| 1. |
- Aiempanakit, Montri, et al.
(författare)
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Effect of peak power in reactive high power impulse magnetron sputtering of titanium dioxide
- 2011
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Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 205:20, s. 4828-4831
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Tidskriftsartikel (refereegranskat)abstract
- The effect of peak power in a high power impulse magnetron sputtering (HiPIMS) reactive deposition of TiO(2) films has been studied with respect to the deposition rate and coating properties. With increasing peak power not only the ionization of the sputtered material increases but also their energy. In order to correlate the variation in the ion energy distributions with the film properties, the phase composition, density and optical properties of the films grown with different HiPIMS-parameters have been investigated and compared to a film grown using direct current magnetron sputtering (DCMS). All experiments were performed for constant average power and pulse on time (100W and 35 mu s, respectively), different peak powers were achieved by varying the frequency of pulsing. Ion energy distributions for Ti and O and its dependence on the process conditions have been studied. It was found that films with the highest density and highest refractive index were grown under moderate HiPIMS conditions (moderate peak powers) resulting in only a small loss in mass-deposition rate compared to DCMS. It was further found that TiO2 films with anatase and rutile phases can be grown at room temperature without substrate heating and without post-deposition annealing.
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| 2. |
- Aiempanakit, Montri, et al.
(författare)
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Hysteresis effect in reactive high power impulse magnetron sputtering of metal oxides
- 2011
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Konferensbidrag (refereegranskat)abstract
- In order to get high deposition rate and good film properties, the stabilization of the transition zone between the metallic and compound modes is beneficial. We have shown earlier that at least in some cases, HiPIMS can reduce hysteresis effect in reactive sputtering. In our previous work, mechanisms for the suppression/elimination of the hysteresis effect have been suggested. Reactive HiPIMS can suppress/eliminate the hysteresis effect in the range of optimum frequency [1] lead to the process stability during the deposition with high deposition rate. The mechanisms behind this optimum frequency may relate with high erosion rate during the pulse [2,3] and gas rarefaction effect in front of the target [4]. In this contribution, reactive sputtering process using high power impulse magnetron sputtering (HiPIMS) has been studied with focus on the gas rarefaction. Through variations in the sputtering conditions such as pulse frequencies, peak powers, and target area, their effect on the shape of current waveforms have been analyzed. The current waveforms in compound mode are strongly affected. Our experiments show that the shape and amplitude of peak current cannot be explained by the change of the secondary electron yield due to target oxidation only. Reduced rarefaction in compound mode contributes to the observed very high peak current values.
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| 3. |
- Aiempanakit, Montri, 1977-, et al.
(författare)
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Understanding the discharge current behavior in reactive high power impulse magnetron sputtering of oxides
- 2013
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 113:13, s. 133302-
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Tidskriftsartikel (refereegranskat)abstract
- The discharge current behavior in reactive high power impulse magnetron sputtering (HiPIMS) of Ti-O and Al-O is investigated. It is found that for both metals, the discharge peak current significantly increases in the oxide mode in contrast to the behavior in reactive direct current magnetron sputtering where the discharge current increases for Al but decreases for Ti when oxygen is introduced. In order to investigate the increase in the discharge current in HiPIMS-mode, the ionic contribution of the discharge in the oxide and metal mode is measured using time-resolved mass spectrometry. The energy distributions and time evolution are investigated during the pulse-on time as well as in the post-discharge. In the oxide mode, the discharge is dominated by ionized oxygen, which has been preferentially sputtered from the target surface. The ionized oxygen determines the discharge behavior in reactive HiPIMS.
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| 4. |
- Aijaz, Asim, et al.
(författare)
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A strategy for increased carbon ionization in magnetron sputtering discharges
- 2012
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Ingår i: Diamond and related materials. - : Elsevier BV. - 0925-9635 .- 1879-0062. ; 23, s. 1-4
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Tidskriftsartikel (refereegranskat)abstract
- A strategy that facilitates a substantial increase of carbon ionization in magnetron sputtering discharges is presented in this work. The strategy is based on increasing the electron temperature in a high power impulse magnetron sputtering discharge by using Ne as the sputtering gas. This allows for the generation of an energetic C+ ion population and a substantial increase in the C+ ion flux as compared to a conventional Ar-HiPIMS process. A direct consequence of the ionization enhancement is demonstrated by an increase in the mass density of the grown films up to 2.8 g/cm(3); the density values achieved are substantially higher than those obtained from conventional magnetron sputtering methods.
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| 5. |
- Aijaz, Asim, et al.
(författare)
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Deposition of thermochromic vanadium dioxide thin films by reactive high power impulse magnetron sputtering
- 2014
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Vanadium dioxide exhibits a reversible phase transition from semiconducting state (monoclinic structure) to a metallic state (tetragonal structure) at ~68 oC. This so-called metal-insulator transition (MIT) entails thermochromic behavior manifested by large changes in optical properties, such as high infrared transmittance modulation in thin films, thereby making VO2-based films a suitable candidate for optical switching applications such as self-tunable infrared filters. Thermochromic VO2 thin films have been widely investigated for optical applications, but high growth temperatures (> 400 oC) required for synthesizing crystalline VO2 thin films, high MIT temperature (68 oC) as well as low visible transmittance (typically ~50%) limit their applicability for example for energy efficient smart windows. Synthesis of metal-oxide thin films using highly ionized vapor fluxes has been shown to facilitate low-temperature film growth as well as control over phase formation and resulting film properties. In the present work, we synthesize VO2 thin films by use of highly ionized vapor fluxes that are generated by high power impulse magnetron sputtering (HiPIMS). In order to establish a correlation between the plasma and film properties, we investigate the discharge characteristics by analyzing the discharge current-voltage characteristics under varied process parameters such as peak-power, pulse-width and gas phase composition and grow VO2 thin films under suitable process conditions. We investigate the effect of growth temperature (room temperature to 500 oC), energy of the deposition flux (controlled by substrate bias potential) and type of substrate (Si, glass, ITO-coated glass) on crystallinity, phase formation and on optical properties (visible transmittance and infrared modulation) of the resulting thin films. For reference, the discharge characteristics and properties of films deposited by pulsed direct current magnetron sputtering are also studied.
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| 6. |
- Aijaz, Asim, et al.
(författare)
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Dual-magnetron open field sputtering system for sideways deposition of thin films
- 2010
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Ingår i: SURFACE and COATINGS TECHNOLOGY. - : Elsevier BV. - 0257-8972. ; 204:14, s. 2165-2169
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Tidskriftsartikel (refereegranskat)abstract
- A dual-magnetron system for deposition inside tubular substrates has been developed. The two magnetrons are facing each other and have opposing magnetic fields forcing electrons and thereby also ionized material to be transported radially towards the substrate. The depositions were made employing direct current magnetron sputtering (DCMS) and high power impulse magnetron sputtering (HiPIMS). To optimize the deposition rate, the system was characterized at different separation distances between the magnetrons under the same sputtering conditions. The deposition rate is found to increase with increasing separation distance independent of discharge technique. The emission spectrum from the HiPIMS plasma shows a highly ionized fraction of the sputtered material. The electron densities of the order of 10(16) m(-3) and 10(18) m(-3) have been determined in the DCMS and the HiPIMS plasma discharges respectively. The results demonstrate a successful implementation of the concept of sideways deposition of thin films providing a solution for coating complex shaped surfaces.
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| 7. |
- Aijaz, Asim, et al.
(författare)
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Exploring the potential of high power impulse magnetron sputtering for the synthesis of scratch resistant, antireflective coatings
- 2013
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Broad band anti-reflective multilayer coatings require the use of a low-index material as a top layer. Normally SiO2 is used which exhibits sufficiently low refractive index (~1.5 at 550 nm) yet its low hardness (~10 GPa) hinders its application in abrasive environments. A strategy to circumnavigate these limitations is the synthesis of multicomponent materials that combine good mechanical and optical performance. In this work we synthesize Al-Si-O thin films seeking to combine the low refractive index of SiO2 and the relatively high hardness of Al2O3. The potential of reactive high power impulse magnetron sputtering (HiPIMS) for synthesizing Al-Si-O suitable for top-layers in anti-reflective coating stacks is explored by depositing films in an Ar+O2 ambient under varied target compositions (Al0.5Si0.5 and Al0.1Si0.9). The behavior of discharge current in metal and oxide mode is correlated with the plasma composition, plasma energetics as well as target surface composition in order to obtain information about the chemical nature and the energy of the film forming species. Plasma composition and plasma energetics are investigated by measuring electron density, electron temperature as well as energy distributions and as fluxes of Ar+, Al+, Si+ and O+ ions. Monte-Carlo based computer simulations are employed to assess the ion-target surface interactions to gain insight into the discharge characteristics as well as film growth. The properties of the grown films (chemical composition, mechanical and optical properties) are investigated and an understanding of the reactive HiPIMS-based growth of anti-reflective Al-Si-O thin films is established. For reference, the plasma and film properties of Al-O are also studied.
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| 8. |
- Aijaz, Asim
(författare)
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HiPIMS-based Novel Deposition Processes for Thin Films
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this research, high power impulse magnetron sputtering (HiPIMS) based new deposition processes are introduced to address; the issue of low degree of ionization of C in magnetron sputtering discharges, and the difficulty encountered in thin film deposition on complex-shaped surfaces. The issue of low degree of C ionization is addressed by introducing a new strategy which is based on promoting the electron impact ionization ofC by increasing the electron temperature in the plasma discharge using Ne, instead of conventionally used Ar. The Ne-based HiPIMS process provides highly ionized C fluxes which are essential for the synthesis of high-density and sp3 rich amorphous carbon (a-C) thin films such as diamond-like carbon (DLC) and tetrahedral a-C (ta-C). The feasibility of coating complex-shaped surfaces is demonstrated by using the dual-magnetron approach in an open-field (magnetic field of the magnetrons) configuration and performing sideways deposition of Ti films. The HiPIMS-based open-field configuration process enhances the sideways transport of the sputtered flux — an effect which is observed in the case of HiPIMS.The characterization of the Ne-HiPIMS discharge using a Langmuir probe and mass spectrometry shows that it provides an increase in the electron temperature resulting in an order of magnitude decrease in the mean ionization length of the sputtered C as compared to the conventional Ar-HiPIMS discharge. The C1+ ion energy distribution functions exhibit the presence of an energetic C1+ ion population and a substantial increase in the total C1+ ion flux. The higher C1+ ion flux facilitates the growth of sp3 rich carbon films with mass densities, measured by x-ray reflectometry, reaching as high as approx. 2.8 gcm-3.The dual-magnetron open-field configuration process is operated in DCMS as well as in HiPIMS modes. The plasma characterization, performed by Langmuir probe measurements and optical emission spectroscopy, shows that the plasma density in the Ti-HiPIMS discharge is higher than that of the Ti-DCMS discharge. This results in the higher ionized fraction of the sputtered Ti in the case of HiPIMS. The film uniformity and the deposition rate of the film growth, obtained by employing scanning electron microscopy, demonstrate that the sideways deposition approach can be used for depositing thin films on complex-shaped surfaces.
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| 9. |
- Aijaz, Asim, et al.
(författare)
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Industrial Scale Deposition of Diamond-like Carbon Thin Films using Ne-based HiPIMS Discharge
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- High power impulse magnetron sputtering (HiPIMS) has been successful in providing highly ionized deposition fluxes for most common metals (Cu, Al, Ti). However, it is challenged when non-metals such as carbon is considered. Highly ionized carbon fluxes (up to 100%) are essential for the synthesis of diamond-like carbon and tetrahedral amorphous carbon thin films. Earlier reports have shown that the C+/C0 ratio in HiPIMS does not exceed 5% and film densities and sp3/sp2 bond fractions are substantially lower than those achieved using ionized physical vapour deposition based methods such as filtered cathodic vacuum arc and pulsed laser deposition. In our previous work, we demonstrated that Ne-based HiPIMS discharge entails energetic electrons as compared to Ar-based HiPIMS discharge facilitating the generation of highly ionized C fluxes as well as diamond-like carbon thin films with mass densities in the order of 2.8 g/cm3In this work, we perform industrial scale deposition of diamond-like carbon thin films using Ne- as well as Ar-based HiPIMS discharge. In order to investigate the effect of electron temperature enhancement and its correlation to generation of C1+ ion fluxes in Ne-based HiPIMS discharge, we perform time-averaged and time-resolved measurements of electron temperature as well as ion density at the substrate position using a flat probe. We also investigate the effect of plasma properties on the ionization of sputtered C as well as buffer gas species by measuring the optical emission from the discharge. In order to correlate the plasma and film properties, we synthesize C thin films under energetic deposition conditions and investigate structural (mass density, sp3/sp2 bond fraction, H content) and mechanical (hardness, elastic modulus, adhesion strength) properties of the resulting diamond-like carbon thin films.
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| 10. |
- Aijaz, Asim, et al.
(författare)
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Ion induced stress relaxation in dense sputter-deposited DLC thin films
- 2017
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 111:5
-
Tidskriftsartikel (refereegranskat)abstract
- Deposition of high-density and low-stress hydrogen-free diamond like carbon (DLC) thin films is demonstrated using a pulsed ionized sputtering process. This process is based on high power impulse magnetron sputtering, and high C ionization is achieved using Ne as the sputtering gas. The intrinsic compressive stress and its evolution with respect to ion energy and ion flux are explained in terms of the compressive stress based subplantation model for DLC growth by Davis. The highest mass density was similar to 2.7 g/cm(3), and the compressive stresses did not exceed similar to 2.5 GPa. The resulting film stresses are substantially lower than those achieved for the films exhibiting similar mass densities grown by filtered cathodic vacuum arc and pulsed laser deposition methods. This unique combination of high mass density and low compressive stress is attributed to the ion induced stress relaxation during the pulse-off time which corresponds to the post thermal spike relaxation timescales. We therefore propose that the temporal ion flux variations determine the magnitude of the compressive stress observed in our films. Published by AIP Publishing.
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| 11. |
- Aijaz, Asim, et al.
(författare)
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Low-temperature synthesis of thermochromic vanadium dioxide thin films by reactive high power impulse magnetron sputtering
- 2016
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 149, s. 137-144
-
Tidskriftsartikel (refereegranskat)abstract
- Thermochromic (TC) vanadium dioxide thin films provide means for controlling solar energy throughput and can be used for energy-saving applications such as smart windows. One of the factors limiting the deployment of VO2 films in TC devices is the growth temperature tau(s). At present, temperatures in excess of 450 degrees C are required, which clearly can be an impediment especially for temperature-sensitive substrates. Here we address the issue of high tau(s) by synthesizing VO2 thin films from highly ionized fluxes of depositing species generated in high power impulse magnetron sputtering (HiPIMS) discharges. The use of ions facilitates low-temperature film growth because the energy of the depositing species can be readily manipulated by substrate bias. For comparison, films were also synthesized by pulsed direct current magnetron sputtering. Structural and optical characterization of VO2 thin films on ITO-coated glass substrates confirms previous results that HiPIMS allows tau(s) to be reduced from 500 to 300 degrees C. Importantly, we demonstrated that HiPIMS permits the composition and TC response of the films to be tuned by altering the energy of the deposition flux via substrate bias. An optimum ion energy of 100 eV was identified, which points at a potential for further reduction of tau(s) thereby opening new possibilities for industrially-relevant applications of VO2-based TC thin films. Weak TC activity was observed even at tau(s) approximate to 200 degrees C in HiPIMS-produced films.
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| 12. |
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| 13. |
- Aijaz, Asim, et al.
(författare)
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Mechanical Properties of Hydrogen Free Diamond-Like Carbon Thin Films Deposited by High Power Impulse Magnetron Sputtering with Ne
- 2018
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Ingår i: Coatings. - : MDPI AG. - 2079-6412. ; 8:11
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen-free diamond-like carbon (DLC) thin films are attractive for a wide range of industrial applications. One of the challenges related to the use of hard DLC lies in the high intrinsic compressive stresses that limit the film adhesion. Here, we report on the mechanical and tribological properties of DLC films deposited by High Power Impulse Magnetron Sputtering (HiPIMS) with Ne as the process gas. In contrast to standard magnetron sputtering as well as standard Ar-based HiPIMS process, the Ne-HiPIMS lead to dense DLC films with increased mass density (up to 2.65 g/cm(3)) and a hardness of 23 GPa when deposited on steel with a Cr + CrN adhesion interlayer. Tribological testing by the pin-on-disk method revealed a friction coefficient of 0.22 against steel and a wear rate of 2 x 10(-17) m(3)/Nm. The wear rate is about an order of magnitude lower than that of the films deposited using Ar. The differences in the film properties are attributed to an enhanced C ionization in the Ne-HiPIMS discharge.
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| 14. |
- Aijaz, Asim, et al.
(författare)
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Principles for designing sputtering-based strategies for high-rate synthesis of dense and hard hydrogenated amorphous carbon thin films
- 2014
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Ingår i: Diamond and related materials. - : Elsevier. - 0925-9635 .- 1879-0062. ; 44, s. 117-122
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Tidskriftsartikel (refereegranskat)abstract
- In the present study we contribute to the understanding that is required for designing sputtering-based routes for high rate synthesis of hard and dense amorphous carbon (a-C) films. We compile and implement a strategy for synthesis of a-C thin films that entails coupling a hydrocarbon gas (acetylene) with high density discharges generated by the superposition of high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (DCMS). Appropriate control of discharge density (by tuning HiPIMS/DCMS power ratio), gas phase composition and energy of the ionized depositing species leads to a route capable of providing ten-fold increase in the deposition rate of a-C film growth compared to HiPIMS Ar discharge (Aijaz et al. Diamond and Related Materials 23 (2012) 1). This is achieved without significant incorporation of H (< 10 %) and with relatively high hardness (> 25 GPa) and mass density (~2.32 g/cm3). Using our experimental data together with Monte-Carlo computer simulations and data from the literature we suggest that: (i) dissociative reactions triggered by the interactions of energetic discharge electrons with hydrocarbon gas molecules is an important additional (to the sputtering cathode) source of film forming species and (ii) film microstructure and film hydrogen content are primarily controlled by interactions of energetic plasma species with surface and sub-surface layers of the growing film.
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| 15. |
- Aijaz, Asim, et al.
(författare)
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Synthesis of amorphous carbon thin films using acetylene-based high power impulse magnetron sputtering discharges
- 2013
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Amorphous carbon (a-C) thin films are synthesized using high power impulse magnetron sputtering (HiPIMS) based Ne-Ar/C2H2 discharges. Plasma properties and film growth are investigated under different gas phase composition and operating pressures. Film mass densities, H content, hardness and compressive stresses are measured. Mass densities in the order of 2.2 g/cm3, hardness close to 25 GPa and H content as low as 11% are obtained. The film properties manifest a dependence on energy and flux of the depositing species and energetic ion bombardment driven structural changes in the films are found to govern the resulting film properties.
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| 16. |
- Aijaz, Asim, 1980-
(författare)
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Synthesis of Carbon-based and Metal-Oxide Thin Films using High Power Impulse Magnetron Sputtering
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work presented in this thesis deals with synthesis of carbon-based as well as metal-oxide thin films using highly ionized plasmas. The principal deposition method employed was high power impulse magnetron sputtering (HiPIMS). The investigations on plasma chemistry, plasma energetics, plasma-film interactions and its correlation to film growth and resulting film properties were made. The thesis is divided into two parts: (i) HiPIMS-based deposition of carbon-based thin films and (ii) HiPIMS-based deposition of metal-oxide thin films.In the first part of the thesis, HiPIMS based strategies are presented that were developed to address the fundamental issues of low degree of carbon ionization and low deposition rates of carbon film growth in magnetron sputtering. In the first study, a new strategy was introduced for increasing the degree of ionization of sputtered carbon via increasing the electron temperature in the discharge by using a higher ionization potential buffer gas (Ne) in place of commonly used Ar. A direct consequence of enhanced electron temperatures was observed in the form of measured large fluxes of ionized carbon at the substrate position. Consequently, high mass densities of the resulting amorphous carbon (a-C) thin films reaching 2.8 g/cm3 were obtained.In another study, feasibility of HiPIMS-based high density discharges for high-rate synthesis of dense and hard a-C thin films was explored. A strategy was compiled and implemented that entailed coupling a hydrocarbon precursor gas (C2H2) with high density discharges generated by the superposition of HiPIMS and direct current magnetron sputtering (DCMS). Appropriate control of discharge density (by tuning HiPIMS/DCMS power ratio), gas phase composition and energy of the ionized depositing species lead to a route capable of providing ten-fold increase in the deposition rate of a-C film growth compared to that obtained using HiPIMS Ar discharge in the first study. The increased deposition rate was achieved without significant incorporation of H (<10 %) and with relatively high hardness (>25 GPa) and mass density (~2.32 g/cm3). The knowledge gained in this work was utilized in a subsequent work where the feasibility of adding high ionization potential buffer gas (Ne) to increase the electron temperature in an Ar/C2H2 HiPIMS discharge was explored. It was found that the increased electron temperature lead to enhanced dissociation of hydrocarbon precursor and an increased H incorporation into the growing film. The resulting a-C thin films exhibited high hardness (~ 25 GPa), mass densities in the order of 2.2 g/cm3 and H content as low as about 11%. The striking feature of the resulting films was low stress levels where the films exhibited compressive stresses in the order of 100 MPa.In the second part of the thesis, investigations on reactive HiPIMS discharge characteristics were made for technologically relevant metal-oxide systems. In the first study, the discharge characteristics of Ti-O and Al-O were investigated by studying the discharge current characteristics and measuring the ion flux composition. Both, Ti-O and Al-O discharges were dominated by large fluxes of ionized metallic as well as sputtering and reactive gases species. The generation of large ionized fluxes influenced the discharge characteristics consequently surpassing the changes in the secondary electron emission yields which, in the case of DCMS discharges entail contrasting behavior of the discharge voltage for the two material systems. The study also suggested that the source of oxygen ions in the case of reactive HiPIMS is both, the target surface (via sputtering) as well as gas phase.In a subsequent study, the knowledge gained from the studies on metal-oxide HiPIMS discharges was utilized for investigating the behavior of reactive HiPIMS discharges related to ternary compound thin film growth. In this work Al-Si-O system, which is a promising candidate for anti-reflective and solar thermal applications, was employed to carry out the investigations under varied target compositions (Al, Al0.5Si0.5, and Al0.1Si0.9). It was found that the discharge current behavior of metal and oxide modes of Al-Si-O HiPIMS discharges were similar to those of Al-O and were independent of the target composition. The influence of energy and composition of the ionized depositing fluxes on the film growth was also investigated. It was shown that stoichiometric Al-Si-O thin films exhibiting a refractive index below 1.6 (which is desired for anti-reflective applications) can be grown. Furthermore, the refractive index and chemical composition of the resulting films were found to be unchanged with respect to the energy of the depositing species.The effect of ionized deposition fluxes that are generated in metal-oxide HiPIMS discharges was also investigated for the phase composition and optical properties of TiO2 thin films. It was found that energetic and ionized sputtered flux in reactive HiPIMS can be used to tailor the phase formation of the TiO2 films with high peak powers facilitating the rutile phase while the anatase phase can be obtained using low peak powers. It was also demonstrated that using HiPIMS, these phases can be obtained at room temperature without external substrate heating or post-deposition annealing. The results on plasma and film properties were also compared with DCMS.
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| 17. |
- Aijaz, Asim, et al.
(författare)
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Synthesis of hydrogenated diamondlike carbon thin films using neon-acetylene based high power impulse magnetron sputtering discharges
- 2016
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 34:6
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogenated diamondlike carbon (DLC:H) thin films exhibit many interesting properties that can be tailored by controlling the composition and energy of the vapor fluxes used for their synthesis. This control can be facilitated by high electron density and/or high electron temperature plasmas that allow one to effectively tune the gas and surface chemistry during film growth, as well as the degree of ionization of the film forming species. The authors have recently demonstrated by adding Ne in an Ar-C high power impulse magnetron sputtering (HiPIMS) discharge that electron temperatures can be effectively increased to substantially ionize C species [Aijaz et al., Diamond Relat. Mater. 23, 1 (2012)]. The authors also developed an Ar-C2H2 HiPIMS process in which the high electron densities provided by the HiPIMS operation mode enhance gas phase dissociation reactions enabling control of the plasma and growth chemistry [Aijaz et al., Diamond Relat. Mater. 44, 117 (2014)]. Seeking to further enhance electron temperature and thereby promote electron impact induced interactions, control plasma chemical reaction pathways, and tune the resulting film properties, in this work, the authors synthesize DLC: H thin films by admixing Ne in a HiPIMS based Ar/C2H2 discharge. The authors investigate the plasma properties and discharge characteristics by measuring electron energy distributions as well as by studying discharge current characteristics showing an electron temperature enhancement in C2H2 based discharges and the role of ionic contribution to the film growth. These discharge conditions allow for the growth of thick (>1 mu m) DLC: H thin films exhibiting low compressive stresses (similar to 0.5 GPa), high hardness (similar to 25 GPa), low H content (similar to 11%), and density in the order of 2.2 g/cm(3). The authors also show that film densification and change of mechanical properties are related to H removal by ion bombardment rather than subplantation.
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| 18. |
- Ferreira, Fabio, et al.
(författare)
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Hard and dense diamond like carbon coatings deposited by deep oscillations magnetron sputtering
- 2018
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Ingår i: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 336, s. 92-98
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Tidskriftsartikel (refereegranskat)abstract
- Recent developments in the automotive industry to improve engine efficiency and minimize pollutant emissions are driving the need for higher operating temperatures and loading densities in internal combustion engines. Future engines for internal combustion engines will require coatings with increased temperature stability (up to 500 degrees C) and wear resistance as compared to present day solutions. Hard tetrahedral DLC coatings (ta-C coatings) very low coefficient of friction and performed very well under mixed and boundary lubrication, and, thus, they are very attractive for automotive industry. In this work, DLC coatings were deposited by deep oscillations magnetron sputtering (DOMS), a variant of high power magnetron sputtering (HiPIMS). The main objective is to increase the sp(3) content in the films, as compared to d.c. magnetron sputtering (DCMS), and thus extend their operating range to higher temperatures. Increasing the bias voltage results in denser and smoother films with increasing hardness, as measured by nano-indentation, and increasing mass density, as measured by x-ray reflectivity. Accordingly, the UV Raman spectroscopy analysis of the films shows that the sp(3)/sp(2) ratio in the films increases with increasing substrate biasing. However, the sp(3) bonds convert back to sp(2) upon annealing. Never the less, a significantly higher amount of sp(3) bonds is formed in the DLC films deposited by DOMS, as compared to the DCMS ones, showing that DOMS is a promising path for the development of hard DLC films.
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| 19. |
- Keller, Jan, et al.
(författare)
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Direct comparison of atomic layer deposition and sputtering of In2O3:H used as transparent conductive oxide layer in CuIn1-xGaxSe2 thin film solar cells
- 2016
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Ingår i: Solar Energy Materials and Solar Cells. - : Elsevier BV. - 0927-0248 .- 1879-3398. ; 157, s. 757-764
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Tidskriftsartikel (refereegranskat)abstract
- In this study thin films of hydrogenated In2O3 (IOH) were fabricated by physical vapor deposition (PVD) with and without a post-annealing step, and by atomic layer deposition (ALD). The electro-optical properties on glass as well as the performance as a transparent conductive oxide (TCO) layer in CuIn1-xGaxSe2 (CIGSe)-based solar cells are compared and related to a ZnO:Al (AZO) baseline TCO. Corresponding TCO film thicknesses were adjusted to a resulting sheet resistance of about R-sh = 20 Omega/sq for all samples. Structural investigations were conducted by X-ray diffraction (XRD) and transmission electron microscopy (TEM), while Hall and optical absorption measurements were performed to analyze the electrical and optical quality of the window layers. It is shown that the fully crystallized IOH layers processed by ALD and PVD show similar microstructural and electro-optical properties, which are superior to the AZO baseline. The finalized solar cells were characterized by current-voltage and reflectance-corrected quantum efficiency measurements. While there is no significant gain in short circuit current density (J(sc)) for as-deposited PVD In2O3 layers, the application of crystalline In2O3 TCOs leads to an improvement of more than 2 mA/cm(2) due to an increase in "optical" band gap energy and less free charge carrier absorption (FCA). The open circuit voltage (V-oc) of the best cells is 10-15 mV higher as compared to the AZO reference, independent of the crystallinity and process of the In2O3 films. The results indicate that the gain in V-oc is due to inherent material properties of the IOH films and does not originate from less sputter damage or an affected i-ZnO/TCO interface. Device simulations show that the higher electron affinity chi of the IOH can explain an increased V-oc if the Fermi level (E-F) is pinned at the CIGSe/CdS interface and why it might not be possible to see the gain when alternative buffer layers are applied.
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| 20. |
- Keller, Jan, et al.
(författare)
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Effect of KF absorber treatment on the functionality of different transparent conductive oxide layers in CIGSe solar cells
- 2018
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Ingår i: Progress in Photovoltaics. - : Wiley. - 1062-7995 .- 1099-159X. ; 26:1, s. 13-23
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Tidskriftsartikel (refereegranskat)abstract
- This contribution studies the impact of the KF-induced Cu(In,Ga)Se2 (CIGSe) absorber modification on the suitability of different transparent conductive oxide (TCO) layers in solar cells. The TCO material was varied between ZnO:Al (AZO), ZnO:B (BZO), and In2O3:H (IOH). It is shown that the thermal stress needed for optimized TCO properties can establish a transport barrier for charge carriers, which results in severe losses in fill factor (FF) for temperatures >150°C. The FF losses are accompanied by a reduction in open circuit voltage (Voc) that might originate from a decreased apparent doping density (Nd,app) after annealing. Thermally activated redistributions of K and Na in the vicinity of the CdS/(Cu,K)-In-Se interface are suggested to be the reason for the observed degradation in solar cell performance. The highest efficiency was measured for a solar cell where the absorber surface modification was removed and a BZO TCO layer was deposited at a temperature of 165°C. The presented results highlight the importance of well-designed TCO and buffer layer processes for CIGSe solar cells when a KF post deposition treatment (KF-PDT) was applied.
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| 21. |
- Keller, Jan, et al.
(författare)
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Using hydrogen‐doped In2O3 films as a transparent back contact in (Ag,Cu)(In,Ga)Se2 solar cells
- 2018
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Ingår i: Progress in Photovoltaics. - : Wiley. - 1062-7995 .- 1099-159X. ; 26:3, s. 159-170
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Tidskriftsartikel (refereegranskat)abstract
- This study evaluates the potential of hydrogen‐doped In2O3 (IOH) as a transparent back contact material in (Agy,Cu1‐y)(In1‐x,Gax)Se2 solar cells. It is found that the presence of Na promotes the creation of Ga2O3 at the back contact during (Agy,Cu1‐y)(In1‐x,Gax)Se2 growth. An excessive Ga2O3 formation results in a Ga depletion, which extends deep into the absorber layer. Consequently, the beneficial back surface field is removed and a detrimental reversed electrical field establishes. However, for more moderate Ga2O3 amounts (obtained with reduced Na supply), the back surface field can be preserved. Characterization of corresponding solar cells suggests the presence of an ohmic back contact, even at absorber deposition temperatures of 550°C. The best solar cell with an IOH back contact shows a fill factor of 74% and an efficiency (η) of 16.1% (without antireflection coating). The results indicate that Ga2O3 does not necessarily act as a transport barrier in the investigated system. Observed losses in open circuit voltage (VOC) as compared to reference samples with a Mo back contact are ascribed to a lower Na concentration in the absorber layer.
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| 22. |
- Kubart, Tomas, et al.
(författare)
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Evolution of sputtering target surface composition in reactive high power impulse magnetron sputtering
- 2017
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 121:17
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between pulsed plasmas and surfaces undergoing chemical changes complicates physics of reactive High Power Impulse Magnetron Sputtering (HiPIMS). In this study, we determine the dynamics of formation and removal of a compound on a titanium surface from the evolution of discharge characteristics in an argon atmosphere with nitrogen and oxygen. We show that the time response of a reactive process is dominated by surface processes. The thickness of the compound layer is several nm and its removal by sputtering requires ion fluence in the order of 1016 cm−2, much larger than the ion fluence in a single HiPIMS pulse. Formation of the nitride or oxide layer is significantly slower in HiPIMS than in dc sputtering under identical conditions. Further, we explain very high discharge currents in HiPIMS by the formation of a truly stoichiometric compound during the discharge off-time. The compound has a very high secondary electron emission coefficient and leads to a large increase in the discharge current upon target poisoning.
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| 23. |
- Kubart, Tomas, 1977-, et al.
(författare)
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High power impulse magnetron sputtering of diamond-like carbon coatings
- 2020
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 38:4
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Tidskriftsartikel (refereegranskat)abstract
- High power impulse magnetron sputtering (HiPIMS) of diamond-like carbon coatings is reviewed. Three variations of HiPIMS were used to deposit diamond-like carbon coatings: use of neon as compared to argon for sputtering, very high discharge peak current density in an Ar atmosphere, and the use of bursts of short sputtering pulses. All three variations were able to provide sufficient ion-to-neutral ratios to effectively control the coating quality using substrate bias. The resulting coatings are typically smooth, amorphous, hard (up to 25 GPa), and dense but have low stress (below 2.5 GPa). The coatings exhibit an increased stability at higher temperature (up to 500 °C) compared to the coatings prepared using standard magnetron sputtering. The resulting coatings also exhibited low wear rates in ambient ball-on-disc tests (2.1 × 10−8 mm3 N−1 m−1). These improvements are explained in terms of the rate of sputtered carbon atom ionization in the plasma and material transport to the substrate. However, the chemical bonding in the films is not yet well understood as relatively low sp3 bond content has been observed.
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| 24. |
- Pedersen, Henrik, et al.
(författare)
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A novel high-power pulse PECVD method
- 2012
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 206:22, s. 4562-4566
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Tidskriftsartikel (refereegranskat)abstract
- A novel plasma enhanced CVD (PECVD) technique has been developed in order to combine energetic particle bombardment and high plasma densities found in ionized PVD with the advantages from PECVD such as a high deposition rate and the capability to coat complex and porous surfaces. In this PECVD method, an ionized plasma is generated above the substrate by means of a hollow cathode discharge. The hollow cathode is known to generate a highly ionized plasma and the discharge can be sustained in direct current (DC) mode, or in high-power pulsed (HiPP) mode using short pulses of a few tens of microsecond. The latter option is similar to the power scheme used in high power impulse magnetron sputtering (HiPIMS), which is known to generate a high degree of ionization of the sputtered material, and thus providing new and added means for the synthesis of tailor-made thin films. In this work amorphous carbon coatings containing copper, have been deposited using both HiPP and DC operating conditions. Investigations of the bulk plasma using optical emission spectroscopy verify the presence of Ar+, C+ as well as Cu+ when running in pulsed mode. Deposition rates in the range 30 mu m/h have been obtained and the amorphous, copper containing carbon films have a low hydrogen content of 4- 5 at%. Furthermore, the results presented here suggest that a more efficient PECVD process is obtained by using a superposition of HiPP and DC mode, compared to using only DC mode at the same average input power.
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| 25. |
- Prusakova, Lucie, et al.
(författare)
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Magnetron sputtering of InGaZnO and ZnSnO amorphous oxide semiconductors
- 2015
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Ingår i: E-MRS Spring meeting 2015, May 11-15, Lille, France.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Amorphous oxide semiconductors (AOS) are exciting materials which combine optical transparency with high electron mobility. AOS are thus suitable for transparent electronics, or, on flexible substrates such as plastic foils, for wearable electronic devices. Although In-Ga-Zn-O is the best performing AOS so far, there is an interest in In-free alternatives. This is due to the concerns about limited In availability and its price. The alternative materials, however, normally require higher deposition temperatures.Here we report on magnetron sputtering of In-Ga-Zn-O (IGZO) and Zn-Sn-O (ZTO) with focus on the effect of deposition conditions on the film properties. IGZO films were deposited by RF sputtering from an oxide target while for ZTO, reactive sputtering from an alloy target was used. All films were deposited without substrate heating and characterized with respect to optical transparency, microstructure, electron mobility and resistivity. The best as-deposited IGZO films had resistivity of about 2∙10-2 ohm∙cm and electron mobility up to 10 cm2∙V-1∙s-1. The properties were very sensitive to the lateral position during deposition. Combination of simulations and experimental characterization was used to understand these effects. There is a strong influence of the composition and energy of the material flux towards the substrate. Reactive deposition process provides more freedom in selecting optimum growth conditions as demonstrated for ZTO films.
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| 26. |
- Prusakova, Lucie, et al.
(författare)
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Room Temperature Reactive Deposition of InGaZnO and ZnSnO Amorphous Oxide Semiconductors for Flexible Electronics
- 2020
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Ingår i: Coatings. - : MDPI. - 2079-6412. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous oxide semiconductors (AOSs) are interesting materials which combine optical transparency with high electron mobility. AOSs can be prepared at low temperatures by high throughput deposition techniques such as magnetron sputtering and are thus suitable for flexible transparent electronics such as flexible displays, thin-film transistors, and sensors. In magnetron sputtering the energy input into the growing film can be controlled by the plasma conditions instead of the substrate temperature. Here, we report on magnetron sputtering of InGaZnO (IGZO) and ZnSnO (ZTO) with a focus on the effect of deposition conditions on the film properties. IGZO films were deposited by radio-frequency (RF) sputtering from an oxide target while for ZTO, reactive sputtering from an alloy target was used. All films were deposited without substrate heating and characterized with respect to microstructure, electron mobility, and resistivity. The best as-deposited IGZO films exhibited a resistivity of about 2 x 10(-2) Ohm center dot cm and an electron mobility of 18 cm(2)center dot V-1 center dot s(-1). The lateral distribution of the electrical properties in such films is mainly related to the activity and amount of oxygen reaching the substrate surface as well as its spatial distribution. The lateral uniformity is strongly influenced by the composition and energy of the material flux towards the substrate.
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| 27. |
- Sønderby, Steffen, et al.
(författare)
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Deposition of yttria-stabilized zirconia thin films by high power impulse magnetron sputtering and pulsed magnetron sputtering
- 2014
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Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 240, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- Yttria-stabilized zirconia (YSZ) thin films were reactively sputter-deposited by high power impulse magnetron sputtering (HiPIMS) and pulsed direct current magnetron sputtering (DCMS). The use of substrate bias voltage was studied in both modes of deposition as a process parameter to promote the growth of dense and less columnar films. Films were deposited on both Si(100) and NiO-YSZ fuel cell anodes. The texture, morphology and composition of the deposited films were investigated with regard to their application as thin electrolytes for solid oxide fuel cells (SOFCs). Independent of the deposition mode the films were found to be stoichiometric. The application of substrate bias voltage had opposite effects on texture and crystallinity of films deposited by pulsed DCMS and HiPIMS. Films deposited by pulsed DCMS became highly crystalline and <220> textured at high bias voltage whereas bias applied to HiPIMS deposited films disrupted crystal growth leading to deterioration of crystallinity. Comparing film morphology, it was found that pulsed DCMS films were columnar and contained voids regardless of the applied substrate bias. When depositing by HiPIMS a window of operation at a bias voltage of -25 V to -50 V was found in which it is possible to deposit non-columnar thin films without voids and cracks as desired for SOFC applications.
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| 28. |
- Vitelaru, Catalin, et al.
(författare)
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Discharge runaway in high power impulse magnetron sputtering of carbon : the effect of gas pressure, composition and target peak voltage
- 2018
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Ingår i: Journal of Physics D. - : IOP PUBLISHING LTD. - 0022-3727 .- 1361-6463. ; 51:16
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Tidskriftsartikel (refereegranskat)abstract
- Pressure and target voltage driven discharge runaway from low to high discharge current density regimes in high power impulse magnetron sputtering of carbon is investigated. The main purpose is to provide a meaningful insight of the discharge dynamics, with the ultimate goal to establish a correlation between discharge properties and process parameters to control the film growth. This is achieved by examining a wide range of pressures (2-20 mTorr) and target voltages (700-850 V) and measuring ion saturation current density at the substrate position. We show that the minimum plasma impedance is an important parameter identifying the discharge transition as well as establishing a stable operating condition. Using the formalism of generalized recycling model, we introduce a new parameter, 'recycling ratio', to quantify the process gas recycling for specific process conditions. The model takes into account the ion flux to the target, the amount of gas available, and the amount of gas required for sustaining the discharge. We show that this parameter describes the relation between the gas recycling and the discharge current density. As a test case, we discuss the pressure and voltage driven transitions by changing the gas composition when adding Ne into the discharge. We propose that standard Ar HiPIMS discharges operated with significant gas recycling do not require Ne to increase the carbon ionization.
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