# Fileset

[Supplementary materials.docx](https://mdr.nims.go.jp/filesets/c325bb09-a8a9-427b-86f3-26859635bf51/download)

## Creator

[Tomoya Nakatani](https://orcid.org/0000-0001-9590-216X), [Hirofumi Suto](https://orcid.org/0000-0003-4387-5862), [Prabhanjan D. Kulkarni](https://orcid.org/0000-0002-4605-5256), Hitoshi Iwasaki, [Yuya Sakuraba](https://orcid.org/0000-0003-4618-9550)

## Rights

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article
appeared in Tomoya Nakatani. Appl. Phys. 134, 213904 (2023) and
may be found at https://doi.org/10.1063/5.0180812[In Copyright](http://rightsstatements.org/vocab/InC/1.0/)

## Other metadata

[Improvement of magnetic field detectivity in electrical 1/f noise-dominated tunnel magnetoresistive sensors by AC magnetic field modulation technique](https://mdr.nims.go.jp/datasets/3b6fb13b-9c3d-41c8-9bff-c568ddb075ac)

## Fulltext

Supplementary materialsImprovement of magnetic field detectivity in electrical 1/f noise-dominated tunnel magnetoresistive sensors by AC magnetic field modulation techniqueTomoya Nakatani,* Hirofumi Suto, Prabhanjan D. Kulkarni, Hitoshi Iwasaki, and Yuya SakurabaResearch Center for Magnetic and Spintronic Materials, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki, 305-0047, Japan* Corresponding author: nakatani.tomoya@nims.go.jp1. Ar plasma damage in MgO tunnel barrierIn the present work, we artificially induced lattice defects in the MgO tunnel barrier of the TMR device to manipulate the intensity of the electrical 1/f nose. This was achieved by exposing the MgO barrier (2 nm) to an Ar plasma. The Ar plasma was generated by an RF reserve-sputtering stage of our sputter deposition system. In the deposition system, there is a significant leakage of the RF power to the ground, thus the exact RF power density on the sample surface is not known. However, we have confirmed that the physical etching rate for MgO by the Ar plasma is negligibly small. From the following experimental observations, we consider that the Ar plasma exposure process creates lattice defects only in the surface of the MgO barrier and the property of the soft-pinned FL remains unchanged. First, we compare the TMR characteristics of two devices, device B and C, which are prepared differently as shown in the flowchart of Fig. S1(a). Device B is the same as in this paper, where the MgO barrier (2 nm) was exposed to the Ar plasma for 30 s. Device C was fabricated similarly, but the Ar plasma exposure for 30 s was placed after the deposition of half of the MgO barrier, i.e., 1 nm, followed by another deposition of 1 nm of MgO. Both devices were annealed at 350 °C for 1 h under a magnetic field of 0.5 T after the device fabrication.Figures S1(b) and (c) show the distributions of RA in the parallel magnetization state vs. TMR ratio of the devices fabricated on the substrates of device B and C, respectively. Device B showed large distributions of RA and TMR ratio among the nominally identical devices, suggesting that the degree of damage caused by the Ar plasma exposure differed from device to device. The TMR ratio of device B was at most 100%, much lower than the TMR ratio of 218% for device A fabricated without Ar plasma exposure (see Fig. 1(b)). On the other hand, device C showed an almost constant TMR ratio of 214%. For this device, the observed RA distribution was as usual for our deposition system, which was due to the non-uniformity of the MgO thickness. The inset of Fig. S1(c) shows the R-H curves of a 40-μm diameter device C, showing a soft-pinning field (Hsp) of 1.1 mT and a coercivity (Hc) of 0.9 mT, very close to those of devices A and B (see Figs. 1(b) and (c)).FIG. S1. (a) Flowchart of the Ar plasma exposure process to the MgO barrier. (b) and (c) Distribution of RA in the parallel magnetization state (RAP) and TMR ratio of the individual devices with diameters of 20−60 μm of devices B and C, respectively.Next, we compare the 1/f noise levels of the devices including device A. Figure S2(a) shows the noise spectra of these devices at Hy = 0, where the magnetizations of the soft-pinned FL and reference layer are in the antiparallel (AP) configuration. Sample B showed a very high 1/f noise level with a Hooge parameter of αH = 4.6×10−6 μm2, due to the electrical 1/f noise caused by the lattice defects induced by the Ar plasma. On the other hand, sample C showed much lower 1/f noise with αH = 1.6×10−8 μm2, comparable to that of sample A, αH = 1.8×10−8 μm2. Figure 2(b) shows the Hy-dependence of αH of devices A and C, both of which shows an increase in αH with increasing Hy. Thus, the 1/f noise of device C is dominated by the magnetic 1/f noise as well as device A.These results indicate that the Ar plasma damage induced in the lower half of the MgO barrier in sample C was healed by the deposition of another half of the MgO barrier, although the mechanism is not clear at present. Possibly, the lattice defects on the MgO surface caused by the Ar plasma, such as oxygen vacancies, are recovered by another MgO deposition. On the other hand, since device C showed a similar 1/f noise level as that of device A, the Ar plasma damage to the soft-pinned FL is considered to be negligible. Therefore, we believe that the Ar plasma exposure process to the MgO barrier induces lattice defects only on the MgO surface, which enhances the intensity of the electrical 1/f noise.FIG. S2. (a) Noise spectra of devices A, B, and C at Hy = 0. The higher white noise level of device A than that of device C is due to the higher resistance of device A (RAP = 182.5 Ω) than that of device C (RAP = 37.6 Ω). (b) Dependence of the Hooge parameter (αH) on the bias field Hy for devices A and C.2image1.emfDeposition up to CoFeB FLDeposition of MgO (2 nm) barrierDeposition of MgO (1 nm)Ar plasma exposure for 30 sDeposition of CoFeB reference layer and the rest of the layerDeposition of another MgO (1 nm)Device fabricationAnnealing at 350 °CR-H and noise measurementsDevice BDevice C(a)(b) Device B(c) Device CEAHAimage2.emf1 10 100 1000 1000010-910-810-710-610-5Device A B Cf  (Hz)(a)(b)Hy= 0 (AP state)