MEMS Package Cap with Integrated Humidity Drift Compensation
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Solution Overview
Problem
Existing MEMS devices with inertial sensors, such as gyroscopes and accelerometers, are vulnerable to humidity penetration through their packaging, leading to mechanical deformations and signal drifts that affect performance.
Innovation Solution
Integration of a capacitive humidity sensor on the MEMS die cap, coupled with a compensation mechanism that uses capacitance variations to correct signal drifts based on humidity levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a resin packaging mass is used to protect the MEMS device, then mechanical protection and electrical insulation are provided, but impermeability to water droplets is not ensured
Solution Approach 1:
The packaging structure is divided into multiple functional layers: an outer resin packaging mass for mechanical protection, an intermediate barrier layer (such as metal foil or ceramic) for humidity blocking, and an inner layer for electrical insulation. This segmentation allows each layer to specialize in one function, resolving the contradiction between mechanical protection and humidity impermeability.
Solution Approach 2:
The packaging structure uses composite materials combining resin with metal foil or ceramic barriers. This composite approach provides both the mechanical protection needed from the resin and the humidity impermeability provided by the metal or ceramic layer, simultaneously satisfying both requirements.
2Reliability
If commercial humidity sensors are used, then humidity detection capability is provided, but device dimensions become too large for integration
Solution Approach 1:
The humidity sensor is merged with the MEMS device by integrating it directly into the same packaging structure. The sensor utilizes the existing packaging layers and space, combining the humidity detection function with the protective enclosure, thereby avoiding the need for separate large commercial sensors.
Solution Approach 2:
The patent replaces mechanical humidity sensing methods with capacitive sensing. The humidity sensor operates by detecting changes in capacitance caused by humidity-induced deformation or dielectric constant changes, eliminating the need for mechanical humidity indicators or larger sensor structures.
3Volume of moving object
If humidity sensors are integrated on the MEMS die, then compact dimensions are achieved, but manufacturing complexity increases
Solution Approach 1:
The humidity sensor structure is prepared and integrated during the initial MEMS device manufacturing process, before final packaging. By performing the sensor integration as a preliminary action in the fabrication sequence, the patent avoids adding complex steps later and leverages existing manufacturing capabilities.
Solution Approach 2:
The integrated humidity sensor structure serves multiple functions: it provides humidity detection, acts as part of the packaging barrier system, and utilizes existing die layers and materials. This multi-functionality reduces the need for separate dedicated humidity sensor components, thereby limiting the increase in manufacturing complexity.
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 integrated humidity sensor allows for real-time compensation of signal errors, enhancing the reliability and accuracy of MEMS devices under varying humidity conditions.
Implementation Method 1
a capacitive humidity sensor (30), formed above the MEMS die (24)... the stress induced on the MEMS die (24) and the deformations of the same MEMS die (24) may cause errors in the output signals
Implementation Method 2
the capacitance variations to correct signal drifts based on humidity levels
Data Source
AI summary
Packaged MEMS device having a MEMS die of semiconductor material formed by a sensor body and a cap mutually bonded. The sensor body incorporates at least one MEMS component and the cap carries a humidity sensor having a first and a second group of electrodes, facing each other and capacitively coupled, configured to provide a humidity signal. A packaging mass, of electrically insulating material, surrounds the MEMS die and the humidity sensor.