Interview with Lambert Alff about his current research topics (in German)

• 2020/11/26

  Cover in Advanced Electronic Materials

  

  Mimicking the human brain with oxygen-engineered yttria-based memory cells go

• 2020/11/17

  Doctoral graduation of Mohanad Al-Mamoori

  

  RMU Doctoral graduation in the ATFT group go

• 2020/09/08

  Doctoral graduation of Lukas Zeinar

  

  Topic: “Dielektrika in epitaktischen Volloxid-Varaktoren für Mikrowellen-Anwendungen” go

• 2020/07/23

  Doctoral graduation of Patrick Salg

  

  Topic: “Interfaces in all-oxide thin-film varactors with highly-conducting SrMoO₃ electrodes for microwave applications” go

• 2020/07/21

  Induction of uniaxial anisotropy by controlled phase separation in Y-Co thin films

  

  Within the new Collaborative Research Center CRC/TRR 270, a method to induce uniaxial anisotropy in materials with easy-plane anisotropy has been shown, in close collaboration with the advanced electron microscopy and the micromagnetic simulation groups. go

• 2020/06/24

  Cover in Advanced Materials Interfaces

  

  Solid Electrolyte Interfaces: The Effect of Interfacial Charge Distribution on Chemical Compatibility and Stability of the High Voltage Electrodes (LiCoPO₄, LiNiPO₄)/Solid Electrolyte (LiPON) Interface go

• 2020/05/08

  In the top 10%

  Our paper is among the top 10% most downloaded papers within the first 12 month after online publication in the last two years in Advanced Electronic Materials. Wow! go

• 2020/04/20

  Doctoral graduation of Shalini Sharma in a video conference

  

  Topic: “Structural and magnetic properties of epitaxial rare-earth cobalt thin films” go

• 2020/03/25

  Signposts for tiny lightning strikes

  

  Memory chips for the next computer generations

  Researchers in Darmstadt around materials scientists Professor Lambert Alff and Professor Leopoldo Molina-Luna are developing memory devices for a new type of chip. go

• 2019/12/13

  Doctoral graduation of Stefan Petzold

  

  Topic: “Defect Engineering in Transition Metal Oxide-Based Resistive Random Access Memory”. go

• 2019/12/05

  APL Materials Excellence in Research Award for Patrick Salg

  

  Dr. Leopoldo Molina-Luna receives the APL Materials Excellence in Research award on behalf of Patrick Salg in Boston, 4th December 2019. go

• 2019/12/04

  EFECS2019 Pilot Lines Impact Workshop

  

  A meeting at highest European level. go

• 2019/12/03

  2nd Symposium within the Joint Graduate Program with Tohoku University in Sendai, Japan

  

  Paving the way for early career exchange with a renowned Japanese university. go

• 2019/11/27

  ALOVA team is a double winnier in the Science4Life Venture Cup

  

  A team from Advanced Thin Film Technology wins two renowned prizes for startup ideas and concepts. go

• 2019/10/30

  Non-Volatile Memory Technology Symposium 2019

  

  Lambert Alff gave an Invited Talk at the NVMTS in Durham, North Carolina. go

• 2019/10/15

  Doctoral graduation of Philipp Kehne

  

  Topic: “Electrochemical investigations of sodium solid state batteries using sodium cobaltate thin film cathodes.” go

• 2019/10/10

  Back Cover in Advanced Electronic Materials

  

  Forming-Free Grain Boundary Engineered Hafnium Oxide Resistive Random Access Memory Devices go

26th International Workshop on Oxide Electronics in Kyoto

The 2019 edition of the International Workshop on Oxide Electronics took place in the historical capital of Japan, Kyoto. The aim of the workshop is to provide an interdisciplinary forum for researchers – theorists as well as experimentalists – on understanding the fundamental electronic and structural properties and also on the design, synthesis, processing, characterization, and applications of (epitaxial) functional oxide materials. The ATFT group presented the work on all-oxide varactor as tunable microwave component needed in mobile communication. A group photo of the participants can be downloaded here.

Forming-Free Grain Boundary Engineered Hafnium Oxide Resistive Random Access Memory Devices

S. Petzold, A. Zintler, R. Eilhardt, E. Piros, N. Kaiser, S. U. Sharath, T. Vogel, M. Major, K. P. McKenna, L. Molina‐Luna, L. Alff

Adv. Electron. Mater., 5, 1900484 (2019)
doi: 10.1002/aelm.201900484

Within the project of WAKeMeUP and in close collaboration with the Advanced Electron Microscopy division of Dr. Molina-Luna, a new method of directed defect engineering has been developed, namely grain boundary engineering.

With this new method it is possible to create low energy grain boundaries of high symmetry which thread the whole dielectric layer, thus, providing a defined path for facilitated filament formation. This method renders forming free devices with a narrow distribution of forming voltages which makes it a powerful tool to overcome one of the main challenges for resistive switching devices: device-to-device variation. An exemplary transmission electron microscopy image and further analysis of the engineered grain boundaries is depicted in the Figure.

Interviews with Lambert Alff and Leo Molina-Luna on the occasion of the E-MRS 2019

Interviews with Lambert Alff and Leo Molina from E-MRS-TV are now online.

Analysis and simulation of the multiple resistive switching modes occurring in HfOₓ-based resistive random access memories using memdiodes

S. Petzold, E. Miranda, S. U. Sharath,, J. Muñoz-Gorriz, T. Vogel E. Piros, N. Kaiser, R. Eilhardt, A. Zintler, L. Molina-Luna, J. Suñé, and L. Alff

J. Appl. Phys. 125, 234503 (2019)
doi: 10.1063/1.5094864

Within the project of WAKeMeUP and in cooperation with Prof. Miranda, a simulation of all observed switching modes reported for hafnium oxide based resistive switching devices has been achieved.
Comparing stoichiometric vs. highly deficient hafnia devices by compact simulation, we found that a single or two memdiodes connected in anti-series can be utilized to simulate all reported switching modes. We found that all switching modes of the stoichiometric device could be simulated utilizing only one memdiode, while for the deficient device a second memdiode in opposite polarity was necessary to fit its switching modes. By correlating the different interfaces to the two memdiodes taken for compact simulation, we were able to gain additional information of the switching process, as e.g. the voltage drop at the individual interfaces.

Tunable capacitors based on all-oxide technology supported by the Pioneer Fund

We received supporting by the Pioneer Fund program for our project ALOVA. Our two PhD students Patrick Salg and Lukas Zeinar are working within an interdisciplinary project together with Prof. Jakoby’s group of Mikrowellentechnik on tunable capacitors (varactors) based on SrMoO₃ bottom electrodes. This approach allows an epitaxial growth of all-oxide heterostructures. This leads to lower defect densities and thus allowing lower tuning voltage extending battery lifetime. This technology could replace expensive platinum based applications in mobile 5G communication.
See Latest News (german) on the TU-Darmstadt homepage.

15th Meeting of the working group materials for nonvolatile memories of the GMM – VDE/VDI at TU Darmstadt

The working group materials for non-volatile memories headed by Thomas Mikolajick deals with current research topics in the field of highly integrated semiconductor memories and future memory cell concepts. One important aspect is the investigation of emerging memories such as phase change, resistive switching and ferroelectric memories. The group covers developments from materials, to devices and systems. From TU Darmstadt ATFT and AEM are jointly involved in the research of HfO₂ based memory cells from structure to function.

Editor’s pick in APL Materials: Our latest article in oxide electronics

Our article on an all-oxide device based on our special material SrMoO₃ which has a higher conductivity than platinum has been chosen editor’s pick by the renowned journal APL Materials. In the paper with the title “Atomically interface engineered micrometer-thick SrMoO₃ oxide electrodes for thin-film BaxSr_1-xTiO₃ ferroelectric varactors tunable at low voltages”, a joint work between ATFT, AEM and IMP we explain the growth (see individual atoms in the figure) of this extraordinary material in devices for application in smart antenna in mobile communication. We congratulate Patrick Salg, Dominik Walk and Lukas Zeinar to their successful work!

P. Salg, D. Walk, L. Zeinar, A. Radetinac, L. Molina-Luna, A. Zintler, R. Jakoby, H. Maune, P. Komissinskiy, and L. Alff
APL Materials 7, 051107 (2019)
doi: 10.1063/1.5094855

Prize for outstanding dissertation 2018 for Dr. Sharath

We are proud to announce that Dr. Sharath Ulhas has received a prize for outstanding scientific achievements within the best dissertation of the Materials Science department in 2018. This prize is part of a new funding concept of the association “Freunde der TU Darmstadt” that took effect for the first time in 2014.

Dr. Sharath graduated about novel non-volatile memory for energy-efficient data storage (see Adv. Funct. Mater. 27, 1700432 (2017), doi: 10.1002/adfm.201700432, Video Abstract).
He is now working at Micron Technology, a world-leading computer memory company. Dr. Sharath said: “My thesis got me my job.” Congratulations!

Gradual Reset and Set Characteristics in Yttrium Oxide based Resistive Random Access Memory

S. Petzold, E. Piros, S. U. Sharath, A. Zintler, E. Hildebrandt, L. Molina-Luna, C. Wenger, and L. Alff

Semicond. Sci. Technol., 34, 075008 (2019)
doi: 10.1088/1361-6641/ab220f

Within the project of WAKeMeUP (https://www.ecsel.eu/projects/wakemeup), funded by BMBF and ECSEL JU, we investigated the resistive switching behavior of yttrium oxide based devices.

In this study, we report for the first time the coexistence of bipolar resistive switching and unipolar resistive switching within one stack combination based on yttrium oxide. The BRS is characterized by low variability, good data retention, high DC endurance, and average on-off-ratio above 100.

The obtained concurrent gradual transitions during BRS set and reset which have been employed in pulse depression and potentiation operations (see figure) with shown plasticity over about two orders of magnitude make RRAM based on yttrium oxide an interesting alternative candidate for neuromorphic synapses. Combined with its characteristic of being forming-free and having low operation voltages, RRAM based on yttrium oxide is highlighted as a suitable material candidate for new high density nonvolatile memory technologies.

Heavy Ion Radiation Effects on Hafnium Oxide based Resistive Random Access Memory

S. Petzold, S.U. Sharath, J. Lemke, E. Hildebrandt, C. Trautmann, and L. Alff

IEEE Trans. Nucl. Sci., Early Access (2019)
doi: 10.1109/TNS.2019.2908637

Within the project of WAKeMeUP, funded by BMBF and ECSEL JU, we investigated the effect of ionizing radiation on resistive switching devices based on hafnium oxide.

Devices were exposed to high energetic heavy ion irradiation with Energies of 5.6 MeV per nucleus resulting in an overall Ion energy of 1.1 GeV. The effect of heavy ion irradiation on different electrical statistics of RRAM devices was investigated showing extraordinary data retention towards ionizing radiation. The written information was found to be stable up to very high total ionization doses of up to 880 Mrad. As a result, RRAM devices based on hafnium oxide are a very interesting candidate for application in high-dose environments, as for example in satellites or other space applications.

Modelling of the vertical deflection of ferroelectric bending tongues loaded at their free end

Juliette Cardoletti, Aldin Radetinac, Daniel Thiem, Julian Walker, Philipp Komissinskiy, Bai-Xiang Xu, Helmut Schlaak, Susan Trolier-McKinstry, and Lambert Alff

AIP Advances 9, 025017 (2019)
doi: 10.1063/1.5082392

Ferroelectric bending tongues loaded at their free end have been modelled to calculate their vertical deflection. The model relies on a ferroelectric switching criterion and on the Euler-Bernoulli beam theory. It takes into account the geometry of the bending tongue, the mechanical and piezoelectric material properties, the applied electrical field, the crystallographic state of the ferroelectric thin film and its built-in strain. The developed model differentiate the different contributions to the bending tongue vertical deflection. The results are characteristic of a ferroelectric with the modelled butterfly loop incorporating strain saturation at high electrical field. It allows accurate estimates of the vertical deflection for ferroelectric bending tongue based applications and show the importance of the ferroelectric thin film crystallographic orientation.

Electrochemical Performance of All-Solid-State Sodium-Ion Model Cells with Crystalline NaₓCoO₂ Thin-Film Cathodes

All-solid-state sodium batteries are attractive due to the abundance of sodium and advantageous for safe battery operation by avoiding flammable organics and liquids and suppressed dendrite formation. Herein, we present a Na_xCoO₂/Nasicon/Na thin-film model sodium solid-state battery using a Sc-substituted Nasicon solid electrolyte. Excellent chemical stability of this solid electrolyte at high voltages of up to 4.2 V increases the accessible sodium (de)intercalation range and battery capacity. Direct extraction of the interface resistances between the electrode materials of the thin-film model cell using electrochemical impedance spectroscopy gives a unique opportunity of correlation the electrochemical performance with properties of electrode materials and their interfaces.

doi: 10.1016/j.jpowsour.2018.10.089
doi: 10.1149/2.0491903jes

Oxide electronics on top

The 25^th International Workshop on Oxide Electronics took place in the mountains of Switzerland. During the interdisciplinary workshop the state-of-the-art of mostly epitaxial functional oxide materials and their potential for electronic application are discussed. The ATFT group was represented by Patrick Salg, Lukas Zeinar and Lambert Alff. Former group member Vikas Shabadi now working for his own technology company also joined the foto. Our contributions to the conference were focusing on the perovskite SrMoO₃ as outstanding electrode material for high-frequency devices.

Doctoral graduation in the ATFT group

We congratulate our colleague Sharath S. Ulhas to his outstanding doctoral defense (January 31,2018). The title of his PhD thesis is Defect engineering in HfO₂/TiN-based resistive random access memory (RRAM) devices by reactive molecular beam epitaxy. As external examiners we had Thomas Schroeder (IKZ Berlin) and Klaus Hofmann (Electrical Engineering department of TU Darmstadt) as our guests. The defense was followed by a social event with food catering in the presence of Dr. Sharath’s parents and wife which traveled all the way from India and US. We are extremely thankful to Sharath for his remarkable advances in science and for having been a much valued member of our research group. We look forward to continuing scientific exchange and wish him all the best for his future career!