CMOS MEMS Shield Electrode Vertical Gap Design
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
MEMS devices face challenges with offset shift over time, stiction, and size reduction, particularly due to capacitance and getter action issues during fabrication.
Innovation Solution
A CMOS MEMS integrated device with a shield electrode positioned in a cavity within the CMOS wafer, creating a larger vertical gap between the shield electrode and the device layer, and a smaller sensing gap, reducing capacitance and getter action by eliminating TiN layers, thereby minimizing offset shift and stiction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the shield electrode is positioned close to the device layer, then the device size is reduced, but capacitance increases causing offset shift over time
Solution Approach 1:
The shield electrode is positioned in a cavity within the CMOS wafer, utilizing the vertical dimension to increase the gap distance between the shield electrode and the device layer. This three-dimensional positioning reduces capacitance and offset shift while maintaining a compact overall device footprint, effectively resolving the contradiction between device size and reliability.
2Ease of manufacture
If TiN layers are used in the shield electrode structure, then manufacturing is simplified, but getter action increases causing stiction
Solution Approach 1:
The patent removes the TiN layer from the shield electrode structure, extracting the source of getter action that causes stiction. This modification eliminates the harmful effect while the shield electrode still performs its capacitance shielding function, resolving the contradiction between manufacturing simplicity and stiction prevention.
3Measurement precision
If the sensing gap is made smaller to improve sensing precision, then measurement precision increases, but stiction risk increases
Solution Approach 1:
The shield electrode acts as an intermediary element that shields the sensing electrode from the device layer. This allows the sensing gap to be made smaller for improved precision while the shield electrode maintains an larger gap to prevent stiction, effectively mediating between the conflicting requirements of sensing precision and stiction prevention.
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 reduces offset shift and stiction in MEMS devices by increasing the distance between the shield electrode and the device layer, improving the functionality and reliability of MEMS devices such as accelerometers and gyroscopes.
Implementation Method 1
the oxide layer and the passivation layer are etched, wherein the etching exposes the shield electrode
Implementation Method 2
A eutectic bond is between a first bonding metal on the bonding electrode and a second bonding metal on the MEMS wafer
Data Source
AI summary
An apparatus includes a MEMS wafer with a device layer and a handle substrate bonded to the device layer. A complementary metal-oxide semiconductor (“CMOS”) wafer includes an oxide layer, and a passivation layer overlying the oxide layer. A bonding electrode overlies the passivation layer. A eutectic bond is between a first bonding metal on the bonding electrode and a second bonding metal on the MEMS wafer. A sensing electrode overlies the passivation layer. A shield electrode is adjacent to the sensing electrode. A sensing gap is positioned between the sensing electrode and the device layer, wherein the sensing gap is smaller than a shield gap positioned between the shield electrode and the device layer.