rus
Issue #6/2023
A.Kh.Abduev, A.Sh.Asvarov, A.K.Akhmedov, E.K.Murliev
ANALYSIS OF DEPOSITION METHODS FOR ZnO BASED AMORPHOUS FUNCTIONAL LAYERS FOR TRANSPARENT ELECTRONICS DEVICES
ANALYSIS OF DEPOSITION METHODS FOR ZnO BASED AMORPHOUS FUNCTIONAL LAYERS FOR TRANSPARENT ELECTRONICS DEVICES
DOI: https://doi.org/10.22184/1993-8578.2023.16.6.362.368
The processes of growth of nanocrystalline and amorphous ZnO-based thin films by magnetron sputtering method are analyzed. The effect of doping components and the level of doping on the degree of film amorphization has been studied. The effect of hydrogen in the composition of the atmosphere on the structural perfection of the deposited ZnO-based thin films is considered. The dependence of the structure of ZnO–SnO2 thin films on the component ratio in sputtered targets is shown. The mechanisms of of ZnO-based amorphous formation films by magnetron sputtering methods are discussed.
The processes of growth of nanocrystalline and amorphous ZnO-based thin films by magnetron sputtering method are analyzed. The effect of doping components and the level of doping on the degree of film amorphization has been studied. The effect of hydrogen in the composition of the atmosphere on the structural perfection of the deposited ZnO-based thin films is considered. The dependence of the structure of ZnO–SnO2 thin films on the component ratio in sputtered targets is shown. The mechanisms of of ZnO-based amorphous formation films by magnetron sputtering methods are discussed.
Теги: amorphization deposition doping magnetron sputtering thin film zno аморфизация магнетронное распыление напыление примесь тонкая пленка
Original paper
ANALYSIS OF DEPOSITION METHODS FOR ZnO BASED AMORPHOUS FUNCTIONAL LAYERS FOR TRANSPARENT ELECTRONICS DEVICES
A.Kh.Abduev1, Docent, Cand. of Sci. (Physics and Mathematics), ORCID: 0000-0002-3948-1206 / a_abduev@mail.ru
A.Sh.Asvarov2, Cand. of Sci. (Physics and Mathematics), Leading Researcher, ORCID: 0000-0001-6426-5006
A.K.Akhmedov2, Cand. of Sci. (Physics and Mathematics), Leading Researcher, ORCID: 0000-0002-9466-9842
E.K.Murliev2, Junior researcher, ORCID: 0009-0009-7742-8527
Abstract. The processes of growth of nanocrystalline and amorphous ZnO-based thin films by magnetron sputtering method are analyzed. The effect of doping components and the level of doping on the degree of film amorphization has been studied. The effect of hydrogen in the composition of the atmosphere on the structural perfection of the deposited ZnO-based thin films is considered. The dependence of the structure of ZnO–SnO2 thin films on the component ratio in sputtered targets is shown. The mechanisms of of ZnO-based amorphous formation films by magnetron sputtering methods are discussed.
Keywords: ZnO, thin film, deposition, amorphization, magnetron sputtering, doping
For citation: A.Kh. Abduev, A.Sh. Asvarov, A.K. Akhmedov, E.K. Murliev. Analysis of deposition methods for ZnO based amorphous functional layers for transparent electronics devices. NANOINDUSTRY. 2023. V. 16, no. 6. PP. 362–368. https://doi.org/10.22184/1993-8578.2023.16.6.362.368.
INTRODUCTION
The rapid growth of volumes and nomenclature of various applications in the transparent electronics industry implies the search for new promising materials and technologies for their synthesis. Studies of the last decades show a clear trend toward transition from single-crystal silicon electronics to the wide use of various polycrystalline and amorphous oxide compositions as a base material [1]. A significant milestone in this direction was creation of a channel of active-matrix thin-film transistors based on a complex amorphous oxide system In-Ga-Zn-O (a-IGZO) [2].
The reasons for displacement of silicon functional layers from transparent electronics are various. First of all, it is due to the fact that silicon is an opaque material. At the same time, carrier mobility in alternative amorphous oxide materials a-IGZO (about 10 cm2 V–1 s–1) is an order of magnitude higher than in layers based on amorphous hydrogenated silicon (less than 1 cm2 V–1 s–1).
Introduction of layers based on the a-IGZO system into the LCD industry has led to the intensification of work aimed at further improvement of their electrical and optical characteristics. Thus, [3] reports a significant increase in the field mobility of charge carriers in the complex amorphous oxide system IGZTO (In-Ga-Zn-Sn-O). The emergence and intensive development of a new direction in transparent electronics – flexible electronics on polymer carriers [4], for which new additional requirements to the used materials and technologies are formulated, also contributed to significant growth of interest in amorphous oxide systems. In particular, the use of polymeric materials implies a significant decrease in the temperatures of synthesis and post-treatment of functional layers while maintaining their high electrical and optical characteristics. One of the possible ways to solve the problem of low-temperature synthesis of functional layers with high characteristics is formation of a new class of functional coatings based on multilayer structures with thickness modulated doping [5]. In this case, the requirements to morphology and structure of single layers are significantly increased. The single layers should have a dense homogeneous amorphous structure with minimal relief, and the technologies used should ensure early coalescence of layers and formation of dense porous interlayer interfaces.
The present work is devoted to the literature data analysis and results obtained by the authors in the study of the mechanisms of amorphous oxide layers formation by different deposition methods.
RESULTS
ZnO:Al layers
In [6], influence of the alloying impurity level on the morphology and structure of ZnO:Al layers was investigated. The authors showed that with increasing aluminum content up to 8.6 at. %, the thickness of nanocrystalline sublayer formed on the substrate increases, contributing to surface topography reduction of the layers and amorphization of their structure (Fig.1).
We have studied structural transformations in ZnO : Al layers synthesized by spray pyrolysis [7]. It was shown that increase of aluminum content in the layers up to 10 at. % leads to amorphization of the structure. In the proposed model of amorphization it is assumed that aluminum atoms, being much to the left of zinc in the metal activity series, are not embedded in the ZnO lattice, but localizing on the surface of ZnO grains, create new crystallization centers, increasing the specific surface area of intergranular boundaries (Fig.2).
Effect of hydrogen in the working gas on the structure of ZnO layers
In [8], influence of the level of hydrogen content in the working gas composition on the structure of ZnO : Ga layers synthesized by dc magnetron sputtering was studied (Fig.3).
It is shown that an increase in hydrogen content in the chamber up to 15 % leads to a significant decrease in grain size from 24 to 3 nm and an increase in the stability of electrical characteristics in layers synthesized at room temperature. It can be assumed that decreasing of grain size in layers synthesized in hydrogen environment is due to formation of new hydrogen crystallization centers.
We have also studied the processes of magnetron synthesis of ZnO : Ga layers in Ar and Ar-H2 atmospheres in a wide range of substrate temperatures [9]. Table 1 shows comparative data of X-ray diffraction studies of layers synthesized at different temperatures in different atmospheres.
The layers synthesized in Ar-H2 medium at 50 °C have grain sizes of about 2 nm, which is close to the results obtained in [8]. At the same time, the grain sizes in the layers synthesized in pure argon atmosphere are significantly higher - about 13 nm. We believe that at low synthesis temperatures hydrogen adsorbed on the growth surface forms new crystallization centers, reducing the grain size. When the synthesis temperature increases up to 200 °C and more, the grain sizes in the layers synthesized in argon and Ar-H2 mixture become close, which may be due to the desorption of hydrogen from the growth surface and, as a consequence, a decrease in its influence on the processes of layer synthesis.
ZnO–SnO2 composite layers
Another relatively simple method of low-temperature synthesis of smooth homogeneous amorphous oxide layers is the method of deposition in the kinetic regime, which is realized by magnetron sputtering of composite oxide targets consisting of equal or close mole fractions of components with minimum mutual solubility. We investigated the formation mechanisms, morphology and structure of ZnO–SnO2 layers synthesized at room temperature by magnetron sputtering of targets with different component ratios [10]. X-ray diffraction studies showed that in the range of tin oxide content from 34 to 50 mol % amorphization of the layers was observed (Fig.4).
Fig.5 shows a micrograph of a chip of a low-temperature ZTO film synthesized by magnetron sputtering of a ZnO–SnO2 (50/50) target. It can be seen that the film has a smooth morphology with no visible signs of structuring.
CONCLUSIONS
This work demonstrates possible ways of low-temperature formation of zinc oxide-based functional amorphous layers for new-generation flexible transparent electronics devices.
ACKNOWLEDGMENTS
The work was carried out with the financial support of the Russian Science Foundation (Grant No. 22-19-00157) using the Analytical Center for Collective Use equipment of the DFRC RAS.
PEER REVIEW INFO
Editorial board thanks the anonymous reviewer(s) for their contribution to the peer review of this work. It is also grateful for their consent to publish papers on the journal’s website and SEL eLibrary eLIBRARY.RU.
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
ANALYSIS OF DEPOSITION METHODS FOR ZnO BASED AMORPHOUS FUNCTIONAL LAYERS FOR TRANSPARENT ELECTRONICS DEVICES
A.Kh.Abduev1, Docent, Cand. of Sci. (Physics and Mathematics), ORCID: 0000-0002-3948-1206 / a_abduev@mail.ru
A.Sh.Asvarov2, Cand. of Sci. (Physics and Mathematics), Leading Researcher, ORCID: 0000-0001-6426-5006
A.K.Akhmedov2, Cand. of Sci. (Physics and Mathematics), Leading Researcher, ORCID: 0000-0002-9466-9842
E.K.Murliev2, Junior researcher, ORCID: 0009-0009-7742-8527
Abstract. The processes of growth of nanocrystalline and amorphous ZnO-based thin films by magnetron sputtering method are analyzed. The effect of doping components and the level of doping on the degree of film amorphization has been studied. The effect of hydrogen in the composition of the atmosphere on the structural perfection of the deposited ZnO-based thin films is considered. The dependence of the structure of ZnO–SnO2 thin films on the component ratio in sputtered targets is shown. The mechanisms of of ZnO-based amorphous formation films by magnetron sputtering methods are discussed.
Keywords: ZnO, thin film, deposition, amorphization, magnetron sputtering, doping
For citation: A.Kh. Abduev, A.Sh. Asvarov, A.K. Akhmedov, E.K. Murliev. Analysis of deposition methods for ZnO based amorphous functional layers for transparent electronics devices. NANOINDUSTRY. 2023. V. 16, no. 6. PP. 362–368. https://doi.org/10.22184/1993-8578.2023.16.6.362.368.
INTRODUCTION
The rapid growth of volumes and nomenclature of various applications in the transparent electronics industry implies the search for new promising materials and technologies for their synthesis. Studies of the last decades show a clear trend toward transition from single-crystal silicon electronics to the wide use of various polycrystalline and amorphous oxide compositions as a base material [1]. A significant milestone in this direction was creation of a channel of active-matrix thin-film transistors based on a complex amorphous oxide system In-Ga-Zn-O (a-IGZO) [2].
The reasons for displacement of silicon functional layers from transparent electronics are various. First of all, it is due to the fact that silicon is an opaque material. At the same time, carrier mobility in alternative amorphous oxide materials a-IGZO (about 10 cm2 V–1 s–1) is an order of magnitude higher than in layers based on amorphous hydrogenated silicon (less than 1 cm2 V–1 s–1).
Introduction of layers based on the a-IGZO system into the LCD industry has led to the intensification of work aimed at further improvement of their electrical and optical characteristics. Thus, [3] reports a significant increase in the field mobility of charge carriers in the complex amorphous oxide system IGZTO (In-Ga-Zn-Sn-O). The emergence and intensive development of a new direction in transparent electronics – flexible electronics on polymer carriers [4], for which new additional requirements to the used materials and technologies are formulated, also contributed to significant growth of interest in amorphous oxide systems. In particular, the use of polymeric materials implies a significant decrease in the temperatures of synthesis and post-treatment of functional layers while maintaining their high electrical and optical characteristics. One of the possible ways to solve the problem of low-temperature synthesis of functional layers with high characteristics is formation of a new class of functional coatings based on multilayer structures with thickness modulated doping [5]. In this case, the requirements to morphology and structure of single layers are significantly increased. The single layers should have a dense homogeneous amorphous structure with minimal relief, and the technologies used should ensure early coalescence of layers and formation of dense porous interlayer interfaces.
The present work is devoted to the literature data analysis and results obtained by the authors in the study of the mechanisms of amorphous oxide layers formation by different deposition methods.
RESULTS
ZnO:Al layers
In [6], influence of the alloying impurity level on the morphology and structure of ZnO:Al layers was investigated. The authors showed that with increasing aluminum content up to 8.6 at. %, the thickness of nanocrystalline sublayer formed on the substrate increases, contributing to surface topography reduction of the layers and amorphization of their structure (Fig.1).
We have studied structural transformations in ZnO : Al layers synthesized by spray pyrolysis [7]. It was shown that increase of aluminum content in the layers up to 10 at. % leads to amorphization of the structure. In the proposed model of amorphization it is assumed that aluminum atoms, being much to the left of zinc in the metal activity series, are not embedded in the ZnO lattice, but localizing on the surface of ZnO grains, create new crystallization centers, increasing the specific surface area of intergranular boundaries (Fig.2).
Effect of hydrogen in the working gas on the structure of ZnO layers
In [8], influence of the level of hydrogen content in the working gas composition on the structure of ZnO : Ga layers synthesized by dc magnetron sputtering was studied (Fig.3).
It is shown that an increase in hydrogen content in the chamber up to 15 % leads to a significant decrease in grain size from 24 to 3 nm and an increase in the stability of electrical characteristics in layers synthesized at room temperature. It can be assumed that decreasing of grain size in layers synthesized in hydrogen environment is due to formation of new hydrogen crystallization centers.
We have also studied the processes of magnetron synthesis of ZnO : Ga layers in Ar and Ar-H2 atmospheres in a wide range of substrate temperatures [9]. Table 1 shows comparative data of X-ray diffraction studies of layers synthesized at different temperatures in different atmospheres.
The layers synthesized in Ar-H2 medium at 50 °C have grain sizes of about 2 nm, which is close to the results obtained in [8]. At the same time, the grain sizes in the layers synthesized in pure argon atmosphere are significantly higher - about 13 nm. We believe that at low synthesis temperatures hydrogen adsorbed on the growth surface forms new crystallization centers, reducing the grain size. When the synthesis temperature increases up to 200 °C and more, the grain sizes in the layers synthesized in argon and Ar-H2 mixture become close, which may be due to the desorption of hydrogen from the growth surface and, as a consequence, a decrease in its influence on the processes of layer synthesis.
ZnO–SnO2 composite layers
Another relatively simple method of low-temperature synthesis of smooth homogeneous amorphous oxide layers is the method of deposition in the kinetic regime, which is realized by magnetron sputtering of composite oxide targets consisting of equal or close mole fractions of components with minimum mutual solubility. We investigated the formation mechanisms, morphology and structure of ZnO–SnO2 layers synthesized at room temperature by magnetron sputtering of targets with different component ratios [10]. X-ray diffraction studies showed that in the range of tin oxide content from 34 to 50 mol % amorphization of the layers was observed (Fig.4).
Fig.5 shows a micrograph of a chip of a low-temperature ZTO film synthesized by magnetron sputtering of a ZnO–SnO2 (50/50) target. It can be seen that the film has a smooth morphology with no visible signs of structuring.
CONCLUSIONS
This work demonstrates possible ways of low-temperature formation of zinc oxide-based functional amorphous layers for new-generation flexible transparent electronics devices.
ACKNOWLEDGMENTS
The work was carried out with the financial support of the Russian Science Foundation (Grant No. 22-19-00157) using the Analytical Center for Collective Use equipment of the DFRC RAS.
PEER REVIEW INFO
Editorial board thanks the anonymous reviewer(s) for their contribution to the peer review of this work. It is also grateful for their consent to publish papers on the journal’s website and SEL eLibrary eLIBRARY.RU.
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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