Tapio Mäkelä

Thin polyaniline films in EMI shielding

Abstract Electromagnetic interference shielding efficiency has been measured for highly electrically conducting Polyaniline-Camphor Sulfonic Acid. The polymer is spin coated from m-cresol solution on an electrically insulating substrate as a 1–30 μm thick layer having a conductivity of 10–100 S/cm. The shielding efficiencies (SE) for these electrically thin polyaniline films have been measured in the near-field with a dual-chamber box and in the far-field with a transmission line method in the frequency range 0.1–1000 MHz. The measurements show that SE depends primarily on the surface resistance both in the far-field and the near-field. An additional effect >10 dB is seen when the two layer structure is measured in the near field. By using layer structures, the SE is >40 dB up to ca. 100 MHz in the near-field and 39 dB at 1 GHz in the far-field.

Continuous Double-Sided Roll-to-Roll Imprinting of Polymer Film

Roll-to-roll imprinting of two-sided structures on thermoplastic polymer film have been studied. Two continuous roll-to-roll approaches to producing structures on both sides of a web have been developed. In the sequential method, two separate printing units are used to the pattern upper and bottom surfaces of the film. In simultaneous roll-to-roll imprinting, two patterned rolls are used in one imprinting unit to pattern both sides simultaneously. In both experiments, flexible Ni-masters with submicron patterns wrapped on supporting metal rolls are used as stamps. The cellulose acetate film 95 µm thick and 50 mm wide has been used as the imprint material in the experiments. Patterned films were studied with an optical microscope and an atomic force microscope (AFM). The results indicate that both methods can be used for double-sided imprinting. However, in sequential imprinting, the first printed pattern is slightly damaged during the second printing phase.

High frequency polyaniline shields

Abstract EMI shields and Salisbury type structures have been constructed from polyaniline. Shield characteristics have been measured in the frequency range of 100 kHz–110 GHz. In case of EMI measurements the shielding efficiency increases as a function of frequency above 1 GHz. The Salisbury structure utilizes a 377 Ohm/sq polyaniline layer and shows a high absorption at 59 GHz. The screen has a 3 mm air gap between the metal surface and the polymer layer.

Roll-to-roll fabricated lab-on-a-chip devices

We present a high-volume fabrication technique for making polymer lab-on-a-chip devices. Microfluidic separation devices, relying on pinched flow fraction, are roll-to-roll fabricated in a cellulose acetate (CA) film at a volume of 360 devices h−1 for a cost of approximately 0.5 euro/device. The manufacturing process consists of two steps: (i) roll-to-roll thermal nanoimprint for patterning the microchannels into a CA film and (ii) roll-to-roll lamination for bonding another CA film onto the imprinted film to seal the microchannels. Reverse gravure coating is used to apply an adhesive polymer onto the CA lid film before roll-to-roll lamination in order to increase the bonding strength. The fabricated devices are compared with planar imprinted devices with regard to the cross-sectional profile of the imprinted channels and their separation functionality. The separation functionality is characterized using fluorescent polystyrene microspheres with diameters ranging from 0.5 to 5 µm.

Roll-to-roll method for producing polyaniline patterns on paper

High speed reel-to-reel manufacturing of electrically conductive polyaniline-dodecylbenzenesulfonic acid (PANI-DBSA) patterns directly onto paper substrate were investigated. A printing speed upto 100 meters per minute and line width down to 60 μm with a 60 cm wide paper web with a industrial scale pilot gravure printer was demonstrated. Additional measurements were made with printability tester using the conducting ink which consist of a PANI-DBSA in toluene solution. We illustrate what influence the concentration of the ink, printing speed and pressure at printing nip have on the conductivity of printed patterns.

Absence of substrate roughness effects on an all-printed organic transistor operating at one volt

A hygroscopic insulator transistor (HIFET) operating at 1V was manufactured using roll-to-roll techniques on a rough, low-cost plastic substrate. The effects of the substrate roughness on the active channel were studied by using two different plastic substrates and comparing HIFETs and organic field-effect transistors (OFETs). We found that the HIFET, as opposed to OFETs, is rather insensitive to changes in the roughness of plastic substrates. Hence, a robust feature of ion modulated transistors is shown.

Lithographic patterning of conductive polyaniline

Abstract Electrically conducting patterns of polyaniline are made by utilizing conventional semiconductor industry process. First polyaniline is spin- or spray-coated on an insulating substrate and has a conductivity of 1–100 S/cm. After that UV resist is spread on top of polyaniline, exposed by UV light, developed and removed. As a result one has a patterned polyaniline layer in insulating and in conducting form on top of the substrate. The conductivity remains essentially unaffected below the resist throughout the process and polyaniline turns insulating at places where the resist is removed. The difference between the electrically conducting part and the electrically insulating part is upto 10 10 . When the linewidth is smaller than 100 μm the square resistance increases slightly, because the deprotonating liquid penetrates somewhat below the resist. Linewidths down to 10 μm have been demonstrated. The process has been utilized in making all-polymer circuit boards having resistors and capacitors made of polyaniline.

Nano-lithography by electron exposure using an atomic force microscope

Abstract We have used a conductive Atomic Force Microscope (AFM) tip to expose a very thin resist film. An exposing current of low energy electrons was induced from the tip to the substrate by applying a small bias voltage. Uniform resist films as thin as 10 nm were fabricated using the Langmuir–Blodgett technique. To orient the defined pattern and to make electrical connections a special larger scale alignment structure was first defined by conventional electron beam lithography, either directly in the Langmuir–Blodgett resist film or in a separate first lift-off process with a thicker resist. The results from the one resist process gave conducting 50 nm lines with a 60 A thick vacuum deposited aluminium film after the pattern transfer. The two step process, which is aiming towards definition of ultra small tunnel junctions, has produced similar conductive lines.

Imprinted electrically conductive polyaniline blends

Imprinting electrically conductive patterns directly into Polymethylmethacrylate/Polyaniline-camphor sulfonic acid (PMMA/PANI-CSA) blends is investigated. The amount of PANI-CSA is 10 - 40 wt% in the blend and the corresponding conductivity 0.07 - 10 S/cm. M-cresol is used as a solvent. The electrically conductive films are spin-coated on glass substrates followed by imprinting with a silicon stamp. Reactive ion etching (RIE) is used to separate imprinted lines from each other. The anisotropy larger than 10 4 in resistance perpendicular and parallel to the imprinted ridges is achieved. Etching rate is 260 nm/min for PMMA and increases by a factor of 3 for PANI-CSA. The conductivity does not change essentially at elevated temperature in the imprint process or due to RIE.

Electrical switching based on dimensionality transitions in nanostructured polymers

Abstract Supramolecular hierarchical conducting nanostructures are obtained by complexing amphiphilic oligomers with block copolymers. Nominally each pyridine group of poly(styrene)- block -poly(4-vinyl pyridine), i.e. (PS- block -P4VP), is first protonated by methane sulphonic acid (MSA) to yield PS- block -P4VP(MSA.) 1.0 . It is further hydrogen bonded with stoichiometric amount of pentadecyl phenol (PDP) to form PS- block -P4VP(MSA) 1.0 (PDP) 1.0 . The polyelectrolytic domains are subject to reversible phase transitions from ”semi Id” slabs to 2d lamellae and further to 1d cylinders upon heating. The transitions manifest in the thermally activated conductivity. Extension to conjugated polymers is discussed to achieve temperature controlled switching based on electronic conductivity.