1. 13th Nanoscience and Nanotechnology Conference NANOTR-13 2017, Antalya, TURKEY (oral presentation)
Kaan Özbozduman, Vedat Karakas, Aisha Gokce, Ali Taha Habiboglu, Sevdenur Arpaci, Ibrahim Cinar, Cenk Yanik, Riccardo Tomasello, Silvia Tacchi, Giulio Siracusano, Mario Carpentieri, Giovanni Finocchio, Thomas Hauet and Ozhan Ozatay
“Stabilization of Magnetic Radial Vortex Structure in Pt-CoFeB-TiMultilayer Stack”
2. 13th Nanoscience and Nanotechnology Conference NANOTR-13 2017, Antalya, TURKEY (oral presentation)
Taha Can Dikici, Kaan Özbozduman, Ali Taha Habiboglu, Ozhan Ozatay
“Nucleation and Annihilation of Isolated Neel Skyrmions via Conductive Atomic Force Microscopy at Room Temperature”
3. 13th Nanoscience and Nanotechnology Conference 2017 NANOTR-13, Antalya, TURKEY (poster presentation)
Ibrahim Cinar, Francois Montaigne, Nicolas Reyren, K. Bouzehouane, D. Maccariello, W. Legrand, Vito Puliafito, Giovanni Finocchio, Ozhan Ozatay and Thomas Hauet
“Magnetic bubble stabilization in wire induced by current pulses”
4. 13th Nanoscience and Nanotechnology Conference 2017 NANOTR-13, Antalya, TURKEY (oral presentation)
Ibrahim Cinar, Francois Montaigne, Nicolas Reyren, K. Bouzehouane, D. Maccariello, W. Legrand, Vito Puliafito, Giovanni Finocchio, Ozhan Ozatay and Thomas Hauet
“Magnetic bubble nucleation in a Spin-Valvestructure and its AC current and/or AC external magnetic field induced dynamic response”
5. IEEE International Magnetics Conference INTERMAG Europe 2017, Dublin, IRELAND (oral presentation)
Vedat Karakas, Kaan Ozbozduman, Aisha Gokce, Ali Taha Habiboglu, Sevdenur Arpaci, Ibrahim Cinar, Cenk Yanik, Riccardo Tomasello, Silvia Tacchi, Giulio Siracusano, Mario Carpentieri, Giovanni Finocchio, Thomas Hauet and Ozhan Ozatay
“Evolution of Magnetic States From Neel Skyrmions to Radial Vortices”
6. IEEE International Magnetics Conference INTERMAG Europe 2017, Dublin, IRELAND (oral presentation)
Giulio Siracusano, Riccardo Tomasello, Anna Giordano, Vito Puliafito, Bruno Azzerboni, Ozhan Ozatay, Mario Carpentieri, Giovanni Finocchio
“Comparison of static and switching dynamical properties between radial and circular vortices”
7. Challenges for Magnetic Skyrmions and opportunities for skyrmionic devices SKYMAG 2017 Workshop, Paris, France (poster presentation)
Tao Liu, Vito Puliafito, C. Deranlot, François. Montaigne, S. Petit, S. Andrieu, Ibrahim Cinar, Ozhan Ozatay, Giovanni Finocchio and Thomas Hauet
“Method for Reproducible Single Bubble Formation in Patterned Dot Array”
1. 13th Joint MMM-Intermag Conference 2016, San Diego, California, USA:
Aisha Gokce, Ozhan Ozatay, Thomas Hauet, Givonni Finocchio, Anna Giordano, Jordan Katine
“Spin Torque Driven Bubble Motion in Magnetic Nanowires with Perpendicular Anisotropy”
2. American Physical Society March Meeting 2016, Baltimore, Maryland, USA:
İbrahim Cinar, Servet Özdemir, Egecan Cogulu, Aisha Gokce, Barry Stipe, Jordan Katine, Gülen Aktas, Ozhan Ozatay
“Towards a drift-free multi-level Phase Change Memory”
3. American Physical Society March Meeting 2016, Baltimore, Maryland, USA:
Kaan Ozbozduman, Vedat Karakas, Sevdenur Arpaci, Ali Taha Habibioglu, Aisha Gokce, Anna Giordano, Federica Celegato, Paula Tiberto, Giovanni Finocchio, Gulen Aktas, Ozhan Ozatay
“Spin Torque induced anti-vortex excitations”
1.Siracusano, Gulio; Tomasello, Ricardo; Giordano, Anna; Puliafito, Vito; Azzerboni, Bruno; Ozatay, Ozhan; Carpentieri, Mario; Finocchio, Giovanni “Magnetic Radial Vortex Stabilization and Efficient Manipulation Driven by the Dzyaloshinskii-Moriya Interaction and Spin-Transfer Torque”
PHYSICAL REVIEW LETTERS, 117, 087204 (2016)
2.Gokce, Aisha; Cinar, Ibrahim; Ozdemir, Servet C; Cogulu, Egecan; Stipe, Barry; Katine, Jordan A; Ozatay, Ozhan “Toward Multiple-Bit-Per-Cell Memory Operation With Stable Resistance Levels in Phase Change Nanodevices”
IEEE TRANSACTIONS ON ELECTRON DEVICES, 63, 3103-3108 (2016)
3.Liu, Tao; Puliafito, Vito; Montaigne, François; Petit, Sebastien; Deranlot, Cyrile; Andrieu, Stephane; Ozatay, Ozhan; Finocchio, Giovanni; Hauet, Thomas “Reproducible formation of single magnetic bubbles in an array of patterned dots”
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 49, 245002 (2016)
4.Gokce,Aisha; Coskuner,Ahmet; Kosoglu,Gulsen; Altunay,Omer; Yumak,Mehmet; Ozatay, Ozhan; Skarlatos, Yani “A Porous Silicon Recipe for Si Solar Cell Applications”
BAOJ Physics, 1 , 1 (2016)
1. Cinar, Ibrahim; Aslan, Ozgur Burak; Gökçe Aisha et al. “Three dimensional finite element modeling and characterization of intermediate states in single active layer phase change memory devices”
JOURNAL OF APPLIED PHYSICS, 117, 214302 (2015)
1. American Physical Society March Meeting 2015, San Antonio, Texas, USA, 2015:
Aisha Gokce, Ozhan Ozatay, Bugra Bulut, Coleman Rainey, Thomas Hauet, Anna Giordano, Giovanni Finocchio
“Lateral Domain Transfer In a Magnetic Nanowire With Perpendicular-to-Plane-Anisotropy For Three-Dimensional Memory Applications”
2. American Physical Society March Meeting 2015, San Antonio, Texas, USA, 2015:
Ali Taha Habiboglu, Vedat Karakas, Mustafa Mete, Ahmet Coskuner, Yemliha Bilal Kalyoncu, Aisha Gokce, Ozhan Ozatay, Anna Giordano, Mario Carpentieri, Giovanni Finocchio, Federica Celegato, Paola Tiberto
“Static and Dynamic Properties of Magnetic Antivortices in Asteroid-Shaped Permalloy Nanomagnets”
3. American Physical Society March Meeting 2015, San Antonio, Texas, USA, 2015:
Ahmet Coskuner, Aisha Gokce, Omer Altunay, Yani Skarlatos, Ozhan Ozatay
“Increasing The Efficiency of Silicon Solar Cells via an Anti-reflecting Nano-porous Surface Layer”
4. American Physical Society March Meeting 2015, San Antonio, Texas, USA, 2015:
Ibrahim Cinar, Egecan Cogulu, Aisha Gokce, Barry Stipe, Jordan Katine, Gulen Aktas, Ozhan Ozatay
“Characterization of structural defects in GST based nano-PCM devices through resistance drift measurements”
5. American Physical Society March Meeting 2015, San Antonio, Texas, USA, 2015:
Mustafa Mete, Ahmet Coşkuner, Ali Taha Habiboğlu, Vedat Karakaş, Yemliha Bilal Kalyoncu, Aisha Gökçe, Özhan Özatay, Anna Giordano, Mario Carpentieri, Giovanni Finocchio, Federica Celegatoi, Paola Tiberto
“Spin Torque Driven Anti-vortex Dynamics in Pattered Nanomagnets”
6. American Physical Society March Meeting 2015, San Antonio, Texas, USA, 2015:
Egecan Cogulu, Ibrahim Cinar, Aisha Gokce, Barry Stipe, Jordan Katine, Gulen Aktas, Ozhan Özatay
“The effect of thermoelectric contributions in switching dynamics and resistance drift of Phase Change Memory devices”
7. Elektrik Elektronik Mühendisliği Kongresi (EEMKON) 2015, İstanbul, Türkiye:
Özhan Özatay (invited)
“Tek Hücrede Çoklu Veri Depolama Amaçlı Faz Değişim Belleği”
8. 21.Yoğun Madde Fiziği Ankara Toplantısı 2015, Ankara,Türkiye :
Aisha Gökçe Özbay, Özhan Özatay, Thomas Hauet, Giovanni Finocchio, Anna Giordano, Jordan Katine
“Yeni Nesil Üç Boyutlu Manyetik Bellek Uygulamalarında Yatay ve Dikey Veri Transferi”
9. 21.Yoğun Madde Fiziği Ankara Toplantısı 2015, Ankara,Türkiye :
Vedat Karakaş, Ali Taha Habiboğlu, Sevdenur Arpacı, Kaan Özbozduman, Aisha Gökçe, Özhan Özatay
“Nano Ölçekli Asteroid Aygıtlarında Antivortekslerin Radyo Frekans Dinamiği”
10. 21.Yoğun Madde Fiziği Ankara Toplantısı 2015, Ankara,Türkiye :
İbrahim Çınar, Aisha Gökçe, Servet Özdemir, Egecan Çoğulu, Barry Stipe, Jordan A. Katine, Gülen Aktaş, Özhan Özatay
“Kararlı Çoklu Direnç Seviyeli Faz Değişim Belleği”
1. American Physical Society March Meeting 2014, Denver, Colorado, USA, 2014 :
Onur Dincer, Ibrahim Cinar, Vedat Karakas, Ozgur Burak Aslan, Aisha Gokce, Barry Stipe, Jordan A. Katine, Gulen Aktas, Ozhan Ozatay
“Three-Dimensional Multiscale Modeling of Stable Intermediate State Formation Mechanism in a Single Active Layer– Phase Change Memory Cell”
2. American Physical Society March Meeting 2014, Denver, Colorado, USA, 2014 :
Ibrahim Cinar, Vedat Karakas, Onur Dincer, Ozgur Burak Aslan, Aisha Gokce, Barry Stipe, Jordan A. Katine, Gulen Aktas, Ozhan Ozatay
“Towards Multiple-Bit-Per-Cell Operation In a Single Active Layer-Phase Change Memory Cell”
3. 59th Annual Magnetism & Magnetic Materials Conference, Honolulu, Hawaii, USA, 2014 :
Vedat Karakas, Mustafa Mete, Ali T. Habiboğlu, Ahmet Coskuner, Aisha Gokce, Ozhan Ozatay, Anna Giordano, Mario Carpentieri, Giovanni Finocchio, Federica Celegato, Paola Tiberto
“Static and Dynamic Properties of Magnetic Antivortices in Patterned Permalloy Nanomagnets”
4. 4th International Conference on Superconductivity and Magnetism, Antalya, TR, 2014 :
Özhan Özatay (Invited)
“Spintronic Devices for Memory and Sensor Applications”
İbrahim Çinar, Aisha Gokce Ozbay, Özgür Burak Aslan, Onur Dinçer and Vedat Karakaş
This project is supported by EU Marie Curie IRG Grant PCM-256281 and Bogazici University Research Fund 12B03M1
Electrical Characterization of Phase Change Memory Switching Conditions and Long Term Drift of Reset Resistance
In order to characterize the switching parameters of phase change memory devices in the time domain as a function of substrate temperature we have built a computer controlled electrical network consisting of a semiconductor device analyzer and a nanosecond pulser connected via a bias tee. The dc and ac grounds were separated using floating ground of the semiconductor device analyzer. The PCM devices to be tested were mounted on a gold-coated vacuum chuck with a variable temperature setting and electrically contacted with RF probes. The stability of the contacts was assured by performing the measurements on a vibration isolation table and the contact quality was constantly monitored with an optical microscope zoomed onto the contact electrodes. The current that flowed through the device during switching and the device resistance was probed using a 6GHz bandwidth oscilloscope connected to a ~1kohm surface mount resistor in series with and in close proximity to the device under test with a constant 20mV (non-destructive) read bias as shown below.
Switching between set and reset states was successfully demonstrated with this setup for device dimensions from 10 µm to 50 nm and previously observed dependence of the reset current on device geometry was reproduced. A representative switching data for a 500 nm diameter circular device is shown below. Such measurements were also repeated at elevated temperatures and a corresponding decrease in threshold reset current values was observed as expected.
Pulsed reset operation for a 500 nm diameter PCM device
PCM devices with various top contact sizes with circular, square or rectangular geometries have been tested. Devices have a range of resistance values from SET levels of 200 Ω – 5 kΩ to RESET levels of 200 kΩ – 10 MΩ. We have consistently observed an intermediate resistance level for a range of programming voltages in square top-contact devices with resistance levels 10 kΩ – 120 kΩ whereas in circular devices we have not seen such a state.
Current-Voltage (IV) characteristics are observed for the complete range of resistances. Figure 2 shows a typical IV sweep initiated when the device is at a RESET state, for a 130 nm square top contact device. The amorphous phase resistance of 3 MΩ switches to 350 Ω , crystalline phase, above the threshold voltage of 800 mV. We have observed that the threshold voltage is not constant and varies (from 350 mV- 1V for this sample) depending on the initial state of system. The sourcemeter is set to a current protection level of 1 mA to protect the device, therefore the IV curves show the compliance value rather than the actual current. Measurements conducted on square top contact geometry devices show a two-step switching behavior as illustrated in Figure 3 which plots the IV curve for a 0.5 µm square top contact device. The resistance first drops to middle state value before changing to set state.
Pulsed-resistance measurements are conducted to determine a programming range for the devices. A voltage pulse is sent to the device which is at a set state and an IV curve up to 100 mV is obtained right after the pulse to determine the resistance level. The device is then set again for the application of the next voltage pulse. The figure below shows the pulsed-resistance measurements comparing circular (a) and square (b) top-contact geometry devices. The circular top contact device displays a sudden change in resistance (from 1.5 kΩ to 900 kΩ) for pulse amplitudes higher than 0.65 V. Such a behavior is representative of circular top contact devices of 60-75 nm diameters that have a range of resistance values from 1 – 8 kΩ for set state and 800 kΩ – 3 MΩ for reset state. We consistently observe a multi-level switching for increasing voltage pulse amplitudes for square as well as rectangular top contact PCM cells. The example shown in Figure 4b is representative of a 90 nm square top contact device which displays a resistance increase from a set state of 700 Ω to a 24 kΩ resistance state, an intermediate resistance state, around 1.2 V and a second switching is observed around 1.45 V to a reset state with a resistance of 197 kΩ. It is clear that the 24 kΩ resistance state is a stable intermediate resistance state since there is a range of programming voltages between 1.25-1.4 V. As will be discussed later, circular top contact geometry devices favor a homogeneous current distribution around the edges of the top contact inside the GST layer whereas the square top contact geometry devices cause current crowding at the corners of the top contact hence allow a heterogeneous current distribution which causes regions with mixed-phase inside the active region for certain voltage pulses.
To elaborate the stability of the three resistance states: reset, set or middle state; we have monitored the time evolution of the resistance of the device under test after a switching operation. We have developed several Labview programming virtual instruments called VIs to perform different types of drift measurements such as drift under constant DC bias with a sourcemeter, or under constant DC bias with a battery (see next section), drift after discrete time intervals (like 5 minutes) recorded as IV curves for long periods of time (up to a day).
Programming of Reset and Intermediate States
Pulsed-Resistance measurements for (a) 75 nm circular top contact device, (b) 90 nm square top contact device. Resistance of the device is measured after the application of a 50 ns width pulse with 2 ns trailing edge for the given amplitude to the set state.
Drift of Resistance Levels
The drift in resistance levels of a reset state is common in PCM devices and is attributed to structural relaxation through annihilation of charge traps which play a major role in the conduction of electrons. The resistance change is indicative of a power-law behavior characterized by a drift coefficient.
Resistance drift data for set (blue diamonds), middle (black circles) and reset (red triangles). The initial resistance levels at t0=100sec are 428Ω, 114kΩ and 1MΩ, respectively. The drift coefficients are 0.0009 for set, 0.0102 for middle and 0.102 for reset states.
We have obtained resistance drift data for set and middle states as well. For set state, there is almost no drift as illustrated above. The device plotted in this figure is a 130 nm square device and it is set via an IV measurement to a resistance level of 428.84Ω. The resistance change is less than 2Ω in a 12 hour period. The drift coefficient of the particular device is 0.0009 and varies between 0.0006-0.001 this value for other samples. Figure 10 shows the resistance drift data for the same sample when it is switched to the middle state by the application of a 1.8 V pulse with 100 ns width and 2 ns trailing edge. Even though this state has much higher resistance than the set state, 116 kΩ, the drift is only slightly different than the set state. The drift coefficient is 0.0102, much smaller than the drift coefficient of the reset state. The υ for middle state varies within the range 0.01-0.015 for other samples.
Drift at Nano-Millisecond Time Scales
The resistance switching of a PCM cell from a set state to a reset state has been captured using a 25ps resolution LeCroy Oscilloscope. An illustration of the circuit design is shown below where the oscilloscope is connected parallel to the device. In order to overcome ground-loop currents and additional noise sources, the source-meter used in pulsed-resistance measurements is replaced with a DC circuit box consisting of two 12 V batteries and a series of ballast resistors to adjust the current running through the device. The ballast resistors and the internal resistance of the oscilloscope are adjusted so that the oscilloscope reads a reasonable change in voltage when the phase of the PCM cell changes from crystalline to amorphous. The best results are obtained when the oscilloscope settings are adjusted to DC coupling to a 1MΩ internal resistance.
Nano-Millisecond Drift Measurement Setup
The resistance drift behaviour for a 130 nm square device after a 100 ns 2V pulse.
Temperature Dependence of Resistance Drift
Temperature dependence of the drift coefficient for a 500 nm square device is obtained for the middle resistance state. The device was switched to middle state with a 2.8 V pulse with 100 ns width and 2 ns trailing edge. For all other devices we have observed that the drift coefficient increases with increasing temperature up until 100 C after which the re-crystallization effect kick in and reduces the device resistance.
Post Switching Pulse Treatment
Post-reset treatments have been examined with the aim to reduce the resistance drift. First, resistance drift data for the particular sample is recorded after a reset operation and the device is set back to crystalline state. Then a reset pulse and a post-reset pulse are sourced to the device and the time evolution of the resistance is observed. Post-reset treatment for a 500 nm square top contact sample is shown in Figure 8. A reset pulse of 2.5V is used to switch this device and a post-reset pulse of 1.8 V is sent to the device right after the switching pulse. The reset resistance appears to have increased slightly after the post-reset treatment, however the drift coefficients are very similar: 0.107 for the reset measurement and 0.108 for the measurement after the post-reset pulse. We have tried post-reset pulses from 1.5 V up to 2.8 V and seen that the drift coefficient remains almost the same.
Finite Element Simulations of Phase Change Memory Devices
To get a detailed description of the temperature and phase distribution in the experimental conditions a finite element code has been implemented using COMSOL multiphysics and critical switching properties such as a large contrast in the resistance states were successfully reproduced. These simulations will help us understand the role of inhomogeneous heating in different contact geometries for long term drift behaviour. We have already gained invaluable insights into the phase change kinetics during switching as shown below. For instance such simulations guide us on how to get stable, reproducible multi-level switching behaviour.
1. Puliafito, Vito; Torres, Luis; Ozatay, Ozhan; et al. “Micromagnetic analysis of dynamical bubble-like solitons based on the time domain evolution of the topological density“ JOURNAL OF APPLIED PHYSICS,115, 17D139 (2014)
Three Dimensional Magnetic Memory
Yemliha Bilal Kalyoncu, Aisha Gokce Ozbay
in collaboration with HGST
Future limitations to the improvements in the data storage density with perpendicular recording act as a driving force for an intensive effort to investigate alternative schemes to reliably store and recall information with ultra-high density on magnetic media. There are several approaches for achieving this goal, such as thermally-assisted recording, microwave assisted recording and ultimately 3-d magnetic storage schemes. IBM has already demonstrated race track memory in which magnetic domains (bits) are moved along a 3D magnetic wire by applying spin-polarized current pulses . Here we will present our investigation of heat-assisted domain transfer in a magnetic multilayer nanowire stack with perpendicular anisotropy using locally applied fields. A recent study in continuous film [CoNi/Pd]/Pd/ [Co/Pd] multilayer stacks has unambiguously shown stray field induced domain replication using element-specific x-ray imaging techniques . For storage device applications it is crucial to understand and gain full control over the conditions that lead to reproducible stray field induced single domain transfer in patterned magnetic nanostructures. For this purpose we have fabricated single magnetic layer (CoNi/Pd) nanowires as well as devices that consist of a SiN-CoNi/Pd-SiN-CoNi/Pd-Ta stack with 50-100 nm constrictions in a cross-wire configuration to study domain transfer between magnetic layers. We use the localized stray field from a magnetic tip to write single-domains in the CoNi/Pd magnetic layer by modulating its coercivity via instantaneous and localized heating from a current pulse .We investigate resulting domain structure in nanowires with various widths as a function of the current pulse amplitude and width to vary the local temperature and the tip height to vary the local field. We also work on the nature of current-induced demagnetization limit and thermally-induced domain transfer between magnetic layers This study establishes the preliminary conditions for the use of 3-D integrated cross-wires of perpendicular anisotropy magnetic materials to boost the data storage capacity of future magnetic memory devices.
This work is supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under the Contract No. 112T205 & Bogazici University Research Fund under the Contract No. 13B03P6
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O.Ozatay and B. D. Terris Read / Write Structures for a Three Dimensional Memory US Patent# 8164940