Vesa Pynttäri

RF Design for Inkjet Technology: Antenna Geometries and Layer Thickness Optimization

The suitability of local conductive print-layer thickness variation for RF applications is demonstrated on flexible substrates. First, the concept is subjected to printed transmission lines as attenuation of one- and two-layer lines is compared to lines having additional layers only on critical high-current areas. Then, two antenna types are studied by applying local additions to the feed line and radiator with optimized print parameters for each layer utilizing low-temperature ink enabling a variety of substrate materials. For a narrow wire-type antenna, efficiency improvement with local thickness increase is observed both at 868 MHz and 2.4 GHz, reaching the efficiency level of a full two-layer antenna. For a wide monopole-type antenna at 2.4 GHz, the similar efficiency improvement up to the full two-layer level is seen already by increasing the edge thickness on the feed line. Accordingly, the antenna type is promising for printing with satisfactory efficiency only with one-layer print on the antenna element. The printed antennas also show good electrical performance, with only approximately 5%-10% decrease in efficiency compared to thick 18-μm copper reference antennas.

PERFORMANCE OF PRINTABLE ANTENNAS WITH DIFFERENT CONDUCTOR THICKNESS

This paper shows that L-shaped monopole antenna on PPS manufactured by inkjet printing of nano silver ink is able to produce very competitive overall antenna performance against Rogers copper foil structures if the thickness of the printed conductor layer is about the skin depth at the operating frequency multiplied by four.

Application of wide-band material parameter extraction techniques to printable electronics characterization

Material characterization is an important part of printable electronics design, since material properties depend strongly on the manufacturing process. This paper reviews application of wide-band extraction techniques to printable electronics characterization. The extraction methods are validated using full-wave simulation data with exactly known reference for material parameters. Suitable test structures are evaluated and applied to printable electronics characterization.

Significance of Conductivity and Thickness of Thin Inkjet Printed Microstrip Lines

The effect of conductor loss of very thin lossy printed silver nano-particle traces manufactured using the printable electronics technology is studied up to 10 GHz by simulations and measurements. First, microstrip resonators are used as test structures with measurements and simulations. In addition to this, the behavior of the attenuation of microstrip lines with different conductivity value and layer thickness pairs have been studied with simulations to achieve basic guidelines for the effects of parameter variation.

High-frequency characterization and simulation of conductor loss in printable electronics technology

The conductor loss of very thin lossy printed silver nanoparticle traces manufactured using the printable electronics technology is characterized up to 10 GHz by simulations and measurements. Microstrip resonators are used as test structures.

Application of Thin-Film RCLG Model for the Modeling of Inkjet Printed Microstrip Lines

Conductor thickness arising from printable electronics manufacturing technology is typically of the order of a skin depth in the frequency range from the upper UHF band to the lower SHF band. Modeling these conductors using standard circuit models however yield inaccurate results whereas full-wave modeling is very time consuming. In this paper, a circuit simulation model based on the surface resistance of a thin penetrable conductor is presented. The proposed model is validated by comparison with full-wave simulation results, Comparison with a conventional circuit-simulation model shows improved accuracy in the loss calculation.

Wide-band Electrical Characterization of printable nano-particle copper conductors

Copper nano-particle ink suitable for printing is a promising substitute for silver- or gold-based inks for consumer electronics applications. However, oxidization must be controlled during the manufacturing and sintering processes. In this work conductors created from a copper nano-particle ink are characterized. In order to mitigate oxidation effects, the ink was formulated in inert atmosphere. Sintering is achieved by exposure to a short light pulse, which, due to the short time scales (ms) and added benefit of photoreduction, can be done in air. Wide-band electrical characterization results up to 20 GHz for copper nano-particle conductors are presented. Structural analysis using scanning-electron microscope (SEM) complements the characterization. Based on high-frequency measurements, wide-band material parameter extraction techniques, and modeling-based analysis of measurement results, the conductivity was found to be of the order of 0.7·107 S/m. All loss mechanisms including impurities deposited within the metal, porosity, surface roughness, and variation in structure geometry are attributed to the conductivity. The electrical performance was found almost comparable to that of silver-based inks. Also the average measured direct-current (dc) conductivity 1.37·107 S/m is similar to that of typical nano-metal conductors.

Comparison of electromagnetic band-gap structures for microstrip antenna arrays on thin substrates

The isolation properties of four different EBG structures are compared in planar antenna arrays. A novel 2-D fork-like structure proposed in this work is found to be the most efficient for the reduction of the mutual coupling between E-plane coupled antennas. The simulation results are validated by measurements

The effect of sintering profile and printed layer variations with inkjet-printed large-area applications

Inkjet-printed conductors with large areas and increased layer thickness may cause challenges with the materials applied. The possibly required increased sintering energy can result in exceeding the heat tolerance of the substrate and cracks in the conductor surface can be formed. The advantages of inkjet print technology can be applied to reduce these challenges by limiting the ink usage by varying the conductor thickness locally or even removing the parts of material from the layout. In this paper, large-area RF applications are studied in terms of varying conductive ink usage and sintering profile. An antenna type with high current density areas is used as a demonstrator of an application requiring larger uniform printed area. The paper shows the advantages of limited local printing on additional layers compared to printing full layers. Two different sintering profiles are applied to differently printed antenna versions fabricated for 868 MHz and 2.4 GHz frequencies. It is shown, that with less sintering energy, the antennas with only local additions perform better than antennas with fully printed antennas with more ink. With longer sintering process time, the local antenna and the fully printed antenna behave equally in terms of total efficiency.

Application of Jacobi-Davidson algorithm to 2-D eigen-mode problems in printable electronics

Thin nano-particle conductors of the order of micrometer in thickness are typical for printable electronics technology. A two-dimensional (2-D) eigenmode solver based on Jacobi-Davidson algorithm is applied to printable transmission lines to evaluate the conductor loss. Efficient preconditioning for the interior solver is utilized to treat poorly-conditioned complex system matrix arising from the fine discretization of conductors required to accurately model the conductor loss. The solver can be used to determine the required layer thickness and conductivity for a desired line loss as well as to the analysis of wide-band material characterization results. The approach is used to determine actual material parameters from wide-band extraction results for inkjet-printed dielectric and nano-silver conductor.