another; a sensing element movable in a sensing direction provided in at least one of the functional layers; a spacing element for providing a defined spacing between the MEMS element and the ASIC element being provided by way of a further functional layer; an abutment element having the spacing element and a first bonding layer being disposed on the sensing element; and an insulating layer being disposed on the ASIC element in an abutment region of the abutment element.