MEMS Capacitor Design for Stress-Resistant CMOS Integration
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing MEMS devices, such as out-of-plane sensors and micro-acoustical sensors, are vulnerable to stress caused by the manufacturing process, leading to inaccurate capacitance measurements and compatibility issues with standard CMOS processes.
Innovation Solution
A MEMS device design featuring misaligned upper and lower electrodes and a mass with outer mass parts connected to capacitor plates at different elevation levels, along with a manufacturing method involving anisotropic reactive ion etching and hydrogen fluoride vapor etching, to reduce stress impact and enable standard CMOS process compatibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large area capacitors are used in MEMS sensors, then capacitance measurement capability is improved, but stress vulnerability from manufacturing process increases
Solution Approach 1:
The capacitor structure is divided into multiple small capacitor units instead of using a single large capacitor. Each small capacitor has reduced area, making it less vulnerable to stress from manufacturing processes, while the combined effect of multiple capacitors maintains the required measurement capability.
Solution Approach 2:
The capacitor plates are arranged at different elevation levels (vertical stacking) rather than in the same plane. This three-dimensional arrangement reduces the horizontal area required for each capacitor while maintaining capacitance, thereby reducing stress vulnerability without sacrificing measurement capability.
2Reliability
If differential capacitor structure is made by wafer bonding, then sensor performance is improved, but process complexity increases and CMOS compatibility is lost
Solution Approach 1:
The differential capacitor structure is integrated with the standard CMOS fabrication process flow, merging the sensor manufacturing with the existing CMOS production line. This eliminates the need for separate wafer bonding processes and specialized manufacturing steps, reducing overall process complexity while maintaining sensor performance.
Solution Approach 2:
The capacitor structure is designed to be compatible with standard CMOS process materials and techniques, allowing the same fabrication infrastructure to produce both CMOS circuits and MEMS sensors. This universal approach enables single-chip integration and eliminates the need for separate processing lines.
3Area of stationary object
If single capacitor structure is used, then device area is reduced, but manufacturing stress impact increases
Solution Approach 1:
Instead of using one large capacitor, the design employs multiple small capacitors arranged in a compact configuration. Each small capacitor experiences less manufacturing stress due to its reduced size, and the compact arrangement keeps the overall device area small.
Solution Approach 2:
Capacitor plates are stacked vertically at different elevation levels, utilizing the third dimension to reduce the horizontal footprint. This vertical arrangement allows multiple capacitors to be packed into a small area while each individual capacitor remains small enough to resist manufacturing stress.
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 design reduces bending and stress-related inaccuracies, enhancing the sensitivity and accuracy of capacitance measurements while allowing for standard CMOS process compatibility, thus improving the reliability of MEMS devices.
Implementation Method 1
first etching the to-be-etched region by an anisotropic reactive ion etch
Implementation Method 2
then etching the to-be-etched region by hydrogen fluoride vapor etch or buffered oxide etch
Implementation Method 3
an upper electrode located above one of the two capacitor plates, forming one capacitor therewith; and a lower electrode located below the other of the two capacitor plates, forming another capacitor therewith
Data Source
AI summary
The present invention discloses a micro-electro-mechanical system (MEMS) device, comprising: a substrate with at least one opening; and a membrane supported on the substrate, the membrane including at least two thin segments and a thick segment connected together, wherein the two thin segments are not at the same level, and the thick segment is formed by a plurality of layers including at least two metal layers and a via layer, such that the membrane has a curve cross section.