Selective SAM Patterning via Sacrificial Germanium Layer
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Solution Overview
Problem
Existing MEMS devices face challenges in achieving improved performance and reliability due to the non-patternable Self-Assembled Monolayer (SAM) coating, which causes charging effects and stiction issues, affecting the accuracy of sensors like accelerometers and gyroscopes.
Innovation Solution
The implementation of selective SAM patterning using a sacrificial germanium layer, where the SAM coating is left only on the proof mass facing the bump stop on the accelerometer side and removed from the gyroscope side, reducing charging effects and enhancing sensor stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SAM coating is applied to the device layer, then stiction issues are reduced, but charging effects occur causing offset shifts in accelerometers
Solution Approach 1:
The patent applies selective SAM patterning to create different surface properties in different regions. The SAM coating is present on the accelerometer proof mass to prevent stiction, while absent from the gyroscope proof mass to eliminate charging effects. This local differentiation resolves the contradiction by tailoring the surface properties to the specific functional requirements of each sensor type.
2Reliability
If SAM coating is applied to the device layer, then stiction issues are reduced, but gyroscope sensitivity and cavity pressure stability deteriorate due to charging effects
Solution Approach 1:
The patent implements region-specific SAM coating distribution where the gyroscope proof mass remains free of SAM coating to prevent charging effects that would compromise sensitivity and pressure stability, while the accelerometer proof mass receives SAM coating for stiction prevention. This spatially differentiated approach resolves the contradiction between stiction prevention and measurement accuracy.
3Reliability
If SAM coating is applied uniformly across the device layer, then stiction is prevented, but manufacturing complexity increases due to the need for selective patterning
Solution Approach 1:
The patent introduces a sacrificial germanium layer as an intermediary element that simplifies the SAM patterning process. This sacrificial layer is deposited selectively on specific regions (accelerometer areas) before SAM coating, and then removed in a controlled manner to leave SAM coating only where needed. This intermediary approach reduces manufacturing complexity compared to direct selective SAM deposition, as the sacrificial layer provides a straightforward masking mechanism.
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 reduces charging-induced offset shifts in accelerometers and improves gyroscope sensitivity and cavity pressure stability by minimizing SAM outgassing during eutectic bonding and post-bond anneal.
Implementation Method 1
Selective self-assembled monolayer patterning with sacrificial layer for devices
Implementation Method 2
the sacrificial layer has been removed
Implementation Method 3
minimizing SAM outgassing during eutectic bonding and post-bond anneal
Implementation Method 4
bonding first portions of a handle layer to a first side of a device layer
Data Source
AI summary
Selective self-assembled monolayer patterning with sacrificial layer for devices is provided herein. A sensor device can include a handle layer and a device layer that comprises a first side and a second side. First portions of the first side are operatively connected to defined portions of the handle layer. At least one area of the second side comprises an anti-stiction area formed with an anti-stiction coating. The device can also include a Complementary Metal-Oxide-Semiconductor (CMOS) wafer operatively connected to second portions of the second side of the device layer. The CMOS wafer comprises at least one bump stop. The anti-stiction area faces the at least one bump stop.