MEMS Capacitive Pressure Sensor Cavity Layout Without Sealing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing MEMS capacitive sensors face challenges in manufacturing absolute pressure sensors without sealing techniques and achieving high reproducibility and sensitivity, particularly in controlling membrane thickness and maintaining a high vacuum cavity.
Innovation Solution
A MEMS device design comprising three layers, with a trench in the top layer creating a cavity and a through-hole in the handling layer exposing the device layer to ambient pressure, allowing for the formation of pressure-sensitive membranes with precise thickness control and high vacuum encapsulation, enhancing sensitivity and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional sealing techniques are used to create vacuum cavities in MEMS pressure sensors, then hermetic sealing can be achieved, but manufacturing complexity and cost increase significantly
Solution Approach 1:
The patent removes the sealing structure entirely from the device architecture. By using a through-hole opening in the handling layer that exposes the device layer to ambient pressure, the cavity is naturally formed without requiring hermetic sealing techniques, thus eliminating the complexity associated with sealing while maintaining vacuum integrity through alternative means
Solution Approach 2:
Instead of sealing the cavity from the outside, the patent inverts the approach by creating an open through-hole structure where the handling layer is removed in specific regions to expose the device layer, allowing the cavity to be formed and maintained without traditional sealing mechanisms
2Manufacturing precision
If membrane thickness is not precisely controlled, then manufacturing is simpler, but sensor sensitivity and reproducibility decrease
Solution Approach 1:
The patent implements preliminary thickness control measures during the fabrication process by forming the device layer with a precisely controlled thickness before subsequent processing steps. This preliminary action ensures that the membrane thickness is established early in the manufacturing process, enabling consistent sensitivity and reproducibility across batches while maintaining ease of manufacture through standardized fabrication procedures
Solution Approach 2:
The patent utilizes parameter changes in the fabrication process, specifically controlling the thickness parameter of the device layer through precise deposition or etching conditions. By adjusting and controlling this critical parameter during manufacturing, the patent achieves both high manufacturing precision and maintained ease of manufacture through optimized process parameters
3Measurement precision
If multiple processing steps are added to improve sensor performance, then measurement accuracy increases, but manufacturing time and cost increase
Solution Approach 1:
The patent merges multiple functions into the existing fabrication process steps. The through-hole opening and cavity formation are integrated into the standard MEMS fabrication sequence, combining structural formation with functional element creation. This merging approach improves measurement precision through better cavity definition while maintaining manufacturing throughput by avoiding separate dedicated processing steps
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 design enables absolute pressure measurement without sealing requirements, improves manufacturing yields, and increases sensor sensitivity and reliability by controlling membrane thickness and maintaining a high vacuum, leading to improved accuracy and stability.
Implementation Method 1
the device layer forms the pressure sensitive membrane of the capacitor
Implementation Method 2
capacitive based pressure sensors are based upon the variation of capacitance arising from pressure induced membrane displacement
Data Source
AI summary
MEMS based sensors, particularly capacitive sensors, potentially can address critical considerations for users including accuracy, repeatability, long-term stability, ease of calibration, resistance to chemical and physical contaminants, size, packaging, and cost effectiveness. Accordingly, it would be beneficial to exploit MEMS processes that allow for manufacturability and integration of resonator elements into cavities within the MEMS sensor that are at low pressure allowing high quality factor resonators and absolute pressure sensors to be implemented. Embodiments of the invention provide capacitive sensors and MEMS elements that can be implemented directly above silicon CMOS electronics.