Low-Frequency 1/f Noise Characteristics of Ultra-Thin AlO_x-Based Resistive Switching Memory Devices with Magneto-Resistive Responses

Round 1

Reviewer 1 Report

The paper investigates the effects of resistance switching in the ferromagnet/ dielectric AlOx/ ferromagnet system with a change in the electric voltage. Resistance measurements were carried out in the current geometry perpendicular to the plane of the layers. It is shown that when the bias voltage changes in the range of ± 1V, the resistance of the system reversibly changes from a state with a high resistance to a state with a low resistance. In each of the indicated states, different magnetoresistive curves are observed. The magnitudes of the magnetoresistance of the two states differ by a factor of 2. Particular attention is paid to the analysis of low-frequency noise spectra as a function of frequency, at various bias voltages. The analysis of the experimental data using the empirical Hooge’s expression for the low-frequency noise spectra showed that the parameters included in the expression turned out to be sensitive to the resistive state of the system. Based on the results obtained the authors concluded that under the action of an electric field, oxygen ions move in the AlOx barrier. According to the authors, this mechanism can play an important role in the dynamics of charge transfer in the system under study.

The presented article is interesting and actual one. It is directly related to the tasks of developing nonvolatile magnetic memory. There are no comments on the text of the article and the experimental results obtained. It can be recommended for publication as presented.

Author Response

We are grateful and encouraged by the positive feedback, and will keep trying our best to study the relative tasks in nonvolatile magnetic memory. Please also find enclosed the change list in correspondence with other referees for your reference.

Author Response File: Author Response.pdf

Reviewer 2 Report

There are a number of problems in this manuscript.

1. This is a followup work to Ref. 15. Here the authors add noise measurement to the study. However, the introduction and methods sections are substantially similar to those of Ref. 15. The authors did not motivate the noise measurement sufficiently in the introduction. The description of the noise measurement in the Methods section ends with "The design of the set-up can  be found elsewhere" and refers to refs. 16 and 17. It would be helpful to the reader if the authors give a brief description on what these two refs are about (they are not about "the design of the set-up").
2. If the electroresistance relies on ion migration within the oxide layer, reproducibility and repeatability would be a great concern. It seems that the authors have more than one sample - at least the data shown in Fig. 1 in this paper seem to be from a different sample than the data shown in Figs 1 and 2 of Ref. 15. I think that the authors should provide some statistics of the samples to give the reader an overall picture of the distribution of the sample performance.
3. The authors have not provided any evidence that connects the noise measurement to oxygen ion migration in AlO layer. The discussion in lines 150-159 is pure speculation. Such unsupported speculation cannot be published as part of a scientific literature.
4. In methods section the authors state that the details are described in Ref. 15, but Ref. 15 states that the details are described in another paper published in 2014. This is not a good practice.
5. The area of the junction is 150 micron x 150 micron, not 150 micron^2 x 150 micron^2

Author Response

We sincerely thank you for the valuable comments and suggestions. According to your suggestions, a series of modification, as stated in details in the following letter, are made to clarify the unclear parts. A Change List summarizing the changes made in the manuscript is attached in the end. We heartedly hope that you find our replies and revision compelling and sufficient, and that our manuscript can be approved for publication in Electronics.

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript focuses on the electrical properties of NiFe/CoFe/AlOx/CoFe multilayer with electric-field controlled nonvolatile resistive switching effect. The most important result presented in the paper is the noise power spectrum density (PSD) followed by the determination of the exponent in the 1/f noise spectra during the resistive switching of the system. The measurements were carried out at room temperature for the low frequency range and showed a clear dependence of the noise parameters on the resistive state of the sample.

The manuscript should be treated as a continuation and complement of the studies presented in the recently published paper J.-Y. Hong et al., Sci. Rep. 11, 6027 (2021). It concerns the same system prepared in the same way and analyzed using similar measurement techniques. The manuscript together with the presented data is written and presented clearly. However, a few issues should be addressed before the paper is accepted for publication:

1. Please add information what was the sweep rate of the voltage during the measurements presented in Figures 1 - 3. What was the timescale of these measurements?
2. How the PSD measurements during the reset depend on the voltage sweep rate?
3. Please explain why the switching voltages of the presented system differ significantly from the voltages reported the system discussed in J.-Y. Hong et al., Sci. Rep. 11, 6027 (2021). The thicknesses and the method of preparation of the samples described in both works were identical, we should therefore expect the same characteristics.
4. Please also explain the differences in MR values which differ significantly from those reported in the published paper J.-Y. Hong et al., Sci. Rep. 11, 6027 (2021). In this context, please comment on the repeatability of the obtained samples and results.
5. Please describe what the yellow area means in Fig. 4b. The authors do not refer to the marked area in any part of the text nor in the figure caption, so it is not clear why it was included in the graph.
6. Please define the LFN abbreviation the first time is used in the manuscript.

Author Response

We sincerely thank you for the valuable comments and suggestions. According to your suggestions, a series of modification, as stated in details in the following letter, are made to clarify the unclear parts. A Change List summarizing the changes made in the manuscript is attached in the end. We heartedly hope that you find our replies and revision compelling and sufficient, and that our manuscript can be approved for publication in Electronics.

Author Response File: Author Response.pdf

Reviewer 4 Report

Hong et al. presented AlOx based resistive switching memory devices with a magneto-resistive response. They carried low-frequency 1/f noise characteristics, which brought insight into oxygen traps and electric-field-driven ionic motions in AlOx. Overall, work is concise and exciting for memory technologies. Authors may consider my minor concern for this work is below.

 

1. Along with typical device analysis, a schematic of the device should be added for clarity.
2. The interfacial issue should be highlighted and should be compared with reported memory devices.
3. Magnetic tunnel junction and spintronic application of the presented device should be discussed.
4. Power consumption of the reported device should be given in the manuscript?

Comments for author File: Comments.pdf

Author Response

We sincerely thank you for the valuable comments and suggestions. According to your suggestions, a series of modification, as stated in details in the following letter, are made to clarify the unclear parts. A Change List summarizing the changes made in the manuscript is attached in the end. We heartedly hope that you find our replies and revision compelling and sufficient, and that our manuscript can be approved for publication in Electronics.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The revised manuscript is significantly improved in the introduction and methods parts. But the conclusion part is still not satisfactory. The rewritten paragraph now contains new citations of three references. However, the added references do not support the case made by the authors, and further exposes a lack of understanding.

All three references (25, 26, and 34) considered oxygen diffusion in perovskites as possible mechanism for electroresistance. Perovskites are notorious for relatively fast oxygen diffusion. Therefore it is reasonable to expect oxygen diffusion as the dominant mechanism for resistance change. Al2O3, on the other hand, is a well-known diffusion barrier for oxygen ions. The diffusion coefficient for oxygen is probably orders of magnitude smaller in Al2O3 than in perovskites. It is not reasonable to apply the same argument for two materials.

The description by the authors about oxygen ions diffusing from and to "conduction path" is puzzling. What is this "conduction path"? Al2O3 is a tunnel barrier. Are the authors suggesting that their samples have pinholes? This description is unclear and is not supported by any experimental data.

Author Response

We thank the referee for being attentive in corresponding with us, and also thank you for the valuable comments and suggestions. According to your suggestions, we have taken more relative references into account and re-examined our experimental analysis. A series of modifications, as stated in details in the following letter, are made to account for the possible mechanism. A Change List summarizing the changes made in the manuscript is attached in the end. We heartedly hope that you find our replies and revision compelling and sufficient, and that our manuscript can be approved for publication in Electronics.

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

The authors have addressed all remaining concerns from the previous report. The paper is now ready to publish.

Author Response

We thank the referee for the valuable comments in corresponding with us, which clarify the important physics in the present work. We heartedly thank you for the suggestions and feedbacks, and that you find our work qualified for publication in Electronics.