Using a floating-gate MOS transistor as a transducer in a MEMS gas sensing system.

Area of Science:

• Materials Science
• Electrical Engineering
• Sensor Technology

Background:

• Floating-gate metal-oxide-semiconductor (MOS) transistors are versatile components in analog and digital systems, including chemical sensors for pH and hydrogen detection.
• Monolithic integration of sensors with control and signal processing electronics is a key goal, leveraging CMOS and MEMS technology compatibility.
• Reliability of these transistors under conditions involving chemical reactions with metallic oxides and gases is crucial for sensor applications.

Purpose of the Study:

• To conduct an in-depth analysis of the reliability of floating-gate MOS transistors.
• To investigate the impact of charge generation from chemical reactions between metallic oxide thin films and gases on transistor reliability.
• To confirm the operational principle of a sensor utilizing a MOS transistor with an iron(II) oxide (Fe2O3) layer for gas detection.

Main Methods:

• Analysis of floating-gate MOS transistor reliability under specific chemical reaction conditions.
• Investigation of metallic oxide thin films reacting with reducing or oxidizing gases at elevated temperatures (around 200 °C or higher).
• Experimental confirmation using a MOS transistor with a Fe2O3 layer in series, monitoring electrochemical potential during propane reaction.

Main Results:

• Demonstrated the presence of an electrochemical potential on the ferrite (Fe2O3) layer when reacting with propane.
• Highlighted the necessity of thermal insulation for sensor electronics operating at room temperature during high-temperature chemical reactions.
• Provided insights into the reliability challenges and operational principles of MOS-based chemical sensors.

Conclusions:

• Floating-gate MOS transistors are viable for chemical sensing applications, particularly when integrated with metallic oxide layers.
• Careful thermal management is essential for reliable operation of integrated sensor systems.
• The study confirms the electrochemical sensing mechanism in MOS transistors with ferrite layers reacting to specific gases.