This paper suggests and demonstrates a novel flow measurement technique, tunable AC mode hotwire ... more This paper suggests and demonstrates a novel flow measurement technique, tunable AC mode hotwire anemometry that allows simple integration, robust measurement, and extremely high accuracy. The principle and simple theoretical analysis of the technique are shown. To find the optimal frequency at which the phase lag becomes most sensitive to flow speed change, the phase lag was measured scanning the heating frequency from 1 to 100 Hz, while the flow speed of ethanol was increased stepwise from 0 to 10 mm/s. To optimize the sensitivity of technique, the periodic thermal characteristic of the hotwire should be understood and is currently under study. 기호설명 cp 비열 [J/kg·K] h 대류열전달계수 [W/m·K] I 전류 [A] l 열선의 길이 [mm] q̇ 단위부피당 열량 [W/m] R 저항 [Ω] r 열선의 반지름 [μm] T 온도 [K] t 시간 [s] U 속도 [m/s] V 전압 [V] 그리스문자 α 저항온도계수 [K] φ 위상 뒤짐 [°] γ 비저항 [Ω·m] ∆ 두 값의 차이 θ 온도차 [K] ρ 밀도 [kg/m] τ 열시간상수 [s] ω 주파수 [rad/s] 하첨자 AC 교류성분 h 열선 opt 최적점 S 부가저항 ∞ 유동 0 진폭
Manipulation of the chemical vapor deposition graphene synthesis conditions, such as operating P,... more Manipulation of the chemical vapor deposition graphene synthesis conditions, such as operating P, T, heating/cooling time intervals, and precursor gas concentration ratios (CH4/H2), allowed for synthesis of polycrystalline single-layered graphene with controlled grain sizes. The graphene samples were then suspended on 8 μm diameter patterned holes on a silicon-nitride (Si3N4) substrate, and the in-plane thermal conductivities k(T) for 320 K < T < 510 K were measured to be 2660-1230, 1890-1020, and 680-340 W/m·K for average grain sizes of 4.1, 2.2, and 0.5 μm, respectively, using an opto-thermal Raman technique. Fitting of these data by a simple linear chain model of polycrystalline thermal transport determined k = 5500-1980 W/m·K for single-crystal graphene for the same temperature range above; thus, significant reduction of k was achieved when the grain size was decreased from infinite down to 0.5 μm. Furthermore, detailed elaborations were performed to assess the measurement...
2010 14th International Heat Transfer Conference, Volume 6, 2010
We developed a measurement technique that can quantitatively map out the dopant density profile o... more We developed a measurement technique that can quantitatively map out the dopant density profile of a silicon integrated-circuit device. This method obtains the quantitative doping density profile by simultaneously carrying out local heating, temperature sensing, and thermoelectric voltage measurement at the tip of a diamond thermocouple probe. This probe, which is the key component of the proposed scheme, is fabricated through a nano-fabrication technique that makes use of boron-doped diamond film that can resist stress up to 10 Gpa, which is necessary for stable electric contact with silicon samples. The tip and cantilever of the probe are made of B-doped diamond by means of the silicon lost-mold technique that guarantees a sharper tip apex than that of a diamond-coated probe. A gold-chromium thermocouple junction is integrated at the tip apex for simultaneous heating and sensing. The size of the thermocouple is about 500 nm and the radius of the tip apex is less than 50 nm. The me...
Thermopower (S) profiling with nanometer resolution is essential for enhancing the thermoelectric... more Thermopower (S) profiling with nanometer resolution is essential for enhancing the thermoelectric figure of merit, ZT, through the nanostructuring of materials and for carrier density profiling in nanoelectronic devices. However, only qualitative and impractical methods or techniques with low resolutions have been reported thus far. Herein, we develop a quantitative S profiling method with nanometer resolution, scanning Seebeck microscopy (SSM), and batch-fabricate diamond thermocouple probes to apply SSM to silicon, which requires a contact stress higher than 10 GPa for stable electrical contact. The distance between the positive and negative peaks of the S profile across the silicon p-n junction measured by SSM is 4 nm, while the theoretical distance is 2 nm. Because of its extremely high spatial resolution, quantitative measurement, and ease of use, SSM could be a crucial tool not only for the characterization of nano-thermoelectric materials and nanoelectronic devices but also f...
This paper presents a technique, scanning thermal wave microscopy (STWM), which can image the pha... more This paper presents a technique, scanning thermal wave microscopy (STWM), which can image the phase lag and amplitude of thermal waves with sub-micrometer resolution by scanning a temperature-sensing nanoscale tip across a sample surface. Phase lag measurements during tip-sample contact showed enhancement of tip-sample heat transfer due to the presence of a liquid film. The measurement accuracy of STWM is proved by a benchmark experiment and comparison to theoretical prediction. The application of STWM for sub-surface imaging of buried structures is demonstrated by measuring the phase lag and amplitude distributions of an interconnect via sample. The measurement showed excellent agreement with a finite element analysis offering the promising prospects of three-dimensional thermal probing of micro and nanostructures. Finally, it was shown that the resolving power of thermal waves for subsurface structures improves as the wavelengths of the thermal waves become shorter at higher modul...
An ac type thermopower measurement technique was suggested and demonstrated with a simple experim... more An ac type thermopower measurement technique was suggested and demonstrated with a simple experimental setup. The thermopower distribution across a silicon p-n junction was measured point by point at every 10nm, so that it was free from the noise due to the built-in potential and photoionization effects, and it was compared with the theoretical result. Although this ac type thermopower measurement technique could not follow the sharp variation of the theoretical thermopower near the p-n junction, it could identify a smooth peak of the thermopower distribution in the depletion layer of the p-n junction.
Although scanning thermal microscope has shown the highest spatial resolution in local temperatur... more Although scanning thermal microscope has shown the highest spatial resolution in local temperature and thermophysical property measurement, its usefulness has been severely limited due to difficulties in quantitative measurement. We propose a double scan technique that measures temperature only from the heat transfer through the tip-sample contact by the subtraction of the signal due to the heat transfer through the air. A rigorous theoretical model for this technique is derived. The effectiveness of the double scan technique in quantitative temperature measurement is demonstrated experimentally.
Abstract Null-point scanning thermal microscopy (NP SThM) quantitatively measures undisturbed tem... more Abstract Null-point scanning thermal microscopy (NP SThM) quantitatively measures undisturbed temperature without the influence of changes in physical properties and surface topography of the specimen. Simultaneously NP SThM measures the ratio of the sum of the tip-specimen contact thermal resistance and the spreading thermal resistance of the specimen to the effective thermal resistance of the SThM probe. Hence, arguably, NP SThM is an ideal SThM that meets all the requirements of SThM. However, in practice, the use of NP SThM has been limited to one-dimensional profiling only, and two-dimensional extension of NP SThM has been virtually impossible so far. This is because NP SThM is very difficult to implement and ensure a sufficient measurement sensitivity. In this study, we enable two-dimensional extension of NP SThM with almost a 20-fold improvement in measurement sensitivity even under mild vacuum conditions (
Using null-point scanning thermal microscopy (NP SThM), we have measured and analyzed the size de... more Using null-point scanning thermal microscopy (NP SThM), we have measured and analyzed the size dependence of the thermal conductivity of graphene. To do so, we rigorously re-derived the principal equation of NP SThM in terms of thermal property measurements so as to explain how this technique can be effectively used to quantitatively measure the local thermal resistance with nanoscale spatial resolution. This technique has already been proven to resolve the major problems of conventional SThM, and to quantitatively measure the temperature profile. Using NP SThM, we measured the variation in the thermal resistance of suspended chemical vapor deposition (CVD)-grown graphene disks with radii of 50-3680 nm from the center to the edge with respect to the size. By thoroughly analyzing the size dependence of the thermal resistance, we show that, with increasing graphene size, the ballistic resistance becomes more dominant in the thermal resistance experienced by a heat source of finite size and that the thermal conductivity experienced by such a heat source can even decrease. The results of this study reveal that the thermal conductivity of graphene detected by a heat source depends on the size of the heat source relative to that of the suspended graphene and on how the heat source and graphene are connected. As demonstrated in this study, NP SThM will be very useful for quantitative thermal characterization of not only CVD-grown graphene but also various other nanomaterials and nanodevices.
Understanding of heat generation in semiconductor devices is important in the thermal management ... more Understanding of heat generation in semiconductor devices is important in the thermal management of integrated circuits and in the analysis of the device physics. Scanning thermal microscopy was used to measure the temperature distribution of the cross-section of an operating metal-oxide-semiconductor field-effect transistor (MOSFET). The temperature distributions were measured both in DC and AC modes in order to take account of the leakage current. The location of the maximum temperature was observed to approach the drain as the drain bias was increased.
This paper suggests and demonstrates a novel flow measurement technique, tunable AC mode hotwire ... more This paper suggests and demonstrates a novel flow measurement technique, tunable AC mode hotwire anemometry that allows simple integration, robust measurement, and extremely high accuracy. The principle and simple theoretical analysis of the technique are shown. To find the optimal frequency at which the phase lag becomes most sensitive to flow speed change, the phase lag was measured scanning the heating frequency from 1 to 100 Hz, while the flow speed of ethanol was increased stepwise from 0 to 10 mm/s. To optimize the sensitivity of technique, the periodic thermal characteristic of the hotwire should be understood and is currently under study. 기호설명 cp 비열 [J/kg·K] h 대류열전달계수 [W/m·K] I 전류 [A] l 열선의 길이 [mm] q̇ 단위부피당 열량 [W/m] R 저항 [Ω] r 열선의 반지름 [μm] T 온도 [K] t 시간 [s] U 속도 [m/s] V 전압 [V] 그리스문자 α 저항온도계수 [K] φ 위상 뒤짐 [°] γ 비저항 [Ω·m] ∆ 두 값의 차이 θ 온도차 [K] ρ 밀도 [kg/m] τ 열시간상수 [s] ω 주파수 [rad/s] 하첨자 AC 교류성분 h 열선 opt 최적점 S 부가저항 ∞ 유동 0 진폭
Manipulation of the chemical vapor deposition graphene synthesis conditions, such as operating P,... more Manipulation of the chemical vapor deposition graphene synthesis conditions, such as operating P, T, heating/cooling time intervals, and precursor gas concentration ratios (CH4/H2), allowed for synthesis of polycrystalline single-layered graphene with controlled grain sizes. The graphene samples were then suspended on 8 μm diameter patterned holes on a silicon-nitride (Si3N4) substrate, and the in-plane thermal conductivities k(T) for 320 K < T < 510 K were measured to be 2660-1230, 1890-1020, and 680-340 W/m·K for average grain sizes of 4.1, 2.2, and 0.5 μm, respectively, using an opto-thermal Raman technique. Fitting of these data by a simple linear chain model of polycrystalline thermal transport determined k = 5500-1980 W/m·K for single-crystal graphene for the same temperature range above; thus, significant reduction of k was achieved when the grain size was decreased from infinite down to 0.5 μm. Furthermore, detailed elaborations were performed to assess the measurement...
2010 14th International Heat Transfer Conference, Volume 6, 2010
We developed a measurement technique that can quantitatively map out the dopant density profile o... more We developed a measurement technique that can quantitatively map out the dopant density profile of a silicon integrated-circuit device. This method obtains the quantitative doping density profile by simultaneously carrying out local heating, temperature sensing, and thermoelectric voltage measurement at the tip of a diamond thermocouple probe. This probe, which is the key component of the proposed scheme, is fabricated through a nano-fabrication technique that makes use of boron-doped diamond film that can resist stress up to 10 Gpa, which is necessary for stable electric contact with silicon samples. The tip and cantilever of the probe are made of B-doped diamond by means of the silicon lost-mold technique that guarantees a sharper tip apex than that of a diamond-coated probe. A gold-chromium thermocouple junction is integrated at the tip apex for simultaneous heating and sensing. The size of the thermocouple is about 500 nm and the radius of the tip apex is less than 50 nm. The me...
Thermopower (S) profiling with nanometer resolution is essential for enhancing the thermoelectric... more Thermopower (S) profiling with nanometer resolution is essential for enhancing the thermoelectric figure of merit, ZT, through the nanostructuring of materials and for carrier density profiling in nanoelectronic devices. However, only qualitative and impractical methods or techniques with low resolutions have been reported thus far. Herein, we develop a quantitative S profiling method with nanometer resolution, scanning Seebeck microscopy (SSM), and batch-fabricate diamond thermocouple probes to apply SSM to silicon, which requires a contact stress higher than 10 GPa for stable electrical contact. The distance between the positive and negative peaks of the S profile across the silicon p-n junction measured by SSM is 4 nm, while the theoretical distance is 2 nm. Because of its extremely high spatial resolution, quantitative measurement, and ease of use, SSM could be a crucial tool not only for the characterization of nano-thermoelectric materials and nanoelectronic devices but also f...
This paper presents a technique, scanning thermal wave microscopy (STWM), which can image the pha... more This paper presents a technique, scanning thermal wave microscopy (STWM), which can image the phase lag and amplitude of thermal waves with sub-micrometer resolution by scanning a temperature-sensing nanoscale tip across a sample surface. Phase lag measurements during tip-sample contact showed enhancement of tip-sample heat transfer due to the presence of a liquid film. The measurement accuracy of STWM is proved by a benchmark experiment and comparison to theoretical prediction. The application of STWM for sub-surface imaging of buried structures is demonstrated by measuring the phase lag and amplitude distributions of an interconnect via sample. The measurement showed excellent agreement with a finite element analysis offering the promising prospects of three-dimensional thermal probing of micro and nanostructures. Finally, it was shown that the resolving power of thermal waves for subsurface structures improves as the wavelengths of the thermal waves become shorter at higher modul...
An ac type thermopower measurement technique was suggested and demonstrated with a simple experim... more An ac type thermopower measurement technique was suggested and demonstrated with a simple experimental setup. The thermopower distribution across a silicon p-n junction was measured point by point at every 10nm, so that it was free from the noise due to the built-in potential and photoionization effects, and it was compared with the theoretical result. Although this ac type thermopower measurement technique could not follow the sharp variation of the theoretical thermopower near the p-n junction, it could identify a smooth peak of the thermopower distribution in the depletion layer of the p-n junction.
Although scanning thermal microscope has shown the highest spatial resolution in local temperatur... more Although scanning thermal microscope has shown the highest spatial resolution in local temperature and thermophysical property measurement, its usefulness has been severely limited due to difficulties in quantitative measurement. We propose a double scan technique that measures temperature only from the heat transfer through the tip-sample contact by the subtraction of the signal due to the heat transfer through the air. A rigorous theoretical model for this technique is derived. The effectiveness of the double scan technique in quantitative temperature measurement is demonstrated experimentally.
Abstract Null-point scanning thermal microscopy (NP SThM) quantitatively measures undisturbed tem... more Abstract Null-point scanning thermal microscopy (NP SThM) quantitatively measures undisturbed temperature without the influence of changes in physical properties and surface topography of the specimen. Simultaneously NP SThM measures the ratio of the sum of the tip-specimen contact thermal resistance and the spreading thermal resistance of the specimen to the effective thermal resistance of the SThM probe. Hence, arguably, NP SThM is an ideal SThM that meets all the requirements of SThM. However, in practice, the use of NP SThM has been limited to one-dimensional profiling only, and two-dimensional extension of NP SThM has been virtually impossible so far. This is because NP SThM is very difficult to implement and ensure a sufficient measurement sensitivity. In this study, we enable two-dimensional extension of NP SThM with almost a 20-fold improvement in measurement sensitivity even under mild vacuum conditions (
Using null-point scanning thermal microscopy (NP SThM), we have measured and analyzed the size de... more Using null-point scanning thermal microscopy (NP SThM), we have measured and analyzed the size dependence of the thermal conductivity of graphene. To do so, we rigorously re-derived the principal equation of NP SThM in terms of thermal property measurements so as to explain how this technique can be effectively used to quantitatively measure the local thermal resistance with nanoscale spatial resolution. This technique has already been proven to resolve the major problems of conventional SThM, and to quantitatively measure the temperature profile. Using NP SThM, we measured the variation in the thermal resistance of suspended chemical vapor deposition (CVD)-grown graphene disks with radii of 50-3680 nm from the center to the edge with respect to the size. By thoroughly analyzing the size dependence of the thermal resistance, we show that, with increasing graphene size, the ballistic resistance becomes more dominant in the thermal resistance experienced by a heat source of finite size and that the thermal conductivity experienced by such a heat source can even decrease. The results of this study reveal that the thermal conductivity of graphene detected by a heat source depends on the size of the heat source relative to that of the suspended graphene and on how the heat source and graphene are connected. As demonstrated in this study, NP SThM will be very useful for quantitative thermal characterization of not only CVD-grown graphene but also various other nanomaterials and nanodevices.
Understanding of heat generation in semiconductor devices is important in the thermal management ... more Understanding of heat generation in semiconductor devices is important in the thermal management of integrated circuits and in the analysis of the device physics. Scanning thermal microscopy was used to measure the temperature distribution of the cross-section of an operating metal-oxide-semiconductor field-effect transistor (MOSFET). The temperature distributions were measured both in DC and AC modes in order to take account of the leakage current. The location of the maximum temperature was observed to approach the drain as the drain bias was increased.
Uploads
Papers