Round 1

Reviewer 1 Report

In this manuscript, the authors focused on the key technologies involved in Micro-LED display technology, such as chip technology, full-color display, bonding and driving technology, and introduces the research history and cutting-edge progress of these technologies in detail.

The manuscript is rejected for publication due to these comments;

1. The expressions and language in this manuscript is poor.

2. The quality of Abstract is poor (in terms of scientific writing and technically).

3. Introduction quality is also not good. Lacks a proper logic and good story. Sequence is very poor.

4. Description of previous work is also very bad (Line 57-76).

5. What are the key outcomes of these literature study?

6. The whole draft of this paper has been expressed in an inappropriate way.

Poor quality

Author Response

Comment:

1. 1. The expressions and language in this manuscript is poor.
2. The quality of Abstract is poor (in terms of scientific writing and technically).
3. Introduction quality is also not good. Lacks a proper logic and good story. Sequence is very poor.
4. Description of previous work is also very bad (Line 57-76).
5. What are the key outcomes of these literature study?
6. The whole draft of this paper has been expressed in an inappropriate way.

Response: Thanks for your comments, which is highly appreciated. According to your suggestion, we have revised some repetitive words in the abstract. In the introduction, descriptions of different display technologies and performance tables are added for comparison to enhance the richness of the content. As for the logic you said, we think the logic of the whole paper is reasonable, including chip epitaxy, chip structure, and the method of transferring and bonding subsequent chips to realize full-color display. In addition, for the driving technology, we not only explain the driving types, but also supplement different driving circuits. In the last part, we explain some commercial applications of Micro-LED in chronological order. Generally speaking, the order of introduction is logical.

In addition, for (line 57-76), we have also made corresponding modifications to make the expression more appropriate and meet the requirements of scientific writing. In view of the main research achievements you mentioned, this review we wrote starts from the Micro-LED chip, introduces the obstacles encountered in the process of becoming a Micro-LED display screen and the corresponding solutions, including its advantages and disadvantages, and provides reference value for the commercialization of Micro-LED display screens. I hope the changes we have made can meet your requirements.

We sincerely hope that this revised manuscript has addressed all your comments and suggestions. We appreciated for reviewers’ warm work earnestly,and hope that the correction will meet with approval.Once again,thank you very much for your comments and suggestions.

Reviewer 2 Report

Title: Research progress of Micro-LED display technology

Authors: Shenghao Zhang, Hua Zheng, Lv Zhou, Huadan Li, Yuanrui Chen, Chenchen Wei, Tao Wu, Wei Lv Geng Zhang, Shaoqiang Zhang, Zheng Gong, Baohua Jia, Han Lin, Zhiwen Gao, Wei Xu and Honglong Ning

The manuscript is an overview of the progress in the field of micro-LED display technology. The activity of researchers in this field has been on the rise every year, in particular after 2020. In 2023, researchers from MIT and from other Universities in the US and Korea developed full-color vertically-stacked micro-LEDs with the highest array density (5100 PPI) and the smallest size (4 µm) reported to date. Many solutions are already being applied in practice. In 2022, Seoul Viosys demonstrated micro-LED based on the laminated structure as well as high-resolution micro-LED display. Now HC Semitek cooperates with AIXTRON on Micro-LED display technology. Unfortunately, the authors do not mention the latest achievements in this field and do not consider the publications of 2022-2023. Among the ninety cited papers, the two most recent ones were published in 2021, which is 2 %. And as a result, many recent breakthroughs have been overlooked. In particular, the important studies by  F. Chen et al. (Int. J. Extrem. Manuf., 2022), J.-E. Ryu et al. (Advanced materials, 2022),  S. Hwangbo et al.(Nature Nanotechnology, online, April 2022), A.R. Anwar et al. (Laser & Photonics Review, 2022), S. Hammami et al. (Proc. SPIE PC12421, 2023), D. Chen et al.  (Research, 2023) and by many others have been ignored in the manuscript. Bearing  in mind that the main purpose of any topical overview has not been achieved by the authors, the manuscript can be recommended for publication only after significant revision.

Author Response

We thank the reviewer for raising these questions.The research on Micro-LED is increasing every year, and our manuscript really ignores the latest research results in the past two years. According to your prompt, we have added in the revised mode, including the research results of MIT and other universities in 2023 (page 3, line 112), the exhibits of Seoul Viosys (page 26, line 948), and the MOCVD equipment of Ai Siqiang (page 4, line 167).We added the recent important research you mentioned, including F. Chen et al. (int.j. extreme.manuf., 2022), and we mainly added it to the huge transfer part. See (page 9, line 349; Page 10, line 384). J.-E. Ryu et al. (Advanced Materials, 2022), this part refers to the tabular part and the full-color display part added in the introduction, for details (page 2, line 46; Page 12, line 478; Page 14, line 559). S. Hwangbo et al. (Nature Nano Technology, Online, April 2022), this part is added in the section of monolithic integration, for details (page 10, line 410; Page 11, line 428). A.R. Anwar et al. (Laser & Photonics Review, 2022), this part is added to the mass transfer and commercial application of Micro-LED, for details (page 2, line 50; Page 9, line 362; Page 26, line 927). S hammami et al. (proc. spiepc12421, 2023), this part is added to the section of epitaxial technology, for details (page 4, line 145). D. Chen et al. (Research, 2023), this part is added in the section of chip structure, monolithic integration and RGB three-color method, for details (page 7, line 267; Page 11, line 442; Page 12, line 506).

In a word, we supplement the latest research on Micro-LED display technology and the recent references. In addition, based on the completeness of the summary, we added the chapter of massive transfer and monolithic integration (Chapter 2).We have tried our best to revise the manuscript according to your kind and construction comments and suggestions. We sincerely hope that this revised manuscript has addressed all your comments and suggestions.

Reviewer 3 Report

1. This is a review paper. It is recommended to set the expectation of the review clearly, e.g. what is the next after this review? 

2. "2.1 epitaxial technique", please correct the minor typo.

3. Heterogeneous integration of GaN led with other technologies is not well cover, e.g. 

Soh, M.Y.; Teo, T.H.; Selvaraj, S.L.; Peng, L.; Disney, D.; Yeo, K.S. Heterogeneous Integration of GaN and BCD Technologies. Electronics 2019, 8, 351. https://doi.org/10.3390/electronics8030351

4. "CMOS driving" or "CMOS driving circuits"

5. Packaging aspects is also not well addressed. 

6. What are the different between "CMOS driving" and "Driving technology" sections? It is recommended to have better paper organization. 

English quality is average.

Author Response

Comment 1: This is a review paper. It is recommended to set the expectation of the review clearly, e.g. what is the next after this review?

Response: We are so grateful for your kind question. The expectation of this review has been given in the summary part. The objective of the evaluation is to propose that the existing Micro-LED display technology will become the future display technology.

Comment 2: "2.1 epitaxial technique", please correct the minor typo.

Response: We have corrected it to “epitaxy technology”.

Comment 3: Heterogeneous integration of GaN led with other technologies is not well cover, e.g. Soh, M.Y.; Teo, T.H.; Selvaraj, S.L.; Peng, L.; Disney, D.; Yeo, K.S. Heterogeneous Integration of GaN and BCD Technologies. Electronics 2019, 8, 351. https://doi.org/10.3390/electronics8030351

Response: We add the heterogeneous integration of GaN LED and other technologies in the section of monolithic integration, hoping to meet the requirements.

Comment 4: "CMOS driving" or "CMOS driving circuits"

Response: We introduced active driving technology in the driving technology part, and CMOS driving in this part. Because TFT driving is also introduced, the driving circuit part includes CMOS driving circuit and TFT driving circuit.

Comment 5: Packaging aspects is also not well addressed.

Response: In terms of packaging, we have mentioned two common packaging forms in the chip structure. See (page 4, line 179). In addition, we added the section of mass transfer, see (page 6, line 238). By describing the transfer method and bonding technology, see (page 17, line 662), the process of chip transfer to bonding is introduced in detail. Because this review involves a lot of content, it may not introduce a specific content in detail. If an article is published again, we will supplement this part in a targeted manner.

Comment 6: What are the different between "CMOS driving" and "Driving technology" sections? It is recommended to have better paper organization.

Response: As mentioned in the fourth reply, CMOS driving is one of the driving technologies and belongs to the active matrix driving type. Because of space reasons, we don't introduce much about this part of the drive, but my colleague's paper published in Chinese journal of liquid crystals and displays introduced the drive technology(DOI：10.37188/CJLCD.2022-0157)

Reviewer 4 Report

Dear Editor,
I was pleased to read the review article titled "Research progress of Micro-LED display technology" that was sent by the authors to your journal Crystals.
I believe that this review article is a good work, correctly written in English, clear, well divided into several paragraphs that allow the reader to understand what the highlights of this work are. The paper reviews a substantial amount of work.
My opinion is that the paper can be considered acceptable after the authors have reached some more details about the state of the art of light-emitting diodes for displays.
I reproduce some comments below:
1) In my opinion, the review article lacks tables showing the performance of different light-emitting diodes. This would be very useful in such an article.
2) Light-emitting diodes based on organic materials (whether conjugated molecules or conjugated polymers) are hardly mentioned in my manuscript. These materials have become very important in this technology and it is a pity not to cover them in this paper.
3) In general, I think there is a lack of a section on "exotic" based light-emitting diodes, which, however, are showing promise for new generations of light-emitting diodes. For example, in recent years light-emitting diodes based on metal halide perovskites, monolayer transition metal dichalcogenides, and carbon nanotubes are reported in the literature.
4) Consistent with the first three points, the bibliography could be significantly expanded by going on to report works on comparisons of device performance, organic light-emitting diodes, light-emitting diodes .

Author Response

Comment 1: In my opinion, the review article lacks tables showing the performance of different light-emitting diodes. This would be very useful in such an article.

Response: Thank you very much for your recommendation. According to your comments and suggestions, we have added performance tables of different display technologies in the introduction, including LCD, OLED and Micro-LED.

Comment 2: Light-emitting diodes based on organic materials (whether conjugated molecules or conjugated polymers) are hardly mentioned in my manuscript. These materials have become very important in this technology and it is a pity not to cover them in this paper.

Response: According to your suggestion, we introduced the organic light-emitting diodes in the introduction, and combined with your first suggestion, we also supplemented the introduction of LCD display. See (page 1, line 43).

Comment 3: In general, I think there is a lack of a section on "exotic" based light-emitting diodes, which, however, are showing promise for new generations of light-emitting diodes. For example, in recent years light-emitting diodes based on metal halide perovskites, monolayer transition metal dichalcogenides, and carbon nanotubes are reported in the literature.

Response: According to your suggestion, we added the contents of these parts in different positions of the manuscript, and added the introduction of metal halide perovskite in the full-color display chapter, as shown in (page 14, line 557), dichalcogenide (page 14, line 428) and carbon nanotubes (page 9, line 353).

Comment 4: Consistent with the first three points, the bibliography could be significantly expanded by going on to report works on comparisons of device performance, organic light-emitting diodes, light-emitting diodes

Response: On the basis of your above suggestions, we also added the part about the mass transfer and monolithic integration involved in Micro-LED display technology, which expanded the number of references.

Round 2

Reviewer 1 Report

Reject

Would not like to review further.

Moderate editing of English language required

Reviewer 2 Report

Thank the authors for attentive attitude to the comments and for following the recommendations.

Reviewer 3 Report

1. Formatting: 2.1. epitaxy technology, should it be 2.1 Epitaxy Technology? Please check other subtitles as well.

Minor formatting issues.