S. Leppävuori

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.

Design aspects of microwave components with LTCC technique

Abstract Low temperature co-fired ceramic (LTCC) technology, widely used in the automotive industry, is now being employed in microwave applications. Several commercial materials with low dielectric losses at microwave frequencies and adequate thermomechanical properties have been introduced. Computer-aided design of three-dimensional circuits has also become available. These advances together with high-quality manufacturing technology have placed LTCCs at the forefront in the development of miniature microwave devices. The paper outlines LTCC technology placing emphasis on those essentials of the materials and processing technologies about which the microwave circuit designer needs to be aware. The discussion is illustrated by examples.The crucial issue of component reliability is also addressed. Although the integration of passive components into the structure improves reliability, the joints between the LTCC module and PCB remain as significant ‘weak link’. Therefore, thermomechanical and structural design is a key to reliable LTCC assemblies.Finally, some future trends the LTCC technology for microwave applications are outlined.

A study of the temperature dependence of the barrier energy in porous tin dioxide

Abstract The dependence of conductance on temperature of some commercial and thick-film SnO2 semiconductor gas sensors is measured in the temperature range 350 K to 875 K at different partial pressures of oxygen in nitrogen. The measurements are carried out using different heating and cooling rates. The values of the barrier enrgy between particles in the ceramic material are also calculated from these results on the basis of the single barrier model for the conductance. The value of the barrier energy in pure oxygen at a fixed temperature is first determined using the temperature-stimulated change in the conductance. The results are discussed in the light of some other experiments and theoretical models given to describe the barrier energy. A discussion on the effect of different barrier heights between different particles is also given on the basis of a random barrier network model. By using quick cooling from 875 K to 350 K, it is possible to get high barrier values also at this low temperature. It is beleived that this may be the modus operandi of temperature-pulsed sensors.

Properties of epitaxial ferroelectric PbZr0.56Ti0.44O3 heterostructures with La0.5Sr0.5CoO3 metallic oxide electrodes

PbZr0.56Ti0.44O3 (PZT) epitaxial ferroelectric thin films on a LaAlO3 (100) substrate, covered by a metallic oxide electrode La0.5Sr0.5CoO3 (LSCO) are demonstrated in this work. The films are fabricated by the sol–gel method and effort was focused on thermal processing to obtain the desired epitaxial heterostructure. The dielectric and ferroelectric properties of PZT thin films were measured and it was found that they are as good as in the films deposited by other thin-film methods. The dielectric constant and the dissipation factor of the PZT films are, respectively, about 500 and 0.06 below 20 kHz. The remanent polarization Pr is about 27 μC/cm2 and the coercive field Ec is about 50 kV/cm. It was found that the ferroelectric properties were significantly influenced by the microstructure of the PZT layers. The present study also showed that the fatigue characteristics of the epitaxial heterostructure with LSCO electrodes under a reversed electrical field are far superior to those obtained with a polycrys...

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.

Dielectric properties of pulsed laser deposited films of PbMg1/3Nb2/3–PbTiO3 and PbSc1/2Nb1/2O3–PbTiO3 relaxor ferroelectrics

Highly oriented perovskite films of PbMg1/3Nb2/3–PbTiO3 and PbSc1/2Nb1/2O3–PbTiO3 with compositions near the morphotropic phase boundary were formed by pulsed laser deposition on La0.5Sr0.5CoO3/MgO (100). The dielectric properties of the films were studied over the frequency range of 100 Hz–1 MHz in the temperature range 20–350 °C. The room temperature polarization and dielectric permittivity of 250-nm-thick films were close to those in bulk ceramics. The films exhibited relaxor-type behavior with thermal hysteresis and with the temperatures of the dielectric peaks corresponding to those in the bulk. The width of the transition in the films was larger than in bulk ceramics. The properties of the films were found to be influenced by the small grain size rather than by the interfaces of the films.

Relaxor behavior of pulsed laser deposited ferroelectric (Pb1−xLax)(Zr0.65Ti0.35)O3 films

The dielectric behavior of pulsed laser deposited ferroelectric (Pb1−xLax)(Zr0.65Ti0.35)O3 films (PLZT x/65/35, x=0–9.75 at. %) has been studied experimentally. Epitaxial stoichiometric PLZT films were formed on a pulsed laser deposited layer of La0.5Sr0.5CoO3 (LSCO) on MgO (100) single-crystal substrates. The dielectric permittivity and loss tangent of the resulting heterostructures were measured in the temperature range of 20–350 °C at a frequency of 100 Hz–1 MHz. A peak around 130–350 °C was observed in the dielectric permittivity versus temperature curves. The peak exhibited a relaxor type behavior. Its position was a nonmonotonic function of the La content and depended on the microstructure of the film. The broadening of the peak of the dielectric permittivity was larger than that in the ceramic PLZT and it also depended on the La content and microstructure of the film. The broadening depended on the temperature and frequency ranges: master curves of the normalized dielectric permittivity versus norm...

Analysis of sway in Parkinson's disease using a new inclinometry‐based method

In order to analyze balance control, we developed a new inclinometry‐based method to provide direct information about body sway in the side‐to‐side and forward–backward directions. We tested the clinical utility of this method for analyzing balance in Parkinsons disease (PD), and studied the clinical correlates of the balance measures in PD. Postural sway was measured during quiet stance with eyes open and eyes closed in 28 PD patients and in 32 age‐ and sex‐matched control subjects. Postural sway was modeled using side‐to‐side and forward–backward directional sway movements, sway velocity, and sway area. The amount of postural sway in the PD patients was greater than in the control subjects, the higher level being most marked in patients with severe or long‐duration PD. All the side‐to‐side directional sway parameters were abnormal in the PD patients compared with the control subjects (P < 0.05), whereas the forward–backward directional parameters did not differentiate the two groups. The most sensitive measures of sway were path length, velocity, and area. The duration and severity of PD seem to be particularly associated with the amount of side‐to‐side directional postural sway. This new inclinometric method appears to be useful in quantifying postural sway and evaluating balance impairment in PD.

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.

Gravure-offset-printing technique for the fabrication of solid films

The development of the modified thick-film technique, gravure-offset printing, was studied. It is a printing technique which has been developed to fill the gap between thin and thick film technologies when considering the conductor line widths. Several factors of the technique which affect the fabrication of solid films were considered. These factors include printing plates, silicone rubber pads, printing inks, printing parameters and substrates. After optimising, the technique was used to print narrow conductor lines on ceramic (also on low-temperature co-fired ceramic, LTCC) and glass substrates. The narrowest width of Au and Ag conductors was 50 μm and their typical fired thickness was around 2 μm. Some sensor and high-frequency applications realised by the gravure-offset-printing technique are also discussed.