MEMS Beam Spiking Prevention via Segmented Metal Layers
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Solution Overview
Problem
The deposition of metal on silicon in MEMS devices leads to silicon absorption, known as spiking, which degrades the mechanical and optical properties of the beams, and adding silicon to the metal alloy to prevent spiking in semiconductors does not yield desired results for MEMS devices.
Innovation Solution
A MEMS device and fabrication method involving a beam structure with a first layer containing 1-2% silicon and a second layer without silicon, where the second layer is significantly thicker than the first, using a substrate and cavity configuration to maintain desired mechanical and optical properties while preventing spiking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a small percentage of silicon (1-2%) is added to the metal alloy to prevent spiking, then spiking is prevented, but the mechanical and optical properties of the beam deteriorate
Solution Approach 1:
The beam is divided into two distinct layers: a first beam layer containing silicon (1-2%) to prevent spiking, and a second beam layer substantially free of silicon to provide the required mechanical and optical properties. This segmentation allows each layer to fulfill its specific function without compromising the other.
Solution Approach 2:
Different regions of the beam are given different compositions tailored to their specific functions. The first beam layer adjacent to the cavity has silicon content optimized for preventing spiking, while the second beam layer has composition optimized for mechanical and optical performance. This local differentiation resolves the contradiction by assigning material properties according to spatial location and functional requirement.
2Ease of manufacture
If metal is deposited on silicon sacrificial layer, then the beam structure is formed, but silicon absorption (spiking) occurs which degrades beam properties
Solution Approach 1:
Silicon is pre-dissolved into the first beam layer material before deposition onto the sacrificial layer. This preliminary incorporation of silicon creates a diffusion barrier that prevents subsequent spiking during the metal deposition process, thereby maintaining manufacturing precision while enabling straightforward beam structure formation.
Solution Approach 2:
The first beam layer containing silicon acts as an intermediary between the silicon sacrificial layer and the second beam layer. This intermediate layer with controlled silicon content prevents direct silicon absorption into the metal, thus preventing spiking while allowing the manufacturing process to proceed easily.
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 approach effectively retains the desired mechanical and optical properties of MEMS beams while preventing spiking, with the second beam layer providing the necessary properties and the first layer controlling silicon absorption.
Implementation Method 1
The deposition of metal on silicon can, however, give rise to a problem of silicon absorption into the metal (known as spiking).
Implementation Method 2
The cavity under a beam is typically formed by depositing the metal beam material over a sacrificial layer which is later removed.
Data Source
AI summary
A MEMS device and method, comprising: a substrate; a beam; and a cavity located therebetween; the beam comprising a first beam layer and a second beam layer, the first beam layer being directly adjacent to the cavity, the second beam layer being directly adjacent to the first beam layer; the first beam layer comprising a metal or a metal alloy containing silicon; and the second beam layer comprising a metal or a metal alloy substantially not containing silicon. Preferably the second beam layer is thicker than the first beam layer e.g. at least five times thicker, and the first beam layer comprises a metal or alloy containing between 1% and 2% of silicon. The second beam layer provides desired mechanical and/or optical properties while the first beam layer prevents spiking.