Inks based on inorganic nanomaterials for printed electronics applications

Abstract In this thesis several novel inks based on dry inorganic powders enabling magnetic, piezoelectric and memory resistive (memristive) function were researched for printed electronics applications. Low curing temperature screen–printable magnetic inks for high frequency applications based on dry cobalt nanoparticles were developed in the first part of the work. Three publications were achieved. The first one concentrated on ink formulation and its process development, the second on the utilization of multifunctional surfactant, and the third on the development of the inks for plastic substrates. The magnetic inks developed were cured at 120 °C. The electrical performance, microstructure, surface quality and mechanical durability of printed and cured layers were investigated. Relative permeability values up to 3 and related loss tangents up to 0.01 were achieved at 2 GHz frequency, as well as a pull–off strength of up to 5.2 MPa. The maximum loading level of cobalt nanoparticles was 60 vol–%, after which the stability of the ink started to degrade. The developed ink enabled the miniaturization of a patch antenna. In the second part of the thesis, the formulation of inks based on piezoelectric ceramic particles in powder form with ferroelectric polymers as a matrix material is introduced. The performance and quality of the printed inks and cured layers were investigated. The measured pull off –strength was up to 3.25 MPa, relative permittivity was up to 48 at 1 kHz and piezoelectric constant d31 up to 17 pm/V. The printed piezoelectric layer can be utilized in a pressure sensor. In the third part of the thesis, the development of inks for a novel printed memory component, a memristor, is researched. A synthesis route was developed for an organometallic precursor solution, which was formulated into inkjet–printable form. The printing tests were carried out in order to find the most feasible layer thickness with memristive behaviour. The influence of substrate materials and different thermal treatments on the components’ electrical properties, durability of read/erase –cycles and overall lifetime were also investigated. The prepared memristive patterns remained functional for up to 35 days, while the precursor solution remained usable for over a year. The memristive areas withstood up to 30 read/erase cycles and by utilizing heat treatments the shift in resistance value increased by up to three orders of magnitude.Tiivistelmä Väitöstyössä kehitettiin epäorgaanisten kuivien jauhemaisten materiaalien pohjalta magneettisia, pietsosähköisiä ja memristiivisiä musteita käytettäviksi painettavan elektroniikan sovelluksissa. Työn ensimmäisessä osassa tutkittiin korkean taajuuden sovelluksissa käytettävien magneettisten, matalassa lämpötilassa kovetettavien, jauhemaisiin kobolttinanopartikkeleihin perustuvien silkkipainomusteiden valmistamista. Tulokset on esitetty kolmessa julkaisussa, joista ensimmäinen keskittyi musteen formulointiin, toinen monifunktionaalisen surfaktantin hyödyntämiseen ja kolmas musteen kehittämiseen muovialustalle sopivaksi. Työssä kehitettiin 120 °C:ssa kovettuvia musteita, joista valmistettujen kalvojen suhteellisen permeabiliteetin maksimiarvoksi saatiin 3 ja häviöiden minimiarvoksi 0,01 kahden gigahertsin taajuudella. Pull–off –vetotestin tulokseksi saatiin jopa 5,2 MPa. Musteet säilyivät vakaina enimmillään 60 tilavuusprosentin metallipitoisuudella. Kehitettyä mustetta käytettiin tasoantennin miniatyrisoinnissa. Toisessa osassa kehitettiin pietsosähköisiä musteita, jotka pohjautuivat keraamijauheeseen ja matriisimateriaalina toimivaan ferrosähköiseen muoviin. Niistä valmistettujen kalvojen parhaaksi pull off –vetotestin tulokseksi saatiin 3,25 MPa, permittiivisyyden maksimiarvoksi 48 yhden kilohertsin taajuudella ja d31–pietsovakion maksimiarvoksi jopa 17 pm/V. Kehitettyjä painettuja rakenteita voidaan käyttää painettavissa paineantureissa. Kolmannessa osassa kehitettiin uudentyyppinen painettava muistikomponentti, memristori ja komponenttien valmistamiseksi uusi prekursoriliuoksen synteesi. Syntetisoitu liuos muokattiin mustesuihkutulostettavaksi. Painokokeiden avulla selvitettiin materiaalin paksuus, jolla saatiin aikaan muistivastukselle ominainen memristiivinen käyttäytyminen. Työssä tutkittiin substraattimateriaalien ja mahdollisten lämpökäsittelyjen vaikutusta komponenttien sähköisiin ominaisuuksiin, luku/kirjoitussyklien kestoon sekä käyttöikään. Valmistetut memristiiviset kalvot säilyivät toimivina 35 vuorokautta ja prekursoriliuos yli vuoden. Memristiiviset pinnat kestivät jopa 30 luku/kirjoitussykliä ja vastusarvon muutos saatiin lämpökäsittelyllä kolmea kertaluokkaa suuremmaksi

Low permittivity environmentally friendly lenses for Ku band

Abstract Lenses can be used to focus and disperse the electric field emitted by the antenna. Sustainable and environmentally friendly lenses were made from lithium molybdenum oxide (LMO) glass composite. Half spherical lenses with a diameter of a 30 mm were fabricated from LMO composite, and the antenna properties were measured with a waveguide feed. The lens enhanced radiation pattern was measured at Ku band, and the improvement in the gain was found to be 2 dB

Influence of coal ashes on fired clay brick quality: Random forest regression and artificial neural networks modeling

Finding a solution to the problem of the large buildup of coal ashes is a vital necessity. Although the use of coal ashes in fired clay bricks has been thoroughly investigated, there is insufficient information on their industrial utilization and researchers do not agree on whether or not this addition improves the quality of the final products. Therefore, a database has gathered 20 years of research containing key factors related to the quality of the bricks (i.e., chemical composition, firing temperature, soaking time, open porosity, water absorption and compressive strength). Then, random forest regression and artificial neural networks (ANN) modeling were used to separately predict the parameters concerning the quality of the final products. The overall conclusions were that the compressive strengths were the highest when using fly ashes and that class F ashes were highly suitable to be used in the brick industry as a replacement material for brick clay. In addition, the ANN models showed higher coefficients of determination and an overall better fit to the experimental data. By changing the chemical makeup of the initial materials and their proportions, the particle size of the ashes, the firing temperature and soaking time, as well as the size of a product, the created models can be used to estimate the quality of the brick containing coal ash. That is crucial because the inconsistent chemical composition of ash is generally the main obstacle to its utilization. The local sensitivity analysis revealed the highest influence of the content of the alkali oxides in the initial clay on the fired clay bricks due to their fluxing effect. In the case of ash-clay bricks, the decisive factors were the type of furnace used, the ashes' class, the Na2O content in raw clay, and the K2O introduced with the ash. The F class ashes containing about 2–3% of K2O and [removed

A printable P(VDF-TrFE)-PZT composite with very high piezoelectric coefficient

Abstract In this paper a significant advance in the piezoelectric properties of poly(vinylidenefluoride-trifluoroethylene)-lead zirconate titanate (P(VDF-TrFE)-PZT) composite ink has been achieved by coating the ceramic particles prior to formulation with a polymeric surfactant containing carboxylic acid anhydride functional groups and the piezoelectric response of a unimorph cantilever is further enhanced by introducing a reinforced substrate. The measured effective transverse piezoelectric coefficient (d31eff) was -56 pm/V, which is 3.3 times higher than that of the same composite without surfactant and is the highest reported for a printable polymer-ceramic composite. In addition, the printability of the ink and dispersion of the ceramic particles was enhanced. The samples were fabricated by stencil printing of a single piezoelectric layer on a flexible PET substrate followed by curing at only 120°C, thus enabling utilization on a wide range of substrates. The results also show the improved particle dispersion and layer quality in 0—3 composite inks with surfactant added and the effect of sample structure and mechanical coupling between the hard ceramic particles and the soft matrix. The developed composite ink is suitable, for example, in sensors in printed wearable and portable electronics

A sensing demonstration of a sub THz radio link incorporating a lens antenna

Abstract We demonstrate that the future sixth generation (6G) radio links can be utilized for sub-THz frequency imaging using narrow beamwidth, high gain, lens antennas. Two different lenses, a bullet or hemispherical shape, were used in radio link setup (220–380 GHz) for an imaging application. Lenses performed with the gain of 28 dBi, 25 dBi, and narrowed the beamwidths of 1° and 2.5°. Plants were used as imaging objects, and their impacts on radio beams were studied. For assessment, the radio link path loss parameter was -48.5 dB, -53.2 dB, and -57.1 dB with the frequency 220 GHz, 300 GHz, and 330 GHz, respectively. Also, the impact of the radio link distance on the imaging was studied by 50 cm and 2 m link distances. In addition, the 3D image was acquired using the phase component of the image, and it showed the leaf surface roughness and the thickness, which was similar to the measured value

An ultralight high-directivity ceramic composite lens antenna for 220–330 GHz

Abstract This work presents the characterization of Lithium molybdenum oxide (Li 2 MoO 4 , LMO) hollow glass microspheres (HGMS) ceramic composite from 0.1 to 1 THz and an associated bullet shaped lens used with WR3.4 for 220‐330 GHz band. LMO-HGMS had permittivity of 1.18 and loss tangent of 0.003 at 300 GHz. The calculated reflectivity for the LMO-HGMS-air interface was 0.2 %. The fabricated bullet lens weighed 5 grams and was characterized using an experimental measurement system. The lens was measured to have a focus spot of diameter 1.5 mm. Simulated results showed the lens to operate with a WR3.4 waveguide having a gain of 27.5 dBi with a narrow beam width of 1-degree, 18 dB sidelobe level (SLL), 40% Fractional Beam Width (FBW), and −13 dB S 11 over the broadband 220‐330 GHz

Screen-printed mechanical switch based on stretchable PU-foam film

Abstract A screen-printed mechanical switch based on an electrode structure on stretchable polyurethane (PU)-foam film, Platilon U 4021, combined with a piezoelectric actuator, Smart Material MFC M-4010-P1, is proposed. The minimum actuation voltage of the prepared component is 300 V. The measured resistance was 2 Ω while closed and >0.5 TΩ when open. The electrode structure endured on average of up to 15.5 M cycles with movement ≥100 times greater than the ≤1 μm required for actuation. The results suggest that the switch could be advantageous for various e-textile applications

Upside-down composites:electroceramics without sintering

Abstract In this work, all-ceramic barium strontium titanate (BST) composite is fabricated for the first time at room temperature without sintering, showing a clear phase transformation behavior at Curie temperature and excellent electrical properties. The samples fabricated using pre-treated BST particles with a ceramic binder and selection of the overall particle size showed the relative permittivity up to 200 and loss tangent of 7 × 10⁻³. Although the technology introduced here is demonstrated to feasible for BST, it is generic and usable also for other inorganic materials. Thus, it can expedite and pave the way for versatile applications of other ceramic based composites with, for instance, piezoelectric, ferroelectric, ferromagnetic or ferrite performance used in a large variety of devices for telecommunications, sensors and actuators