Performance of Co/Al2O3/NiFe magnetic tunnel junctions prepared by a two-step rf plasma oxidation method

Abstract

A two-step rf plasma oxidation technique of an insulating layer has been performed to enhance electrical and structural properties of magnetic tunnel junction (MTJ) devices. Comparison was made by analyzing properties of the MTJ oxidized by conventional rf and two-step rf plasma oxidation methods. Experimentally observed results give improved surface imaging and sufficient oxygen contents of the insulating layer under the two-step oxidation method. In addition, electrical breakdown voltage and magnetoresistance of the MTJ were increased from 0.7 to 1.8 V and from 4.5% to 6.8%, respectively, correlated with improved structural information.

Reduced resistance drift in tunnel junctions using confined tunnel barriers

“…The O:Al ratio does not increase significantly until the oxidation front reaches an underlying layer acting as a diffusion stop, e.g., the cobalt under layer in our tunnel junctions. 8,36 Compared to the confined case, the unconfined barrier does not have an oxidation stop beneath the barrier and the WKB fit parameters confirm a relatively wide barrier with low barrier heights (less oxygen), which contracts with increasing time. In the confined devices, the large difference in $\mathrm{normal\Delta }{G}_f^0$ between Al 2 O 3 and the Co oxides allows all of the metallic Al to be oxidized prior to the oxidation front moving beyond the Al.…”

“…10 Alternatively, improving the oxygen concentration profile created during the initial oxidation can also reduce the resistance drift, since the system is initially closer to a relaxed state. 36,37 It should be noted that the use of plasma oxidation plays an important role in this context, as oxides formed by plasma oxidation opposed to thermal oxidation typically have much higher O:Al ratios which are closer to stoichiometric Al 2 O 3 . 8 While we have only studied plasma oxides, the use of confinement is expected to benefit oxide tunnel barriers independent of oxidation method.…”

Thermal and Electrical Stability Behavior of a Magnetic Tunnel Junction With a New Zr-Alloyed Al-Oxide Barrier

“…The barrier height also increased from 2.03 to 2.3 eV same as does. The MTJ with a ZrAl-oxide (9.89 at.% Zr) barrier had the highest reported of 1.75 V. This breakdown voltage was slightly higher than that reported by other groups [4], [13]. The high breakdown voltage indicated that the junction was a high-quality tunnel barrier that was pinhole-free with a low defect density.…”

“…The most important factors affecting MTJ stability are the microstructure and interface quality, and the chemical stability of the barrier materials. To satisfy these prerequisites, proper oxidation methods for tunnel junctions [1]- [4], new barrier materials [5]- [9], [15], [16] and modified materials [10]- [12] have been studied.…”

Effects of temperature, deposition conditions, and magnetic field on Ni/sub 80/Fe/sub 20//Fe/sub 50/Mn/sub 50//Ni/sub 80/Fe/sub 20//Al/sub 2/O/sub 3//Co and Ni/sub 80/Fe/sub 20//Al/sub 2/O/sub 3//Co magnetic tunnel junctions

“…1). The Al O barrier was deposited using a two-step rf plasma oxidation method [14]. 1500 of silicon dioxide passivation layer was evaporated at room temperature onto the MTJ devices using Korean Vacuum Tech EV2000 evaporator system by electron beam evaporation.…”