Anita Spetz | Linköping University (original) (raw)

Papers by Anita Spetz

Comptes Rendus Chimie, 2013

Sensors and Actuators B: Chemical, 2015

ABSTRACT

TRANSDUCERS '91: 1991 International Conference on Solid-State Sensors and Actuators. Digest of Technical Papers, 1991

Page 1. Wide Range Pyroelectric Anemometers for Gas Flow Measurements HY Hsieh, A. Spetz* and J N... more Page 1. Wide Range Pyroelectric Anemometers for Gas Flow Measurements HY Hsieh, A. Spetz* and J N. Zemel !kpartment of Electrical Engineering and Center for Sensor Technologies University of Pennsylvania Philadelphia PA 19 104-6390 ...

TRANSDUCERS '91: 1991 International Conference on Solid-State Sensors and Actuators. Digest of Technical Papers, 1991

Page 1. Wide Range Pyroelectric Anemometers for Gas Flow Measurements HY Hsieh, A. Spetz* and J N... more Page 1. Wide Range Pyroelectric Anemometers for Gas Flow Measurements HY Hsieh, A. Spetz* and J N. Zemel !kpartment of Electrical Engineering and Center for Sensor Technologies University of Pennsylvania Philadelphia PA 19 104-6390 ...

2008 IEEE Sensors, 2008

In this work the effect of ambient influence on the electrical conductivity of ZnO films has been... more In this work the effect of ambient influence on the electrical conductivity of ZnO films has been studied. Nanostructured ZnO films (undoped and Ga, Co, Mn doped) were exposed to oxygen (1 -80 vol. %) at temperature range 300 -500 ºС. A dominant effect of ambient influence via oxygen absorption was observed: the intensity of conductivity decrease was found to be proportional with temperature and tends to saturation with time. After oxygen saturation the reversible effect of oxygen adsorption became dominant and contributed to the films conductivity. Oxygen exposed undoped ZnO films revealed high sensitivity for oxygen content change in the ambience, therefore they have been further processed for gas sensor fabrication.

Materials Science Forum, 2013

Large variations have been observed in the thickness uniformity and carrier concentration of epit... more Large variations have been observed in the thickness uniformity and carrier concentration of epitaxial graphene grown on SiC by sublimation for samples grown under identical conditions and on nominally on-axis hexagonal SiC (0001) substrates. We have previously shown that these issues are both related to the morphology of the graphene-SiC surface after sublimation growth.

Materials Science Forum, 2012

ABSTRACT Epitaxially grown single layer graphene on silicon carbide (SiC) resistive sensors were ... more ABSTRACT Epitaxially grown single layer graphene on silicon carbide (SiC) resistive sensors were characterised for NO2 response at room and elevated temperatures, with an n-p type transition observed with increasing NO2 concentration for all sensors. The concentration of NO2 required to cause this transition varied for different graphene samples and is attributed to varying degrees of substrate induced Fermi-level (EF) pinning above the Dirac point. The work function of a single layer device increased steadily with increasing NO2 concentration indicating no change in reaction mechanism for high and low concentrations despite a change in sensor response direction. Epitaxially grown graphene device preparation is challenging due to poor adhesion of the graphene layer to the substrate. A field effect transistor (FET) device is presented which does not require wire bonding to contacts on graphene.

Frontiers in bioscience (Elite edition), 2012

ZnO nanostructured materials, such as films and nanoparticles, could provide a suitable platform ... more ZnO nanostructured materials, such as films and nanoparticles, could provide a suitable platform for development of high performance biosensors due to their unique fundamental material properties. This paper reviews different preparation techniques of ZnO nanocrystals and material issues like wettability, biocompatibility and toxicity, which have an important relevance to biosensor functionality. Efforts are made to summarize and analyze existing results regarding surface modification and molecular attachments for successful biofunctionalization and understanding of the mechanisms involved. A section is devoted to implementations of tailored surfaces in biosensors. We end with conclusions on the feasibility of using ZnO nanocrystals for biosensing.

Smart Sensors, Actuators, and MEMS IV, 2009

Wide bandgap materials like SiC, ZnO, AlN form a strong platform as transducers for biosensors re... more Wide bandgap materials like SiC, ZnO, AlN form a strong platform as transducers for biosensors realized as eg ISFET (ion selective field effect transistor) devices or resonators. We have taken two main steps towards a multifunctional biosensor transducer. First we have successfully ...

IEEE Sensors, 2005., 2005

A thin film thickness excited shear acoustic wave resonator is presented. Utilizing a newly devel... more A thin film thickness excited shear acoustic wave resonator is presented. Utilizing a newly developed reactive sputtering process AlN thin films with inclined c-axis relative to the surface normal with a mean tilt of around 30deg are successfully grown. Using the above process, a biosensor consisting of a shear mode thin film bulk acoustic resonator (FBAR) and a microfluidic transport

We report the results of the effect of three different stacks of ohmic contacts such as TiW (180 ... more We report the results of the effect of three different stacks of ohmic contacts such as TiW (180 nm)/Ti (30 nm)/Pt (300 nm), Ni (100 nm)/TaSi x (200 nm)/Pt (400 nm), and TaSi x (200 nm)/Pt (400 nm) on a highly doped n-type 4H-silicon carbide for high temperature measurements in oxidizing ambient. The ohmic contacts in the transmission line method (TLM) structures were cut to 2 · 2 mm 2 chips, and glued on heater, which has a built-in Pt-100 element, for the temperature measurement. Finally the contacts on the heater were mounted on a 16-pin socket, which was placed in an Al-block with a gas flow channel. For this measurement, we used 20% O 2 in N 2 flowing at a rate of 80 ml/min at temperatures of 500°C and 600°C. The long-term reliability test of each ohmic contact in an oxidizing environment up to 520 h showed that TiW/Ti/Pt had the best stability and the lowest contact resistivity, while other contacts (Ni/TaSi x /Pt and TaSi x /Pt) had a severe degradation of contacts due to the oxidation. Therefore, we believe that our TiW based metallization schemes can be applied in harsh environment such as the automobile and aerospace exhaust systems.

Scripta Materialia, 2015

We report a single-step procedure for growth of ohmic Ti 3 SiC 2 on 4H-SiC by sputter-deposition ... more We report a single-step procedure for growth of ohmic Ti 3 SiC 2 on 4H-SiC by sputter-deposition of Ti at 960°C, based on the Ti-SiC solid-state reaction during deposition. X-ray diffraction and electron microscopy show the growth of interfacial Ti 3 SiC 2 . The as-deposited contacts are ohmic, in contrast to multistep processes with deposition followed by rapid thermal annealing. This procedure also offers the possibility of direct synthesis of oxygen-barrier capping layers before exposure to air, potentially improving contact stability in high-temperature and high-power devices.

Sensors and Actuators B: Chemical, 1993

A personal description of the history of gas-sensitive field-effect devices is given . It is show... more A personal description of the history of gas-sensitive field-effect devices is given . It is shown how the originally described palladium-gate metal-oxide-semiconductor field-effect transistor has developed into sensing surfaces enabling the production of response images to odours. Images obtained for the odour from different cheeses are presented as examples of such `artificial olfactory images'.

The Journal of Physical Chemistry B, 2005

Vibrational properties of surface species formed upon H2 and D2 exposure of silica supported plat... more Vibrational properties of surface species formed upon H2 and D2 exposure of silica supported platinum particles have been investigated with in situ diffuse reflection infrared Fourier transform spectroscopy. Experiments have been performed at 50-250 degrees C, using different platinum loading of the samples in the absence and presence of oxygen. In addition, electronic structure calculations and vibrational analysis have been performed within the density functional theory for H adsorption on a silica cluster, (HO)3SiOSi(OH)3. The spectroscopy experiments showed reversible formation of isolated OH and OD groups on the silica surface when the samples were exposed to H2 and D2, respectively. In addition to the absorption peak corresponding to isolated OH and OD groups, an intense broad band was observed around 3270 cm(-1) (2500 cm(-1)) during H2 (D2) exposure. Supported by the calculations, this band was assigned to perturbed OH groups on the silica surface. The surface coverage of new OH groups was found to correlate to the platinum loading in the samples, indicating that the new silanol groups were formed in the vicinity of the Pt particles. In the investigated temperature interval, the formation rate of OH groups was not found to be temperature dependent.

Sensors and Actuators B: Chemical, 2009

Zinc oxide is an interesting material for bio and chemical sensors. It is a semiconducting metal ... more Zinc oxide is an interesting material for bio and chemical sensors. It is a semiconducting metal oxide with potential as an integrated multisensing sensor platform, which simultaneously detects parameters like change in field effect, mass and surface resistivity. In this investigation we have used resistive sensor measurements regarding the oxygen gas sensitivity in order to characterize sensing layers based on electrochemically produced ZnO nanoparticles and PE-MOCVD grown ZnO films. Proper annealing procedures were developed in order to get stable sensing properties and the oxygen sensitivity towards operation temperature was investigated. The ZnO nanoparticles showed a considerably increased response to oxygen as compared to the films. Preliminary investigations were also performed regarding the selectivity to other gases present in car exhausts or flue gases.

Sensors and Actuators B: Chemical, 2003

The metal oxide silicon carbide field effect transistor (MISiCFET) sensor has several possible ca... more The metal oxide silicon carbide field effect transistor (MISiCFET) sensor has several possible car engine applications, such as an ammonia sensor in selective catalytic reduction (SCR) systems or as a lambda-sensitive device for enhancing catalytic converter efficiency. Both these applications involve closed loop control of the engine and thereby require fast sensors, that is why it is important to investigate the speed of response of the devices. The sensor consists of a SiC-based MOSFET device with a buried channel design and a catalytic gate metal, which makes it sensitive to a wide range of different gases. The selectivity and sensitivity of the sensor to a specific gas depends mainly on the choice of gate metal, its structure and the operating temperature. In this presentation, the speed of response of MISiCFET devices with many different gate metals at several operating temperatures are compared. The tests have been performed in the laboratory using the moving gas outlet (MGO) equipment. The equipment allows two gas outlets to move back and forth under the sensor, which makes it possible to change the atmosphere surrounding the sensor from synthetic air to the test gas quickly. The method is verified by changing the temperature of the device and frequency of the moving gas outlets. The test gas is either ammonia or hydrogen. The time constant of the sensors is shown to be very small; <100 ms when exposing a 25 nm porous Pt sensor to ammonia at 300 8C and <10 ms for a 10 nm TaSi x 100 nm Pt device exposed to hydrogen. The temperature is found to have a large influence on the speed of response. The results show that the speed of response is well beyond the current requirements for use in both SCR and lambda control systems, respectively. #

Sensors and Actuators B: Chemical, 1992

Polymer membranes are used to increase the selectivity to certain gases of metal-silicon dioxide-... more Polymer membranes are used to increase the selectivity to certain gases of metal-silicon dioxide-semiconductor (MOS) structures. Other parameters which influence the selectivity of MOS structures are the type of gate metal, its microstructure (dense or porous) and the operating temperature of the device. Photoresists as membranes can be patterned by photolithographic methods. Membranes, 1-2 pm thick, of positive and negative photoresist are applied on MOS capacitors with 6 nm iridium as the gate metal, operated at 150 "C. The influence of the membranes on the response to three gases, hydrogen, ammonia and ethanol, has been investigated. The hydrogen response decreases by about half with the use of a photoresist membrane. The ammonia response shows a characteristic change in the kinetics, while the ethanol response almost disappears. Positive and negative resist influence the gas response in similar ways, in spite of their different molecular structures.

Sensors and Actuators A: Physical, 1995

The characteristics of a vector pyroelectric anemometer that measures the orthogonal components o... more The characteristics of a vector pyroelectric anemometer that measures the orthogonal components of mass flow are presented. This anemometer consists of three measuring electrodes and two heater elements on a 6 mmX6 mm chip that form two orthogonal linear anemometers. The characteristics of a single pair of electrodes forming an in-line linear anemometer are in good agreement with recent measurements and theory. A wall-mounted vector pyroelectric anemometer is used to measure the decay of swirl in air flowing through a 45 mm inner diameter, 5 m long flow system. The swirl flow is produced by a 90" out-of-plane double elbow at the flow system inlet. The tube flow generated by a squirrel-cage fan has a Reynolds number of = 24 000, well into the turbulent regime. Measurements are conducted at the wall at a uniform distance along the length of the flow section for both straight and swirl flow. The measured decay length is ~40 pipe diameters, in good agreement with measurements on water.

Comptes Rendus Chimie, 2013

Sensors and Actuators B: Chemical, 2015

ABSTRACT

TRANSDUCERS '91: 1991 International Conference on Solid-State Sensors and Actuators. Digest of Technical Papers, 1991

Page 1. Wide Range Pyroelectric Anemometers for Gas Flow Measurements HY Hsieh, A. Spetz* and J N... more Page 1. Wide Range Pyroelectric Anemometers for Gas Flow Measurements HY Hsieh, A. Spetz* and J N. Zemel !kpartment of Electrical Engineering and Center for Sensor Technologies University of Pennsylvania Philadelphia PA 19 104-6390 ...

TRANSDUCERS '91: 1991 International Conference on Solid-State Sensors and Actuators. Digest of Technical Papers, 1991

Page 1. Wide Range Pyroelectric Anemometers for Gas Flow Measurements HY Hsieh, A. Spetz* and J N... more Page 1. Wide Range Pyroelectric Anemometers for Gas Flow Measurements HY Hsieh, A. Spetz* and J N. Zemel !kpartment of Electrical Engineering and Center for Sensor Technologies University of Pennsylvania Philadelphia PA 19 104-6390 ...

2008 IEEE Sensors, 2008

In this work the effect of ambient influence on the electrical conductivity of ZnO films has been... more In this work the effect of ambient influence on the electrical conductivity of ZnO films has been studied. Nanostructured ZnO films (undoped and Ga, Co, Mn doped) were exposed to oxygen (1 -80 vol. %) at temperature range 300 -500 ºС. A dominant effect of ambient influence via oxygen absorption was observed: the intensity of conductivity decrease was found to be proportional with temperature and tends to saturation with time. After oxygen saturation the reversible effect of oxygen adsorption became dominant and contributed to the films conductivity. Oxygen exposed undoped ZnO films revealed high sensitivity for oxygen content change in the ambience, therefore they have been further processed for gas sensor fabrication.

Materials Science Forum, 2013

Large variations have been observed in the thickness uniformity and carrier concentration of epit... more Large variations have been observed in the thickness uniformity and carrier concentration of epitaxial graphene grown on SiC by sublimation for samples grown under identical conditions and on nominally on-axis hexagonal SiC (0001) substrates. We have previously shown that these issues are both related to the morphology of the graphene-SiC surface after sublimation growth.

Materials Science Forum, 2012

ABSTRACT Epitaxially grown single layer graphene on silicon carbide (SiC) resistive sensors were ... more ABSTRACT Epitaxially grown single layer graphene on silicon carbide (SiC) resistive sensors were characterised for NO2 response at room and elevated temperatures, with an n-p type transition observed with increasing NO2 concentration for all sensors. The concentration of NO2 required to cause this transition varied for different graphene samples and is attributed to varying degrees of substrate induced Fermi-level (EF) pinning above the Dirac point. The work function of a single layer device increased steadily with increasing NO2 concentration indicating no change in reaction mechanism for high and low concentrations despite a change in sensor response direction. Epitaxially grown graphene device preparation is challenging due to poor adhesion of the graphene layer to the substrate. A field effect transistor (FET) device is presented which does not require wire bonding to contacts on graphene.

Frontiers in bioscience (Elite edition), 2012

ZnO nanostructured materials, such as films and nanoparticles, could provide a suitable platform ... more ZnO nanostructured materials, such as films and nanoparticles, could provide a suitable platform for development of high performance biosensors due to their unique fundamental material properties. This paper reviews different preparation techniques of ZnO nanocrystals and material issues like wettability, biocompatibility and toxicity, which have an important relevance to biosensor functionality. Efforts are made to summarize and analyze existing results regarding surface modification and molecular attachments for successful biofunctionalization and understanding of the mechanisms involved. A section is devoted to implementations of tailored surfaces in biosensors. We end with conclusions on the feasibility of using ZnO nanocrystals for biosensing.

Smart Sensors, Actuators, and MEMS IV, 2009

Wide bandgap materials like SiC, ZnO, AlN form a strong platform as transducers for biosensors re... more Wide bandgap materials like SiC, ZnO, AlN form a strong platform as transducers for biosensors realized as eg ISFET (ion selective field effect transistor) devices or resonators. We have taken two main steps towards a multifunctional biosensor transducer. First we have successfully ...

IEEE Sensors, 2005., 2005

A thin film thickness excited shear acoustic wave resonator is presented. Utilizing a newly devel... more A thin film thickness excited shear acoustic wave resonator is presented. Utilizing a newly developed reactive sputtering process AlN thin films with inclined c-axis relative to the surface normal with a mean tilt of around 30deg are successfully grown. Using the above process, a biosensor consisting of a shear mode thin film bulk acoustic resonator (FBAR) and a microfluidic transport

We report the results of the effect of three different stacks of ohmic contacts such as TiW (180 ... more We report the results of the effect of three different stacks of ohmic contacts such as TiW (180 nm)/Ti (30 nm)/Pt (300 nm), Ni (100 nm)/TaSi x (200 nm)/Pt (400 nm), and TaSi x (200 nm)/Pt (400 nm) on a highly doped n-type 4H-silicon carbide for high temperature measurements in oxidizing ambient. The ohmic contacts in the transmission line method (TLM) structures were cut to 2 · 2 mm 2 chips, and glued on heater, which has a built-in Pt-100 element, for the temperature measurement. Finally the contacts on the heater were mounted on a 16-pin socket, which was placed in an Al-block with a gas flow channel. For this measurement, we used 20% O 2 in N 2 flowing at a rate of 80 ml/min at temperatures of 500°C and 600°C. The long-term reliability test of each ohmic contact in an oxidizing environment up to 520 h showed that TiW/Ti/Pt had the best stability and the lowest contact resistivity, while other contacts (Ni/TaSi x /Pt and TaSi x /Pt) had a severe degradation of contacts due to the oxidation. Therefore, we believe that our TiW based metallization schemes can be applied in harsh environment such as the automobile and aerospace exhaust systems.

Scripta Materialia, 2015

We report a single-step procedure for growth of ohmic Ti 3 SiC 2 on 4H-SiC by sputter-deposition ... more We report a single-step procedure for growth of ohmic Ti 3 SiC 2 on 4H-SiC by sputter-deposition of Ti at 960°C, based on the Ti-SiC solid-state reaction during deposition. X-ray diffraction and electron microscopy show the growth of interfacial Ti 3 SiC 2 . The as-deposited contacts are ohmic, in contrast to multistep processes with deposition followed by rapid thermal annealing. This procedure also offers the possibility of direct synthesis of oxygen-barrier capping layers before exposure to air, potentially improving contact stability in high-temperature and high-power devices.

Sensors and Actuators B: Chemical, 1993

A personal description of the history of gas-sensitive field-effect devices is given . It is show... more A personal description of the history of gas-sensitive field-effect devices is given . It is shown how the originally described palladium-gate metal-oxide-semiconductor field-effect transistor has developed into sensing surfaces enabling the production of response images to odours. Images obtained for the odour from different cheeses are presented as examples of such `artificial olfactory images'.

The Journal of Physical Chemistry B, 2005

Vibrational properties of surface species formed upon H2 and D2 exposure of silica supported plat... more Vibrational properties of surface species formed upon H2 and D2 exposure of silica supported platinum particles have been investigated with in situ diffuse reflection infrared Fourier transform spectroscopy. Experiments have been performed at 50-250 degrees C, using different platinum loading of the samples in the absence and presence of oxygen. In addition, electronic structure calculations and vibrational analysis have been performed within the density functional theory for H adsorption on a silica cluster, (HO)3SiOSi(OH)3. The spectroscopy experiments showed reversible formation of isolated OH and OD groups on the silica surface when the samples were exposed to H2 and D2, respectively. In addition to the absorption peak corresponding to isolated OH and OD groups, an intense broad band was observed around 3270 cm(-1) (2500 cm(-1)) during H2 (D2) exposure. Supported by the calculations, this band was assigned to perturbed OH groups on the silica surface. The surface coverage of new OH groups was found to correlate to the platinum loading in the samples, indicating that the new silanol groups were formed in the vicinity of the Pt particles. In the investigated temperature interval, the formation rate of OH groups was not found to be temperature dependent.

Sensors and Actuators B: Chemical, 2009

Zinc oxide is an interesting material for bio and chemical sensors. It is a semiconducting metal ... more Zinc oxide is an interesting material for bio and chemical sensors. It is a semiconducting metal oxide with potential as an integrated multisensing sensor platform, which simultaneously detects parameters like change in field effect, mass and surface resistivity. In this investigation we have used resistive sensor measurements regarding the oxygen gas sensitivity in order to characterize sensing layers based on electrochemically produced ZnO nanoparticles and PE-MOCVD grown ZnO films. Proper annealing procedures were developed in order to get stable sensing properties and the oxygen sensitivity towards operation temperature was investigated. The ZnO nanoparticles showed a considerably increased response to oxygen as compared to the films. Preliminary investigations were also performed regarding the selectivity to other gases present in car exhausts or flue gases.

Sensors and Actuators B: Chemical, 2003

The metal oxide silicon carbide field effect transistor (MISiCFET) sensor has several possible ca... more The metal oxide silicon carbide field effect transistor (MISiCFET) sensor has several possible car engine applications, such as an ammonia sensor in selective catalytic reduction (SCR) systems or as a lambda-sensitive device for enhancing catalytic converter efficiency. Both these applications involve closed loop control of the engine and thereby require fast sensors, that is why it is important to investigate the speed of response of the devices. The sensor consists of a SiC-based MOSFET device with a buried channel design and a catalytic gate metal, which makes it sensitive to a wide range of different gases. The selectivity and sensitivity of the sensor to a specific gas depends mainly on the choice of gate metal, its structure and the operating temperature. In this presentation, the speed of response of MISiCFET devices with many different gate metals at several operating temperatures are compared. The tests have been performed in the laboratory using the moving gas outlet (MGO) equipment. The equipment allows two gas outlets to move back and forth under the sensor, which makes it possible to change the atmosphere surrounding the sensor from synthetic air to the test gas quickly. The method is verified by changing the temperature of the device and frequency of the moving gas outlets. The test gas is either ammonia or hydrogen. The time constant of the sensors is shown to be very small; <100 ms when exposing a 25 nm porous Pt sensor to ammonia at 300 8C and <10 ms for a 10 nm TaSi x 100 nm Pt device exposed to hydrogen. The temperature is found to have a large influence on the speed of response. The results show that the speed of response is well beyond the current requirements for use in both SCR and lambda control systems, respectively. #

Sensors and Actuators B: Chemical, 1992

Polymer membranes are used to increase the selectivity to certain gases of metal-silicon dioxide-... more Polymer membranes are used to increase the selectivity to certain gases of metal-silicon dioxide-semiconductor (MOS) structures. Other parameters which influence the selectivity of MOS structures are the type of gate metal, its microstructure (dense or porous) and the operating temperature of the device. Photoresists as membranes can be patterned by photolithographic methods. Membranes, 1-2 pm thick, of positive and negative photoresist are applied on MOS capacitors with 6 nm iridium as the gate metal, operated at 150 "C. The influence of the membranes on the response to three gases, hydrogen, ammonia and ethanol, has been investigated. The hydrogen response decreases by about half with the use of a photoresist membrane. The ammonia response shows a characteristic change in the kinetics, while the ethanol response almost disappears. Positive and negative resist influence the gas response in similar ways, in spite of their different molecular structures.

Sensors and Actuators A: Physical, 1995

The characteristics of a vector pyroelectric anemometer that measures the orthogonal components o... more The characteristics of a vector pyroelectric anemometer that measures the orthogonal components of mass flow are presented. This anemometer consists of three measuring electrodes and two heater elements on a 6 mmX6 mm chip that form two orthogonal linear anemometers. The characteristics of a single pair of electrodes forming an in-line linear anemometer are in good agreement with recent measurements and theory. A wall-mounted vector pyroelectric anemometer is used to measure the decay of swirl in air flowing through a 45 mm inner diameter, 5 m long flow system. The swirl flow is produced by a 90" out-of-plane double elbow at the flow system inlet. The tube flow generated by a squirrel-cage fan has a Reynolds number of = 24 000, well into the turbulent regime. Measurements are conducted at the wall at a uniform distance along the length of the flow section for both straight and swirl flow. The measured decay length is ~40 pipe diameters, in good agreement with measurements on water.