University of Oulu
INFOTECH OULU

Electronics Materials, Packaging and Reliability Techniques (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 Oulu

heja(at)ee.oulu.fi, osmo.hormi(at)oulu.fi

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

Background and Mission

The EMPART (Electronics Materials, Packaging and Reliability Techniques) research group is a multidisciplinary research unit acting mainly within the information technology focus area of the University of Oulu, especially in the electronics, photonics and nanotechnology subfields. The research also has links with biotechnology, the other focus area of the University. The group is a key player in the Micro and Nanotechnology Center of the University of Oulu, where the overall target is to integrate nanostructures enabling novel functionality of electronic, telecommunication, bio/medical and environmental devices.

The group comprises of specialists in microelectronics, materials and mechanical engineering, measuring techniques, and in chemical and physical sciences, represented by five (5) professors, 13 other post-doctoral researchers, including five docents, and 31 doctoral students. The group leaders, Professor Heli Jantunen and Professor Osmo Hormi supervise the postgraduate studies in the group with co-operating professors and docents from the University of Oulu and from the Technical Research Centre of Finland in Oulu (VTT).

Research integration of the EMPART group.

 

The research of the EMPART group in 2008 was funded by the University of Oulu, the National Technology Agency of Finland (Tekes), the EU, the Academy of Finland, the Nordic Innovation Centre, the Scientific Advisory Board for Defence and by national and overseas industry. International research co-operation is a characteristic feature of the EMPART group, which plays key roles in several projects of the EU Research Programs and Thematic Networks that are strategically important for European industry. In addition, EMPART is a member of POLECER (Polar Electroceramics European network organization). The group is also a partner in the EU FP6 Network of Excellence, MIND (Multifunctional & Integrated Piezoelectric Devices) and Patent-DfMM (Design for Micro & Nano Manufacturing).

The overall vision of the EMPART research group is to be an internationally recognized, high excellence research and education unit, with significant scientific impact in the fields of micro and nano system technologies. Our ultimate goal is to provide competitive solutions for our research and industrial partners via multifunctional applications of novel materials and integration platforms.

During the research year 2008, in accordance with our long term research targets, we have continued the integration of interdisciplinary topics towards future advanced device and component implementations. Altogether the EMPART group has been continuously able to establish a wide range of application areas utilizing generic materials knowledge. In the following sections, we show examples of applications of new materials and methods in the fields of micro and nanotechnologies. Other research topics not reported this year (c.f. earlier Annual Reports) are, for example, Metal-Insulator Transformation materials (MITs), reliability prognostics of electronic devices, proximity sensors for mobile phones and electrocalorimetric materials. After summarizing the main scientific results, we shall also describe the most relevant key technologies that represent the bridge between new materials and innovative electrical components/devices.

 

Electronics materials - manufacturing - components - characterization: evaluation of printed film dimensions, laser ablation, microscope sample preparation and a microwave characterization system.

Scientific Progress

Integrated Actuators, Sensors, Electronics and Functional Composites

The overall aim of this research subfield is the development of new 1) multifunctional materials and structures and 2) integrated and self-sustainable low power consumption devices with different functionalities and remote control possibilities. Such devices can be, for example, energy harvesters or microwave driven piezoelectric actuators/sensors with wireless control. The flexible manufacturing methods developed in the group enable production of customized systems for various industrial applications such as alarm systems, sensors, switches, pumps and mechanical controller/regulator/tuning devices. For example, research and development of low temperature co-fired ceramics (LTCC) embedded piezoelectric actuators have been continued in cooperation with Wroclaw University (Poland) enabling the manufacturing of an electronic circuit board and complex, internally or externally leveraged, piezoelectric actuators and sensors inside the sealed ceramic package by the single LTCC firing process. At the same time, the actuator properties are maintained or exceeded compared to, for example, conventional benders together the with benefits gained from integration. Due to the excellent chemical resistance of the ceramic and the temperature resilient bonding mechanism, such actuators enable operation even in harsh environmental conditions. The aforementioned goals are being continued collectively in the various projects listed below:

In the "Composites of Nanomaterials and Polymers - Extension - CoNaPo-Ext" project, funded by Tekes and four industrial partners, the group has researched magnetic-dielectric polymer-ceramic composites with conductive and semiconductive nanoparticle additions and surfactants. New injection moldable high permeability and permittivity, and low loss materials have been developed utilizing ,for example, yttrium iron garnet (YIG) and hexaferrite fillers and novel gradient structures. A combination of different material properties of matrix, fillers and additives enables wide and flexible adjustment of material properties that can be utilized in various RF applications and integrated devices such as antennas, embedded capacitors and circuit boards.

 

The real part of permeability of ceramic-polymer composites as a function of magnetic filler loading at different frequencies.

 

Schematics of gradient structures made from 0-3 type polymer-ceramic composites with different filler loading (in the middle) and relative permittivity and dielectric losses of the structures as a function of frequency.

 

In the NORD-Pie project, funded by the Nordic Innovations Center - NICe (www.nordicinnovation.net) and project partners, MEMS packaging and modeling and a piezoelectric MEMS accelerometer, gas sensor and ultrasonic microphone, and hydrophone arrays based on chemical solution deposition (CSD) were developed in co-operation with SINTEF (www.sintef.no/nord-pie) and six industrial partners (from Norway, Iceland, Sweden and Denmark). Special attention at University of Oulu was given to acoustic modeling of MEMS structures at ultrasonic frequencies by Comsol Multiphysics, electromechanical characterization of CSD hydrophone and its LTCC package development for harsh underwater conditions.

 

An etched silicon wafer with four different prototypes, a diced hydrophone matrix and the matrix assembled into LTCC package (105 I/O’s) made in the NORD-Pie project.

 

In the "NOvel SPectroscopic technologies based on Interferometry - NOSPI" project novel next generation interferometer modules have been developed together with VTT for pulp and paper, pharmaceutical, food and chemical industries, ranging from low cost to high-end devices. For example, an extremely compact miniaturized optical interferometer module was developed based on piezoelectric control which enables adjustments of mirrors with nanometer accuracy and 0.1 ms settling time. The project is funded by Tekes, VTT and 12 industrial partners from four different countries.

The "MAGnetic nanoparticles for Ink Applications - MAGIA" project was started in co-operation with VTT, the University of Kuopio and four industrial partners. The aim of the project is to develop magnetic inks and substrates utilizing metallic nanoparticles for printed electronics applications. The project is funded by Tekes and all project partners.

Vibration energy harvesters based on conventional and pre-stressed piezoelectric benders was developed in the "Energy harvesting with piezoelectric components - EKKO" project funded by the Scientific Advisory Board for Defence (MATINE). The developed harvesters produced power density up to 308 µW/cm3 with 1 g acceleration and ~3 µm displacement amplitude. Such performance already enables, for example, continuous temperature measurement, dozens of acceleration measurements or a ~4 min wireless connection by ZigBee on a daily basis. In addition, electronics and wideband piezoelectric energy harvester were developed which doubled the most efficient frequency range for energy mining/scavenging.

A post-doctoral researcher's project called "High performance Piezoelectric actuators with functional gradients - Hi-Piezo", funded by the Academy of Finland, was started. In the project, piezoelectric functionally graded actuators are researched in order to improve displacement, force and fatigue resistance characteristics. Properties and behavior of the piezoelectric materials are studied on a macro and micro scale as a function of pre-stress to optimize the electromechanical properties of actuators. Basic research on pre-stressed piezoelectric bending actuators was conducted to characterize the physical background and structural effects in their electrical and electromechanical behavior. Laser micro-machined structurally graded monolithic benders were realized to research the effect of a non-uniform electric field and strain distribution, and the relation between actuator geometry, stiffness and pre-stress. The research facilitates ceramic MEMS development, enhancement of displacement capabilities of benders and a better understanding of the mechanisms affecting different actuator structures. Accurate and reliable electromechanical modeling facilitated the design of new actuator structures. Additionally, development of pre-stressed piezoelectric actuators was extended to multiple monomorph actuators on the same disc, thus enabling wafer level manufacturing of small actuator/sensor matrices for individual or complex operations in motors or deformable mirrors. Furthermore, a lead free (Bi1/2Na1/2)TiO3-(Bi 1/2K1/2)TiO3-BaTiO 3 (BNBK) based piezoelectric material and thick film paste was developed and characterized in cooperation with Wroclaw University, Poland.

A laser-cut monomorph actuator with three individual piezoelectric cantilevers for optical adjustments.

 

Throughout the research and development, the ATILA and Comsol Multiphysics software were extensively employed to optimize and understand the behavior of various electromechanical structures, e.g. MEMS devices, interferometer modules and LTCC embedded actuators.

 

 

Total displacement distribution of a piezo disc with an applied voltage of 20 Vpp at 10 Hz, modeled with ATILA software.

 

Carbon Nanotube Research

Nanotechnology requires collaboration of researchers from different disciplines: chemists, physicists and engineers. The research topics of the EMPART research group on this area include synthesis and application of nano-porous silicon/alumina structures, assemblies based on carbon nanotube (CNT) thin and thick films, and nanofabrication/integration technologies. The main goal is synthesis and integration of nanomaterials and structures that are used in advanced electronic applications such as fuel cells, printed transistors, sensors, components for thermal management and flexible contacts - thus nanotechnology is foreseen as an important emerging field of future research and development. As an example of these nanotechnology activities, some recent results from carbon nanotube research are discussed.

Bottom-gated FET structures with CNT channels for sensing applications. Novel integrated self-adjusting nanoelectronic sensors based on functionalized carbon nanotubes as active elements are the objects of one of our projects. The multifunctional sensor micromodule will consist of a matrix of differently functionalized CNTs that are integrated into an electronics package (electronics and software also developed in the framework of the project) capable of:

  • recording and analyzing the signal of a very small number of sensing elements
  • monitoring several factors (e.g. temperature, pressure, atmosphere etc.) simultaneously
  • actively change the local chemical environment of the sensor component CNTs

The primary task of the research group is to design and construct Si chip platforms to investigate chemically functionalized CNTs under various external stimuli. Sensor operation based on a resistive, chemical field-effect transistor, and noise enhanced sensing protocols were studied and demonstrated earlier.

 

Relative difference of channel conductance for 100 ppm H2S gas in synthetic air (analyte) and synthetic air (reference) for the resistive (left) and chem-FET sensors (right).

 

Conventional ceramic (a) and custom made suspended chip die packages (c, d). Panel (b) shows a micrograph of the die area where the nanotubes are to be inkjet printed.

 

Controlled catalytic CVD synthesis of robust multi-walled carbon nanotube films. The emerging interest towards applications of robust, highly aligned carbon nanotube forests requires synthesis of such films in a controlled manner. In this paper, the growth mechanism and the influence of growth parameters on the structural properties of multi-walled carbon nanotube films grown by catalytic chemical vapor deposition on SiO2 surfaces are investigated. The experimental studies are complemented with computational finite element simulations of temperature and flow fields in the reactor to have a better understanding of tailored synthesis. Film thickness, mass, density, purity, alignment and nanotube size distribution data were assessed as a function of several growth parameters by electron microscopy, electron and X-ray diffraction techniques.

Catalytic synthesis of carbon nanotubes from ferrocene/xylene precursors is a multi-step sequential process involving ferrocene decomposition, catalyst nanoparticle nucleation and growth; xylene decomposition in the gas phase, carbon dissolution on and diffusion in the catalyst, to finally precipitate and grow carbon nanotubes on the catalyst surface. Due to its complex nature, growth occurs in a narrow process window of experimental parameters that are eventually interdependent.

The thickness of nanotube films shows square-root dependence with time, suggesting diffusion controlled transport of reactants in the forest; however, we cannot rule out the possibility of gradual catalyst poisoning which can also result in the temporal decay of the initial rapid growth rate. In the case of very long synthesis, the catalyst particles lose their activity and mainly pyrolytic carbon forms, which deposits on the already formed nanotubes causing significant densification of the film.

Nonlinear current-voltage transport in inkjet printed single-walled CNT networks. Fabrication of single-walled CNT (SWCNT) films having controlled thickness is demonstrated by the means of inkjet printing of aqueous solutions of carboxyl functionalized nanotubes. Film thickness-dependent conduction processes have been revealed and explained. In the case of low-density films, where a percolated network of s-CNT and m-CNT dominates, the electrical transport could be well-explained by thermionic emission taking place at the junctions forming between crossing semiconducting and metallic CNTs. The conduction becomes gradually Ohmic with increased film thickness, which is attributed to the formation of a parallel metallic network of the deposited m-CNTs.

 

 

A Field-emission scanning electron microscopy (FESEM) image of highly aligned multiwalled carbon nanotubes (60 min growth at 770 °C, reactor pressure 760 Torr, carrier Ar flow rate 40 mL/min, and precursor 20 g/L ferrocene in xylene with a feeding rate of 0.1 mL/min). Inset: multi-walled CNT film detached from the template (side view) and CNT film mass vs growth temperature and Arrhenius plot of mass growth.

 

In nanotube films, the network consists of metallic and semiconducting wires. Statistically, the amount of semiconducting nanotubes is twice as much as the metallic ones. In rare networks, only a few contiguous conduction paths exist, which are composed of a random sequence of both p-type semiconducting CNT (s-CNT) and metallic CNT (m-CNT). At the junctions of the two types of nanotubes, a Schottky-type potential barrier forms, since the valence band edge in s-CNTs lies below the Fermi energy of m-CNTs. In the related picture presented, carriers that have energy larger than the barrier height will be injected via thermionic emission into the nanotube. In this picture, for a metal-semiconductor interface, the potential and temperature dependent current density J(V,T) is described as:

 

 

where Φb is the Schottky barrier height,

 

 

is the Richardson constant, q is the elementary charge, m* = 0.037 me is the effective mass of the carriers, and k and h are Boltzmann's and Planck's constants, respectively. The potential drop in the series intrinsic resistance R of CNTs is taken into account by considering V* = V - RI, where R is the reciprocal of the I-V slope at large bias voltages. Applying the first equation for a thin CNT film with A average cross-section and m number of junctions along a percolated path, the current I becomes:

 

 

The average area of cross-section A can be estimated from the amount of deposited CNTs between the electrodes of spacing gap. Now, fitting the second equation to the measured I-V plots, we get Φb and m parameters. For a film of 3 printed layers, the average barrier height is Φb ≈ 254 mV, which is reasonable considering a typical band gap of 300 - 900 mV for s-CNTs, and the corresponding Schottky barrier of 150 - 450 eV at the interface of semiconducting and metallic SWCNTs. The deduced barrier height is also in good agreement with the values (150 - 290 mV) of measurements performed on single junctions of metallic and semiconducting CNTs. The number of Schottky junctions being in series in a percolated path is m ≈ 66 gives also a reasonable estimate since the distance between the electrodes (200 µm) is connected with CNT bundles having a length of approximately a micrometer. In the case of more dense films, the calculated average barrier height gradually decreases with layer thickness. Also, the number of Schottky junctions being involved in a percolation path decreases as the surface coverage gets higher since the metallic bundles/nanotubes cause parallel short circuits within a percolated path, enabling carriers to bypass the high resistance Schottky junctions. As a result of increased surface coverage/thickness, most charge carriers see a lowered effective barrier, which gives rise to pronounced linear I-V curves.

The results complement well the existing experimental data published in the literature, and provide important information about the synthesis of SWCNT films with good control on layer thickness and consequently on electrical transport. In addition, our results also highlight the significance of water absorption as it can alter the electrical behavior of the films in ambient conditions.

 

 

I-VSD and I-VG sweeps on (a) diluted and (b) thick nanotube networks.

 

Projects that are related to carbon nanotube research are:

  • Integrated self-adjusting nanoelectronic sensors (2006-2009, EU FP6)
  • Industrially relevant, novel reaction routes for catalytic transformation of renewable biomaterials (2007-2010, Tekes)
  • Invisible electric tagging with nanomaterials (2009-2010, Tekes)
  • New, innovative sustainable transportation fuels for mobile applications: from biocomponents to flexible liquid fuels (2007-2010, the Academy of Finland)
  • Novel catalyst materials based on robust carbon nanotube membranes (2009-2012, Academy of Finland)
  • Nanoscale thermal management of electrical components using carbon nanotubes (2009-2011, Academy of Finland, post-doctoral researcher project by Geza Tóth)
  • Applications of carbon nanotube films (postgraduate post of Niina Halonen at the Graduate School of NGS-Nano)
Nanoscale Engineering of Ferroelectric Functionality

In ABO3-type perovskites exhibiting ferroelectric (FE) behavior, several effects (pyroelectric, piezoelectric, electro-optic, piezo-optic, electrocaloric, etc.) coexist, with a strong dependence of properties on temperature and the applied field. This enables versatile device applications of functional and smart FEs in crystal, ceramic, thick-film, and thin-film form. In bulk FEs, functionality can be engineered by A-site and/or B-site doping or ordering, formation of solid solutions of two or more FEs, controlling domain and grain configurations, and by creating composites.

In heteroepitaxial thin-film FEs, another approach to engineering FE functionality is possible: due to strain-polarization coupling, the epitaxial strain determines polarization, phase diagrams, and all properties of FEs. Controlling strain allows designing thin-film FEs with functionality not readily obtained in bulk FEs. However, epitaxial misfit strain relaxes with increasing film thickness above a certain critical thickness (typically only few nanometers). Large enough strain can be achieved in ultrathin films and superlattices (consisting of alternating thin-film layers of two or more constituents with the thickness of each layer smaller than critical). In epitaxial FE heterostructures, besides strain, also electrostatic and interfacial coupling between the layers, presence of surface, and small thickness itself affect functionality. Physical phenomena at interfaces and surfaces, and size effects remain practically unstudied due to the usually dominant effects of strain. Knowledge-based control of STRAIN - SURFACE - INTERFACE - SIZE effects is a key requirement for nanoscale engineering of FE functionality. The main research results achieved in 2008, supported by the Academy of Finland, Infotech Oulu Graduate School, EU FP5 and FP6, can be summarized as follows.

Strain - energy band structure. To form epitaxial FE heterostructures with large enough strain and smooth surfaces, an appropriate technology of growth should be worked out. This includes control of out-of-plane and in-plane crystal orientations, misfit and thermal strain, density of dislocations, morphological stability, and compositional stoichiometry. Such control is realized by adjusting the parameters of the pulsed laser deposition (PLD) process. In addition to the previously optimized growth of numerous FE heterostructures, special effort is being focused on the growth of strained thin-film SrTiO3, Pb0.5Sr0.5TiO3, KTaO3, KNbO3, and superlattices using SrRuO3 electrode layers. Microstructure analysis is performed using room-temperature x-ray diffraction measurements and numerical simulations of kinematic diffraction intensity. High-quality epitaxial FEs with either compressive or tensile biaxial in-plane strain are being grown.

 

Θ-2Θ x-ray diffraction pattern in the vicinity of (002) peak of ultrathin epitaxial SrTiO3 film on DyScO3 substrate. The intensity of substrate reflection is reduced by filtering. The satellites around (002) reflection are the peaks of Laue function due to small thickness (12 nm) of high-quality smooth crystalline film.

 

A record tensile in-plane strain as large as 2.1% is obtained in 13 nm thick SrTiO3 on KTaO3 substrate (maximum theoretically estimated strain is 2.2%). Its effect on energy band structure, important for FE tunnel junction and optical devices, is under study.

Interface - enhanced permittivity. The experimental studies on the influence of interfaces on the functionality of FE heterostructures include studies of FE superlattices. To avoid or minimize the effects of strain and interfacial coupling of polarization, quantum paraelectric SrTiO3 and NaNbO3 are chosen as constituent materials. In such superlattices, an unexpected increase in unit cell volume exceeding that of the bulk constituents and their solid solutions is found, indicating the importance of atomic structure of interfaces. An ideal near-interface region between the layers can be presented as a sequence of AO and BO2 planes in the out-of-plane direction. Both the A-site and B-site ions of the constituents have different ionic charges and radii.

To screen the Coulomb field created by the ionic mismatch, the ions should be displaced, leading to an increase in inter-ionic distances. The first-principles analysis of such lattice distortions is in progress. Remarkably, the dielectric permittivity of the near-interface regions is high. The discovered effect opens the way to designing multilayers with enhanced permittivity.

 

Schematics of two possible types of near interface regions between SrTiO3 and NaNbO3, with Sr and Na ions at the corners of the cells, and Ti and Nb ions in the centers of the cells. Also oxygen octahedra are shown. The ionic mismatch at A-site (Na+1 and Sr+2) and mismatch at B-site (Ti4+ and Nb5+) exist.

 

Size - dynamic performance. One of numerous size effects in FEs is the scaling of the FE domain configuration. In contrast to micro-domains in bulk FEs, nanodomains (with the width at nanoscale) are formed in the films with submicron thickness. In thin-film FEs, polar nanoregions (clusters) can exist too. Sub-switching nanodomain/cluster behavior, important for device applications, is poorly understood. To identify the nature and dynamics of polar units, the dielectric response of thin-film FEs is experimentally determined in a broad range of conditions. By analyzing dynamic dielectric nonlinearity in the temperature-frequency-drive space, the FE domain wall motion (Pb0.5Sr0.5TiO3), the dipolar flips (PbMg1/3Nb2/3O3), and the coexistence of both processes (BaTiO3) are detected. This is combined with local domain investigations using piezo-response force microscopy. The developed methodology appeared to be useful for performance analysis in FE varactors and novel multiferroic composites.

Design and Modeling of Printable Electronics Applications

In everyday life, the number of mobile wireless communication applications is increasing. Wireless devices need at least one antenna for communication flow with each other or with a base station. For instance, up to date mobile phones can have more than ten antennas, mainly for data transfer. New mobile applications are also being intensively developed, such as health care monitoring systems and applications using wearable devices having antennas close to the human body.

 

Simulated human hand model.

 

In the DEMOprint project, the EMPART group is focusing on the design, simulation, and manufacturing of antennas suitable for wrist applications working at 2.4 GHz frequency band. This is clearly a new approach, since all earlier applications so far communicate at a MHz frequency range or below. Additionally, in this project an inexpensive printed electronics technology is preformed to fabricate the devices. This task includes inkjet printing of silver nanoparticle pastes on polymer substrates. The challenge is first to find and apply the right design and verification methods, and then to design such an antenna with high radiation efficiency. The project is being carried out together with Department of Electronics and Department of Materials Science, Tampere University of Technology. Thus a summary of the objectives of the project are to establish design guidelines for printable electronics, develop design and modeling knowledge for printable applications, and modeling as a design tool for a printable wrist application.

In recent years, there has been an increase in the potential of printable electronics in the electronics industry. It is creating new value into electronic devices, focusing on cost reduction and unique product features of flexibility or wearability of the product. Printing technology provides new features for products such as flexibility and ultra thinness. In addition, printable electronics offers reel-to-reel fashion production with very thin, low cost, lightweight and flexible structures.

In the project, the antennas are manufactured using an inkjet printing method well suited to high volume mass production. The antennas are printed by the Tampere University of Technology. Antenna design and all RF measurements are made by the EMPART group. The DEMOprint project also strives to extract the material parameters of the inkjet printed silver conductors using probe station measurements in the frequency range of 0.1-20 GHz.

The design of antennas suitable for wrist application is a challenging task owing to surrounding complex, high permittivity and dielectric loss of the user's hand. The radiation pattern and radiation polarization of the antenna should be taken in the account because a user's hand can be positioned almost in any direction compared to the base station, which can be a mobile phone in one's pocket for instance. The antennas are designed and simulated using Ansoft's HFSS program, first in free space, and after evaluation of a suitable design, the simulation is performed using a simulated human hand model. Different human hand models are available, some taking into account even different layers and contents of the hand (like bones). To save computing time, and to perform the simulations within a reasonable time, simplified averaging models are the most preferable.

 

Satimo Starlab with a phantom hand and a test antenna on it.

 

Measured radiation pattern of printed and reference IFA antennas placed in free space and on a human hand.

 

To verify the performance of the designed antennas, they first are to be manufactured and then measured. For evaluation, in addition to inkjet printed antennas, metal made antennas are manufactured. The radiation pattern and the total radiation efficiency are evaluated from the measurements made with a Satimo Starlab measuring system. The measurement system consists of 15 antennas with 22.5 degree steps on a circle of the measuring chamber. The antenna of the device under test (DUT) is situated in the middle. The measurement is performed by rotating the DUT antenna in the middle of the chamber and measuring the radiation response with the 15 measurement antennas.

Microfabrication Technologies: From Materials to Devices

To be able to implement the novel materials developed by our group, a number of different processing methods are used. The research described in the section "Scientific Progress" was accomplished mainly using the facilities of the Microelectronics and Materials Physics Laboratories and the Micro and Nanotechnology Centre of the University of Oulu. The techniques combine processing of robust ceramic modules (LTCC line, laser fabrication, thick film printing), fabrication of Si wafers/chips, moulding of polymers and various composite materials, mounting macroscopic films of nanostructured materials, inkjet printing of nanoparticles and pulsed laser deposition of nanostructured thin films. In the following, examples of key processes are described.

The LTCC line. Utilizing the LTCC prototype manufacturing and sample production line, the EMPART group is able to offer an attractive platform for customized RF and microwave applications, as well as electronics micromodules. Potential support in the fields of mobile communications, wireless, automotive, sensor technology, space and various consumer products is enabled. The transition from research to the prototype/final product is assisted by close co-operation with materials suppliers. In addition, the LTCC process team is composed of experienced researchers capable of designing, modeling and developing novel customized/engineered LTCC materials and processes. Recently developed LTCC materials can perform ferroelectric, varistor, piezoelectric and dielectric functions which are prepared in tape or paste forms.

The group engages also in computer-aided component design and modeling with tools like HFSS, ATILA, FEMLab and Sonnet. With laser-aided micromachining, cavities, channels and vias are also made inside LTCC modules. Final testing/characterization and post-processing such as surface mount techniques, wire bonding and dicing complete the prototype service.

Laser-assisted surface processing. When rapid maskless laser processing with an accuracy of a few micrometers is aimed for, pulsed solid state lasers (Q-switched Nd:YAG, Nd:YVO4, Er3+:YAG, Ti:Saphire) equipped with harmonic frequency generating optics (non-linear optical crystals) give the best results. Our group has at its disposal a diode pumped high-performance frequency-tripled neodymium-doped yttrium vanadate laser system (Siemens, Microbeam 3200 model, 3w Nd:YVO4, λ = 355 nm, P = 0.2 - 3.2 W, t = 30 ns, f = 20 - 100 kHz, w0 ~15 µm, scan rate up to 2000 mm/s, work table 610 × 710 mm2, accuracy 1 µm in the galvanometric scan field of 50 × 50 mm2).

Due to the short wavelength (UV, 355 nm) and short pulse duration (30 ns), the laser-matter interaction is rather photolytic than thermal, which makes the materials processing "clean", avoiding thermal reactions (oxidation, re-crystallization, crack formations) in the processed materials, and resulting in a very precise machining of most materials used in microelectronics. The high pulse repetition rate, high average power and the fast scanning capabilities enable extremely fast maskless materials processing (e.g. in a PCB having 65 µm RCC and 12 µm Cu layers ~200 pieces of micro-vias can be drilled within a second). The controlling software enables fine tuning of materials processing parameters. The different sequential process tool options provide excellent opportunities to structure/cut/drill/modify a large variety of single and multilayer materials. The files containing the patterns can be made using any CAD software.

 

Laser processing with Siemens Microbeam 3200 model.

 

Injection molding and mixing extrusion. Development of new polymer based functional composite materials by mixing extruder, integration of electronic components with plastic parts via injection molding, and a combination of these two processes, offer attractive possibilities for numerous applications and material innovations. Injection moulding enables a cost effective manufacturing method for 3D structures, while the properties of ceramic-polymer composites, for example, can be seamlessly adjusted, filling the gap of properties between polymer and ceramic. The group uses a laboratory-scale Haake Minijet injection moulding unit and a Haake Minilab mixing extruder with co-rotating or counter rotating screws and mixing chamber especially designed for abrasive materials.

National and International Co-operation

The EMPART research group co-operated in 2008 in the form of common research projects with other Infotech Oulu research groups, mainly with OPME (Optoelectronics and Measurement Unit), CAS (Circuits and Systems Group) and Wireless Communication Systems. OPME and EMPART together with VTT have won funding through the Finland Distinguished Professor Programme for Professor Ghassan Jabbour (Arizona State University), who established The Center for Nano Organic and Hybrid Electronics and Photonics during the year 2007.

National and international research co-operation in the form of common projects, scientific publications or student, researcher and lecturer exchanges with the following partners has been carried out: VTT, Finland; Helsinki University of Technology, Helsinki, Finland; ORC Tampere University of Technology, Tampere, Finland; University of Joensuu, Joensuu, Finland; Åbo Akademi, Turku, Finland; North Karelia University of Applied Sciences, Joensuu, Finland; Kemi-Tornio University of Applied Sciences, Kemi, Finland; Technical University of Ilmenau, Ilmenau, Germany; Technical University of Luleå, Luleå, Sweden; Regional Research Laboratory, Thiruvananthapuram, India; Yonsei University, Soul, Korea; University of Birmingham, Birmingham, UK; EPFL, Lausanne, Switzerland; SINTEF, Oslo, Norway; Chalmers University of Technology, Gothenburg, Sweden; Advanced Technology Institute, University of Surrey, UK; Jozef Stefan Institute, Ljubljana, Slovenia; Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic; Wroclaw University of Technology, Wroclaw, Poland; St. Petersburg Electrotechnical University, St. Petersburg, Russia; Royal Institute of Technology, Stockholm, Sweden; Rensselaer Polytechnic Institute, Troy, NY, USA; University of Szeged, Budapest, Hungary; Linköping University, Linköping, Sweden; National United University, Taipei, Taiwan, National Taiwan Normal University, Taipei, Taiwan; University of Iasi, Iasi, Romania; Tsinghua University, Beijing, China; University of Salford,UK; Ioffe Physico-Technical Institute, St. Petersburg, Russia, Moscow State University, Moscow, Russia.

The EMPART research group also acknowledges Finnish and foreign industrial partners for their active participation in research projects, as well as the Academy of Finland, Tekes, the EU, the Nordic Innovation Centre and the University of Oulu for financial support.

Exploitation of Results

Materials, components and technologies developed by the group are widely applied in the national electronics industry, especially in the wireless telecommunication industry. LTCC micromodules for telecommunication applications and ceramic MEMS modules must be mentioned as examples of present exploitation. In 2008, emphasis has been laid on a continuous extension of our recent scientific achievements, also in the field of nanotechnology with integrated nanostructured assemblies for electronics, biotechnology/medicine, photonics, and catalyst systems. Additionally, several novel materials and material systems recently developed, as well as the progress in fabrication, have been utilized in antennas, multichip modules, ceramic/polymer integrations, filters, micropumps, lens and mirror positioning systems, energy harvesters, etc.

Personnel

professors & doctors

18

graduate students

31

total

49

person years

20

External Funding

Source

EUR

Academy of Finland

268 000

Ministry of Education

151 000

Tekes

843 000

other domestic public

49 000

domestic private

191 000

international

417 000

total

1 919 000

 

Doctoral Theses

Lahti M (2008) Gravure offset printing for fabrication of electronic devices and integrated components in LTCC modules. Acta Universitatis Ouluensis Technica C 303.

Hiltunen J (2008) Microstructure and superlattice effects on the optical properties of ferroelectric thin films. VTT Publications 684.

Särkkä J (2008) A novel method for hazard rate estimates of the second level interconnections in infrastructure electronics. Acta Universitatis Ouluensis C 300.

Selected Publications

Lappalainen J, Heinilehto S, Jantunen H & Lantto V (2008) Electrical and optical properties of metal-insulator-transition VO2 thin films. Journal of Electroceramics. DOI 10.1007/s10832-008- 9433-2.

Nuzhnyy D, Petzelt J, Kamba S, Yamada T, Tyunina M, Tagantsev AK, Levoska J & Setter N (2008) Polar phonons in some compressively stressed epitaxial and polycrystalline SrTiO3 thin films. Journal of Electroceramics. DOI 10.1007/s10832-008-9494-2.

Tyunina M, Jaakola I, Plekh M & Levoska J (2008) Nanoscale engineering of ferroelectric functionality. Journal of Electroceramics. DOI 10.1007/s10832-008-9435-0.

Heinonen E, Juuti J, Moilanen VP, Palosaari J & Jantunen H (2008) Structurally graded monolithic piezoelectric actuator modelling and optimization with FEM. Journal of Intelligent Material Systems and Structures. DOI 10.1177/ 1045389X08097384.

Sobocinski M, Juuti J, Jantunen H & Golonka L (2008) Piezoelectric unimorph valve assembled on LTCC substrate. Sensors and Actuators A: Physical. DOI 10.1016/j.sna.2008.11.025.

Puustinen J, Lappalainen J, Hiltunen J & Lantto V (2008) Variations of Optical Properties with Phase Co-Existence in PZT Thin Films. Ferroelectrics 370(1): 46-56.

Palosaari J, Juuti J, Heinonen E, Moilanen P & Jantunen H (2008) Electromechanical Performance of Structurally Graded Monolithic Piezoelectric Actuator. Journal of Electroceramics. DOI 10.1007/s10832-008-9440-3.

Hiltunen J, Seneviratne D, Tuller HL, Lappalainen J & Lantto V (2008) Crystallographic and dielectric properties of highly oriented BaTiO3 films: Influence of oxygen pressure utilized during pulsed laser deposition. Journal of Electroceramics. DOI 10.1007/ s10832-008-9443-0.

Hiltunen J, Seneviratne D, Sun R, Stolfi M, Tuller HL, Lappalainen J & Lantto V (2008) Optical properties of BaTiO3 thin films: Influence of oxygen pressure utilized during pulsed laser deposition. Journal of Electroceramics. DOI 10.1007/s10832-008-9463- 9.

Palosaari J, Juuti J & Jantunen H (2008) Displacement distribution of the PRESTO actuator with multiple passive and active regions. Sensors and Actuators A: Physical 148(1): 129-133.

Kangasvieri T, Halme J, Vahakangas J & Lahti M (2008) Low loss and broadband BGA package transition for LTCC-SiP applications. Microwave and Optical Technology Letters 50(4): 1036-1040.

Kangasvieri T, Halme J, Vahakangas J & Lahti M (2008) Broadband BGA-via transitions for reliable RF/microwave LTCC-SiP module packaging Source. IEEE Microwave and Wireless Components Letters 18(1): 34-36.

Heszler P, Gingl Z, Mingesz R, Csengeri A, Haspel H, Kukovecz Á, Kónya Z, Kiricsi I, Ionescu R, Mäklin J, Mustonen T, Tóth G, Halonen N, Kordás K, Vähäkangas J & Moilanen H (2008) Drift effect of fluctuation enhanced gas sensing on carbon nanotube sensors. Physica status solidi (b) 245(10): 2343.

Haspel H, Ionescu R, Heszler P, Kukovecz Á, Kónya Z, Gingl Z, Mäklin J, Mustonen T, Kordás K, Vajtai R & Ajayan PM (2008) Fluctuation enhanced gas sensing on functionalized carbon nanotube thin films. Physica status solidi (b) 245(10): 2339.

Mäklin J, Mustonen T, Halonen N, Tóth G, Kordás K, Vähäkangas J, Moilanen H, Kukovecz Á, Kónya Z, Haspel H, Gingl Z, Heszler P, Vajtai R & Ajayan PM (2008) Inkjet printed resistive and chemical- FET carbon nanotube gas sensors. Physica status solidi (b) 245(10): 2335.

Komulainen M, Kangasvieri T, Jäntti J & Jantunen H (2008) Compact surface-mountable LTCC-BGA antenna module for X-band applications. International Journal of Microwave and Optical Technology 3(4): 451-459.

Juuti J, Leinonen M & Jantunen H (2008) Micropositioning, Book Chapt. in Piezoelectric and Acoustic Materials for Transducer Applications, ed. by Safari A & Akdogan EK, Springer, 319- 339.

Peräntie J, Hagberg J, Uusimäki A & Jantunen H (2008) Temperature characteristics and development of field-induced phase transition in relaxor ferroelectric Pb(Mg1/3Nb2/3)0.87 Ti0.13O3 ceramics. Applied Physics Letters 93: 32905.

Hsi CS, Chen YC, Jantunen H, Wu MJ & Lin TC (2008) Barium titanate based dielectric sintered with a two-stage process. Journal of the European Ceramic Society 28(13): 2581-2588.

Putaala J, Kangasvieri T, Nousiainen O, Jantunen H & Moilanen M (2008) Detection of thermal cycling-induced failures in RF/ microwave BGA assemblies. IEEE Transactions on Electronics Packaging Manufacturing 31(3): 240-247.

Puustinen J, Lappalainen J & Lantto V (2008) Effect of microstructure and surface morphology evolution on optical properties of Nd-modified Pb(ZrxTi1-x)O3 thin films. Thin Solid films 516(18): 6458-6463.

Hiltunen J, Lappalainen J, Puustinen J, Lantto V & Tuller HL (2008) Size-dependent optical properties of BaTiO3-SrTiO3 superlattices. Optics Express 16(11): 8219-8228.

Palukuru VK, Komulainen M, Tick T, Peräntie J & Jantunen H (2008) Low-sintering-temperature ferroelectric thick films; RF properties and an application in a frequency-tunable folded slot antenna. IEEE Antennas & Wireless Propagation Letters. DOI 10.1109/LAWP.2008.2001120.

Tick T, Peräntie J, Rentsch S, Müller J, Hein M & Jantunen H (2008) Co-sintering of barium strontium titanate (BST) thick films inside a LTCC substrate with pressure-assisted sintering. Journal of the European Ceramic Society 28(14): 2765-2769.

Sebastian MT & Jantunen H (2008) Low loss dielectric materials for LTCC applications: a review. International Materials Reviews 53(2): 57-90.

Tick T & Jantunen H (2008) An X-Ray Imaging-Based Layer Alignment and Tape Deformation Inspection System for Multilayer Ceramic Circuit Boards. IEEE Transactions on Electronics Packaging Manufacturing 31(2): 168-173.

Hagberg J, Uusimäki A & Jantunen H (2008) Electrocaloric characteristics in reactive sintered 0.87Pb(Mg1/3Nb2/3)O3 - 0.13PbTiO3. Applied Physics Letters 92: 132909.

Mustonen T, Mäklin J, Kordás K, Halonen N, Tóth G, Vähäkangas J, Jantunen H, Kar S, Ajayan PM, Vajtai R, Helistö P & Seppä H (2008) Controlled Ohmic and nonlinear electrical transport in inkjet printed single-wall carbon nanotube films. Physical Review B 77: 125430.

Halonen N, Kordás K, Tóth G, Mustonen T, Mäklin J, Vähäkangas J, Ajayan PM & Vajtai R (2008) Controlled CCVD synthesis of robust multi-walled carbon nanotube films. Journal of Physical Chemistry C 112(17): 6723 -6728.

Murzina EV, Tokarev AV, Kordás K, Karhu H, Mikkola JP & Murzin DY (2008) D-Lactose oxidation over gold catalysts. Catalysis Today 131(3): 385-392.

Komulainen M, Berg M, Jantunen H, Salonen E & Free C (2008) A frequency-tuning method for a planar inverted-F antenna. IEEE Transactions on Antennas and Propagation 56(4): 944-950.

Lappalainen J, Heinilehto S, Saukko S , Lantto V & Jantunen H (2008) Microstructure dependent switching properties of VO2 thin films. Sensors and Actuators A: Physical 142(1): 250-255.

Tick T, Peräntie J, Jantunen H & Uusimäki A (2008) Screen printed low-sintering-temperature barium strontium titanate (BST) thick films. Journal of the European Ceramic Society 28(4): 837-842.

Kangasvieri T, Komulainen M, Jantunen H & Vähäkangas J (2008) Low-loss and wideband package transitions for microwave and millimeter-wave MCMs. IEEE Transactions on Advanced packaging 31(1): 170-181.

Tick T, Palukuru V, Komulainen M, Peräntie J & Jantunen H (2008) Method for manufacturing embedded variable capacitors in low-temperature cofired ceramic substrate. Electronics Letters 44(2): 94-95.

Tuktarov AR, Akhmetov AR, Pudas M, Ibragimov AG & Dzhemilev UM (2008) Selective addition of H2O to fullerene C60 catalyzed by Ti, Zr, and Hf catalysts. Tetrahedron Letters 49(5): 808-810.

Tóth G, Kordás K, Ajayan PM & Vajtai R (2008) Cooling with integrated carbon nanotube films, Nanostructures in Electronics, ed. by Rahman F, Pan Stanford Publications, Singapore.

Fan J, Leppävuori S, Luusua I, Henttinen K, Eränen S, Hietanen I & Juntunen M (2008) Fabrication of silicon based through-wafer interconnects for advanced chip scale packaging. Sensors and Actuators A: Physical 142(1): 405-412.

Fan J, Kalliopuska J, Eränen S, Juntunen M, Hietanen I & Leppävuori S (2008) Via-in-pixel design of truly 2D extendable photodiode detector for medical CT imaging. Sensors and Actuators A: Physical 145-146: 59-65.