Study on initial current leakage spots in CoFeB-capped MgO tunnel barrier by conductive atomic force microscopy

Abstract

Although a microscopic study on a MgO tunnel barrier by atomic force microscopy has been required to study the reliability of magnetic tunnel junctions, the deterioration of bare MgO due to the adsorption of H2O and CO2 has been a problem. For an accurate evaluation of the initial current leakage spots distributed in a MgO tunnel barrier, a CoFeB-capped MgO tunnel barrier structure is proposed for evaluation by means of conductive atomic force microscopy. The CoFeB capping layer thickness was optimized to be 2.0 nm to prevent H2O and CO2 adsorption on the MgO and to minimize the series resistance due to the capping layer. The initial current leakage spot density of the MgO tunnel barrier with the optimized CoFeB capping layer exponentially increased as the thickness of the MgO tunnel barrier decreased from 1.6 to 0.8 nm, and was 157 spots/µm2 at the MgO thickness of 1.2 nm and the bias voltage of 0.5 V.

Two-dimensional materials prospects for non-volatile spintronic memories

“…The spintronics community is struggling to achieve and control ultra-thin MgO tunnel barriers with homogeneous thickness over a large scale. 89,90 The natural aptitude of 2DM tunnel barriers, which can be defined layer by layer with atomic precision, is one of the key advantages (Figs. 2b and 2f).…”

Non‐Oxidative Mechanism in Oxygen‐Based Magneto‐Ionics

“…Hydration (thermal dehydration) of MgO (Mg(OH) 2 ) is well documented in the literature [26][27][28][29][30][31] and in particular, the dehydration of Mg(OH) 2 into MgO has been discussed in the context of the development of strategies to improve interface quality in CoFeB/MgO based stacks and magnetic tunnel junctions. [7,[32][33][34] A potential hydration/dehydration process of the MgO/Mg(OH) 2 can have a large impact on the crystalline order of the system, as MgO hydration can lead to the formation of Mg(OH) 2 with brucite-like crystalline structure. [7,28,31] Therefore, the evaluation of a potential gate-induced MgO hydration/dehydration mechanism requires an investigation of the effects of gating on the crystalline structure of the MgO layer.…”

(Invited) Interface Control of Advanced Electronic Devices - High-k/Metal Gate System and Magnetic Tunneling Junction

“…Rapid decrease of the tunneling current spots between tCoFeB = 2.0 and 3.0 nm can be interpreted as the additional resistance increase when the tCoFeB becomes thicker. As a result, the CoFeB capping layer thickness is optimized to be 2.0 nm to prevent the H2O and CO2 adsorption on the MgO and to minimize the series resistance of the capping layer [19].…”

“…Under this optimized cap layer thickness, the current leakage spot density revealed a drastic decrease as the MgO barrier thickness increased. The tunneling current density drastically decreases as the MgO tunnel barrier thickness increases under the bias voltage of 0.5V [19]. This phenomenon is considered as a normal tunneling seen at MIM structure.…”

“…On the other hand, for the samples with tCoFeB = 2.0 and 3.0 nm, intact MgO was observed as shown in (b), (c) indicating that the H2O adsorption was successfully prevented by the CoFeB capping layer for tCoFeB ≥ 2.0 nm. Overall, tCoFeB ≥ 2.0 nm is requisite to prevent both H2O and CO2 adsorption on MgO in air[19].…”