A Study of Device Parameters Affecting the Current Error Rate in a Low-Temperature Polycrystalline Silicon Thin-Film Transistor Pixel Circuit for Active-Matrix Organic Light-Emitting Diode Display Applications
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsOverall the paper has good analysis. Here are few of the comments:
1. What are the other factors that could be responsible for affecting the CER in terms of the charging capability and the capacitive coupling effect?
2. What is ELVDD?
3. Avoid long sentences. Difficult to follow: “At the end of the second step, T4’s gate node voltage suffers a considerable swing from turn-on level to turn-off level, so T4’s drain node voltage or T1’s gate node voltage changes abruptly due to charge injection which originates from the elimination of T4’s channel charges, and then changes additionally due to capacitive coupling related to the parasitic capacitance between T4’s gate and T4’s drain”
4. Is there a reference? “In industrial fabrication lines, these physical dimensions would vary very gradually at most 5% of the variation rate”.
5. Since it is the same data set, is it necessary to have both table 4 and fig 7?
6. Is there a reason for the values chosen for comparison of the CER for two extreme cases, high SS of 0.55 V/dec and low SS of 0.25 V/dec ?
7. Can the units for SS (V/dec) be added to the table 5 title common to all columns rather than just added to the first column?
Author Response
Thank you very much for taking the time to review our manuscript. Please find the detailed responses below and the corresponding revisions in the re-submitted manuscript.
- Comments 1
What are the other factors that could be responsible for affecting the CER in terms of the charging capability and the capacitive coupling effect?
- Response 1
We have provided the main factors affecting CER in Table 2 of our submitted manuscript. The answer to the reviewers' question about additional factors is as follows. Firstly, one of additional factors related to the charging capability is the variation of the rise & fall time of the signal to turn-on & -off T3 and T4 (Both are PMOS), which are used as switches. Another one is the variation of the turn-on resistance of T3 and T4. Secondly, in the viewpoint of the capacitive coupling, the variation of the rise time of the signal to turn-off T4 can be an additional factor. However, we consider that these factors are negligible compared to the factors listed in Table 2.
- Comments 2
What is ELVDD?
- Response 2
We are sorry for our lack of explanation. ELVDD means the supply voltage of OLED. OLED was once called organic EL, so the supply voltage of OLED has been called ELVDD. However, in our manuscript, it is not necessary to maintain the name as ELVDD, so we have changed it to VDD in the revised manuscript, which is easy for most readers to understand. In addition, we have also changed ELVSS to VSS.
- Location of corresponding change in the re-submitted manuscript
Page #2, Fig. 1
Page #3, Fig. 2
Page #6, Fig. 6
Page #4, Line #117 : “VGS of T1 or VG2 minus VDD”
- Comments 3
Avoid long sentences. Difficult to follow: “At the end of the second step, T4’s gate node voltage suffers a considerable swing from turn-on level to turn-off level, so T4’s drain node voltage or T1’s gate node voltage changes abruptly due to charge injection which originates from the elimination of T4’s channel charges, and then changes additionally due to capacitive coupling related to the parasitic capacitance between T4’s gate and T4’s drain”
- Response 3
We appreciate the reviewer’s good advice. Based on the reviewer's advice, we have revised the sentence into several shorter sentences as shown below.
“At the end of the second step, another factor affects T1’s VG through the switch TFT, T4. At the end of the second step, T4’s gate node voltage suffers a considerable swing from turn-on level to turn-off level. This abrupt change can induce the change of T4’s drain node voltage which is also T1’s VG. One inducing mechanism is related to charge injection which originates from the elimination of T4’s channel charges. Another inducing mechanism is related to capacitive coupling via the parasitic capacitance between T4’s gate and T4’s drain.”
- Location of corresponding change in the re-submitted manuscript
Page #3, Lines from #93 to #99
- Comments 4
Is there a reference? “In industrial fabrication lines, these physical dimensions would vary very gradually at most 5% of the variation rate”.
- Response 4
In general, spatial non-uniformity in the display manufacturing process can appear as non-uniformity in the brightness of the display screen, so we understand that in industrial manufacturing lines, each unit process is managed to minimize the non-uniformity. Several references confirm that deposition processes and patterning processes, except for the laser annealing process, are managed to meet a deviation of less than 5%. Two related papers have been added to the reference list of our revised manuscript.
Choi, M.; Yu, K.; Jeon, O.; Lee, S.; Kim, S.; Kim, H.; Seo, J.; Jeong, K. No P14: Key Technology of 8G In-Line Deposition System for OLED TV. SID EuroDisplay Symp. Dig. Tech. Pap. 2015, 46, 81.
Parker, I.; Johnson, A.; Frischknecht, K.; Stainer, M. Measurement Methods for Quality Control of Coating Uniformity in Solution Processed OLED Displays. SID Symp. Dig. Tech. Pap. 2015, 46, 207-210.
- Location of corresponding change in the re-submitted manuscript
Page #11, Lines #316 and #318
- Comments 5
Since it is the same data set, is it necessary to have both table 4 and fig 7?
- Response 5
We thought that Fig.7 was required to show trends and Table 4 was necessary to deliver accurate numerical data. However, as the reviewer pointed out, the two overlapped a lot, so we have decided to delete Table 4 in the revised manuscript.
- Location of corresponding change in the re-submitted manuscript
Page #7, Fig. 7
- Comments 6
Is there a reason for the values chosen for comparison of the CER for two extreme cases, high SS of 0.55 V/dec and low SS of 0.25 V/dec ?
- Response 6
The reason why we selected the two cases of 0.55 V/dec and 0.25 V/dec is because the average SS values ​​of the two extreme TFT characteristics shown in Figure 9 are 0.57 V/dec and 0.26 V/dec, respectively. Based on the measured average values, we selected the two cases for the comparison although there were slight differences with them.
- Comments 7
Can the units for SS (V/dec) be added to the table 5 title common to all columns rather than just added to the first column?
- Response 7
We appreciate the reviewer’s comment. In accordance with the reviewer's comment, we have added the units for SS (V/dec) to the titles of all columns of Table 5 (changed to Table 4 in the revised manuscript). In addition, the units for SS in Table 6 (changed to Table 5) have been also added in the same way.
- Location of corresponding change in the re-submitted manuscript
Page #8, Table 4
Page #9, Table 5
Reviewer 2 Report
Comments and Suggestions for AuthorsWhy does the title of the paper suggest research on OLED screens and the aim of the paper is to study LTPS TFT screens: “In this work, we have analyzed the influence of various TFT parameters on the CER based on 7T1C pixel circuit. The study has been conducted by using SPICE simulation results and the measured electrical characteristics of LTPS TFTs.” This is a big mistake, strange and unauthorized assumption, or deliberate misinformation.
The differences in the interchangeable types of screens are large. This makes it very difficult to reliably assess the work. For this purpose, it is necessary to analyze and prove the correctness of the indicated assumption. An alternative is to change the title of the work and its content.
It is important as in Figure 4. We can see: “Plane-view SEM image of LTPS grain structure.” While the subject of analysis is OLED.
Minor corrections
Please indicate the sources of the data used in Table 1.
Author Response
Thank you very much for taking the time to review our manuscript. Please find the detailed responses below and the corresponding revisions in the re-submitted manuscript.
- Comments 1
Why does the title of the paper suggest research on OLED screens and the aim of the paper is to study LTPS TFT screens: “In this work, we have analyzed the influence of various TFT parameters on the CER based on 7T1C pixel circuit. The study has been conducted by using SPICE simulation results and the measured electrical characteristics of LTPS TFTs.” This is a big mistake, strange and unauthorized assumption, or deliberate misinformation.
- Response 1
We sincerely appreciate the reviewer’s comment for pointing out our great mistake. When we initially decided on the title, we included “OLED” in the title because LTPS TFT pixel circuit which we mainly studied is utilized in OLED display. However, we have unintentionally left room for misunderstanding that our research seems to be about OLED due to that title. LTPS TFT cannot be a display by itself, but it is an indispensable component in each pixel of OLED display to control the OLED current. As the reviewer pointed out, we have revised the title as shown below to clearly indicate that our research subject is about LTPS TFT pixel circuit of an OLED display.
“A Study of Device Parameters Affecting Current Error in LTPS TFT Pixel Circuit for AMOLED Display Applications”
The revised title still includes “AMOLED”, but we have cleared that OLED is just an application where LTPS TFT pixel circuit is utilized.
- Location of corresponding change in the re-submitted manuscript
Page #1, Title
- Comments 2
The differences in the interchangeable types of screens are large. This makes it very difficult to reliably assess the work. For this purpose, it is necessary to analyze and prove the correctness of the indicated assumption. An alternative is to change the title of the work and its content.
- Response 2
As we mentioned above, LTPS TFT pixel circuit which we studied cannot be a display by itself, but it is an indispensable component that implements an OLED display. We have modified the title to clearly show what exactly we studied. Thank you again for pointing out our mistake.
- Comments 3
It is important as in Figure 4. We can see: “Plane-view SEM image of LTPS grain structure.” While the subject of analysis is OLED.
- Response 3
As mentioned above, our research subject is LTPS TFT pixel circuit of an OLED display, and the title has been modified to reflect this. Figure 4 is a SEM image showing the grain structure of LTPS. The grain structure can affect the effective mobility and threshold voltage of TFT. Therefore, the SEM image was included to explain the variation of T1’s characteristics.
- Comments 4
Please indicate the sources of the data used in Table 1.
- Response 4
We are sorry for our lack of explanation. In accordance with the reviewer's comment, we have added the sentence which indicates the sources in the revised manuscript as shown below. “The efficiency values of OELD in Table 1 was extracted from the actual test cells, and the maximum OLED current values were calculated based on those efficiency values to meet the typical brightness and white balance specifications of smartphones.”
- Location of corresponding change in the re-submitted manuscript
Page #2, Lines from #53 to #56
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsText corrected sufficiently.
