GMR Film Research Articles

Fully epitaxial giant magnetoresistive devices with half-metallic Heusler alloy fabricated on poly-crystalline electrode using three-dimensional integration technology

Fully-epitaxial magnetoresistance (MR) devices with half-metallic Heusler alloys has attracted considerable attention for years due to their excellent spin-dependent transport properties such as high MR ratio and ultra-low resistance-area product. However, their poor manufacturability due to the necessity of epitaxial growth on a special single crystalline substrate such as MgO(001) hinders their practical applications. To overcome this issue, in this study, we fabricated Heusler-based epitaxial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) film grown on Si substrate and directly bonded it to poly-crystalline electrode wafer by using three-dimensional (3D) integration processes such as direct wafer bonding and removal of backside Si substrate. First we explored suitable seed/buffer layers for the (001)-oriented epitaxial growth of Heusler CPP-GMR on Si(001) substrate. Si-subs/NiAl/CoFe seed/buffer structure was found to induce (001)-oriented epitaxial growth and to suppress an Al diffusion from NiAl to the Heusler electrode even after annealing at 500 °C, resulting in large MR ratio comparable to that with MgO substrate. After direct wafer bonding process, the microstructure analysis revealed clean damage-free bonded interface between the epitaxial Heusler GMR and poly-crystalline electrode films with Au capping layers. After the 3D integration processes, high MR performance has been successfully reproduced. This unique processing method enables the integration of high performance Heusler-based epitaxial spintronic devices for various practical applications.

Magnetostriction Measurement of Giant Magnetoresistance Films on the Practical Substrates by using Inverse-magnetostriction Effect

After forming electric devices, a magnetostriction effect sometimes deteriorates the sensitivity of sensors such as read heads of hard disk devices, or the bit stability of memories such as magnetic random access memories through the inverse-magnetostriction phenomenon. We should, therefore, know the magnetostriction constant of magnetic films on the practical substrates. In this paper, I present a new method by detecting the changes in coercive force, Hc, with mechanically bending the substrates. This method uses the inverse-magnetostriction effect and I show the magnetostriction constant can be calculated from the gradient of the applied stress vs. Hc curves. With this method, I have successfully measured the magnetostriction constant of the GMR films fabricated on the practical substrates with a high sensitivity over 10-7. This method will be useful for the magnetic thin films with a large anisotropy field.

Magnetostriction measurement of GMR films on practical substrates

The magnetostriction constant λS of a magnetic film is usually measured by detecting the mechanical distortion of the film deposited on a thin glass substrate under an applied field using a laser beam. This method, however, cannot be applied to a film deposited on a rigid substrate such as Si and AlTiC used widely in real-world application. This is because that the distortion of the sample is too small to be detected. In addition, λS of the film deposited on the glass substrate sometimes differ from those of the film deposited on the Si or AlTiC substrate. Thus, it is very important to evaluate λS of a film deposited on an actual substrate. In this paper, a new method for measuring λS of a film deposited on a substrate used in actual products is proposed by detecting the change of the anisotropic field Hk of the film under bending load. λS can be calculated from the gradient of the applied mechanical stress dependence of the HK. Utilizing this method, we have successfully measured λS of GMR films fabricated on the practical substrate by a very high resolution of 2×10−8.

2-11 Pt/Co多層膜を用いた垂直磁化GMR薄膜の磁気光学的評価(第2部門 コンシューマエレクトロニクス&マルチメディアストレージ)

2-11 Pt/Co多層膜を用いた垂直磁化GMR薄膜の磁気光学的評価(第2部門 コンシューマエレクトロニクス&マルチメディアストレージ)

Ｃｏ基ホイスラー合金を用いたＧＭＲ積層膜の作製

GMR multilayer films using Co2MnGe(CMG) and Mn-Ir/CMG exchange-coupled films were fabricated on thermally oxidized Si substrate, and their crystal orientation, magnetic properties, and interfacial roughness were investigated. The main results are stated as follows. (1) (100) oriented MnIr/CMG exchange-coupled films were realized when Ni-Ta underlayer/Cr buffer layer were deposited on thermally oxidized Si substrate. After thermal annealing for 2h at 250°C in a magnetic field of 5 kOe, the unidirectional anisotropy constant (JK) of bilayers was 0.13 erg/cm2. (2) Dependence of saturation field (Hs) on Cr thickness for GMR films with (100) oriented CMG/Cr/CMG trilayer was investigated. Hs was minimum when Cr thickness was 1 nm and 5 nm. (3) Surface roughness (Ra) of Ni-Ta 5 nm on Al-Cr bottom electrode layer(100 nm) was 0.108 nm. (4) Flat and (100) oriented CMG/Cr films was formed on Al-Cr bottom electrode layer (100 nm)/Ni-Ta underlayer (15 nm)/Cr buffer layer (60 nm) when Cr content of the Al-Cr layer was 18.7-24.6 at%.

Fabrication of Magnetic Nanostructures for MRAM using Electron Beam and Focused Ion Beam Exposure of HSQ

ABSTRACTGiant magnetoresistive (GMR) materials-based magnetic random access memory (MRAM) has become attractive due to non-volatility, speed and density1. The vertical MRAM (VMRAM) design model shows good signal level and high speed and density potential. The memory cell for the VMRAM model is a ring shaped magnetic material multilayer, which ensures high repeatability and low switching energy. This GMR structure, however, is difficult to pattern as it contains materials such as Ni, Fe, Co, and Cu, which are difficult to dry etch because they lack volatile etch products. This work shows that it is possible to overcome the difficulties associated with etching GMR materials by using hydrogen silsesquioxane (HSQ) as an etch mask. We have used HSQ in a direct-write electron-beam lithography system with a dose of 600 μC/cm2, and in a Ga+ ion focused ion beam (FIB) system with a dose of 12 μC/cm2. Both are followed by development and an argon plasma etch at 10mTorr and 100W RIE power. The HSQ layer provides high resolution as well as good etching resistance. Electron-beam exposed HSQ shows a 1:1.5 selectivity over the GMR film stack and the FIB exposed HSQ showed an improved etch selectivity of 1:1. Ring shaped GMR structures with a 75/225 nm (ID/OD) have been fabricated, which corresponds to a memory density of 4Gb/in2.

Fabrication of ferromagnetic Fe3Si thin films by pulsed laser deposition using an Fe3Si target

Ferromagnetic Fe 3 Si thin films were fabricated on Si and quartz substrates by pulsed laser deposition. It was found that the polycrystalline Fe 3 Si thin films were grown at the substrate temperature of 300°C, and this is a candidate for the ferromagnetic layer of the multi-layered GMR film. At room temperature, the ferromagnetic amorphous Fe 3 Si thin film were grown and it is also extremely expectative as a ferromagnetic layer due to its nearly the same resistivity as that of semiconducting amorphous FeSi 2 . At substrate temperatures higher than 400°C, the FeSi crystallites were co-generated with Fe 3 Si crystallites on the Si substrate probably due to the diffusion of the Si atoms from the substrate into the film.

Fabrication of ferromagnetic Fe 3Si thin films by pulsed laser deposition using an Fe 3Si target

Ferromagnetic Fe 3Si thin films were fabricated on Si and quartz substrates by pulsed laser deposition. It was found that the polycrystalline Fe 3Si thin films were grown at the substrate temperature of 300°C, and this is a candidate for the ferromagnetic layer of the multi-layered GMR film. At room temperature, the ferromagnetic amorphous Fe 3Si thin film were grown and it is also extremely expectative as a ferromagnetic layer due to its nearly the same resistivity as that of semiconducting amorphous FeSi 2. At substrate temperatures higher than 400°C, the FeSi crystallites were co-generated with Fe 3Si crystallites on the Si substrate probably due to the diffusion of the Si atoms from the substrate into the film.

高抵抗シールド膜を用いた狭ギャップ再生ヘッド

A narrow-gap read head with a high-resistance magnetic film was investigated. The film has a resistance of more than 10 m Ω cm and good soft magnetic properties. The high-resistance shield head comprises a GMR film, insulator films for the read-gap, high-resistance magnetic films, insulator films to prevent breakdown of the head, and magnetic shield films. The fabricated high-resistance shield head shows a good output waveform. However, it has a slightly larger half-amplitude pulse width (PW50) value than a conventional shield head, because the permeability of the high-resistance magnetic film is insufficiently high. We concluded that a read head using a high-resistance shield with high permeability would be a suitable candidate for a narrow-gap read head.

Etch characteristics of giant magnetoresistive materials

The continued growth in communications has increased the need for non-volatile memories. One particular approach is magnetoresistive random access memory (MRAM). Because there is no wear-out mechanism, read/write endurance is virtually unlimited, making the technology attractive for a variety of different memory applications. Historically, reactive etching of magnetic thin films has proven to be difficult and ion milling is typically used to pattern the GMR layer. In this work, a high density Cl 2/Ar plasma is used to etch the GMR film stack. Redeposition effects were eliminated, with no serious effect on the underlying oxide layer. Acceptable GMR ratios were obtained for larger bit features, however the ratio drops significantly as bit size decreases. The decrease appears to be a result of corrosion in the copper interlayer of the GMR film stack.

ＧｄＦｅ合金垂直磁化膜を用いたＧＭＲ膜およびＴＭＲ膜

We observed hysteresis loops of resistance in GMR and TMR films using GdFe alloy with perpendicular. The MR ratio of GMR film was approximately 0.036% when the thickness of Cu film was 4 nm. Al50Cu50 film with a surface roughness of approximately 0.2 nm was used for the under electrode of TMR film. The Al2O3 film was prepared by direct deposition on an Al2O3 target, and atomic ratio O/Al of the Al2O3 film was 1.52 according to an RBS analysis. The MR ratio of TMR film was approximately 0.95% when the thickness of Al2O3 film was 2.2 nm.

ＣｏＦｅ／Ｃｕ多層膜のＣＰＰ（Ｃｕｒｒｅｎｔ Ｐｅｒｐｅｎｄｉｃｕｌａｒ ｔｏ ｔｈｅ Ｐｌａｎｅ）‐ＧＭＲ特性

Multilayer GMR films have a larger MR ratio than spin-valve films and, therefore, have great potential for use as read sensors in HDD (hard disk drive) heads for ultra-high-density recording. Moreover, the MR ratio of multilayer GMR films is twice as large when the sense current flows perpendicular to the plane (CPP) than when it flows in the plane (CIP). We investigated the GMR properties of CPP elements of a Co0.9Fe0.1/Cu multilayer in a structure where the GMR film is under the top terminal layer and connected to the bottom terminal layer through a micron-sized contact hole. An MR ratio of 13.1% and saturation field (Hs) of 150 Oe were obtained. The field sensitivity of 0.1 %/Oe was much larger than that of CIP elements. The value of Hs of the CPP elements was almost constant as a function of the element dimension, because the demagnetization field was insensitive of the sensor size in our CPP element structure and small enough even for submicron elements.

Giant magnetoresistance properties of CoFe/Cu multilayer in the CPP (Current Perpendicular to the Plane) geometry

The MR ratio of multilayer GMR sensors with the CPP (current perpendicular to the plane) structure is expected to be much larger than that of CIP (current in the plane) sensors. We investigated the GMR properties of CIP and CPP elements of a Co/sub 0.9/Fe/sub 0.1//Cu 10-bilayer. For CPP elements, the GMR film was connected to the top and bottom terminal layers with a micron-sized contact hole. The measured data was analyzed using a model taking into account of the distribution of sense current. The measured resistance change (l R) increased rapidly as the GMR diameter became smaller, and showed close agreement with the calculated results when we assumed the MR ratio of CPP films to be around 30%. This MR ratio was twice as large as that of the CIP film of Co/sub 0.9/Fe/sub 0.1//Cu 10-bilayer. In this study, we used the CPP elements which had wide GMR films and fine contact holes. So, the measured saturation field (/sub H/s) of the CPP elements was almost constant as a function of the contact hole dimension, because the demagnetization field was insensitive to the sensor size. The CPP element in this study will obtain a high output when the GMR diameter becomes small.

Enhanced GMR in [NiFe/Cu/Co] with specular reflective capping layers

Enhancement of MR ratio with addition of Cu/Ag capping layers was found in NiFe/Cu/Co GMR films prepared on MgO substrates with Pt/Cu buffer layers. Simulation of the MR ratio was carried out using the theoretical model given by J. Barnas, A. Fuss, R.E. Camley, P. Grünberg, W. Zinn [Phys. Rev. B 42 (1990) 8110] to clarify the origin of the enhancement of GMR. The results show that the specular scattering plays an important role in the films and the enhanced GMR can be explained by assuming the increase of specularity factor of the capping layer.

Comparison of flicker noise in single layer, AMR and GMR sandwich magnetic film devices

Flicker noise comparison has been made on single layer NiFeCo, Sandwich AMR NiFeCo/TaN/NiFeCo and GMR NiFeCo/CoFe/Cu/CoFe/NiFeCo films. In a single magnetic domain state, AMR films have noise close to the thermal noise, GMR has 2-3 times higher noise, and in a state having a useful MR ratio, the GMR film has 10 times higher noise than AMR sandwich film, while the sandwich film has 10 times higher noise than single layer AMR film.

Very high sensitivity GMR spin-valve magnetometer

A NiFe/Co/Cu GMR spin-valve magnetometer is designed, built, and tested. Thin-film flux-concentrators provide 50/spl times/ gain, yielding hysteresis-free sensitivity 1/R dR/dH=11%/0e in a 1 mm/sup 2/, internally temperature compensated device. Detection levels of 2 /spl mu/Oe/(Hz)/sup 1/2/ (at 1 Hz) are limited by 1/f resistance noise in the GMR films, which is examined in detail. Improvement by 10/spl times/ is possible via increased device size, as well as lower noise MR films.

マルチメディア時代における真空装置と薄膜応用 ＧＭＲ膜と成膜装置

マルチメディア時代における真空装置と薄膜応用 ＧＭＲ膜と成膜装置

Giant Magnetoresistance of NiFe/Cu Multilayers Prepared by Magnetron Sputtering Enhanced with an Inductively Coupled rf Plasma

(NiFe/Cu)8NiFe/Fe GMR multilayers were prepared by means of a newly developed magnetron sputtering system based on a process that we have termed "magnetron sputtering enhanced with an inductively coupled rf plasma." The cathode in this system has an rf coil attached to the planar magnetron sputtering target. The sputtering method was found to ionize the sputtered atoms very efficiently, and to be able to sustain the plasma even in an Ar gas atmosphere of 10-2Pa. A second peak of the MR oscillation of the multilayers was observed in the vicinity of 2 nm of the Cu layer thickness, and the maximum value of the MR ratio was 5.8% in a GMR film of [NiFe(1.8 nm)/ Cu(1.1nm)] ×8/NiFe(10nm)/Fe(10nm). The full width at half maximum of the GMR curve was 35 Oe.

The effect of biquadratic exchange coupling on the magnetization configuration in multilayered films

The effect of biquadratic exchange coupling ( J 2) on the magnetization in multilayered GMR films as a function of field in the easy and hard directions has been investigated. The complexity of the configurations caused by J 2 may explain varieties of hysteresis and GMR curves obtained experimentally. Transverse biased permeability measurements make it possible to estimate both the bilinear ( J 1) and biquadratic ( J 2) effective fields.