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Papers by Guruswamy Rajaram

Research paper thumbnail of Development of GaAs/AlGaAs Micro Hall Sensors for Magnetic Flux Leakage Measurements

Magnetic flux leakage (MFL) technique is one of the most widely used Nondestructive evaluation (N... more Magnetic flux leakage (MFL) technique is one of the most widely used Nondestructive evaluation (NDE) techniques for detection of surface and sub-surface defects in ferro-magnetic materials. Magnetic Hall sensors are preferred in such applications for their ease of use and linear response with magnetic field. GaAs/AlGaAs hetero-structure based Hall sensors are new generation of sensors with higher sensitivity (~1000 V/AT). Photolithographic patterning technique is very useful for miniaturization of Hall sensors. This paper discusses the development of 2-dimensional electron gas (2-DEG) GaAs micro-Hall sensors by photolithographic technique. The micro-Hall sensors developed have an active area of 50μm×50μm. The sensor is fabricated using a five mask photolithographic process which includes (a) Alignment marks using (Cr/Au); (b) Wet chemical etching for device isolation; (c) Ohmic contacts using AuGe/Cr/Au metallisation followed by a rapid thermal anneal; (d) Interconnect metallisation...

Research paper thumbnail of Resistivity and longitudinal magnetoresistance studies in amorphous FeNiCrMoSiB

Journal of Magnetism and Magnetic Materials, 1988

With a view to study the effect of Cr on the transport properties of Fe-Ni based amorphous magnet... more With a view to study the effect of Cr on the transport properties of Fe-Ni based amorphous magnetic materials, electrical resistivity and magnetoresistance measurements have been carried out on a

Research paper thumbnail of Single composite target magnetron sputter deposition of crystalline and amorphous SiC thin films

Materials Research Express

The formation of crystalline and amorphous SiC films by single-composite target magnetron sputter... more The formation of crystalline and amorphous SiC films by single-composite target magnetron sputter deposition process is demonstrated. In this process, graphite pieces were placed on a Si target to form a composite single target. The graphite coverage area (GCA) was varied between 4 to 18% to achieve controllable carbon content in the films with stoichiometry being achieved at ~13% GCA. The films on Si substrates crystallized into the 21 H polytype of SiC, without any additional heating during deposition. However, SiC films deposited on quartz substrates under the same processing conditions are amorphous. These films show high transparency (greater than 80%) in the visible and near infrared regions with an optically measured band gap of 3.4 eV and refractive index of 1.96 at a wavelength of 1300 nm.

Research paper thumbnail of A Highly Tunable Barium Strontium Titanate Thin Film MIM Varactor With Floating Metal

IEEE Microwave and Wireless Components Letters

Research paper thumbnail of Characteristics of 21H-SiC Thin Film-Based Schottky Barrier Diodes Using TiN Contacts

Journal of Electronic Materials

Research paper thumbnail of Resistive switching behaviour of amorphous silicon carbide thin films fabricated by a single composite magnetron sputter deposition method

Bulletin of Materials Science

Research paper thumbnail of Optical confinement in TiO2 waveguides fabricated by resist free electron beam lithography

Optics & Laser Technology

Research paper thumbnail of Continuity and temperature dependence of the vortex-phase boundary ofBi2Sr2CaCu2O8+δ

Physical Review B

Local magnetization data of Bi 2 Sr 2 CaCu 2 O 8ϩ␦ crystals measured using a Hall sensor array ar... more Local magnetization data of Bi 2 Sr 2 CaCu 2 O 8ϩ␦ crystals measured using a Hall sensor array are reported for underdoped, optimally doped, and overdoped samples. Magnetization data just inside the sample edge provide the most reliable values for the vortex-phase transition field in the magnetic phase diagram among those at other positions. The first-order melting line ͑ML͒, which manifests itself as a step in magnetization M (H), is detected at relatively high temperatures for all the samples. The position in the field of the second peak in magnetization at low temperatures can be determined unambiguously from the relaxed magnetization after a sufficiently long waiting time. It is found that in all the samples the onset field of the second peak, which is interpreted as an entanglement line ͑EL͒, connects continuously with ML as the temperature is increased. At intermediate temperatures, for the underdoped and optimally doped samples, either the second peak or the magnetization cusp, whose position connects with that of the step, is observed at the same temperature and the same field but in different experimental time scales. The ML for the three samples corresponds to a single curve when a scaling of (T C 2 ϪT 2)/T C T 2 ␥ 2 ͑T C is the superconducting transition temperature, is the penetration depth, and ␥ is the anisotropy constant͒ is used against the induction B, consistent with the decoupling theory. The EL is well fitted by Bϰ(1ϩcT 2)/␥ 2 , with cϾ0, suggesting a presence of dimensional crossover. The positions of the depinning line and the irreversibility line, measured by temperature sweep and field sweep, respectively, are found to depend on the time scale of the sweep rate, suggesting that they represent crossovers between two different vortex-creep mechanisms. Only the ML-EL is suggested to be the real phase boundary.

Research paper thumbnail of Effect of Bi–Sr replacement and oxygen doping on vortex-matter phase transitions in Bi 2+ x Sr 2− x CaCu 2O 8+ δ

Physica C, 1998

To investigate the effect of oxygen doping level with a wide range on vortex-matter phase transit... more To investigate the effect of oxygen doping level with a wide range on vortex-matter phase transitions, magnetization for H‖ c was measured for Bi2+ xSr2− xCaCu2O8+ δ single crystal with x= 0.05–0.25 and various doping level δ. Optimum condition against δ for the ...

Research paper thumbnail of Effect of Small Transport Currents on the Flux-Line Lattice Melting in Bi-2212 Crystal

Research paper thumbnail of Effect of Bi-Sr replacement and oxygen doping on vortex-matter phase transitions in Bi2+xSr2- xCaCu2O8+delta

Physica C, 1998

To investigate the effect of oxygen doping level with a wide range on vortex-matter phase transit... more To investigate the effect of oxygen doping level with a wide range on vortex-matter phase transitions, magnetization for H‖ c was measured for Bi2+ xSr2− xCaCu2O8+ δ single crystal with x= 0.05–0.25 and various doping level δ. Optimum condition against δ for the ...

Research paper thumbnail of High selective etching GaAs/Al 0.3 Ga 0.7 As for the high electron mobility transistor (HEMT) applications using citric buffer solution

2015 International Conference on Communication Information Computing Technology, 2015

Research paper thumbnail of Agglomeration and Diffusion of Ag Associated with Electrical Contacts on Single Crystal $ bf Bi_{2}Sr_{2}CaCu_{2}O_{ ninmbi y}$

Japanese Journal of Applied Physics, 1996

For the purpose of obtaining good small-area electrical contacts on single crystals of Bi 2 Sr... more For the purpose of obtaining good small-area electrical contacts on single crystals of Bi 2 Sr 2 CaCu 2 Oy(Bi-2212) for transport study, the nature of the Ag film on a Bi-2212 single crystal was examined. Ag films of ∼ 100 nm thickness deposited on cleaved ...

Research paper thumbnail of Moessbauer studies in sputtered A-Fe/sub 80/B/sub 20/ foils

Moessbauer studies have been carried out on sputtered amorphous Fe/sub 80/B/sub 20/ foils in the ... more Moessbauer studies have been carried out on sputtered amorphous Fe/sub 80/B/sub 20/ foils in the temperature range of 4.4 K to 300 K. The results have been analysed using Window's method. The coefficients B and C in Bloch's law are evaluated from the data. One finds a smaller value of B in sputtered foils in comparison to the liquid quenched ribbons. There are indications that the mean square range of exchange interaction is larger in these foils.

Research paper thumbnail of Moessbauer studies in sputtered A-FeââBââ foils

Moessbauer studies have been carried out on sputtered amorphous FeââBââ foils in the temperature ... more Moessbauer studies have been carried out on sputtered amorphous FeââBââ foils in the temperature range of 4.4 K to 300 K. The results have been analysed using Window's method. The coefficients B and C in Bloch's law are evaluated from the data. One finds a smaller value of B in sputtered foils in comparison to the liquid quenched ribbons. There are indications that the mean square range of exchange interaction is larger in these foils.

Research paper thumbnail of Remarkable change in resistivity minimum temperature in the presence of Ni in a-Fe-Cr-B-Si alloys

Materials Research Bulletin, 1987

Research paper thumbnail of Electrical Transport Studies in Amorpohous Fe<sub>80-x</sub>Cr<sub>x</sub>B<sub>12</sub>Si<sub>8</sub> Alloys

Key Engineering Materials, 1987

Research paper thumbnail of High selective etching GaAs/Al<inf>0.3</inf>Ga<inf>0.7</inf>As for the high electron mobility transistor (HEMT) applications using citric buffer solution

2015 International Conference on Communication, Information & Computing Technology (ICCICT), 2015

Research paper thumbnail of GaAs/AlGaAs heterostructure based Micro-Hall Sensors and response to A.C. excitation

Hall sensors are fabricated from GaAs/AlGaAs based heterostructures. The sensors are characterize... more Hall sensors are fabricated from GaAs/AlGaAs based heterostructures. The sensors are characterized for sensitivity using A.C and D.C. excitation techniques w.r.to a known magnetic field in the range of 0-100Oe. Sensitivities of the order of 1000V/AT are obtained with a low variation of 0.15% in the temperature range of 30°C-100°C. A.C excitation (30Hz to 1 kHz) for the sensor current and phase-sensitive detection of the Hall Voltage are used to eliminate thermo-emfs and its drift with a consequent improvement in data acquisition rates of >50% over that of D.C excitation. This improves scan rates in applications such as magnetic flux leakage (MFL) measurements. The sensitivity is independent of the frequency of excitation as expected; however, the zero-field Hall voltage ‘offset’ value is found to have small frequency dependence.

Research paper thumbnail of Magnetic field sensor using III-V multilayer structures: New insights into Ohmic contact formation to GaAs from magnetization measurements

The utility of GaAs/AlGaAs multilayers on GaAs substrate with the two dimensional electron Gas (2... more The utility of GaAs/AlGaAs multilayers on GaAs substrate with the two dimensional electron Gas (2DEG) layer as materials for Hall effect based magnetic field sensors is discussed. The structures offer useable hi gh sensitivities (~1200V/AT) by combining low carrier density with high mobility. Results of scanning across notches on magnetic steels using Hall magnetic field sensors micro-fabricated for non-destructive testing (NDT) are presented. A process issue arising from the use of Ni in the Ohmic contact metallization, Au Ge/Ni/Au is studied in the context of magnetic field sensor application. The dependence of resistance, surface roughness and magnetism of the processed contacts on parameters such as Ni layer thickness, anneal temperature and Au-Ge alloy composition are discussed. The magnetization results indicate that the contacts are rendered non-magnetic for anneals at te mperature well below the alloying temperature at which the contact resistance drops. A solubility limited...

Research paper thumbnail of Development of GaAs/AlGaAs Micro Hall Sensors for Magnetic Flux Leakage Measurements

Magnetic flux leakage (MFL) technique is one of the most widely used Nondestructive evaluation (N... more Magnetic flux leakage (MFL) technique is one of the most widely used Nondestructive evaluation (NDE) techniques for detection of surface and sub-surface defects in ferro-magnetic materials. Magnetic Hall sensors are preferred in such applications for their ease of use and linear response with magnetic field. GaAs/AlGaAs hetero-structure based Hall sensors are new generation of sensors with higher sensitivity (~1000 V/AT). Photolithographic patterning technique is very useful for miniaturization of Hall sensors. This paper discusses the development of 2-dimensional electron gas (2-DEG) GaAs micro-Hall sensors by photolithographic technique. The micro-Hall sensors developed have an active area of 50μm×50μm. The sensor is fabricated using a five mask photolithographic process which includes (a) Alignment marks using (Cr/Au); (b) Wet chemical etching for device isolation; (c) Ohmic contacts using AuGe/Cr/Au metallisation followed by a rapid thermal anneal; (d) Interconnect metallisation...

Research paper thumbnail of Resistivity and longitudinal magnetoresistance studies in amorphous FeNiCrMoSiB

Journal of Magnetism and Magnetic Materials, 1988

With a view to study the effect of Cr on the transport properties of Fe-Ni based amorphous magnet... more With a view to study the effect of Cr on the transport properties of Fe-Ni based amorphous magnetic materials, electrical resistivity and magnetoresistance measurements have been carried out on a

Research paper thumbnail of Single composite target magnetron sputter deposition of crystalline and amorphous SiC thin films

Materials Research Express

The formation of crystalline and amorphous SiC films by single-composite target magnetron sputter... more The formation of crystalline and amorphous SiC films by single-composite target magnetron sputter deposition process is demonstrated. In this process, graphite pieces were placed on a Si target to form a composite single target. The graphite coverage area (GCA) was varied between 4 to 18% to achieve controllable carbon content in the films with stoichiometry being achieved at ~13% GCA. The films on Si substrates crystallized into the 21 H polytype of SiC, without any additional heating during deposition. However, SiC films deposited on quartz substrates under the same processing conditions are amorphous. These films show high transparency (greater than 80%) in the visible and near infrared regions with an optically measured band gap of 3.4 eV and refractive index of 1.96 at a wavelength of 1300 nm.

Research paper thumbnail of A Highly Tunable Barium Strontium Titanate Thin Film MIM Varactor With Floating Metal

IEEE Microwave and Wireless Components Letters

Research paper thumbnail of Characteristics of 21H-SiC Thin Film-Based Schottky Barrier Diodes Using TiN Contacts

Journal of Electronic Materials

Research paper thumbnail of Resistive switching behaviour of amorphous silicon carbide thin films fabricated by a single composite magnetron sputter deposition method

Bulletin of Materials Science

Research paper thumbnail of Optical confinement in TiO2 waveguides fabricated by resist free electron beam lithography

Optics & Laser Technology

Research paper thumbnail of Continuity and temperature dependence of the vortex-phase boundary ofBi2Sr2CaCu2O8+δ

Physical Review B

Local magnetization data of Bi 2 Sr 2 CaCu 2 O 8ϩ␦ crystals measured using a Hall sensor array ar... more Local magnetization data of Bi 2 Sr 2 CaCu 2 O 8ϩ␦ crystals measured using a Hall sensor array are reported for underdoped, optimally doped, and overdoped samples. Magnetization data just inside the sample edge provide the most reliable values for the vortex-phase transition field in the magnetic phase diagram among those at other positions. The first-order melting line ͑ML͒, which manifests itself as a step in magnetization M (H), is detected at relatively high temperatures for all the samples. The position in the field of the second peak in magnetization at low temperatures can be determined unambiguously from the relaxed magnetization after a sufficiently long waiting time. It is found that in all the samples the onset field of the second peak, which is interpreted as an entanglement line ͑EL͒, connects continuously with ML as the temperature is increased. At intermediate temperatures, for the underdoped and optimally doped samples, either the second peak or the magnetization cusp, whose position connects with that of the step, is observed at the same temperature and the same field but in different experimental time scales. The ML for the three samples corresponds to a single curve when a scaling of (T C 2 ϪT 2)/T C T 2 ␥ 2 ͑T C is the superconducting transition temperature, is the penetration depth, and ␥ is the anisotropy constant͒ is used against the induction B, consistent with the decoupling theory. The EL is well fitted by Bϰ(1ϩcT 2)/␥ 2 , with cϾ0, suggesting a presence of dimensional crossover. The positions of the depinning line and the irreversibility line, measured by temperature sweep and field sweep, respectively, are found to depend on the time scale of the sweep rate, suggesting that they represent crossovers between two different vortex-creep mechanisms. Only the ML-EL is suggested to be the real phase boundary.

Research paper thumbnail of Effect of Bi–Sr replacement and oxygen doping on vortex-matter phase transitions in Bi 2+ x Sr 2− x CaCu 2O 8+ δ

Physica C, 1998

To investigate the effect of oxygen doping level with a wide range on vortex-matter phase transit... more To investigate the effect of oxygen doping level with a wide range on vortex-matter phase transitions, magnetization for H‖ c was measured for Bi2+ xSr2− xCaCu2O8+ δ single crystal with x= 0.05–0.25 and various doping level δ. Optimum condition against δ for the ...

Research paper thumbnail of Effect of Small Transport Currents on the Flux-Line Lattice Melting in Bi-2212 Crystal

Research paper thumbnail of Effect of Bi-Sr replacement and oxygen doping on vortex-matter phase transitions in Bi2+xSr2- xCaCu2O8+delta

Physica C, 1998

To investigate the effect of oxygen doping level with a wide range on vortex-matter phase transit... more To investigate the effect of oxygen doping level with a wide range on vortex-matter phase transitions, magnetization for H‖ c was measured for Bi2+ xSr2− xCaCu2O8+ δ single crystal with x= 0.05–0.25 and various doping level δ. Optimum condition against δ for the ...

Research paper thumbnail of High selective etching GaAs/Al 0.3 Ga 0.7 As for the high electron mobility transistor (HEMT) applications using citric buffer solution

2015 International Conference on Communication Information Computing Technology, 2015

Research paper thumbnail of Agglomeration and Diffusion of Ag Associated with Electrical Contacts on Single Crystal $ bf Bi_{2}Sr_{2}CaCu_{2}O_{ ninmbi y}$

Japanese Journal of Applied Physics, 1996

For the purpose of obtaining good small-area electrical contacts on single crystals of Bi 2 Sr... more For the purpose of obtaining good small-area electrical contacts on single crystals of Bi 2 Sr 2 CaCu 2 Oy(Bi-2212) for transport study, the nature of the Ag film on a Bi-2212 single crystal was examined. Ag films of ∼ 100 nm thickness deposited on cleaved ...

Research paper thumbnail of Moessbauer studies in sputtered A-Fe/sub 80/B/sub 20/ foils

Moessbauer studies have been carried out on sputtered amorphous Fe/sub 80/B/sub 20/ foils in the ... more Moessbauer studies have been carried out on sputtered amorphous Fe/sub 80/B/sub 20/ foils in the temperature range of 4.4 K to 300 K. The results have been analysed using Window's method. The coefficients B and C in Bloch's law are evaluated from the data. One finds a smaller value of B in sputtered foils in comparison to the liquid quenched ribbons. There are indications that the mean square range of exchange interaction is larger in these foils.

Research paper thumbnail of Moessbauer studies in sputtered A-FeââBââ foils

Moessbauer studies have been carried out on sputtered amorphous FeââBââ foils in the temperature ... more Moessbauer studies have been carried out on sputtered amorphous FeââBââ foils in the temperature range of 4.4 K to 300 K. The results have been analysed using Window's method. The coefficients B and C in Bloch's law are evaluated from the data. One finds a smaller value of B in sputtered foils in comparison to the liquid quenched ribbons. There are indications that the mean square range of exchange interaction is larger in these foils.

Research paper thumbnail of Remarkable change in resistivity minimum temperature in the presence of Ni in a-Fe-Cr-B-Si alloys

Materials Research Bulletin, 1987

Research paper thumbnail of Electrical Transport Studies in Amorpohous Fe<sub>80-x</sub>Cr<sub>x</sub>B<sub>12</sub>Si<sub>8</sub> Alloys

Key Engineering Materials, 1987

Research paper thumbnail of High selective etching GaAs/Al<inf>0.3</inf>Ga<inf>0.7</inf>As for the high electron mobility transistor (HEMT) applications using citric buffer solution

2015 International Conference on Communication, Information & Computing Technology (ICCICT), 2015

Research paper thumbnail of GaAs/AlGaAs heterostructure based Micro-Hall Sensors and response to A.C. excitation

Hall sensors are fabricated from GaAs/AlGaAs based heterostructures. The sensors are characterize... more Hall sensors are fabricated from GaAs/AlGaAs based heterostructures. The sensors are characterized for sensitivity using A.C and D.C. excitation techniques w.r.to a known magnetic field in the range of 0-100Oe. Sensitivities of the order of 1000V/AT are obtained with a low variation of 0.15% in the temperature range of 30°C-100°C. A.C excitation (30Hz to 1 kHz) for the sensor current and phase-sensitive detection of the Hall Voltage are used to eliminate thermo-emfs and its drift with a consequent improvement in data acquisition rates of >50% over that of D.C excitation. This improves scan rates in applications such as magnetic flux leakage (MFL) measurements. The sensitivity is independent of the frequency of excitation as expected; however, the zero-field Hall voltage ‘offset’ value is found to have small frequency dependence.

Research paper thumbnail of Magnetic field sensor using III-V multilayer structures: New insights into Ohmic contact formation to GaAs from magnetization measurements

The utility of GaAs/AlGaAs multilayers on GaAs substrate with the two dimensional electron Gas (2... more The utility of GaAs/AlGaAs multilayers on GaAs substrate with the two dimensional electron Gas (2DEG) layer as materials for Hall effect based magnetic field sensors is discussed. The structures offer useable hi gh sensitivities (~1200V/AT) by combining low carrier density with high mobility. Results of scanning across notches on magnetic steels using Hall magnetic field sensors micro-fabricated for non-destructive testing (NDT) are presented. A process issue arising from the use of Ni in the Ohmic contact metallization, Au Ge/Ni/Au is studied in the context of magnetic field sensor application. The dependence of resistance, surface roughness and magnetism of the processed contacts on parameters such as Ni layer thickness, anneal temperature and Au-Ge alloy composition are discussed. The magnetization results indicate that the contacts are rendered non-magnetic for anneals at te mperature well below the alloying temperature at which the contact resistance drops. A solubility limited...