David Nminibapiel

Intel (United States)

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Helmut Baumgart

Thomas Jefferson National Accelerator Facility

Pragya R. Shrestha

Theiss Research

Kin P. Cheung

Center for Nanoscale Science and Technology

J. P. Campbell

National Institute of Standards and Technology

Madhavi Tangirala

Old Dominion University

Vladimir Kochergin

MicroXact (United States)

Dmitry Veksler

HRL Laboratories (United States)

Jason T. Ryan

National Institute of Standards and Technology

Kai Zhang

University of Göttingen

Christian Kübel

Karlsruhe Institute of Technology

Cooperative Institutions

Intel (United States)

Old Dominion University

National Institute of Standards and Technology

Dominion University College

National Institute of Standards

Thomas Jefferson National Accelerator Facility

Physical Measurement Laboratory

Pennsylvania State University

IMEC

Arizona State University

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ZnS Films Deposited by ALD for Solar Cell Applications

ECS Transactions (2013)

Yunus Erkaya David Nminibapiel Krishna Aryal Nitin Hegde Grace Rajan

Alternative deposition methods and materials are of interest for the fabrication of thin film solar cells since they offer potential enhancements for either low cost, high speed or high efficiency but also because they can help in better understanding the underlying physical and chemical processes that could lead to the next generation of solar cells. In this study, we will present new results on the deposition of ZnS by atomic layer deposition (ALD) as an alternate to CdS deposited by chemical bath deposition. More specifically, in-situ real time and ex-situ measurements by spectroscopic ellipsometry will be performed, allowing for the analysis of the growth processes as a function of deposition parameters. These measurements also allow for a parameterization of the dielectric functions of ZnS and the evolution of its grain size and band gap as a function of thickness. These measurements will then be correlated with ex-situ measurements, such as XRD, AFM and T&R, which is expected to validate the model used for spectroscopic ellipsometry data analysis.

Ellipsometry

Deposition

Chemical bath deposition

10.1149/05051.0045ecst

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Citations (2)

(Invited) Compliance-Free Pulse Forming of Filamentary RRAM

Meeting abstracts/Meeting abstracts (Electrochemical Society. CD-ROM) (2016)

Pragya R. Shrestha David Nminibapiel J. H. Kim Helmut Baumgart Kin P. Cheung

Despite the overwhelming effort to improve the efficacy of resistive random access memory (RRAM), the underlying physics governing RRAM operation have proven elusive. Consequently, substantial effort has been spent to empirically develop transition metal oxide (filamentary) RRAM structures which exhibit reasonable behavior [1,2]. A survey of the recent literature almost universally indicates that the remaining glaring issues center around device variability as well as endurance. Perhaps the only consensus in the RRAM community is that these issues are linked to the forming process [2,3]. The forming process is an initial conditioning step in which voltage is applied across the dielectric stack to form, or break-down, the oxide via the formation of a resistive filament [2,3]. The forming process is thought to greatly determine the subsequent behavior of the device [2,3]. Thus, the vast majority of this presentation will detail our recent efforts to bring the forming process under control and the resulting improvements in RRAM viability in HfO 2 -based devices. The vast majority of efforts to control the forming process all involve the inclusion of an additional series resistor element to limit the current that flows through the RRAM during forming (compliance). Our efforts show that even the most careful series resistor implementation still invokes a serious forming variability due to the unavoidable parasitic capacitance [4]. These parasitics introduce a current overshoot which greatly alters the ability to terminate forming (i.e. a large current continues to flow through the filament for some uncontrollable time before the compliance element can clamp) [4]. This introduces a relatively large uncertainty in the forming energy ((forming voltage) x (current) x (time)) and consequent variability in the filament [5]. This pitfall can be avoided by removing all current compliance elements, and their associated parasitics, and utilizing ultrashort voltage pulses to induce forming [5,6]. In this approach, the forming process can occur uncontrolled at any point in time during the voltage pulse. However, utilization of the ultrashort pulse width minimizes the timing uncertainty and bring the forming energy under control [5]. One can, of course, invoke multi-pulse approaches to further tune the forming energy to the specific RRAM device stack [5]. Using this approach, we show for nominally identical RRAM devices, varying the forming energy using ~100 ps pulses can greatly alter the variability as measured via the endurance window [5]. In extreme cases, we show that a change in forming energy can effectively open up an endurance window in a device which was unusable using more traditional forming methods [5]. In addition, we show (figure 1) further improvement in endurance when applying multiple pulse forming schemes to “tune” the forming energy to the desired value and consequent endurance [5]. In summary, we describe a new compliance-free RRAM forming technique that greatly enhances the energy control of the forming process and improves the device endurance characteristics proportionately. [1] Y. Shimeng, et al. , IEDM, pp. 26.1.1 (2012) [2] B. Butcher, et al. , IIRW, pp. 146 (2011) [3] A. Kalantarian, IRPS, pp. 6C.4.1 (2012) [4] P. Shrestha, et al. , IIRW, pp. 55 (2013) [5] P. Shrestha, et al. , IRPS, pp. MY.10.1 (2014) [6] P. Shrestha, et al., VLSI-TSA, pp. TR82 (2014) Figure 1

Overshoot (microwave communication)

Electroforming

10.1149/ma2016-02/37/2324

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Accurate RRAM transient currents during forming

Pragya R. Shrestha David Nminibapiel J. P. Campbell Jin‐Hyuk Kim C. A. F. Vaz

The magnitude of overshoot current during forming has been shown to be a serious issue. Recently we showed that the overshoot duration is equally important in impacting device performance. Shorter duration overshoot in the range of ns yields better performance, suggesting extremely short forming pulse to be desirable. But investigation of such short forming transients is severely limited experimentally due to parasitic. In this study we demonstrate a technique to accurately de-embed these parasitic components yielding accurate forming current transients in the ps range, paving the road to careful study of the forming process.

Overshoot (microwave communication)

Transient (computer programming)

Rise time

10.1109/vlsi-tsa.2014.6839688

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Citations (5)

Parasitic engineering for RRAM control

Solid-State Electronics (2018)

Pragya R. Shrestha David Nminibapiel Dmitry Veksler J. P. Campbell Jason T. Ryan

Overshoot (microwave communication)

Parasitic capacitance

10.1016/j.sse.2018.10.006

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Citations (5)

ALD Growth of PbTe and PbSe Superlattices for Thermoelectric Applications

ECS Transactions (2013)

Kai Zhang Arun Deepak Ramalingom Pillai David Nminibapiel Madhavi Tangirala Venkata Sai Kiran Chakravadhanula

For this study PbTe and PbSe thin films have been prepared on silicon substrates with native oxide by Atomic Layer Deposition (ALD) using lead (II)bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (Pb(C 11 H 19 O 2 ) 2 ), (trimethylsilyl) telluride ((Me 3 Si) 2 Te) and bis-(triethyl silyl) selane ((Et 3 Si) 2 Se) as ALD precursors for lead, tellurium and selenium . Instead of classic layer by layer ALD growth the initial ALD nucleation of lead telluride was found to follow the Vollmer-Weber island growth model. We found a strong dependence of the nucleation process on the temperature. In this project, we present the optimized conditions for growing PbTe and PbSe thin films within the ALD process window range of 170 °C to 210 °C and discuss early nanolaminate structures. Results of various physical characterizations techniques and analysis are reported.

Lead telluride

Tellurium

Telluride

Chalcogen

Cadmium telluride photovoltaics

10.1149/05810.0131ecst

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Citations (10)

Microstructure Analysis of ALD Bi₂Te₃/Sb₂Te₃ Thermoelectric Nanolaminates

ECS Transactions (2013)

David Nminibapiel Kai Zhang Madhavi Tangirala Helmut Baumgart Venkata Sai Kiran Chakravadhanula

The fabrication of thermoelectric nanolaminate structures of alternating Bi 2 Te 3 and Sb 2 Te 3 ALD layers for thermoelectric application is reported. Trimethylsilyl telluride ((Me 3 Si) 2 Te), bismuth trichloride (BiCl 3 ) and antimony trichloride (SbCl 3 ) were utilized as chemical ALD precursors for tellurium, bismuth and antimony, respectively. The results of field emission scanning electron microscopy (FE-SEM) indicate that both metal tellurides exhibit the prevalent Volmer-Weber island growth mechanism with characteristic hexagonal crystallites. High resolution TEM X-section analysis reveals localized epitaxial growth of alternating ALD Bi 2 Te 3 and Sb 2 Te 3 layers within the large islands.

Bismuth

Tellurium

Bismuth telluride

Antimonide

10.1149/05810.0059ecst

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Citations (4)

Synthesis of VO₂ Thin Films by Atomic Layer Deposition with TEMAV as Precursor

ECS Transactions (2013)

Kai Zhang Madhavi Tangirala David Nminibapiel Wei Cao Venkateswara Pallem

Synthesis and growth of Vanadium dioxide on Silicon substrates has been investigated by Atomic Layer Deposition (ALD). ALD Vanadium oxide films were synthesized by using the novel Tetrakis[ethylmethylamino] vanadium {V(NEtMe)4} [TEMAV], as the vanadium precursor source and H2O vapor as the oxidizing source. The as-prepared ALD thin films were amorphous due to low temperature growth at 150 oC and exhibit a mixture of V2O5 and VO2 phases, which originiate from the V4+ and V5+ valence states of Vanadium found in the initially amorphous ALD thin film. We found that VO2 formation is strongly dependent on the amount of pressure and oxygen. The VO2 films were formed at 450 -500 oC and with an oxygen flow rate of less than 1 sccm in a vacuum of 2.7 E-2 Torr. ALD VO2 films, after furnace annealing, demonstrate well-formed roundish grains. The ALD VO2 thin films yielded an rms roughness of 3 nm by AFM analysis and are random polycrystalline after annealing.

Vanadium Oxide

Oxidizing agent

Torr

10.1149/05013.0175ecst

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Citations (26)

The Efficacy of Programming Energy Controlled Switching in Resistive Random Access Memory (RRAM)

David Nminibapiel

Random access

10.25777/b5dj-7c62

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Citations (1)

VO₂ Films Prepared by Atomic Layer Deposition and RF Magnetron Sputtering

ECS Transactions (2013)

Madhavi Tangirala Kai Zhang David Nminibapiel Venkateswara Pallem Christian Dussarrat

Among the many vanadium suboxides and different stoichiometries, VO 2 has received considerable attention due to its remarkable metal-insulator transition (MIT) behavior, which causes a significant reversible change in its electrical and optical properties occurring across the phase transition at 67 ºC. The initially amorphous VO 2 thin films were fabricated by the emerging, Atomic Layer Deposition (ALD) technique with (tetrakis[ethylmethylamino]vanadium) {V(NEtMe) 4 } as precursor and H 2 O vapor as oxidation agent. For benchmarking we have also used the RF Magnetron Sputtering technique to deposit metallic vanadium thin films, which were later oxidized during furnace annealing. Post annealing of the as-deposited ALD films was performed in order to obtain the technologically important form of crystallized VO 2 thin films using furnace annealing. All film depositions were carried out on native oxide covered (100) Si substrates. The conditions for successful furnace annealing are reported in terms of temperature and annealing gas composition and the physical characterization results are presented.

Stoichiometry

Vanadium Oxide

Cavity magnetron

10.1149/05810.0049ecst

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Citations (3)

Energy control paradigm for compliance-free reliable operation of RRAM

Pragya R. Shrestha David Nminibapiel Jin‐Hyuk Kim Joe Campbell Kin P. Cheung

We demonstrate reliable RRAM operation by controlling the forming energy via short voltage pulses (picosecond range) which eliminates the need for a current compliance element. We further show that the dissipated energy during forming and SET/RESET processes plays a critical role. The SET/RESET cycling endurance of thus formed devices is shown to also be dependent on the SET/RESET energy. Multiple-pulse forming is also investigated as a method to further tighten the control of forming energy with promising endurance results.

Reset (finance)

Picosecond

10.1109/irps.2014.6861164

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Citations (11)