Infotech Oulu Annual Report 2004 - 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

ee.oulu.fi, osmo.hormi

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

Background and Mission

The EMPART (Electronics Materials, Packaging and Reliability Techniques) research group consists of specialists in microelectronics, materials engineering, measuring techniques and chemistry and physics. There are seven professors, three docents, three post-doctoral researchers and 19 doctoral students in the group. In addition to the Empart group leaders, Professor Heli Jantunen and Professor Osmo Hormi, co-operating professors from the University of Oulu and the Technical Research Centre of Finland in Oulu (VTT Electronics) also act as supervisors of research and studies.

The research activities of the group concentrate on new materials, components and future manufacturing and packaging technologies required in the development of multifunctional smart electronics. Research is focused on overcoming technical barriers to novel and reliable electronics products.

The research of the EMPART group has been funded by the University of Oulu, the National Technology Agency of Finland (TEKES), the EU, the Academy of Finland and national industry. International research co-operation has been a characteristic feature of the EMPART group. The group has held key roles in several projects of EU Research Programs and Thematic Networks which are strategically important for European industry. Additionally, it has been a member of NEXUS (a Network of Excellence in Multifunctional Microsystems), EUSPEN (European Society for Precision Engineering and Nanotechnology) and POLECER (Polar Electroceramics European network organization).

Research integration of the EMPART group.

The figure above shows how the research of the EMPART group has been integrated. Some representative examples of the research are:

A) Realizing multilayer ceramics using a low temperature co-fired ceramics (LTCC) process. A breakthrough for multichip LTCC modules is in progress in telecommunication, medical electronics and automobile electronics. The group has been a pioneer in thick-film technology since 1972, and recently has pioneered LTCC circuit technology. The know-how and the facilities that we have built up in LTCC technology enable in-depth study and manufacturing prototype modules for industry. There are several projects in progress in co-operation with industry, and an EU IST project called “Microwave Electronics with Tunable Dielectric Layers” (Melody) for future multilayer high frequency telecommunication devices (up to 50 GHz) is under way.

B) Laser processing applications in electronics manufacturing. The Microelectronics Laboratory has been a source of expertise in laser applications for over twenty years. Recently, pulsed-laser deposition (PLD) of ferroelectric and relaxor thin film heterostructures, laser-assisted chemical synthesis of nanoparticles, laser annealing and soldering represent the main fields of interest.

C) Research on additive electronics manufacturing technologies which is replacing subtractive printed circuit board technology. Additive electrolyte based methods and printable electronics are being investigated and developed for a wide range of applications manufactured on ceramic, organic HDI, plastic and paper substrates.

D) A completed European IST project ”Micro Air Vehicles for Multi-purpose Remote Monitoring and Sensing” (Marvel) acts as a representative example of micromodule packaging technology development. The group has developed packaging technologies (LTCC and alumina substrate based) for the packaging of various miniature modules, especially for the packaging of sensors for optical flow, pressure, temperature and humidity measurements. Higher packaging density has been achieved by introducing laser machining into conductor path manufacturing, which enables considerably narrower line widths and spaces.

E) Non-destructive testing of BGA (ball grid arrays), CSP and flip-chip bonding joints and dense multilayer conductor structures using novel micro-focus X-ray microscopy (µXRM), scanning acoustic microscopy (SAM) and Moiré techniques. This research is performed in co-operation with industry to develop existing production testing methods.

F) The nanotechnology research group is being formed, and is committed to contribute to the contemporary advanced science via development of new materials, which in turn are of great use for humans and for the environment we live in. The topics we are currently pursuing include synthesis and application of nano-porous silicon structures, carbon nanotube assemblies, metal and metal oxide thin films and nanoparticles, as well as nanofabrication technologies.

Scientific Progress

During the research year of 2004, long term research in the focus areas of the group has continued:

1. Research on pulsed laser deposited layered ferroelectric thin film structures, and the fundamentals of ferroelectrics and relaxors in thin films has continued. The research concentrates on the deposition, structural aspects and dielectric and ferroelectric properties of epitaxial perovskite relaxor and ferroelectric films, multilayers and superlattices, and their heterostructures with conducting oxides. The relaxor ferroelectric materials have excellent electromechanical, electro-optic and dielectric properties, and their thin film heterostructures are promising candidates for microelectromechanical applications. Pioneering studies of the dynamics of the relaxor state and dielectric non-linearities in thin films have been performed. In barium-strontium titanate films, special attention has been paid to the epitaxy, strains and phase transitions in the heterostructures. Room-temperature tunabilities of 30-40 % at 1.5 V have been obtained; this is very promising for integrated RF applications. In international co-operation, the dielectric and optical properties of heterostructures are being investigated in co-operation with the Institute of Solid State Physics at the University of Latvia in Riga, the Technical University of Liberec and the Institute of Physics in Prague in the Czech Republic. Piezoelectric properties on a nanoscale have been studied in co-operation with the University of Aveiro in Portugal and Cranfield University in the UK. The research results have been published in international scientific journals of high standing (Physical Review B, Applied Physics Letters, etc.).

2. Research on Ar+ ion laser-induced chemical liquid-phase deposition of Au micro-patterns on p+-Si surfaces has been performed. The investigations dealt with surface temperature modeling and precursor development. It has been concluded that the localized reduction of gold ions is a consequence of the locally negative surface potential caused by the Seebeck effect.

3. Porous silicon (PS) films were synthesized via the anodization of p+-Si wafers in HF/EtOH electrolyte. Both free-standing and on-Si films were made to analyze the optical properties of the layers. Optical scattering of visible and near-IR photons on the nanostructures was revealed. The refractive index of PS was found to obey the effective medium approximation calculated for the proper mixture of air and silicon using Bruggeman’s theory.

Besides optical measurements, the chemical behavior of PS in an oxidative environment was also investigated. Studies on the reaction kinetics of oxidation revealed a two-step oxidation mechanism, both having first order kinetics. The oxidation of PS was found to be significantly faster than that for Si. XRD analyses of the oxidized samples showed amorphous oxide and revealed significant strain in the residual Si skeleton. Using computer-assisted FEM calculations, the arising thermal and intrinsic stresses were found to be responsible for the measured strain.

As compared to porous silicon, the oxidized films were found to be suitable for applying as substrates for carbon nanotube growth. Networks of multi-walled carbon nanotubes were synthesized via the catalytic chemical vapor deposition (CCVD) method (in collaboration with RPI, Troy, USA).

Currently, a CVD system is being built for the catalytic synthesis of MWCNTs, to develop and implement advanced nano-systems based on well-aligned and organized CNT architectures.

A vertically aligned CNT matrix concept on a pre-patterned Si-wafer.

Obelisks of aligned multi-walled CNT bundles grown using the catalytic CVD method.

4. A project concentrating on piezoelectric actuators for fine and micro mechanical applications was concluded in the PRESTO program of Tekes. Piezo ceramic technology developed in the PRESTO and TUKEVA program (funded by the Academy of Finland) was utilized in the MELA project (MEMS in Laminates, funded by Tekes). In the project, piezoelectric bender type actuators were embedded into a plastic and an LTCC base to carry out dosing/pumping functions in a medical application. High displacements (>100 µm) were obtained by the actuators in both approaches, and very minor degrading of the piezoelectric properties due to the LTCC processing. Consecutively, after the LTCC process the active ceramic parts, the mechanical base structure, the hermetic package and the wiring are all a ready system to be utilized in a wide range of applications (relays, switches, valves, pumps, mechanical controller/regulator/tuning devices). LTCC as a base material enables also further integration, for example, RF devices and different sensors. Piezoresistive pressure sensors on LTCC were also realized in the MELA project showing good characteristics for the implementation into the dosing unit. Currently, a sensor is under miniaturization including integrated amplifier electronics and signal digitizing. Basic research has been continued on optimization of the pre-stressed piezoelectric bending actuators introducing new materials and better characteristics. ATILA and FEMLAB modeling software has been used for optimization of the sensor and actuator structures, showing very good correspondence with measured results.

The MINIMI (MINI- and MIcro parts for demanding industrial applications) project under the LIMU concept (LIsäarvoa MUovituotteisiin, Added Value for Plastic Products) funded by Tekes was started. The project will concentrate on the manufacturing of micro and miniature parts or features for plastic with different methods.

5. The European IST project called Marvel finished in the year 2004. The EMPART group was involved in the study of sensors for different gases, noise, pressure-temperature-humidity and optical flow. The need to keep the mass of a vehicle low requires the use of non-conventional design, components and packaging solutions. In the year 2004, electronics and miniaturized modules were manufactured for a sensor and an optical flow measuring system. The other partners in the project were Centro Riserche Fiat in Italy, Politechnico of Turin in Italy and CNRS in France.

6. Research on novel electroceramic compositions for LTCC modules has been continued. The main development has been achieved with electrically tunable ferroelectric compositions for high frequency applications: the tunability at 25 GHz is 19-38 %, the permittivity is 130-160, the dissipation is comparable with pure barium-strontium-titanate compositions and the firing temperature is ~ 900 °C. These compositions have been utilized in several multilayer components like phase shifters, matching networks and power combiners within the EU IST MELODY project (co-ordinated by Ericsson in Sweden) with various partners e.g. Chalmers University of Technology in Sweden, the University of Birmingham in the UK, Filtronic Comtek in the UK and Ecole Polytechnique Federale de Lausanne in Switzerland. Research has also been started on the development of piezoelectric LTCC compositions for actuators, sensors, microphones and micropumps. Test structures with the combination of piezoelectric, ferromagnetic, ferroelectric and dielectric layers in the same modules have also been prepared. This work aims for multifunctional smart packages. The results have been widely reported at international conferences (PacRim, Japan, EuMW, Germany, ACeS meeting, USA) and in international scientific journals (JECeS, IEEE etc.).


Tunable ferroelectric devices for telecommunication applications.

7. Studies have been continued on the design, modeling and manufacturing of LTCC structures and modules, and on the reliability of LTCC/BGA/PCB joints. The work has been performed in a series of projects funded by the Academy of Finland, Tekes, the EU and industry. In 2004, materials characterization (complex permittivity & loss tangent) of commercial LTCC ceramics was continued and performed together with the St. Petersburg Electrotechnical University (Russia) and the Institute of Physics (Czech). Modeling of signal behavior in coplanar BGA, flip-chip and via structures has been done by using the latest electromagnetic simulation software versions of Sonnet and Ansoft HFSS, in co-operation with the Technical University of Ilmenau (Germany), supported by the Academy of Finland and DAAD. Also work to improve the accuracy of EM modeling of various loss mechanisms (conductor, dielectric, surface roughness loss) was continued. A 3D integrated BGA filter module and an LNA amplifier module were designed and manufactured in co-operation with industry and VTT Electronics. The measured results showed good electrical performance of both modules and correlated very well with the EM simulated results. The design results were reported in the European Microwave Conference on Wireless Technology held in Amsterdam, the Netherlands.


An optimized multilayer BGA packaging structure from DC up to 35 GHz. Current distribution is shown on the metallic surfaces of the EM model.	A miniaturized low-loss Wilkinson power divider utilizing coupled meander lines. Current density is shown on the metallic surfaces of the EM model.

8. The results of reliability investigations on LTCC/printed circuit board (PCB) assemblies based on earlier national Tekes projects were finalized and submitted for publication in Soldering and Surface Mount Technology. Moreover, novel plastic core joint structures of the LTCC/PCB assemblies to be used in RF solutions with leadfree interconnections have been investigated. Preliminary results show them to be better in terms of reliability than the earlier lead containing joint structures. In addition, FEM simulation models have been developed for the assemblies with leadfree interconnections.

9. In additive manufacturing with printed structures, the focus has been on high speed gravure printing of conductive ink on paper and plastic in the project called “Printable Optics and Electronics” (PRINTO). The applications are, for example, inductors and antennas printed on packages. With PCB manufacturing techniques, the interest of the EMPART group has been focused on developing fine-line additive HDI laminate techniques. The work combines techniques of photoresist, lamination and electroplating. The group is testing new additive HDI manufacturing technology in the Tekes ELMO (Miniaturizing Electronics) program. The application areas of additive laminate copper circuits in the Additive Fine-line Circuits project (ADJO) are wide: from RF-ID TAG antennas to HDI substrates.

10. In the framework of a Tekes research project on MEMS in laminates (MELA 2003-), various MEMS solutions using laminate technology are targeted. The project deals with (a) the development of well-controllable large-displacement piezoelectric actuators and (b) concept verification of a high-density optoelectronic laminate structure.

(a) Bridge and lever-type mechanical amplification mechanisms were designed and constructed to enhance the displacements of pre-stressed PZT piezoceramics. Mechanical translations larger than 1 mm were achieved using the developed amplifiers (with gain of up to 25).

(b) A pioneering X-ray detector concept is being approved with a demonstrator built in the Microelectronics Laboratory. The unique design requires state-of-the-art manufacturing and assembly techniques. Methods such as laser micro-patterning of laminate components, UBM (Under Bump Metallization) for reliable chip bonding and BGA for laminate assembly have been investigated and tailored to be able to accomplish the complex multilayer radiation detector. In addition, benchmarking of quality standards were determined in order to support further design and testing to obtain micromodules with high-reliability.

11. During the year 2004, the financing of the OLED group was expanded by grants from the Tauno Tönning Foundation and funding from the Council of Oulu Region. During 2004, the OLED group researcher Kirsi Kuivila funded by Infotech Oulu Graduate School obtained a Fulbright grant by which the group will expand the international OLED network from University of Arizona (Optical Sciences Centre) to Arizona State University (Prof. Ghassan Jabbour´s group). During 2004, the group also received a University of Oulu honor award for efficient research in organic materials chemistry.

Exploitation of Results

Materials, components and technologies developed by the group are already widely applied in the national electronics industry, especially in the mobile phone industry. As an important example of the present exploitation, LTCC micro modules for telecommunication applications and ceramic MEMS modules must be mentioned.

Future Goals

The long term research of the EMPART research group will continue with the focus areas of electronics materials, thin films, components, packaging and reliability techniques. A growing research area of the group is LTCC micro modules for MOEMS applications in the telecommunication, instrumentation and medical fields. Co-operation with other experts at the University of Oulu in the field of nanomaterials and their applications will be increased. The new Micro and Nanotechnology Center with advanced manufacturing facilities offers excellent opportunities for multidisciplinary research. The group has a key role in the Micro and Nanotechnology program of the Oulu region for the years 2002-2006. The EMPART group will form a high excellence research and education organization in the field of micromodule and nanotechnologies.

Personnel

External Funding

Doctoral Theses

Selected Publications

Tyunina M, Levoska J, Kundzinsh K & Zauls V (2004) Polar state in epitaxial films of relaxor ferroelectric PbMg_1/3Nb_2/3O₃. Physical Review B 69:224101/1-10.

Tyunina M & Levoska J (2004) Coexistence of ferroelectric and relaxor properties in epitaxial films of Ba_1-xSr_xTiO₃. Physical Review B 70:132105/1-4.

Tyunina M & Levoska J (2004) Dielectric nonlinearity in relaxor and ferroelectric thin films of chemically ordered PbSc_0.5Nb_0.5O₃. Applied Physics Letters 85:4720-4722.

Shvartsman V, Tyunina M, Levoska J & Kholkin A (2004) Local electromechanical properties of PbMg_1/3Nb_2/3O₃ thin films studied by piezoelectric force microscopy. Ferroelectrics 302:323-326.

Tyunina M & Levoska J (2004) Thin films of perovskite relaxor ferroelectrics. Ferroelectrics 298:353-359.

Tyunina M, Kundzinsh K, Zauls V & Levoska J (2004) Ferroelectric behavior in epitaxial films of relaxor PbMg_1/3Nb_2/3O₃. Ferroelectrics 302:285-288.

Kordás K, Pap AE, Beke S & Leppävuori S (2004) Optical properties of porous silicon (Part I) - Fabrication and investigation of single layers. Optical Materials 25:251-255.

Kordás K, Beke S, Pap AE, Uusimäki A & Leppävuori S (2004) Optical properties of porous silicon (Part II) - Fabrication and investigation of multilayer structures. Optical Materials 25:257-260.

Pap AE, Kordás K & Leppävuori S (2004) Thermal oxidation of porous silicon; study on reaction kinetics. Journal of Physical Chemistry B 108:12744-12747.

Jantunen H, Hu T, Uusimäki A & Leppävuori S (2004) Tape casting of ferroelectric, dielectric, piezoelectric and ferromagnetic materials. Journal of the European Ceramic Society 24:1077-1081.

Hu T, Jantunen H, Uusimäki A & Leppävuori S (2004) BST powder with sol-gel process in tape casting and firing. Journal of the European Ceramic Society 24:1111-1116.

Piatnitsa V, Jakku E & Leppävuori S (2004) Design of a 2-pole LTCC filter for wireless communications. IEEE Transactions on Wireless Communications 3(2):379-381.

Kruusing A (2004) Underwater and water-assisted laser processing, Part 1. General features, steam cleaning and shock processing. Optics and Lasers in Engineering 41:307-327.

Kruusing A (2004) Underwater and water-assisted laser processing, Part 2. Etching, cutting and rarely used methods. Optics and Lasers in Engineering 41:329-352.

Jantunen H, Hu T, Uusimäki A & Leppävuori S (2004) Ferroelectric LTCC for multilayer devices. Journal of Ceramic Society of Japan 112(5):1552-1556.

Hu T, Jantunen H, Deleniv A, Leppävuori S & Gevorgian S (2004) Electric-field-controlled permittivity ferroelectric composition for microwave LTCC modules. Journal of the American Ceramic Society 87(4):578-583.

Juuti J, Heinonen E, Moilanen V-P & Leppävuori S (2004) Displacement, stiffness and load behaviour of laser-cut RAINBOW actuators. Journal of the European Ceramic Society 24(6):1901-1904.

Juuti J, Lozinski A & Leppävuori S (2004) LTCC compatible PLZT thick-films for piezoelectric devices. Sensors and Actuators A: Physical 110(1-3):361-364.

Pudas M, Hagberg J & Leppävuori S (2004) The self-cleaning gravure (SCG), a solution for gravure groove blocking and a novel printing method. The Journal of Imaging Science and Technology 48(4):374-380.

Pudas M, Hagberg J & Leppävuori S (2004) Printing parameters and ink components affecting ultra-fine-line gravure-offset printing for electronics applications. Journal of the European Ceramic Society 24:2943-2950.

Junttila MH, Hormi OEO (2004) Sodium chlorite as an efficient oxidant and hydroxy-ion pump in osmium-catalyzed asymmetric dihydroxylation. J. Org. Chem., 69, 4816.