Bio

Asir Intisar Khan is a Ph.D. candidate in the Electrical Engineering department at Stanford University, supervised by Professor Eric Pop while also working very closely with Profs. H.-S. Philip Wong, Kenneth Goodson, and Krishna Saraswat. He received his M.S. in Electrical Engineering from the same department at Stanford. Prior to joining Stanford in 2018, he received another M.S. (2018) and a B.S. (2016) from the Bangladesh University of Engineering and Technology. His research effort and vision encompass exploring novel materials and their functionalities to enable energy-efficient memory, computing devices and interconnects for 3D heterogeneous integration. His research work has enabled the lowest-to-date switching current density in phase-change memory technology and has been featured in Forbes Magazine and IEEE Spectrum. He received the Best Student Paper award at the 2022 IEEE VLSI Technology Symposium and Best Presenter Award at the 2022 MRS Fall Meeting. He has held Research Intern positions at TSMC and IBM TJ Watson Research Center. Asir is a recipient of the Stanford Graduate Fellowship, 2022 IEEE EDS Ph.D. Student Fellowship, and 2022 MRS Fall Meeting Gold Student Award.

Honors & Awards

  • IEEE Electron Device Society PhD Student Fellowship, IEEE (2022)
  • Materials Research Society (MRS) Gold Graduate Student Award, Materials Research Society (MRS) (2022)
  • Best Student Paper Award, 2022 Symposium on VLSI Technology and Circuits, IEEE (2022)
  • Best Student Presentation Award (MRS Fall 2022), Materials Research Society (MRS) (2022)
  • Stanford Graduate Fellowship, Stanford University (2020 - 2023)
  • Departmental Fellowship, Electrical Engineering, Stanford University (2018-2019)

Education & Certifications

  • PhD Candidate, Stanford University, Electrical Engineering
  • MS, Stanford University, Electrical Engineering (2021)
  • M.Sc, Bangladesh University of Engineering and Technology, Electrical and Electronic Engineering (2018)
  • B.Sc, Bangladesh University of Engineering and Technology, Electrical and Electronic Engineering (2016)

Personal Interests

Traveling, Cooking, Table Tennis

Contact

  • Academic
    asir@stanford.edu
    University - Student Department: Electrical Engineering Position: Graduate

Additional Info

Links

Current Research and Scholarly Interests

My research involves atomic-scale engineering and electro-thermal transport of new electronic materials to open new functionalities in nanoscale devices as a platform for energy-efficient nanoelectronics. I have demonstrated how controlling the heat transport using ultrathin (~nm) chalcogenide and their nanocomposite superlattices enable ultralow power (~100x energy-efficient) and neuro-inspired phase-change memory for both rigid and flexible electronics, unlike existing data-storage technology. I have also worked on establishing the correlations between these chalcogenide functionalities and improved memory device performances and their tunability, crucial for robustness and optimization. On the other hand, I have been exploring an unconventional resistivity scaling in ultrathin topological semimetals as a new paradigm for ultra-scaled interconnect going beyond the power-dissipation bottleneck in conventional metals. My research efforts illustrate how combining these versatile material functionalities and probing their transport fundamentals can unlock decade-spanning advances in energy-efficient computing and heterogeneously integrated nanoelectronics.

Lab Affiliations

All Publications

  • Energy Efficient Neuro-inspired Phase Change Memory Based on Ge4 Sb6 Te7 as a Novel Epitaxial Nanocomposite. Advanced materials (Deerfield Beach, Fla.) Khan, A. I., Yu, H., Zhang, H., Goggin, J. R., Kwon, H., Wu, X., Perez, C., Neilson, K. M., Asheghi, M., Goodson, K. E., Vora, P. M., Davydov, A., Takeuchi, I., Pop, E. 2023: e2300107

    Abstract

    Phase change memory (PCM) is a promising candidate for neuro-inspired, data-intensive artificial intelligence applications, which relies on the physical attributes of PCM materials including gradual change of resistance states and multilevel operation with low resistance drift. However, achieving these attributes simultaneously remains a fundamental challenge for PCM materials such as Ge2 Sb2 Te5 , the most commonly used material. Here we demonstrate bi-directional gradual resistance changes with ∼10x resistance window using low energy pulses in nanoscale PCM devices based on Ge4 Sb6 Te7 , a new phase change nanocomposite material. These devices show 13 resistance levels with low resistance drift for the first 8 levels, resistance on/off ratio of ∼1000, and low variability. These attributes are enabled by the unique microstructural and electrothermal properties of Ge4 Sb6 Te7 , a nanocomposite consisting of epitaxial SbTe nanoclusters within the Ge-Sb-Te matrix, and a higher crystallization but lower melting temperature than Ge2 Sb2 Te5 . These results advance the pathway towards energy-efficient analog computing using PCM. This article is protected by copyright. All rights reserved.

    View details for DOI 10.1002/adma.202300107

    View details for PubMedID 36720651

  • Unveiling the Effect of Superlattice Interfaces and Intermixing on Phase Change Memory Performance. Nano letters Khan, A. I., Wu, X., Perez, C., Won, B., Kim, K., Ramesh, P., Kwon, H., Tung, M. C., Lee, Z., Oh, I., Saraswat, K., Asheghi, M., Goodson, K. E., Wong, H. P., Pop, E. 2022

    Abstract

    Superlattice (SL) phase change materials have shown promise to reduce the switching current and resistance drift of phase change memory (PCM). However, the effects of internal SL interfaces and intermixing on PCM performance remain unexplored, although these are essential to understand and ensure reliable memory operation. Here, using nanometer-thin layers of Ge2Sb2Te5 and Sb2Te3 in SL-PCM, we uncover that both switching current density (Jreset) and resistance drift coefficient (v) decrease as the SL period thickness is reduced (i.e., higher interface density); however, interface intermixing within the SL increases both. The signatures of distinct versus intermixed interfaces also show up in transmission electron microscopy, X-ray diffraction, and thermal conductivity measurements of our SL films. Combining the lessons learned, we simultaneously achieve low Jreset 3-4 MA/cm2 and ultralow v 0.002 in mushroom-cell SL-PCM with 110 nm bottom contact diameter, thus advancing SL-PCM technology for high-density storage and neuromorphic applications.

    View details for DOI 10.1021/acs.nanolett.2c01869

    View details for PubMedID 35876819

  • Ultralow-switching current density multilevel phase-change memory on a flexible substrate. Science (New York, N.Y.) Khan, A. I., Daus, A., Islam, R., Neilson, K. M., Lee, H. R., Wong, H. P., Pop, E. 2021; 373 (6560): 1243-1247

    Abstract

    [Figure: see text].

    View details for DOI 10.1126/science.abj1261

    View details for PubMedID 34516795

  • Probing the Melting Transitions in Phase-Change Superlattices via Thin Film Nanocalorimetry. Nano letters Zhao, J., Khan, A. I., Efremov, M. Y., Ye, Z., Wu, X., Kim, K., Lee, Z., Wong, H. P., Pop, E., Allen, L. H. 2023

    Abstract

    Phase-change superlattices with nanometer thin sublayers are promising for low-power phase-change memory (PCM) on rigid and flexible platforms. However, the thermodynamics of the phase transition in such nanoscale superlattices remain unexplored, especially at ultrafast scanning rates, which is crucial for our fundamental understanding of superlattice-based PCM. Here, we probe the phase transition of Sb2Te3 (ST)/Ge2Sb2Te5 (GST) superlattices using nanocalorimetry with a monolayer sensitivity (∼1 Å) and a fast scanning rate (105 K/s). For a 2/1.8 nm/nm Sb2Te3/GST superlattice, we observe an endothermic melting transition with an ∼240 °C decrease in temperature and an ∼8-fold decrease in enthalpy compared to those for the melting of GST, providing key thermodynamic insights into the low-power switching of superlattice-based PCM. Nanocalorimetry measurements for Sb2Te3 alone demonstrate an intrinsic premelting similar to the unique phase transition of superlattices, thus revealing a critical role of the Sb2Te3 sublayer within our superlattices. These results advance our understanding of superlattices for energy-efficient data storage and computing.

    View details for DOI 10.1021/acs.nanolett.3c01049

    View details for PubMedID 37171275

  • Understanding Interface-Controlled Resistance Drift in Superlattice Phase Change Memory IEEE ELECTRON DEVICE LETTERS Wu, X., Khan, A., Ramesh, P., Perez, C., Kim, K., Lee, Z., Saraswat, K., Goodson, K. E., Wong, H., Pop, E. 2022; 43 (10): 1669-1672

    View details for DOI 10.1109/LED.2022.3203971

    View details for Web of Science ID 000861441600023

  • Improved gradual resistive switching range and 1000x on/off ratio in HfOx PRAM achieved with a Ge2Sb2Te5 thermal barrier APPLIED PHYSICS LETTERS Islam, R., Qin, S., Deshmukh, S., Yu, Z., Koroglu, C., Khan, A. I., Schauble, K., Saraswat, K. C., Pop, E., Wong, H. P. 2022; 121 (8)

    View details for DOI 10.1063/5.0101417

    View details for Web of Science ID 000892460800016

  • Fast-Response Flexible Temperature Sensors with Atomically Thin Molybdenum Disulfide. Nano letters Daus, A., Jaikissoon, M., Khan, A. I., Kumar, A., Grady, R. W., Saraswat, K. C., Pop, E. 2022

    Abstract

    Real-time thermal sensing on flexible substrates could enable a plethora of new applications. However, achieving fast, sub-millisecond response times even in a single sensor is difficult, due to the thermal mass of the sensor and encapsulation. Here, we fabricate flexible monolayer molybdenum disulfide (MoS2) temperature sensors and arrays, which can detect temperature changes within a few microseconds, over 100× faster than flexible thin-film metal sensors. Thermal simulations indicate the sensors' response time is only limited by the MoS2 interfaces and encapsulation. The sensors also have high temperature coefficient of resistance, ∼1-2%/K and stable operation upon cycling and long-term measurement when they are encapsulated with alumina. These results, together with their biocompatibility, make these devices excellent candidates for biomedical sensor arrays and many other Internet of Things applications.

    View details for DOI 10.1021/acs.nanolett.2c01344

    View details for PubMedID 35899996

  • Ultra-low-energy programmable non-volatile silicon photonics based on phase-change materials with graphene heaters NATURE NANOTECHNOLOGY Fang, Z., Chen, R., Zheng, J., Khan, A., Neilson, K. M., Geiger, S. J., Callahan, D. M., Moebius, M. G., Saxena, A., Chen, M. E., Rios, C., Hu, J., Pop, E., Majumdar, A. 2022

    Abstract

    Silicon photonics is evolving from laboratory research to real-world applications with the potential to transform many technologies, including optical neural networks and quantum information processing. A key element for these applications is a reconfigurable switch operating at ultra-low programming energy-a challenging proposition for traditional thermo-optic or free carrier switches. Recent advances in non-volatile programmable silicon photonics based on phase-change materials (PCMs) provide an attractive solution to energy-efficient photonic switches with zero static power, but the programming energy density remains high (hundreds of attojoules per cubic nanometre). Here we demonstrate a non-volatile electrically reconfigurable silicon photonic platform leveraging a monolayer graphene heater with high energy efficiency and endurance. In particular, we show a broadband switch based on the technologically mature PCM Ge2Sb2Te5 and a phase shifter employing the emerging low-loss PCM Sb2Se3. The graphene-assisted photonic switches exhibited an endurance of over 1,000 cycles and a programming energy density of 8.7 ± 1.4 aJ nm-3, that is, within an order of magnitude of the PCM thermodynamic switching energy limit (~1.2 aJ nm-3) and at least a 20-fold reduction in switching energy compared with the state of the art. Our work shows that graphene is a reliable and energy-efficient heater compatible with dielectric platforms, including Si3N4, for technologically relevant non-volatile programmable silicon photonics.

    View details for DOI 10.1038/s41565-022-01153-w

    View details for Web of Science ID 000820548600001

    View details for PubMedID 35788188

  • Electro-Thermal Confinement Enables Improved Superlattice Phase Change Memory IEEE ELECTRON DEVICE LETTERS Khan, A., Kwon, H., Chen, M. E., Asheghi, M., Wong, H., Goodson, K. E., Pop, E. 2022; 43 (2): 204-207

    View details for DOI 10.1109/LED.2021.3133906

    View details for Web of Science ID 000748371400013

  • Nanoscale Phase Change Memory Arrays Patterned by Block Copolymer Directed Self-Assembly Tung, M. C., Khan, A., Kwon, H., Asheghi, M., Goodson, K. E., Pop, E., Wong, H., Panning, E. M., Liddle, J. A. SPIE-INT SOC OPTICAL ENGINEERING. 2022

    View details for DOI 10.1117/12.2611737

    View details for Web of Science ID 000839339400005

  • Ultra-low energy programmable non-volatile silicon photonics based on phase-change materials with graphene heaters Fang, Z., Chen, R., Zheng, J., Khan, A., Neilson, K. M., Geiger, S. J., Callahan, D. M., Moebius, M. G., Saxena, A., Chen, M. E., Rios, C., Hu, J., Pop, E., Majumdar, A., Subramania, G. S., Foteinopoulou, S. SPIE-INT SOC OPTICAL ENGINEERING. 2022

    View details for DOI 10.1117/12.2632208

    View details for Web of Science ID 000870730200001

  • Lateral electrical transport and field-effect characteristics of sputtered p-type chalcogenide thin films APPLIED PHYSICS LETTERS Wahid, S., Daus, A., Khan, A., Chen, V., Neilson, K. M., Islam, M., Chen, M. E., Pop, E. 2021; 119 (23)

    View details for DOI 10.1063/5.0063759

    View details for Web of Science ID 000729364800005

  • Modeling and computation of thermal and optical properties in silicene supported honeycomb bilayer and heterobilayer nanostructures MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING Noshin, M., Khan, A., Chakraborty, R., Subrina, S. 2021; 129

    View details for DOI 10.1016/j.mssp.2021.105776

    View details for Web of Science ID 000641416200007

  • Uncovering Thermal and Electrical Properties of Sb2Te3/GeTe Superlattice Films. Nano letters Kwon, H., Khan, A. I., Perez, C., Asheghi, M., Pop, E., Goodson, K. E. 2021

    Abstract

    Superlattice-like phase change memory (SL-PCM) promises lower switching current than conventional PCM based on Ge2Sb2Te5 (GST); however, a fundamental understanding of SL-PCM requires detailed characterization of the interfaces within such an SL. Here we explore the electrical and thermal transport of SLs with deposited Sb2Te3 and GeTe alternating layers of various thicknesses. We find up to an approximately four-fold reduction of the effective cross-plane thermal conductivity of the SL stack (as-deposited polycrystalline) compared with polycrystalline GST (as-deposited amorphous and later annealed) due to the thermal interface resistances within the SL. Thermal measurements with varying periods of our SLs show a signature of phonon coherence with a transition from wave-like to particle-like phonon transport, further described by our modeling. Electrical resistivity measurements of such SLs reveal strong anisotropy (∼2000×) between the in-plane and cross-plane directions due to the weakly interacting van der Waals-like gaps. This work uncovers electrothermal transport in SLs based on Sb2Te3 and GeTe for the improved design of low-power PCM.

    View details for DOI 10.1021/acs.nanolett.1c00947

    View details for PubMedID 34270270

  • Two-Fold Reduction of Switching Current Density in Phase Change Memory Using Bi2Te3 Thermoelectric Interfacial Layer IEEE ELECTRON DEVICE LETTERS Khan, A., Kwon, H., Islam, R., Perez, C., Chen, M. E., Asheghi, M., Goodson, K. E., Wong, H., Pop, E. 2020; 41 (11): 1657–60

    View details for DOI 10.1109/LED.2020.3028271

    View details for Web of Science ID 000584248800011

  • Large temperature coefficient of resistance in atomically thin two-dimensional semiconductors Applied Physics Letters Khan, A., Khakbaz, P., Brenner, K. A., Smithe, K., Mleczko, M. J., Esseni, D., Pop, E. 2020; 116 (20)

    View details for DOI 10.1063/5.0003312

  • Flexible Low-Power Superlattice-Like Phase Change Memory Khan, A., Daus, A., Pop, E., IEEE IEEE. 2020

    View details for Web of Science ID 000615719100024

  • Flexible Low-Power Superlattice-Like Phase Change Memory 2020 Device Research Conference (DRC) Khan, A., Daus, A., Pop, E. 2020: 1–1

    View details for DOI 10.1109/DRC50226.2020.9135166

  • Large Temperature Coefficient of Resistance in Atomically Thin 2D Devices IEEE Device Research Conference (DRC) Khan, A., Brenner, K., Smithe, K., Mleczko, M., Pop, E. 2019: 125–126

    View details for DOI 10.1109/DRC46940.2019.9046401

  • Thermal transport characterization of stanene/silicene heterobilayer and stanene bilayer nanostructures NANOTECHNOLOGY Noshin, M., Khan, A., Subrina, S. 2018; 29 (18): 185706

    Abstract

    Recently, stanene and silicene based nanostructures with low thermal conductivity have incited noteworthy interest due to their prospect in thermoelectrics. Aiming at the possibility of extracting lower thermal conductivity, in this study, we have proposed and modeled stanene/silicene heterobilayer nanoribbons, a new heterostructure and subsequently characterized their thermal transport by using an equilibrium molecular dynamics simulation. In addition, the thermal transport in bilayer stanene is also studied and compared. We have computed the thermal conductivity of the stanene/silicene and bilayer stanene nanostructures to characterize their thermal transport phenomena. The studied nanostructures show good thermal stability within the temperature range of 100-600 K. The room temperature thermal conductivities of pristine 10 nm × 3 nm stanene/silicene hetero-bilayer and stanene bilayer are estimated to be 3.63 ± 0.27 W m-1 K-1 and 1.31 ± 0.34 W m-1 K-1, respectively, which are smaller than that of silicene, graphene and some other 2D monolayers as well as heterobilayers such as stanene/graphene and silicene/graphene. In the temperature range of 100-600 K, the thermal conductivity of our studied bilayer nanoribbons decreases with an increase in the temperature. Furthermore, we have investigated the dependence of our estimated thermal conductivity on the size of the considered nanoribbons. The thermal conductivities of both the nanoribbons are found to increase with an increase in the width of the structure. The thermal conductivity shows a similar increasing trend with the increase in the ribbon length, as well. Our results suggest that, the low thermal conductivity of our studied bilayer structures can be further decreased by nanostructuring. The significantly low thermal conductivity of the stanene/silicene heterobilayer and stanene bilayer nanoribbons realized in our study would provide a good insight and encouragement into their appealing prospect in the thermoelectric applications.

    View details for PubMedID 29438099

  • Impact of tensile strain on the thermal transport of zigzag hexagonal boron nitride nanoribbon: An equilibrium molecular dynamics study MATERIALS RESEARCH EXPRESS Navid, I., Khan, A., Subrina, S. 2018; 5 (2)

    View details for DOI 10.1088/2053-1591/aaaa89

    View details for Web of Science ID 000424687300001

  • Stanene-hexagonal boron nitride heterobilayer: Structure and characterization of electronic property SCIENTIFIC REPORTS Khan, A., Chakraborty, T., Acharjee, N., Subrina, S. 2017; 7

    View details for DOI 10.1038/s41598-017-16650-5

    View details for Web of Science ID 000416307300001

  • Stanene-hexagonal boron nitride heterobilayer: Structure and characterization of electronic property. Scientific reports Khan, A. I., Chakraborty, T., Acharjee, N., Subrina, S. 2017; 7 (1): 16347

    Abstract

    The structural and electronic properties of stanene/hexagonal boron nitride (Sn/h-BN) heterobilayer with different stacking patterns are studied using first principle calculations within the framework of density functional theory. The electronic band structure of different stacking patterns shows a direct band gap of ~30 meV at Dirac point and at the Fermi energy level with a Fermi velocity of ~0.53 × 106 ms-1. Linear Dirac dispersion relation is nearly preserved and the calculated small effective mass in the order of 0.05mo suggests high carrier mobility. Density of states and space charge distribution of the considered heterobilayer structure near the conduction and the valence bands show unsaturated π orbitals of stanene. This indicates that electronic carriers are expected to transport only through the stanene layer, thereby leaving the h-BN layer to be a good choice as a substrate for the heterostructure. We have also explored the modulation of the obtained band gap by changing the interlayer spacing between h-BN and Sn layer and by applying tensile biaxial strain to the heterostructure. A small increase in the band gap is observed with the increasing percentage of strain. Our results suggest that, Sn/h-BN heterostructure can be a potential candidate for Sn-based nanoelectronics and spintronic applications.

    View details for DOI 10.1038/s41598-017-16650-5

    View details for PubMedID 29180696

    View details for PubMedCentralID PMC5703857

  • Thermal transport characterization of hexagonal boron nitride nanoribbons using molecular dynamics simulation AIP ADVANCES Khan, A., Navid, I., Noshin, M., Subrina, S. 2017; 7 (10)

    View details for DOI 10.1063/1.4997036

    View details for Web of Science ID 000414246100036

  • Characterization of thermal and mechanical properties of stanene nanoribbons: a molecular dynamics study RSC ADVANCES Khan, A., Paul, R., Subrina, S. 2017; 7 (80): 50485–95

    View details for DOI 10.1039/c7ra09209a

    View details for Web of Science ID 000414405800009

  • Automatic Bengali Number Plate Reader Shahed, M., Udoy, M., Saha, B., Khan, A., Subrina, S., IEEE IEEE. 2017: 1364–68

    View details for Web of Science ID 000426330001075

  • Thermal Transport in Defected Armchair Graphene Nanoribbon: A Molecular Dynamics Study Noshin, M., Khan, A., Navid, I., Subrina, S., IEEE IEEE. 2017: 2600–2603

    View details for Web of Science ID 000426330002119

  • Thermal transport in graphene/stanene heterobilayer nanostructures with vacancies: an equilibrium molecular dynamics study RSC ADVANCES Khan, A., Paul, R., Subrina, S. 2017; 7 (71): 44780–87

    View details for DOI 10.1039/c7ra07843a

    View details for Web of Science ID 000411662100021

  • Impact of vacancies on the thermal conductivity of graphene nanoribbons: A molecular dynamics simulation study AIP ADVANCES Noshin, M., Khan, A., Navid, I., Uddin, H., Subrina, S. 2017; 7 (1)

    View details for DOI 10.1063/1.4974996

    View details for Web of Science ID 000395789900054

  • Bangla Voice Controlled Robot for Rescue Operation in Noisy Environment Bhattacharjee, A., Khan, A., Haider, M. Z., Fattah, S. A., Chowdhury, D., Sarkar, M., Shahnaz, C., IEEE IEEE. 2016: 3284–88

    View details for Web of Science ID 000400378903087

  • Equilibrium Molecular Dynamics (MD) Simulation Study of Thermal Conductivity of Graphene Nanoribbon: A Comparative Study on MD Potentials ELECTRONICS Khan, A., Navid, I., Noshin, M., Uddin, H., Hossain, F., Subrina, S. 2015; 4 (4): 1109–24

    View details for DOI 10.3390/electronics4041109

    View details for Web of Science ID 000367793000023

https://orcid.org/0000-0003-4635-4667