Multi-Depth MEMS Cavities for Independent Pressure Control
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Solution Overview
Problem
Integrating multiple MEMS devices on a single chip poses a challenge as each device requires operation at different pressures to achieve optimal performance, and existing technologies fail to effectively manage and maintain these varying pressures within sealed cavities.
Innovation Solution
The integration of MEMS devices with multiple cavities of different depths, allowing for adjustment of enclosed volumes and pressures, is achieved by bonding engineered silicon on insulator wafers with standard CMOS wafers, using techniques such as eutectic bonding and out-gassing mechanisms to create hermetically sealed environments with controlled pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple MEMS devices are integrated on a single chip, then device integration density is improved, but pressure control for each device becomes difficult to maintain
Solution Approach 1:
The chip is divided into multiple separate cavities, each capable of being hermetically sealed and maintained at different pressures. Each cavity acts as an independent pressure-controlled environment, allowing multiple MEMS devices to operate at their respective optimal pressures simultaneously while being integrated on the same chip.
Solution Approach 2:
Each cavity is designed with specific local characteristics including different volumes, pressure levels, and sealing configurations tailored to the requirements of individual MEMS devices. This allows each device to experience its optimal local pressure environment rather than a uniform pressure across the entire chip.
2Reliability
If cavities are sealed at different pressures, then optimal performance for each device is achieved, but manufacturing complexity increases
Solution Approach 1:
The cavities are hermetically sealed during the wafer fabrication process before the chip is packaged. This preliminary sealing action allows pressure differentials to be established and maintained without requiring complex post-packaging pressure control mechanisms, thereby reducing overall manufacturing complexity while achieving optimal device performance.
3Stability of the object's composition
If hermetic sealing is used to maintain pressure differentials, then pressure stability is improved, but manufacturing difficulty increases
Solution Approach 1:
Hermetic sealing is performed during the wafer fabrication process using established semiconductor manufacturing techniques. By executing the sealing action preliminarily during fabrication rather than as a separate post-processing step, the patent achieves pressure stability without significantly increasing manufacturing difficulty, as the sealing is integrated into the existing fabrication workflow.
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 each movable structure within the MEMS device to operate at its optimal pressure, allowing for the integration of multiple devices with different pressure requirements, such as inertial gyroscope and accelerometers, while providing mechanical stops to prevent damage from shocks.
Implementation Method 1
using techniques such as eutectic bonding and out-gassing mechanisms to create hermetically sealed environments with controlled pressures
Implementation Method 2
bonding engineered silicon on insulator wafers with standard CMOS wafers, using techniques such as eutectic bonding
Data Source
AI summary
An integrated MEMS device comprises a wafer where the wafer contains two or more cavities of different depths. The MEMS device includes one movable structure within a first cavity of a first depth and a second movable structure within a second cavity of a second depth. The cavities are sealed to maintain different pressures for the different movable structures for optimal operation. MEMS stops can be formed in the same multiple cavity depth processing flow. The MEMS device can be integrated with a CMOS wafer.