Browsing by Author "Ronkainen, Helena"
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- Aluminum oxide/titanium dioxide nanolaminates grown by atomic layer deposition: Growth and mechanical properties
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2017-01-01) Ylivaara, Oili M E; Kilpi, Lauri; Liu, Xuwen; Sintonen, Sakari; Ali, Saima; Laitinen, Mikko; Julin, Jaakko; Haimi, Eero; Sajavaara, Timo; Lipsanen, Harri; Hannula, Simo-Pekka; Ronkainen, Helena; Puurunen, RiikkaAtomic layer deposition (ALD) is based on self-limiting surface reactions. This and cyclic process enable the growth of conformal thin films with precise thickness control and sharp interfaces. A multilayered thin film, which is nanolaminate, can be grown using ALD with tuneable electrical and optical properties to be exploited, for example, in the microelectromechanical systems. In this work, the tunability of the residual stress, adhesion, and mechanical properties of the ALD nanolaminates composed of aluminum oxide (Al2O3) and titanium dioxide (TiO2) films on silicon were explored as a function of growth temperature (110-300 °C), film thickness (20-300 nm), bilayer thickness (0.1-100 nm), and TiO2 content (0%-100%). Al2O3 was grown from Me3Al and H2O, and TiO2 from TiCl4 and H2O. According to wafer curvature measurements, Al2O3/TiO2 nanolaminates were under tensile stress; bilayer thickness and growth temperature were the major parameters affecting the stress; the residual stress decreased with increasing bilayer thickness and ALD temperature. Hardness increased with increasing ALD temperature and decreased with increasing TiO2 fraction. Contact modulus remained approximately stable. The adhesion of the nanolaminate film was good on silicon. - Characterization of thin film adhesion by MEMS shaft-loading blister testing
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2013) Berdova, Maria; Lyytinen, Jussi; Grigoras, Kestuti; Baby, Anu; Kilpi, Lauri; Ronkainen, Helena; Franssila, Sami; Koskinen, Jari - Comparison of mechanical properties and composition of magnetron sputter and plasma enhanced atomic layer deposition aluminum nitride films
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2018-09-01) Sippola, Perttu; Pyymaki Perros, Alexander; Ylivaara, Oili M.E.; Ronkainen, Helena; Julin, Jaakko; Liu, Xuwen; Sajavaara, Timo; Etula, Jarkko; Lipsanen, Harri; Puurunen, Riikka L.A comparative study of mechanical properties and elemental and structural composition was made for aluminum nitride thin films deposited with reactive magnetron sputtering and plasma enhanced atomic layer deposition (PEALD). The sputtered films were deposited on Si (100), Mo (110), and Al (111) oriented substrates to study the effect of substrate texture on film properties. For the PEALD trimethylaluminum-ammonia films, the effects of process parameters, such as temperature, bias voltage, and plasma gas (ammonia versus N2/H2), on the AlN properties were studied. All the AlN films had a nominal thickness of 100 nm. Time-of-flight elastic recoil detection analysis showed the sputtered films to have lower impurity concentration with an Al/N ratio of 0.95, while the Al/N ratio for the PEALD films was 0.81-0.90. The mass densities were ∼3.10 and ∼2.70 g/cm3 for sputtered and PEALD AlN, respectively. The sputtered films were found to have higher degrees of preferential crystallinity, whereas the PEALD films were more polycrystalline as determined by x-ray diffraction. Nanoindentation experiments showed the elastic modulus and hardness to be 250 and 22 GPa, respectively, for sputtered AlN on the (110) substrate, whereas with PEALD AlN, values of 180 and 19 GPa, respectively, were obtained. The sputtered films were under tensile residual stress (61-421 MPa), whereas the PEALD films had a residual stress ranging from tensile to compressive (846 to −47 MPa), and high plasma bias resulted in compressive films. The adhesion of both films was good on Si, although sputtered films showed more inconsistent critical load behavior. Also, the substrate underneath the sputtered AlN did not withstand high wear forces as with the PEALD AlN. The coefficient of friction was determined to be ∼0.2 for both AlN types, and their wear characteristics were almost identical. - Kulumishiukkasanalyysin käyttö koneiden kunnonseurannassa
Helsinki University of Technology | Master's thesis(1985) Ronkainen, Helena - Matrix morphology and the particle dispersion in HDPE nanocomposites with enhanced wear resistance
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019-08-01) Pelto, Jani; Verho, Tuukka; Ronkainen, Helena; Kaunisto, Kimmo; Metsäjoki, Jarkko; Seitsonen, Jani; Karttunen, MikkoHigh density polyethylene nanocomposites were prepared by melt mixing of varying type of nanopowders in the presence of vinyltrimethoxysilane (VTMS) coupling agent. Three spherical/irregular-shaped nanopowders, fumed Al2O3, γ-Al2O3, cubic titanium nitride (TiN) (1.5 vol-%), and high aspect ratio graphene oxide platelets (GO) (0.5 vol-%) were investigated in a high molecular weight HDPE matrix. Significant differences in the dispersion quality between the nanopowders were found by TEM and AFM. Degree of crystallinity of the nanocomposites (DSC/XRD) was consistently lower than in the neat HDPE polymer. The particularly well dispersed fumed Al2O3, γ-Al2O3 and GO nanopowders induced significant modification on the micromechanical properties of the HDPE. For the first time, great enhancement in the sliding wear performance, and an improvement in the abrasive wear performance was found in the high molecular weight HDPE nanocomposites. DSC analyses showed elevations in the glass transition temperatures and the peak melting temperatures of the nanocomposites. XRD peak splitting in the HDPE + GO and the HDPE + γ-Al2O3 nanocomposites suggest the emergence of a concurrent orthorhombic HDPE phase. Formation of new phases was also supported by DSC analyses showing broad and multimodal melting peaks. Scherrer analyses of XRD data showed slightly increased HDPE crystalline thicknesses in the range of 15–20 nm in the nanocomposites, which was in line with the TEM and AFM observations. The great elevation in the melting temperatures of the HDPE nanocomposites with fumed Al2O3 and γ-Al2O3 could not be attributed to the polymer lamellar thickness, but rather to the altered properties of the solid amorphous phase stemming for the nanopowder additives. - Microscratch testing method for systematic evaluation of the adhesion of atomic layer deposited thin films on silicon
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2016-01-01) Kilpi, Lauri; Ylivaara, Oili M. E.; Vaajoki, Antti; Malm, Jari; Sintonen, Sakari; Tuominen, Marko; Puurunen, Riikka L.; Ronkainen, HelenaThe scratch test method is widely used for adhesion evaluation of thin films and coatings. Usual critical load criteria designed for scratch testing of coatings were not applicable to thin atomic layer deposition (ALD) films on silicon wafers. Thus, the bases for critical load evaluation were established and the critical loads suitable for ALD coating adhesion evaluation on silicon wafers were determined in this paper as LCSi1, LCSi2, LCALD1, and LCALD2, representing the failure points of the silicon substrate and the coating delamination points of the ALD coating. The adhesion performance of the ALD Al2O3, TiO2, TiN, and TaCN+Ru coatings with a thickness range between 20 and 600 nm and deposition temperature between 30 and 410°C on silicon wafers was investigated. In addition, the impact of the annealing process after deposition on adhesion was evaluated for selected cases. The tests carried out using scratch and Scotch tape test showed that the coating deposition and annealing temperature, thickness of the coating, and surface pretreatments of the Si wafer had an impact on the adhesion performance of the ALD coatings on the silicon wafer. There was also an improved load carrying capacity due to Al2O3, the magnitude of which depended on the coating thickness and the deposition temperature. The tape tests were carried out for selected coatings as a comparison. The results show that the scratch test is a useful and applicable tool for adhesion evaluation of ALD coatings, even when carried out for thin (20 nm thick) coatings. - Tribological properties of thin films made by atomic layer deposition sliding against silicon
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2018-01-01) Kilpi, Lauri; Ylivaara, Oili M.E.; Vaajoki, Antti; Liu, Xuwen; Rontu, Ville; Sintonen, Sakari; Haimi, Eero; Malm, Jari; Bosund, Markus; Tuominen, Marko; Sajavaara, Timo; Lipsanen, Harri; Hannula, Simo Pekka; Puurunen, Riikka L.; Ronkainen, HelenaInterfacial phenomena, such as adhesion, friction, and wear, can dominate the performance and reliability of microelectromechanical (MEMS) devices. Here, thin films made by atomic layer deposition (ALD) were tested for their tribological properties. Tribological tests were carried out with silicon counterpart sliding against ALD thin films in order to simulate the contacts occurring in the MEMS devices. The counterpart was sliding in a linear reciprocating motion against the ALD films with the total sliding distances of 5 and 20 m. Al2O3 and TiO2 coatings with different deposition temperatures were investigated in addition to Al2O3-TiO2-nanolaminate, TiN, NbN, TiAlCN, a-C:H [diamondlike carbon (DLC)] coatings, and uncoated Si. The formation of the tribolayer in the contact area was the dominating phenomenon for friction and wear performance. Hardness, elastic modulus, and crystallinity of the materials were also investigated. The nitride coatings had the most favorable friction and wear performance of the ALD coatings, yet lower friction coefficient was measured with DLC a-C:H coating. These results help us to take steps toward improved coating solutions in, e.g., MEMS applications.