16 INFOTECH OULU Annual Report 2005

ELECTRONICS MATERIALS, PACKAGING AND RELIABILITYTECHNIQUES (EMPART)

Professor Heli Jantunen, Microelectronics and Materials Physics Laboratories,Department of Electrical and Information Engineering, University of Oulu

Professor Osmo Hormi, Department of Chemistry, University of Ouluheja@ee.oulu.fi, osmo.hormi@oulu.fi

http://www.infotech.oulu.fi/empart

Background and Mission

The EMPART (Electronics Materials, Packagingand Reliability Techniques) research group is amultidisciplinary research unit with specialists in mi-croelectronics, materials engineering, measuring tech-niques and in chemical and physical sciences; sixprofessors, three docents, three other doctors and 20doctoral students. The group leaders, Professor HeliJantunen and Professor Osmo Hormi supervise thepostgraduate studies in the group with co-operatingprofessors from the University of Oulu and from theTechnical Research Centre of Finland in Oulu (VTTElectronics).

The research activities concentrate on new materials,components and future manufacturing and packagingtechnologies required in the development of multi-functional smart electronics:

• Electronics materials of thin and thick films (ferro-electrics, dielectrics, organic luminescent materials,porous semiconductors and carbon nanotubes) aresynthesized using powder synthesis, synthetic or-ganic chemistry, electrochemical etching, laser-as-sisted and chemical vapour deposition methods.

• The above advanced materials are integrated in novelcomponents applying the state of the art manufac-turing and packaging methods towards multifunc-tional silicon, ceramic and hybrid packages andmicromodules.

• The results of the research include components anddevices in the fields of electronics, RF (radio fre-quency) applications, piezoelectric sensors and ac-tuators and optical components. Currently the fieldof interest is also being extended towards thermalmanagement of the electronic circuits by nano-material assemblies, chemical sensors / catalysts andbiochemical carriers based on nanostructured ma-terials.

The electrical, optical and thermomechanical designand modeling in conjunction with standard measur-ing and materials characterization techniques as wellas fault and reliability analysis are organic elementsof the research.

The research of the EMPART group was funded bythe University of Oulu, the National TechnologyAgency of Finland (TEKES), the EU, the Academyof Finland and by the national industry. Internationalresearch co-operation has been a characteristic fea-ture of the EMPART group with key roles in severalprojects of the EU Research Programs and ThematicNetworks being strategically important for the Euro-pean industry. In addtion, EMPART is a member ofNEXUS (a Network of Excellence in MultifunctionalMicrosystems), EUSPEN (European Society for Pre-cision Engineering and Nanotechnology) andPOLECER (Polar Electroceramics European networkorganization).

Scientific Progress

During the research year 2005, in accordance with thelong term research targets of the group, we have con-tinued the integration of interdisciplinary topics to-wards future advanced device and componentimplementations. In the following sections, selectedresearch areas of the group are presented.

1. MaterialsThe long term experience of the group in the researchof linear and nonlinear materials (dielectrics and elec-trically tunable ceramics for telecommunication de-vices and piezoelectric and pyroelectric materials forsensors and actuators) as well as organic materials forOLEDs (organic light emitting diodes) enabled a natu-ral extension of the research to nanostructured mate-rials and micro modules.

Research integration of the EMPART group.

INFOTECH OULU Annual Report 2005 17

Nanostructured materials

Nanotechnology offers and eventually requires, thecollaboration of different disciplines by which a col-orful mixture of thinking is formed in the researchteam. The team consists of chemists, physicists andengineers, and the topics researched include synthe-sis and application of nano-porous silicon structures,carbon nanotube assemblies, metal and metal oxidethin films and nanoparticles, nanofabrication technolo-gies, polymer/ceramic nanocomposites and varistormaterials with doping, enabling their cofiring withcommercial LTCC (low temperature co-fired ceramic)materials.

Thermal oxidation of porous silicon: Study onstructure

The structural changes of porous silicon samples dur-ing oxidation are being investigated and analyzed us-ing various microscopy techniques and x-raydiffraction. The surface roughness of oxidized PS lay-ers increases with the oxidation at 200 - 400 °C anddecreased at 600 - 800 °C. At 800 °C a partially fusedsurface is observed. The oxide formed on the wall ofa porous silicon skeleton is amorphous. The shifts ofSi (400) peaks are observed in the x-ray diffractionpatterns, which are correlated to the lattice deforma-tion induced by a thermal expansion coefficient mis-match between the grown SiO

2 and the residual Si,

and to the intrinsic stress caused by the Si-O bonds atthe Si-SiO

2 interface. These explanations are supported

by thermomechanical modeling using a three-dimen-sional finite element method.

Origin and FEM-assisted evaluation of residualstress in thermally oxidized porous silicon

The origin of residual strain is being investigated inthermally oxidized porous silicon structures by com-puter supported finite element modeling. As revealed,the residual strain is caused by both thermal and in-trinsic stress components. The results show strain val-ues between 1.69 · 10-3 and 2.26 · 10-3 according to thedifferent extent of oxidation, which is in good agree-ment with the experimental strain data obtained byXRD.

Laser-induced gold deposition on p+-Si from liq-uid precursors

Gold micropatterns are deposited from aqueous solu-tions of NaAuCl

4 on boron-doped Si (100) surfaces

(1.5 · 10-4 Ω·m) using a focused Ar+ laser beam (TEM00

,λ = 488 nm, w

0 = 1.5 µm, P = 20 - 80 mW). The maxi-

mum temperature at the precursor/silicon interface in-creases only to the range of 316 - 372 K, which is nothigh enough for chemical reactions with formaldehydein the precursor. This suggests a different mechanismis responsible for the reduction of gold ions; namely,changes in the surface potential of Si caused by theDember and Seebeck effects.

Carbon nanotube synthesis on oxidized poroussilicon

Carbon nanotubes were grown on thermally oxidizedporous silicon by catalytic chemical vapor depositionfrom a mixture of ferrocene and xylene precursor. Thegrowth rate of carbon nanotubes showed dependenceon the oxidation extent of porous silicon. On pristineporous silicon surfaces, only poor nanotube growthwas observed, whilst samples oxidized in air at 200,400, 600 and 800 ºC prior to the deposition processproved to be suitable substrates for carbon nanotubesynthesis. Networks of carbon tubes with diametersof ~ 40 and ~ 10 nm observed on the surfaces ofsamples were investigated by electron microscopy andby energy dispersive X-ray analysis.

At a higher oxidation temperature, Si is increasingly trans-formed to SiO2, with consequential loss of crystalline struc-ture, resulting in a partly-amorphous form. Images are madeby TEM for non-oxidized (a), at 200 °C (b) and 600 °C (c)during 1 h oxidations.

(a) Residual strain due to the different thermal expansioncoefficients of Si and SiO2 (oxidation at 473 K). (b) Intrinsicresidual strain at room temperature after oxidation at 473 K.

(a) Lower and (b) higher magnification FESEM images ofgold nanoparticles in a micro-spot on p+-Si deposited froman aqueous precursor of 8 · 10-3 M NaAuCl4 and 2.5 M HCOHusing a focused Ar+ laser beam.

18 INFOTECH OULU Annual Report 2005

Integrated ferroics

The main effort of the research was directed to thedevelopment of thin-film integrated varactor in theframe of the Tekes project “Adaptive RF circuits basedon ferroelectric thin films” (in cooperation with VTTInformation Technology). The RF varactor with satis-factory performance (tunability to 2.5 at bias 5 V andfrequency to 2 GHz) has been prepared using thin filmsof Ba

1-xSr

xTiO

3. The epitaxial quality of Ba

1-xSr

xTiO

3

films, and the effects of buffer layers, of sequence andcomposition of the layers on the microstructure wereanalyzed.

A combined methodology of laser ellipsometry andoptical reflectivity spectroscopy has been developedfor studies of ferroelectric thin-film multilayers (incooperation with the Institute of Solid State Physics,University of Latvia, and supported by a CIMO grantto I. Aulika). Studies of the thin-film nonlinear dielec-trics have been continued.

Materials for multilayer modules

LTCC compositions for varistor components meantfor protection of electrical circuits against transientshave been researched. Because of its excellent non-linearity, zinc oxide has been applied as a basic mate-rial in the varistors. The group has been able to developa novel composition suitable for the LTCC process(~ 900 ºC) by light doping of ZnO with semi-conductive glass. The work was done in the project“Advanced Devices through Light Element Doping

of Electroceramics” (ADLE) financed by the Univer-sity of Oulu in cooperation with the Inorganic Chem-istry and the Optoelectronics and MeasurementTechniques Laboratories (University of Oulu). A newcomposition based on ZnO with 10 wt% of added glassshowed good varistor characteristics: V

bk= 378 V/mm,

α = 33 and JL = 15 µA/cm2. Currently, multilayer com-

ponents utilizing this material with commercial dielec-tric LTCCs are under research with the WroclawUniversity of Technology, Poland.

Additionally, research on composites made of ceramicmicro- and nanoparticles and polymers has been con-ducted to develop novel multifunctional materials,which can be used as discrete components or integratedwith other materials. This project (Composites withnanoparticle addition) is funded by TEKES and in-dustrial partners. For deeper understanding of the di-electric properties of 0 - 3 composites, a microstructure-based numerical dielectric modeling method for ce-ramic/polymer composites has been studied in collabo-ration with the Electromagnetics Laboratory of theHelsinki University of Technology. The microstruc-ture of Epoxy/TiO

2 composites with ceramic loading

of 35 vol% was studied to reveal the correlation be-tween the theoretical and experimental permittivities.

Organic light emitting diodes

The use of organic compounds in the preparation ofLEDs has created completely new approaches to dis-plays which are thin, flexible and bright. The researchis financed by the Academy of Finland (Compoundsfor Organic Light Emitting Diodes) which concen-trates on the organic chemistry of thermally stableemitters in organic LEDs. The group has also won aprize for excellence in team work.

The focus of the research is to concentrate especiallyon electron transmitters and emitters used in organic

(a) CNT structures grown after 20 min CCVD on a cross-sectioned and oxidized (at 800 °C for 1 h) PS on Si sample.

(b) Well-aligned high density array of CNTs evolved on oxi-dized Si wafer. The inset shows a closer view of the bundle.

(a) (004) reflections of BSTO, fitted with a symmetric pseudo-Voigt Cu Kα1 -α2 doublet.

(b) Lattice parameters of the BSTO films as a function ofcomposition. Parameters for bulk ceramics also shown.

Maxwell Garnett effective-medium model applied directly(dashed) and iteratively (dash-dotted line) for the mixturewith randomly oriented spheroids.

INFOTECH OULU Annual Report 2005 19

LEDs in order to enhance the thermal and chemicalstability of the final LED device. Suitably substitutedderivatives of monomeric Alq3 and poly(thiophene)with enhanced light emitting and electron transmit-ting ability will be prepared. In the case of monomericemitters, they will be bound to a polysiloxane matrixprior to the preparation of the final device. The meth-ods used in the organic LEDs sub-project will con-centrate on organic and polymer synthesis. Thepreparation of final devices and their testing will becarried out at VTT Electronics (Oulu), OSC (OpticalSciences Center, University of Arizona), State Uni-versity of Arizona and at Braggone company (Oulu).

2. Processes

LTCC line

Utilizing the LTCC prototype manufacturing andsample production line, the EMPART group offers anattractive platform for customized RF and microwaveapplications. Potential support in the fields of mobilecommunications, wireless, automotive, sensor tech-nology, space and various consumer products is en-abled. The transition from research to the final product/demo is helped by long-term cooperation with mate-rials suppliers. In addition, our LTCC process team iscomposed of experienced researchers capable of de-signing, modeling and developing novel customized/engineered LTCC materials and processes. Final test-ing/characterization and post-processing such as sur-face mount techniques, wire bonding and dicingcomplete the prototype service.

Laser-assisted surface processing

When rapid mask-less laser processing with an accu-racy of a few micrometers is aimed, pulsed solid statelasers (Q-switched Nd:YAG, Nd:YVO

4, Er3+:YAG,

Ti:Saphire) equipped with harmonic frequency gen-erating optics (non-linear optical crystals) give the bestresults. Our group has a diode pumped high-perfor-mance frequency-tripled neodymium-doped yttriumvanadate laser system (Siemens, Microbeam 3200model, 3ω Nd:YVO

4, λ = 355 nm, P = 0.2 - 3.2 W,

τ = 30 ns, f = 20 - 100 kHz, w0 ~15 µm, scan rate up to

2000 mm/s, work table 610 × 710 mm2, accuracy 1 µmin the galvanometric scan field of 50 × 50 mm2).

Due to the short wavelength (UV, 355 nm) and shortpulse duration (30 ns), the laser-matter interaction israther photolytic than thermal, which makes the ma-terials processing “clean”, avoiding thermal reactions(oxidation, re-crystallization, crack formations) in theresidual materials and resulting in a very preciseprocessing of most materials used in the microelec-tronics. The high pulse repetition rate, high averagepower and the fast scanning capabilities enable ex-tremely fast mask-less materials processing (e.g. in a

PCB having 65 µm RCC and 12 µm Cu layers ~ 200pieces of micro-vias can be drilled within a second).The controlling software package installed on the fa-cility enables fine tuning of the laser and materialsprocessing parameters. The different sequential proc-ess tool options provide excellent opportunities tostructure/cut/drill/modify a large variety of single andmultilayer materials. The files containing the patternscan be made using any CAD software.

Chemical vapor deposition of carbon nanotubesin an Si environment

Both porous silicon (PS) and carbon nanotubes (CNTs)are considered as alternative building blocks in futurenanoelectronic, field emission, photonic and nano-sensor devices. Currently, it is a challenging task tointegrate CNTs into an Si environment and to find se-lective synthesis methods compatible with standardfabrication processes. Recently, at one of our collabo-rating laboratories (Rensselaer Polytechnic Institute,Troy, USA), a highly selective synthesis method ofmulti-walled carbon nanotubes MWCNTs on Si wa-fers having SiO

2 patterns on its surfaces was demon-

strated in a catalytic chemical vapor deposition(CCVD) batch reactor, using ferrocene and xylene assources for Fe nano-catalyst and carbon, respectively.

Growth takes place at temperatures above 750 ºC. Thesubstrate materials have to fulfill two important con-ditions: (1) They should stand the processing tempera-ture without melting, and (b) they should showchemical inertness with the precursor and with the

50 µm thick steel foil micro-structured using an Nd:YVO4

laser beam. The structure cannot be made by any othermethod.

1×1×1 mm3 blocks of 10×10 fin ar-rays etched in a thick carbonnanotube mattress. The pattern can-not be etched in the mat by anychemical methods.

20 INFOTECH OULU Annual Report 2005

catalyst in order to avoid catalyst poisoning. There-fore, the combinations of materials in the substratesproved to be quite critical. The best performance syn-thesis of CNTs was achieved on SiO

2 and on Al

2O

3

surfaces masked with Cr/Au, i.e. the process is com-patible with other Si fabrication methods.

Nanostructured porous materials by anodization

Highly porous SiO2 and Al

2O

3 templates are made by

the anodization (electrochemical etching in acids) ofSi and Al surfaces, respectively. Since the porosityand pore dimensions of the substrates depend on theanodization conditions, a number of different poroustemplates with pre-defined properties can be created.Because both processes are compatible with conven-tional Si fabrication, the porous structures and theirderivatives enable component integration on the chiplevel, by which new sensor and catalyst devices willbe accomplished.

Injection molding and extrusion for integratedelectronics and functional composites

Integration of electronics components into injectionmold plastic parts is an interesting possibility for addedvalue plastic products. In a project, funded by Tekesand industrial partners, the group has researched, incooperation with research partners at VTT and theNorth Karelian University of Applied Sciences, in-jection molding of plastic miniature parts with microscale features. The two main subjects of the projectare to reveal the limitations of plastic molding and tointegrate microelectronics enabling smart plastic de-vices. The aim is also to research injection moldingof the ceramic/polymer composites, the developmentof which is described in the materials section.

Summary of nanostructured support synthesis andbasic properties

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Laser and FIB micromachining

A method based on laser-assisted deposition of cop-per was utilized to complement focused ion beam(FIB) circuit editing work. Tungsten (W) patterns de-posited by FIB have too high resistance, which subse-quently can be reduced through applying alaser-assisted chemical vapor deposition of copperover the W pattern by scanning the beam on the top ofthe W line. With proper LCVD parameters, the depo-sition mechanism of copper is self-limiting and selec-tive between ASIC passivation and the FIB depositedtungsten line, enabling high lateral resolution.

LCVD copper deposition on FIB deposited tungstenis shown in the figures below. This particular deposi-tion was carried out only on the middle part of theFIB deposited tungsten wire to give better contrastbetween the two deposits. Before copper depositionthe resistivity, as measured by the four point probemethod, of the FIB deposited tungsten was found to

CCVD reactor (on the left) and the reactant feeding sys-tem, which consists of a membrane pump, valves, flow-meters and a pressure gauge.

CNT bundles grown by CCVD on Au masked Si/SiO2 wafer.

A mini mould made in ceramic.

INFOTECH OULU Annual Report 2005 21

be of the order of 400 µΩcm. Subsequent LCVD cop-per deposition resulted in a significant decrease in theline resistance (from 90 Ω to 40 Ω). The resistivity ofthe laser deposited Cu was found to be 16 µΩcm. FIBcross sectioning showed that the original tungstenthickness was 400 nm and the copper deposition 500nm. The line widths were 5.9 µm and 4.4 µm for tung-sten and copper, respectively. The aluminum four-pointprobe measurement pads and fingers are also visible.The close-up image shows the small crystallites in themiddle of the trace where the laser induced tempera-ture was higher than on the edges.

3. Components

Sensors and actuators

Electromechanically active ceramic parts, mainly foractuators, have been integrated and optimized in theLTCC environment. Due to the excellent chemicalresistance of the ceramic and the temperature resil-ient bonding mechanism, such actuators enable op-eration in harsh environmental conditions. Theresearch work is targeted at microwave driven pre-stressed piezoelectric bender actuators with wirelesscontrol. The flexible manufacturing methods we de-veloped enable production of customized systems forconsumer electronics such as alarming systems, sen-sors, relays, switches, valves, pumps, and mechanicalcontroller/regulator/tuning devices. Preliminary re-search has been conducted for utilizing ceramicMEMS based on piezoelectric tapes.

Control and sensor systems using resonance and non-resonance driven piezoelectric actuators have beenapplied in tunable capacitive sensors having promis-ing characteristics. The first prototype showed largedisplacement ~ 70 µm with a resolution of ~ 0.4 µmwith a bender type piezoelectric actuator. The actua-tor is simple, thermally inert, tunable, and it can beintegrated with various materials e.g. ceramic andprinted circuit boards.

Basic research on pre-stressed piezoelectric bendingactuators was conducted to profoundly characterizethe physical background of their electrical and elec-tromechanical behavior. Information on the differenttypes of pre-stressed actuators was gathered and ana-lyzed in order to develop special actuators (namedPRESTO by us) with, to the best of our knowledge,the highest d

31 characteristics ever made. The tran-

sient computer-assisted analysis of the structures andthe arbitrary driving functions for the piezoelectric ac-tuators enable us to model pre-stressing the actuators,as well as to calculate the hysteresis of actuators. TheATILA software - with a new efficient modelingmethod developed in our group - has been recentlyemployed to optimize the LTCC embedded actuatorstructures.

RF and microwave components, interconnectionsand materials characterization

Cost-effective packaging design is becoming a pre-condition for the larger adaptation of multi-chip mod-ule (MCM) technologies in emerging microwave and

LCVD copper deposition onFIB deposited tungsten todecrease the resistance(from 90 Ω to 40 Ω). Close-up of the deposition mor-phology.

Typical circuit edit where tung-sten rewire has been depos-ited to connect two top-metalconductors followed by a sub-sequent resistivity reductionby LCVD copper encapsula-tion.

The resistance was diminished to 1/10th of the original valueby encapsulating it in copper.

Modeled piezoelectric traveling wave ultrasonic motor.

Piezoactuators on wafer.

22 INFOTECH OULU Annual Report 2005

mm-wave communication systems. To satisfy the lowcost, high performance and miniaturization demands,it is necessary to increase system integration with theuse of well-established manufacturing technologies.The key solutions considered here are highly integratedmodules realized with standard multilayer ceramic(LTCC) technology as well as high-density ball-gridarray (BGA) and flip-chip package interconnections.Furthermore, to ensure the high reliability of moduleassemblies, efficient thermo-mechanical, thermal andelectromagnetic (EM) co-design of module intercon-nections is needed.

The work done in 2005 mainly covers the design andconstruction of RF filter modules and interconnec-tions, as well as some electrically tunable devices,phase shifters and dividers, for 26 GHz frequency uti-lizing customized ferroelectric LTCCs. Studies on thedesign, modeling and manufacturing of LTCC struc-tures and modules, as well as the reliability of LTCC/BGA/PCB joints were carried out in a series of projectsfunded by the Academy of Finland, Tekes, the EU andindustry.

One of the main achievements was that new LTCCelectroceramics for high frequency applications weresynthesized with electrically tunable permittivity.Compositions with a tunability of 19 - 38 % for rela-tive permittivities between 130 - 160 at 25 GHz, andwith a dissipation close to that of pure barium-stron-tium-titanate compositions and a firing temperatureof ~ 900 °C were obtained. These compositions wereutilized in several multilayer components e.g. phaseshifters, matching networks and power combinerswithin the EU IST MELODY project (coordinated byEricsson in Sweden) with various partners e.g.Chalmers University of Technology in Sweden, theUniversity of Birmingham in the UK, Filtronic Comtekin the UK and Ecole Polytechnique Federale deLausanne in Switzerland. Research has also beenstarted on the development of piezoelectric LTCCcompositions for actuators, sensors, microphones andmicropumps. Test structures with the combination ofpiezoelectric, ferromagnetic, ferroelectric and dielec-tric layers in the same modules were also prepared,aiming for future multifunctional smart packages. Theresults were disseminated at international conferences

(PacRim, Japan, EuMW, Germany, ACeS meeting,USA) and in international scientific journals (JECeS,IEEE etc.).

Materials characterization (dielectric permittivity &loss tangent) of commercial LTCC ceramics was con-tinued and performed together with the St. PetersburgElectrotechnical University (Russia) and the Instituteof Physics (Czech Republic) enabling as wide a fre-quency range as from kHz up to THz. An importantresearch area has also been high frequency and reli-ability studies of LTCC/BGA/PCB interconnections.The signal behavior in coplanar BGA, flip-chip andvia structures was modeled using Sonnet and AnsoftHFSS software (in co-operation with the TechnicalUniversity of Ilmenau (Germany), supported by theAcademy of Finland and DAAD). A 3D integratedBGA filter module and an LNA amplifier module weredesigned and manufactured in co-operation with in-dustry and VTT. The measured results showed goodelectrical performance for both modules and corre-lated very well with the EM simulations.

The results of lead-free reliability investigations onLTCC/PCB assemblies were accomplished, wherenovel BGA solder joints with a compliant plastic corewere demonstrated for use in high-performance mi-crowave modules. In addition, thermo-mechanicalFEM analyses were performed for the developed BGAmodule assemblies.

Exploitation of Results

Materials, components and technologies developed bythe group are already widely applied in the nationalelectronics industry, especially in the mobile phoneindustry. As an important example of the present ex-ploitation, LTCC micro modules for telecommunica-

Soldered BGA ball of 800 µm diameter and SEM cross-section image.

A close up of a BGA solder joint in a filter module.

Tunable ferroelectric devices for telecommunication appli-cations.

INFOTECH OULU Annual Report 2005 23

tion applications and ceramic MEMS modules mustbe mentioned. In 2005, emphasis has been laid on acontinuous extension of our recent scientific achieve-ments also in the field of nanotechnology with inte-grated nanostructured assemblies for electronics,biotechnology/medicine, photonics, and catalyst sys-tems.

Future Goals

The long term research of the EMPART research groupwill continue with the focus areas of electronics ma-terials, thin films, components, packaging and reli-ability techniques. A growing research area of thegroup is LTCC micro modules for MOEMS applica-tions in telecommunication, instrumentation and medi-cal fields. Co-operation with other experts at theUniversity of Oulu in the field of nanomaterials andtheir applications will be increased. The new Microand Nanotechnology Centre with advanced manufac-turing facilities offers excellent opportunities formultidisciplinary research. The group has a key rolein the micro and nanotechnology research of the Ouluregion. The EMPART group will form a high excel-lence research and education organization in the fieldof micromodule and nanotechnologies.

Personnel

srotcod&srosseforp 41

stnedutsetaudarg 32

srehto 1

latot 83

sraeynosrep 72

External Funding

ecruoS RUE

dnalniFfoymedacA 000811

noitacudEfoyrtsiniM 000301

sekeT 000659

cilbupcitsemodrehto 00084

etavirpcitsemod 000431

lanoitanretnirehto+UE 00063

latot 0005931

Doctoral Theses

Pap AE (2005) Investigation of pristine and oxidized po-rous silicon. Acta Universitatis Ouluensis C 225.

Selected Publications

Pap AE, Kordás K, Tóth G, Levoska J, Uusimäki A,Vähäkangas J, Leppävuori S & George TF (2005) Thermaloxidation of porous silicon: Study on structure. AppliedPhysics Letters 86(4):041501/1-3.

Kordás K, Pap AE, Saavalainen J, Jantunen H, MoilanenVP, Haapaniemi E & Leppävuori S (2005), Laser-inducedsurface activation of LTCC materials for chemical metalli-zation. IEEE Transactions on Advanced Packaging28(2):259-263.

Kordás K, Pap AE, Vähäkangas J, Uusimäki A & LeppävuoriS (2005) Carbon nanotube synthesis on oxidized poroussilicon. Applied Surface Science 252(5):1471-1475.

Kordás K, Tóth G, Remes J, Nánai L & Szatmári S (2005),Current trends in depositing and patterning metal films.Pulsed Laser Deposition of Optoelectronic Films. Series:Optoelectronic Material and Devices 2:239-263.

Hu T, Uusimäki A, Jantunen H, Leppävuori S, SoponmaneeK & Sirisoonthorn S (2005) Optimization of MgTiO

3-

CaTiO3 based LTCC tapes containing B

2O

3 for use in mi-

crowave applications. Ceramics International 31(1):85-93.

Juuti J, Kordás K, Lonnakko R, Moilanen VP & LeppävuoriS (2005) Mechanically amplified large displacement piezo-electric actuators. Sensors and Actuators A-Physical120(1):225-231.

Hu T, Price TJ, Iddles DM, Uusimäki A & Jantunen H (2005)The effect of Mn on the microstructure and properties ofBaSrTiO

3 with B

2O

3-Li

2CO

3. Journal of the European Ce-

ramic Society 25(12):2531-2535.

Tyunina M & Levoska J (2005) Phase diagram of thin filmrelaxor PbMg

1/3Nb

2/3O

3. Journal of Applied Physics

97(11):114107/1-7.

Tyunina M & Levoska J (2005) Epitaxial films of relaxorferroelectric PbMg

1/3Nb

2/3O

3 in strong electric fields. Fer-

roelectrics 318(1):29-34.

Tyunina M, Levoska J & Jaakola I (2005) Compositionalevolution of structure and dielectric properties inBa

1-xSr

xTiO

3 epitaxial thin-film heterostructures. Ferroelec-

trics 318(1):49-53.

Tyunina M & Levoska J (2005) Compositional evolutionof properties in epitaxial films of relaxor PbMg

1/3Nb

2/3O

3 -

PbTiO3. Ferroelectrics 318(1):63-66.

Jylhä L, Honkamo J, Jantunen H & Sihvola A (2005) Mi-crostructure-based numerical dielectric modelling methodfor ceramic/polymer composites. Journal of Applied Phys-ics 97(10):104104/1-7.

Tóth G, Kordás K, Pap AE, Vähäkangas J, Uusimaki A &Leppävuori S (2005) Origin and FEM-assisted evaluationof residual stress in thermally oxidized porous silicon. Com-putational Materials Science 34(2):123-128.

24 INFOTECH OULU Annual Report 2005

Tóth G, Kordás K, Vähäkangas J, Uusimäki S, George TF& Nanai L (2005) Laser-induced gold deposition on p(+)-Si from liquid precursors: A study on the reduction of goldions through competing Dember and Seebeck effects. Jour-nal of Physical Chemistry B 109(15):6925-6928.

Juuti J, Jantunen H, Moilanen VP & Leppävuori S (2006)Poling Conditions of Pre-stressed Piezoelectric Actuatorsand their Displacement, Journal of Electroceramics.

Pap AE, Kordás K, Vähäkangas J, Uusimäki A, LeppävuoriS, Pilon L & Szatmári S (2005) Optical properties of po-rous silicon. Part III: Comparison of experimental and theo-retical results. Optical Materials 28(5):506-513.

Kordás K, Pap AE, Tóth G, Pudas M, Jääskeläinen J,Uusimäki A & Vähäkangas J (2006) Laser soldering of flip-chips. Optics and Lasers in Engineering 44(2):112-121.

Kordás K, Pap AE, Vähäkangas J, Uusimäki A & LeppävuoriS (2005) Carbon nanotube synthesis on oxidized poroussilicon. Applied Surface Science 252(5):1471-1475.

Kangasvieri T, Nousiainen O, Putaala J, Rautioaho R &Vähäkangas J (2005) Reliability and RF performance ofBGA solder joints with plastic-core solder balls in LTCC/PWB assemblies.

Kangasvieri T, Komulainen M, Jantunen H & VähäkangasJ (2005) High performance vertical interconnections formillimeter-wave multichip modules. European MicrowaveConference, October, Paris, France.

Lum KL, Tick T, Free C & Jantunen H (2005) Design andmeasurement data for a microwave CP antenna using a new

travelling-wave feed concept, in co-operation with the Ad-vanced Technology Institute, University of Surrey, UK. Proc.EuMC 2005 Conference (European Microwave Week), 261-264.

Piatnitsa V, Jantunen H, Turalchuk P, Fichshuk I, Simine A,Kholodnyak D & Vendik I (2005) Miniature front-end mod-ule base on low temperature cofired ceramics for Bluetoothand WLAN devices, in co-operation with the St.-PetersburgElectrotechnical University, Russia. The 2005 InternationalCrimean Microwave Conference CriMiCo’2005, May 12-16, Sevastopol, Ukraina.

Simine A, Kholodnyak D, Turalchuk P, Piatnitsa V, JantunenH & Vendik I (2005) Enhancement of Inductance Q-factorfor LTCC Filter Design, in co-operation with the St.-Pe-tersburg Electrotechnical University, Russia. Proc. EuMC2005 Conference (European Microwave Week), 1319-1323.

Kangasvieri T, Komulainen M, Jantunen H & VähäkangasJ (2005) High performance vertical interconnections formillimeter-wave multichip modules. Proc. EuMC 2005Conference (European Microwave Week),169-172.

Leinonen M, Juuti J & Jantunen H (2005) Equivalent cir-cuit based modification of a pre-stressed piezo actuator.Smart Systems, May 3-4, Seinäjoki, Finland.

Deleniv A, Spartak S, Jantunen H & Hu T (2005) LTCCcompatible ferroelectric phase shifter, in cooperation withthe Chalmers University of Technology and Ericsson AB,Sweden. 2005 IEEE International Microwave SymposiumDigest, June 12-17, Long Beach, California, USA, 599-602.