Design of Large Area Electronics with
Organic Transistors
Makoto Takamiya, Koichi Ishida, Tsuyoshi Sekitani, Takao Someya, and Takayasu Sakurai
University of TokyoTokyo, Japan
Table I. Comparison between organic FETs (OFETs) developed in our groupand the state-of-the-art 45-nm silicon MOSFETs.

Abstract— Organic electronics is attracting a lot of attention forlarge-area pervasive electronics applications, because organic
transistors can be fabricated using printing technologies on
arbitrary substrates and this enables both high-throughput andlow-cost production. In this paper, some examples of the large
area electronics with the organic transistors including a wirelesspower transmission sheet and a communication sheet arepresented. Challenges for future large area electronics are also
described.

I.

OFETs

INTRODUCTION

Organic electronics is attracting a lot of attention for largearea pervasive electronics applications, because organic
transistors can be fabricated with printing technologies onarbitrary substrates, enabling both high-throughput and lowcost production. In this paper, some examples of large area
electronics using organic transistors are shown. Section II
describes the advantage of the organic electronics over silicon
VLSI’s and shows the reason why large area applications are
suitable for organic transistors. Section III presents applicationsof large area electronics including a wireless powertransmission sheet and a communication sheet. Section IV
describes challenges for future large area electronics and someconcluding remarks are given in Section V.
II.

Minimum gate length

20 μm

45 nm

Mechanical flexibility

Flexible

Very limited

Normalized ON current

3 nA / μm @ 3 V

1 mA / μm @ 1 V

Gate delay

0.1 s @ 3 V

10 ps @ 1 VCost / area

LowHigh

Cost / transistor

HighLow

LifetimeMonths

Years

flexibility and the low cost per area, is a good application of theOFETs. Intense research and development work is thus
focusing on large area devices based on organic materials suchas an organic electroluminescence (EL) displays, e-paper,organic EL lighting, organic solar cells, and human-size sensor
and actuator devices.

LARGE AREA ELECTRONICS WITH ORGANICTRANSISTORSIn order to find the suitable applications of organicelectronics, the advantages of this technology overconventional electronics should be clarified. Table I shows acomparison between our organic FETs (OFETs) and state-ofthe-art 45-nm silicon MOSFETs. OFETs are flexible, because
OFETs are fabricated on a film. Low voltage operation (3V) ispossible already using organic CMOS technology. The gate
delay of the OFETs, however, is 1010 times larger than that ofthe silicon MOSFETs, because the minimum gate lenght ofOFETs is 440 times larger than that of the silicon MOSFETs
and the on-current of OFETs is 1/300000 of that of the silicon
MOSFETs (mostly due to the much lower mobility of organic
semiconductors). The device lifetime of OFETs is severalmonths, while that of the silicon MOSFETs is more than 10years, because OFETs are chemically degraded by the oxygenand moisture in the atmosphere. The cost per area of OFETs islower than that of the silicon MOSFETs, while the cost pertransistor of OFETs is higher than that of the silicon MOSFETs.
Therefore, large area electronics, which takes advantage of the

978-1-4244-8192-7/10/$26.00 ©2010 IEEE

Si MOSFETs

500Fig. 1 shows the relation between conventional ITapplications based on silicon VLSI and human interface
applications using large area electronics. The IT applications
such as computers and communications are supported by theconventional silicon VLSI’s, because silicon MOSFETs arefast and the cost per transistor (=cost per function) is low. In
contrast, human interface applications such as human interfaces
and ambient intelligence can well be supported by large area
electronics with OFETs, because OFETs are flexible and theDisplay

E-paper
Education

Illumination
IT applications basedon silicon VLSI’sPowersupplyCommunication

Actuator

Solar cellSensorHuman interface applications
based on large area electronics
Fig.1 Relation between conventional IT applications using the silicon VLSIand human interface applications using large area electronics.

E-skin ScannerEMIBrailledisplay

Power Communication
sheet

User Customizable
Logic Paper

Fig.2 Examples of large area electronics applications. An E-skin is a sheet containing an array of pressures sensors and OFETs. A sheet scanner is a sheet
integrating an array of photodetectors and OFETs. An EMI measurement sheet is a sheet supporting an array of silicon VLSI circuits and OFETs. A Brailledisplay is a sheet integrating an array of plastic actuators and OFETs. A wireless power transmission sheet and a communication sheet combine on foil an array ofcoils, plastic MEMS switches, and OFETs. User Customizable Logic Paper can enable users to fabricate custom integrated circuits by printing interconnects withat-home ink-jet printers for the prototyping of large-area electronics and educational purposes.

communication between so many devices will be prohibitively
high.

cost per area is low. Thus silicon VLSI and OFETs are notcompeting technologies but more complement each other. By
combining silicon VLSI’s and OFETs, large area electronics
has the potential to expand both the application field and themarket size of electronic industry. Therefore, the developmentof the large area electronics which sophisticatedly combines
silicon VLSI’s and OFETs is strategically very important.
III.

To solve these problems, both a wireless powertransmission sheet and a communication sheet have beendeveloped. These sheets are made with plastic MEMS switches
and organic FET’s as printable low-cost and large-area
electronics can be embedded in furniture, walls and ceiling.
These sheets detect the position of the electronic device placed
nearby and provide the wireless power supply and low-power
wireless communication.

APPLICATIONS OF LARGE AREA ELECTRONICS

A. Examples of Large Area Electronics Applications
Fig. 2 shows show examples of large area electronics
applications. An E-skin [1-3] is a sheet containing an array ofpressures sensors and OFETs. A sheet scanner [4-7] is a sheet
integrating an array of photodetectors and OFETs. An EMI
measurement sheet [8-9] is a sheet supporting an array ofsilicon VLSI circuits and OFETs. A Braille display [10-13] is asheet integrating an array of plastic actuators and OFETs. A
wireless power transmission sheet [14-15] and acommunication sheet [16-19] combine on foil an array of coils,
plastic MEMS switches, and OFETs. User Customizable Logic
Paper (UCLP) [20] can enable users to fabricate custom
integrated circuits by printing 200µm wide interconnects withat-home ink-jet printers for the prototyping of large-area
electronics and educational purposes. The E-skin, the sheet
scanner, and the EMI measurement sheet are examples ofsensor applications. The Braille display is an actuator. The
wireless power transmission sheet and the communication
sheet are possible human-size IT applications and details areshown in the next section.

a) Wireless Power Transmission Sheet
A pictorial view of the wireless power transmission sheet[14-15] is shown in Fig. 3. The developed power transmission
sheet detects the position of the electronic devices on the sheet
and delivers power as EM waves. The sheet is flexible, large
area, and can be manufactured at low cost, because it isfabricated using a printing process on a polyimide film. The
principle of the wireless power transmission is based on anarray of transmission coils (TX-coil) made on the plastic sheet
which are selectively driven by plastic MEMS switches and arecoupled magnetically with a receiver coil (RX-coil) mounted
on the power-receiving object. The typical problem of wirelesspower transmission using electromagnetic induction is theefficiency loss due to the displacement between the TX-coil

B. Ubiquitous Power Supply and Communications
In future ubiquitous electronics, also known as ambient
intelligence, 1000 to 10000 electronic devices will be
distributed around the user’s environment and will contributeto security, promote healthcare and welfare, and provide
entertainment and convenience. In the ubiquitous electronics
environment, distributing power supply to the electronic
devices and ensuring communication between them are serious
problems. This is because battery replacement is not acceptablein this scenario and the power consumption for wirelessWireless transmission

Contactless position sensing

Large-area & low-cost

Lightweight & flexible

Fig.3 Overview of the developed wireless power transmission sheet.

501

RX LSITX LSI
TXpadsIn the wall

Capacitivecoupling

RX pads

Wall-mounted TV
Cell-phone & PC

DatainIn the table
Communication sheet(Only pads andinterconnects)

Ambient
illumination
Home-carerobot

Vacuum cleaner

power performance of wireline communication. The sheet
enables multiple electronic objects scattered over tables, walls,
and ceilings to communicate contactlessly with each other by
establishing communication paths without cumbersome
physical connections.
Fig. 6 shows a measurement setup of the communication
sheet. The TX/RX Si chips are bonded to the TX/RX pads on
the TX/RX sheet, and the pads are capacitively coupled to thecommunication sheet. In this measurement, to check thefeasibility of the communication through the communication
sheet, the MEMS switching matrices, the organic nonvolatilememory array, and the position-detection coil array are notincluded, and the communication route is laid out as a 60 cm
hard-wired connection. A 100-kb/s communication at 10.7µW
was demonstrated, which corresponds to 107 pJ/bit. The
developed transceiver [17, 19] in 0.18-µm CMOS with a dataedge-signaling transmitter and DC power-free pulse detector
contributes to the low power communication.

Fig. 4 shows a mock-up of expected applications of thewireless power transmission sheet. The sheet embedded in thewalls delivers power wirelessly to a wall-mount TV. The sheet
embedded in the table delivers power wirelessly to a cell phone
and a laptop PC. The sheet embedded in the floor delivers
power wirelessly to a moving home-care robot, a vacuum
cleaner, and an ambient illumination. In this way the wirelesspower transmission sheet, an example of large area electronics
made possible by OTFT technology, will enable ubiquitouselectronics.
b) Communication Sheet
An overview of the communication sheet that our groupdeveloped [16-19] is shown in Fig. 5. By combining meterscale wireline communication and micrometer-scale wirelesscapacitive-coupling communication, the communication sheet
combines the mobility of wireless communication and the low-Security,
Frees-up RF Band

100kbps

Fig.6
Measurement setup of the communication sheet. A 100-kb/s
communication at 10.7µW was demonstrated at a distance of 60 cm.

and the RX-coil. The segmentation and selective activation ofTX-coils introduced in this approach greatly reduce efficiency
loss. Position detection of the receiving object is needed for theselective activation of TX-coils. This is achieved scanning
through many TX-coils and measuring the antenna impedanceof the TX-coil to detect if an RX-coil is placed nearby.

μm-scalewireless

0110010101

60cm

In the floor

Fig.4 Expected applications of the wireless power transmission sheet.

Low Cost, Flexible

Dataout

IV.

CHALLENGES FOR FUTURE LARGE AREA ELECTRONICS

Several challenges for the future large area electronics are
itemized below.

Mobility

Wireless•

Improvements of organic device reliability are required.

•Variability of organic devices should be reduced.

•Faster operation speed of organic devices without
increasing the manufacturing cost is required.

•Circuit and system-level design to solve the above
issues.

The reliability of organic devices has been rapidly
improved by the advancement in encapsulation technologies.
Just as VLSI technologies have reduced the variability ofsilicon MOSFETs in past 40 years, the variability of organic
devices will be reduced by the improvement of themanufacturing process. Faster operation speed of organic
devices is required to extend the applications. Theminiaturization of organic FETs is a straightforward approach
to increase the speed. The increasing manufacturing cost withmeter-scale wireline

Low Powercommunication

Fig.5 Overview of the developed communication sheet.

502

is miniaturization, however, should be avoided to maintain thelow-cost advantage of organic devices. Improvements inprocess and device as well as circuit and system-level design
are required to solve the reliability, variability, and low speed
issues in organic devices.
V.

SUMMARY

Large area electronics, which takes advantage of theflexibility and the low cost per area, is a good application ofOFETs. By combining the silicon VLSI’s and OFETs, large
area electronics has the potential to expand both the application
field of electronics and the total market of electronic industry.
Therefore, the development of the large area electronics which
sophisticatedly combines the silicon VLSI’s and the OFETs isof great scientific and commercial interest.
ACKNOWLEDGMENT
This work was partially supported by CREST/JST, theGrant-in-Aid for Scientific Research, Special Coordination
Funds for Promoting and Technology, and NEDO.
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