Asir Intisar Khan is a Ph.D. candidate in Electrical Engineering, Stanford University. His research focuses on the design, fabrication, and electro-thermal measurements of novel phase change superlattices and 2D heterostructures for high density, low-power memory both on the flexible and non-flexible platform. His research further expands into pushing these emerging memory technologies towards a novel and large design space for low-power brain-inspired computing. He is also interested in the prospect of these novel superlattices in thermoelectrics and energy harvesting.
Honors & Awards
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)
Traveling, Cooking, Table Tennis
Current Research and Scholarly Interests
· Design, fabrication and characterization of superlattice-like Phase Change Memory (PCM) low power memory application: demonstrated ~8-10x reduction in the switching power compared to conventional PCM
· Interfacial thermoelectric engineering of PCM: Conceptualized and implemented the novel idea of incorporating interfacial thermoelectric heating in a conventional phase-change memory; Realization of ~2x reduction in the switching current density in conventional PCM using thermoelectric material
· Low power flexible nonvolatile memory: Fabrication and characterization of low power non-volatile memory on a flexible platform; achieved record-low switching current for flexible PCM to-date
· Low-power solid-state reflective display: Working on the optimization of low power solid-state reflective display using novel phase change heterostructures
As an aside, I have a general interest in quantum phenomena in nanostructures.
Unveiling the Effect of Superlattice Interfaces and Intermixing on Phase Change Memory Performance.
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.) 2021; 373 (6560): 1243-1247
Fast-Response Flexible Temperature Sensors with Atomically Thin Molybdenum Disulfide.
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
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 2022; 43 (2): 204-207
- Lateral electrical transport and field-effect characteristics of sputtered p-type chalcogenide thin films APPLIED PHYSICS LETTERS 2021; 119 (23)
- Modeling and computation of thermal and optical properties in silicene supported honeycomb bilayer and heterobilayer nanostructures MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING 2021; 129
Uncovering Thermal and Electrical Properties of Sb2Te3/GeTe Superlattice Films.
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 2020; 41 (11): 1657–60
Flexible Low-Power Superlattice-Like Phase Change Memory
2020 Device Research Conference (DRC)
View details for DOI 10.1109/DRC50226.2020.9135166
Large temperature coefficient of resistance in atomically thin two-dimensional semiconductors
Applied Physics Letters
2020; 116 (20)
View details for DOI 10.1063/5.0003312
Flexible Low-Power Superlattice-Like Phase Change Memory
View details for Web of Science ID 000615719100024
Large Temperature Coefficient of Resistance in Atomically Thin 2D Devices
IEEE Device Research Conference (DRC)
View details for DOI 10.1109/DRC46940.2019.9046401
Thermal transport characterization of stanene/silicene heterobilayer and stanene bilayer nanostructures
2018; 29 (18): 185706
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 2018; 5 (2)
- Stanene-hexagonal boron nitride heterobilayer: Structure and characterization of electronic property SCIENTIFIC REPORTS 2017; 7
Stanene-hexagonal boron nitride heterobilayer: Structure and characterization of electronic property.
2017; 7 (1): 16347
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 2017; 7 (10)
- Characterization of thermal and mechanical properties of stanene nanoribbons: a molecular dynamics study RSC ADVANCES 2017; 7 (80): 50485–95
Automatic Bengali Number Plate Reader
IEEE. 2017: 1364–68
View details for Web of Science ID 000426330001075
Thermal Transport in Defected Armchair Graphene Nanoribbon: A Molecular Dynamics Study
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 2017; 7 (71): 44780–87
- Impact of vacancies on the thermal conductivity of graphene nanoribbons: A molecular dynamics simulation study AIP ADVANCES 2017; 7 (1)
Bangla Voice Controlled Robot for Rescue Operation in Noisy Environment
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 2015; 4 (4): 1109–24