Browsing by Author "Koskinen, Tomi"
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- Siirtokonetehtaan voimayksikkötoimitusten analysointi ja kehittäminen
Helsinki University of Technology | Master's thesis(1997) Koskinen, Tomi - Atomic layer deposition of Zr-sandwiched ZnO thin films for transparent thermoelectrics
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2023-01-15) Koskinen, Tomi; Volin, Ulrika; Tossi, Camilla; Raju, Ramesh; Tittonen, IlkkaAtomic layer deposited (ALD) transparent thermoelectric materials enable the introduction of energy harvesting and sensing devices onto surfaces of various shapes and sizes in imperceptible manner. Amongst these materials, ZnO has shown promising results in terms of both thermoelectric and optical characteristics. The thermoelectric performance of ZnO can be further optimized by introducing extrinsic doping, to the realization of which ALD provides excellent control. Here, we explore the effects of sandwiching of ZrO2 layers with ZnO on glass substrates. The room-temperature thermoelectric power factor is maximised at 116μW m−1 K−2 with samples containing a 2% nominal percentage of ZrO2. The addition of ZrO2 layers is further shown to reduce the thermal conductivity, resulting in a 20.2% decrease from the undoped ZnO at 2% doping. Our results contribute to increasing the understanding of the effects of Zr inclusion in structural properties and growth of ALD ZnO, as well as the thermal and thermoelectric properties of Zr-doped ZnO films in general. - Browser performance in Qt environment
School of Science | Master's thesis(2012) Riikkala, VilleThe usage of browser applications becomes more and more common all the time. They are replacing traditional applications, for example, as email clients. In addition, social media services are typically available for a browser application. Webkit is one of the most widespread browser engines available and it is used, for example, by Google in its Chrome browser. Webkit offers two different versions. Qt is a development framework managed by Digia. Qt can be used to deploy applications to several platforms using the same source code. A Qt port of the Webkit is also provided with a Qt development framework. Webkit 2 is a newer version of this famous engine and is also provided when installing Qt version 5. A Qt version of both Webkit and Webkit 2 is available. The purpose of my thesis is to explain the difference between the two versions of Webkits, in addition to measuring and analyzing the found differences. Webkit and Webkit 2 differ from each other from an architectural point of view so that Webkit 2 is split to work in two processes while the older version of Webkit runs the entire code in a single process. In Webkit and Webkit 2, the actual rendering occurs in the same manner. Better stability and reactivity as well as the possibility to use an environment of several processors are the most significant advantages of Webkit 2 architecture. Webkit and Webkit 2engines are compared in four different performance tests. These are page load speed, DOM speed, JavaScript speed, and CSS speed. Tests are driven in a virtual Linux environment first using one and then two processors. Test results prove that the Webkit 2 -based browser is not faster in any measured area, compared to the older version of Webkit. Instead, the Webkit 2 -based browser is clearly slower, especially when calculating differences using percentages, in all other areas except in DOM speed. If results are viewed using milliseconds, only the results of tests measuring page load speed show notable differences. Webkit 2 could, in theory, be faster than its predecessor if a multiprocessing environment could have better been taken into account in a code level. However, this never occurred in the conducted test drives. As a conclusion, better stability and responsiveness can be achieved at a minimal cost of time. - Design and implementation of control electronics for evaporation based hydrovoltaic energy harvesters
Sähkötekniikan korkeakoulu | Bachelor's thesis(2020-12-07) Ortela, Joni - Kotelokoneistuksen kehitys: koneistusmenetelmät sekä alihankintaverkoston oikea käyttö
School of Engineering | Master's thesis(2010) Sivonen, TeemuSubject of this thesis was to develop the operations of Metso Drives Oy machining workshop for gear housings. Year 2003 housing manufacturing of Metso Drives Oy was at critical period. The machining load was intense and the range of products was very high. The methods for controlling the capacity and supplier network were found lacking. High load for machining workshop was putting pressure on process development. The main goals for this study were to find potential development areas from housing machining and to create clear criteria for make or buy decisions. In addition aim was to develop tools to help control the capacity and to optimize the use of supplier network. This study for potential development areas concentrated on the housing type with biggest yearly volumes. The methods for capacity control and optimization of supplier network concentrated on developing long term planning. The development project of housing manufacturing was done using 7-step development tool. Present condition of capacity planning and the use of suppliers were started by checking the machining hours and the costs of products both at internal manufacturing and at suppliers. Based on these studies an Excel-based tool was created to help with long term capacity planning. As a result of this thesis numerous potential development areas for housing machining were found. In addition it was noticed that the use of capacity planning tool brought significant cost savings for the company. - Droplet Friction on Superhydrophobic Surfaces Scales With Liquid-Solid Contact Fraction
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2024-09-17) Lepikko, Sakari; Turkki, Valtteri; Koskinen, Tomi; Raju, Ramesh; Jokinen, Ville; Kiseleva, Mariia S.; Rantataro, Samuel; Timonen, Jaakko V.I.; Backholm, Matilda; Tittonen, Ilkka; Ras, Robin H.A.It is generally assumed that contact angle hysteresis of superhydrophobic surfaces scales with liquid–solid contact fraction, however, its experimental verification has been problematic due to the limited accuracy of contact angle and sliding angle goniometry. Advances in cantilever-based friction probes enable accurate droplet friction measurements down to the nanonewton regime, thus suiting much better for characterizing the wetting of superhydrophobic surfaces than contact angle hysteresis measurements. This work quantifies the relationship between droplet friction and liquid–solid contact fraction, through theory and experimental validation. Well-defined micropillar and microcone structures are used as model surfaces to provide a wide range of different liquid–solid contact fractions. Micropillars are known to be able to hold the water on top of them, and a theoretical analysis together with confocal laser scanning microscopy shows that despite the spiky nature of the microcones droplets do not sink into the conical structure either, rendering a diminishingly small liquid–solid contact fraction. Droplet friction characterization with a micropipette force sensor technique reveals a strong dependence of the droplet friction on the contact fraction, and the dependency is described with a simple physical equation, despite the nearly three-orders-of-magnitude difference in liquid–solid contact fraction between the sparsest cone surface and the densest pillar surface. - Inkjet-printed thermoelectrics
Sähkötekniikan korkeakoulu | Bachelor's thesis(2021-05-04) Vaara, Pyry - InSb Nanowire Direct Growth on Plastic for Monolithic Flexible Device Fabrication
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-01-25) Khayrudinov, Vladislav; Koskinen, Tomi; Grodecki, Kacper; Murawski, Krzysztof; Kopytko, Małgorzata; Yao, Lide; Jiang, Hua; Tittonen, Ilkka Juhani; Lipsanen, Harri; Haggren, TuomasWe report direct growth of InSb nanowires (NWs) and monolithic device fabrication on flexible plastic substrates. The nanowires were grown using metal–organic vapor-phase epitaxy (MOVPE) in self-catalyzed mode. The InSb NWs are shown to form in the zinc-blende crystal structure and to exhibit strong photoluminescence at room temperature. The NW array light-trapping properties are evidenced by reflectance that is significantly reduced compared to bulk material. Finally, the InSb NWs are used to demonstrate a metal–semiconductor–metal photoresistor directly on the flexible plastic substrate. The results are believed to advance the integration of III–V nanowires to flexible devices, and infrared photodetectors in particular. - Johdinratkaisut taipuisaan ja läpinäkyvään lämpösähköiseen kosketuspaneeliin
Sähkötekniikan korkeakoulu | Bachelor's thesis(2016-12-20) Koskinen, Tomi - Large-area thermal distribution sensor based on multilayer graphene ink
Letter(2020-09-02) Koskinen, Tomi; Juntunen, Taneli; Tittonen, IlkkaEmergent applications in wearable electronics require inexpensive sensors suited to scalable manufacturing. This work demonstrates a large-area thermal sensor based on distributed thermocouple architecture and ink-based multilayer graphene film. The proposed device combines the exceptional mechanical properties of multilayer graphene nanocomposite with the reliability and passive sensing performance enabled by thermoelectrics. The Seebeck coefficient of the spray-deposited films revealed an inverse thickness dependence with the largest value of 44.7 µV K−1 at 78 nm, which makes thinner films preferable for sensor applications. Device performance was demonstrated by touch sensing and thermal distribution mapping-based shape detection. Sensor output voltage in the latter application was on the order of 300 µV with a signal-to-noise ratio (SNR) of 35, thus enabling accurate detection of objects of different shapes and sizes. The results imply that films based on multilayer graphene ink are highly suitable to thermoelectric sensing applications, while the ink phase enables facile integration into existing fabrication processes. - Nanostructured copper iodide thin films for transparent thermoelectrics
Kemiantekniikan korkeakoulu | Bachelor's thesis(2022-09-09) Wojnicka, Weronika - Nanostructured thermoelectric materials for transparent and flexible applications
School of Electrical Engineering | Doctoral dissertation (article-based)(2023) Koskinen, TomiThe global energy use is predicted to grow by up to 50% in the coming decades, placing both pressure on resources and heavy demands on the energy efficiency of technologies around us. The majority of primary energy consumption is wasted as heat, which is ubiquitous in a difficult-to-use low-grade form. At the same time, the number of electronic devices in both everyday life and industry is increasing rapidly. Thermoelectric materials enable converting heat into electricity, but their large-scale use is hindered by a low power per cost figure. The use of nanostructuring has enabled improving the thermoelectric performance by careful engineering of both electronic and thermal properties of these materials. Concurrently, also other material properties, such as optical transparency or mechanical flexibility, can be improved. The emergence of thermoelectric materials with functional properties could promote the widespread adoption of thermoelectric devices by providing novel uses and application domains. This thesis presents ways to engineer thermoelectric materials for functional applications using nanostructuring as well as demonstrates a few proof-of-concept devices based on these materials. The thesis first studies the thermal properties of core-shell GaAs-AlAs nanowire arrays, a material system important for a variety of optoelectronic devices. Characterization by the transient thermoreflectance technique indicates that the thickness of the introduced epitaxial AlAs shell can be exploited in controlling the thermal properties of the heterostructure. Second, widely studied transparent thermoelectric material, ZnO, is grown using atomic layer deposition (ALD). Sandwiching of Zr in between ZnO layers grown by ALD is found to improve the room-temperature thermoelectric performance of ZnO at a 2% nominal concentration of Zr. Further, nanoporous grass-like alumina (GLA) surface is used as a template for ALD of Al-doped ZnO (AZO), showing increased carrier concentration and subsequently improved electrical conductivity and thermoelectric power factor. In addition, the transparency of the AZO film grown on GLA is enhanced due to the antireflective behaviour partly inherited from GLA. Finally, nanostructured materials are used in two instances to realize flexible thermoelectric devices. First, a thermoelectric generator based on InAs nanowire networks grown directly on flexible plastic is demonstrated. Second, a thermal distribution sensor based on spray-deposited multilayer graphene is presented. The results obtained in this thesis demonstrate various ways for engineering the properties of thermoelectric materials for functional applications. Further, approaches enabling the scalable and cost-efficient fabrication of these materials are presented, drafting routes for practical utilization of functional thermoelectric devices. - Securing a shared memory architecture in Symbian OS
Helsinki University of Technology | Master's thesis(2008) Koskinen, TomiÄlypuhelimet ovat tärkeä osa käyttäjiensä arkea, niiden tehokkaat tiedonsiirto- ja multimediaominaisuudet mahdollistavat esimerkiksi reaaliaikaisen videokuvan katselun ja turvallisen sähköpostin käyttämisen. Tällaiset toiminnot tekevät tietoturvasta entistä tärkeämpää matkapuhelinten käyttäjille, valmistajille ja verkko-operaattoreille. Tässä työssä tutkitaan ja parannetaan olemassa olevan jaettua muistia hyödyntävän palveluohjelmiston tietoturvaa Symbian-ympäristössä. Palvelun haavoittuvuuksien analysointiin käytetään uhka-analyysiä ja abstraktia muistimallia, jonka avulla tutkitaan jaetun muistin käyttötapauksia ja tiedon suojattomuutta. Löydetyille haavoittuvuuksille määrätään riskiarvo ja ne todistetaan olemassa oleviksi käyttäen apuna uhkatestijoukkoa. Uhkalistaa ja abstraktia muistimallia hyödyntäen haavoittuvuuksille kehitetään vastatoimenpiteitä. Hyödyntämällä mittaustuloksia ympäristön ominaisuuksista, palvelun laatuattribuuteista ja uhan riskistä, sopivin vastatoimenpide voidaan valita niin, ettei yhteensopivuus nykyisten asiakasohjelmistojen kanssa kärsi. Sovellettujen vastatoimenpiteiden toimivuus varmennetaan hyödyntäen aiemmin toteutettuja uhkatestejä. Työ osoittaa, että jaettua muistia hyödyntävän palvelun tietoturvaa voidaan parantaa ilman että sen laatuattribuuteissa tapahtuu suurehkoja muutoksia. Lisäksi uhkatestijoukkoa voidaan käyttää apuna laadun valvonnassa vastatoimia kehitettäessä. Ohjelmistoinsinöörit voivat hyödyntää työssä kehitettyä abstraktia muistimallia tutkiakseen ja parantaakseen jaettuun muistiin perustuvien arkkitehtuurien tietoturvaa. Tämä mahdollistaa erityisesti vaativien sovellusalueitten, kuten multimediasovellusten, tiedonsiirtokapasiteetin parantamisen ja tehokkaamman muistin hyödyntämisen. Lisäksi ohjelmistoprojektit voivat hyödyntää työssä käytettyä uhkatestimetodologiaa ohjelmistojensa tietoturvan arvioimiseen ja parantamiseen. Toteutetut vastatoimenpidetaktiikat ovat sovellettavissa vastaaviin ohjelmistoarkkitehtuureihin. - Studies on an amplitude hologram as the collimator in a submillimeter-wave compact antenna test range
Doctoral dissertation (article-based)(2007-06-20) Koskinen, TomiThis thesis is based on the research work, the objective of which has been to develop a hologram-based compact antenna test range (CATR) for submillimeter wavelengths. Such a measurement facility is needed for testing antennas of, e.g., astronomical and Earth observation satellites. The further objective has been to improve electrical characteristics of the hologram, as well as its manufacturing properties. The hologram studied in this thesis is a slot pattern processed on a thin metal-plated Mylar film and it is used as a transmission-type collimating element. A hologram-based CATR was designed and constructed for 322 GHz and was used for testing a 1.5 meter reflector antenna (Admirals RTO). A hologram of 3 meters in diameter was soldered together from three pieces, which were manufactured on 50 µm-thick copper-plated Mylar film by using laser-exposure and wet-etching. Partly due to manufacturing errors, the measured quiet-zone amplitude and phase deviations were appr. 1.2 dB and 250° within a region of 1.5 meters in diameter. The effect of these deviations on antenna measurement results was estimated by simulations. Feasibility of the hologram for 650 GHz has also been studied. Laser-exposure and wet-etching has been found to be a potentially suitable manufacturing method for frequencies up to 1000 GHz. The 50 µm Mylar film is a suitable material for frequencies up to 650 GHz, but at higher frequencies the film has to be thinner to avoid resonances inside the film. The 25 µm Mylar film is estimated to be suitable for frequencies up to 1000 GHz. According to studies at 310 GHz, the hologram works well also as a reflection-type element. In the reflection-type setup, the power loss of the hologram is appr. 7.4 dB that is 4 dB lower than that in the transmission-type setup. Using a shaped beam for illumination has been studied at 310 GHz. A hologram pattern designed for such an illumination can be simplified from one designed for a conventional horn illumination. A simplified hologram pattern is easier to manufacture and it is more robust against manufacturing errors. In addition, its polarization properties are significantly improved: operation at the horizontal polarization is possible and cross-polarization is reduced substantially. Earlier, the operation of the hologram has been possible only at the vertical polarization. According to these studies, it appears that by using a shaped illumination the operation can be designed to be almost independent of polarization. - Thermal Boundary Conductance of Direct Bonded Aluminum Nitride to Silicon Interfaces
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2024-04-23) Nieminen, Tarmo; Koskinen, Tomi; Kornienko, Vladimir; Ross, Glenn; Paulasto-Kröckel, MerviHeat accumulation and self-heating have become key issues in microelectronics owing to the ever-decreasing size of components and the move toward three-dimensional structures. A significant challenge for solving these issues is thermally isolating materials, such as silicon dioxide (SiO2), which are commonly used in microelectronics. The silicon-on-insulator (SOI) structure is a great demonstrator of the limitations of SiO2 as the low thermal conductivity insulator prevents heat dissipation through the bottom of a device built on a SOI wafer. Replacing SiO2 with a more thermally conductive material could yield immediate results for improved heat dissipation of SOI structures. However, the introduction of alternate materials creates unknown interfaces, which can have a large impact on the overall thermal conductivity of the structure. In this work, we studied a direct bonded AlN-to-SOI wafer (AlN-SOI) by measuring the thermal conductivity of AlN and the thermal boundary conductance (TBC) of silicon (Si)/AlN and Si/SiO2/aluminum-oxygen-nitrogen (AlON)/AlN interfaces, the latter of which were formed during plasma-activated bonding. The results show that the AlN-SOI possesses superior thermal properties to those of a traditional SOI wafer, with the thermal conductivity of AlN measured at roughly 40 W m-1 K-1 and the TBC of both interfaces at roughly 100 MW m-2 K-1. These results show that AlN-SOI is a very promising structure for improving heat dissipation in future microelectronics. - Thermal characterization of III–V semiconductor core-shell nanowire arrays
Sähkötekniikan korkeakoulu | Master's thesis(2019-03-11) Koskinen, TomiThermal management in electronics has become increasingly important due to the possibility of fabricating very small structures using different nanotechnologies. On the other hand, III–V semiconductor materials have gained interest especially in optoelectronics and photovoltaics due to their excellent optoelectronic properties. Each of these properties may be further engineered by introducing artificial nanostructures. A pivotal structure is the nanowire, which may be realized also as arrays consisting of countless nanowires, thus facilitating device integration. Moreover, the thermal conductivity of nanowires may be engineered by introducing thin coating layers, creating core-shell nanowires (CSNWs). Here we investigate the thermal properties of GaAs-AlAs and GaAs-AlGaAs CSNW arrays epitaxially grown by metal-organic vapor phase epitaxy (MOVPE). The nanowire array samples are embedded in spin-on-glass (SOG), chemi-mechanically polished (CMP) and deposited with Ti and Au layers acting as transducer layers prior to the transient thermoreflectance (TTR) measurement. The aim of this work is to establish the experimental thermal conductivity values for GaAs-based nanowire arrays and to evaluate the origin of heteroshell-induced effects on the thermal conductivity of the arrays. The experimental results display a reduction of thermal conductivity for 56 nm thick GaAs nanowires coated with AlAs shells of different thicknesses, the maximum reduction taking place with shell thickness of 35 nm. Additionally, a 6.59 W m^−1 K^−1 thermal conductivity for 105 nm GaAs nanowire arrays was measured, congruent with the previous publications on the subject. Addition of different shells resulted in a suppressed thermal conductivity with the average reduction amounting to 21.6%. The reduction is theorized to origin from the interplay of phonon trapping and increased scattering at the core-shell interface. Further measurements are required to determinate the interface quality and its effect on the phenomenon. - Thermal conductivity suppression in GaAs–AlAs core–shell nanowire arrays
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2019) Juntunen, Taneli; Koskinen, Tomi; Khayrudinov, Vladislav; Haggren, Tuomas; Jiang, Hua; Lipsanen, Harri; Tittonen, IlkkaSemiconductor nanowire heterostructures have been shown to provide appealing properties for optoelectronics and solid-state energy harvesting by thermoelectrics. Among these nanoarchitectures, coaxial core–shell nanowires have been of primary interest due to their electrical functionality, as well as intriguing phonon localization effects in the surface-dominated regime predicted via atomic simulations. However, experimental studies on the thermophysical properties of III–V semiconductor core–shell nanowires remain scarce regardless of the ubiquitous nature of these compounds in solid-state applications. Here, we present thermal conductivity measurements of the arrays of GaAs nanowires coated with AlAs shells. We unveil a strong suppression in thermal transport facilitated by the AlAs shells, up to ∼60%, producing a non-monotonous dependence of thermal conductivity on the shell thickness. Such translation of the novel heat transport phenomena to macroscopic nanowire arrays paves the way for rational thermal design in nanoscale applications. - Thermoelectric and Optical Properties of Nanostructured p-Type CuI Thin Films Grown by Glancing Angle Deposition for Transparent Energy-Harvesting Applications
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2024-12-27) Goel, Priyanka; Tittonen, Ilkka; Raju, Ramesh; Koskinen, Tomi; Kornienko, Vladimir; Wojnicka, WeronikaCopper iodide (CuI) is recognized as a promising p-type transparent material with excellent thermoelectric properties. CuI thin films are typically produced by depositing a copper layer, followed by iodination. However, this process poses challenges in controlling the film’s structure, often leading to excessive grain growth in CuI and reduced optical clarity due to increased light scattering from larger grains. In our study, we introduce an innovative method to regulate the structural characteristics of CuI films by employing the glancing angle deposition (GLAD) technique in depositing the initial copper layer. This method creates nanostructured copper films that guide the formation of CuI grains during vapor iodination. By varying the deposition angle and iodination time, we adjust the size and shape of the synthesized CuI nanostructure-sized grains. This directly enhances the thermoelectric properties and the transmittance of the CuI films. We observe that our CuI films result in a 43% increase in Seebeck coefficient (S) of 352 μV/K, leading to a 90% enhancement at room temperature with a power factor of 339 μW/mK2 compared to the previously reported CuI prepared by the vapor iodination method. Additionally, these nanostructured films exhibit high transparency with a transmittance of 85% at a 560 nm wavelength, demonstrating superior optical properties at this wavelength. These results highlight the potential for integrating nanostructured p-type transparent materials into smart windows and cooling systems for optical chips. - Thermoelectric Characteristics of InAs Nanowire Networks Directly Grown on Flexible Plastic Substrates
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2021-12-27) Koskinen, Tomi; Khayrudinov, Vladislav; Emadi, Fahimeh; Jiang, Hua; Haggren, Tuomas; Lipsanen, Harri; Tittonen, IlkkaIII-V semiconductor nanowires have shown promise for thermoelectric applications, but their use in practical devices has conventionally been hindered by complex fabrication processes and device integration. Here, we characterize the thermoelectric properties of InAs nanowire networks directly grown on flexible polyimide plastic. The n-type nanowire networks achieve a high room-temperature Seebeck coefficient of -110.8 mu V K-1 and electrical conductivity of 41 S cm(-1), resulting in a thermoelectric power factor of 50.4 mu W m(-1) K-2. Moreover, the nanowire networks show remarkable mechanical flexibility with a relative change in resistance below 0.01 at bending radii below 5.2 mm. We further establish the thermoelectric performance of InAs nanowire networks on plastic using a facile proof-of-concept thermoelectric generator producing a maximum power of 0.44 nW at a temperature gradient of 5 K. The findings indicate that direct growth of III-V nanowire networks on plastic substrates shows promise for the development of flexible thermoelectrics applications. - Thermoelectric properties of two-dimensional nanomaterials
Sähkötekniikan korkeakoulu | Bachelor's thesis(2020-12-15) Liimatainen, Mikael