All Publications

  • Spatially-Resolved Thermometry of Filamentary Nanoscale Hot Spots in TiO2 Resistive Random Access Memories to Address Device Variability. ACS applied electronic materials Swoboda, T., Gao, X., Rosário, C. M., Hui, F., Zhu, K., Yuan, Y., Deshmukh, S., Köroǧlu, Ç., Pop, E., Lanza, M., Hilgenkamp, H., Rojo, M. M. 2023; 5 (9): 5025-5031


    Resistive random access memories (RRAM), based on the formation and rupture of conductive nanoscale filaments, have attracted increased attention for application in neuromorphic and in-memory computing. However, this technology is, in part, limited by its variability, which originates from the stochastic formation and extreme heating of its nanoscale filaments. In this study, we used scanning thermal microscopy (SThM) to assess the effect of filament-induced heat spreading on the surface of metal oxide RRAMs with different device designs. We evaluate the variability of TiO2 RRAM devices with area sizes of 2 × 2 and 5 × 5 μm2. Electrical characterization shows that the variability indicated by the standard deviation of the forming voltage is ∼2 times larger for 5 × 5 μm2 devices than for the 2 × 2 μm2 ones. Further knowledge on the reason for this variability is gained through the SThM thermal maps. These maps show that for 2 × 2 μm2 devices the formation of one filament, i.e., hot spot at the device surface, happens reliably at the same location, while the filament location varies for the 5 × 5 μm2 devices. The thermal information, combined with the electrical, interfacial, and geometric characteristics of the device, provides additional insights into the operation and variability of RRAMs. This work suggests thermal engineering and characterization routes to optimize the efficiency and reliability of these devices.

    View details for DOI 10.1021/acsaelm.3c00782

    View details for PubMedID 37779889

    View details for PubMedCentralID PMC10537448

  • Ambipolar Thickness-Dependent Thermoelectric Measurements of WSe2. Nano letters Chen, V., Lee, H. R., Köroğlu, Ç., McClellan, C. J., Daus, A., Pop, E. 2023


    Thermoelectric materials can harvest electrical energy from temperature gradients, and could play a role as power supplies for sensors and other devices. Here, we characterize fundamental in-plane electrical and thermoelectric properties of layered WSe2 over a range of thicknesses, from 10 to 96 nm, between 300 and 400 K. The devices are electrostatically gated with an ion gel, enabling us to probe both electron and hole regimes over a large range of carrier densities. We extract the highest n- and p-type Seebeck coefficients for thin-film WSe2, -500 and 950 μV/K respectively, reported to date at room temperature. We also emphasize the importance of low substrate thermal conductivity on such lateral thermoelectric measurements, improving this platform for future studies on other nanomaterials.

    View details for DOI 10.1021/acs.nanolett.2c03468

    View details for PubMedID 37141159

  • Nanoscale temperature sensing of electronic devices with calibrated scanning thermal microscopy. Nanoscale Swoboda, T., Wainstein, N., Deshmukh, S., Koroglu, C., Gao, X., Lanza, M., Hilgenkamp, H., Pop, E., Yalon, E., Munoz Rojo, M. 2023


    Heat dissipation threatens the performance and lifetime of many electronic devices. As the size of devices shrinks to the nanoscale, we require spatially and thermally resolved thermometry to observe their fine thermal features. Scanning thermal microscopy (SThM) has proven to be a versatile measurement tool for characterizing the temperature at the surface of devices with nanoscale resolution. SThM can obtain qualitative thermal maps of a device using an operating principle based on a heat exchange process between a thermo-sensitive probe and the sample surface. However, the quantification of these thermal features is one of the most challenging parts of this technique. Developing reliable calibration approaches for SThM is therefore an essential aspect to accurately determine the temperature at the surface of a sample or device. In this work, we calibrate a thermo-resistive SThM probe using heater-thermometer metal lines with different widths (50 nm to 750 nm), which mimic variable probe-sample thermal exchange processes. The sensitivity of the SThM probe when scanning the metal lines is also evaluated under different probe and line temperatures. Our results reveal that the calibration factor depends on the probe measuring conditions and on the size of the surface heating features. This approach is validated by mapping the temperature profile of a phase change electronic device. Our analysis provides new insights on how to convert the thermo-resistive SThM probe signal to the scanned device temperature more accurately.

    View details for DOI 10.1039/d3nr00343d

    View details for PubMedID 37006192

  • High Thermal Conductivity Insulators for Thermal Management in 3D Integrated Circuits IEEE ELECTRON DEVICE LETTERS Koroglu, C., Pop, E. 2023; 44 (3): 496-499
  • Approaching the quantum limit in two-dimensional semiconductor contacts. Nature Li, W., Gong, X., Yu, Z., Ma, L., Sun, W., Gao, S., Köroğlu, Ç., Wang, W., Liu, L., Li, T., Ning, H., Fan, D., Xu, Y., Tu, X., Xu, T., Sun, L., Wang, W., Lu, J., Ni, Z., Li, J., Duan, X., Wang, P., Nie, Y., Qiu, H., Shi, Y., Pop, E., Wang, J., Wang, X. 2023; 613 (7943): 274-279


    The development of next-generation electronics requires scaling of channel material thickness down to the two-dimensional limit while maintaining ultralow contact resistance1,2. Transition-metal dichalcogenides can sustain transistor scaling to the end of roadmap, but despite a myriad of efforts, the device performance remains contact-limited3-12. In particular, the contact resistance has not surpassed that of covalently bonded metal-semiconductor junctions owing to the intrinsic van der Waals gap, and the best contact technologies are facing stability issues3,7. Here we push the electrical contact of monolayer molybdenum disulfide close to the quantum limit by hybridization of energy bands with semi-metallic antimony ([Formula: see text]) through strong van der Waals interactions. The contacts exhibit a low contact resistance of 42 ohm micrometres and excellent stability at 125 degrees Celsius. Owing to improved contacts, short-channel molybdenum disulfide transistors show current saturation under one-volt drain bias with an on-state current of 1.23 milliamperes per micrometre, an on/off ratio over 108 and an intrinsic delay of 74 femtoseconds. These performances outperformed equivalent silicon complementary metal-oxide-semiconductor technologies and satisfied the 2028 roadmap target. We further fabricate large-area device arrays and demonstrate low variability in contact resistance, threshold voltage, subthreshold swing, on/off ratio, on-state current and transconductance13. The excellent electrical performance, stability and variability make antimony ([Formula: see text]) a promising contact technology for transition-metal-dichalcogenide-based electronics beyond silicon.

    View details for DOI 10.1038/s41586-022-05431-4

    View details for PubMedID 36631650

  • 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

  • Substrate-dependence of monolayer MoS2 thermal conductivity and thermal boundary conductance JOURNAL OF APPLIED PHYSICS Gabourie, A. J., Koroglu, C., Pop, E. 2022; 131 (19)

    View details for DOI 10.1063/5.0089247

    View details for Web of Science ID 000827597400006

  • Direct measurement of nanoscale filamentary hot spots in resistive memory devices. Science advances Deshmukh, S., Rojo, M. M., Yalon, E., Vaziri, S., Koroglu, C., Islam, R., Iglesias, R. A., Saraswat, K., Pop, E. 2022; 8 (13): eabk1514


    Resistive random access memory (RRAM) is an important candidate for both digital, high-density data storage and for analog, neuromorphic computing. RRAM operation relies on the formation and rupture of nanoscale conductive filaments that carry enormous current densities and whose behavior lies at the heart of this technology. Here, we directly measure the temperature of these filaments in realistic RRAM with nanoscale resolution using scanning thermal microscopy. We use both conventional metal and ultrathin graphene electrodes, which enable the most thermally intimate measurement to date. Filaments can reach 1300°C during steady-state operation, but electrode temperatures seldom exceed 350°C because of thermal interface resistance. These results reveal the importance of thermal engineering for nanoscale RRAM toward ultradense data storage or neuromorphic operation.

    View details for DOI 10.1126/sciadv.abk1514

    View details for PubMedID 35353574

  • High-performance flexible nanoscale transistors based on transition metal dichalcogenides NATURE ELECTRONICS Daus, A., Vaziri, S., Chen, V., Koroglu, C., Grady, R. W., Bailey, C. S., Lee, H., Schauble, K., Brenner, K., Pop, E. 2021
  • Analysis of Field-Effect Passivation in Textured and Undiffused Silicon Surfaces PHYSICAL REVIEW APPLIED Turkay, D., Koroglu, C., Yerci, S. 2019; 12 (3)