Abstract
In this thesis, field effect gas sensors (Schottky diodes, MOS capacitors, and MOSFET transistors) based on wide band gap semiconductors like silicon carbide (SiC) and gallium nitride (GaN), as well as resistive gas sensors based on indium oxide (In{sub 2}O{sub 3}), have been developed for the detection of reducing gases (H{sub 2}, D{sub 2}) and oxidising gases (NO{sub x}, O{sub 2}). The development of the sensors has been performed at the Institute for Micro- and Nanoelectronic, Technical University Ilmenau in cooperation with (GE) General Electric Global Research (USA) and Umwelt-Sensor- Technik GmbH (Geschwenda). Chapter 1: serves as an introduction into the scientific fields related to this work. The theoretical fundamentals of solid-state gas sensors are provided and the relevant properties of wide band gap materials (SiC and GaN) are summarized. In chapter 2: The performance of Pt/GaN Schottky diodes with different thickness of the catalytic metal were investigated as hydrogen gas detectors. The area as well as the thickness of the Pt were varied between 250 {proportional_to} 250 {mu}m{sup 2} and 1000 {proportional_to} 1000 {mu}m{sup 2}, 8 and 40 nm, respectively. The response to hydrogen gas was investigated in dependence on the active area, the Pt thickness and the operating
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Citation Formats
Ali, Majdeddin.
Wide band gap materials and devices for NO{sub x}, H{sub 2} and O{sub 2} gas sensing applications.
Germany: N. p.,
2008.
Web.
Ali, Majdeddin.
Wide band gap materials and devices for NO{sub x}, H{sub 2} and O{sub 2} gas sensing applications.
Germany.
Ali, Majdeddin.
2008.
"Wide band gap materials and devices for NO{sub x}, H{sub 2} and O{sub 2} gas sensing applications."
Germany.
@misc{etde_21122067,
title = {Wide band gap materials and devices for NO{sub x}, H{sub 2} and O{sub 2} gas sensing applications}
author = {Ali, Majdeddin}
abstractNote = {In this thesis, field effect gas sensors (Schottky diodes, MOS capacitors, and MOSFET transistors) based on wide band gap semiconductors like silicon carbide (SiC) and gallium nitride (GaN), as well as resistive gas sensors based on indium oxide (In{sub 2}O{sub 3}), have been developed for the detection of reducing gases (H{sub 2}, D{sub 2}) and oxidising gases (NO{sub x}, O{sub 2}). The development of the sensors has been performed at the Institute for Micro- and Nanoelectronic, Technical University Ilmenau in cooperation with (GE) General Electric Global Research (USA) and Umwelt-Sensor- Technik GmbH (Geschwenda). Chapter 1: serves as an introduction into the scientific fields related to this work. The theoretical fundamentals of solid-state gas sensors are provided and the relevant properties of wide band gap materials (SiC and GaN) are summarized. In chapter 2: The performance of Pt/GaN Schottky diodes with different thickness of the catalytic metal were investigated as hydrogen gas detectors. The area as well as the thickness of the Pt were varied between 250 {proportional_to} 250 {mu}m{sup 2} and 1000 {proportional_to} 1000 {mu}m{sup 2}, 8 and 40 nm, respectively. The response to hydrogen gas was investigated in dependence on the active area, the Pt thickness and the operating temperature for 1 vol.% hydrogen in synthetic air. We observed a significant increase of the sensitivity and a decrease of the response and recovery times by increasing the temperature of operation to about 350{sup o}C and by decreasing the Pt thickness down to 8 nm. Electron microscopy of the microstructure showed that the thinner platinum had a higher grain boundary density. The increase in sensitivity with decreasing Pt thickness points to the dissociation of molecular hydrogen on the surface, the diffusion of atomic hydrogen along the platinum grain boundaries and the adsorption of hydrogen at the Pt/GaN interface as a possible mechanism of sensing hydrogen by Schottky diodes. The response to deuterium D{sub 2}, NO{sub x}, and O{sub 2} of metal-oxide-semiconductor (MOS) and metal-metal oxide-oxide-semiconductor (MMOOS) structures with rhodium (Rh) gate were investigated in dependence on the operating temperature and gas partial pressures was investigated in chapter 3. The response of the sensor was measured as a shift in the capacitance-voltage (C-V) curve along the voltage axis. Positive and negative flat-band voltage shifts up to 1 V were observed for oxidizing and reducing gases, respectively. Depending on the type of insulator that is chosen, differences in the sensitivity of the sensor were observed. In chapter 4: The performance of SiC-based field effect transistors (FETs) with different gate materials (mixture of metal oxides: indium oxide and tin oxide (In{sub x}Sn{sub y}O{sub z}), indium oxide and vanadium oxide (In{sub x}V{sub y}O{sub z}), as well as mixtures of metal oxides with metal additives) were investigated as NO{sub x}, O{sub 2}, and D{sub 2} gas detectors. The response to these gases was investigated in dependence on the operating temperature and gas partial pressures. The composition and microstructure of the sensing gate electrode are the key parameters that influence the sensing mechanism, and hence key performance parameters: sensitivity, selectivity, and response time. By choosing the appropriate temperature and catalyst material (gate material), devices that are significantly sensitive to certain gases may be realized. In addition, the temperature of maximum response varies dependent on the gas species being measured. This information, along with a careful choice of catalyst (gate material) can be used to enhance device selectivity. In chapter 5: Polycrystalline and nano-structured In{sub 2}O{sub 3} thin films were investigated with the aim to obtain information about their NO{sub x} and O{sub 2} gas sensing properties. The response to these gases was investigated in dependence on the operating temperature and gas partial pressures. The analysis in the presence of different partial pressures of NO{sub x} has shown that both thin films are able to detect nitrogen oxide, but their responses exhibit different characteristics. In particular, nano-structured In{sub 2}O{sub 3} thin films were found to have the higher response to NO{sub x}. This is most probably due to the enlarged overall active surface area of the sensing layer as a consequence of the small grain size (higher surface to volume ratio) so that the relative interactive surface area is larger, and the density of charged carriers per volume is higher. We have found that reducing the grain size of the sensing material to the {proportional_to}10 nm regime can have a substantial effect on performance. The optimum detection temperatures of the nano-structured In{sub 2}O{sub 3} occur in the range of 100-175 C for NO{sub x} considering the sensitivity as well as the response time. In this range of temperatures the response to O{sub 2} is very low indicating that the sensor is very suitable for selective detection of NO{sub x} at low temperatures In addition, nano-structured In{sub 2}O{sub 3} thin films were found to be more suitable to be used in the field of application for detecting low partial pressures. Chapter 6: offers conclusions of the current work. In this chapter we compare also all studied gas sensors according to their sensitivity, selectivity, and response time and then we compare them with the related works by other authors available in the scientific literature. (orig.)}
place = {Germany}
year = {2008}
month = {Jan}
}
title = {Wide band gap materials and devices for NO{sub x}, H{sub 2} and O{sub 2} gas sensing applications}
author = {Ali, Majdeddin}
abstractNote = {In this thesis, field effect gas sensors (Schottky diodes, MOS capacitors, and MOSFET transistors) based on wide band gap semiconductors like silicon carbide (SiC) and gallium nitride (GaN), as well as resistive gas sensors based on indium oxide (In{sub 2}O{sub 3}), have been developed for the detection of reducing gases (H{sub 2}, D{sub 2}) and oxidising gases (NO{sub x}, O{sub 2}). The development of the sensors has been performed at the Institute for Micro- and Nanoelectronic, Technical University Ilmenau in cooperation with (GE) General Electric Global Research (USA) and Umwelt-Sensor- Technik GmbH (Geschwenda). Chapter 1: serves as an introduction into the scientific fields related to this work. The theoretical fundamentals of solid-state gas sensors are provided and the relevant properties of wide band gap materials (SiC and GaN) are summarized. In chapter 2: The performance of Pt/GaN Schottky diodes with different thickness of the catalytic metal were investigated as hydrogen gas detectors. The area as well as the thickness of the Pt were varied between 250 {proportional_to} 250 {mu}m{sup 2} and 1000 {proportional_to} 1000 {mu}m{sup 2}, 8 and 40 nm, respectively. The response to hydrogen gas was investigated in dependence on the active area, the Pt thickness and the operating temperature for 1 vol.% hydrogen in synthetic air. We observed a significant increase of the sensitivity and a decrease of the response and recovery times by increasing the temperature of operation to about 350{sup o}C and by decreasing the Pt thickness down to 8 nm. Electron microscopy of the microstructure showed that the thinner platinum had a higher grain boundary density. The increase in sensitivity with decreasing Pt thickness points to the dissociation of molecular hydrogen on the surface, the diffusion of atomic hydrogen along the platinum grain boundaries and the adsorption of hydrogen at the Pt/GaN interface as a possible mechanism of sensing hydrogen by Schottky diodes. The response to deuterium D{sub 2}, NO{sub x}, and O{sub 2} of metal-oxide-semiconductor (MOS) and metal-metal oxide-oxide-semiconductor (MMOOS) structures with rhodium (Rh) gate were investigated in dependence on the operating temperature and gas partial pressures was investigated in chapter 3. The response of the sensor was measured as a shift in the capacitance-voltage (C-V) curve along the voltage axis. Positive and negative flat-band voltage shifts up to 1 V were observed for oxidizing and reducing gases, respectively. Depending on the type of insulator that is chosen, differences in the sensitivity of the sensor were observed. In chapter 4: The performance of SiC-based field effect transistors (FETs) with different gate materials (mixture of metal oxides: indium oxide and tin oxide (In{sub x}Sn{sub y}O{sub z}), indium oxide and vanadium oxide (In{sub x}V{sub y}O{sub z}), as well as mixtures of metal oxides with metal additives) were investigated as NO{sub x}, O{sub 2}, and D{sub 2} gas detectors. The response to these gases was investigated in dependence on the operating temperature and gas partial pressures. The composition and microstructure of the sensing gate electrode are the key parameters that influence the sensing mechanism, and hence key performance parameters: sensitivity, selectivity, and response time. By choosing the appropriate temperature and catalyst material (gate material), devices that are significantly sensitive to certain gases may be realized. In addition, the temperature of maximum response varies dependent on the gas species being measured. This information, along with a careful choice of catalyst (gate material) can be used to enhance device selectivity. In chapter 5: Polycrystalline and nano-structured In{sub 2}O{sub 3} thin films were investigated with the aim to obtain information about their NO{sub x} and O{sub 2} gas sensing properties. The response to these gases was investigated in dependence on the operating temperature and gas partial pressures. The analysis in the presence of different partial pressures of NO{sub x} has shown that both thin films are able to detect nitrogen oxide, but their responses exhibit different characteristics. In particular, nano-structured In{sub 2}O{sub 3} thin films were found to have the higher response to NO{sub x}. This is most probably due to the enlarged overall active surface area of the sensing layer as a consequence of the small grain size (higher surface to volume ratio) so that the relative interactive surface area is larger, and the density of charged carriers per volume is higher. We have found that reducing the grain size of the sensing material to the {proportional_to}10 nm regime can have a substantial effect on performance. The optimum detection temperatures of the nano-structured In{sub 2}O{sub 3} occur in the range of 100-175 C for NO{sub x} considering the sensitivity as well as the response time. In this range of temperatures the response to O{sub 2} is very low indicating that the sensor is very suitable for selective detection of NO{sub x} at low temperatures In addition, nano-structured In{sub 2}O{sub 3} thin films were found to be more suitable to be used in the field of application for detecting low partial pressures. Chapter 6: offers conclusions of the current work. In this chapter we compare also all studied gas sensors according to their sensitivity, selectivity, and response time and then we compare them with the related works by other authors available in the scientific literature. (orig.)}
place = {Germany}
year = {2008}
month = {Jan}
}