MEMS Array Segmentation for CMOS Integration
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Solution Overview
Problem
MEMS devices, such as accelerometers and variable capacitors, face challenges in being integrated into a single chip due to size constraints and packaging complexities, leading to increased costs and limited integration capabilities.
Innovation Solution
Replacing a single larger MEMS device with an array of smaller MEMS devices, allowing for encapsulation within a CMOS-compatible process, which enables accurate signal averaging and integration within standard semiconductor processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a single larger MEMS device is used, then the device can cover the required sensing area for desired physical properties, but the device cannot be sealed in a cavity using typical interlayer dielectrics and metallization
Solution Approach 1:
The patent divides a single large MEMS device into multiple smaller MEMS devices arranged in an array. Each smaller device has a reduced area that allows it to be successfully sealed within a cavity using standard interlayer dielectric and metallization layers, while the collective array maintains the required total sensing area for proper device function
2Reliability
If MEMS devices are separately packaged to prevent cavity collapse under pressure, then the cavity can maintain structural integrity, but the production cost doubles
Solution Approach 1:
By segmenting the MEMS device into smaller units, the patent enables the use of standard thin interlayer dielectric and metallization layers to form sealed cavities that can withstand operational pressures without requiring expensive separate packaging or hermetic sealing processes
Solution Approach 2:
The patent changes the size parameter of the MEMS devices from large to small, which fundamentally alters the mechanical stress distribution and allows standard fabrication materials to provide sufficient structural support without additional packaging layers
3Reliability
If a large MEMS device is used for variable capacitor applications, then the device can provide the required capacitance range, but the device cannot be integrated on the same chip as micro controller or logic devices
Solution Approach 1:
The patent segments the large MEMS variable capacitor into an array of smaller MEMS variable capacitors, allowing the entire array to be fabricated on the same chip as micro controllers or logic devices using standard CMOS-compatible processes, while maintaining the required total capacitance range through the combined effect of multiple smaller capacitor elements
4Ease of manufacture
If an array of smaller MEMS devices is used, then the devices can be encapsulated in a cavity using CMOS compatible processes, but the signal averaging is required to maintain accuracy
Solution Approach 1:
The patent merges the output signals from multiple smaller MEMS devices through averaging or summation operations, combining their individual measurements to achieve the same accuracy and sensitivity as a single large device, while enabling CMOS-compatible fabrication and integration
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 reduces production costs, enhances integration capabilities, and improves sensitivity and switching speed by leveraging the collective performance of the array of smaller devices, while maintaining or improving accuracy and reducing noise immunity.
Implementation Method 1
The typical sensing scheme is capacitance based
Implementation Method 2
MEMS based accelerometers have been built using a variety of micro-machining techniques for many years
Data Source
Figure 1A~1B
Figure 1C~1D
Figure 1E~1F
AI summary
Embodiments disclosed herein generally include using a large number of small MEMS devices to replace the function of an individual larger MEMS device or digital variable capacitor. The large number of smaller MEMS devices perform the same function as the larger device, but because of the smaller size, they can be encapsulated in a cavity using complementary metal oxide semiconductor (CMOS) compatible processes. Signal averaging over a large number of the smaller devices allows the accuracy of the array of smaller devices to be equivalent to the larger device. The process is exemplified by considering the use of a MEMS based accelerometer switch array with an integrated analog to digital conversion of the inertial response. The process is also exemplified by considering the use of a MEMS based device structure where the MEMS devices operate in parallel as a digital variable capacitor.