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Kohno Y, Seki T, Tsuruoka S, Ohya S, Shibata N. Magnetic field observation in a magnetic tunnel junction by scanning transmission electron microscopy. Microscopy (Oxf) 2024; 73:329-334. [PMID: 38155605 DOI: 10.1093/jmicro/dfad063] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Revised: 11/30/2023] [Accepted: 12/21/2023] [Indexed: 12/30/2023] Open
Abstract
A magnetic tunnel junction (MTJ) consists of two ferromagnetic layers separated by a thin insulating layer. MTJs show tunnel magnetoresistance effect, where the resistance in the direction perpendicular to the insulator layer drastically changes depending on the magnetization directions (parallel or antiparallel) in the ferromagnetic layers. However, direct observation of local magnetizations inside MTJs has been challenging. In this study, we demonstrate direct observation of magnetic flux density distribution inside epitaxially grown Fe/MgO/Fe layers using differential phase contrast scanning transmission electron microscopy. By utilizing newly developed tilt-scan averaging system for suppressing diffraction contrasts, we clearly visualize parallel and antiparallel states of ferromagnetic layers at nanometer resolution.
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Affiliation(s)
- Yuji Kohno
- JEOL Ltd, 3-1-2, Musashino, Akishima, Tokyo 196-8558, Japan
| | - Takehito Seki
- Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Yayoi 2-11-16, Bunkyo-ku, Tokyo 113-8656, Japan
- PRESTO, Japan Science and Technology Agency, Honcho 4-1-8, Kawaguchi, Saitama 332-0012, Japan
| | - Shun Tsuruoka
- Department of Electrical Engineering and Information Systems, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Shinobu Ohya
- Department of Electrical Engineering and Information Systems, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
- Center for Spintronics Research Network (CSRN), School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
- Institute for Nano Quantum Information Electronics (NanoQuine), The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
| | - Naoya Shibata
- Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Yayoi 2-11-16, Bunkyo-ku, Tokyo 113-8656, Japan
- Nanostructures Research Laboratory, Japan Fine Ceramic Center, 2-4-1 Mutsuno, Atsuta-ku, Nagoya 456-8587, Japan
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Cooper D, Bruas L, Bryan M, Boureau V. Measuring electrical properties in semiconductor devices by pixelated STEM and off-axis electron holography (or convergent beams vs. plane waves). Micron 2024; 179:103594. [PMID: 38340549 DOI: 10.1016/j.micron.2024.103594] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2023] [Revised: 01/24/2024] [Accepted: 01/25/2024] [Indexed: 02/12/2024]
Abstract
We demonstrate the use of both pixelated differential phase contrast (DPC) scanning transmission electron microscopy (STEM) and off-axis electron holography (EH) for the measurement of electric fields and assess the advantages and limitations of each technique when applied to technologically relevant samples. Three different types of samples are examined, firstly a simple highly-doped Si pn junction. Then a SiGe superlattice is examined to evaluate the effects of the mean inner potential on the measured signal. Finally, an InGaN/GaN microwire light-emitting diode (LED) device is examined which has a polarization field, variations of mean inner potential and a wurtzite crystal lattice. We discuss aspects such as spatial resolution and sensitivity, and the concept of pseudo-field is defined. However, the most important point is the need to limit the influence of diffraction contrast to obtain accurate measurements. In this respect, the use of a plane electron wave for EH is clearly beneficial when compared to the use of a convergent beam for pixelated DPC STEM.
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Affiliation(s)
- David Cooper
- Universite Grenoble Alpes, CEA, LETI, F-38000 Grenoble, France.
| | - Lucas Bruas
- Universite Grenoble Alpes, CEA, LETI, F-38000 Grenoble, France
| | - Matthew Bryan
- Universite Grenoble Alpes, CEA, LETI, F-38000 Grenoble, France
| | - Victor Boureau
- Universite Grenoble Alpes, CEA, LETI, F-38000 Grenoble, France; Interdisciplinary Center for Electron Microscopy, EPFL, 1015 Lausanne, Switzerland
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Chejarla VS, Ahmed S, Belz J, Scheunert J, Beyer A, Volz K. Measuring Spatially-Resolved Potential Drops at Semiconductor Hetero-Interfaces Using 4D-STEM. SMALL METHODS 2023; 7:e2300453. [PMID: 37246264 DOI: 10.1002/smtd.202300453] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2023] [Indexed: 05/30/2023]
Abstract
Characterizing long-range electric fields and built-in potentials in functional materials at nano to micrometer scales is of supreme importance for optimizing devices, e.g., the functionality of semiconductor hetero-structures or battery materials is determined by the electric fields established at interfaces which can also vary spatially. In this study, momentum-resolved four-dimensional scanning transmission electron microscopy (4D-STEM) is proposed for the quantification of these potentials and the optimization steps required to reach quantitative agreement with simulations for the GaAs/AlAs hetero-junction model system are shown. Using STEM the differences in the mean inner potentials (∆MIP) of two materials forming an interface and resulting dynamic diffraction effects have to be considered. This study shows that the measurement quality is significantly improved by precession, energy filtering and a off-zone-axis alignment of the specimen. Complementary simulations yielding a ∆MIP of 1.3 V confirm that the potential drop due to charge transfer at the intrinsic interface is ≈0.1 V, in agreement with experimental and theoretical values found in literture. These results show the feasibility of accurately measuring built-in potentials across hetero-interfaces of real device structures and its promising application for more complex interfaces of other polycrystalline materials on the nanometer scale.
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Affiliation(s)
- Varun Shankar Chejarla
- Department of Physics and Materials Science Center, Philipps-University Marburg, Hans-Meerwein Str. 6, 35032, Marburg, Germany
| | - Shamail Ahmed
- Department of Physics and Materials Science Center, Philipps-University Marburg, Hans-Meerwein Str. 6, 35032, Marburg, Germany
| | - Jürgen Belz
- Department of Physics and Materials Science Center, Philipps-University Marburg, Hans-Meerwein Str. 6, 35032, Marburg, Germany
| | - Jonas Scheunert
- Department of Physics and Materials Science Center, Philipps-University Marburg, Hans-Meerwein Str. 6, 35032, Marburg, Germany
| | - Andreas Beyer
- Department of Physics and Materials Science Center, Philipps-University Marburg, Hans-Meerwein Str. 6, 35032, Marburg, Germany
| | - Kerstin Volz
- Department of Physics and Materials Science Center, Philipps-University Marburg, Hans-Meerwein Str. 6, 35032, Marburg, Germany
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Toyama S, Seki T, Kanitani Y, Kudo Y, Tomiya S, Ikuhara Y, Shibata N. Real-space observation of a two-dimensional electron gas at semiconductor heterointerfaces. NATURE NANOTECHNOLOGY 2023; 18:521-528. [PMID: 36941362 DOI: 10.1038/s41565-023-01349-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Accepted: 02/12/2023] [Indexed: 05/21/2023]
Abstract
Mobile charge carriers are essential components in high-performance, nano-engineered semiconductor devices. Employing charge carriers confined to heterointerfaces, the so-called two-dimensional electron gas, is essential for improving device performance. The real-space visualization of a two-dimensional electron gas at the nanometre scale is desirable. However, it is challenging to accomplish by means of electron microscopy due to an unavoidable strong diffraction contrast formation at the heterointerfaces. We performed direct, nanoscale electric field imaging across a GaN-based semiconductor heterointerface using differential phase contrast scanning transmission electron microscopy by suppressing diffraction contrasts. For both nearly the lattice-matched GaN/Al0.81In0.19N interface and pseudomorphic GaN/Al0.88In0.12N interface, the extracted quantitative electric field profiles show excellent agreement with profiles predicted using Poisson simulation. Furthermore, we used the electric field profiles to quantify the density and distribution of the two-dimensional electron gas across the heterointerfaces with nanometre precision. This study is expected to guide the real-space characterization of local charge carrier density and distribution in semiconductor devices.
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Affiliation(s)
- Satoko Toyama
- Institute of Engineering Innovation, School of Engineering, University of Tokyo, Tokyo, Japan
| | - Takehito Seki
- Institute of Engineering Innovation, School of Engineering, University of Tokyo, Tokyo, Japan.
- PRESTO, Japan Science and Technology Agency, Kawaguchi, Japan.
| | - Yuya Kanitani
- Sony Group Corporation, Atsugi, Japan
- Sony Semiconductor Solutions Corporation, Atsugi, Japan
| | - Yoshihiro Kudo
- Sony Group Corporation, Atsugi, Japan
- Sony Semiconductor Solutions Corporation, Atsugi, Japan
| | - Shigetaka Tomiya
- Sony Group Corporation, Atsugi, Japan
- Sony Semiconductor Solutions Corporation, Atsugi, Japan
| | - Yuichi Ikuhara
- Institute of Engineering Innovation, School of Engineering, University of Tokyo, Tokyo, Japan
- Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya, Japan
| | - Naoya Shibata
- Institute of Engineering Innovation, School of Engineering, University of Tokyo, Tokyo, Japan.
- Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya, Japan.
- Quantum-Phase Electronics Center (QPEC), The University of Tokyo, Tokyo, Japan.
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Seki T, Khare K, Murakami YO, Toyama S, Sánchez-Santolino G, Sasaki H, Findlay SD, Petersen TC, Ikuhara Y, Shibata N. Linear imaging theory for differential phase contrast and other phase imaging modes in scanning transmission electron microscopy. Ultramicroscopy 2022; 240:113580. [DOI: 10.1016/j.ultramic.2022.113580] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2022] [Revised: 06/13/2022] [Accepted: 06/21/2022] [Indexed: 11/17/2022]
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Quantitative electric field mapping in semiconductor heterostructures via tilt-scan averaged DPC STEM. Ultramicroscopy 2022; 238:113538. [DOI: 10.1016/j.ultramic.2022.113538] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2022] [Revised: 04/14/2022] [Accepted: 04/23/2022] [Indexed: 11/23/2022]
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Hong X, Zeltmann SE, Savitzky BH, Rangel DaCosta L, Müller A, Minor AM, Bustillo KC, Ophus C. Multibeam Electron Diffraction. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2021; 27:129-139. [PMID: 33303043 DOI: 10.1017/s1431927620024770] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
One of the primary uses for transmission electron microscopy (TEM) is to measure diffraction pattern images in order to determine a crystal structure and orientation. In nanobeam electron diffraction (NBED), we scan a moderately converged electron probe over the sample to acquire thousands or even millions of sequential diffraction images, a technique that is especially appropriate for polycrystalline samples. However, due to the large Ewald sphere of TEM, excitation of Bragg peaks can be extremely sensitive to sample tilt, varying strongly for even a few degrees of sample tilt for crystalline samples. In this paper, we present multibeam electron diffraction (MBED), where multiple probe-forming apertures are used to create multiple scanning transmission electron microscopy (STEM) probes, all of which interact with the sample simultaneously. We detail designs for MBED experiments, and a method for using a focused ion beam to produce MBED apertures. We show the efficacy of the MBED technique for crystalline orientation mapping using both simulations and proof-of-principle experiments. We also show how the angular information in MBED can be used to perform 3D tomographic reconstruction of samples without needing to tilt or scan the sample multiple times. Finally, we also discuss future opportunities for the MBED method.
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Affiliation(s)
- Xuhao Hong
- School of Physics, Nanjing University, Nanjing210093, PR China
| | - Steven E Zeltmann
- Department of Materials Science and Engineering, University of California, Berkeley, CA94720, USA
| | - Benjamin H Savitzky
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
| | - Luis Rangel DaCosta
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
| | - Alexander Müller
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
| | - Andrew M Minor
- Department of Materials Science and Engineering, University of California, Berkeley, CA94720, USA
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
| | - Karen C Bustillo
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
| | - Colin Ophus
- National Center for Electron Microscopy, Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA94720, USA
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