Substrate-Based Package for MEMS Capacitive Sensors
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Solution Overview
Problem
The high manufacturing costs and limitations of standard wafer fab technology restrict the widespread integration of pressure sensors, microphones, and accelerometers in industries like automotive, medical, and aerospace, due to the expensive fabrication processes and material compatibility issues with standard wafer processes.
Innovation Solution
Integrating movable MEMS device parts, such as mechanical elements and sensors, into low-cost device materials and packages, using a substrate-based package that separates movable parts from electronics, allowing for standard CMOS chip usage and packaging with movable structures built into the package, such as leadframe-based or substrate-based plastic molded housing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If standard wafer fab technology is used for MEMS device fabrication, then manufacturing precision and device performance are improved, but manufacturing cost increases significantly
Solution Approach 1:
The patent divides the MEMS device into two separate fabrication processes: (1) standard wafer fab process for fabricating the semiconductor chip with high precision, and (2) a separate low-cost packaging process that integrates the movable MEMS elements into the package substrate. This segmentation allows each part to be optimized independently - the chip maintains high precision requirements while the package uses cost-effective materials and processes.
Solution Approach 2:
The patent extracts the movable MEMS elements (such as the membrane for pressure sensors or diaphragm for microphones) from the expensive semiconductor chip fabrication process and relocates them to the package substrate. This extraction eliminates the need for costly wafer fab processes for these specific components while maintaining their functional performance.
2Reliability
If hermetic packages or ceramic packages are used for MEMS devices, then device protection and reliability are improved, but manufacturing cost increases significantly
Solution Approach 1:
The patent merges the protective packaging function with the structural substrate into a single integrated package. The package substrate itself serves as both the mechanical support and the protective enclosure, eliminating the need for separate hermetic sealing layers or ceramic encapsulation. This integration maintains device protection while using cost-effective plastic or composite materials.
Solution Approach 2:
The patent changes the material parameters of the package substrate to achieve both protection and cost-effectiveness. By selecting specific plastic materials or composite structures with appropriate mechanical and environmental resistance properties, the package provides sufficient protection without requiring expensive ceramic or metal hermetic sealing.
3Adaptability or versatility
If movable MEMS parts are fabricated using bulk micromachining or surface micromachining techniques, then device functionality is improved, but manufacturing time and complexity increase
Solution Approach 1:
The patent performs preliminary action by pre-fabricating the movable MEMS elements (such as membranes, diaphragms, or proof masses) directly into the package substrate during the packaging process itself, rather than fabricating them separately through time-consuming micromachining steps. This preliminary integration into the substrate structure eliminates subsequent complex processing steps and accelerates manufacturing throughput.
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 significantly reduces fabrication costs by up to 80% for MEMS devices like pressure sensors and enables greater system-level integration, enhancing electrical product efficiency and compatibility with various applications.
Implementation Method 1
In the capacitive operation, the pressure causes a displacement-dependent output signal. The change in pressure causes a displacement, the displacement causes a capacitor change, and the capacitor change causes electrical signal
Implementation Method 2
the capacitor change causes electrical signal—similar to the operation of a condenser microphone
Data Source
AI summary
A method of fabricating a MEMS device is disclosed. A metal layer is provided over a first surface of a substrate including over an opening. The metal layer is patterned to define a membrane segment and a pad, with the membrane segment extending at least partially across the opening. An integrated circuit chip is attached over the opening to the membrane segment and pad, with the integrated circuit separated from an extending portion of the membrane segment by a gap. The integrated circuit chip includes a conductive member so that deflection of the extending portion relative to the conductive member can be measured as a change in capacitance.