Capacitance Pressure Sensor with Suspended Void
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Solution Overview
Problem
Conventional pressure sensors face challenges with size reduction, cost minimization, and reduced current consumption due to different fabrication processes for various sensors, and are prone to temperature and stress-induced inaccuracies from external package effects.
Innovation Solution
The development of capacitance-based pressure sensors using a pressure vessel with a cross-section defining a void that changes shape with pressure differences, embedded in a semiconductor substrate, and a capacitive structure that changes capacitance with the void's shape, allowing for reduced stress and thermal sensitivity, shared fabrication processes with inertial sensors, and vertical capacitor plates for increased sensitivity and area efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional pressure sensors use membrane supported by surrounding electronic package, then structure is simple to manufacture, but temperature and stress changes are transmitted into supports creating false readings
Solution Approach 1:
The pressure sensing membrane is extracted from the surrounding electronic package structure and suspended within a cavity formed in the substrate. This isolation removes the membrane from direct mechanical coupling with external supports, preventing transmission of temperature-induced stresses and package expansions to the sensing element, thereby eliminating false readings while maintaining manufacturing simplicity
Solution Approach 2:
A cavity is introduced as an intermediary space between the membrane and the external environment. This cavity acts as a mechanical isolator, allowing the membrane to respond only to pressure changes while blocking transmission of thermal stresses and package deformations, thus protecting measurement accuracy without complicating the manufacturing process
2Measurement precision
If piezoelectric materials are used in the membrane for strain sensing, then sensitivity to pressure changes is improved, but sensitivity to temperature changes increases
Solution Approach 1:
The piezoelectric membrane is extracted from direct contact with external supports and placed in a suspended configuration within a cavity. This isolation removes the primary pathway for temperature-induced stresses from external sources to reach the piezoelectric material, reducing temperature sensitivity while preserving the material's inherent pressure sensitivity
Solution Approach 2:
The patent acknowledges that piezoelectric materials are inherently sensitive to temperature changes, but converts this potential harm into a benefit by using the suspended membrane configuration to selectively isolate the material. The same structural configuration that provides pressure sensitivity also blocks thermal stress transmission, turning the material's sensitivity into a selective response characteristic
3Measurement precision
If calibration techniques with reference sensing element are used, then inaccuracies from internal tensions are removed, but substantial area on substrate is consumed
Solution Approach 1:
The pressure sensing membrane is extracted from the surrounding electronic package structure and suspended within a cavity formed in the substrate. This isolation removes the membrane from direct mechanical coupling with external supports, preventing transmission of temperature-induced stresses and package expansions to the sensing element, thereby eliminating false readings while maintaining manufacturing simplicity
4Ease of manufacture
If membrane is made coplanar with substrate, then fabrication process is simplified, but area consumption is increased
Solution Approach 1:
The membrane structure transitions from a coplanar configuration to a three-dimensional suspended configuration within a cavity. This dimensional change allows the membrane to be formed using standard planar fabrication processes while the vertical suspension within the cavity reduces the horizontal area footprint, effectively consuming less substrate area without complicating the fabrication process
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 solution results in pressure sensors with low manufacturing costs, high sensitivity to pressure changes, immunity to external stress and temperature, and reduced area consumption, enabling integration with inertial sensors on the same wafer.
Implementation Method 1
Capacitance-based principles can be used to detect a magnitude of the change, such that a greater capacitance corresponds to a greater magnitude. When a voltage is applied between the membrane and the electrode, a difference between the charges on the membrane and the electrode is related to their separation.
Implementation Method 2
The void has a shape that is configured to change based on a change of pressure difference between a cavity pressure in a cavity in which at least a portion of the pressure vessel is suspended and a vessel pressure in the pressure vessel.
Implementation Method 3
A relative change of a pressure above the membrane with respect to a pressure below the membrane causes a net force that deforms the membrane.
Data Source
AI summary
Techniques are described herein that perform capacitance-based pressure sensing using pressure vessel(s). A pressure vessel is an object that has a cross section that defines a void. The void has a shape that is configured to change based on a change of pressure difference between a cavity pressure in a cavity in which at least a portion of the pressure vessel is suspended and a vessel pressure in the pressure vessel. The pressure vessel may be formed in the shape of an enclosed loop (e.g., along a path that is perpendicular to the cross section), resulting in a looped pressure vessel. For instance, an end of the pressure vessel may be connected to another end of the pressure vessel to form the enclosed loop.