Weakened Substrate MEMS Fabrication for Uniform Capacitor Spacing
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Solution Overview
Problem
Conventional micromachining techniques struggle to maintain uniform spacing between capacitor plates in electrostatic MEMS devices, particularly in CMUTs, leading to inefficiencies and increased costs due to the use of expensive silicon-on-insulator wafers.
Innovation Solution
A method involving a weakened substrate is used, where one substrate is cleaved to a reduced thickness and secured to another substrate with conductive walls forming capacitive elements, allowing for uniform spacing and reducing material waste by eliminating the need for expensive SOI wafers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional micromachining techniques are used to form CMUTs, then the capacitor plates can be formed, but the spacing between plates becomes irregular and non-uniform
Solution Approach 1:
The patent applies preliminary action by forming the weakened plane in the substrate before forming the capacitor plates and other device structures. This pre-established reference plane guides subsequent fabrication steps to achieve uniform spacing between plates, solving the spacing uniformity problem without requiring expensive SOI wafers.
Solution Approach 2:
The patent changes the physical state of the substrate by creating a weakened plane with specific mechanical properties (reduced strength, controlled fracture behavior). This parameter change allows the substrate to be selectively removed along the weakened plane, establishing a precise reference surface that ensures uniform capacitor plate spacing.
2Manufacturing precision
If expensive silicon-on-insulator wafers are used to achieve uniform spacing, then manufacturing precision improves, but fabrication costs increase significantly
Solution Approach 1:
The patent replaces expensive SOI wafers with a conventional substrate that has a weakened plane. The weakened substrate serves as a disposable reference structure that can be selectively removed, providing the same spacing uniformity function as SOI wafers but at much lower cost.
Solution Approach 2:
The patent changes the mechanical parameters of a conventional substrate by introducing a weakened plane, transforming it into a cost-effective alternative to expensive SOI wafers. The weakened plane provides the necessary reference surface for uniform spacing without requiring the expensive insulator layer of SOI technology.
3Loss of substance
If conventional substrates are used without weakening, then material utilization is high, but the substrate cannot be selectively removed to achieve thin uniform thickness
Solution Approach 1:
The patent segments the substrate by creating a weakened plane that divides the substrate into removable and retained portions. This segmentation allows selective removal of excess substrate material while retaining the thin uniform portion needed for device operation, achieving both low material waste and high thickness uniformity.
Solution Approach 2:
The patent applies preliminary action by forming the weakened plane before device fabrication, creating a pre-defined separation path. This allows the substrate to be selectively removed along the weakened plane to achieve the desired thin uniform thickness without wasting material.
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 production of MEMS devices with uniform spacing between capacitive elements, reducing fabrication costs and improving the efficiency of CMUTs without the need for expensive silicon-on-insulator wafers.
Implementation Method 1
separates a portion of the first substrate along the plane generally parallel to the first interior surface after securing the first and second substrates
Data Source
AI summary
A method of producing a MEMS device provides a first substrate having a first interior surface and thickness, and a second substrate having a second interior surface. The method also forms at least one closed wall on at least one of the first and second substrates, weakens the first substrate in a plane generally parallel to the first interior surface, and secures the first substrate to the second substrate. The at least one closed wall extends between the first interior surface and the second interior surface. The method further separates a portion of the first substrate along the plane generally parallel to the first interior surface after securing the first and second substrates, and removes an excess portion of the first substrate to produce a reduced thickness first substrate of no greater than about 20 microns.