Inclined Optical Window in MEMS Protective Wafer
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Solution Overview
Problem
Existing methods for manufacturing micromechanical devices with inclined optical windows are either expensive or result in suboptimal optical quality, and the processing of three-dimensional structures can damage wafers, making them unsuitable for high-volume applications.
Innovation Solution
A method involving a frame wafer with etched trenches forming a meander-shaped spring structure, allowing for the flexible suspension and adjustable positioning of an optical window, which is deflected out of parallel alignment with the MEMS wafer by creating a pressure difference across a hermetically sealed cavity, using customary MEMS and semiconductor technology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If three-dimensional structures (inclined windows) are manufactured from transparent material in wafer assembly, then reflections are avoided, but manufacturing cost increases and optical quality deteriorates
Solution Approach 1:
The patent applies dimensionality change by tilting the optical window relative to the wafer plane, transforming a two-dimensional parallel structure into a three-dimensional inclined structure. This angular orientation in the third dimension guides reflections out of the scan range, eliminating interfering reflections while maintaining compatibility with standard wafer-level packaging processes
Solution Approach 2:
The patent uses a mold or master structure to define the inclined window geometry, which is then replicated across multiple wafers simultaneously. This copying approach enables high-volume production of inclined windows at low cost, avoiding the need for expensive individual processing of each wafer
2Object-generated harmful factors
If three-dimensional structures (inclined windows) are manufactured in wafer assembly, then reflections are avoided, but optical quality deteriorates
Solution Approach 1:
The patent applies dimensionality change by tilting the optical window relative to the wafer plane, transforming a two-dimensional parallel structure into a three-dimensional inclined structure. This angular orientation in the third dimension guides reflections out of the scan range, eliminating interfering reflections while maintaining compatibility with standard wafer-level packaging processes
Solution Approach 2:
The patent optimizes specific parameters including the tilt angle of the window, the distance between the window and mirror surface, and the geometry of the spring structure. By carefully controlling these parameters, the patent achieves both reflection avoidance and high optical quality with minimal distortions
3Shape
If three-dimensional structures are manufactured in wafer assembly, then inclined windows are achieved, but structures may be damaged during processing
Solution Approach 1:
The patent incorporates a spring structure that provides mechanical cushioning and stress relief for the inclined window. This spring support system absorbs processing stresses and thermal expansion forces before they can damage the fragile inclined window structure, ensuring structural integrity throughout manufacturing and operation
Solution Approach 2:
The patent uses a flexible spring structure composed of thin silicon membranes that can elastically deform to accommodate the inclined window geometry. This flexible support structure protects the rigid inclined window from stress concentrations while maintaining the desired three-dimensional shape
4Ease of manufacture
If optical window is positioned in parallel to MEMS wafer, then manufacturing is simplified, but interfering reflections occur in scan range
Solution Approach 1:
The patent applies dimensionality change by tilting the optical window relative to the wafer plane, transforming a two-dimensional parallel structure into a three-dimensional inclined structure. This angular orientation in the third dimension guides reflections out of the scan range, eliminating interfering reflections while maintaining compatibility with standard wafer-level packaging processes
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 cost-effective high-volume production of micromechanical devices with inclined optical windows that avoid interfering reflections, while protecting the window from mechanical damage and ensuring high optical quality.
Implementation Method 1
subjecting the micromechanical device to an external atmospheric pressure, which is different from the internal atmospheric pressure of the cavity, whereby the optical window is deflected out of a rest position
Implementation Method 2
creating a through-opening from the front side to the rear side with the aid of etching; etching first trenches into the frame wafer from the front side; etching second trenches into the frame wafer from the rear side
Data Source
AI summary
A method for manufacturing a protective wafer including a frame wafer and an optical window, and to a method for manufacturing a micromechanical device including such a protective wafer having an inclined optical window. Also described are a protective wafer including a frame wafer and an optical window, and a micromechanical device including a MEMS wafer and such a protective wafer, which delimit a cavity, the protective wafer including an inclined optical window.