Sequential Wafer Bonding for Multi-Cavity MEMS Sensors
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Solution Overview
Problem
Microelectromechanical system (MEMS) sensor devices face packaging challenges, particularly in sealing and integrating multiple sensors with different pressure requirements on a single die, as existing bonding materials can remelt during assembly or operation, leading to part shifting and performance tradeoffs.
Innovation Solution
The use of sequential wafer bonding with different bond materials and trench cuts to secure wafers, allowing for the use of underfill materials to maintain structural integrity and prevent shifting, enabling the integration of sensors with varying pressure requirements in a compact form factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high reflow temperature bonding materials are used to bond wafers, then strong bonding strength is achieved, but parts shift during subsequent processing or assembly
Solution Approach 1:
The patent applies preliminary action by using underfill material to secure wafers to the substrate before subsequent high-temperature processing steps. The underfill material is applied in advance to prevent wafer shifting during assembly and reflow operations, addressing the position stability issue before it occurs during manufacturing
Solution Approach 2:
The underfill material serves as an intermediary substance between the wafer and substrate. This intermediary provides both mechanical support to prevent shifting and thermal management during bonding processes, resolving the contradiction between achieving strong bonds and maintaining position stability
2Adaptability or versatility
If multiple sensors with different pressure requirements are integrated on a single die, then device functionality is improved, but packaging complexity increases
Solution Approach 1:
The patent applies segmentation by creating separate sealed cavities within the single die structure. Each cavity can be independently pressurized to meet the specific requirements of different sensor types (e.g., accelerometer vs. gyroscope), allowing multiple sensors with different pressure needs to coexist on one die without interfering with each other
Solution Approach 2:
The patent uses vertical stacking and three-dimensional cavity formation to integrate multiple sensors on a single die. By utilizing the depth dimension and creating multiple sealed chambers at different levels, the design accommodates different pressure requirements without increasing the horizontal footprint, thus managing packaging complexity
3Ease of manufacture
If wafer bonding is performed without underfill material, then manufacturing process is simplified, but wafers shift during assembly
Solution Approach 1:
The underfill material acts as an intermediary that simplifies the overall manufacturing process by providing self-alignment and securing properties. While it adds a material step, it eliminates the need for complex alignment fixtures and repositioning operations, thereby improving ease of manufacture while ensuring positioning accuracy
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 allows for the reliable integration of multiple MEMS sensors with different pressure requirements in a smaller footprint and thickness, maintaining structural integrity during assembly and operation, while avoiding the remelting issues of traditional bonding materials.
Implementation Method 1
providing an underfill material through the opening to further secure the second wafer to the sensor wafer
Data Source
AI summary
Embodiments of a sensor device include a sensor substrate and a first cap substrate attached to the sensor substrate with a first bond material. The first bond material is arranged to define a first device cavity. A second cap substrate is attached to the sensor substrate with a second bond material. The second bond material is arranged to define a second device cavity. The second bond material has a lower bonding temperature than the first bond material. The second cap substrate is further secured to the sensor substrate by an adhesive material disposed between the sensor substrate and the second cap substrate.