Effects of Electrode Structure on H2S Sensing and Low-Frequency Noise Characteristics in In2O3-Based Resistor-Type Gas Sensors

Abstract

Most studies on gas sensors are focusing on improving the response of the sensor. However, noise characteristics should also be considered for the design of gas sensors with optimal performance. This paper investigates the effects of electrode structure on H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S gas sensing and low-frequency noise (LFN) characteristics in In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> resistor-type gas sensors. We mainly analyze the response and noise performances of the interdigitated electrode (IDE) sensors with different combinations of spacing between the fingers ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{\mathrm{f}}$ </tex-math></inline-formula> ) and the number of electrode fingers ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N}_{\mathrm{f}}$ </tex-math></inline-formula> ). Parallel electrode (PE) sensors are also compared as a reference. For the IDE sensors, the response increases as the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{\mathrm{f}}$ </tex-math></inline-formula> decreases (or N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> increases), while the PE sensors show constant response regardless of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{\mathrm{f}}$ </tex-math></inline-formula> . The gas response characteristics of the IDE and PE sensors are further analyzed using the gas sensing results of a transmission line method (TLM) pattern. It is shown that the contributions of bulk and contact to the overall gas response differ depending on electrode spacing. The normalized LFN of the IDE sensors is at least 100 times smaller than that of the PE sensors since <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{\mathrm{f}}$ </tex-math></inline-formula> greatly affects the noise characteristics. The limit of detection (LOD) of the sensor for H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S gas can be improved from 8380 ppb ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{\mathrm{f}}= 100\,\,\mu \text{m}$ </tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N}_{\mathrm{f}} = 2$ </tex-math></inline-formula> ) to 6.42 ppb ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{\mathrm{f}}= 2\,\,\mu \text{m}$ </tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N}_{\mathrm{f}} = 30$ </tex-math></inline-formula> ) by adopting a shortly spaced interdigitated electrode structure. The results provide an electrode design guidance for the resistor-type gas sensors that show optimal performance considering both the noise and gas response.