Vented Membrane Differential Pressure Sensor
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Solution Overview
Problem
Existing differential pressure sensors face challenges such as signal drift due to unstable reference cavity pressure, temperature dependency, and sensitivity issues related to membrane spring constant, which complicates the implementation of accurate and linear pressure measurements.
Innovation Solution
A differential pressure sensor design featuring a cavity with a suspended membrane and capacitive read-out system, integrated on top of an integrated circuit, allowing for two-port connections and ultra-low power consumption, which addresses the limitations of piezoresistive read-out and enables sensitivity and temperature correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a reference cavity with hermetic sealing is used to stabilize pressure, then signal drift is reduced, but manufacturing complexity and cost increase due to high-level sealing requirements
Solution Approach 1:
The patent removes the reference cavity entirely from the sensor structure. Instead of using a hermetically sealed reference cavity with stable but complex-to-manufacture sealing, the invention uses a vented cavity that opens to the environment through a controlled opening in the membrane, simplifying manufacturing while maintaining measurement reliability through differential capacitive sensing
Solution Approach 2:
The patent introduces a vented membrane structure as an intermediary between the reference environment and the sensing cavity. The membrane with controlled openings allows pressure equalization while maintaining the differential measurement capability, avoiding the need for high-level hermetic sealing
2Measurement precision
If thin membranes are used to increase deflection and sensitivity, then measurement sensitivity improves, but hermetic sealing becomes difficult to achieve
Solution Approach 1:
Instead of trying to make thin membranes hermetically sealed, the patent inverts the approach by deliberately creating controlled openings in the membrane and using the vented cavity design. This allows thin membranes to be used for high sensitivity while accepting that they cannot be hermetically sealed, resolving the contradiction by changing the fundamental assumption about membrane sealing
3Strength
If membrane spring constant is increased to reduce deformation under external pressure, then structural stability improves, but sensitivity decreases
Solution Approach 1:
The patent changes the measurement parameter from absolute pressure measurement (which requires high membrane stability) to differential pressure measurement. By measuring the pressure difference between the sensing cavity and the reference environment through the vented membrane, the system can use membranes with lower spring constants while maintaining structural stability through the differential measurement approach
4Measurement precision
If large deflection is achieved to improve sensitivity, then measurement range increases, but non-linearity in read-out circuitry increases
Solution Approach 1:
The patent replaces the piezoresistive mechanical read-out system with a capacitive sensing system. The capacitive measurement method is less sensitive to large deflections and non-linearities, allowing the membrane to deflect more freely while maintaining measurement linearity and accuracy through electrical field sensing rather than mechanical resistance measurement
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 reduces the form factor, enables cost-effective manufacturing, and provides high sensitivity and reliability by using standard CMOS materials and processes, while allowing for accurate differential pressure measurement with reduced thermal expansion effects.
Implementation Method 1
A differential pressure sensor is provided comprising a cavity having a base including a base electrode and a membrane suspended above the base which includes a membrane electrode... A capacitive read out system is used to measure the capacitance between the base electrode and membrane electrode
Implementation Method 2
Differential pressure is measured via deflection of the membrane due to a pressure difference between an external pressure and a gauge pressure which can be the ambient environmental pressure
Data Source
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AI summary
A differential pressure sensor comprises a cavity having a base including a base electrode and a membrane suspended above the base which includes a membrane electrode, wherein the first membrane is sealed with the cavity defined beneath the first membrane. A first pressure input port is coupled to the space above the sealed first membrane. A capacitive read out system is used to measure the capacitance between the base electrode and membrane electrode. An interconnecting channel is between the cavity and a second pressure input port, so that the sensor is responsive to the differential pressure applied to opposite sides of the membrane by the two input ports.