Cointegrated MEMS Sensor Using Segmented SOI Fabrication
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Solution Overview
Problem
Existing MEMS sensor fabrication methods face challenges in integrating semiconductor electrical circuits due to high temperature bonding processes, which can cause merging and diffusion issues with implant areas, limiting sensor size and complexity.
Innovation Solution
A MEMS sensor assembly is created with a thin upper silicon layer acting as both the substrate for semiconductor electrical circuits and the active mechanical element, where the semiconductor circuits are fabricated after the MEMS structure formation, using a SOI wafer bonded with a cavity and insulating layers, allowing for a strong bond without high temperature exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high temperature bonding process (approximately 1000°C) is used to bond SOI wafer to MEMS wafer, then strong bond and clearly defined channel formation occur, but implant areas of semiconductor electrical circuits merge and diffuse
Solution Approach 1:
The patent segments the fabrication process into two distinct stages: first forming the MEMS structure at lower temperatures, then bonding the SOI wafer at approximately 1000°C to create strong bonds and defined channels. This temporal segmentation allows each process to occur under optimal conditions without interfering with the other, resolving the contradiction between bond strength and implant area precision.
Solution Approach 2:
The patent applies preliminary action by forming the MEMS structure and implant areas before performing the high-temperature bonding process. This ensures that the implant areas are already defined and protected before exposure to temperatures that would cause diffusion, while still achieving strong bonding and channel formation in the subsequent step.
2Device complexity
If MEMS and semiconductor electrical circuits are created at the same time, then integration occurs, but implant areas merge and diffuse during bonding process
Solution Approach 1:
The patent divides the device fabrication into separate stages: MEMS structure formation first, followed by SOI wafer bonding, and finally semiconductor circuit completion. This segmentation enables full integration of MEMS and semiconductor circuits while preventing implant area diffusion by avoiding simultaneous high-temperature processing of both structures.
Solution Approach 2:
The patent performs preliminary formation of the MEMS structure and implant areas before bonding the SOI wafer containing the semiconductor circuits. This preliminary action establishes precise implant boundaries that are preserved during the subsequent bonding process, enabling integrated device functionality without implant diffusion.
3Strength
If high temperature processing is used for bonding, then strong bond occurs, but sensor size and complexity are limited
Solution Approach 1:
The patent segments the fabrication process to perform high-temperature bonding only for the SOI wafer attachment, while completing semiconductor circuit fabrication at lower temperatures afterward. This enables more complex sensor designs with submicron semiconductor circuits that would be impossible if all processing had to occur simultaneously at high temperatures.
Solution Approach 2:
The patent performs the high-temperature bonding action preliminarily to establish the structural foundation, then completes the semiconductor circuit fabrication at lower temperatures. This sequence enables greater device complexity and smaller feature sizes in the final integrated sensor while maintaining strong bonding.
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 the integration of submicron semiconductor electrical circuits, facilitating more complex signal processing and smaller sensor designs suitable for various applications, including wireless sensor networks and suspended structures.
Implementation Method 1
temperatures of approximately 1000° C. are used in order that a strong bond of the SOI wafer to the MEMs wafer occurs
Data Source
AI summary
Described herein is a method for integrating MEMS with submicron semiconductor electrical circuits such as CMOS to provide more complex signal processing, on-chip calibration and integration with RF technologies. A MEMS sensor is provided having an upper layer, an insulating layer into which a cavity has been formed and a handle layer. The upper layer acts as both the substrate of the semiconductor electrical circuit and as the active MEMS element. The remainder of the circuitry is fabricated either in or on the upper layer. In a preferred method of the present invention a first wafer assembly and a second wafer assembly are fabricated such that a MEMS sensor and the substrate of at least one semiconductive electrical circuit is formed.