Sangwoo Kang | Texas Instruments (original) (raw)

Papers by Sangwoo Kang

Bulletin of the American Physical Society, 2017

2D materials are promising for future electronic and optoelectronic applications. In this regard,... more 2D materials are promising for future electronic and optoelectronic applications. In this regard, it is important to realize p-n diodes, the most fundamental building block of all modern semiconductor devices, based on these 2D materials. While it is challenging to achieve homojunction diodes in 2D semiconductors due to lack of reliable selective doping techniques, it is relatively easier to achieve diode-like behavior in van der Waals (vdW) heterostructures comprising different 2D semiconductors. Here, we demonstrate dual-gated vdW heterojunction p-n diodes based on p-type MoTe 2 and n-type MoS 2 , with hBN as the top and bottom gate dielectric. The heterostructure stack is assembled using a polymer-based 'dry-transfer' technique. Pt contact is used for hole injection in MoTe 2 , whereas Ag is used for electron injection in MoS 2. The dual-gates allow for independent electrostatic tuning of the carriers in MoTe 2 and MoS 2. Room temperature interlayer current-voltage characteristics reveal a strong gate-tunable rectification behavior. At low temperatures, the diode turn-on voltage increases, whereas the reverse saturation current decreases, in accordance with conventional p-n diode behavior.

Nano letters, Jan 15, 2016

Nano letters, Jan 20, 2016

Interlayer tunnel field-effect transistors based on graphene and hexagonal boron nitride (hBN) ha... more Interlayer tunnel field-effect transistors based on graphene and hexagonal boron nitride (hBN) have recently attracted much interest for their potential as beyond-CMOS devices. Using a recently developed method for fabricating rotationally aligned two-dimensional heterostructures, we show experimental results for devices with varying thicknesses and stacking order of the graphene electrode layers and also model the current-voltage behavior. We show that an increase in the graphene layer thickness results in narrower resonance. However, due to a simultaneous increase in the number of sub-bands and decrease of sub-band separation with an increase in thickness, the negative differential resistance peaks becomes less prominent and do not appear for certain conditions at room temperature. Also, we show that due to the unique band structure of odd number of layer Bernal-stacked graphene, the number of closely spaced resonance conditions increase, causing interference between neighboring r...

Journal of Applied Physics, 2016

Many factors have been identified to influence the electrical transport characteristics of graphe... more Many factors have been identified to influence the electrical transport characteristics of graphene fieldeffect transistors. In this report, we examine the influence of the exposure current level used during electron beam lithography (EBL) for active region patterning. In the presence of a self-assembled hydrophobic residual layer generated by oxygen plasma etching covering the top surface of the graphene channel, we show that the use of low EBL current level results in higher mobility, lower residual carrier density, and charge neutrality point closer to 0 V, with reduced device-to-device variations. We show that this correlation originates from the resist heating dependent release of radicals from the resist material, near its interface with graphene, and its subsequent trapping by the hydrophobic polymer layer. Using a general model for resist heating, we calculate the difference in resist heating for different EBL current levels. We further corroborate our argument through control experiments, where radicals are either intentionally added or removed by other processes. We also utilize this finding to obtain mobilities in excess of 18,000 cm 2 /Vs on silicon dioxide substrates. We believe these results are applicable to other 2D materials such as transition metal dichalcogenides and nanoscale devices in general.

Nano Letters, 2016

We describe the realization of van der Waals (vdW) heterostructures with accurate rotational alig... more We describe the realization of van der Waals (vdW) heterostructures with accurate rotational alignment of individual layer crystal axes. We illustrate the approach by demonstrating a Bernal-stacked bilayer graphene formed using successive transfers of monolayer graphene flakes. The Raman spectra of this artificial bilayer graphene possess a wide 2D band, which is best fit by four Lorentzians, consistent with Bernal stacking. Scanning tunneling microscopy reveals no moiré pattern on the artificial bilayer graphene, and tunneling spectroscopy as a function of gate voltage reveals a constant density of states, also in agreement with Bernal stacking. In addition, electron transport probed in dual-gated samples reveals a band gap opening as a function of transverse electric field. To illustrate the applicability of this technique to realize vdW heterostructuctures in which the functionality is critically dependent on rotational alignment, we demonstrate resonant tunneling double bilayer graphene heterostructures separated by hexagonal boron-nitride dielectric.

ACS Nano, 2015

We demonstrate dual-gated p-type field-effect transistors (FETs) based on few-layer tungsten dise... more We demonstrate dual-gated p-type field-effect transistors (FETs) based on few-layer tungsten diselenide (WSe 2) using high work-function platinum source/drain contacts, and a hexagonal boron nitride top-gate dielectric. A device topology with contacts underneath the WSe 2 results in p-FETs with I ON /I OFF ratios exceeding 10 7 , and contacts that remain Ohmic down to cryogenic temperatures. The output characteristics show current saturation and gate tunable negative differential resistance. The devices show intrinsic hole mobilities around 140 cm 2 /Vs at room temperature, and approaching 4,000 cm 2 /Vs at 2 K. Temperaturedependent transport measurements show a metalinsulator transition, with an insulating phase at low densities, and a metallic phase at high densities. The mobility shows a strong temperature dependence consistent with phonon scattering, and saturates at low temperatures, possibly limited by Coulomb scattering, or defects. The isolation of graphene, and study of its exceptional properties has triggered an interest in several other two-dimensional (2D) layered materials, 1 semiconducting transition metal dichalcogenides (TMDs) 2,3 being one of them. In con-* To whom correspondence should be addressed

Banerjee for his trust and support. Without his gracious offer for me to work at the Microelectro... more Banerjee for his trust and support. Without his gracious offer for me to work at the Microelectronics Research Center, none of this would have ever happened. His patience allowed me to steadily and joyously work on the some of the most interesting projects that I have worked on. I thank members of my committee for the time and effort they took to review my work. I appreciate my mentor Seyoung Kim for training and guiding me as a new student. I also acknowledge Hema, Amritesh, Kyoung, Babak and all my colleagues at MRC who were more than willing to share their knowledge and expertise, and to whom I am greatly indebted. I would like to thank my parents and other family members in Korea for their trust and support. And last but not least, I thank my wife for her unwavering support through all the tough times, and also my two young children for bringing much joy into my life.

Applied Physics Letters, 2014

ABSTRACT

Nano Letters, 2015

To reduce Schottky-barrier-induced contact and access resistance, and the impact of charged impur... more To reduce Schottky-barrier-induced contact and access resistance, and the impact of charged impurity and phonon scattering on mobility in devices based on 2D transition metal dichalcogenides (TMDs), considerable effort has been put into exploring various doping techniques and dielectric engineering using high-κ oxides, respectively. The goal of this work is to demonstrate a high-κ dielectric that serves as an effective n-type charge transfer dopant on monolayer (ML) molybdenum disulfide (MoS2). Utilizing amorphous titanium suboxide (ATO) as the "high-κ dopant", we achieved a contact resistance of ∼180 Ω·μm that is the lowest reported value for ML MoS2. An ON current as high as 240 μA/μm and field effect mobility as high as 83 cm(2)/V-s were realized using this doping technique. Moreover, intrinsic mobility as high as 102 cm(2)/V-s at 300 K and 501 cm(2)/V-s at 77 K were achieved after ATO encapsulation that are among the highest mobility values reported on ML MoS2. We also analyzed the doping effect of ATO films on ML MoS2, a phenomenon that is absent when stoichiometric TiO2 is used, using ab initio density functional theory (DFT) calculations that shows excellent agreement with our experimental findings. On the basis of the interfacial-oxygen-vacancy mediated doping as seen in the case of high-κ ATO-ML MoS2, we propose a mechanism for the mobility enhancement effect observed in TMD-based devices after encapsulation in a high-κ dielectric environment.

A novel complementary metal-oxide-semiconductor (CMOS) process compatible and self-aligned fabric... more A novel complementary metal-oxide-semiconductor (CMOS) process compatible and self-aligned fabrication method for the dual-gate single-electron transistor (DG-SET) is presented. The performance of previous versions of the DG-SET was limited by inherent parasitic elements and its fabrication process was divergent from conventional CMOS, limiting the possibility of co-integration. Through simulation, the parasitic elements are confirmed to be caused by the non-self-alignment of the control gate, side gates, and source/drain. To resolve such issues, a new type of DG-SET was fabricated using a self-aligned process. Measurement results obtained at room temperature revealed clear Coulomb oscillation peaks in the trans-conductance curve. Through parameter extraction and its comparison with previous results, this is confirmed to be the consequence of singleelectron tunneling. Also, in order to confirm that the single-electron tunneling is caused by the electrically induced tunneling barriers, and not by random fluctuations along the SOI active, low temperature measurement results for devices with different parameters is compared.

ABSTRACT Field effect transistors based on ultra-thin transition metal dichalcogenides suffer fro... more ABSTRACT Field effect transistors based on ultra-thin transition metal dichalcogenides suffer from high contact resistances due to the Schottky barrier formed between the metal and the semiconducting channel. An effective way to overcome this issue is to dope the semiconducting channel in order to reduce the Schottky barrier width, thereby enabling efficient electron injection via tunneling. Previously used charge transfer doping techniques employed the use of potassium ions and PEI. However, these doping reagents are unstable in air. Here we report the use of an air stable, self encapsulating, spin on n-type doping technique on MoS2 utilizing TiOx sol-gel. The doping of the channel is confirmed by the broadening of the A1g Raman mode of MoS2. High performance field effect transistors are demonstrated which show three times improvement in the field effect mobility as well as a two-fold increase in the intrinsic mobility of the MoS2 channel. The enhancement of intrinsic mobility can be attributed to the suppression of the A1g phonon modes of MoS2 as well as screening of charged impurities by the TiOX layer. The devices show extended air stability over two to three weeks. The use of TiOx sol-gel can be a promising way to enhance the performance of TMD based transistors.

Journal of Applied Physics, 2009

Charging damage can critically degrade oxide reliability. Antenna-structured metal-oxide-semicond... more Charging damage can critically degrade oxide reliability. Antenna-structured metal-oxide-semiconductor field-effect transistors were fabricated to examine the effect of process parameters on charging damage. Charging damage to threshold voltage (Vth) was investigated experimentally as well as by constructing a neural network model. For a systematic modeling, charging damage process was characterized by means of a face-centered Box-Wilson experiment. The prediction performance

Extended Abstracts of the 2006 International Conference on Solid State Devices and Materials, 2006

Bulletin of the American Physical Society, Mar 5, 2015

We present the realization and characterization of independently contacted and rotationally align... more We present the realization and characterization of independently contacted and rotationally aligned double bilayer graphene heterostructures, that show gate-tunable tunneling resonances and negative differential resistance in their interlayer current-voltage characteristics. Our devices are fabricated by successively stacking mechanically exfoliated bilayer graphene and hexagonal boron nitride dielectric using a layer-by-layer transfer technique. The bilayers are rotationally aligned during the device fabrication by selecting flakes with straight edges, and using them as a reference for alignment. We determine the heterostructure energy band alignment at the tunneling resonance using the individual layer carrier densities, and including the chemical potential dependence on the carrier density. Our analysis show that the tunneling resonances occur when the charge neutrality points of the two bilayer graphene are energetically aligned, which suggests the resonances stem from the momentum conserving tunneling.

Abstracts -50 nm dots were fabricated by using an etch-back process. The dots have the advantage ... more Abstracts -50 nm dots were fabricated by using an etch-back process. The dots have the advantage of alignment and reproduction in Single Electron Transistor area which has not been able to realize a reproducible and controllable device at room temperature. As a result, the small dots were reproducibly fabricated with planarization and an etch-back process.

Nano Letters, 2015

To reduce Schottky-barrier-induced contact and access resistance, and the impact of charged impur... more To reduce Schottky-barrier-induced contact and access resistance, and the impact of charged impurity and phonon scattering on mobility in devices based on 2D transition metal dichalcogenides (TMDs), considerable effort has been put into exploring various doping techniques and dielectric engineering using high-κ oxides, respectively. The goal of this work is to demonstrate a high-κ dielectric that serves as an effective n-type charge transfer dopant on monolayer (ML) molybdenum disulfide (MoS2). Utilizing amorphous titanium suboxide (ATO) as the "high-κ dopant", we achieved a contact resistance of ∼180 Ω·μm that is the lowest reported value for ML MoS2. An ON current as high as 240 μA/μm and field effect mobility as high as 83 cm(2)/V-s were realized using this doping technique. Moreover, intrinsic mobility as high as 102 cm(2)/V-s at 300 K and 501 cm(2)/V-s at 77 K were achieved after ATO encapsulation that are among the highest mobility values reported on ML MoS2. We also analyzed the doping effect of ATO films on ML MoS2, a phenomenon that is absent when stoichiometric TiO2 is used, using ab initio density functional theory (DFT) calculations that shows excellent agreement with our experimental findings. On the basis of the interfacial-oxygen-vacancy mediated doping as seen in the case of high-κ ATO-ML MoS2, we propose a mechanism for the mobility enhancement effect observed in TMD-based devices after encapsulation in a high-κ dielectric environment.

A new structure of Single-Electron Transistor (SET) with electric tunneling barrier is designed a... more A new structure of Single-Electron Transistor (SET) with electric tunneling barrier is designed and simulated with device simulation tool (SILVACO). Control gate of the designed structure covers only the top surface of the active SOI fin, while side gates inducing the electric tunneling barriers surround all three surfaces of the silicon active region. Characteristics of the electrical tunneling barriers, internal

2007 IEEE International Reliability Physics Symposium Proceedings. 45th Annual, 2007

One of the most important issues of NAND flash memory is reliability problems caused by oxide and... more One of the most important issues of NAND flash memory is reliability problems caused by oxide and interface traps. But it has been revealed that their generation rate increases by Fowler-Nordheim current stressing on the tunnel oxide as the channel width of shallow trench isolation (STI) isolated NAND flash cells shrinks and electric field is increased at active edge of

Bulletin of the American Physical Society, 2017

2D materials are promising for future electronic and optoelectronic applications. In this regard,... more 2D materials are promising for future electronic and optoelectronic applications. In this regard, it is important to realize p-n diodes, the most fundamental building block of all modern semiconductor devices, based on these 2D materials. While it is challenging to achieve homojunction diodes in 2D semiconductors due to lack of reliable selective doping techniques, it is relatively easier to achieve diode-like behavior in van der Waals (vdW) heterostructures comprising different 2D semiconductors. Here, we demonstrate dual-gated vdW heterojunction p-n diodes based on p-type MoTe 2 and n-type MoS 2 , with hBN as the top and bottom gate dielectric. The heterostructure stack is assembled using a polymer-based 'dry-transfer' technique. Pt contact is used for hole injection in MoTe 2 , whereas Ag is used for electron injection in MoS 2. The dual-gates allow for independent electrostatic tuning of the carriers in MoTe 2 and MoS 2. Room temperature interlayer current-voltage characteristics reveal a strong gate-tunable rectification behavior. At low temperatures, the diode turn-on voltage increases, whereas the reverse saturation current decreases, in accordance with conventional p-n diode behavior.

Nano letters, Jan 15, 2016

Nano letters, Jan 20, 2016

Interlayer tunnel field-effect transistors based on graphene and hexagonal boron nitride (hBN) ha... more Interlayer tunnel field-effect transistors based on graphene and hexagonal boron nitride (hBN) have recently attracted much interest for their potential as beyond-CMOS devices. Using a recently developed method for fabricating rotationally aligned two-dimensional heterostructures, we show experimental results for devices with varying thicknesses and stacking order of the graphene electrode layers and also model the current-voltage behavior. We show that an increase in the graphene layer thickness results in narrower resonance. However, due to a simultaneous increase in the number of sub-bands and decrease of sub-band separation with an increase in thickness, the negative differential resistance peaks becomes less prominent and do not appear for certain conditions at room temperature. Also, we show that due to the unique band structure of odd number of layer Bernal-stacked graphene, the number of closely spaced resonance conditions increase, causing interference between neighboring r...

Journal of Applied Physics, 2016

Many factors have been identified to influence the electrical transport characteristics of graphe... more Many factors have been identified to influence the electrical transport characteristics of graphene fieldeffect transistors. In this report, we examine the influence of the exposure current level used during electron beam lithography (EBL) for active region patterning. In the presence of a self-assembled hydrophobic residual layer generated by oxygen plasma etching covering the top surface of the graphene channel, we show that the use of low EBL current level results in higher mobility, lower residual carrier density, and charge neutrality point closer to 0 V, with reduced device-to-device variations. We show that this correlation originates from the resist heating dependent release of radicals from the resist material, near its interface with graphene, and its subsequent trapping by the hydrophobic polymer layer. Using a general model for resist heating, we calculate the difference in resist heating for different EBL current levels. We further corroborate our argument through control experiments, where radicals are either intentionally added or removed by other processes. We also utilize this finding to obtain mobilities in excess of 18,000 cm 2 /Vs on silicon dioxide substrates. We believe these results are applicable to other 2D materials such as transition metal dichalcogenides and nanoscale devices in general.

Nano Letters, 2016

We describe the realization of van der Waals (vdW) heterostructures with accurate rotational alig... more We describe the realization of van der Waals (vdW) heterostructures with accurate rotational alignment of individual layer crystal axes. We illustrate the approach by demonstrating a Bernal-stacked bilayer graphene formed using successive transfers of monolayer graphene flakes. The Raman spectra of this artificial bilayer graphene possess a wide 2D band, which is best fit by four Lorentzians, consistent with Bernal stacking. Scanning tunneling microscopy reveals no moiré pattern on the artificial bilayer graphene, and tunneling spectroscopy as a function of gate voltage reveals a constant density of states, also in agreement with Bernal stacking. In addition, electron transport probed in dual-gated samples reveals a band gap opening as a function of transverse electric field. To illustrate the applicability of this technique to realize vdW heterostructuctures in which the functionality is critically dependent on rotational alignment, we demonstrate resonant tunneling double bilayer graphene heterostructures separated by hexagonal boron-nitride dielectric.

ACS Nano, 2015

We demonstrate dual-gated p-type field-effect transistors (FETs) based on few-layer tungsten dise... more We demonstrate dual-gated p-type field-effect transistors (FETs) based on few-layer tungsten diselenide (WSe 2) using high work-function platinum source/drain contacts, and a hexagonal boron nitride top-gate dielectric. A device topology with contacts underneath the WSe 2 results in p-FETs with I ON /I OFF ratios exceeding 10 7 , and contacts that remain Ohmic down to cryogenic temperatures. The output characteristics show current saturation and gate tunable negative differential resistance. The devices show intrinsic hole mobilities around 140 cm 2 /Vs at room temperature, and approaching 4,000 cm 2 /Vs at 2 K. Temperaturedependent transport measurements show a metalinsulator transition, with an insulating phase at low densities, and a metallic phase at high densities. The mobility shows a strong temperature dependence consistent with phonon scattering, and saturates at low temperatures, possibly limited by Coulomb scattering, or defects. The isolation of graphene, and study of its exceptional properties has triggered an interest in several other two-dimensional (2D) layered materials, 1 semiconducting transition metal dichalcogenides (TMDs) 2,3 being one of them. In con-* To whom correspondence should be addressed

Banerjee for his trust and support. Without his gracious offer for me to work at the Microelectro... more Banerjee for his trust and support. Without his gracious offer for me to work at the Microelectronics Research Center, none of this would have ever happened. His patience allowed me to steadily and joyously work on the some of the most interesting projects that I have worked on. I thank members of my committee for the time and effort they took to review my work. I appreciate my mentor Seyoung Kim for training and guiding me as a new student. I also acknowledge Hema, Amritesh, Kyoung, Babak and all my colleagues at MRC who were more than willing to share their knowledge and expertise, and to whom I am greatly indebted. I would like to thank my parents and other family members in Korea for their trust and support. And last but not least, I thank my wife for her unwavering support through all the tough times, and also my two young children for bringing much joy into my life.

Applied Physics Letters, 2014

ABSTRACT

Nano Letters, 2015

To reduce Schottky-barrier-induced contact and access resistance, and the impact of charged impur... more To reduce Schottky-barrier-induced contact and access resistance, and the impact of charged impurity and phonon scattering on mobility in devices based on 2D transition metal dichalcogenides (TMDs), considerable effort has been put into exploring various doping techniques and dielectric engineering using high-κ oxides, respectively. The goal of this work is to demonstrate a high-κ dielectric that serves as an effective n-type charge transfer dopant on monolayer (ML) molybdenum disulfide (MoS2). Utilizing amorphous titanium suboxide (ATO) as the "high-κ dopant", we achieved a contact resistance of ∼180 Ω·μm that is the lowest reported value for ML MoS2. An ON current as high as 240 μA/μm and field effect mobility as high as 83 cm(2)/V-s were realized using this doping technique. Moreover, intrinsic mobility as high as 102 cm(2)/V-s at 300 K and 501 cm(2)/V-s at 77 K were achieved after ATO encapsulation that are among the highest mobility values reported on ML MoS2. We also analyzed the doping effect of ATO films on ML MoS2, a phenomenon that is absent when stoichiometric TiO2 is used, using ab initio density functional theory (DFT) calculations that shows excellent agreement with our experimental findings. On the basis of the interfacial-oxygen-vacancy mediated doping as seen in the case of high-κ ATO-ML MoS2, we propose a mechanism for the mobility enhancement effect observed in TMD-based devices after encapsulation in a high-κ dielectric environment.

A novel complementary metal-oxide-semiconductor (CMOS) process compatible and self-aligned fabric... more A novel complementary metal-oxide-semiconductor (CMOS) process compatible and self-aligned fabrication method for the dual-gate single-electron transistor (DG-SET) is presented. The performance of previous versions of the DG-SET was limited by inherent parasitic elements and its fabrication process was divergent from conventional CMOS, limiting the possibility of co-integration. Through simulation, the parasitic elements are confirmed to be caused by the non-self-alignment of the control gate, side gates, and source/drain. To resolve such issues, a new type of DG-SET was fabricated using a self-aligned process. Measurement results obtained at room temperature revealed clear Coulomb oscillation peaks in the trans-conductance curve. Through parameter extraction and its comparison with previous results, this is confirmed to be the consequence of singleelectron tunneling. Also, in order to confirm that the single-electron tunneling is caused by the electrically induced tunneling barriers, and not by random fluctuations along the SOI active, low temperature measurement results for devices with different parameters is compared.

ABSTRACT Field effect transistors based on ultra-thin transition metal dichalcogenides suffer fro... more ABSTRACT Field effect transistors based on ultra-thin transition metal dichalcogenides suffer from high contact resistances due to the Schottky barrier formed between the metal and the semiconducting channel. An effective way to overcome this issue is to dope the semiconducting channel in order to reduce the Schottky barrier width, thereby enabling efficient electron injection via tunneling. Previously used charge transfer doping techniques employed the use of potassium ions and PEI. However, these doping reagents are unstable in air. Here we report the use of an air stable, self encapsulating, spin on n-type doping technique on MoS2 utilizing TiOx sol-gel. The doping of the channel is confirmed by the broadening of the A1g Raman mode of MoS2. High performance field effect transistors are demonstrated which show three times improvement in the field effect mobility as well as a two-fold increase in the intrinsic mobility of the MoS2 channel. The enhancement of intrinsic mobility can be attributed to the suppression of the A1g phonon modes of MoS2 as well as screening of charged impurities by the TiOX layer. The devices show extended air stability over two to three weeks. The use of TiOx sol-gel can be a promising way to enhance the performance of TMD based transistors.

Journal of Applied Physics, 2009

Charging damage can critically degrade oxide reliability. Antenna-structured metal-oxide-semicond... more Charging damage can critically degrade oxide reliability. Antenna-structured metal-oxide-semiconductor field-effect transistors were fabricated to examine the effect of process parameters on charging damage. Charging damage to threshold voltage (Vth) was investigated experimentally as well as by constructing a neural network model. For a systematic modeling, charging damage process was characterized by means of a face-centered Box-Wilson experiment. The prediction performance

Extended Abstracts of the 2006 International Conference on Solid State Devices and Materials, 2006

Bulletin of the American Physical Society, Mar 5, 2015

We present the realization and characterization of independently contacted and rotationally align... more We present the realization and characterization of independently contacted and rotationally aligned double bilayer graphene heterostructures, that show gate-tunable tunneling resonances and negative differential resistance in their interlayer current-voltage characteristics. Our devices are fabricated by successively stacking mechanically exfoliated bilayer graphene and hexagonal boron nitride dielectric using a layer-by-layer transfer technique. The bilayers are rotationally aligned during the device fabrication by selecting flakes with straight edges, and using them as a reference for alignment. We determine the heterostructure energy band alignment at the tunneling resonance using the individual layer carrier densities, and including the chemical potential dependence on the carrier density. Our analysis show that the tunneling resonances occur when the charge neutrality points of the two bilayer graphene are energetically aligned, which suggests the resonances stem from the momentum conserving tunneling.

Abstracts -50 nm dots were fabricated by using an etch-back process. The dots have the advantage ... more Abstracts -50 nm dots were fabricated by using an etch-back process. The dots have the advantage of alignment and reproduction in Single Electron Transistor area which has not been able to realize a reproducible and controllable device at room temperature. As a result, the small dots were reproducibly fabricated with planarization and an etch-back process.

Nano Letters, 2015

To reduce Schottky-barrier-induced contact and access resistance, and the impact of charged impur... more To reduce Schottky-barrier-induced contact and access resistance, and the impact of charged impurity and phonon scattering on mobility in devices based on 2D transition metal dichalcogenides (TMDs), considerable effort has been put into exploring various doping techniques and dielectric engineering using high-κ oxides, respectively. The goal of this work is to demonstrate a high-κ dielectric that serves as an effective n-type charge transfer dopant on monolayer (ML) molybdenum disulfide (MoS2). Utilizing amorphous titanium suboxide (ATO) as the "high-κ dopant", we achieved a contact resistance of ∼180 Ω·μm that is the lowest reported value for ML MoS2. An ON current as high as 240 μA/μm and field effect mobility as high as 83 cm(2)/V-s were realized using this doping technique. Moreover, intrinsic mobility as high as 102 cm(2)/V-s at 300 K and 501 cm(2)/V-s at 77 K were achieved after ATO encapsulation that are among the highest mobility values reported on ML MoS2. We also analyzed the doping effect of ATO films on ML MoS2, a phenomenon that is absent when stoichiometric TiO2 is used, using ab initio density functional theory (DFT) calculations that shows excellent agreement with our experimental findings. On the basis of the interfacial-oxygen-vacancy mediated doping as seen in the case of high-κ ATO-ML MoS2, we propose a mechanism for the mobility enhancement effect observed in TMD-based devices after encapsulation in a high-κ dielectric environment.

A new structure of Single-Electron Transistor (SET) with electric tunneling barrier is designed a... more A new structure of Single-Electron Transistor (SET) with electric tunneling barrier is designed and simulated with device simulation tool (SILVACO). Control gate of the designed structure covers only the top surface of the active SOI fin, while side gates inducing the electric tunneling barriers surround all three surfaces of the silicon active region. Characteristics of the electrical tunneling barriers, internal

2007 IEEE International Reliability Physics Symposium Proceedings. 45th Annual, 2007

One of the most important issues of NAND flash memory is reliability problems caused by oxide and... more One of the most important issues of NAND flash memory is reliability problems caused by oxide and interface traps. But it has been revealed that their generation rate increases by Fowler-Nordheim current stressing on the tunnel oxide as the channel width of shallow trench isolation (STI) isolated NAND flash cells shrinks and electric field is increased at active edge of