• JSTS:Journal of Semiconductor Technology and Science
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• v.2 no.3
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• pp.173-179
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• 2002

We propose a novel sensing circuit for 2T-2MTJ MRAM that can be used for high speed synchronous operation. Proposed bit-line sense amplifier detects small voltage difference in bit-lines and develops it into rail-to-rail swing while maintaining small voltage difference on TMR cells. It is small enough to fit into each column that the whole data array on selected word line are activated as in DRAMs for high-speed read-out by changing column addresses only. We designed a 256Kb read-only MRAM in a $0.35\mu\textrm{m}$ logic technology to verify the new sensing scheme. Simulation result shows a 25ns RAS access time and a cycle time shorter than 10 ns.

• Proceedings of the IEEK Conference
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• 2003.07b
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• pp.1181-1184
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• 2003

This paper proposes a new Sense Amplifier for MRAM. Current Sense Amplifier employs a latch-type circuit to amplify a signal from the selected memory cell. The proposed Sense Amplifier simplifies the circuit by amplifying the signal using cross-coupled PMOS transistors. It shows the same operation speed as the latch-type Sense Amplifier in simulation and occupies only 85% of the area taken by the latch-type Sense Amplifier.

• Proceedings of the IEEK Conference
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• 2003.07b
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• pp.863-866
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• 2003

Recently, there has been growing interests in the magneto-resistive random access memory (MRAM) because of its great potential as a future nonvolatile memory. In this paper, a CMOS macro-model for MRAM cell based on a twin cell structure is proposed. The READ and WRITE operations of the MTJ cell can be emulated by adopting data latch and switch blocks. The behavior of the circuit is confirmed by HSPICE simulations in a 0.35-${\mu}{\textrm}{m}$ CMOS process. We expect the macro model can be utilized to develope the core architecture and the peripheral circuitry. It can also be used for the characterization and the direction of the real MTJ cells.

• Proceedings of the Korean Magnestics Society Conference
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• 2007.05a
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• pp.61.2-61.2
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• 2007

• Journal of the Korean Magnetics Society
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• v.15 no.6
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• pp.315-319
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• 2005

To obtain low switching field ($H_{SW}$) we introduced amorphous ferromagnetic $Co_{70.5}Fe_{4,5}Si_{15}B_{10}$ single and synthetic antiferromagnet (SAF) free layers in magnetic tunnel junctions (MTJs). The switching characteristics for MTJs with structures $Si/SiO_2/Ta$ 45/Ru 9.5/IrMn 10/CoFe 7/AlOx/CoFeSiB 7 or CoFeSiB (t)/Ru 1.0/CoFeSiB (7-t)/Ru 60 (in nm) were investigated and compared to MTJs with $Co_{75}Fe_{25}$ and $Ni_{80}Fe_{20}$ free layers. CoFeSiB showed a lower saturation magnetization of $560 emu/cm^3$ and a higher anisotropy constant of $2800\;erg/cm^3$ than CoFe and NiFe, respectively. An exchange coupling energy ($J_{ex}$) of $-0.003erg/cm^2$ was observed by inserting a 1.0 nm Ru layer in between CoFeSiB layers. In the CoFeSiB single and SAF free layer MTJs, it was frond that the size dependence of the $H_{SW}$ originated from the lower $J_{ex}$ experimentally and by micromagnetic simulation based on the Landau-Lisfschitz-Gilbert equation. The CoFeSiB SAF structures showed lower $H_{SW}$ than that of NiFe, CoFe and CoFeSiB single structures. The CoFeSiB SAF structures were proved to be beneficial far the switching characteristics such as reducing the coercivity and increasing the sensitivity in micrometer to submicrometer-sized elements.

• JSTS:Journal of Semiconductor Technology and Science
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• v.4 no.2
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• pp.110-116
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• 2004

We propose a novel sensing scheme, which operates by sensing the difference in voltage between a memory cell and a reference cell for a magneto-resistive random access memory (MRAM). A new midpoint-reference generation circuit is adopted for the reference cell to improve the sensing margin and to guarantee correct operation of sensing circuit for wide range of tunnel magneto resistance (TMR) voltages. In this scheme, the output voltage of the reference cell becomes nearly the midpoint between the cell voltages of high and low states even if the voltage across the magnetic tunnel junction (MTJ) varies.

• Journal of the Korean Magnetics Society
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• v.17 no.3
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• pp.124-127
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• 2007

Magnetic tunnel junctions (MTJs), which consisted of amorphous CoFeSiB layers, were investigated. The CoFeSiB layers were used to substitute for the traditionally used CoFe and/or NiFe layers with an emphasis given on understanding the effect of the amorphous free layer on the switching characteristics of the MTJs. CoFeSiB has a lower saturation magnetization ($M_s\;:\;560\;emu/cm^3$) and a higher anisotropy constant ($K_u\;:\;2800\;erg/cm^3$) than CoFe and NiFe, respectively. An exchange coupling energy ($J_{ex}$) of $-0.003\;erg/cm^2$ was observed by inserting a 1.0 nm Ru layer in between CoFeSiB layers. In the Si/$SiO_2$/Ta 45/Ru 9.5/IrMn 10/CoFe 7/$AlO_x$/CoFeSiB 7 or CoFeSiB (t)/Ru 1.0/CoFeSiB (7-t)/Ru 60 (in nm) MTJs structure, it was found that the size dependence of the switching field originated in the lower $J_{ex}$ using the experimental and simulation results. The CoFeSiB synthetic antiferromagnet structures were proved to be beneficial for the switching characteristics such as reducing the coercivity ($H_c$) and increasing the sensitivity in micrometer size, even in submicrometer sized elements.

• Journal of the Korean Magnetics Society
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• v.16 no.6
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• pp.279-282
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• 2006

Magnetic tunnel junctions (MTJs), which consisted of amorphous ferromagnetic NiFeSiB free layers, were investigated. The NiFeSiB layers were used to substitute for the traditionally used CoFe and/or NiFe layers with the emphasis being given to obtaining an understanding of the effect of the amorphous free layer on the switching characteristics of the MTJs. $Ni_{16}Fe_{62}Si_{8}B_{14}$ has a lower saturation magnetization ($M_{s}:\;800\;emu/cm^{3}$) than $Co_{90}Fe_{10}$ and a higher anisotropy constant ($K_{u}:\;2700\;erg/cm^{3}$) than $Ni_{80}Fe_{20}$. The $Si/SiO_{2}/Ta$ 45/Ru 9.5/IrMn 10/CoFe $7/AlO_{x}/CoFeSiB\;(t)/Ru\;60\;(in\;nanometers)$structure was found to be beneficial for the switching characteristics of the MTJ, leading to a reduction in the coercivity ($H_{c}$) and an increase in the sensitivity resulted from its lower saturation magnetization and higher uniaxial anisotropy. Furthermore, by inserting a very thin CoFe layer at the tunnel barrier/NiFeSiB interface, the TMR ratio and switching squareness were improved more with the increase of NiFeSiB layer thickness up to 11 nm.

• Proceedings of the Korean Magnestics Society Conference
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• 2000.09a
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• pp.325-326
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• 2000

Low temperature diagnosis was performed as a probe for the integrity of MTJ(Magnetic tunnel junction) process which is optimised for the given plasma oxidation condition. TMR ratio increased slowly with decreasing temperature than that expected from spin wave exitation theory〔1〕. Junction resistance (RJ) does not follow T$\^$-$\frac{1}{2}$/ law below 200 K, indicating another conduction path besides spin polarized tunneling is involved at low temperature. Temperature dependence of conductance dip and bias dependence of TMR with temperature are discussed, from which the quality of tunnel barrier and its formation process can be inferred.

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