Enhanced Tunability of BaTixSn1−xO3 Films on Dielectric Substrate
Round 1
Reviewer 1 Report
The article is of scientific and practical interest, and I believe it can be published after a minor revision.
1. In Introduction there are few references to works of recent years, including those on other ferroelectric materials. I recommend expanding this part.
2. There is no information about the properties of the substrate selected for the study. It needs to be added.
3. The method for measuring the capacitance and quality factor of capacitor structures is not described in sufficient detail.
4. The parameters of the crystal lattice of the obtained films are not given and it is not explained how the composition was calculated. Please add clarifications.
Author Response
Response to Reviewer 1 Comments
The authors are grateful to the reviewer for the appreciation of this work and useful comments that will help us to improve the quality of the publication. Here we try to revise our paper in order to meet the reviewer’s remarks.
Point 1 In Introduction there are few references to works of recent years, including those on other ferroelectric materials. I recommend expanding this part.
Response 1: We have added some new references (11-14).
Point 2: There is no information about the properties of the substrate selected for the study. It needs to be added.
Response 2: We have added the following text to Introduction at page 2.
Therefore, more investigations are necessary in order to obtain enhanced tunability of BTS thin films on dielectric substrates with high Q-factor and low cost.
As one of such substrate material polycrystalline aluminum oxide can be proposed. Alumina has excellent mechanical and dielectric properties: surface roughness of about 0.05 mm, thermal coefficient of linear expansion 8*10-6, which is close to BTS one, high thermal conductivity coefficient of about 30 W/m*K, stable dielectric permittivity 9.7, low losses at microwaves (tan d < 10-4), and extremely low cost.
Point 3: The method for measuring the capacitance and quality factor of capacitor structures is not described in sufficient detail.
Response 3: We have added reference to the article that describes the microwave resonator method in details (Ref.37).
Point 4: The parameters of the crystal lattice of the obtained films are not given and it is not explained how the composition was calculated. Please add clarifications.
Response 4: We have added the following text:
The parameters of the crystal lattice of BTS films were calculated based on the angular positions of X-ray reflexes, using reflections from the substrate as a reference.
Moreover we have added the data about the lattice parameters to the descriptions of Figures 1-3.
Author Response File: 
Author Response.docx
Reviewer 2 Report
I recommend considering rewrite the 1st sentence claiming that: " ...FE demonstrate abnormally high nonlinearity of dielectric properties..."
I think that just "high nonlinearity: is enough. Otherwise, for comparison, explain what should demonstrate "normal high nonlinearity"?
There are some remarks to be explained/rewrite by authors:
1) line 36: there is a lack of dielectric permittivity unit;
2) line 91: a sign of "%" is not needed;
3) there is something missing in fig. 1, 2, and 3 over the red lines:
4) it may be needed to explain in fig. 1 what is the structure of BTS (the Ti & Sn ratio - is it 0.28 to 0.72?), it is not clear;
5) line 199: there is no "graph" specified before, just figures? Better to keep the same description, still.
6) pp. 9 of 13: it must be Figure 6, isn't it?; what is the structure of BTS in Figure 6?
7) Table 1 compare Compositions including "this work", but it presents anly Ti0.8Sn0.2; this work describes compositions e.g. Ti0.2Sn0.8 (Fig. 3); Ti0.4Sn0.6 (Fig.5); Fig 6. unknown?
It should be explained, why there is so many structures study, and conclusions about tunability drown just from one structure: Ti0.8Sn0.2? Is shows there is no correlation between few studied structures? If it is, please explain.
Author Response
Response to Reviewer 2 Comments
The authors are grateful to the reviewer for the appreciation of this work and useful comments that will help us to improve the quality of the publication. Here we try to revise our paper in order to meet the reviewer’s remarks.
Point 1: line 36: there is a lack of dielectric permittivity unit.
Response 1: We have corrected it.
Point 2: line 91: a sign of "%" is not needed.
Response 2: We have corrected it.
Point 3: there is something missing in fig. 1, 2, and 3 over the red lines.
Response 3: We have corrected it.
Point 4: it may be needed to explain in fig. 1 what is the structure of BTS (the Ti & Sn ratio - is it 0.28 to 0.72?), it is not clear.
Response 4: We have added the following text:
“The reflexes from the BTS phase in Fig. 1 are significantly shifted towards large angles when the oxygen content in the gas medium decreases from 40 to 20%, that for polycrystalline samples means a change in the composition of the solid solution (the ratio of Ti and Sn) according to the Vegard's law (see the inset in Fig.1) [41]. The deposition of the BTS film in a gas medium containing 20% oxygen leads to the formation of (211) textured coating with the lattice parameter 4.09 Å, which corresponds to the composition BaTi0.28Sn0.72O3 solid solution.”
Point 5: line 199: there is no "graph" specified before, just figures? Better to keep the same description
Response 5: We have corrected it.
Point 6: pp. 9 of 13: it must be Figure 6, isn't it?; what is the structure of BTS in Figure 6?
Response 6: The structure of BTS films in Figs 5 and 6 is the same. We have added the following text to make it clear:
“It follows from the figure that the capacitor based on the non-annealed film exhibits minimal tunability, which is explained by the composition of the solid solution BaTi0.4Sn0.6O3, most of which is a linear dielectric BaSnO3. The tunability of capacitors formed on the basis of annealed films of BaTi0.8Sn0.2O3 composition depends on film thickness. For films of 400 nm thickness it increases from 2.8 to 3.4 with an increase in the deposition temperature from 650 to 850 oC. The tunability of capacitor based on 800 nm film is 6.8 times (85%), which is the best result for BTS capacitors today.
Point 7: Table 1 compare Compositions including "this work", but it presents only Ti0.8Sn0.2; this work describes compositions e.g. Ti0.2Sn0.8 (Fig. 3); Ti0.4Sn0.6 (Fig.5); Fig 6. unknown?
Response 7: According to previous investigations, the component composition BaTi0.8Sn0.2O3 is the optimal one for this solid solution from the combination of tunability and losses point of view. It explains a lot of publications dedicated to this composition. As for our work, the main point of it that all films investigated have been made by sputtering one target with composition BaTi0.8Sn0.2O3, but only films prepared in low oxygen ambient and subjected to annealing reveal the same composition as the target one. And only these films (after annealing) demonstrate high dielectric properties, which are presented in Table 1 in comparison to other works.
Author Response File: Author Response.docx
