Novel Bio-Optoelectronics Enabled by Flexible Micro Light-Emitting Diodes

Round 1

Reviewer 1 Report

In this manuscript, Lee reviewed novel bio-optoelectronics enabled by flexible μLEDs. The manuscript is well written and well organized. But there are two major issues: 1. lack of tables. 2. lack of summary. So I suggest a major revision to this manuscript. Details are following:

1. In the introduction part, I can't really see a solid motivation. There is actually some motivation here, but not well discussed. So I suggest the author discuss more about the superiority of LED over the bulk LED/lasers and traditional-semiconductor-based μLED over other LEDs (like OLEDs, QLEDs). If there will be two tables summarizing the advantages and disadvantages of these two comparisons, that would be the best.
2. In the abstract, the author said, In this paper, we introduce the re14 search tendency of μLEDs and the latest bio-applications. So I assume the author is not just focusing on the application side, but also the device (principle, mechanism, structure, material, etc.) side. So I suggest the author introducing the principle/mechanisms of μLED and how it will enable bio-optoelectronics before reviewing previous works. This will help the readers who don't know this research field a lot. It's better to have a graph to illustrate it. Regarding the structure and material sides, the contents are also not adequate. I suggest the author making an organized discussion on this to lead the readers through the progress in this field, e.g., how the substrates are improved, how the structures are improved, and how the semiconductor materials are improved. It's also better to have tables summarizing them.
3. It's good that the author discussed a lot about the application, but still, there is no proper summary. For an easy and straightforward summary, I also recommend the author adding a table to summarize the applications and how is the progress for each application.

Author Response

[Reviewers’ Comments]

Reviewer #1:

[Overall Comments] In this manuscript, Lee reviewed novel bio-optoelectronics enabled by flexible μLEDs. The manuscript is well written and well organized. But there are two major issues: 1. lack of tables. 2. lack of summary. So I suggest a major revision to this manuscript. Details are following:

[Our response] We appreciate the reviewer for thoughtful evaluation of our manuscript. Our responses to the comments are described as below.

 

[Comment 1] In the introduction part, I can't really see a solid motivation. There is actually some motivation here, but not well discussed. So I suggest the author discuss more about the superiority of LED over the bulk LED/lasers and traditional-semiconductor-based μLED over other LEDs (like OLEDs, QLEDs). If there will be two tables summarizing the advantages and disadvantages of these two comparisons, that would be the best.

[Our response] We truly appreciate the reviewer’s valuable comments regarding the comparison of microLED with other light sources. We agree that there is not enough description about “superiority of microLED compared to LASER and bulk LED”, and “superiority of microLED compared to OLED and QLED”. Accepting the reviewer’s comment, we added the more descriptions and comparison tables in the revised manuscript. Furthermore, in order to fit the point, it is more appropriate to compare with QLED than to compare with LCD. Therefore, Figure 1 and some body texts were also modified.

[Modification to the manuscript] We have accordingly modified the manuscript to adopt the reviewer’s opinions.

1. We have added the following detailed explanation about Table 1.

“Since light-based healthcare devices collect accurate vital information or efficiently cure physical illnesses without tissue damages, numerous medical teams are actively utilizing lasers or bulk light-emitting diodes (LEDs) as therapeutic equipment. However, these equipment have some drawbacks such as huge size, low power efficiency, high cost and difficulty of frequent uses, as shown in Table 1.” on page 2 in the revised manuscript.

2. We added the comparison table of LASER, bulk LED, and microLED in the revised manuscript

Table 1 Comparison of LASER, Bulk LED and μLED as a light source for biomedical applications (red: disadvantages, blue: advantages).

3. We have added the following detailed explanation about Table 2.

“Table 2 shows comparison table among QLED, OLED and μLED displays in terms of their emission type, thickness, optical property, lifetime and cost. The μLEDs are self-emissive light source with high brightness and long lifetime than OLED and QLED, displaying excellent image quality.” on page 3 in the revised manuscript.

4. We added the comparison table of QLED, OLED, and microLED in the revised manuscript

Table 2 Comparison of QLED, OLED and μLED display in terms of structure, optical/electrical properties, lifetime and cost (red: disadvantages, blue: advantages).

5. We revised the desciption of Figure 1 for unifying the point of arguments.

“Therefore, in display industry, it is predicted that high-performance μLEDs will even enter fine pitch display fields that are dominated by OLEDs and QLEDs, as shown in Figure 1.” on page 4 in the revised manuscript.

6. We modified Figure 1.

Figure 1 Development prospect of light sources as display components.

 

[Comment 2] In the abstract, the author said, In this paper, we introduce the research tendency of μLEDs and the latest bio-applications. So I assume the author is not just focusing on the application side, but also the device (principle, mechanism, structure, material, etc.) side. So I suggest the author introducing the principle/mechanisms of μLED and how it will enable bio-optoelectronics before reviewing previous works. This will help the readers who don't know this research field a lot. It's better to have a graph to illustrate it. Regarding the structure and material sides, the contents are also not adequate. I suggest the author making an organized discussion on this to lead the readers through the progress in this field, e.g., how the substrates are improved, how the structures are improved, and how the semiconductor materials are improved. It's also better to have tables summarizing them.

[Our response] We truly appreciate the reviewer’s valuable comments regarding the explanation about the device side of μLEDs. (principle, mechanism, structure, material, etc.). We tended to briefly explain the device side, and intensively review the application of μLEDs. However, as the reviewer said, we think simple explanations with a table are needed for the device side. Accepting the reviewer’s comment, we added the more descriptions and comparison tables in the revised manuscript.

[Modification to the manuscript] We have accordingly modified the manuscript to adopt the reviewer’s opinions.

1. We have added the following detailed explanation about the device side of μLEDs. (mechanism, structure, material, etc.)..

 “The μLEDs can be typically divided into three types (Table 3). It is a fully packaged bulk LED, a lateral-, and vertical-structured μLEDs, which are made by III-V or III-N com-pound semiconductors on epitaxial substrate (e.g., III-V: GaAs, III-N: Si, SiC, and sapphire). They have different characteristics in thermal, electrical, and optical properties, resulted from structural differences of bulk/thin-film and electrode location. Lateral μLEDs have a long current path of about 50~100 μm between electrodes, whereas vertical μLEDs have short current path under 5 μm, inducing negligible Joule heating during device operation. Thanks to this structural advantage, vertical-structured microLEDs have various superiorities compared to others, including small size, fast/cheap process, superior electrical/thermal properties and simple wiring. Particularly, vertical-structured μLEDs with low heating are most suitable to realize biomedical application due to its thermally non-invasive property.” on page 4 in the revised manuscript.

2. We added the comparison table of bulk LED, lateral- and vertical-structured microLED in the revised manuscript

Table 3 Comparison of bulk LED, a lateral-, and vertical-structured μLEDs red: disadvantages, blue: advantages).

 

[Comment 3] It's good that the author discussed a lot about the application, but still, there is no proper summary. For an easy and straightforward summary, I also recommend the author adding a table to summarize the applications and how is the progress for each application.

[Our response] We truly appreciate the reviewer’s valuable comments regarding the summary of μLED-based biomedical applications. Accepting the reviewer’s comment, we added new Figure about more detailed summary, and modified the conclusion in the revised manuscript.

 [Modification to the manuscript] We have accordingly modified the manuscript to adopt the reviewer’s opinions.

1. We revised the description in the conclution.

“Therefore, it is essential to develop a wearable biomedical device using μLED, which is well-known as a display light source and biocompatible device with excellent opto-electrical properties as well as environmental stability.” on page 15 in the revised manuscript.

2. We added the description about development roadmap of μLEDs (Figure 7).

“As shown in Figure 7, the μLED-based devices have been used to not only the introduced applications, but also low-power sensors and patch for skin beauty (e.g., whitening, and anti-aging).” on page 15 in the revised manuscript.

3. We added the additional explanation about future development of μLED-based biomedical applications.

 “By solving the above-mentioned problems and moving on to a bio-friendly patch form, it is expected to be developed oxygen saturation (SpO2) sensors, glucose sensors for diabetic patients, and skin patch for treatment of chronic skin diseases (e.g., acne, psoriasis, and skin cancer). If this kind of progress is made in the future, novel μLED technology will establish as a new industrial field in the smart healthcare as well as display field.” on page 16 in the revised manuscript.

4. We added the development roadmap of μLEDs for display and biomedical applications.

Figure 7 Development roadmap of μLEDs for display and biomedical applications.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript “Novel Bio-Optoelectronics Enabled by Flexible Micro Light Emitting Diodes” reviewed recent progress on μLEDs in terms of the fabrication methods, and powerless μLED arrays as optogenetics and hair-regrowth. The μLEDs have the advantages of low power required, extra small size on flexible substrate, low heat generation, high strength and high stability when implanted in mouse or human body, so it is a good candidate for wearable devices based on optical stimuli. The author also highlighted in conclusion part that (1) the difficulties of integration with other devices such as power supply and (2) difficulties on mass production are issues to be solved for μLED to be widely used in future. This review gave an overall picture of the development of μLED for biological applications, I would recommend its publication on Electronics with following typo revisions:

1. In line 27, “has accustomed” should be “has been accustomed”.
2. In line 108, “were compoased of” should be “were composed of”.
3. In line 110, “The inset image is a magnified top-view of the device”, the inset image of the μLEDs is actually smaller than that in Figure 2(b). The sentence should be revised to “The inset image is a top-view of the device”.
4. In line 219, Cu-PI should be written as “copper-polyimide (Cu-PI)”.
5. In line 290, “Figure 5b” should be “Figure 5e”.

Author Response

[Reviewers’ Comments]

Reviewer #2:

[Overall Comments] The manuscript “Novel Bio-Optoelectronics Enabled by Flexible Micro Light Emitting Diodes” reviewed recent progress on μLEDs in terms of the fabrication methods, and powerless μLED arrays as optogenetics and hair-regrowth. The μLEDs have the advantages of low power required, extra small size on flexible substrate, low heat generation, high strength and high stability when implanted in mouse or human body, so it is a good candidate for wearable devices based on optical stimuli. The author also highlighted in conclusion part that (1) the difficulties of integration with other devices such as power supply and (2) difficulties on mass production are issues to be solved for μLED to be widely used in future. This review gave an overall picture of the development of μLED for biological applications, I would recommend its publication on Electronics with following typo revisions:

[Our response] We deeply appreciate the reviewer’s high evaluation on our manuscript.

 

[Comments]

1. In line 27, “has accustomed” should be “has been accustomed”.
2. In line 108, “were compoased of” should be “were composed of”.
3. In line 110, “The inset image is a magnified top-view of the device”, the inset image of the μLEDs is actually smaller than that in Figure 2(b). The sentence should be revised to “The inset image is a top-view of the device”.
4. In line 219, Cu-PI should be written as “copper-polyimide (Cu-PI)”.
5. In line 290, “Figure 5b” should be “Figure 5e”.

[Our response] We truly appreciate the reviewer’s helpful comment about typos. According to the reviewer’s comment, we have revised the manuscript.

[Modification to the manuscript] We have accordingly modified the manuscript.

1. “Since modern people has been accustomed to lots of information, desires to check their body/disease information have increased to easily monitor and treat them.” on page 1 in the revised manuscript.
2. “(a) Schematic image of self-powered flexible μLEDs which were composed of flexible red μLEDs and thin-film piezoelectric power generator.” on page 6 in the revised manuscript.
3. “The inset image is a top-view of the device.” on page 6 in the revised manuscript.
4. “The μLED was fabricated on a copper-polyimide (Cu-PI) substrate with a needle structure, which was integrated with a wireless radio-frequency (RF) power system (Figure 4d).” on page 10 in the revised manuscript.
5. “Figure 5e indicates the movement tracking of a living mouse whisker after artificial optical stimulation.” on page 12 in the revised manuscript.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The revised manuscript looks generally good. I suggest accepting after minor revision. Just another comment associated with previous comment 2:

I highly recommend the authors adding a illustration to show a sample structure and dimensions of both lateral and vertical microLED. If the bulk LED can be shown, that would be the best. By the sample structure and dimensions, you can elaborate how the vertical microLED will reduce the complexity of wiring and solve other problems.

Author Response

[Reviewers’ Comments]

Reviewer #1:

[Overall Comments] The revised manuscript looks generally good. I suggest accepting after minor revision. Just another comment associated with previous comment 2:

[Our response] We deeply appreciate the reviewer’s high evaluation on our manuscript.

 

[Comment 1] I highly recommend the authors adding a illustration to show a sample structure and dimensions of both lateral and vertical microLED. If the bulk LED can be shown, that would be the best. By the sample structure and dimensions, you can elaborate how the vertical microLED will reduce the complexity of wiring and solve other problems.

[Our response] We truly appreciate the reviewer’s valuable comments regarding illustrations in Table 3. We agree that the illustrations about bulk LED, lateral-, and vertical μLED will help the understanding of readers. Accepting the reviewer’s comment, we added illustrations in Table 3 of the revised manuscript.

[Modification to the manuscript] We have accordingly modified the manuscript to adopt the reviewer’s opinions.

1. We modified Table 3 in the revised manuscript

Table 3 Comparison of bulk LED, a lateral-, and vertical-structured μLEDs red: disadvantages, blue: advantages).

Author Response File: Author Response.pdf