Electro-Acoustic Properties of Scandium-Doped Aluminum Nitride (Sc_xAl_1-xN) Material and its Application to Phononic Crystal-Coupled SAW Devices

Round 1

Reviewer 1 Report

This paper reports the elastic, dielectric and piezoelectric coefficients of w-Sc_xAl_1−xN material for scandium (Sc) concentrations x = 0 to 0.375. The electro-acoustic properties are used to investigate the frequency response of the SAW delay line, based on the tilt θ° of the normal c-axis of the w-Sc_xAl_1−xN piezoelectric thin film. It is  a good paper and the investigation has been carried out in a careful and systematic manner. The quality of the research is evident and the methodology used is entirely appropriate to the aims of the investigation. This manuscript could be accepted once these issues are addressed..

 

1. In introduction, the author said that Despite the large number of studies on SAW-PnCs, none of them have examined the effect of Sc_xAl_1-xN or c-tilted Sc_xAl_1-xN on PnC band gaps. Since no study has reported about this,the importance of the effect should be clarified in detail.

2. What’s the effects of PnC band gaps on SAW sensors?

3. “Furthermore, when the Sc concentration increased, the lattice constants (a and c) increased respectively by 5.6% and 1%, while the c/a ratio decreased by 4.6%. This effect can be related to the dependence on the Sc proportion and with the different bonds lengths and angles of the MN₄ tetrahedral where M is the metallic atom)”. What is the relationship between bonds lengths and the Sc proportion?

4. “ε₃₃ is more sensitive than ε₁₁”, why?

5. It is mentioned that the dielectric and the piezoelectric coefficients of AlN are affected by the doping concentration in Sc. It is better to given the detailed influence of Sc concentrations on these performances.

Author Response

 

Subject: Revision and resubmission of manuscript: crystals-1937066

Dear Sir, Madam,

        Thank you for giving us the opportunity to submit a revised draft of our manuscript titled ‘Electro-acoustic properties of Scandium Doped Aluminum Nitride (ScxAl1-xN) Material and its Application to Phononic Cristal Coupled SAW Devices’ to ‘Crystals’ journal

        We appreciate the time and effort that you and the reviewers have dedicated to providing your valuable feedback on our manuscript. The suggestions offered by the reviewers have been deeply helpful. We have carried out the modifications that the reviewers suggested and revised the manuscript accordingly.

       We have highlighted the changes within the manuscript. Please find attached a point-by-point response to reviewer’s concerns. We hope that you find our responses satisfactory and that our manuscript is now suitable for publication.

 

Response to Reviewer # 1:  

Comment 01: 1. In introduction, the author said that despite the large number of studies on SAW-PnCs, none of them have examined the effect of ScxAl1-xN or c-tilted ScxAl1-xN on PnC band gaps. Since no study has reported about this, the importance of the effect should be clarified in detail.

• Response: Thank you for your assessment. As suggested by the reviewer, the choice of scandium has been highlighted in detail in the introduction (upper page 2):

Compared to other transition metals, scandium as a dopant exhibits a structural transition from the wurtzite phase to the rocky phase which occurs at low alloying concentrations, leading to easily synthesized and more stable and alloys. Second, the piezoelectric coefficients are much higher in AlScN than in pure AlN. This can be explained by the fact that in the growth process of the AlScN thin film, a competition between Al³⁺ and Sc³⁺ for coordination with nitrogen is introduced, which weakens the resistance to nitrogen displacement in the crystal structure and increases the volume of the unit cell. This remark has been added in the text, page 2.

 

 

Comment 02:  What’s the effects of PnC band gaps on SAW sensors?

• Response: Thank you for pointing this out. The role of PnC in sensing applications is now detailed in the new version, on top of page 3.

Phononic crystals have been recently proposed as a platform for the investigation of the acoustic velocity and/or the density of a liquid filling parts of the structure. The sensing phenomena are based on the high sensitivity to external stimuli (temperature, pressure, nature of the liquid...), of localized modes, associated with defects, appearing inside absolute phononic band gaps.

 

Comment 03: Furthermore, when the Sc concentration increased, the lattice constants (a and c) increased respectively by 5.6% and 1%, while the c/a ratio decreased by 4.6%. This effect can be related to the dependence on the Sc proportion and with the different bonds lengths and angles of the MN4 tetrahedral where M is the metallic atom)”. What is the relationship between bonds lengths and the Sc proportion?

• Response: We fully agree with the referee's comment. This effect may be due to changes in the bond lengths and angles of the AlN4 tetrahedron, which deforms when Al atoms are replaced by Sc atoms [19, 65]. This effect can then be estimated geometrically from the determination of the lattice constants a and c [9]. Theoretical and experimental details of the impact of scandium concentration on bond length can be found in several papers [9, 19, 65, 74]. This remark has been added in the text, page 4 and page 5.

 

Comment 04: “ε33 is more sensitive than ε11”, why?

• Response 04: Thank you for pointing this out. Thank you for pointing this out. The longitudinal permittivity ε33 (ε33 - along the direction of polarization) is more sensitive than ε11 (ε11 perpendicular to the direction of polarization), mainly due to the strong lattice polarization induced by the out-of-plane (c-axis) Sc atom. This remark has been added in the text, page 7.

 

Comment 05: It is mentioned that the dielectric and the piezoelectric coefficients of AlN are affected by the doping concentration in Sc. It is better to given the detailed influence of Sc concentrations on these performances.

• Response: Thank you for this observation. This result indicates that the addition of a trivalent dopant (Sc³⁺) constrains the displacement along the c Moreover, the electronegativity of the Sc atom being lower than that of the Al atom, it makes the w-Sc_xAl_1-xN material more electrovalent, which improves the piezoelectric properties [19]. This remark has been added in the text, page 6

 

We hope that the revision done in the manuscript and our accompanying responses will be sufficient to make our manuscript suitable for publication. We hope to hear from you soon regarding our submission.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

The article considers studies on the use of density functional theory to study the elastic, dielectric and piezoelectric coefficients of the w-ScxAl1-xN material for scandium (Sc) concentrations from x = 0 to 0.375. In general, the presented work has rather great prospects in practical application and description of complex compounds, which can later be used in materials science. However, before accepting the article for publication, the authors should answer the following questions of the reviewer. The article corresponds to the subject of the declared journal.

 

1. In general, the presented study is quite interesting, but the authors should describe in more detail the purpose and novelty of this study, as well as explain the choice of scandium as a dopant.

2. The authors should consider combining a number of figures together, since the main problem of the presented work is the large amount of illustrative material that can be combined together.

3. The authors should provide a more detailed description of the evidence for the incorporation of scandium into the AlN structure, as well as what structural effects are observed when the dopant concentration changes.

4. The authors should describe in more detail the effects of adding scandium on changing the piezoelectric response in materials.

5. In conclusion, the authors should reflect the future prospects of this study.

6. All the given experimental values ​​must be presented taking into account the measurement error, as well as the value of the standard deviation.

Author Response

 

 

Subject: Revision and resubmission of manuscript: crystals-1937066

        Thank you for giving us the opportunity to submit a revised draft of our manuscript titled ‘Electro-acoustic properties of Scandium Doped Aluminum Nitride (ScxAl1-xN) Material and its Application to Phononic Cristal Coupled SAW Devices’ to ‘Crystals’ journal

        We appreciate the time and effort that you and the reviewers have dedicated to providing your valuable feedback on our manuscript. The suggestions offered by the reviewers have been deeply helpful. We have carried out the modifications that the reviewers suggested and revised the manuscript accordingly.

       We have highlighted the changes within the manuscript. Please find attached a point-by-point response to reviewer’s concerns. We hope that you find our responses satisfactory and that our manuscript is now suitable for publication.

 

Response to Reviewer # 2: 

 

Comment 01: In general, the presented study is quite interesting, but the authors should describe in more detail the purpose and novelty of this study, as well as explain the choice of scandium as a dopant.

• Response: Thank you. The purpose and novelty of this study, as well as explain the choice of scandium as a dopant, have been upgraded in the introduction (red color in the new version. Compared to other transition metals, scandium as a dopant exhibits a structural transition from the wurtzite phase to the rocky phase which occurs at low alloying concentrations, leading to easily synthesized and more stable and alloys. Second, the piezoelectric coefficients are much higher in AlScN than in pure AlN. This can be explained by the fact that in the growth process of the AlScN thin film, a competition between Al³⁺ and Sc³⁺ for coordination with nitrogen is introduced, which weakens the resistance to nitrogen displacement in the crystal structure and increases the volume of the unit cell. This remark has been added in the text, page 2.and page 3.

Comment 02: The authors should consider combining a number of figures together, since the main problem of the presented work is the large amount of illustrative material that can be combined together.

• Response: We appreciate this recommendation. Therefore, in the new version, the figures describe the same phenomena are combined together: Fig.2 et Fig .3, and (Fig. 5, Fig. 6, et Fig. 7). This remark has been added in the text page 6 and page 8.

Comment 03: The authors should provide a more detailed description of the evidence for the incorporation of scandium into the AlN structure, as well as what structural effects are observed when the dopant concentration changes.

• Response:

This effect may be due to changes in the bond lengths and angles of the AlN4 tetrahedron, which deforms when Al atoms are replaced by Sc atoms [19, 65]. This effect can then be estimated geometrically from the determination of the lattice constants a and c [9]. Theoretical and experimental details of the impact of scandium concentration on bond length can be found in several papers [9, 19, 65, 74]. This remark has been added in the text (red color in the new version) page 4 and page 5.

Comment 04 The authors should describe in more detail the effects of adding scandium on changing the piezoelectric response in materials.

• Response:

• This result indicates that the addition of a trivalent dopant (Sc³⁺) constrains the displacement along the c Moreover, the electronegativity of the Sc atom being lower than that of the Al atom, it makes the w-Sc_xAl_1-xN material more electrovalent, which improves the piezoelectric properties [19]. This remark has been added in the text, page 6

 

Comment 05 In conclusion, the authors should reflect the future prospects of this study.

• Response: Short term prospect of the study has been added in conclusion:

On-going work are dealing with AlScN-SAW devices coupled with 2D phononic crystal as highly sensitive micro-sensor for liquid properties determination. This remark has been added in the text, page 18

 

Comment 06 All the given experimental values must be presented taking into account the measurement error, as well as the value of the standard deviation.

• Response: the measurement error, as well as the value of the standard deviation are presented in (Figure. 2 page 6, Table 1 page 5, and Table 2 page 7).

 

We hope that the revision done in the manuscript and our accompanying responses will be sufficient to make our manuscript suitable for publication. We hope to hear from you soon regarding our submission.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors answered all the questions, the article can be accepted for publication.