Sapphire AlN Piezoelectric Sensor for High Temperature Pressure Sensing
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Solution Overview
Problem
Conventional piezoelectric pressure sensors are limited to low-temperature applications due to material and integration challenges, making them unsuitable for high-temperature environments like aircraft turbines, where materials must maintain piezoelectric properties and stability.
Innovation Solution
A flexural mode pressure sensor is developed using a single crystal sapphire substrate and membrane with a piezoelectric aluminum nitride (AlN) layer, integrated with platinum electrodes, allowing for high-temperature operation by leveraging the high-temperature stability of sapphire and AlN materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional piezoelectric materials are used in pressure sensors, then the sensors can be manufactured with standard materials and processes, but the sensors are limited to low-temperature applications (T<700°C) due to material thermal stability limitations
Solution Approach 1:
The patent changes the material parameters by selecting sapphire (Al2O3) with specific crystallographic orientation (c-plane) and aluminum nitride (AlN) piezoelectric layer with matched thermal and mechanical properties. This parameter selection enables the sensor to operate reliably at temperatures up to 1150°C while maintaining piezoelectric functionality and material stability.
Solution Approach 2:
The patent employs a composite material structure consisting of sapphire substrate, sapphire membrane, AlN piezoelectric layer, and platinum electrodes. This composite approach combines materials with complementary properties: sapphire provides high-temperature structural stability, AlN provides piezoelectric functionality at high temperatures, and platinum provides electrode stability. The composite structure achieves both high-temperature operation and material reliability.
2Temperature
If piezoelectric materials are selected for high-temperature stability, then the sensor can operate at elevated temperatures, but most commonly used piezoelectric materials lose their piezoelectric properties or become unstable
Solution Approach 1:
The patent identifies and utilizes the specific parameter range where AlN maintains stable piezoelectric properties at high temperatures. By carefully controlling the AlN layer thickness, crystal orientation (c-plane), and deposition parameters, the sensor achieves reliable piezoelectric functionality at temperatures up to 1150°C, overcoming the limitation of conventional piezoelectric materials that lose their properties above 700°C.
3Ease of manufacture
If traditional piezoelectric sensor configurations are used, then the manufacturing process is well-established, but the integration of materials with different thermal properties creates manufacturing challenges at high temperatures
Solution Approach 1:
The patent uses sapphire for both the substrate and the membrane, creating a homogeneous material system with matched thermal expansion coefficients and compatible processing requirements. This homogeneity simplifies the manufacturing process by eliminating interfacial compatibility issues between dissimilar materials, while still enabling high-temperature operation through the inherent properties of sapphire and AlN.
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 sensor maintains piezoelectric properties up to 1150°C, enabling effective pressure sensing in harsh environments beyond the limitations of traditional sensors, with improved chemical, electrical, and mechanical stability.
Implementation Method 1
When pressure (stress) is applied to a material it creates a strain or deformation in the material. In a piezoelectric material this strain creates an electrical charge.
Data Source
Figure 1~2
AI summary
A method for forming a pressure sensor 100 includes forming a base 122 of a sapphire material, the base including a cavity 12 formed therein; forming a sapphire membrane 104 on top of the base 122 and over the cavity 12; forming a lower electrode 108 on top of the membrane 104; forming a piezoelectric material layer on an upper surface of the lower electrode 108, the piezoelectric material layer being formed of aluminum nitride (AIN); and forming at least one upper electrode 112 on an upper surface of the piezoelectric material layer.