Capacitive MEMS Sensor Vacuum Sealing via Through-Substrate Vias
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Solution Overview
Problem
Conventional MEMS processes face challenges in producing cost-effective small-sized packaged MEMS sensor devices and defining a robust integration scheme, particularly in sealing the MEMS cavity at low pressure to achieve high-Q sensor performance.
Innovation Solution
The introduction of through-substrate vias (TSVs) provides access to the fixed and released MEMS electrodes, allowing for vacuum diffusion bonding with a third capping substrate to seal the MEMS cavity, eliminating the need for conventional passivation layers and creating a self-packaged capacitive MEMS sensor device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional release layers are used to seal the MEMS cavity, then the MEMS structure can be released, but the sealing quality and vacuum integrity are insufficient to achieve high-Q sensor performance
Solution Approach 1:
The patent removes the conventional release layer entirely and replaces it with through-substrate vias (TSVs) that provide both release functionality and electrical access. This extraction of the release layer's sealing function eliminates the vacuum leakage problem while maintaining device release capability.
Solution Approach 2:
The TSV structure serves multiple functions simultaneously: it provides mechanical release of the MEMS structure, electrical access to the fixed electrode, and vacuum sealing of the MEMS cavity. This multi-functionality resolves the contradiction by improving sealing quality without adding integration complexity.
2Reliability
If the MEMS cavity is sealed at low pressure to achieve high-Q performance, then sensor performance improves, but the sealing process becomes more difficult and complex
Solution Approach 1:
The patent replaces complex low-pressure sealing processes with a TSV-based vacuum diffusion bonding approach. The TSVs create inherent vacuum pathways that enable sealing at manageable pressures while achieving the required vacuum integrity for high-Q performance.
3Strength
If conventional passivation layers are used, then the MEMS structure is protected, but the device size increases and cost effectiveness decreases
Solution Approach 1:
The patent extracts and eliminates the conventional passivation layer by using TSVs with integrated sealing functionality. The TSV structure provides both protection and sealing without requiring additional passivation layers, thereby reducing device size and manufacturing cost.
4Adaptability or versatility
If through-substrate vias are used to access electrodes, then device integration is improved, but the manufacturing process complexity increases
Solution Approach 1:
The TSV structure provides universal access to both the fixed electrode and released MEMS electrode while simultaneously providing vacuum sealing. This multi-functional approach improves electrode accessibility without proportionally increasing manufacturing complexity, as the same TSV structure accomplishes multiple tasks.
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 production of cost-effective, small-sized MEMS sensor devices with superior vacuum sealing and mechanical isolation, enhancing sensor performance and reducing manufacturing complexity.
Implementation Method 1
The MEMS cavity of each sensing cell is sealed, such as by vacuum diffusion bonding, to another substrate (e.g., wafer) referred to as a third 'capping' substrate
Data Source
AI summary
A method of forming a capacitive micro-electro-mechanical system (MEMS) sensor device includes at least one capacitive MEMS sensor element with at least one capacitive MEMS sensor cell. A patterned dielectric layer including a thick dielectric region and a thin dielectric region is formed on a top side of a first substrate. A second substrate is bonded to the thick dielectric region to provide at least one sealed micro-electro-mechanical system (MEMS) cavity. The second substrate is thinned to reduce a thickness of said second substrate to provide a membrane layer. Vias are etched through the membrane layer and said thick dielectric region extending into the first substrate to form embedded vias. A dielectric liner which lines the embedded vias is formed within the first substrate. The embedded vias are filed with electrically conductive TSV filler material to form a plurality of through-substrate vias (TSVs), said plurality of TSVs extending to at least a top of said membrane layer. A patterned metal cap layer including metal caps is formed on top of said plurality of TSVs. Trenches are etched through regions of the membrane layer for releasing a first portion of the membrane layer over said MEMS cavity to provide a MEMS electrode and to define a fixed electrode. A third substrate including an inner cavity and outer protruding portions framing said inner cavity is bonded to the thick dielectric. The protruding portions are bonded to the thick dielectric region and, together with said first substrate vacuum, seals said MEMS electrode. The plurality of TSVs on a bottom side of said first substrate are exposed.