Iwamoto M., Kwon Y.-S., Lee T. (Eds.) Nanoscale Interface for Organic Electronics

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Morphology Control of Nanostructured Conjugated Polymer Films 289

drying in air, as mentioned in the previous paper. To improve the device

performance, the ITO electrodes served as anode are coated with

approximately 50 nm-thick PEDOT:PSS layer by spin-coating the

aqueous suspension.

Fig. 10. (a) Emission intensity-voltage characteristics of the light-

emitting devices using

PDOF-

MEHPV films prepared by the electrophoretic deposition with various deposition

periods. The case of spin-coated PDOF-

MEHPV film is also indicated. The thickness of

PDOF-MEHPV are indicated in the parentheses. Accompanying emission intensity-

current characteristics are shown in (b). The emission area of the devices is approximately

3 mm × 3 mm.

M. Onoda and K. Tada 290

The thickness of the PDOF-MEHPV films is estimated by using the

relationship that unit peak absorbance approximately corresponds to

120 nm in thickness. The device structure is similar to that reported in

our previous paper as shown in Fig. 10.

The light-emitting devices with

a ITO/PEDOT:PSS/ PDOF-MEHPV/ MgAg structure were fabricated

with various thickness of PDOF-MEHPV films by the electrophoretic

deposition. PDOF-MEHPV films have been deposited on the PEDOT:

PSS-coated ITO films by the application of DC 300 V between 5 mm in

a suspension containing 0.05 g/l of polymer for 4-10 s, resulting in the

PDOF-MEHPV films with thickness ranging from 80 nm to 250 nm. The

emission area of the devices is approximately 3 mm × 3 mm square, and

the emission intensity was measured with a Si-photodiode attached on

the emission face of the devices. The vacuum deposition of cathode

composed of Mg and Ag, as well as the characterization of the devices

was performed in a glove-box filled with nitrogen. The devices with

the same structure using spin-coated PDOF-MEHPV films were also

prepared for comparison.

5.2. Chracterization of PDOF-MEHPV Light-Emitting Devices

The inset of Fig. 11 shows tha snapshot photograph of the device using

the PDOF-MEHPV film prepared by electrophoretic deposition. The

uniformity of the green emission from the device can be confirmed by

this snapshot.

Fig. 11. Structure of PDOF-MEHPV Light-

Emitting Diodes Prepared by electrophoretic

Deposition. The inset shows tha snapshot of the device using the PDOF-MEHPV fi

prepared by electrophoretic deposition.

Morphology Control of Nanostructured Conjugated Polymer Films 291

Typical emission intensity-voltage and the emission intensity-current

characteristics of the devices are shown in Figs. 10(a) and 10(b),

respectively. Since the emission onset voltage as well as the quantum

efficiency of the devices does not seem to seriously depend on the

preparation method. It can be concluded that the characteristics of the

devices fabricated by the electrophoretic deposition are comparable to

those by the spin-coating.

The dependence of the emission onset voltage on the polymer

thickness is plotted in Fig. 12. The onset voltage seems to be determined

by the film thickness, and there is no significant difference due to the

difference in the preparation method. The onset voltage is monotonically

increased with the increasing thickness of the PDOF-MEHPV layer, as

commonly observed in the study of polymer light-emitting devices.

For the preparation of the devices by the spin-coating technique, a

chloroform solution containing 10 g/l of the polymer and the spin-speeds

ranging from 1000-5000 rpm have been employed. Generally, the spin-

coating from the chloroform solution of a polymer gives thicker film

easily than that from the toluene solution at a constant polymer

Fig. 12. Dependence of the emission onset voltage on the PDOF-

MEHPV thickness of

the light-emitting devices using PDOF-

MEHPV films prepared by the electrophoretic

deposition. The cases of spin-coated PDOF-MEHPV films are also indicated. The li

shows the linear fitting.

M. Onoda and K. Tada 292

concentration because of the difference in the evaporation rate, and a

spin-speed below 1000 rpm results in inhomogeneous films. Despite of

the concentrated polymer solution used, the maximum thickness of the

spin-coated films obtained was below 150 nm.

6. Electric Current in PDOF-MEHPV Suspensions

The electric current during the electrophoretic deposition has been

measured as shown in Fig. 13. The decays observed apparently do not

have single-exponential feature. It is clearly found that the electric

current increases with increased polymer concentration for the

suspensions containing polymer more than 0.2 g/l. However, the electric

current found in the suspensions containing smaller amount of polymer is

almost identical to that in pure toluene/acetonitrile mixture. The electric

current in the pure mixture of solvents, which tends to change from

trial to trial, may mainly come from dissolved impurities such as

oxygen and water. The suppression of this kind of electric current must

be a key to reduce the power consumption during the deposition.

Detailed measurement and analysis of the electric current during the

electrophoretic deposition are under way.

Fig. 13. Electrical current during the electrophoretic deposition in the suspensions with

various PDOF-MEHPV concentrations.

Morphology Control of Nanostructured Conjugated Polymer Films 293

7. Conclusions

In this chapter, we have reported some experimental results on the

lectrophoretic deposition of the conjugated polymer. The electrophoretic

deposition of a fluorene-based conjugated polymer, poly(9,9-dioctyl-2,7-

divinylene-fluorenylene)-alt-{2-methoxy-5-(2-ethylhexyloxy)-1,4-phen-

ylene}], PDOF-MEHPV has been carried out from suspensions with

various good/poor solvent ratios.

The optical absorption spectra and atomic force microscopy show that

the roughness of the resultant film strongly depends on the good/poor

solvent ratio of the parent suspension. That is, rough and turbid films are

obtained when the content of the poor solvent is high, while uniform and

transparent films, which may be suitable for polymer devices such as

light-emitting devices and photocells, can be obtained in the case of low

poor solvent content.

The scanning electron micrographs clearly indicate the dependence

of the morphology of the PDOF-MEHPV films by the electrophoretic

deposition on the toluene/acetonitrile ratio of the parent suspensions. It is

also shown that the suspension prepared from a 0.1 g/l toluene solution

of the polymer, can give the polymer film with a thickness of a few

100 nm.

That is, the PDOF-MEHPV films prepared by the electrophoretic

deposition in a suspension prepared by mixing equivalent volumes of

0.1 g/l toluene solution of the polymer with pure acetonitrile can be more

than 200 nm in thickness, which could not be achieved by the

conventional spin-coating technique using 100-times thick polymer

solution. It has been shown that the coating of ITO electrodes with

PEDOT:PSS thin layer on the results in low and nonlinear deposition

rates.

It has been mentioned that the electrophoretic deposition using a

suspension derived from a toluene solution containing only 0.1 g/l of the

polymer can yield films with thickness >200 nm, which were not

obtained by a single spin-coating shot with a 10 g/l chloroform solution.

The electrical current originating from the movement of colloidal

particles is clearly detectable for the suspensions containing polymer

more than 0.2 g/l. However, the electrical current due to the impurities

M. Onoda and K. Tada 294

dissolved in the solvent makes it difficult to detect the electrical current

corresponding to the particle movement in the suspensions containing

smaller amount of the polymer.

The demonstration of the polymer light-emitting device confirmed

that the electrophoretic deposition technique can yield uniform films

instantly from dilute polymer solutions.

Thus, it has been shown that the electrophoretic deposition is a useful

technique to obtain conjugated polymer films with thickness of few

100 nm from dilute polymer solution. This method can provide an

alternative way for producing large-area polymer electronic devices.

These features indicate that the electrophoretic deposition can be an

important candidate for the film deposition technique for polymer-based

electronic devices.

Acknowledgments

We acknowledge the supports by Grant-in-Aid for Young Scientists from

JSPS, the research-grant from the IKETANI Science and Technology

Foundation and the research-grant from the Hyogo Science and

Technology Association.

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297

CHAPTER 14

WAY OF ROLL-TO-ROLL PRINTED 13.56 MHz

OPERATED RFID TAGS

Minhun Jung

1,2

, Jinsoo Noh

, Hwangyou Oh

, Hwiwon Kang

, Dongsun Yeom

Donghwan Kim

2,3

and Gyoujin Cho

1,3,4,

Department of Chemical Engineering, Sunchon National University,

315 Maegok-dong, Sunchon 540-742, Korea

Printed Electronics Research Institute,

Paru Co. 42-4 Sunchon Industrial Complex, Sunchon 540-813, Korea

Department of Printed Electronics Engineering in World Class University

(WCU) Program, Sunchon National University,

315 Maegok-dong, Sunchon 540-742, Korea

Green Technology Fused Advanced Materials (GTFAM)

Regional Innovation Center (RIC), Sunchon National University,

315 Maegok-dong, Sunchon 540-742, Korea

E-mail: gcho@sunchon.ac.kr

Roll-to-roll printing process has been recently considered as a key

technology for the realization of a penny RFID tag. To employ the

current commercially avaiable R2R printing process to print RFID tags

including antenna, rectifier, and digital processors on plastic or paper

foils, materials and device circuits should be first well optimized to the

R2R printers and substrates. In this chapter, we would like to briefly

discuss about our own device circuits with our designed materials for

R2R gravure printing RFID tags on plastic foils.

1. Introduction

Radio frequency idenification (RFID) tags will take a key role for

bringing the ubquitous society at 21

century.

For the realization of the

true ubiqutous society, all goods should be able to sense their

surroundings and exchange information via wireless communication

instaneously. In other words, all goods should have their own RFID tags

M. Jung et al.

298

in which sensors, displays, CPU etc. may be integrated depending on

their usages. In fact, current Si and MEMs technologies are fully able to

produce the RFID tags with the integration of sensors, displays or CPU if

the cost of the tags is not a matter. However, in markets, the cost is

everthing to be considered so that 20 cent of an eraser can not have

20 cent of RFID tag.

2,3

Therefore, the manufacturing cost of RFID tags

should be first resolved for the realiztion of ubiqutous society.

Based on the current Si and MEMs technologies, ultra-low cost of the

tags can not be attained beacuse about 80% of the manufacturing cost is

originated from Si chip bonding and labelling processes, not from the

cost of Si chips. Futhermore, if we want to integrate sensors, displays or

CPU on the tags, the portion of bonding and labelling cost will be

drastically increased. Therefore, in recent, a roll to roll (R2R) printing

process has been drawn a lot of attention to manufacture the tags through

an inline printing process so that chips, sensors, CPU and antenna can be

directly R2R printed on palstic or paper foils without any bonding and

labelling processes.

To employ R2R printing process to manufacture only RFID tags

without sensors, displays and CPU, four different major parts should be

simultaneously developed. First, materials for R2R printing antenna,

wires, thin film transistors, diodes, capacitors and resistors should be

first available. Second, R2R printers with overlay printing registration

accuray (OPA) of less than 10 µm to integrate a number of transistors

for multi-bit digital circuits should be developed. Third, inexpensive

rollable substrates with a relatively good surface roughness and less

coefficient of thermal expansion (CTE) should be available. Finally, a

new circuit design to efficiently utilize a less number of integrated

transistors to overcome the limit of the OPA of R2R printers should be

developed.

In this chapter, among four major parts for R2R printed RFID tags,

the new circuit design and performance of the designed circuit for R2R

printed RFID tags will be discussed based on our own R2R printed thin

films transistors (TFTs) on poly(ethylene terephtalate) (PET) foils with a

brief introduction on our materials, R2R printer and substrates to print

the digital circuit.