title: Design, Optimisation and Characterisation of 3C-SiC/Si Pressure Sensors
Creators: name: Tong, Braiden T
Publisher: name: Griffith University
Year: 2024
Subjects: subject: silicon carbide
subject: pressure sensors
subject: MEMS technology

description: This thesis presents a comprehensive investigation into the design, optimization, and characterization of 3C-SiC pressure sensors for pressure monitoring applications, particularly focusing on the challenges of operating in extreme environments. Micro Electro Mechanical Systems (MEMS) technology has significantly advanced sensor design with its miniaturization, low power consumption, and mass production potential. Pressure sensors, as one of the primary applications of MEMS, are widely used across industries such as automotive, healthcare, and environmental monitoring, as well as in the growing Internet of Things (IoT). Silicon carbide (SiC) emerges as a promising material for pressure sensors in harsh environments due to its superior mechanical, electrical, thermal, and chemical properties when compared to traditional silicon-based sensors. Despite SiC's potential, SiC-based pressure sensors have historically faced challenges in sensitivity, necessitating innovative design and material optimization methods.The thesis is structured into several key chapters. In Chapter 2, a literature review examines the fundamental principles of MEMS pressure sensors, emphasizing the piezoresistive effect, as well as the core properties of SiC and SiC/Si heterojunctions and their applications in pressure sensors. Furthermore, Chapter 2 explores techniques used to enhance sensor sensitivity and enable self-powered operation in state-of-the-art sensors.Chapter 3 focuses on the design, fabrication, and characterization of a highly sensitive and robust 3C-SiC/Si pressure sensor featuring a stress amplification structure. This design includes four Si pillars that amplify strain in the sensing elements, resulting in significantly higher stress concentrations compared to traditional designs. Additionally, the front side of the sensor is coated with a 3C-SiC thin film for chemical protection, enabling the sensor to operate in corrosive environments. The sensor demonstrates a high sensitivity of 0.276 mV/V/kPa and a non-linearity of 2.2% within the 0-100 kPa range.In Chapter 4, a proof-of-concept optoelectronic pressure sensor is introduced. This sensor leverages the piezo-optoelectronic effect to convert mechanical stress into photovoltage changes. By integrating a circular diaphragm with specific electrode placement and utilizing the properties of the 3C-SiC/Si junction, the sensor exhibits a sensitivity of 1.59 µV/kPa and maintains non-linearity of 4.12% under controlled light conditions. Testing under dynamic and static pressures confirms the sensor's capability to accurately track pressure changes and maintain long-term stability, with minimal drift observed over extended periods. This chapter highlights the potential for light-powered sensing applications across various fields.Overall, this research contributes to the advancement of 3C-SiC pressure sensors for harsh environments, offering innovative designs and optimization methods that enhance sensor performance and reliability. The work paves the way for future applications in fields requiring precise pressure sensing in extreme conditions.