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h-BN has potential as an ideal dielectric material for 2D electronics. As a gate dielectric, h-BN provides improved carrier mobility and resists dielectric breakdown at high electric fields. When used as a substrate, h-BN enhances graphene conductivity and mobility while improving reliability by facilitating better heat dissipation than conventional dielectrics like SiO2. Overall, h-BN shows promise as an ubiquitous dielectric that can fulfill critical roles in 2D heterostructures and devices.

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Hexagonal Boron Nitride: Ubiquitous Layered Dielectric for Two-Dimensional Electronics Nikhil Jain Thesis Committee Members: Prof. Bin Yu (Research Advisor) Prof. Carl Ventrice Jr. Prof. Vincent LaBella Prof. Ernest Levine Prof. Sergey Rumyantsev (RPI)
WWW.SUNYCNSE.COM  Introduction to 2D materials  Graphene/h-BN heterostructures  h-BN as an ubiquitous dielectric  Substrate  Gate dielectric  Passivation layer  Intercalation layer  Conclusions and future directions Outline of Presentation 2
WWW.SUNYCNSE.COM  Introduction to 2D materials  Graphene/h-BN heterostructures  h-BN as an ubiquitous dielectric  Substrate  Gate dielectric  Passivation layer  Intercalation layer  Conclusions and future directions Outline of Presentation 3
WWW.SUNYCNSE.COM A Paradigm Shift New Material Platform “Ubiquitous” Electronics  Ultra-thin materials  Self-limited processing  Ultimate scalability  Hetero-integration  Flexible, soft, transparent  Open, connected “Things” Silicon Platform Micro/Nano Electronics  Bulk materials  Low scalability  Stiff, hard, brittle  Externally powered  Packed, isolated “chips” 4
WWW.SUNYCNSE.COM What are 2D Layered Materials? (Courtesy: Y. Cui, Stanford Univ.) Materials where individual layers of covalently bonded atoms/molecules are held together by van der Waals forces 5
WWW.SUNYCNSE.COM Graphene Molybdenum Disulfide 2D Semi-Metal 3-atom-thick monolayer Gallium Selenide 4-atom-thick monolayer 5-atom-thick monolayer Bismuth Selenide Hexagonal boron nitride 2D Insulator 2D Semiconductors Classification of 2D Materials based on electronic structure 6
WWW.SUNYCNSE.COM 2004 Extraction of graphene by Andre Geim and Konstantin Novoselov using scotch tape method 1937 R. E. Peierls and L. D. Landau suggest that strictly 2D crystals could not exist 1962 Hanns-Peter Boehm coins the terms graphene 1980s Theoretical studies on graphene confirm massless Dirac equation & anomalous Hall effect 2005 Geim and Novoselov exhibit free-standing 2D crystals of boron nitride, several transition metal dichalcogenides, and complex oxides 2D Materials: Brief History 1947 Wallace calculates the band structure of single-layer graphite 7
WWW.SUNYCNSE.COM 2D Materials – Extraction Methods The crystalline quality and correspondingly the electronic properties rely on the method used to extract the 2D material nanosheet under study. Micromechanical exfoliation Liquid-phase or chemical exfoliation Chemical vapor deposition K. S. Novoselov et al, Phys. Scr., 2012 Image Source: http://www.azonano.com Image Source: http://emps.exeter.ac.uk/ 8
WWW.SUNYCNSE.COM Why Graphene? The electrons in the pz orbital hybridize to give Π and Π* bands  Momentum confined to two dimensions  Zero-gap semiconductor  Two sets of 3 Dirac points  Fermi energy at Dirac Point  Cone like linear dispersion relation within 1eV of Dirac point  Zero effective mass of charge carriers in the region  Fermi velocity, vF ≈ 106 m/s Dirac Points 9 D. R. Cooper et al, International Scholarly Research Notices 2012
WWW.SUNYCNSE.COM  Intrinsic advantages  Superior electrical conduction (µ ~ 20,000 cm2/Vs: 20X of silicon  Excellent thermal conduction (~5.3x103 W/m-K: 10X of copper)  High mechanical strength (Young’s modulus: 0.5 TPa)  3-5% light absorption (monolayer) Graphene: Key Properties TEM Optical ImageLattice Structure AFM 10
WWW.SUNYCNSE.COM Electrical Analysis  Charge carrier density, n = ε0 ε 𝑉𝑔 𝑡 𝑒 ε0ε: Permittivity of SiO2 e: Electron charge t: SiO2 thickness  Resistivity, 𝜌 = 𝑊 𝐿 . 𝑉 𝐼  Mobility, µ = 1 𝑒𝑛ρ  Alternately, field-effect mobility is given by: µ = 1 𝐶 . 𝑑σ 𝑑𝑉 𝑔 C = 𝑊.𝐿 𝑡 . ε0ε (Gate Capacitance) In this work, the term mobility refers to field-effect mobility. At Vg = 0, n should vanish but minimum conductivity is introduced by thermally generated carriers and electrostatic spatial inhomogeneity. 11
WWW.SUNYCNSE.COM Graphene: One-atom-thick sheet with no “bulk”, but all surfaces Behavior is extremely sensitive to its interface with neighboring materials like:  Supporting substrate  Top surface (ambient environment) The “Real Significance” 12
WWW.SUNYCNSE.COM Carrier mobility ~ 200,000 cm2/V.s for suspended graphene. – Actual values: 1000 ~ 3000 cm2/V.s on SiO2 substrate Graphene/Dielectric Interface Graphene electrical conduction is largely impacted by interface with dielectrics. Images Courtesy: Enrico Rossi, CMTC, University of Maryland Spatial inhomogeneity increases ON current and scattering sites decrease the OFF current. 13
WWW.SUNYCNSE.COM Joule-heating Induced Breakdown Carrier scattering mechanisms increase resistivity in graphene.  Impurity and defect scattering – Interface effect  Longitudinal acoustic (LA) phonon scattering – Intrinsic effect  Surface polar phonon (SPP) scattering – Substrate effect Voltag e Current Temperatur eJoule Heating I2R Resistivit y Causes Breakdown LA and SPP scattering increases with temperature. Images Courtesy: H.-S. P. Wong, Stanford University 14 Graphene Breakdown creates a gap
WWW.SUNYCNSE.COM h-BN: An Ideal 2D Dielectric Hexagonal Boron Nitride  High crystal quality (negligible defect density)  Atomically smooth surface  Free of surface state  High-energy surface polar phonons  Thermal conductivity: ~20 W/m-K (20X of SiO2) Image Courtesy: C Casiraghi 15
WWW.SUNYCNSE.COM Problem Statement  While 2D material-based heterostructures can be immensely useful for next generation electronics, 2D materials are extremely sensitive to their immediate environment.  SiO2 and other dielectrics currently used in the fab make a highly invasive interface with 2D materials.  Pristine properties of graphene can be seen in suspended orientations but it is not feasible to make chips using structures suspended in vacuum. Can h-BN fulfill the role of an ideal dielectric neighbor to graphene for the purpose of making on-chip components? 16
WWW.SUNYCNSE.COM Research Goals  Develop effective processes to prepare 2D material- based functional heterostructures  Demonstrate prototypes of applications: field-effect transistors (FETs) and on-chip Interconnects using graphene/h-BN heterostructures  Study the role of h-BN as a non-invasive dielectric neighbor for graphene  Explore basic physical/electrical behavior of interest from the performance and reliability standpoint 17
WWW.SUNYCNSE.COM  Introduction to 2D materials  Graphene/h-BN heterostructures  h-BN as an ubiquitous dielectric  Substrate  Gate dielectric  Passivation layer  Intercalation layer  Conclusions and future directions Outline of Presentation 18
WWW.SUNYCNSE.COM 2D Based New 3D Solids Rational Stacking-By-Design A. K. Geim, Nature, 2013 Selective assembly of 2D materials can lead to innovative device design 19
WWW.SUNYCNSE.COM Heterostructure Formation 2D heterostructures: building elements in future electronics ACVD over Bex ACVD stacked over BCVD ACVD grown over over BCVD/ex In situ CVD growth of A/B • Subscript “Ex” signifies exfoliated material • Subscript CVD signifies material growth by chemical vapor deposition 20
WWW.SUNYCNSE.COM CVD Graphene Growth Step 1: Ramp up to 1000C with Ar (80 sccm) + H2 (5 sccm) Step 2: Anneal the Cu strip at 1000C (Same gas flow) Step 3: Graphene growth in CH4 (30 sccm) + H2 (5 sscm) Step 4: Cool down in Ar (80 sccm) + H2 (5 sccm) 21
WWW.SUNYCNSE.COM  Layer by Layer (LbL) fabrication is efficiently used for emerging 2D layered structures.  Large-area assembly using CVD grown graphene monolayer is possible. CVD graphene growth Monolayer transferring Multilayer stacking Assembly of CVD Graphene 22
WWW.SUNYCNSE.COM ** CAB – Cellulose Acetate Butyrate Assembly of Exfoliated h-BN 23
WWW.SUNYCNSE.COM Summary Facile processes to make 2D heterostructures have been developed.  CVD growth of graphene and transfer to any target substrate has been demonstrated.  Assembly of exfoliated materials to target substrate has been demonstrated with multiple methods.  Necessary as long as CVD growth methods for other materials are still being developed.  Layer-by-layer stacking of nanosheets to create ternary (or thicker) heterostructures has been shown.  With controlled precision on where the third layer is assembled. 24
WWW.SUNYCNSE.COM  Introduction to 2D materials  Graphene/h-BN heterostructures  h-BN as an ubiquitous dielectric  Substrate  Gate dielectric  Passivation layer  Intercalation layer  Conclusions and future directions Outline of Presentation 25
WWW.SUNYCNSE.COM Hexagonal Boron Nitride  Single-crystalline  Atomically smooth surface  Free of surface state  High-energy surface phonons  Thermal conductivity: ~20 W/m-K (20X of SiO2) Silicon Dioxide  Amorphous  Surface roughness  Rich in trapped charges  Low-energy surface phonons  Thermal conductivity: ~1.04 W/m-K Graphene h-BN (lattice mismatch ~ 1.6%) h-BN: Substrate for Graphene Image Courtesy: Jarillo-Herrero Group, Quantum Nanoelectronics, MIT 26
WWW.SUNYCNSE.COM Graphene On h-BN (GOBON) 27
WWW.SUNYCNSE.COM Electrical Performance of GOBON Conductivity and mobility improvement is observed in GOBON when compared with graphene (CVD or exfoliated) on SiO2.  Resistivity (at VG = 0V) drops by approximately 19x in GOBON as compared with that on SiO2.  At the carrier density of 1×1012 cm-2, carrier mobility in GOBON is improved by about 17x compared with CVD graphene on SiO2. N. Jain et al, IEEE Electron Device Letters, 33 (7), 2012 28
WWW.SUNYCNSE.COM Reliability Enhancement in GOBON Due to improved thermal conductivity of h-BN, the permissible current and voltage before permanent breakdown in graphene are enhanced. PBD = JBD (VBD – JBDRC)  ~ 7X increased power density @ breakdown  Thermal conductivity: ~20 W/m-K): ~20 times that in SiO2 (1.04 W/m-K)  Prevent Joule heat built up in graphene where, JBD = Current density at breakdown VBD = Voltage at breakdown RC = Contact resistance N. Jain et al, IEEE Electron Device Letters, 33 (7), 2012 29
WWW.SUNYCNSE.COM Electrical Annealing Effect Electrical annealing shifts the Dirac point in graphene on SiO2, but this change is avoided in GOBON due to less interfacial trap charges G/h-BN G/SiO2 T. Yu, Applied Physics Letters 2011, 98, 243105. N. Jain et al, IEEE Electron Device Letters, 33 (7), 2012 30
WWW.SUNYCNSE.COM Summary h-BN has been shown to be an excellent substrate for graphene.  Graphene resistivity on h-BN is found to be 19 times lower than on SiO2 (the current standard substrate).  There is a 17-fold improvement in graphene mobility when placed on h-BN compared with SiO2.  Improved heat dissipation through h-BN results in higher values of current density and power density required to cause Joule heating-induced breakdown in graphene.  The Dirac point in GOBON structures is stable under the effect of electrical annealing. 31
WWW.SUNYCNSE.COM  Introduction to 2D materials  Graphene/h-BN heterostructures  h-BN as an ubiquitous dielectric  Substrate  Gate dielectric  Passivation layer  Intercalation layer  Conclusions and future directions Outline of Presentation 32
WWW.SUNYCNSE.COM h-BN as Gate Dielectric h-BN could also serve as gate dielectric k = 3.9 EG = 5.97 eV self-terminating surface chemically inert Key questions: What is the dielectric behavior? 33
WWW.SUNYCNSE.COM Titanium Nitride (TiN) filled trenches are created in a Si/SiO2 wafer to act as a gate for GOBON FET Buried Gate Structures: Fabrication * This process is done in the fab 34
WWW.SUNYCNSE.COM GOBON FET with h-BN as Gate Insulator * FET fabrication process is same as shown in previous section. G/h-BN/TiN 35
WWW.SUNYCNSE.COM Performance of GOBON FETs Carrier mobility of CVD graphene on h-BN (on TiN) is 1.4X higher than mechanically exfoliated graphene on SiO2 at effective electric field of 2x105 V-cm-1 N. Jain et al. Carbon, 54, 396–402 (2013) 36
WWW.SUNYCNSE.COM Dielectric Strength of h-BN  No dielectric breakdown up to very high electric field (15 MV/cm)  Transition from insulating to leakage occurs at a voltage that is directly proportional to h-BN multilayer thickness N. Jain et al. Carbon, 54, 396–402 (2013) h-BN is a robust dielectric which resists dielectric breakdown at high electric fields. 37
WWW.SUNYCNSE.COM Summary h-BN has been shown to be a robust gate dielectric for FETs made with graphene.  Graphene mobility is enhanced in GOBON FETs compared with graphene FETs with SiO2 as gate dielectric.  As a gate dielectric, h-BN does not undergo dielectric breakdown even under very high electric field of 15MV/cm.  h-BN undergoes a reversible transition to a leaky dielectric at high fields, which is dependent on layer thickness. 38
WWW.SUNYCNSE.COM  Introduction to 2D materials  Graphene/h-BN heterostructures  h-BN as an ubiquitous dielectric  Substrate  Gate dielectric  Passivation layer  Intercalation layer  Conclusions and future directions Outline of Presentation 39
WWW.SUNYCNSE.COM Need for graphene encapsulation  Whatever be the substrate, environmental adsorbents reduce graphene conduction  Adsorbent sites act as charge traps  Encapsulation with traditional capping materials degrades graphene quality  h-BN as a passivating layer conforms to graphene surface 40
WWW.SUNYCNSE.COM Fully Encapsulated Graphene * CAB – Cellulose Acetate Butyrate 41
WWW.SUNYCNSE.COM Passivation Effect of Top h-BN  Insensitive to environmental (ambient) impact  R-V characteristics show no variation in air and in vacuum for encapsulated device  No variation in contact resistance between ambient and vacuum N. Jain et al, Nanotechnology, 24, 355202 (2013) 42
WWW.SUNYCNSE.COM  67% increase in breakdown power density compared to uncovered GOBON devices due to increased heat dissipation through both graphene surfaces  No reduction in carrier mobility Electrical Behavior N. Jain et al, Nanotechnology, 24, 355202 (2013) 43
WWW.SUNYCNSE.COM Summary h-BN has been shown to be an effective passivation layer for graphene devices.  When passivated with h-BN, graphene performance becomes insensitive to the measurement conditions (ambient or vacuum).  Graphene – Metal contact performance is improved.  Higher current density and power density are needed to cause breakdown in encapsulated graphene devices.  The improvement is achieved without a compromise on carrier mobility. 44
WWW.SUNYCNSE.COM  Introduction to 2D materials  Graphene/h-BN heterostructures  h-BN as an ubiquitous dielectric  Substrate  Gate dielectric  Passivation layer  Intercalation layer  Conclusions and future directions Outline of Presentation 45
WWW.SUNYCNSE.COM Cu CNT Graphene Max current density (A/cm2) ~106 > 1x108 > 1x108 Melting Point (K) 1356 3800 (graphite) 3800 (graphite) Tensile Strength (GPa) 0.22 22.2 23.5 Thermal Conductivity (×103 W/m-K) 0.385 1.75 Hone, et al. Phys. Rev. B 1999 3 - 5 Balandin, et al. Nano Let., 2008 Temp. Coefficient of Resistance (10-3 /K) 4 < 1.1 Kane, et al. Europhys. Lett.,1998 -1.47 Shao et al. Appl Phys. Lett., 2008 Mean Free Path @ room-T (nm) 40 > 1000 McEuen, et al. Trans. Nano., 2002 ~ 1000 Bolotin, et al. Phys. Rev. Let. 2008 x102 x10 x25 x102 Graphene as a Conductor
WWW.SUNYCNSE.COM Towards “3-D Graphene”  At small critical dimensions (width < 100 nm), ρGraphene < ρCu  Small cross section in monolayer graphene limits conduction.  Multilayer graphene has less sheet resistance than monolayer graphene.  Onset of inter-layer scattering of charge carriers in multi-layer graphene doesn’t allow the sheet resistance to scale down as expected 47
WWW.SUNYCNSE.COM Double-Layer Graphene (DLG): Fabrication DLG structure with h-BN between two monolayer graphene sheets with direct metal contact with both graphene layers 48
WWW.SUNYCNSE.COM Massless Dirac Fermions in DLG DFT simulation of the dispersion relation of the DLG structure indicates that carriers are massless Dirac fermions * DFT analysis was performed by our collaborators at University of Washington.  Band splitting in BLG  Π and Π* bands divide in four bands due to interlayer scattering  Degeneracy is restored in DLG 49
WWW.SUNYCNSE.COM Raman Spectra of Graphene  Single 2D peak in monolayer graphene  Due to coupling between layers, two or four peaks exist in 2D band (>2 layers) 1400 1600 1800 2000 2200 2400 2600 2800 3000 2D band Normalizedintensity Wavenumber (cm -1 ) 1layer 2layer 3layer 4layers 5layer Graphite G band More layer number - Intensity ratio of G/2D increased 50 Freitag, M. Nat Phys, 2011, 7, 596–597
WWW.SUNYCNSE.COM Raman Spectral Analysis for Scattering Measurement 2D peak in the Raman spectrum of bilayer graphene is composed of four components arising from the band split at Dirac point.  Reduced height of the overall 2D peak  Increase in IG/I2D  Increase in FWHM2D 51
WWW.SUNYCNSE.COM Raman Spectral Analysis for Scattering Measurement Addition of graphene layers results in increase in IG/I2D and FWHM2D.  For stacked turbostratic graphene, addition of each layer results in lesser increase than in exfoliated graphene, indicating reduced scattering in stacked graphene  Similar effect is seen in FWHM2D 52
WWW.SUNYCNSE.COM Raman Spectral Analysis IG/I2D and FWHM2D in DLG is similar to monolayer graphene (much lower than stacked or exfoliated BLG) Introduction of h-BN as an intercalation layer in double-layer graphene reduces interlayer carrier scattering. 53
WWW.SUNYCNSE.COM Electrical Characterization Reduced interlayer scattering allows higher current in DLG. Current and conductivity in DLG ~ MLG > BLG 54
WWW.SUNYCNSE.COM Performance Enhancement Mobility and breakdown current density in DLG show enhancement.  Carrier Mobility in DLG > MLG  JBD in DLG > 2x JBD in BLG 55
WWW.SUNYCNSE.COM Reliability Improvement Under extreme electrical stress, DLG resists breakdown more than MLG and BLG.  At an elevated temperature (150C) under the effect of a constant voltage (10V), the DLG sample withstands a current density of ~ 475 mA/cm2  The mean time to failure (MTTF) for DLG is ~ 75 and ~4000 times higher than that for BLG and MLG systems 56
WWW.SUNYCNSE.COM Summary h-BN has been shown to be an interposer layer that prevents interlayer scattering from degrading the performance of double-layer graphene.  Increase in the IG/I2D ratio and FWHM2D have been shown as indicators of interlayer scattering.  Random-stacked (turbostratic) graphene shows lower interlayer scattering than Bernal-stacked graphene.  As an intercalation layer, h-BN removes interlayer scattering resulting in ideal current scaling due to layer stacking.  Higher carrier mobility and resistance to breakdown at extreme electrical stressing conditions are also observed in DLG. 57
WWW.SUNYCNSE.COM  Introduction to 2D materials  Graphene/h-BN heterostructures  h-BN as an ubiquitous dielectric  Substrate  Gate dielectric  Passivation layer  Intercalation layer  Conclusions and future directions Outline of Presentation 58
WWW.SUNYCNSE.COM Conclusions  h-BN has been explored as a multi-function dielectric for future 2D material enabled electronics.  Facile assembly/fabrication processes for 2D heterostructures have been demonstrated.  h-BN serves as excellent supporting substrate, largely preserving “pristine” graphene electronic transport.  h-BN is demonstrated as a highly robust gate dielectric (medium-k value).  Fully encapsulated 2D heterostructure (h-BN/graphene/h-BN) provides passivation and enhancement of maximum power density in graphene without compromising electrical conduction.  As an intercalation layer between graphene layers, h-BN reduces interlayer scattering and restores mobility to ‘monolayer-like’ value while also making the structures more robust to stress. 59
WWW.SUNYCNSE.COM Future Directions (1) Direct all-CVD growth process  GOBON: Graphene growth on exfoliated h-BN  BNOG: h-BN growth on CVD/exfoliated graphene (2) Study of 2D heterostructure properties (3) On-chip device, interconnect, circuit demonstration 60
WWW.SUNYCNSE.COM Future Directions CVD growth of h-BN on copper 61
WWW.SUNYCNSE.COM Superlattice-like structures of graphene/h-BN Future Directions 62
WWW.SUNYCNSE.COM Acknowledgments Lab Members (Present and Past):  Dr. Bhaskar Nagabhirava  Dr. Tianhua Yu  Dr. Tanesh Bansal  Dr. Mariyappan Shanmugam  Dr. Fan Yang  Robin Jacobs-Gedrim  Eui Sang Song  Thibault Sohier  Christopher Durcan Our Collaborator:  Prof. M. P. Anantram (Univ. of Washington, Seattle) CNSE CSR Team:  Dr. Vidya Kaushik  Dr. Prasanna Khare  Megha Rao 63
WWW.SUNYCNSE.COM Journal Publications 1. N. Jain, M. Murphy, R. B. Jacobs-Gedrim, M. Shanmugam, F. Yang, E. S. Song, and B. Yu, “Electrical Conduction and Reliability in Dual-Layered Graphene Heterostructure Interconnects,” IEEE Electro Device Letters, vol. 35, no. 12, 1311-1313 (2014). 2. R. B. Jacobs-Gedrim, M. Shanmugam, N. Jain, C. A. Durcan, M. T. Murphy, T. M. Murray, R. J. Matyi, R. L. Moore, and B. Yu, “Extraordinary photoresponse in two-dimensional In2Se3 nanosheets,” ACS Nano, 8, 1, 514-521 (2014). 3. N. Jain, C. A. Durcan, R. B. Jacobs-Gedrim, Y. Xu, and B. Yu, “Graphene interconnects fully encapsulated in layered insulator hexagonal boron nitride,” Nanotechnology, 24, 355202 (2013). 4. N. Jain, T. Bansal, C. A. Durcan, Y. Xu, and B. Yu, “Monolayer Graphene/Hexagonal Boron Nitride Heterostructure,” Carbon, 54, 396– 402 (2013). 5. T. Bansal, C. A. Durcan, N. Jain, R. B. Jacobs-Gedrim, Y. Xu, and B. Yu, “Synthesis of Few-to-Monolayer Graphene on Rutile Titanium Dioxide,” Carbon, 55, 168-175 (2013). 6. M. Shanmugam, N. Jain, R. B. Jacobs-Gedrim, Y. Xu, and B. Yu, “Layered insulator hexagonal boron nitride for surface passivation in quantum dot solar cell,” Applied Physics Letters, 103, 243904 (2013). 7. R. B. Jacobs-Gedrim, C. A. Durcan, N. Jain, and B. Yu, “Chemical Assembly and Electrical Characteristics of Surface-Rich Topological Insulator Bi2Se3 Nanoplates and Nanoribbons,” Applied Physics Letters, 101, 143103 (2012). 8. E. Kim, N. Jain, R. Jacobs-Gedrim, Y. Xu, and B. Yu, “Exploring Carrier Transport Phenomena in CVD-Assembled Graphene FET on Hexagonal Boron Nitride,” Nanotechnology, 23, 125706 (2012). 9. N. Jain, T. Bansal, C. Durcan, and B. Yu, “Graphene-Based Interconnects on Hexagonal Boron Nitride (h-BN) Substrate,” IEEE Electro Device Letters, vol. 33, no. 7, 925-927 (2012). ARTICLES UNDER REVIEW 1. N. Jain, R. Jacobs-Gedrim, Y. Xu, and B. Yu, “Resistive Switching in Ultra-Thin Two-Dimensional van der Waals Dielectric” Nature Communications (2015). 2. N. Jain, R. B. Jacobs-Gedrim, M. Murphy, M. Shanmugam, F. Yang, Y. Xu, and B. Yu, “Electrical Conduction in Two-Dimensional Graphene/Hexagonal Boron Nitride/Graphene Heterostructure,” Nano Letters (2015). 3. R. Jacobs-Gedrim, M. Murphy, N. Jain, F. Yang, M. Shanmugam, E. Song, Y. Kandel, P. Hesamaddin, D. B. Janes, and B. Yu, “Reversible Crystalline-Amorphous Phase Transition in Chalcogenide Nanosheets”, Nature Materials (2015). 64
WWW.SUNYCNSE.COM Thank You for Your Attention 65
WWW.SUNYCNSE.COM Significance of Environment Open graphene is subject to severe degradation over time due to the effect of adsorption of ambient molecules like N2, H2O and O2 Graphene/metal contact I-V behavior Time-dependent contact resistance shift Demand: Graphene covered with an insulator which protects its pristine electrical behavior
WWW.SUNYCNSE.COM Metal Contacts Graphene at 1-D Edge Fabrication made simpler with only one patterning step for the G/h-BN/G stack and one metallization step L Wang et al, Science 342, 614 (2013)
WWW.SUNYCNSE.COM 2D Band Curve Fitting Results Bilayer Graphene Trilayer Graphene 2600 2650 2700 2750 2800 P1: 2656 P2: 2688 P3: 2707 P4: 2722 Wavenumber (cm -1 ) 2600 2650 2700 2750 2800 P1: 2694 P2: 2719 Wavenubmer (cm -1 ) 2600 2650 2700 2750 2800 P1: 2696 P2: 2722 Wavenumber (cm -1 ) Four Layer Graphene 2600 2650 2700 2750 2800 P1: 2695 P2: 2725 Wavenumber (cm -1 ) Five Layer Graphene
WWW.SUNYCNSE.COM Raman Spectra of s-MLG More layer number: •2D band blue shift •Intensity ratio of G/2D increased. • Less coupling between layers, only one peak exists in 2D band (2~5 layers) 1400 1600 1800 2000 2200 2400 2600 2800 3000 Wavenumber (cm -1 ) as -- -- -- -- -- 2D bandG band 400 1600 1800 2000 2200 2400 2600 2800 3000 2D band Wavenumber (cm -1 ) 1layer 2layer 3layer 4layers 5layer Graphite G band
WWW.SUNYCNSE.COM Lifetime Reliability Study  Sustained current in graphene can lead to degradation and eventual failure of the wire  Comparison of stacked BLG and G-BN-G heterostructure can provide information about improvement in graphene interconnect reliability by incorporation of h-BN between graphene layers  Mean Time to fail (MTTF) in G-BN-G heterostructure will be higher than MLG and stacked BLG at same current density X Chen et al, IEEE EDL 2012

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PPT thesis defense_nikhil

  • 1.
    Hexagonal Boron Nitride:Ubiquitous Layered Dielectric for Two-Dimensional Electronics Nikhil Jain Thesis Committee Members: Prof. Bin Yu (Research Advisor) Prof. Carl Ventrice Jr. Prof. Vincent LaBella Prof. Ernest Levine Prof. Sergey Rumyantsev (RPI)
  • 2.
    WWW.SUNYCNSE.COM  Introduction to2D materials  Graphene/h-BN heterostructures  h-BN as an ubiquitous dielectric  Substrate  Gate dielectric  Passivation layer  Intercalation layer  Conclusions and future directions Outline of Presentation 2
  • 3.
    WWW.SUNYCNSE.COM  Introduction to2D materials  Graphene/h-BN heterostructures  h-BN as an ubiquitous dielectric  Substrate  Gate dielectric  Passivation layer  Intercalation layer  Conclusions and future directions Outline of Presentation 3
  • 4.
    WWW.SUNYCNSE.COM A Paradigm Shift NewMaterial Platform “Ubiquitous” Electronics  Ultra-thin materials  Self-limited processing  Ultimate scalability  Hetero-integration  Flexible, soft, transparent  Open, connected “Things” Silicon Platform Micro/Nano Electronics  Bulk materials  Low scalability  Stiff, hard, brittle  Externally powered  Packed, isolated “chips” 4
  • 5.
    WWW.SUNYCNSE.COM What are 2DLayered Materials? (Courtesy: Y. Cui, Stanford Univ.) Materials where individual layers of covalently bonded atoms/molecules are held together by van der Waals forces 5
  • 6.
    WWW.SUNYCNSE.COM Graphene Molybdenum Disulfide 2D Semi-Metal 3-atom-thickmonolayer Gallium Selenide 4-atom-thick monolayer 5-atom-thick monolayer Bismuth Selenide Hexagonal boron nitride 2D Insulator 2D Semiconductors Classification of 2D Materials based on electronic structure 6
  • 7.
    WWW.SUNYCNSE.COM 2004 Extraction ofgraphene by Andre Geim and Konstantin Novoselov using scotch tape method 1937 R. E. Peierls and L. D. Landau suggest that strictly 2D crystals could not exist 1962 Hanns-Peter Boehm coins the terms graphene 1980s Theoretical studies on graphene confirm massless Dirac equation & anomalous Hall effect 2005 Geim and Novoselov exhibit free-standing 2D crystals of boron nitride, several transition metal dichalcogenides, and complex oxides 2D Materials: Brief History 1947 Wallace calculates the band structure of single-layer graphite 7
  • 8.
    WWW.SUNYCNSE.COM 2D Materials –Extraction Methods The crystalline quality and correspondingly the electronic properties rely on the method used to extract the 2D material nanosheet under study. Micromechanical exfoliation Liquid-phase or chemical exfoliation Chemical vapor deposition K. S. Novoselov et al, Phys. Scr., 2012 Image Source: http://www.azonano.com Image Source: http://emps.exeter.ac.uk/ 8
  • 9.
    WWW.SUNYCNSE.COM Why Graphene? The electronsin the pz orbital hybridize to give Π and Π* bands  Momentum confined to two dimensions  Zero-gap semiconductor  Two sets of 3 Dirac points  Fermi energy at Dirac Point  Cone like linear dispersion relation within 1eV of Dirac point  Zero effective mass of charge carriers in the region  Fermi velocity, vF ≈ 106 m/s Dirac Points 9 D. R. Cooper et al, International Scholarly Research Notices 2012
  • 10.
    WWW.SUNYCNSE.COM  Intrinsic advantages Superior electrical conduction (µ ~ 20,000 cm2/Vs: 20X of silicon  Excellent thermal conduction (~5.3x103 W/m-K: 10X of copper)  High mechanical strength (Young’s modulus: 0.5 TPa)  3-5% light absorption (monolayer) Graphene: Key Properties TEM Optical ImageLattice Structure AFM 10
  • 11.
    WWW.SUNYCNSE.COM Electrical Analysis  Chargecarrier density, n = ε0 ε 𝑉𝑔 𝑡 𝑒 ε0ε: Permittivity of SiO2 e: Electron charge t: SiO2 thickness  Resistivity, 𝜌 = 𝑊 𝐿 . 𝑉 𝐼  Mobility, µ = 1 𝑒𝑛ρ  Alternately, field-effect mobility is given by: µ = 1 𝐶 . 𝑑σ 𝑑𝑉 𝑔 C = 𝑊.𝐿 𝑡 . ε0ε (Gate Capacitance) In this work, the term mobility refers to field-effect mobility. At Vg = 0, n should vanish but minimum conductivity is introduced by thermally generated carriers and electrostatic spatial inhomogeneity. 11
  • 12.
    WWW.SUNYCNSE.COM Graphene: One-atom-thick sheet withno “bulk”, but all surfaces Behavior is extremely sensitive to its interface with neighboring materials like:  Supporting substrate  Top surface (ambient environment) The “Real Significance” 12
  • 13.
    WWW.SUNYCNSE.COM Carrier mobility ~200,000 cm2/V.s for suspended graphene. – Actual values: 1000 ~ 3000 cm2/V.s on SiO2 substrate Graphene/Dielectric Interface Graphene electrical conduction is largely impacted by interface with dielectrics. Images Courtesy: Enrico Rossi, CMTC, University of Maryland Spatial inhomogeneity increases ON current and scattering sites decrease the OFF current. 13
  • 14.
    WWW.SUNYCNSE.COM Joule-heating Induced Breakdown Carrierscattering mechanisms increase resistivity in graphene.  Impurity and defect scattering – Interface effect  Longitudinal acoustic (LA) phonon scattering – Intrinsic effect  Surface polar phonon (SPP) scattering – Substrate effect Voltag e Current Temperatur eJoule Heating I2R Resistivit y Causes Breakdown LA and SPP scattering increases with temperature. Images Courtesy: H.-S. P. Wong, Stanford University 14 Graphene Breakdown creates a gap
  • 15.
    WWW.SUNYCNSE.COM h-BN: An Ideal2D Dielectric Hexagonal Boron Nitride  High crystal quality (negligible defect density)  Atomically smooth surface  Free of surface state  High-energy surface polar phonons  Thermal conductivity: ~20 W/m-K (20X of SiO2) Image Courtesy: C Casiraghi 15
  • 16.
    WWW.SUNYCNSE.COM Problem Statement  While2D material-based heterostructures can be immensely useful for next generation electronics, 2D materials are extremely sensitive to their immediate environment.  SiO2 and other dielectrics currently used in the fab make a highly invasive interface with 2D materials.  Pristine properties of graphene can be seen in suspended orientations but it is not feasible to make chips using structures suspended in vacuum. Can h-BN fulfill the role of an ideal dielectric neighbor to graphene for the purpose of making on-chip components? 16
  • 17.
    WWW.SUNYCNSE.COM Research Goals  Developeffective processes to prepare 2D material- based functional heterostructures  Demonstrate prototypes of applications: field-effect transistors (FETs) and on-chip Interconnects using graphene/h-BN heterostructures  Study the role of h-BN as a non-invasive dielectric neighbor for graphene  Explore basic physical/electrical behavior of interest from the performance and reliability standpoint 17
  • 18.
    WWW.SUNYCNSE.COM  Introduction to2D materials  Graphene/h-BN heterostructures  h-BN as an ubiquitous dielectric  Substrate  Gate dielectric  Passivation layer  Intercalation layer  Conclusions and future directions Outline of Presentation 18
  • 19.
    WWW.SUNYCNSE.COM 2D Based New3D Solids Rational Stacking-By-Design A. K. Geim, Nature, 2013 Selective assembly of 2D materials can lead to innovative device design 19
  • 20.
    WWW.SUNYCNSE.COM Heterostructure Formation 2D heterostructures:building elements in future electronics ACVD over Bex ACVD stacked over BCVD ACVD grown over over BCVD/ex In situ CVD growth of A/B • Subscript “Ex” signifies exfoliated material • Subscript CVD signifies material growth by chemical vapor deposition 20
  • 21.
    WWW.SUNYCNSE.COM CVD Graphene Growth Step1: Ramp up to 1000C with Ar (80 sccm) + H2 (5 sccm) Step 2: Anneal the Cu strip at 1000C (Same gas flow) Step 3: Graphene growth in CH4 (30 sccm) + H2 (5 sscm) Step 4: Cool down in Ar (80 sccm) + H2 (5 sccm) 21
  • 22.
    WWW.SUNYCNSE.COM  Layer byLayer (LbL) fabrication is efficiently used for emerging 2D layered structures.  Large-area assembly using CVD grown graphene monolayer is possible. CVD graphene growth Monolayer transferring Multilayer stacking Assembly of CVD Graphene 22
  • 23.
    WWW.SUNYCNSE.COM ** CAB –Cellulose Acetate Butyrate Assembly of Exfoliated h-BN 23
  • 24.
    WWW.SUNYCNSE.COM Summary Facile processes tomake 2D heterostructures have been developed.  CVD growth of graphene and transfer to any target substrate has been demonstrated.  Assembly of exfoliated materials to target substrate has been demonstrated with multiple methods.  Necessary as long as CVD growth methods for other materials are still being developed.  Layer-by-layer stacking of nanosheets to create ternary (or thicker) heterostructures has been shown.  With controlled precision on where the third layer is assembled. 24
  • 25.
    WWW.SUNYCNSE.COM  Introduction to2D materials  Graphene/h-BN heterostructures  h-BN as an ubiquitous dielectric  Substrate  Gate dielectric  Passivation layer  Intercalation layer  Conclusions and future directions Outline of Presentation 25
  • 26.
    WWW.SUNYCNSE.COM Hexagonal Boron Nitride Single-crystalline  Atomically smooth surface  Free of surface state  High-energy surface phonons  Thermal conductivity: ~20 W/m-K (20X of SiO2) Silicon Dioxide  Amorphous  Surface roughness  Rich in trapped charges  Low-energy surface phonons  Thermal conductivity: ~1.04 W/m-K Graphene h-BN (lattice mismatch ~ 1.6%) h-BN: Substrate for Graphene Image Courtesy: Jarillo-Herrero Group, Quantum Nanoelectronics, MIT 26
  • 27.
  • 28.
    WWW.SUNYCNSE.COM Electrical Performance ofGOBON Conductivity and mobility improvement is observed in GOBON when compared with graphene (CVD or exfoliated) on SiO2.  Resistivity (at VG = 0V) drops by approximately 19x in GOBON as compared with that on SiO2.  At the carrier density of 1×1012 cm-2, carrier mobility in GOBON is improved by about 17x compared with CVD graphene on SiO2. N. Jain et al, IEEE Electron Device Letters, 33 (7), 2012 28
  • 29.
    WWW.SUNYCNSE.COM Reliability Enhancement inGOBON Due to improved thermal conductivity of h-BN, the permissible current and voltage before permanent breakdown in graphene are enhanced. PBD = JBD (VBD – JBDRC)  ~ 7X increased power density @ breakdown  Thermal conductivity: ~20 W/m-K): ~20 times that in SiO2 (1.04 W/m-K)  Prevent Joule heat built up in graphene where, JBD = Current density at breakdown VBD = Voltage at breakdown RC = Contact resistance N. Jain et al, IEEE Electron Device Letters, 33 (7), 2012 29
  • 30.
    WWW.SUNYCNSE.COM Electrical Annealing Effect Electricalannealing shifts the Dirac point in graphene on SiO2, but this change is avoided in GOBON due to less interfacial trap charges G/h-BN G/SiO2 T. Yu, Applied Physics Letters 2011, 98, 243105. N. Jain et al, IEEE Electron Device Letters, 33 (7), 2012 30
  • 31.
    WWW.SUNYCNSE.COM Summary h-BN has beenshown to be an excellent substrate for graphene.  Graphene resistivity on h-BN is found to be 19 times lower than on SiO2 (the current standard substrate).  There is a 17-fold improvement in graphene mobility when placed on h-BN compared with SiO2.  Improved heat dissipation through h-BN results in higher values of current density and power density required to cause Joule heating-induced breakdown in graphene.  The Dirac point in GOBON structures is stable under the effect of electrical annealing. 31
  • 32.
    WWW.SUNYCNSE.COM  Introduction to2D materials  Graphene/h-BN heterostructures  h-BN as an ubiquitous dielectric  Substrate  Gate dielectric  Passivation layer  Intercalation layer  Conclusions and future directions Outline of Presentation 32
  • 33.
    WWW.SUNYCNSE.COM h-BN as GateDielectric h-BN could also serve as gate dielectric k = 3.9 EG = 5.97 eV self-terminating surface chemically inert Key questions: What is the dielectric behavior? 33
  • 34.
    WWW.SUNYCNSE.COM Titanium Nitride (TiN)filled trenches are created in a Si/SiO2 wafer to act as a gate for GOBON FET Buried Gate Structures: Fabrication * This process is done in the fab 34
  • 35.
    WWW.SUNYCNSE.COM GOBON FET withh-BN as Gate Insulator * FET fabrication process is same as shown in previous section. G/h-BN/TiN 35
  • 36.
    WWW.SUNYCNSE.COM Performance of GOBONFETs Carrier mobility of CVD graphene on h-BN (on TiN) is 1.4X higher than mechanically exfoliated graphene on SiO2 at effective electric field of 2x105 V-cm-1 N. Jain et al. Carbon, 54, 396–402 (2013) 36
  • 37.
    WWW.SUNYCNSE.COM Dielectric Strength ofh-BN  No dielectric breakdown up to very high electric field (15 MV/cm)  Transition from insulating to leakage occurs at a voltage that is directly proportional to h-BN multilayer thickness N. Jain et al. Carbon, 54, 396–402 (2013) h-BN is a robust dielectric which resists dielectric breakdown at high electric fields. 37
  • 38.
    WWW.SUNYCNSE.COM Summary h-BN has beenshown to be a robust gate dielectric for FETs made with graphene.  Graphene mobility is enhanced in GOBON FETs compared with graphene FETs with SiO2 as gate dielectric.  As a gate dielectric, h-BN does not undergo dielectric breakdown even under very high electric field of 15MV/cm.  h-BN undergoes a reversible transition to a leaky dielectric at high fields, which is dependent on layer thickness. 38
  • 39.
    WWW.SUNYCNSE.COM  Introduction to2D materials  Graphene/h-BN heterostructures  h-BN as an ubiquitous dielectric  Substrate  Gate dielectric  Passivation layer  Intercalation layer  Conclusions and future directions Outline of Presentation 39
  • 40.
    WWW.SUNYCNSE.COM Need for grapheneencapsulation  Whatever be the substrate, environmental adsorbents reduce graphene conduction  Adsorbent sites act as charge traps  Encapsulation with traditional capping materials degrades graphene quality  h-BN as a passivating layer conforms to graphene surface 40
  • 41.
    WWW.SUNYCNSE.COM Fully Encapsulated Graphene *CAB – Cellulose Acetate Butyrate 41
  • 42.
    WWW.SUNYCNSE.COM Passivation Effect ofTop h-BN  Insensitive to environmental (ambient) impact  R-V characteristics show no variation in air and in vacuum for encapsulated device  No variation in contact resistance between ambient and vacuum N. Jain et al, Nanotechnology, 24, 355202 (2013) 42
  • 43.
    WWW.SUNYCNSE.COM  67% increasein breakdown power density compared to uncovered GOBON devices due to increased heat dissipation through both graphene surfaces  No reduction in carrier mobility Electrical Behavior N. Jain et al, Nanotechnology, 24, 355202 (2013) 43
  • 44.
    WWW.SUNYCNSE.COM Summary h-BN has beenshown to be an effective passivation layer for graphene devices.  When passivated with h-BN, graphene performance becomes insensitive to the measurement conditions (ambient or vacuum).  Graphene – Metal contact performance is improved.  Higher current density and power density are needed to cause breakdown in encapsulated graphene devices.  The improvement is achieved without a compromise on carrier mobility. 44
  • 45.
    WWW.SUNYCNSE.COM  Introduction to2D materials  Graphene/h-BN heterostructures  h-BN as an ubiquitous dielectric  Substrate  Gate dielectric  Passivation layer  Intercalation layer  Conclusions and future directions Outline of Presentation 45
  • 46.
    WWW.SUNYCNSE.COM Cu CNT Graphene Maxcurrent density (A/cm2) ~106 > 1x108 > 1x108 Melting Point (K) 1356 3800 (graphite) 3800 (graphite) Tensile Strength (GPa) 0.22 22.2 23.5 Thermal Conductivity (×103 W/m-K) 0.385 1.75 Hone, et al. Phys. Rev. B 1999 3 - 5 Balandin, et al. Nano Let., 2008 Temp. Coefficient of Resistance (10-3 /K) 4 < 1.1 Kane, et al. Europhys. Lett.,1998 -1.47 Shao et al. Appl Phys. Lett., 2008 Mean Free Path @ room-T (nm) 40 > 1000 McEuen, et al. Trans. Nano., 2002 ~ 1000 Bolotin, et al. Phys. Rev. Let. 2008 x102 x10 x25 x102 Graphene as a Conductor
  • 47.
    WWW.SUNYCNSE.COM Towards “3-D Graphene” At small critical dimensions (width < 100 nm), ρGraphene < ρCu  Small cross section in monolayer graphene limits conduction.  Multilayer graphene has less sheet resistance than monolayer graphene.  Onset of inter-layer scattering of charge carriers in multi-layer graphene doesn’t allow the sheet resistance to scale down as expected 47
  • 48.
    WWW.SUNYCNSE.COM Double-Layer Graphene (DLG): Fabrication DLGstructure with h-BN between two monolayer graphene sheets with direct metal contact with both graphene layers 48
  • 49.
    WWW.SUNYCNSE.COM Massless Dirac Fermionsin DLG DFT simulation of the dispersion relation of the DLG structure indicates that carriers are massless Dirac fermions * DFT analysis was performed by our collaborators at University of Washington.  Band splitting in BLG  Π and Π* bands divide in four bands due to interlayer scattering  Degeneracy is restored in DLG 49
  • 50.
    WWW.SUNYCNSE.COM Raman Spectra ofGraphene  Single 2D peak in monolayer graphene  Due to coupling between layers, two or four peaks exist in 2D band (>2 layers) 1400 1600 1800 2000 2200 2400 2600 2800 3000 2D band Normalizedintensity Wavenumber (cm -1 ) 1layer 2layer 3layer 4layers 5layer Graphite G band More layer number - Intensity ratio of G/2D increased 50 Freitag, M. Nat Phys, 2011, 7, 596–597
  • 51.
    WWW.SUNYCNSE.COM Raman Spectral Analysisfor Scattering Measurement 2D peak in the Raman spectrum of bilayer graphene is composed of four components arising from the band split at Dirac point.  Reduced height of the overall 2D peak  Increase in IG/I2D  Increase in FWHM2D 51
  • 52.
    WWW.SUNYCNSE.COM Raman Spectral Analysisfor Scattering Measurement Addition of graphene layers results in increase in IG/I2D and FWHM2D.  For stacked turbostratic graphene, addition of each layer results in lesser increase than in exfoliated graphene, indicating reduced scattering in stacked graphene  Similar effect is seen in FWHM2D 52
  • 53.
    WWW.SUNYCNSE.COM Raman Spectral Analysis IG/I2Dand FWHM2D in DLG is similar to monolayer graphene (much lower than stacked or exfoliated BLG) Introduction of h-BN as an intercalation layer in double-layer graphene reduces interlayer carrier scattering. 53
  • 54.
    WWW.SUNYCNSE.COM Electrical Characterization Reduced interlayerscattering allows higher current in DLG. Current and conductivity in DLG ~ MLG > BLG 54
  • 55.
    WWW.SUNYCNSE.COM Performance Enhancement Mobility andbreakdown current density in DLG show enhancement.  Carrier Mobility in DLG > MLG  JBD in DLG > 2x JBD in BLG 55
  • 56.
    WWW.SUNYCNSE.COM Reliability Improvement Under extremeelectrical stress, DLG resists breakdown more than MLG and BLG.  At an elevated temperature (150C) under the effect of a constant voltage (10V), the DLG sample withstands a current density of ~ 475 mA/cm2  The mean time to failure (MTTF) for DLG is ~ 75 and ~4000 times higher than that for BLG and MLG systems 56
  • 57.
    WWW.SUNYCNSE.COM Summary h-BN has beenshown to be an interposer layer that prevents interlayer scattering from degrading the performance of double-layer graphene.  Increase in the IG/I2D ratio and FWHM2D have been shown as indicators of interlayer scattering.  Random-stacked (turbostratic) graphene shows lower interlayer scattering than Bernal-stacked graphene.  As an intercalation layer, h-BN removes interlayer scattering resulting in ideal current scaling due to layer stacking.  Higher carrier mobility and resistance to breakdown at extreme electrical stressing conditions are also observed in DLG. 57
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    WWW.SUNYCNSE.COM  Introduction to2D materials  Graphene/h-BN heterostructures  h-BN as an ubiquitous dielectric  Substrate  Gate dielectric  Passivation layer  Intercalation layer  Conclusions and future directions Outline of Presentation 58
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    WWW.SUNYCNSE.COM Conclusions  h-BN hasbeen explored as a multi-function dielectric for future 2D material enabled electronics.  Facile assembly/fabrication processes for 2D heterostructures have been demonstrated.  h-BN serves as excellent supporting substrate, largely preserving “pristine” graphene electronic transport.  h-BN is demonstrated as a highly robust gate dielectric (medium-k value).  Fully encapsulated 2D heterostructure (h-BN/graphene/h-BN) provides passivation and enhancement of maximum power density in graphene without compromising electrical conduction.  As an intercalation layer between graphene layers, h-BN reduces interlayer scattering and restores mobility to ‘monolayer-like’ value while also making the structures more robust to stress. 59
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    WWW.SUNYCNSE.COM Future Directions (1) Directall-CVD growth process  GOBON: Graphene growth on exfoliated h-BN  BNOG: h-BN growth on CVD/exfoliated graphene (2) Study of 2D heterostructure properties (3) On-chip device, interconnect, circuit demonstration 60
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    WWW.SUNYCNSE.COM Superlattice-like structures ofgraphene/h-BN Future Directions 62
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    WWW.SUNYCNSE.COM Acknowledgments Lab Members (Presentand Past):  Dr. Bhaskar Nagabhirava  Dr. Tianhua Yu  Dr. Tanesh Bansal  Dr. Mariyappan Shanmugam  Dr. Fan Yang  Robin Jacobs-Gedrim  Eui Sang Song  Thibault Sohier  Christopher Durcan Our Collaborator:  Prof. M. P. Anantram (Univ. of Washington, Seattle) CNSE CSR Team:  Dr. Vidya Kaushik  Dr. Prasanna Khare  Megha Rao 63
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    WWW.SUNYCNSE.COM Journal Publications 1. N.Jain, M. Murphy, R. B. Jacobs-Gedrim, M. Shanmugam, F. Yang, E. S. Song, and B. Yu, “Electrical Conduction and Reliability in Dual-Layered Graphene Heterostructure Interconnects,” IEEE Electro Device Letters, vol. 35, no. 12, 1311-1313 (2014). 2. R. B. Jacobs-Gedrim, M. Shanmugam, N. Jain, C. A. Durcan, M. T. Murphy, T. M. Murray, R. J. Matyi, R. L. Moore, and B. Yu, “Extraordinary photoresponse in two-dimensional In2Se3 nanosheets,” ACS Nano, 8, 1, 514-521 (2014). 3. N. Jain, C. A. Durcan, R. B. Jacobs-Gedrim, Y. Xu, and B. Yu, “Graphene interconnects fully encapsulated in layered insulator hexagonal boron nitride,” Nanotechnology, 24, 355202 (2013). 4. N. Jain, T. Bansal, C. A. Durcan, Y. Xu, and B. Yu, “Monolayer Graphene/Hexagonal Boron Nitride Heterostructure,” Carbon, 54, 396– 402 (2013). 5. T. Bansal, C. A. Durcan, N. Jain, R. B. Jacobs-Gedrim, Y. Xu, and B. Yu, “Synthesis of Few-to-Monolayer Graphene on Rutile Titanium Dioxide,” Carbon, 55, 168-175 (2013). 6. M. Shanmugam, N. Jain, R. B. Jacobs-Gedrim, Y. Xu, and B. Yu, “Layered insulator hexagonal boron nitride for surface passivation in quantum dot solar cell,” Applied Physics Letters, 103, 243904 (2013). 7. R. B. Jacobs-Gedrim, C. A. Durcan, N. Jain, and B. Yu, “Chemical Assembly and Electrical Characteristics of Surface-Rich Topological Insulator Bi2Se3 Nanoplates and Nanoribbons,” Applied Physics Letters, 101, 143103 (2012). 8. E. Kim, N. Jain, R. Jacobs-Gedrim, Y. Xu, and B. Yu, “Exploring Carrier Transport Phenomena in CVD-Assembled Graphene FET on Hexagonal Boron Nitride,” Nanotechnology, 23, 125706 (2012). 9. N. Jain, T. Bansal, C. Durcan, and B. Yu, “Graphene-Based Interconnects on Hexagonal Boron Nitride (h-BN) Substrate,” IEEE Electro Device Letters, vol. 33, no. 7, 925-927 (2012). ARTICLES UNDER REVIEW 1. N. Jain, R. Jacobs-Gedrim, Y. Xu, and B. Yu, “Resistive Switching in Ultra-Thin Two-Dimensional van der Waals Dielectric” Nature Communications (2015). 2. N. Jain, R. B. Jacobs-Gedrim, M. Murphy, M. Shanmugam, F. Yang, Y. Xu, and B. Yu, “Electrical Conduction in Two-Dimensional Graphene/Hexagonal Boron Nitride/Graphene Heterostructure,” Nano Letters (2015). 3. R. Jacobs-Gedrim, M. Murphy, N. Jain, F. Yang, M. Shanmugam, E. Song, Y. Kandel, P. Hesamaddin, D. B. Janes, and B. Yu, “Reversible Crystalline-Amorphous Phase Transition in Chalcogenide Nanosheets”, Nature Materials (2015). 64
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    WWW.SUNYCNSE.COM Significance of Environment Opengraphene is subject to severe degradation over time due to the effect of adsorption of ambient molecules like N2, H2O and O2 Graphene/metal contact I-V behavior Time-dependent contact resistance shift Demand: Graphene covered with an insulator which protects its pristine electrical behavior
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    WWW.SUNYCNSE.COM Metal Contacts Grapheneat 1-D Edge Fabrication made simpler with only one patterning step for the G/h-BN/G stack and one metallization step L Wang et al, Science 342, 614 (2013)
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    WWW.SUNYCNSE.COM 2D Band CurveFitting Results Bilayer Graphene Trilayer Graphene 2600 2650 2700 2750 2800 P1: 2656 P2: 2688 P3: 2707 P4: 2722 Wavenumber (cm -1 ) 2600 2650 2700 2750 2800 P1: 2694 P2: 2719 Wavenubmer (cm -1 ) 2600 2650 2700 2750 2800 P1: 2696 P2: 2722 Wavenumber (cm -1 ) Four Layer Graphene 2600 2650 2700 2750 2800 P1: 2695 P2: 2725 Wavenumber (cm -1 ) Five Layer Graphene
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    WWW.SUNYCNSE.COM Raman Spectra ofs-MLG More layer number: •2D band blue shift •Intensity ratio of G/2D increased. • Less coupling between layers, only one peak exists in 2D band (2~5 layers) 1400 1600 1800 2000 2200 2400 2600 2800 3000 Wavenumber (cm -1 ) as -- -- -- -- -- 2D bandG band 400 1600 1800 2000 2200 2400 2600 2800 3000 2D band Wavenumber (cm -1 ) 1layer 2layer 3layer 4layers 5layer Graphite G band
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    WWW.SUNYCNSE.COM Lifetime Reliability Study Sustained current in graphene can lead to degradation and eventual failure of the wire  Comparison of stacked BLG and G-BN-G heterostructure can provide information about improvement in graphene interconnect reliability by incorporation of h-BN between graphene layers  Mean Time to fail (MTTF) in G-BN-G heterostructure will be higher than MLG and stacked BLG at same current density X Chen et al, IEEE EDL 2012

Editor's Notes

  • #48 Change problem statement