Browsing by Author "Orlowski, Marius K."

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    Coexistence of filamentary and homogeneous resistive switching with memristive and meminductive memory effects in Al/MnO2/SS thin film metal–insulator–metal device
    Kamble, Girish U.; Shetake, Nitin P.; Yadav, Suhas D.; Teli, Aviraj M.; Patil, Dipali S.; Pawar, Sachin A.; Karanjkar, Milind M.; Patil, Pramod S.; Shin, Jae C.; Orlowski, Marius K.; Kamat, Rajanish K.; Dongale, Tukaram D. (2018-09-19)
    In the present investigation, we have experimentally demonstrated the coexistence of filamentary and homogeneous resistive switching mechanisms in single Al/MnO2/SS thin film metal–insulator–metal device. The voltage-induced resistive switching leads to clockwise and counter-clockwise resistive switching effects. The present investigations confirm that the coexistence of both RS mechanisms is dependent on input voltage, charge-flux and time. Furthermore, the non-zero I–V crossing locations and crossovers hysteresis loops suggested that the developed device has memristive and meminductive properties. The memristive and meminductive memory effects are further confirmed by electrochemical impedance spectroscopy. The results suggested that the mem-device dynamics and electrochemical kinetics during different voltage sweeps and sweep rates are responsible for the coexistence of filamentary and homogeneous resistive switching mechanisms as well as memristive and meminductive memory effect in single Al/MnO2/SS metal–insulator–metal device. The coexistence of both RS effects is useful for the development of high-performance resistive memory and electronic synapse devices. Furthermore, the coexistence of memristive and meminductive memory effects is important for the development of adaptive and self-resonating devices and circuits.
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    Electron tunneling between vibrating atoms in a copper nano-filament
    Al-Mamun, Mohammad Shah; Orlowski, Marius K. (Springer, 2021-04)
    Nanowires, atomic point contacts, and chains of atoms are one-dimensional nanostructures, which display size-dependent quantum effects in electrical and thermal conductivity. In this work a Cu nanofilament of a defined resistance and formed between a Cu and Pt electrode is heated remotely in a controlled way. Depending on the robustness of the conductive filament and the amount of heat transferred several resistance-changing effects are observed. In case of sufficiently fragile nanofilament exhibiting electrical quantum conductance effects and moderate heating applied to it, a dramatic increase of resistance is observed just after the completion of the heating cycle. However, when the filament is allowed to cool off, a spontaneous restoration of the originally set resistance of the filament is observed within less than couple tens of seconds. When the filament is sufficiently fragile or the heating too excessive, the filament is permanently ruptured, resulting in a high resistance of the cell. In contrast, for robust, low resistance filaments, the remote heating does not affect the resistance. The spontaneous restoration of the initial resistance value is explained by electron tunneling between neighboring vibrating Cu atoms. As the vibrations of the Cu atoms subside during the cooling off period, the electron tunneling between the Cu atoms becomes more likely. At elevated temperatures, the average tunneling distance increases, leading to a sharp decrease of the tunneling probability and, consequently, to a sharp increase in transient resistance.
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    Electron Tunneling between Vibrating Cu Atoms in a Cu Filament in a Memristive ReRAM Memory Cell
    Orlowski, Marius K.; Al-Mamun, Mohammad Shah (Springer, 2021-12-01)
    Depending on the amount of heat transport, thermal cross-talk between ReRAM cells of a crossbar array (Fig. 1) may cause permanent or transient erasure of programmed cells by a neighboring cell subject to frequent write/erase cycles. The transient erasure is explained by local temperature dependence of a 3D resistor network built of unit quantum conductance. The process of the spontaneous recovery of the electric conductivity of the conductive filament (CF) is explained as an attenuation of Cu atom vibrations in the CF with the attendant increase of electron tunneling effects for which the variation of the average tunneling distance between the vibrating Cu atoms is proportional to the square root of the absolute temperature. At high temperatures, the average tunneling distance increases, leading to a sharp decrease of the tunneling probability and, consequently, to a sharp increase in transient resistance. The thermal cross-talk allows heat to pass controllably from a neighboring cell to the target cell. The heating of the neighboring cell can be accomplished by application of frequent heating cycles, by selecting the level of compliance current level during the set process, and or by applying a low voltage ramp rate to both the set and reset operation. Here, we focus probed cells as indicated in Fig. 2 that have been set, prior to the heating of a neighboring cell and we monitor the resistance of the probed cell before and after the thermal-cross-talk with the heated cell. We observe several phenomena including a temporary erasure of the target cell and its spontaneous recovery to a preset value. Such spontaneous recovery as a function of time is shown in Fig. 3 90-110 s after the heating of the cell has ceased. The spontaneous recover is explained by 3D resistor model of the CF (see Fig. 5), consisting of identical resistors of Ro=1/Go, where Go is given by the Landauer Go=(2e2/h)×t where t is the tunneling transmission probability between two neighboring Cu atoms. The observation of quantum conductance of our memristive cell is shown in Fig. 4. The tunneling probability t depends exponentially on the local temperature T of the CF and explains the restoration of the initial resistance of the CF after the filament has cooled off. The transient and permanent erasure effects may be mitigated by the use of composite electrodes with high a thermal conductivity.
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    The Investigation of Inorganic Co Based ReRAM Devices and Organic Cu Doped PANI-CSA Top Electrode Based ReRAM Devices
    Li, Yanlong (Virginia Tech, 2020)
    Recently, the resistance switching random access memory (ReRAM) in several MIM systems has been studied extensively for applications to the next generation non-volatile memory (NVM) devices and memristors since the scaling of conventional memories based on floating gate MOSFETs is getting increasingly difficult. ReRAM is being considered one of the most promising candidates for next generation non-volatile memory due to its relatively high switching speed, superior scalability, low power consumption, good retention and simple fabrication method. Cu/TaOX/Pt resistive switching device is a very good candidate due to its well performance and well characterization. However, since platinum (Pt) acting as the inert electrode is not economical efficient for industrial production, a compatible replacement of Pt is highly desirable. The device property of Co based resistive switching devices has been explored in this work. Compared with Pt devices, electric characterization of the fabricated Cu/TaOX/Co devices exhibits very similar FORM, SET and RESET voltages for Cu conductive filaments. However, for the oxygen vacancy (VO) filament the Co device has a significant smaller FORM, SET and RESET voltages of VO filament, which can be partly attributed to the work function difference between Pt and Co of 1.35 V and partly to the impaired integrity properties of Co vs Pt inert electrode. The limit of SET-RESET operations is mainly due to the geometrical shape of the Cu conductive filament is more cylindered rather than Cone-like shape as well as the high Joules heat dissipation. What’s more, ReRAM is also the most promising candidate for a flexible memory, as a variety of materials can be used both inorganics, organics and even hybrid nanocomposites. Besides inorganic ReRAM device, we also fabricated an organic ReRAM device with the structure Cu doped PANI-CSA/O-AA/Al. We have manufactured ReRAM based on Cu-doped PANI-CSA polymer electrode, O-AA as the polymer solid electrolyte and Al as the bottom electrode for the first time. This polymer device shows a significantly lower forming voltage than inorganic ReRAM devices such as Cu/TaOX/Pt. Our results also demonstrate that our organic ReRAM is a promising candidate for inexpensive candidate for inexpensive and environmentally friendly memory devices. We have demonstrated that the FORM operation of the polymer devices depends on the concentration of Cu+ ions as well as the thickness of the polymer electrode.
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    Multiple exposure with image reversal in a single photoresist layer
    (United States Patent and Trademark Office, 2015-08-25)
    Multiple patterned exposures of a single layer of image reversal resist prior to and following image reversal processing, upon development, respond to the respective exposures as either a positive or a negative resist, allowing a desired shape of a resist structure to be built up from any of a number of combinations of primitive masks. Exploiting the image reversal resist in this manner allows several types of diffraction distortion to be entirely avoided and for many sophisticated lithographic processes to he reduced in complexity by one-half or more while any desired resist structure shape can be formed form a limited number of primitive mask patterns. A regimen, which may be automated as an executable algorithm for a computer may be followed to evaluate different combinations of masks which are valid to produce a desired resist structure shape and select the optimum mask pattern combination to do so.
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    Observation of Quantized and Partial Quantized Conductance in Polymer- Suspended Graphene Nanoplatelets
    Kang, Yuhong; Ruan, Hang; Claus, Richard O.; Heremans, Jean J.; Orlowski, Marius K. (SpringerOpen, 2016)
    Quantized conductance is observed at zero magnetic field and room temperature in metal-insulator-metal structures with graphene submicron-sized nanoplatelets embedded in a 3-hexylthiophene (P3HT) polymer layer. In devices with medium concentration of graphene platelets, integer multiples of Go = 2e2/h (=12.91 kΩ−1), and in some devices partially quantized including a series of with (n/7) × Go, steps are observed. Such an organic memory device exhibits reliable memory operation with an on/off ratio of more than 10. We attribute the quantized conductance to the existence of a 1-D electron waveguide along the conductive path. The partial quantized conductance results likely from imperfect transmission coefficient due to impedance mismatch of the first waveguide modes.
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    Performance Degradation of Nanofilament Switching Due to Joule Heat Dissipation
    Al-Mamun, Mohammad Shah; Orlowski, Marius K. (MDPI, 2020-01-09)
    When a memory cell of a Resistive Random Access Memory (ReRAM) crossbar array is switched repeatedly, a considerable amount of Joule heat is dissipated in the cell, and the heat may spread to neighboring cells that share one of the electrode lines with the heat source device. The remote heating of a probed memory cell by another cell allows separating the influence of temperature effects from the impact of the electric field on the resistive switching kinetics. We find that the cell-to-cell heat transfer causes severe degradation of electrical performance of the unheated neighboring cells. A metric for the thermal degradation of the I–V characteristics is established by a specific conditioning of a so-called “marginal” device used as a temperature-sensitive probe of electrical performance degradation. We find that even neighboring cells with no common metal electrode lines with the heated cell suffer substantial electrical performance degradation provided that intermediate cells of the array are set into a conductive state establishing a continuous thermal path via nanofilaments between the heated and probed cells. The cell-to-cell thermal cross-talk poses a serious electro-thermal reliability problem for the operation of a memory crossbar array requiring modified write/erase algorithms to program the cells (a thermal sneak path effect). The thermal cross-talk appears to be more severe in nanometer-sized memory arrays even if operated with ultra-fast, nanosecond-wide voltage/current pulses.
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    Resistive volatile/non-volatile floating electrode logic/memory cell
    (United States Patent and Trademark Office, 2017-10-17)
    A resistive floating electrode device (RFED) provides a logic cell or non-volatile storage or dynamic or static random access memory on an extremely compact matrix with individual cells scalable to the minimum available lithographic feature size regime by providing atomic switches connected in anti-parallel relationship, preferably with a common inert electrode. Programming is facilitated by limiting current to a compliance current level in order to maintain an OB state from which the cell can be written to either the 0 or 1 state. A perfecting feature of the invention provides for selective operation of a cell as a diode or in a volatile or non-volatile storage mode within the same memory array. A series connection of three or more RFEDs in accordance with the invention having different ON state currents, OFF state currents and reset currents can be used as adaptive, neural or chaotic logic cells.
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    Tensile-Strained Ge/InₓGa₁₋ₓAs Heterostructures for Electronic and Photonic Applications
    Clavel, Michael Brian (Virginia Tech, 2015-12-01)
    The continued scaling of feature size in silicon (Si)-based complimentary metal-oxide-semiconductor (CMOS) technology has led to a rapid increase in compute power. Resulting from increases in device densities and advances in materials and transistor design, integrated circuit (IC) performance has continued to improve while operational power (VDD) has been substantially reduced. However, as feature sizes approach the atomic length scale, fundamental limitations in switching characteristics (such as subthreshold slope, SS, and OFF-state power dissipation) pose key technical challenges moving forward. Novel material innovations and device architectures, such as group IV and III-V materials and tunnel field-effect transistors (TFETs), have been proposed as solutions for the beyond Si era. TFETs benefit from steep switching characteristics due to the band-to-band tunneling injection of carriers from source to channel. Moreover, the narrow bandgaps of III-V and germanium (Ge) make them attractive material choices for TFETs in order to improve ON-state current and reduce SS. Further, Ge grown on InₓGa₁₋ₓAs experiences epitaxy-induced strain (ε), further reducing the Ge bandgap and improving carrier mobility. Due to these reasons, the ε-Ge/InₓGa₁₋ₓAs system is a promising candidate for future TFET architectures. In addition, the ability to tune the bandgap of Ge via strain engineering makes ε-Ge/InₓGa₁₋ₓAs heterostructures attractive for nanoscale group IV-based photonics, thereby benefitting the monolithic integration of electronics and photonics on Si. This research systematically investigates the material, optical, and heterointerface properties of ε-Ge/InₓGa₁₋ₓAs heterostructures on GaAs and Si substrates. The effect of strain on the heterointerface band alignment is comprehensively studied, demonstrating the ability to modulate the effective tunneling barrier height (Ebeff) and thus the threshold voltage (VT), ON-state current, and SS in future ε-Ge/InₓGa₁₋ₓAs TFETs. Further, band structure engineering via strain modulation is shown to be an effective technique for tuning the emission properties of Ge. Moreover, the ability to heterogeneously integrate these structures on Si is demonstrated for the first time, indicating their viability for the development of next-generation high performance, low-power logic and photonic integrated circuits on Si.
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    Volatile resistive switching in Cu/TaOx/delta-Cu/Pt devices
    Liu, T.; Verma, Meghna; Kang, Y. H.; Orlowski, Marius K. (AIP Publishing, 2012-08-01)
    A volatile switching of conductive filament (CF) in a Cu/TaOx/delta-Cu/Pt device has been observed. The device differs from a conventional Cu/TaOx/Pt device by the insertion of a thin Cu-layer (delta-Cu) between the electrolyte and the inert electrode. The Cu CF is formed the same way as in the conventional nonvolatile devices. However, when applied voltage becomes zero, CF ruptures spontaneously. The dynamic balance between Cu+ field-supported hopping transport and the Cu self-diffusion explains the effect of CF volatility. The device can operate reliably in volatile and nonvolatile modes. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4746276]