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Magnetic Devices for Ultrafast switching

Introduction

This area addresses the challenging task of ultrafast switching phenomena in magnetic sub-micron structures, focusing on coherent switching phenomena in the sub-nanosecond time regime. The research field is motivated by the high demands from industry of increasing storage density together with increased bit writing and reading speed. The objectives of this complementary project are to fabricate devices where the active element (magnetic tunnel junction) has a submicron size (<100nm) and to characterize their dynamic magnetization reversal (switching) under high frequency, ultrafast (<10ns) current pulses. Since the installation at INESC-MN of the new e-beam system, we have been improving and developing the microfabrication process aiming the patterning of magnetic structures under 100nm dimensions and integrating them in a pillar device or using point contact geometry. Defining isolated magnetic features for domain wall characterization is also been done, as a test for the nanofabrication process.

For more information on this topic, contact Paulo Freitas or Susana Cardoso Freitas.

 

Main Results

  1. A RAITH 150 e-beam tool was installed at INESC MN at the beginning of October 2006. The first objective was to optimize the exposure processtowards sub-100nm features. At this moment we are able to define squares with dimensions between 100-500 nm, using a clearing dose around 40-50 mC/m2 and line widths down to 70 nm with 30-40 mC/m2. To integrate these structures in devices two options are being used for top contact to the pillar: Chemical Mechanical Polishing (CMP) and Back Etch Process, using Reactive Ion Etching (RIE). Spin Valves were already processed using E-Beam Lithography with patterns down to 70 nm.

  2. Demonstration of precessional switching, where pulsed Oersted field (few 100 ps range) is used for 180º coherent magnetic reversal (half period precessional switching). The samples studied in this work were prepared before 2004, but the measurements have been extended since then.

  3. MRAM cells based on low resistance tunnel junctions were deposited at INESC-MN and processed at Leti with 100nm for current assisted switching. These experiments were carried out during 2003-2004. Thermally assisted magnetic reversal, by heating above the Blocking temperature was successfully demonstrated during 2003-2004, and was the starting point for the work on thermally assisted switching incorporating thermal barriers. Today, is being considered by industry (Crocus, France, in collaboration with INESC-MN) as an alternative MRAM architecture.

  4. INESC-MN started also to develop point contact devices. One application in progress is the fabrication of point contact devices (using CPP spin valves) for spin injection experiments.

  5. A special geometry is used to manipulate the position of magnetic domains and their domain walls in a thin line of ferromagnetic material through the application of current pulses at zero or low external magnetic field. This dislocation induces a resistance variation due to the AMR effect (at the domain wall) or to the GMR effect (in the domain, if a spin-valve is used). For this, 200nm wide NiFe lines are fabricated using e-beam lithography and ion milling. Afterwards, the resistance measurement leads are defined through e-beam lithography and lift-off.

  6. Low RxA materials as AlOx (minimum 10 W.mm2) or MgO (0.8 W.mm2) have being integrated in nanodevices down to90x120 nm2. Spin transfer has been measured at critical currents of 3x106 A/cm2. 

 

Projects and Collaborations 2004 - present

“Ultrafast Magnetic Switching for Advanced Devices” (ULTRASWITCH), HPRN-CT-2002-00318 , collaboration between Univ. Kaiserslautern (DE), INESC-MN (Lisbon), CNRS, Tech.Univ.Eindhoven (The Netherlands), Univ.Glasgow (UK), Univ.Durham (UK), IMEC (B), FIAT (I), IBM (Germany), Siemens (DE), (2002-2006)

“Spin Current Induced Ultrafast Switching” (SPINSWITCH), MRTN-CT-2006-035327, collaboration between Univ. Kaiserslautern (DE), INESC-MN (Lisbon), CNRS, Univ.Glasgow (UK), Imperial Col. (UK), IMEC (B), Univ.Salamanca (ES), Thales (FR), Siemens (DE), Univ Konstanz (DE), CEA (FR), UPS (FR), AGH (PL), AMU (PL), NIRDTP (RO), (2006-2010)

Collaboration with the Univ.Muenster (Germany) for the point contact injection experiments. (2006-2007)

Collaboration with the Univ.Porto for the study of transport phenomena on low resistance junctions.

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