Bias voltage and temperature dependence of magnetotunneling effect

Long, Yu; Li, X. W.; Xiao, Gang; Altman, Rick; Gallagher, W. J.; Marley, A. C.; Roche, K. P.; Parkin, S. S. P.

doi:10.1063/1.367813

Cited by 83 publications

(27 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In general, as reported before [6,11], for a FM-I-FM junction the JMR decreases monotonically as a function of bias voltage (see t Au 0.0 nm data in Fig. 3).…”

Section: (Received 21 January 1999)supporting

confidence: 49%

Quantum Well States in Spin-Dependent Tunnel Structures

et al. 1999

View full text Add to dashboard Cite

“…In general, as reported before [6,11], for a FM-I-FM junction the JMR decreases monotonically as a function of bias voltage (see t Au 0.0 nm data in Fig. 3).…”

Section: (Received 21 January 1999)supporting

confidence: 49%

Quantum Well States in Spin-Dependent Tunnel Structures

et al. 1999

View full text Add to dashboard Cite

“…On the other hand an optimized plasma oxidation technique can give similar RA products but superior low-bias TMR values. 10,11 Nonetheless, the bias dependence for both methods looks similar and gives voltages V 1/2 from 0.3 V for natural oxidation to 0.45 V for plasma oxidation. We believe that the observed improvement in bias dependence originates from the oxidation process itself.…”

mentioning

confidence: 98%

Strongly reduced bias dependence in spin–tunnel junctions obtained by ultraviolet light assisted oxidation

Boeve¹,

Girgis

Schelten

et al. 2000

Applied Physics Letters

View full text Add to dashboard Cite

For future implementation of ferromagnetic tunnel junctions, we need a better understanding of the influence of the insulating barrier preparation method on the junction resistance, tunnel magnetoresistance ͑TMR͒, and its voltage bias dependence. In this letter, we focus on the bias dependence of junctions (Co-Al 2 O 3 -Ni 80 Fe 20 ) prepared by ultraviolet light assisted in situ oxidation in an O 2 ambient. For an initial Al thickness of 1.3 nm, the resistance times area product of the junctions is 60 k⍀ m 2 , while showing up to 20% TMR at 5 mV bias. The decrease of TMR with bias voltage up to 1 V is remarkably small leading to V 1/2 , for which half of the low-bias TMR remains, well over 0.6 V. © 2000 American Institute of Physics. ͓S0003-6951͑00͒02908-9͔Tunnel-type magnetoresistance ͑TMR͒ occurring in devices, which consist of two ferromagnetic films separated by an insulating layer, has received great attention in recent years. 1 In these tunnel-type magnetic nanostructures, the charge transport is governed by tunneling through the insulating layer, generally produced by sputter deposition of a thin aluminum layer followed by oxidation. The electron tunneling current depends on the relative orientation of the magnetic moments in the two ferromagnetic films. More exactly, it is directly proportional to the polarization values of the electrons at the two insulator/metal interfaces, which may be different from the bulk polarization of the two magnetic films.For the future implementation of ferromagnetic tunnel junctions in practical applications, such as read heads and magnetoresistive random access memories, all characteristics of the tunnel devices have to be critically controlled. The small device size required by the applications leads to the need of small resistance-area ͑RA͒ products of 1-10 k⍀ m 2 , in order to keep the device resistance and RC time constant at an acceptable level. Another important parameter in the tunneling process between the two magnetic films is the bias voltage over the insulating layer. 2,3 The bias voltage dependence of the TMR may convey information about the detailed process of spin-polarized tunneling. 4 In general, we need a more complete understanding of the relationships between the resistance, the low-bias TMR, and the reliability of the junctions measured by the breakdown voltage of the junctions. The preparation of the insulator barrier is key in the behavior of these characteristics. In this letter we focus on the excellent bias voltage dependence of junctions prepared by ultraviolet light assisted in situ oxidation in an O 2 ambient.Ferromagnet-insulator-ferromagnet junctions were fabricated on ͑100͒-oriented 4-in. silicon wafers capped with a 200 nm thermally grown SiO 2 . The top and the bottom ferromagnetic layers consist of either Co or Ni 80 Fe 20 . After deposition of the bottom electrode using dc magnetron sputtering in an Ar ambient of 6ϫ10 Ϫ3 mbar, the aluminum layer with a thickness of 1.3 nm was produced using rf sputtering in 2ϫ10 Ϫ2 mbar, followed by an i...

show abstract

“…Although the decrease in JMR with V dc is significant, it is similar to initial results on Al 2 O 3 barriers. 17,18 In the latter case, there has been a steady improvement-the dc bias, at which JMR reduces to half its zero bias value, reaching Ͼ0.5 V, as the junction quality improved. 7 The bias dependence has been addressed before, although not well understood.…”

mentioning

confidence: 99%

Gallium oxide as an insulating barrier for spin-dependent tunneling junctions

Groot

Moodera

2000

Applied Physics Letters

115

View full text Add to dashboard Cite

Spin-dependent tunneling has been shown to occur through Ga 2 O 3 as the insulating tunnel barrier. Magnetic tunnel junctions of the type Co/Ga 2 O 3 /Ni 80 Fe 20 were prepared by oxidizing thin metal layer of Ga in oxygen plasma and characterized. The highest junction magnetoresistance observed was 18.2% at room temperature, increasing to 27.6% at 77 K. The average barrier height was estimated to be about 2 eV, as opposed to over 3 eV for junctions with Al 2 O 3 barrier of comparable quality. Otherwise these junctions behave similar to those with Al 2 O 3 . This shows the feasibility of obtaining lower resistance junctions with Ga 2 O 3 as the barrier for magnetic storage applications. © 2000 American Institute of Physics. ͓S0003-6951͑00͒04348-5͔Tunneling studies in magnetic tunnel junctions ͑MTJs͒ are being actively pursued in the last few years for their fundamental complexity as well as their application potential in data storage industry.1-3 It has been shown that the quality of the tunnel barriers plays a critical role in the success of spin tunneling in MTJs.1 Aluminum oxide is widely used as the insulating barrier since Al metal film can be reproducibly grown as ultrathin layer. [4][5][6][7] The excellent insulating properties of ultrathin Al 2 O 3 as well as its large forbidden gap, in general, lead to high resistance-area ͑RA͒ product, which is unfavorable from the application point of view. Recently there are reports wherein MTJs having lower RA values were obtained, using ultrathin Al 2 O 3 barriers.6-8 Also, from the fundamental physics viewpoint, there are theoretical predictions and some experimental interpretations of barrier dependence of spin polarized tunneling. 9 The motivation and necessity to study alternative tunnel barrier materials that show good spin tunneling properties is thus apparent. In this letter, our successful study of spin tunneling with Ga 2 O 3 as tunnel barrier, in MTJs, is described. Ga 2 O 3 is an insulator with a forbidden gap of 4.8 eV and is the only reported stable phase.10-12 However, there have been studies about the nonstoichiometric compound formation. Ga 2 O 3Ϫx becomes n-type semiconductor due to oxygen vacancies, which act as shallow donors with activation energy of 30-40 meV.11 Ga metal can be readily oxidized, relatively slower than Al 2 O 3 , having a heat of formation energy ͑kJ/mol͒ of 1080.2 compared to 1675.6 for Al 2 O 3 . 10MTJs were prepared in a high vacuum system ͑base pressure of 10 Ϫ8 Torr͒ thermal evaporation system. 1 Initially the LN 2 cooled glass substrate was covered with a 1 nm thick Si seed layer, followed by an 8-nm-thick Co electrode of long strips. Shadow metal masks were used to define the film and the junction pattern. A gallium film with the thickness ranging from 0.4 to 1.8 nm was deposited to cover the entire Co layer. After the substrate was warmed to room temperature ͑RT͒ the Ga layer was oxidized in oxygen glow discharge plasma at a pressure of 80 mTorr and a dc voltage of 1.6-1.8 kV for varying time ͑5-110 s͒. After pumping dow...

show abstract

Bias voltage and temperature dependence of magnetotunneling effect

Cited by 83 publications

References 11 publications

Quantum Well States in Spin-Dependent Tunnel Structures

Quantum Well States in Spin-Dependent Tunnel Structures

Strongly reduced bias dependence in spin–tunnel junctions obtained by ultraviolet light assisted oxidation

Gallium oxide as an insulating barrier for spin-dependent tunneling junctions

Contact Info

Product

Resources

About