Multi-Pressure MEMS Enclosures via Segmented Wafer Bonding
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Solution Overview
Problem
Current MEMS device integration technologies face challenges in sealing multiple devices on a single chip at different pressures or gas compositions, requiring minimal processing steps and precise control, while also optimizing space usage.
Innovation Solution
The development of methods for creating multiple sealed enclosures on a chip using wafer bonding techniques, including secondary sealed enclosures, internal gas reservoirs, and controlled leak/breach methods, allows for independent pressure and gas composition control in each enclosure, achieved through various approaches such as multiple material systems, outgassing/gettering, and controlled solder flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional wafer bonding is used to seal multiple MEMS devices on a single chip, then hermetic sealing is achieved, but all devices are sealed at the same pressure and gas composition
Solution Approach 1:
The chip is divided into multiple independent sealed enclosures, each capable of maintaining different pressure and gas composition environments. The wafer bonding process is segmented into multiple stages, with intermediate bonding steps that allow selective sealing of different regions at different pressures before final integration
Solution Approach 2:
Pressure control structures and gas reservoirs are pre-configured during wafer fabrication before bonding. Sacrificial layers are deposited and patterned in advance to define sealed regions, and pressure equalization channels are pre-formed to enable controlled pressure differential establishment after bonding
2Adaptability or versatility
If multiple sealed enclosures are created with different pressures, then operational flexibility for different MEMS devices is improved, but processing steps and control precision requirements increase
Solution Approach 1:
Pressure equalization channels and flow control structures act as intermediaries between different sealed enclosures and external pressure sources. These intermediary structures enable precise pressure control in each enclosure through controlled gas flow, allowing independent pressure adjustment without affecting other sealed regions
Solution Approach 2:
The system utilizes changes in gas flow rate, pressure differential, and temporal sequencing of bonding steps to achieve precise pressure control. By dynamically adjusting these parameters during and after bonding, different pressure environments are established and maintained in each sealed enclosure with high precision
3Productivity
If wafer level packaging is used for MEMS devices, then integration efficiency and cost effectiveness are improved, but the ability to provide different ambient environments for different devices is limited
Solution Approach 1:
The wafer is segmented into multiple independently sealable regions during fabrication, with each region capable of forming its own sealed enclosure. This segmentation is achieved through patterned sacrificial layers and selective bonding structures that allow each region to be sealed at different pressures while maintaining wafer-level processing efficiency
Solution Approach 2:
The wafer bonding process is designed to perform multiple functions simultaneously: hermetic sealing, electrical interconnection, and pressure differential establishment. The bonding structure serves as a universal platform that integrates mechanical support, electrical contacts, and pressure control pathways across all sealed enclosures on the wafer
4Adaptability or versatility
If secondary sealed enclosures are integrated alongside main sealed enclosures, then multiple pressure environments are achieved, but device complexity and space requirements increase
Solution Approach 1:
Secondary sealed enclosures are nested within or adjacent to main sealed enclosures, sharing common bonding interfaces and pressure control pathways. This nested configuration allows multiple pressure environments to coexist on the chip with minimized space utilization, as inner enclosures share structural support and control infrastructure with outer enclosures
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
Enables the integration of MEMS devices with different operational requirements on a single chip, providing precise control over pressure and gas composition for each device, enhancing operational efficiency and flexibility.
Implementation Method 1
The MEMS wafer is bonded to the CMOS wafer using AlGe eutectic bonding between the Al on the CMOS and the Ge on the MEMS wafer at 140, for example
Implementation Method 2
removing a sacrificial layer to provide open cavities
Implementation Method 3
A laser is used to open the sealed enclosures
Data Source
AI summary
A Microelectromechanical systems (MEMS) structure comprises a MEMS wafer. A MEMS wafer includes a handle wafer with cavities bonded to a device wafer through a dielectric layer disposed between the handle and device wafers. The MEMS wafer also includes a moveable portion of the device wafer suspended over a cavity in the handle wafer. Four methods are described to create two or more enclosures having multiple gas pressure or compositions on a single substrate including, each enclosure containing a moveable portion. The methods include: A. Forming a secondary sealed enclosure, B. Creating multiple ambient enclosures during wafer bonding, C. Creating and breaching an internal gas reservoir, and D. Forming and subsequently sealing a controlled leak/breach into the enclosure.