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Papers by Tommi Riekkinen
Tommi Riekkinen. Fabrication and characterization of ferro-and piezoelectric multilayer devices f... more Tommi Riekkinen. Fabrication and characterization of ferro-and piezoelectric multilayer devices for high frequency applications [Ferro-ja pietsosähköisten monikerroskomponenttien valmistus ja karakterisointi suurtaajuussovelluksiin]. Espoo 2009. VTT Publications 716. 90 p. + app. 38 p.
A fabrication method for parallel-plate structures and a parallel-plate structure arrangement, wh... more A fabrication method for parallel-plate structures and a parallel-plate structure arrangement, wherein the structures have a middle layer, grown on a substrate and disposed between top and bottom electrode layers, wherein the middle layer and the top and bottom electrode layers are deposited on a bottom substrate, and wherein the middle layer is grown first and the top and bottom electrodes are essentially deposited afterwards.
ABSTRACT Epitaxial GaAs material shows a great potential in X-ray spectroscopy and radiography ap... more ABSTRACT Epitaxial GaAs material shows a great potential in X-ray spectroscopy and radiography applications due to its high absorption efficiency and low defect density. Fabrication of pixel radiation detectors from high-purtity epitaxial GaAs has been developed further. The process is based on mesa etching for pixellisation and sputtering for metallization. The leakage currents of processed pad detectors are below 10 nA/cm(2) at a reverse bias of 100V and decrease exponentially with the temperature. Measurement with transient current technique (TCT) shows that electrons have a trapping time of 8 ns. Good spectroscopic result were obtained from both a pad detector and a hybridized Medipix GaAs detector.
Applied Physics Letters, Dec 17, 2007
Sr 1−x TiO 3 / Cu parallel-plate structure have been fabricated using a layer transfer method. Th... more Sr 1−x TiO 3 / Cu parallel-plate structure have been fabricated using a layer transfer method. The use of a Cu bottom electrode results in a giant electrode Q-factor ϫ capacitor area product of Q elec A = 3.79ϫ 10 5 m 2 at 1 GHz. The dielectric constant at room temperature is 420 and the tunability amounts to 73% near a breakdown voltage of 35 V. The major advantages of the layer transfer method include low electrode losses, the freedom to select an auxiliary substrate and seed layer for ferroelectric film growth irrespective of their high-frequency properties, and the possibility to utilize a large variety of device substrates as they no longer act as template for film growth.
Microelectronic Engineering, 2003
The aim of this work was to develop a deposition process for a high-dielectric constant tantalum ... more The aim of this work was to develop a deposition process for a high-dielectric constant tantalum pentoxide for integrated capacitors. Thin films were deposited reactively on glass wafers using a radio-frequency magnetron sputtering cluster tool at 4 1 various O /Ar flow ratios. By using 2 MeV He backscattering spectroscopy and X-ray diffraction, the films obtained 2 showed a stoichiometric orthorhombic b-Ta O phase at 20% O in the sputtering gas flow. With low-frequency 2 5 2 2 measurements (f 5 100 kHz), a 2003200-mm square metal–insulator–metal (MIM) capacitor with copper electrodes and a 2 340-nm thick dielectric gave a capacitance density of 0.066 mF / cm , with a quality factor (Q) of 650. The value of the relative permittivity) was approximately 25 determined from MIM capacitors of various sizes. The surface roughness of r 2 the 376-nm thick oxide film was found to be small: 0.255 nm. The largest measured capacitor (2003200 mm) gave reasonable results at low frequencies. When ...
Thin Solid Films, 2009
The growth of high-quality AlN films has been studied by reactive sputtering onto Mo electrodes w... more The growth of high-quality AlN films has been studied by reactive sputtering onto Mo electrodes with Ni, Ti, and TiW seed layers and subsequent integration into thin film bulk acoustic wave resonators. The crystalline structure and morphology of the Mo and c-axis oriented AlN ...
2014 IEEE International Ultrasonics Symposium, 2014
Angewandte Chemie International Edition
Bridging the Micro and Nano Worlds, 2015
Microelectronic Engineering, 2002
The reactions in the Si/TaC/Cu and Si/Ta2N/Cu metallisation systems were investigated by X-ray di... more The reactions in the Si/TaC/Cu and Si/Ta2N/Cu metallisation systems were investigated by X-ray diffraction, Rutherford backscattering, scanning electron microscope and the transmission electron microscopy. The results were then combined with the assessed ternary Si–Ta–C, Ta–C–Cu, Si–Ta–N and Ta–N–Cu phase diagrams. It was found that both barriers ultimately failed due to diffusion of Cu through the barrier and accompanied formation of
Journal of Physics: Condensed Matter, 2015
2007 IEEE Ultrasonics Symposium Proceedings, 2007
... The mode shape can be approximated by X(x, t) = X0(t) sin (πx/L) , where x denotes the positi... more ... The mode shape can be approximated by X(x, t) = X0(t) sin (πx/L) , where x denotes the position along the resonator arm, and X0 is the resonator endpoint displacement. ... The beam dimensions are L × w × h, and the piezolayer size is Lpz × wpz × hpz. ...
Journal of Physics: Condensed Matter, 2015
We present a computational study of spontaneous polarization and piezoelectricity in ScxAl1−xN al... more We present a computational study of spontaneous polarization and piezoelectricity in ScxAl1−xN alloys in the compositional range from x = 0 to x = 0.5, obtained in the context of density functional theory and the Berry-phase theory of electric polarization using large periodic supercells. We report composition-dependent values of piezoelectric coefficients eij, piezoelectric moduli dij and elastic constants Cij. The theoretical findings are complemented with experimental measurement of e33 for a series of sputtered ScAlN films carried out with a piezoelectric resonator. The rapid increase with Sc content of the piezoelectric response reported in previous studies is confirmed for the available data. A detailed description of the full methodology required to calculate the piezoelectric properties of ScAlN, with application to other complex alloys, is presented. In particular, we find that the large amount of internal strain present in ScAlN and its intricate relation with electric polarization make configurational sampling and the use of large supercells at different compositions necessary in order to accurately derive the piezoelectric response of the material.
Tommi Riekkinen. Fabrication and characterization of ferro-and piezoelectric multilayer devices f... more Tommi Riekkinen. Fabrication and characterization of ferro-and piezoelectric multilayer devices for high frequency applications [Ferro-ja pietsosähköisten monikerroskomponenttien valmistus ja karakterisointi suurtaajuussovelluksiin]. Espoo 2009. VTT Publications 716. 90 p. + app. 38 p.
A fabrication method for parallel-plate structures and a parallel-plate structure arrangement, wh... more A fabrication method for parallel-plate structures and a parallel-plate structure arrangement, wherein the structures have a middle layer, grown on a substrate and disposed between top and bottom electrode layers, wherein the middle layer and the top and bottom electrode layers are deposited on a bottom substrate, and wherein the middle layer is grown first and the top and bottom electrodes are essentially deposited afterwards.
ABSTRACT Epitaxial GaAs material shows a great potential in X-ray spectroscopy and radiography ap... more ABSTRACT Epitaxial GaAs material shows a great potential in X-ray spectroscopy and radiography applications due to its high absorption efficiency and low defect density. Fabrication of pixel radiation detectors from high-purtity epitaxial GaAs has been developed further. The process is based on mesa etching for pixellisation and sputtering for metallization. The leakage currents of processed pad detectors are below 10 nA/cm(2) at a reverse bias of 100V and decrease exponentially with the temperature. Measurement with transient current technique (TCT) shows that electrons have a trapping time of 8 ns. Good spectroscopic result were obtained from both a pad detector and a hybridized Medipix GaAs detector.
Applied Physics Letters, Dec 17, 2007
Sr 1−x TiO 3 / Cu parallel-plate structure have been fabricated using a layer transfer method. Th... more Sr 1−x TiO 3 / Cu parallel-plate structure have been fabricated using a layer transfer method. The use of a Cu bottom electrode results in a giant electrode Q-factor ϫ capacitor area product of Q elec A = 3.79ϫ 10 5 m 2 at 1 GHz. The dielectric constant at room temperature is 420 and the tunability amounts to 73% near a breakdown voltage of 35 V. The major advantages of the layer transfer method include low electrode losses, the freedom to select an auxiliary substrate and seed layer for ferroelectric film growth irrespective of their high-frequency properties, and the possibility to utilize a large variety of device substrates as they no longer act as template for film growth.
Microelectronic Engineering, 2003
The aim of this work was to develop a deposition process for a high-dielectric constant tantalum ... more The aim of this work was to develop a deposition process for a high-dielectric constant tantalum pentoxide for integrated capacitors. Thin films were deposited reactively on glass wafers using a radio-frequency magnetron sputtering cluster tool at 4 1 various O /Ar flow ratios. By using 2 MeV He backscattering spectroscopy and X-ray diffraction, the films obtained 2 showed a stoichiometric orthorhombic b-Ta O phase at 20% O in the sputtering gas flow. With low-frequency 2 5 2 2 measurements (f 5 100 kHz), a 2003200-mm square metal–insulator–metal (MIM) capacitor with copper electrodes and a 2 340-nm thick dielectric gave a capacitance density of 0.066 mF / cm , with a quality factor (Q) of 650. The value of the relative permittivity) was approximately 25 determined from MIM capacitors of various sizes. The surface roughness of r 2 the 376-nm thick oxide film was found to be small: 0.255 nm. The largest measured capacitor (2003200 mm) gave reasonable results at low frequencies. When ...
Thin Solid Films, 2009
The growth of high-quality AlN films has been studied by reactive sputtering onto Mo electrodes w... more The growth of high-quality AlN films has been studied by reactive sputtering onto Mo electrodes with Ni, Ti, and TiW seed layers and subsequent integration into thin film bulk acoustic wave resonators. The crystalline structure and morphology of the Mo and c-axis oriented AlN ...
2014 IEEE International Ultrasonics Symposium, 2014
Angewandte Chemie International Edition
Bridging the Micro and Nano Worlds, 2015
Microelectronic Engineering, 2002
The reactions in the Si/TaC/Cu and Si/Ta2N/Cu metallisation systems were investigated by X-ray di... more The reactions in the Si/TaC/Cu and Si/Ta2N/Cu metallisation systems were investigated by X-ray diffraction, Rutherford backscattering, scanning electron microscope and the transmission electron microscopy. The results were then combined with the assessed ternary Si–Ta–C, Ta–C–Cu, Si–Ta–N and Ta–N–Cu phase diagrams. It was found that both barriers ultimately failed due to diffusion of Cu through the barrier and accompanied formation of
Journal of Physics: Condensed Matter, 2015
2007 IEEE Ultrasonics Symposium Proceedings, 2007
... The mode shape can be approximated by X(x, t) = X0(t) sin (πx/L) , where x denotes the positi... more ... The mode shape can be approximated by X(x, t) = X0(t) sin (πx/L) , where x denotes the position along the resonator arm, and X0 is the resonator endpoint displacement. ... The beam dimensions are L × w × h, and the piezolayer size is Lpz × wpz × hpz. ...
Journal of Physics: Condensed Matter, 2015
We present a computational study of spontaneous polarization and piezoelectricity in ScxAl1−xN al... more We present a computational study of spontaneous polarization and piezoelectricity in ScxAl1−xN alloys in the compositional range from x = 0 to x = 0.5, obtained in the context of density functional theory and the Berry-phase theory of electric polarization using large periodic supercells. We report composition-dependent values of piezoelectric coefficients eij, piezoelectric moduli dij and elastic constants Cij. The theoretical findings are complemented with experimental measurement of e33 for a series of sputtered ScAlN films carried out with a piezoelectric resonator. The rapid increase with Sc content of the piezoelectric response reported in previous studies is confirmed for the available data. A detailed description of the full methodology required to calculate the piezoelectric properties of ScAlN, with application to other complex alloys, is presented. In particular, we find that the large amount of internal strain present in ScAlN and its intricate relation with electric polarization make configurational sampling and the use of large supercells at different compositions necessary in order to accurately derive the piezoelectric response of the material.