202IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 54, NO. 2, FEBRUARY 2007

Sheet-Type Braille Displays by Integrating Organic
Field-Effect Transistors and Polymeric Actuators
Yusaku Kato, Student Member, IEEE, Tsuyoshi Sekitani, Makoto Takamiya, Member, IEEE, Masao Doi,
Kinji Asaka, Takayasu Sakurai, Fellow, IEEE, and Takao Someya, Member, IEEE

Abstract—A large-area, flexible, and lightweight sheet-type
Braille display has been successfully fabricated on a plastic film byintegrating high-quality organic transistors and soft actuators. An
array of rectangular plastic actuators is mechanically processedfrom a perfluorinated polymer electrolyte membrane. A small
semisphere, which projects upward from the rubberlike surfaceof the display, is attached to the tip of each rectangular actuator.
The effective display size is 4 × 4 cm2 . Each Braille letter consistsof 3 × 2 dots and 24 letters; in other words, 6 letters × 4 lines canbe displayed. Pentacene field-effect transistors with top-contact
geometry have a channel length of 20 µm and a mobility of
1 cm2 /V · s. The Braille dots on one line are driven for 0.9 s. The
total thickness and weight of the entire device are 1 mm and 5.3 g,
respectively. The present scheme will enable people with visual
impairments to carry the Braille sheet display in their pockets andread Braille e-books at any time. Since all the device components
are manufactured on plastic films, these sheet-type Braille displays
are mechanically flexible, lightweight, shock resistant, and potentially inexpensive to manufacture; therefore, they are suitable formobile electronics.
Index Terms—Braille display, large-area electronics, organic
transistor, polymer actuator, tactile display.

I. INTRODUCTIONAN ORGANIC field-effect transistor (FET) [1]–[12] belongs to a new class of electronics that can be fabricateddirectly on plastic films at ambient temperatures; therefore, it
is mechanically flexible, lightweight, very thin, shock resistant,and easy to transport. It is potentially inexpensive since it can be
manufactured by low-cost processes using printing machines.
These attributes of organic transistors cannot be achieved easily
by the present silicon-based electronic materials.
Recent studies of organic transistors are driven by two major applications. The first includes flexible displays such as
paperlike displays or e-paper [1], [2]. The second includes
radio-frequency identification (RFID) tags [3], [4]. Since organic transistors can be manufactured by printing technologies[5], [6], they should facilitate the implementation of RFID tags
on packages.
Flexible large-area sensors are recently developed applications of organic transistors. The earliest example of an organic
transistor-based large-area sensor is a pressure sensor matrix.
Organic transistor active matrices are used to readout pressure
data from sensors. The new pressure sensor could be ideal forelectronic artificial-skin applications in the future generationsof robots [7], [8]. Another new development is a flexible,
large-area, and sheet-type image scanner; it comprises a twodimensional array of organic photodetectors coupled with anorganic transistor active matrix for data readout [9].
Organic transistors are also suitable for large-area actuators.
We have recently fabricated a prototype of a flexible, shockresistant, and lightweight sheet-type Braille display on a plastic
film by integrating high-quality organic FETs with soft actuators; this display was presented at the IEEE International Electron Device Meeting [10]. In this paper, we present a detailed
technical report on this new device. An array of rectangular
plastic actuators is processed from a perfluorinated polymer
electrolyte membrane. A small semisphere, which projects
upward from the rubberlike surface of the display, is attached tothe tip of each rectangular actuator. The effective display sizeis 4 × 4 cm2 . Each letter consists of 3 × 2 Braille dots, andthe total number of dots is 144; thus, 24 letters or 6 letters ×
4 lines can be displayed. Pentacene transistors with top-contact
geometry have a channel length of 20 µm and a mobility of
1 cm2 /V · s. The Braille dots on one line are driven for 0.9 s.
The total thickness and weight of the entire device are 1 mm
and 5.3 g, respectively. The present scheme will enable people
with visual impairments to carry the Braille sheet display intheir pockets and read Braille e-books at any time.

II. MANUFACTURING PROCESS
A. Device Structure and Principles

Manuscript received February 7, 2006. This work was supported in part by
JST/CREST, TOKUTEI (15073204), and IT program, MEXT. Y. Kato also
thanks JSPS Research Fellowships for their financial support. The review ofthis paper was arranged by Editor J. Kanicki.
Y. Kato, T. Sekitani, and T. Someya are with the Quantum-Phase Electronics
Center, School of Engineering, The University of Tokyo, Tokyo 113-8656,
Japan (e-mail: someya@ap.t.u-tokyo.ac.jp).
M. Takamiya and T. Sakurai are with the Center for Collaborative Research,
The University of Tokyo, Tokyo 153-8904, Japan.
M. Doi is with the Department of Applied Physics, School of Engineering,
The University of Tokyo, Tokyo 113-8656, Japan.
K. Asaka is with the National Institute of Advanced Industrial Science andTechnology (AIST), Osaka 563-8577, Japan.
Digital Object Identifier 10.1109/TED.2006.888678

The Braille sheet displays are manufactured by laminating
three layers: the organic transistor sheet, the polymeric actuator
sheet, and the cover layer. Since all the materials except themetal electrodes are made of soft materials, the entire system isthin, lightweight, and mechanically flexible (Fig. 1). A pictureof a Braille sheet display in plan view is shown in Fig. 1(b).
Some sections of the layers have been intentionally removed inorder to reveal the internal three-layer structure, although thesizes of all three layers are identical. Fig. 1(c) shows a circuit
diagram of the Braille display.

0018-9383/$25.00 © 2007 IEEE

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Fig. 2. Design. A cross-sectional illustration of a single Braille dot of thisdevice. An organic transistor is connected to a polymeric actuator with silver
paste patterned by a microdispenser. A semisphere is attached to the tip of eachactuator.

Fig. 1. Images of a Braille sheet display. (a) Image of the Braille sheet
display which is manufactured on a plastic film integrating the active matrixof organic transistors with polymer actuator array based on a perfluorinatedpolymer electrolyte membrane. The device is a thin, lightweight, flexile sheet
Braille display. (b) Picture of the device assembly. Some parts of the device
are removed intentionally to show inner structures of this device. This device
is composed of three layers, an organic transistor sheet, a polymeric actuator
sheet, and a cover layer. (c) Circuit diagram of the Braille sheet display. Eachpolymeric actuator is connected to one organic transistor. The vertical and thehorizontal lines represent bit and word lines, respectively.

Fig. 2 shows the cross-sectional structure of a single Braillecell comprising one transistor and one actuator. The manufacturing process flow will be explained in the next section. Whena voltage is applied to the polymeric actuators, the sheet-type
actuators bend, as shown in Fig. 2. The semisphere placedon the actuator rises with the voltage supply and pushes up a
rubberlike surface. An organic transistor active matrix is used
to address the pop-up dots.
B. Organic Transistors
The base films for the organic transistors are made of polyimide or poly(ethylenenapthalate) with a thickness of about
100 µm. The detailed manufacturing process flow is available
in [11]. The base film is coated with a 5-nm-thick chromium
adhesion layer and a 50-nm-thick gold layer. Then, a polyimide
precursor (Kemitite CT4112, Kyocera Chemical) is spin coatedand baked in a clean oven at 180 ◦ C for 1 h to form a gate
dielectric layer [11]. The thickness of the gate insulator is
240 nm. Next, a 50-nm-thick pentacene layer is deposited as achannel layer by using a vacuum chamber with a shadow mask.
The 50-nm-thick gold is evaporated through the metal mask toform the source and drain electrodes. The organic transistor
sheet is covered by an 8-µm-thick poly-chloro-para-xylylene(parylene) passivation layer. Parts of the parylene layers are
removed by a CO2 laser drilling machine to generate via
holes [12].
Fig. 3 shows three images of the organic transistor sheet ofdifferent magnifications: 1) the entire chip; 2) six transistors
required to display one Braille letter (six dots); and 3) one transistor. The channel length L and the width W of the transistors
are 20 µm and 49 mm, respectively, which corresponds to a
W/L ratio of 2450. This large W/L ratio is required to ensure
a good time response of the actuators, which will be explainedlater. The size of the entire active matrix is 4 × 4 cm2 , whilethat of a single transistor is 1.5 × 1.5 mm2 .
C. Polymeric Actuators
The thin-film actuators are made of an ionic polymer metalcomposite (IPMC) [13]. Several soft actuators, such as dielectric elastomers [14] and conjugated polymer actuators [15], areavailable; however, we used IPMCs as soft actuators for the
Braille displays because it is known to exhibit large displacements and high response rates.
By employing electroless plating, electrodes are formedon surfaces of a 300-µm-thick perfluoronated ion-exchange
membrane, Nafion (NE-1110, DuPont) [16]. Before the plating process, both surfaces of the membrane are roughened
with sandpaper in order to increase the net surface area.
The membrane is immersed in a dichloro-phenanthroline-gold(III)-chloride complex ([AuCl2 (phen)Cl]) solution overnight atroom temperature in order to impregnate the gold ion into
the membrane. It is then placed in sodium sulfite solution
at 60 ◦ C for 5 h to form electrodes on both surfaces of themembrane. This plating process is repeated five or six times.
The capacitance of the membrane increases with increasing
repetitions of the plating process [17]. The actuator sheet isimmersed in lithium chloride solution to exchange the protons

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Fig. 4. Plastic actuator array. Picture of whole sheet of polymeric actuators(12 × 12 array) and magnified image of actuators for one letter (3 × 2 dots).
The size of each actuator is 4 mm in length and 1 mm in width. A semisphere ofradius 0.9 mm is attached to the tip of each actuator. The scales for the pictureof whole sheet and magnified image are 2 cm and 2 mm, respectively.

Fig. 3. Organic transistor active matrix in the chip. (a) Pictures of a whole ofthe organic transistor active matrix sheet, which includes 144 transistors. The
scale is 1 cm. (144 dots) (b) Magnified view of transistor active matrix. The
white line indicates an area of transistors for switching one character. (six dots)
The scale is 5 mm. (c) A further magnified view of a single transistor. G, D,
and S indicate gate, drain, and source electrode, respectively. The channel
length and width are 20 µm and 49 mm, respectively. The scale is 1 mm.

inside the membrane with lithium ions. This process facilitatesa large displacement, high speed, and a large generating force.
The actuator sheet is mechanically processed using a numerically controlled (NC) cutting machine to form an array of
12 × 12 rectangular actuators whose size is 1 × 4 mm2 . Notethat in Fig. 4, the rectangular actuators are aligned alternately
and diagonally. Due to this unique design, the present actuator
array exhibits displacements, time responses, and forces ofactuators that are sufficient for Braille displays; this will be
explained later.
Each rectangular actuator remains connected to the parent
sheet while being isolated electrically. For the isolation, insulating grooves with a depth of 80 µm are prepared on one sideof the actuator sheet by using an NC drilling machine; the otherside is not processed and is used as a common electrode.
We describe a supplemental experiment for the insulating
groove. The groove is prepared on the surface of 1-mm-width
rectangular actuators, and the resistance between the two electrodes that are separated by this groove is measured by changing
the depth of the groove. As shown in Fig. 5, the two electrodes
are perfectly isolated when the depth exceeds 30 µm. In thismanner, all the 144 actuators on the same sheet are isolated
electrically and operated separately.

Fig. 5. Insulating grooves. Insulating property of insulating groove preparedon the actuator sheet. Two electrodes are perfectly isolated when the depth of
insulating groove exceeds 30 µm.

Plastic balls with a radius of 0.9 mm are polished to be usedas semispheres, which are attached by an adhesion bond on the
top of the actuators. Semispheres are used instead of spheres
because the former can be tightly bound to the surface of theactuator sheet. Moreover, their usage also leads to the reductionin the total thickness of the Braille displays.
D. Integration of Transistors With Actuators
The transistor and actuator sheets are laminated together
after their fabrication. In order to realize via interconnections
between the electrode pads of the transistors and the surface
electrodes of the actuators, anisotropic conductive tapes orsilver pastes patterned by a microdispenser are used. The

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205

laminated sheets are covered by a plastic frame made of
650-µm-thick poly(ethylenentereapthalate) whose surface iscoated by a 10-µm-thick polydimethylsiloxane (PDMS) film.
The PDMS layer is fluorinated by drop casting (Kanto Kasei
Ltd., HANARL RX-410) to obtain a smooth surface.
III. DEVICE CHARACTERISTICS
In this section, we report the characteristics of discrete
transistors and discrete actuators prior to integration. Then, wecharacterize the Braille cells that comprise transistors, actuators, and the rubberlike surface.
A. Organic Transistors
All electric measurements were performed in air by using
a semiconductor parameter analyzer (Agilent 4156 C). The
typical I–V characteristics are shown in Fig. 6(a) and (b).
The mobility in the saturation regime is 1 cm2 /V · s, and the6
ON / OFF ratio is 10 when the OFF current is defined as theminimum current with a positive voltage bias. In order to reduce
the operation voltage to 10 V, the thickness of the gate dielectric
layer is set to a value as small as 240 nm. A large current(∼ 600 µA) is obtained at low voltages (VGS = VDS = −10 V)
for the organic transistors.
As will be explained later in detail, IPMC-based actuators
are usually operated in wet conditions. We have monitored
the changes in the electric characteristics of organic transistors
floated in purified water. We have measured a test device, which
has different structural sizes, manufactured by the aforementioned process. For this device, the thickness of gate dielectric
layer is 580 nm and the channel width W and length L of thetransistor are 1 mm and 100 µm, respectively. As shown in
Fig. 6(c), the transistors continue to exhibit a large ON current
and small OFF current (ON/OFF = 104 ) after a period of three
weeks.
B. Polymeric Actuators
One of the actuators (1 × 4 mm2 ) is characterized before its
integration with the organic transistors. The rectangular voltage
of ±3 V is applied to the actuator at a repetition rate of 2 Hz.
The time response of the actuators is measured. Fig. 7(a) and(b) shows the voltage between the two actuator electrodes andthe displacement of the actuators, respectively, as a functionof time.
The displacement and the generating force of the actuators
are measured as a function of voltage for three actuators withidentical sizes of 1 × 4 mm2 and plotted in Fig. 7(c) and (d),respectively. The force was measured using a load cell. The
displacement and the generating force increase with the applied
voltage and peak at 0.4 mm and 1.5 gf, respectively, at 2.5 V.
Although the performance of the actuators depends on theirstructural parameters such as width, length, and thickness, thepresent design using actuators with a size of 1 × 4 mm2 exhibitsa good performance that is suitable for application in Braillesheet displays.

Fig. 6. Stand-alone organic transistors. (a) VDS –IDS characteristics of theorganic transistors measured by gate voltage bias VGS from 0 to −10 V witha step of −2 V. (b) VGS –IDS characteristic measured by VDS = −30 V andgate voltage bias VGS from 15 to −30 V. W and L are 49 mm and 20 µm,
respectively. The ON / OFF ratio exceeds 106 when the OFF current is definedas the minimum current at positive voltage bias. (c) Degradation of transistor
characteristics in wet condition. For this device, the thickness of gate dielectric
layer is 580 nm, and the channel width W and length L of the transistor are
1 mm and 100 µm, respectively. The ON current at VGS = VDS = −40 Vand minimum current at positive gate voltage bias of the organic transistor
with parylene passivation layer immersed in deionized water are measured. The
device exhibits no significant degradation over three weeks.

C. Braille Cells
In this section, one of the completed Braille cells is characterized. The time response of the actuators is measured
at different gate voltages—VGS = 0, −10, −20, and −30 V.
The power supply voltage (VDD ) is −10 V for the up statesand 10 V for the down states. Fig. 8(a) and (b) shows the206IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 54, NO. 2, FEBRUARY 2007

Fig. 7. Stand-alone plastic sheet actuators. A stand-alone polymeric actuator of 4 mm in length and 1 mm in width is measured. When a series of rectangularvoltage of ±3 V is input, the frequency response of the actuators extends up to 2 Hz. The voltage between two electrodes of actuator and displacement of actuatoris shown in (a) and (b) in the same time scale, respectively. (c) The displacement and (d) the generating force of an actuator are plotted as a function of the input
voltage.

voltage between two actuator electrodes and the displacementof the actuators, respectively, as a function of time. Fig. 8(c)is the magnified view of the initial elevation of the Braille dot.
The time required to obtain a displacement of 0.2 mm decreases
with the increase in VGS and reduces to 0.9 s at VGS = −30 V,
thus indicating that a frame rate of 1 Hz would be feasible.
We investigate the duration for which the Braille dots canmaintain their displacement or upward state. A voltage VDDof −10 V is applied for an initial several seconds, and it isthen removed to obtain a ground state. As shown in Fig. 8(d),the displacement gradually decreases when VDD is removed.
However, the decay time is of the order of several minutes,
which is considerably greater than the time required for visually
impaired individuals to read Braille. When a longer hold time isrequired, the device should be refreshed at intervals of several
minutes.
Fig. 9(a) shows one of the Braille dots moving upward anddownward. Four Braille letters displayed by the present device
are shown in Fig. 9(b). We will describe the readability of thepresent device in the Discussion section.
IV. DISCUSSION
In the present device, the response of the actuators is limitedby the time required to charge and discharge the actuator
electrodes, which is analogous to large capacitors. In order toobtain a faster response, it is very important to increase themagnitude of current flowing into the actuator electrodes. In
Fig. 10, we plot IDS of the transistor at VDS = −10 V andthe velocity of the actuators at VDD = −10 V as functionsof VGS . Here, the velocity is defined as the displacement of

0.2 mm divided by the time required to obtain a displacementof 0.2 mm. As shown in Fig. 10, the IDS curve is traced overthe velocity data points. This result indicates that the speed ofthis device is not limited by the high-frequency response of thetransistors or actuators but by the magnitude of current flow.
Therefore, a larger W/L ratio of the transistors facilitates theincrease in the response time.
We briefly describe the readability of the present Brailledisplay. Four visually impaired individuals participated in thereading tests. When the operator input “Na” and “Wa” in
the Japanese Braille format, all four individuals were able
to recognize the letters correctly. This result shows that thegenerating force and the displacement of this device are sufficient to facilitate reading by the visually impaired. Further, it
demonstrates the feasibility of this new design that integrates
organic transistors and polymer actuators for realizing Braillesheet displays.
However, it is known that the ability of reading Braillevaries across the visually impaired and, in general, a larger
displacement and a larger force help them in reading Braillemore easily. In particular, the variations in the displacement andthe generating force of the Braille dots must be minimized forbetter readability, although the present device shows fairly large
performance variations, as shown in Fig. 7. These variations
may be ascribed to the unevenness in the electroless platingprocess and/or the fluctuations in the size of the actuators thatarise due to the inaccuracy of the mechanical process. Theseimperfections would be removed by optimizing the process
conditions.
The issues that remain to be addressed are the reliability andstability of the device. The IPMC-based actuators are usually

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Fig. 9. Display operation. (a) Magnified pictures of one Braille dot moving
upward and downward. The scale is 1 mm. (b) Pictures of Braille sheet display
showing the characters “l,” “w,” “b,” and “f” in the American Braille style.

Fig. 8. Braille cells. The displacement of a Braille cell when gate voltage bias
VGS = 0, −10, −20, and − 30 V is measured as a function of time. The power
supply voltage VDD is rectangular voltage of ±10 V. The voltages between
two electrodes of actuator and displacement of actuator are shown in (a) and(b), respectively. (c) Magnified view of initial rise retraced from (b). The risetime required to displace a Braille dot from 0 to 0.2 mm becomes 0.9 s at
−30 V. (d) Retention property of Braille dot. A voltage VDD of −10 V isapplied for initial several seconds, and voltage is changed to ground state at
the time indicated by the arrows. The displacement of actuator is plotted as afunction of time.

operated in wet conditions, while organic transistors degrade
easily in moisture and/or oxygen. The organic transistors withparylene passivation layers can function for more than three
weeks under humid conditions, as shown in Fig. 6(c); however,a longer lifetime is required for most of their practical applications. The straightforward approach toward suppressing suchdegradations is to employ more sophisticated encapsulation
techniques. Alternately, IPMC-based actuators can operate inambient air when their membranes are filled with an ionicliquid [18]. Another option involves the use of carbon nanotube
actuators that are soft, yet functional in air [19].

Fig. 10. Relationship between displacement of actuator and current. Twoexperimental results are plotted; the one is IDS –VGS transistor characteristic(VDS = −10 V) and the other is the effective velocity of the dot as a functionof VGS (VDD = −10 V). The velocity of the dot is limited by the magnitudeof the current.

Commercial Braille displays that utilize piezoelectric orsolenoid actuators are available. Such actuators can control
displacement with a high accuracy and also obtain large forces;
however, their miniaturization is complicated. Recently, conductive polymer actuators [20] and dielectric elastomer actuators [21] have been proposed as actuators for Braille displays.
However, the displacement of conductive polymer actuators
was not sufficiently large, and the driving voltage of the elastomer actuators was high (> 100 V).
V. CONCLUSION
A lightweight, thin, and flexible sheet-type Braille display
has been fabricated on a plastic film by integrating highquality organic FETs and IPMC-based polymer actuators. The
effective display size is 4 × 4 cm2 and 24 Braille letters,

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6 letters × 4 lines, can be displayed. The total thickness andweight of the entire device are 1 mm and 5.3 g, respectively. The
new design in this paper offers an attractive scheme for reducing
the thickness and weight of Braille displays and yet maintains areasonable performance. The sheet-type Braille displays can beeasily carried in pockets; therefore, they are suitable for mobile
applications such as Braille e-books. It is also expected that the
sheet-type Braille can be easily implemented in many digitaland information appliances including cell phones without necessitating major changes in the design of the parent appliances.
Thus, Braille would be more conveniently used by the visually
impaired in various situations.
ACKNOWLEDGMENT
The authors would like to thank Y. Noguchi, K. Hizu,
X. Wang, K. Takenoshita, Y. Takamatsu, S. Nakano, andK. Fukuda for their assistance of manufacturing process oforganic transistors, K. Nakamura and Dr. T. Yamaue for fruitful
discussions on soft actuators. The authors would also like tothank Prof. Y. Nakano and the members of Barrier-free Projectat University of Tokyo for their cooperation to conduct thereading test and valuable advice.
R EFERENCES[1] J. A. Rogers, Z. Bao, K. Baldwin, A. Dodabalapur, B. Crone, V. R. Raju,
V. Kuck, H. Katz, K. Amundson, J. Ewing, and P. Drzaic, “Paperlike electronic displays: Large-area rubberstamped plastic sheets of electronics and microencapsulated electrophoretic inks,” Proc. Nat. Acad.
Sci., vol. 98, no. 9, pp. 4835–4840, Apr. 2001.
[2] H. Edzer, A. Huitema, G. H. Gelinck, J. B. P. H. van der Putten, K. E.
Kuijk, C. M. Hart, E. Cantatore, and D. M. de Leeuw, “Active-matrix
displays driven by solution-processed polymeric transistors,” Adv. Mater.,vol. 14, no. 17, pp. 1201–1204, Sep. 2002.
[3] P. F. Baude, D. A. Ender, M. A. Haase, T. W. Kelley, D. V. Muyres, andS. D. Theiss, “Pentacene-based radio-frequency identification circuitry,”
Appl. Phys. Lett., vol. 82, no. 22, pp. 3964–3966, Jun. 2003.
[4] R. Rotzoll, S. Mohapatra, V. Olario, R. Wens, M. Grigas, O. Shchekin,
K. Dimmler, and A. Dodabalapur, “13.56 MHz organic transistor based
rectifier circuits for RFID tags,” presented at the Material ResearchSociety Spring Meeting, San Francisco, CA, 2005, session I 11.6.
[5] A. C. Arias, S. E. Ready, R. Lujan, W. S. Wong, K. E. Paul, A. Salleo,
M. L. Chabinyc, R. Apte, R. A. Street, Y. Wu, P. Liu, and B. Ong,
“All jet-printed polymer thin-film transistor active-matrix backplanes,”
Appl. Phys. Lett., vol. 85, no. 15, pp. 3304–3306, Oct. 2004.
[6] H. Sirringhaus, T. Kawase, R. H. Friend, T. Shimoda, M. Inbasekaran,
W. Wu, and E. P. Woo, “High-resolution inkjet printing of allpolymer transistor circuits,” Science, vol. 290, no. 5499, pp. 2123–2126,
Dec. 2000.
[7] T. Someya, T. Sekitani, S. Iba, Y. Kato, H. Kawaguchi, and T. Sakurai,“A large-area, flexible pressure sensor matrix with organic field-effecttransistors for artificial skin applications,” Proc. Nat. Acad. Sci., vol. 101,
no. 27, pp. 9966–9970, Jul. 2004.
[8] T. Someya, Y. Kato, T. Sekitani, S. Iba, Y. Noguchi, Y. Murase,
H. Kawaguchi, and T. Sakurai, “Conformable, flexible, large-area networks of pressure and thermal sensors with organic transistor active
matrixes,” Proc. Nat. Acad. Sci., vol. 102, no. 35, pp. 12 321–12 325,
Aug. 2005.
[9] T. Someya, Y. Kato, S. Iba, H. Kawaguchi, and T. Sakurai, “Integrationof organic field-effect transistors with organic photodiodes for a largearea, flexible, and lightweight sheet image scanner,” IEEE Trans. Electron
Devices, vol. 52, no. 11, pp. 2502–2511, Nov. 2005.
[10] Y. Kato, S. Iba, T. Sekitani, Y. Noguchi, K. Hizu, X. Wang,
K. Takenoshita, Y. Takamatsu, S. Nakano, K. Fukuda, K. Nakamura,T. Yamaue, M. Doi, K. Asaka, H. Kawaguchi, M. Takamiya, T. Sakurai,
and T. Someya, “Flexible, lightweight Braille sheet display with plastic actuators driven by an organic field-effect transistor active matrix,”
in IEDM Tech. Dig., 2005, pp. 105–108.

[11] Y. Kato, S. Iba, R. Teramoto, T. Sekitani, T. Someya, H. Kawaguchi,
and T. Sakurai, “High mobility of pentacene field-effect transistors withpolyimide gate dielectric layers,” Appl. Phys. Lett., vol. 84, no. 19,
pp. 3789–3791, May 2004.
[12] S. Iba, Y. Kato, T. Sekitani, H. Kawaguchi, T. Sakurai, and T. Someya,“Use of laser drilling in the manufacture of organic inverter circuits,”
Anal. Bioanal. Chem., vol. 384, no. 2, pp. 374–377, Jan. 2006.
[13] M. Shahinpoor, Y. Bar-Cohen, J. O. Simpson, and J. Smith, “Ionicpolymer-metal composites (IPMCs) as biomimetic sensors, actuators
and artificial muscles—A review,” Smart Mater. Struct., vol. 7, no. 6,
pp. R15–R30, Dec. 1998.
[14] R. Pelrine, R. Kornbluh, Q. Pei, and J. Joseph, “High-speed electricallyactuated elastomers with strain greater than 100%,” Science, vol. 287,
no. 5454, pp. 836–839, Feb. 2000.
[15] S. Hara, T. Zama, W. Takashima, and K. Kaneto, “Artificial muscles basedon polypyrrole actuators with large strain and stress induced electrically,”
Polym. J., vol. 36, no. 3, pp. 151–161, Feb. 2004.
[16] N. Fujiwara, K. Asaka, Y. Nishimura, K. Oguro, and E. Torikai, “Preparation of gold-solid polymer electrolyte composites as electric stimuliresponsive materials,” Chem. Mater., vol. 12, no. 6, pp. 1750–1754,
May 2000.
[17] K. Onishi, S. Sewa, K. Asaka, N. Fujiwara, and K. Oguro, “Morphologyof electrodes and bending response of the polymer electrolyte actuator,”
Electrochim. Acta, vol. 46, no. 5, pp. 737–743, Jan. 2001.
[18] M. D. Bennett and D. J. Leo, “Ionic liquids as stable solvents forionic polymer transducers,” Sens. Actuators A, Phys., vol. 115, no. 1,
pp. 79–90, Sep. 2004.
[19] T. Fukushima, K. Asaka, A. Kosaka, and T. Aida, “Fully plastic actuator
through layer-by-layer casting with ionic-liquid-based bucky gel,” Angew.
Chem. Int. Ed., vol. 44, no. 16, pp. 2410–2413, Apr. 2005.
[20] G. M. Spinks, G. G. Wallace, J. Ding, D. Zhou, B. Xi, and J. Gillespie,“Ionic liquids and polypyrrole helix tubes: Bringing the electronic Braillescreen closer to reality,” in Proc. SPIE Smart Struct. and Mater.: EAPAD,
2003, pp. 372–380.
[21] S. Lee, K. Jung, J. Koo, S. Lee, H. Choi, J. Jeon, J. Nam, and H. Choi,“Braille display device using soft actuator,” in Proc. SPIE Smart Struct.
and Mater.: EAPAD, 2004, pp. 368–379.

Yusaku Kato (S’05) was born in Tokyo, Japan,
in 1981. He received the M.S. degree in applied
physics from the University of Tokyo, in 2006, where
he is currently working toward the Ph.D. degree inapplied physics.
He is currently involved in the development of the
new large-area integrated devices that are composedof organic transistors and other function elements.
Mr. Kato is a student member of the Materials
Research Society (MRS) and the Japanese Societyof Applied Physics. He is also a member of JSPS
Research Fellowships.

Tsuyoshi Sekitani was born in Yamaguchi, Japan,
in 1977. He received the B.S. degree from Osaka
University, Osaka, Japan, in 1999 and the Ph.D.
degree in applied physics from University of Tokyo,
Tokyo, Japan, in 2003.
From 1999 to 2003, he was with the Institutefor Solid State Physics (ISSP), University of Tokyo,
where he developed measurement techniques inmagnetic fields up to 600 T and studied the solidstate physics of condensed matter, especially inhigh-Tc superconductors. Since 2003, he has been a
Research Associate with the Quantum-Phase Electronics Center, University ofTokyo. His current object of physics research is in organic semiconductors andorganic-FET devices.
Dr. Sekitani is a member of the American Physical Society (APS), theMaterials Research Society (MRS), the Physical Society of Japan, and theJapanese Society of Applied Physics.

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Makoto Takamiya (S’98–M’00) received the B.S.,
M.S., and Ph.D. degrees in electronic engineeringfrom the University of Tokyo, Tokyo, Japan, in 1995,
1997, and 2000, respectively.
In 2000, he joined NEC Corporation, Japan, where
he was engaged in the circuit design of high-speed
digital LSIs and developed the field of on-chip measurement macros to solve the power integrity issues.
In 2005, he joined University of Tokyo, where he isan Associate Professor of VLSI Design and Education Center. His research interests include power andsignal integrity issues in LSIs, low-power RF integrated circuits, low-power
digital circuits, and large-area electronics with organic transistors.

Takayasu Sakurai (S’77–M’78–SM’01–F’03) received the Ph.D. degree in electrical engineeringfrom the University of Tokyo, Tokyo, Japan, in 1981.
In 1981, he joined Toshiba Corporation, where hedesigned CMOS DRAM, SRAM, RISC processors,
DSPs, and SoC Solutions. He has worked extensively on interconnect delay and capacitance modeling known as Sakurai model and alpha power-law
MOS model. From 1988 to 1990, he was a Visiting
Researcher with University of California at Berkeley,
where he conducted research in the field of VLSICAD. Since 1996, he has been a Professor with University of Tokyo, working
on low-power high-speed VLSI, memory design, interconnects, and wirelesssystems. He has published more than 400 technical papers including 70 invited
papers and several books, and has filed more than 100 patents. He is also a
consultant to U.S. startup companies.
Prof. Sakurai served as a Conference Chair for IEEE/JSAP Symposium
on VLSI Circuits, and IEEE ICICDT, a Vice Chair for ACM/IEEE Asia andSouth Pacific DAC, and a program committee member for IEEE International
Solid-State Circuits Conference, IEEE Custom Integrated Circuits Conference,
ACM/IEEE Design Automation Conference, ACM/IEEE International Conference on CAD, ACM FPGA workshop, ACM/IEEE International Symposiumon Low-Power Electronics and Design, ACM/IEEE International Workshop on
Timing Issues, and other international conferences. He was a plenary speaker
for the 2003 ISSCC. He is an elected AdCom member for the IEEE SolidState Circuits Society and an IEEE Circuits and Systems Society Distinguished
Lecturer.

Masao Doi received the degree from the Department
of Applied Physics, University of Tokyo, Tokyo,
Japan, in 1970.
He developed his academic career with Tokyo
Metropolitan University and Nagoya University before he moved to the current position. He has beenworking on the flow and deformation of soft materials such as polymers, gels, and colloids and is now
interested in the coupling of deformation, diffusion,and electric current taking place in the materials.

Kinji Asaka received the Ph.D. degree in sciencefrom Kyoto University, Kyoto, Japan, in 1991.
He is currently a Group Leader with the Artificial Cell Research Group, Research Institute for
Cell Engineering of National Institute of Advanced
Industrial Science and Technology (AIST), Osaka,
Japan. His current research interests include interfacial electrochemistry and polymer actuators.
Dr. Asaka is a member of the Society of Polymer
Science, Japan, and The Society of Instrument andControl and Engineers.

Takao Someya (M’03) received the Ph.D. degree
in electrical engineering from University of Tokyo,
Tokyo, Japan, in 1997.
In 1997, he joined Institute of Industrial Science(IIS), University of Tokyo, as a Research Associate
and was appointed to be a Lecturer with the Research Center for Advanced Science and Technology (RCAST), University of Tokyo, Tokyo, Japan,
in 1998, and an Associate Professor with RCASTin 2002. From 2001 to 2003, he worked with the
Nanocenter (NSEC) of Columbia University andBell Labs-Lucent Technologies, as a Visiting Scholar. Since 2003, he has beenan Associate Professor with the Department of Applied Physics and QuantumPhase Electronics Center, University of Tokyo. His current research interests
include organic transistors, flexible electronics, plastic integrated circuits,
large-area sensors, and plastic actuators.
Prof. Someya is a member of the IEEE Electron Devices Society, the Materials Research Society (MRS), and the Japanese Society of Applied Physics. He
serves as a subcommittee member for IEEE/IEDM and a program cochair for
the Third Organic Microelectronics Workshop.