• Journal of the Korean Magnetics Society
• /
• v.15 no.4
• /
• pp.231-235
• /
• 2005

We studied the microstructural evolution of ZrTM-Al (TM=Nb and Ti) alloy films, MR and electrical properties of the MTJ with $ZrTM-AlO_x$ barrier as a function of Zr/TM ratio. We observed that the ternary-oxide barrier reduced the TMR ratio due mainly to the structural defects such as the surface roughness. The change in TMR ratio and $V_h$ with Zr/TM ratio exactly corresponds to the systematic changes in the microstructural variation. Although the MTJ with ternary oxide reduced the TMR and the electrical stabilities, the junction resistances decreased as the Ti and Nb concentration increased due to the band-gap reduction caused by the formation of extra bands

• Journal of the Microelectronics and Packaging Society
• /
• v.23 no.4
• /
• pp.49-55
• /
• 2016

Nowadays there are magnetic sensors in a wide variety of equipment such as computers, cars, airplanes, medical and industrial instruments. In many of these applications the magnetic sensors offer safe and non-invasive means of detection and are more reliable than other technologies. The electric current in a conductor generates a magnetic field detected by this type of sensor. This work aims to define a package dedicated to an electrical current sensor using a MTJ (Magnetic Tunnel Junction) as a sensing device. Four different proposals of packaging, three variations of the chip on board (CoB) package type and one variation of the thin small outline package (TSOP) were analyzed by COMSOL modeling software by simulating a brad range of current injection. The results obtained from the thermal and magnetic analysis has proven to be very important for package improvements, specially for heat dissipation performance.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.02a
• /
• pp.167-167
• /
• 2011

Magnetic random access memory (MRAM) is one of the prospective semiconductor memories for next generation. It has the excellent features including nonvolatility, fast access time, unlimited read/write endurance, low operating voltage, and high storage density. MRAM consists of magnetic tunnel junction (MTJ) stack and complementary metal-oxide semiconductor (CMOS). The MTJ stack is composed of various magnetic materials, metals, and a tunneling barrier layer. For the successful realization of high density MRAM, the etching process of magnetic materials should be developed. Among various magnetic materials, FePt has been used for pinned layer of MTJ stack. The previous etch study of FePt magnetic thin films was carried out using $CH_4/O_2/NH_3$. It reported only the etch characteristics with respect to the variation of RF bias powers. In this study, the etch characteristics of FePt thin films have been investigated using an inductively coupled plasma reactive ion etcher in various etch chemistries containing $CH_4$/Ar and $CH_4/O_2/Ar$ gas mixes. TiN thin film was employed as a hard mask. FePt thin films are etched by varying the gas concentration. The etch characteristics have been investigated in terms of etch rate, etch selectivity and etch profile. Furthermore, x-ray photoelectron spectroscopy is applied to elucidate the etch mechanism of FePt thin films in $CH_4$/Ar and $CH_4/O_2/Ar$ chemistries.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.18 no.3
• /
• pp.276-283
• /
• 2005

Magnetic tunneling transistor (MTT) device using the amorphous n-type Si semiconductor film for base and collector consisting of the [CoFe/NiFe](free layer) and Si(top layer) multilayers was used to study the spin-dependent hot electron magnetocurrent (MC) and tunneling magnetoresistance (TMR) at room temperature. A large MC of 40.2 % was observed at the emitter-base bias voltage ( $V_{EB}$ ) of 0.62 V. The increasing emitter hot current and transfer ratio ( $I_{C}$/ $I_{E}$) as $V_{EB}$ are mainly due to a rapid increase of the number of conduction band states in the Si collector. However, above the $V_{EB}$ of 0.62 V, the rapid decrease of MC was observed in amorphous Si-based MTT because of hot electron spin-dependent elastic scattering across CoFe/Si interfaces.

• Journal of the Korean Magnetics Society
• /
• v.12 no.2
• /
• pp.68-72
• /
• 2002

In this research, the effects of capacitance to the access time were studied at the junction area of tunneling magnetoresistance when these were used as memory devices. These results were obtained by applying electric signal input and magnetic field was not used. We applied bipolar square waves of 1MHz to the MTJ samples to obtain the results and time constant ($\tau$) calculated by observing wave responses utilizing an oscilloscope. And time constant was compared with junction area. Each part of MTJ sample, such as electrical pad, lead and contact area, was modeled as an electrical equivalent circuit based on experimental results. For the 200㎛$\times$200㎛ cell, junction capacitance was 90 pF. Also, measurement and simulation results were compared, which showed those similarity.

• Journal of the Korean Magnetics Society
• /
• v.15 no.6
• /
• pp.311-314
• /
• 2005

We investigated the composition dependence of the tunneling magnetoresistance (TMR) behavior and the stability of the magnetic tunnel junctions (MTJs) with TiAlOx barrier and the microstructural evolution of TiAl alloy films. The TMR ratio increased up to $49\%$ at $5.33\;at\%$ Ti. In addition, a significant tunneling magnetoresistance (TMR) value of $20\%$ was maintained after annealing at $450^{\circ}C$, and the breakdown voltage ($V_B$) of and 1.35 V were obtained in the MTJ with $5.33\;at\%$ Ti-alloyed AlOx barrier. These results were closely related to the enhanced quality of the barrier material microstructure in the pre-oxidation state. Ti alloying enhanced the barrier/electrode interface uniformity and reduced microstructural defects. These structural improvements enhanced not only the TMR effect but also the thermal and electrical stability of the MTJs.

• Journal of the Korean Magnetics Society
• /
• v.25 no.2
• /
• pp.47-51
• /
• 2015

To achieve a high tunneling magneto resistance (TMR) of sputtered magnetic tunnel junctions (MTJs) with an MgO barrier, the annealing process is indispensable. The structural and compositional changes as consequences of the annealing greatly affect the spin-dependent transport properties of MTJs. Higher TMR could be obtained for MTJs annealed at higher annealing temperature. The diffusion of Ru, Mn and/or Ta in the MTJs may occur during annealing process, which is known to be detrimental to spin-dependent tunneling effect. The rapid thermal annealing (RTA) process was used for annealing the MTJs with synthetic antiferromagnets. To suppress the diffusion of Mn, Ru and/or Ta in the MTJs, the process time and temperature of RTA were minutely controlled.

• Journal of Magnetics
• /
• v.15 no.4
• /
• pp.185-189
• /
• 2010

Spin polarized tunneling through a hybrid tunnel barrier of a Spin filter (SF) based on a EuO ferro-magnetic semiconductor and an organic semiconductor (OSC) (rubrene in this case) was investigated. For quasi-magnetic tunnel junction (MTJ) structures, such as Co/rubrene/EuO/Al, we observed a strong spin filtering effect of the EuO layer exhibiting I-V curves with high spin polarization (P) of up to 99% measured at 4 K. However, a magnetoresistance (MR) value of 9% was obtained at 4.2 K. The low MR compared to the high P could be attributed to spin scattering caused by structural defects at the interface between the EuO and rubrene, due to nonstoichiometry in the EuO.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.02a
• /
• pp.77-77
• /
• 2011

These days, a growing demand for memory device is filled up with the flash memory and the dynamic random access memory (DRAM). Although DRAM is a reasonable solution for current demand, the universal novel memory with high density, high speed and nonvolatility, needs to be developed. Among various new memories, the magnetic random access memory (MRAM) device is considered as one of good candidate memories because of excellent features including high density, high speed, low operating power and nonvolatility. The etching of MTJ stack which is composed of magnetic materials and insulator such as MgO is one of the vital process for MRAM. Recently, MgO has attracted great interest in the MTJ stack as tunneling barrier layer for its high tunneling magnetoresistance values. For the successful realization of high density MRAM, the etching process of MgO thin films should be investigated. Until now, there were some works devoted to the investigations on etch characteristics of MgO thin films. Initially, ion milling was applied to the etching of MgO thin films. However, ion milling has many disadvantages such as sidewall redeposition and etching damage. High density plasma etching containing the magnetically enhanced reactive ion etching and high density reactive ion etching have been employed for the improvement of etching process. In this work, inductively coupled plasma reactive ion etching (ICPRIE) system was adopted for the improvement of etching process using MgO thin films and etching gas mixes of $CH_4$/Ar and $CH_4$/$O_2$/Ar have been employed. The etch rates are measured by a surface profilometer and etch profiles are observed using field emission scanning emission microscopy (FESEM). The effects of gas concentration and etch parameters such as coil rf power, dc-bias voltage to substrate, and gas pressure on etch characteristics will be systematically explored.

• Proceedings of the Korean Magnestics Society Conference
• /
• 2000.09a
• /
• pp.5-32
• /
• 2000

MRAM, High performance MRAM using MTJS demostrated, fully integrated MTJ MRAM with CMOS circuits, write time ~2.3 nsec; read time ~3 nsec, Thermally stable up to ~350 C, Switching field distibution controlled by size & shape. Magnetic Tunnel Junction Properties, Magnetoresistance: ~50% at room temperature, enhanced by thermal treatment, Negative and Positive MR by interface modification, Spin Polarization: >55% at 0.25K, Insensitive ot FM composition, Resistance $\times$ Area product, ranging from ~20 to 10$^{9}$ $\Omega$(${\mu}{\textrm}{m}$)$^{2}$, Spin valve transistor, Tunnel injected spin polarization for "hot" electrons, Decrease of MTJMR at high bias originates from anode.