Thermal Bimorph Sensor - A Sensor For Flight Applications

This paper presents a robust and capable set of MEMS temperature sensors with a high dynamic range that I developed with a friend. The sensors are designed for flight applications, where a high dynamic range is essential due to the quick changes in temperature from both the quick changes in altitude and extreme heat often generated by aircraft propulsion systems. The sensors are created using several bimorph beams placed together to form a MEMS comb capacitor. The key manufacturing features that make this structure robust are as follows: a SiO2 layer is grown and coated with Ti to interact with the Al to create a bimorph cantilever beam, and the fabrication process is relatively simple, resulting in a high yield of manufacturing. The sensors’ changing fringing fields due to the motion of the cantilevers result in a highly reliable sensor. They tend to have higher sensitivity at the upper end of our temperature ranges due to the exponential relationship between capacitance and temperature. The sensors’ frequency responses also have a linear relationship with temperature. 

Introduction

Temperature sensors are essential for flight applications such as commercial or military aeronautics, where they are used to monitor many aspects of aircraft, such as external temperature and pressure, as well as internal temperature or pressure in both passenger and pilot areas, and in key components such as jet engines. Due to the quick changes in temperature from both the quick changes in altitude, as well as the extreme heat often generated by aircraft propulsion systems, having a temperature sensor with a high dynamic range is essential. I present a set of MEMS temperature sensors with a high dynamic range. 

Design

The sensor is created using several bimorph beams placed together to form a MEMS comb capacitor. The key manufacturing features that make this structure robust are as follows. A SiO2 layer is grown and coated with Ti to interact with the Al to create a bimorph cantilever beam. Additionally, the fabrication process is relatively simple, resulting in a high yield of manufacturing. The bimorph design for capacitive sensing is one such sensor with capabilities of high dynamic range and robustness, as well as quick response time which meets the aforementioned criteria. The sensor can also be manufactured relatively cheaply from metal (i.e. Aluminum) and a thermal oxide (SiO2). The sensor also operates passively and needs only to be read to derive a value for temperature, while other typical CMOS sensors would not. 

Evaluation

The design of the sensor takes into consideration how we want it to operate along its designed range. It is preferable that the bimorphs lay flat at the sensor’s max operating temperature while also not flexing too much at the minimum operating temperature to avoid compromising the structural integrity of the beams. The sensor’s capacitance across the temperature range is difficult to analytically derive due to the complexity of the fringing field of the sensor. However, it is possible to calculate the max temperature when all beams lay flat, as well as model a general expected pattern from other experimental examples. It is also possible to find the capacitance empirically through either testing or simulation. The sensors’ frequency responses have a linear relationship with temperature.

Regarding the results below:
The boxed section on the right were properties that I selected for our specific purpose. Along with that, the other important note is that I set that the middle point of the sensor does not experience any deflection at room temperature.

Conclusion

The MEMS temperature sensors I presented in this paper are a robust and capable set of sensors with a high dynamic range. The sensors are designed for flight applications, where a high dynamic range is essential due to the quick changes in temperature from both the quick changes in altitude and extreme heat often generated by aircraft propulsion systems. The sensor is created using several bimorph beams placed together to form a MEMS comb capacitor. The key manufacturing features that make this structure robust are a SiO2 layer grown and coated with Ti to interact with the Al to create a bimorph cantilever beam, and the fabrication process is relatively simple, resulting in a high yield of manufacturing.

Overall, the success of a research study relies heavily on the strength of its design and the rigor of its evaluation. Researchers must carefully consider all aspects of the study design, from selecting appropriate participants and measures to minimizing sources of bias and controlling for confounding variables. Additionally, the evaluation process must be thorough and transparent, ensuring that the results are both valid and reliable.

While the research process can be complex and challenging, following best practices in study design and evaluation can help ensure that the results are meaningful and contribute to our understanding of the world around us. With careful planning and execution, research studies can have a significant impact on both academic and real-world contexts.