Antti Uusimäki

Compositions of MgTiO3-CaTiO3 ceramic with two borosilicate glasses for LTCC technology

Abstract Mixtures of ZnO–SiO 2 –B 2 O 3 /MgTiO 3 –CaTiO 3 (ZSB/MMT-20) and BaO–SiO 2 –B 2 O 3 /MgTiO 3 –CaTiO 3 (BSB/MMT-20) have been investigated as new candidates for LTCC dielectric materials. Two-stage sintering behaviour was observed in both materials, starting at around 600 and 850°C. Nearly full density (97%) was achieved in ZSB/MMT-20 after sintering at 900°C, while a high porosity of 23% was measured in BSB/MMT-20 after firing at 875°C followed by partial melting of samples during sintering at 900°C. After firing, fully crystalline structure with phases of ZnTiO 3 , Zn 2 SiO 4 , Mg 4/3 Zn 2/3 B 2 O 5 and TiO 2 were found in ZSB/MMT-20, while the structure of BSB/MMT-20 consisted of crystalline TiO 2 and BaTi(BO 3 ) 2 and amorphous SiBa(BO 3 ) 2 and SiB 2 O 5 . ZSB/MMT-20 fired at 900 o C showed promising microwave properties having the dissipation factor of 0.001 and a permittivity of 10.6 at 7 GHz. The corresponding values for BSB/MMT-20 fired at 875°C were 0.002 and 8.2, respectively.

Chip cooling with integrated carbon nanotube microfin architectures

Efficient cooling of silicon chips using microfin structures made of aligned multiwalled carbon nanotube arrays is achieved. The tiny cooling elements mounted on the back side of the chips enable power dissipation from the heated chips on the level of modern electronics demands. The nanotube fins are mechanically superior compared to other materials being ten times lighter, flexible, and stiff at the same time. These properties accompanied with the relative simplicity of the fabrication makes the nanotube structures strong candidates for future on-chip thermal management applications.

Electrocaloric characteristics in reactive sintered 0.87Pb(Mg1∕3Nb2∕3)O3–0.13PbTiO3

Only little data have been published on direct electrocaloric measurement of Pb(Mg1∕3Nb2∕3)O3–PbTiO3 (PMN-PT) ceramics. In this paper, the electrocaloric characteristics of 0.87PMN-0.13PT ceramic were determined by direct measurements. A strong transition in the electrocaloric effect was found at about 18°C, which is the same as the depolarization temperature Td. The maximum electrocaloric temperature rise was ΔT=0.558°C at TECm=70°C and E=2400kV∕m, well above the transition at Td=18°C. The existence of two maximums could be an indication of several mechanisms being responsible for the electrocaloric effect.

Thermal oxidation of porous silicon: Study on structure

The structural changes of porous silicon (PS) samples during oxidation are investigated and analyzed using various microscopy techniques and x-ray diffraction. It is found that the surface roughness of oxidized PS layers increases with the oxidation at 200–400°C and decreased at 600–800°C. At 800°C a partially fused surface is observed. The oxide formed on the wall of porous silicon skeleton is amorphous. The shifts of Si(400) peaks are observed in the x-ray diffraction patterns, which are correlated to the lattice deformation induced by thermal expansion coefficient mismatch between the grown SiO2 and the residual Si, and to the intrinsic stress caused by the Si–O bonds at the Si–SiO2 interface. These explanations are supported by thermomechanical modeling using three-dimensional finite element method.

Laser-assisted metal deposition from liquid-phase precursors on polymers

Abstract In this work, a short review is presented for results utilizing the technique of laser-assisted metallization of dielectrics. Experimental efforts and results related to the metal (palladium (Pd), copper (Cu) and silver (Ag)) deposition on polymeric materials (polyimide (PI), mylar) are reported. These polymers and metals are chosen due to their growing importance in the rapidly-developing microelectronics packaging industry. The method of laser-induced chemical liquid-phase deposition (LCLD) offers many advantages compared to other techniques such as laser-induced forward transfer (LIFT), pulsed-laser deposition (PLD) and laser-assisted chemical vapor-phase deposition (LCVD). The LCLD is time and cost effective because vacuum tools and special pre-treatments are not required. The consumed chemicals used in precursors are non-harmful and easy to handle due to the liquid phase. For the optimal physical and chemical properties of deposits, the laser and solution parameters are varied. XeCl and KrF excimer and Ar + lasers are employed for executing the palladium, Ag and/or Cu formation on the polymer substrates. Chemical and physical analyses of the formed metal patterns are performed by EDX, XRD, FESEM, SEM, resistance and adhesion measurements.

Laser direct writing of copper on polyimide surfaces from solution

Conductive copper patterns were deposited on polyimide (PI) substrates by using a focused, scanned continuous wave (cw) Ar+ laser beam at 488 nm wavelength. The deposition process was initiated by a photothermal reaction of a tartarate-complex solution of Cu2+ ions in an alkaline and reducing environment. Deposits were characterised by Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-ray (EDX) Spectrometry, DEKTAK profilometer and resistance measurements. The dependence of the characteristics of laser direct written patterns on the scanning speed of the laser beam, number of scans and laser power was examined. Uniform copper lines covered with copper-oxide (line width from 30 to 60 μm and height from 2 to 20 μm) with high conductivity and adhesion were achieved under optimised conditions.

Ba0.7Sr0.3TiO3 powders with B2O3 additive prepared by the sol–gel method for use as microwave material

Abstract Ferroelectric films based on barium strontium titanates have been widely investigated in microwave devices, such as tunable filters and phase shifters. Recent trends include integration of ferroelectric layers into multilayer dielectric modules by a tape casting procedure. The sintering temperature of BST prepared by the conventional oxide mixing method is, however, very high (1350°C), and only platinum or refractory metals can be used for conductors and electrodes in the co-sintering process of tapes. Decrease of the sintering temperature of BST below 1000°C would result in good compatibility of the ferroelectric layers with embedded electrodes made of highly conductive metals, such as silver. The effects of B2O3 addition and powder properties on the sintering behavior and the dielectric properties were investigated. The sol–gel method was used to prepare all powders because of its high purity and homogeneity control and its ability to produce fine powders. The BET results showed that all powders had high specific surface areas, but in dilatometric studies, only boron addition produced the desired shrinkage and dense microstructure at low temperatures (

PLZT thick films for pyroelectric sensors

The production of thick-film (TF) PLZT layers for pyroelectric sensors prepared from perovskite-type (Pb,La)(Zr,Ti) powders is described. The powder manufacture, paste preparation and layer production processes are detailed and flow charts of the powder and layer production and diagrams of the layer structure are presented. The relative permittivity and dielectric loss of PLZT layers were measured as functions of temperature. The temperature dependence of the pyroelectric coefficient was measured and the influence of the poling electric field on the pyroelectric coefficient was investigated. The room-temperature pyroelectric coefficients of the PLZT layers are of the order of and are comparable with commonly used materials, but thick-film technology offers the advantage of a mature and simplified production route. The experimental results made it possible to define parameters for the production process necessary to achieve improved layers for pyroelectric sensors.

Tape casting of ferroelectric, dielectric, piezoelectric and ferromagnetic materials

Tape casting is a feasible method for preparing ceramic tapes with different electrical and magnetic properties for multilayer ceramic devices. This paper describes the tape casting process for several different electroceramic materials (BST, PZT, NZF and ZSB) utilising similar organic additive and solvent systems. The properties of tapes with different ceramic compositions before and after sintering are investigated, including surface roughness, shrinkage and microstructures. The parameters affecting the casting, shrinkage, lamination, thickness and tensile strength of green tape are also presented. This enables process design for tape which can be used in devices with true integration of dielectric and piezoelectric, ferroelectric and ferromagnetic layers in 3-dimensional multilayer structures.

Phase transition revealed by Raman spectroscopy in screen‐printed lead zirconate titanate thick films

The transition from rhombohedral phase to tetragonal in screen‐printed lead zirconate titanate (PZT) thick films was studied using Raman‐scattering spectroscopy, and the results were compared with those of x‐ray‐diffractometry investigations. The unfired films were subjected to rapid firing in an air atmosphere at temperatures ranging from 960 to 1150 °C. During firing the composition of the films changed gradually as lead evaporated, which moved the composition of films to the ZrO2‐PZT region and resulted in precipitation of ZrO2. This caused the original rhombohedral structure to be converted to tetragonal. Correspondingly, the Raman spectra also changed with increasing firing temperature. The variation in Raman spectra was characterized by three frequency regions, denoted as the low‐, intermediate‐, and high‐frequency region, respectively, which are related to three cubic T1u modes. Moreover, it was also observed that the appearance of tetragonal modes was delayed from the formation of tetragonal struc...