Combining Chemical Functionalization and FinFET Geometry for Field Effect Sensors as Accessible Technology to Optimize pH Sensing

Round 1

Reviewer 1 Report

The paper presents a FinFET chemical sensor functionalized with APTES for pH measurement. The authors have tested the sensor with and without APTES functionalization and have shown how the functionalized sensor is characterized by slight better performance. The paper needs revisions and following are the comments to improve the paper quality.

1. The authors present the designed chemical sensor and the measurement to show the sensor performance. However, there is nothing in the manuscript that shows how the proposed sensor performance compares with other pH sensors from literature. I suggest to add such discussion in the text and also a table to point out advantages and drawbacks of the proposed sensor if compared with other sensors from literature. This to clearly point out how the proposed pH sensor improves the state of the art.
2. More information are needed about how the measurements have been carried out. For example, in Figure 3 the solution pH is estimated from the gate-source voltage of the sensor. What is the value of the drain-source voltage? Similarly, in Figure 5 the solution pH is estimated from the sensor conductance. What is the measurement point in this case (Vgs and Vds)?
3. The authors should check the manuscript for typos. For example in the Supplementary material in the title there is the word Fin instead of FinFET and at the beginning of section 2 there is a reference to Figure SI 3 that I think is Figure SI 2.

Author Response

We would like to acknowledge the reviewers and thank them for their constructive comments.

In the following document we answer jointly to both reviewers as both had similar observations. Additionally we add the document with track changes for the reviewers consideration.

Reviewer 1

The paper presents a FinFET chemical sensor functionalized with APTES for pH measurement. The authors have tested the sensor with and without APTES functionalization and have shown how the functionalized sensor is characterized by slight better performance. The paper needs revisions and following are the comments to improve the paper quality.

1. The authors present the designed chemical sensor and the measurement to show the sensor performance. However, there is nothing in the manuscript that shows how the proposed sensor performance compares with other pH sensors from literature. I suggest to add such discussion in the text and also a table to point out advantages and drawbacks of the proposed sensor if compared with other sensors from literature. This to clearly point out how the proposed pH sensor improves the state of the art.

Reference 7 contains an exhaustive table with the comparison between different ISFET technologies. We have added some clarifications in the introduction and in the conclusions that adds the difference of the FinFET technology we propose..

In particular, in the introduction, we pointed out the downsides of planar sensors and NWs in lines 41-46, and 69-71, respectively, while we highlighted the advantages on lines 93 to 105. In the conclusions we added the advantages in lines 364 to 368.

2. More information are needed about how the measurements have been carried out. For example, in Figure 3 the solution pH is estimated from the gate-source voltage of the sensor. What is the value of the drain-source voltage? Similarly, in Figure 5 the solution pH is estimated from the sensor conductance. What is the measurement point in this case (Vgs and Vds)?

We added that information to the text and the captions of the figures.

3. The authors should check the manuscript for typos. For example in the Supplementary material in the title there is the word Fin instead of FinFET and at the beginning of section 2 there is a reference to Figure SI 3 that I think is Figure SI 2.

We mended the errors that reviewed pointed out and checked the full manuscript adding several modifications in the manuscript to improve clarity.

Reviewer 2

This manuscript by Rani and coworkers reported a modified pH sensor device which a well-defined thickness of APTES molecules linked onto the surface SiO₂ surface used vapor-phase silanization method.

I think this is an interesting study and is worthy of publication. However, there are some questions need to be addressed.

1. Please highlight the advantages of this method for pH sensing.

See answer to reviewer 1.

2. More evidences should be provided to confirm the formation of APTES layer.

We added more clarifications and data using the intrinsic buffering capacitance and did a comparison between other authors that used ellipsometry and AFM with our experiments:

-We could not use AFM measurements due to the high-aspect ratio of our devices

-Ellipsometry was used as other authors cited in the text (reference 19)

-We included the comparison of the buffering capacitance extracted from the experimental data of SiO2 and APTES surfaces in the supplementary information.

3. “We attribute the enhanced pH sensitivity and response linearity of the chemically modified FinFET devices to the presence of amine groups at the sensing oxide…” please provide the evidences.

See answer to point 2

4. “We tested the sensitivity of the FinFET devices before and after chemical modification with APTES in a buffer pH range of 3 to12. ΔVGS/ΔpH improved from 31 mV/pH measured on the devices with SiO2 to 36 mV/pH with APTES”. I do not think that this is a big improvement

We included the appreciation of the reviewer, we admit it is a modest improvement.

5. I think the structure of the section of results need to be reconsidered.

We introduced sections into the structure that we hope clarify the intention of the text.

Author Response File: Author Response.pdf

Reviewer 2 Report

This manuscript by Rani and coworkers reported a modified pH sensor device which a well-defined thickness of APTES molecules linked onto the surface SiO₂ surface used vapor-phase silanization method.

I think this is an interesting study and is worthy of publication. However, there are some questions need to be addressed.

1. Please highlight the advantages of this method for pH sensing.
2. More evidences should be provided to confirm the formation of APTES layer.
3. “We attribute the enhanced pH sensitivity and response linearity of the chemically modified FinFET devices to the presence of amine groups at the sensing oxide…” please provide the evidences.
4. “We tested the sensitivity of the FinFET devices before and after chemical modification with APTES in a buffer pH range of 3 to12. ΔVGS/ΔpH improved from 31 mV/pH measured on the devices with SiO2 to 36 mV/pH with APTES”. I do not think that this is a big improvement.
5. I think the structure of the section of results need to be reconsidered.

Author Response

We would like to acknowledge the reviewers and thank them for their constructive comments.

In the following document we answer jointly to both reviewers as both had similar observations. Additionally we add the document with track changes for the reviewers consideration.

Reviewer 1

The paper presents a FinFET chemical sensor functionalized with APTES for pH measurement. The authors have tested the sensor with and without APTES functionalization and have shown how the functionalized sensor is characterized by slight better performance. The paper needs revisions and following are the comments to improve the paper quality.

1. The authors present the designed chemical sensor and the measurement to show the sensor performance. However, there is nothing in the manuscript that shows how the proposed sensor performance compares with other pH sensors from literature. I suggest to add such discussion in the text and also a table to point out advantages and drawbacks of the proposed sensor if compared with other sensors from literature. This to clearly point out how the proposed pH sensor improves the state of the art.

Reference 7 contains an exhaustive table with the comparison between different ISFET technologies. We have added some clarifications in the introduction and in the conclusions that adds the difference of the FinFET technology we propose..

In particular, in the introduction, we pointed out the downsides of planar sensors and NWs in lines 41-46, and 69-71, respectively, while we highlighted the advantages on lines 93 to 105. In the conclusions we added the advantages in lines 364 to 368.

2. More information are needed about how the measurements have been carried out. For example, in Figure 3 the solution pH is estimated from the gate-source voltage of the sensor. What is the value of the drain-source voltage? Similarly, in Figure 5 the solution pH is estimated from the sensor conductance. What is the measurement point in this case (Vgs and Vds)?

We added that information to the text and the captions of the figures.

3. The authors should check the manuscript for typos. For example in the Supplementary material in the title there is the word Fin instead of FinFET and at the beginning of section 2 there is a reference to Figure SI 3 that I think is Figure SI 2.

We mended the errors that reviewed pointed out and checked the full manuscript adding several modifications in the manuscript to improve clarity.

Reviewer 2

This manuscript by Rani and coworkers reported a modified pH sensor device which a well-defined thickness of APTES molecules linked onto the surface SiO₂ surface used vapor-phase silanization method.

I think this is an interesting study and is worthy of publication. However, there are some questions need to be addressed.

1. Please highlight the advantages of this method for pH sensing.

See answer to reviewer 1.

2. More evidences should be provided to confirm the formation of APTES layer.

We added more clarifications and data using the intrinsic buffering capacitance and did a comparison between other authors that used ellipsometry and AFM with our experiments:

-We could not use AFM measurements due to the high-aspect ratio of our devices

-Ellipsometry was used as other authors cited in the text (reference 19)

-We included the comparison of the buffering capacitance extracted from the experimental data of SiO2 and APTES surfaces in the supplementary information.

3. “We attribute the enhanced pH sensitivity and response linearity of the chemically modified FinFET devices to the presence of amine groups at the sensing oxide…” please provide the evidences.

See answer to point 2

4. “We tested the sensitivity of the FinFET devices before and after chemical modification with APTES in a buffer pH range of 3 to12. ΔVGS/ΔpH improved from 31 mV/pH measured on the devices with SiO2 to 36 mV/pH with APTES”. I do not think that this is a big improvement

We included the appreciation of the reviewer, we admit it is a modest improvement.

5. I think the structure of the section of results need to be reconsidered.

We introduced sections into the structure that we hope clarify the intention of the text.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors revised the manuscript according to the reviewers’ comments. I think it can be accepted after the following typos are corrected:

• Equations 2, 5, 7, 8, 9 and 10 present typos where some symbols are replaced by “??”.
• Line 341: “high” and not “hitgh”.

Author Response

We thank the reviewer for his comments. 

We checked equations in the last version from that arrived from the editor, and we do not have visualisation errors. 

We thank the reviewer for his revision, we corrected the spelling mistake in line 341. 

Due to the complains from the second reviewer, we compiled a list of corrections from the first version. As it seems the second reviewer did not received or did not find appropriate the corrections in the track of changes version, we have added a list of the changes together with the pdf version, as we view it. 

We hope these comments satisfy both reviewers. 

Author Response File: Author Response.pdf

Reviewer 2 Report

I do not get the desired changes.So, I think authors should respond carefully to reviewers' comments.

Author Response

We thank the reviewer for his comments. 

We checked equations in the last version from that arrived from the editor, and we do not have visualisation errors. 

We thank the reviewer for his revision, we corrected the spelling mistake in line 341. 

Due to the complains from the second reviewer, we compiled a list of corrections from the first version. As it seems the second reviewer did not received or did not find appropriate the corrections in the track of changes version, we have added a list of the changes together with the pdf version, as we view it. 

We hope these comments satisfy both reviewers. 

Author Response File: Author Response.pdf