Flexible, Large-Area, and Distributed Organic
Electronics Closely Contacted with Skin forHealthcare Applications
Makoto Takamiya1,2, Hiroshi Fuketa1,2, Koichi Ishida1,3, Tomoyuki Yokota1,2, Tsuyoshi Sekitani1,2,4, Takao Someya1,2,and Takayasu Sakurai1,2
1

University of Tokyo, Tokyo, Japan
2
JST/ERATO, Tokyo, Japan3
Now with Dresden University of Technology, Dresden, Germany4
Now with Osaka University, Osaka, Japan
and/or actuator array and is suitable for the wearingunconscious devices. Fig. 1 shows our developed flexible andlarge-area applications using organic transistors [1-11]. In thispaper, new healthcare applications including an insole
pedometer with piezoelectric energy harvester, a surface
electromyogram measurement sheet for the prosthetic handcontrol, and a flexible wet sensor sheet to detect the urinationin diapers are shown. New design solutions for the organic
electronics are also shown.

Abstract— Flexible, large-area, and distributed sensor and/oractuator array closely contacted with the human skin are humanfriendly and sophisticated tools for biomedical and healthcare
applications. In this paper, new applications and design solutionsin organic electronics are shown. In an insole pedometer withpiezoelectric energy harvesters, an all-pMOS negative voltage
generator for a pseudo-CMOS inverter is shown. In a surface
electromyogram measurement sheet for the prosthetic handcontrol, a post-fabrication select-and-connect method to reduce
the transistor mismatch is shown. In a flexible wet sensor sheet todetect the urination in diapers, ESD protection with organic
schottky diodes is shown.

I.

II.

INTRODUCTION

A. Overview of Insole Pedometer
Fig. 2 shows a photograph of the proposed insolepedometer [9] including the piezoelectric energy harvester andthe 2V organic PMOS rectifier and counter. A polyvinylidene
difluoride (PVDF) sheet is used as the piezoelectric energy
harvester. Twenty-one rolls of PVDF film are embedded in theinsole. Each time the insole is pressed by the foot during
walking, the harvested energy is rectified by the organic
rectifier and the number of the steps is counted by the organic

Wearing-unconscious devices are required for biomedicaland healthcare applications, because bulky devices closelycontacted with the human skin irritate users. The organic
electronics enables flexible, large-area, and distributed sensor

e-skin[1] Scanner[2]Brailledisplay[3]WirelessPower[4]INSOLE PEDOMETER WITH PIEZOELECTRIC ENERGYHARVESTER [9]2V organic PMOS
analog circuits

Communication[5]2V organic
pseudo-CMOS
logic circuits
EMI
User customizable
Measurement[6]logic paper[7]22cm100-V ACenergy meter[8]PVDF sheet(Energy harvester)
Insole pedometer[9] Electromyogram[10]Flexible PCB(Polyimide)

Wet sensor[11]Fig. 1. Developed flexible and large-area applications usingorganic transistors [1-11].

978-1-4799-4132-2/14/$31.00 ©2014 IEEE

Fig. 2. Insole pedometer with piezoelectric energy harvester.

829

VDD≈2VPVDF

≈2V

≈2V

All-PMOS
full-wave
rectifier

All-PMOS negative ≈-2V
voltage generator
0V

0V
PVDF
0V

≈2V
≈-2V
Pulse shaping(Pseudo-CMOS
Schmitt trigger)

generated by a charge pump and is applied as the bias ofPseudo-CMOS inverters.

Pulse

14bit
pseudoCMOS
stepcounter(Gateboosted
PMOSswitches)

Figs. 5(a) and (b) shows a schematic and a photo of theproposed all-PMOS negative voltage generator, respectively,
which consists of a Pseudo-CMOS inverter, two diodeconnected PMOS transistors, and two MIM capacitors. The
measured waveforms are shown in Fig. 6. The output voltage(VOUT) of the negative voltage generator is -1.6V in the case of10Hz clock pulses and can provide a power of at least 10µWpower to the load circuit.

redaertaadlanretxeoT

VDD(2V)
Pulse0V0V470nFFig. 3. Block diagram of insole pedometer.
counter.

0V 0V0VFig. 3 shows a block diagram of the proposed organic
insole pedometer. It consists of four circuit blocks. The allPMOS full-wave rectifier supplies a voltage VDD ofapproximately 2V to all circuit blocks. In the clock generator,
the output of the PVDF harvester is half-wave-rectified and a
Schmitt trigger inverter converts the half-wave-rectified signal
into a clock signal. The generated clock signal is sent to boththe PMOS negative voltage generator and a 14-bit PseudoCMOS counter with gate-boosted PMOS switches. The
negative voltage generator supplies a voltage VSS (e.g., -2V) tothe counter.
B. All-PMOS Negative Voltage Generator for Pseudo-CMOS
Inverter
In organic circuit design, PMOS-only circuits are often
used, because the mobility of PMOS transistors is much higher
than that of NMOS transistors in our process. As shown in Fig.
4, a Pseudo-CMOS inverter [9] that consists of four PMOS
transistors has high gain, but it requires a negative voltage bias.
In energy-harvesting applications, however, a single power
supply is typical. Therefore, in this work, to increase the noisemargin of PMOS-only logic circuits, a negative voltage isCMOS inverter
20VIN]20
V[15TU
10O

Gain=3.2V00

16.0mm(b)
Fig. 5. (a) Schematic and (b) photo of proposed all-PMOS
negative voltage generator.

10Hz

VIN [V]

Pulse+2V

VOUT

-1.6V

OUT

20-20V 0V][V15Gain=148

T
U
10O

IOUT˜ 055 10 15 20

IOUT

0V

21.9mm

V5RL

VOUT(0 to -2V)(a)Pseudo-CMOS inverter
20V
PMOS onlyIN

OUT
0V0V

00

5 10 15 20

VIN [V]

Fig. 6. Measured waveforms of negative voltage generator.

Fig. 4. Organic circuits. (a) Conventional CMOS inverter. (b)Proposed Pseudo-CMOS inverter.

830

Single transistor

N parallel transistors

Pair

Pair

Prosthetic handNN(a) Conventional parallel transistors(Step 1)I-V characteristics (e.g. threshold voltage and ONcurrent(ION)) of each transistor are measured.
Pair

Surface electromyogram measurement sheet (SEMS)
8 x 2 amplifier array8 x 8 EMG electrode arraymm
54

Stacked 2 sheets

NEMG electrodes(0.7mm x 0.7mm)

Organic transistors

1 m-thickultra-flexiblePEN film
40mm

N(Step 2)
N1 and N2 transistors are selected out of N
transistors to minimize mismatch.

Electrode pitch = 5mm

PairNNFig. 7. Surface EMG measurement sheet.
III.

SURFACE ELECTROMYOGRAM MEASUREMENT SHEETFOR PROSTHETIC HAND CONTROL [10]N1

N2(Step 3)
Connect N1(N2) transistors by printed interconnects
Pair

A. Overview of Electromyogram Measurement Sheet
A surface EMG measurement sheet [10] on which an EMG
electrode array and a front-end amplifier array with 2V organic
transistors are integrated on a 1µm-thick ultra-flexible film isdeveloped to control prosthetic hands. Fig. 7 shows aphotograph of the developed 45x40mm2 64-channel SEMS. In
SEMS, an 8x8 EMG electrode array sheet and an 8x2 front-end
amplifier array sheet with 2V organic transistors on a 1µmthick ultra-flexible polyethylene naphthalate (PEN) film arestacked.
B. Post-Fabrication Select-and-Connect (SAC) Method toReduce Transistor Mismatch
One of the design challenges of organic circuits for theamplifier array is the mismatch of amplifiers due to the large
mismatch of organic transistors. To solve the problem, thepost-fabrication select-and-connect (SAC) method that reduces
the transistor mismatch is proposed. Figs. 8(a) and (b) show
conventional and proposed transistor mismatch reduction
techniques for the amplifier array, respectively. In the SAC
method, first, the I-V characteristics (e.g., threshold voltageand ON-current (ION)) of each transistor are measured. 2N
measurements are required. Then, N1 and N2 transistors are
selected from the left and right groups in Fig. 8(b),respectively, on the basis of the results of calculation tominimize the target mismatch. N1 and N2 are not always equal.
Finally, the selected N1 (N2) transistors are connected byinkjet-printed interconnects, as shown in Fig. 8(c). Although
the proposed SAC is too costly and impractical in the silicon
VLSI technology, the SAC takes advantage of the printedelectronics. Fig. 8(d) shows the simulated N dependence of ION
mismatch. Compared with the conventional parallel transistors,
the proposed SAC reduces the ION mismatch by 54%, 92%, and99.7% at N = 2, 4, and 8, respectively.

(1 ≤ N1 , N 2 ≤ N )N1

N2(b) Proposed select-and-connect (SAC) method

Before print

After print

4 transistors(N=4)

Inkjet-printed interconnects(N1=2)(c))%(100Parallel transistors (Conv.))N
10O )N(I IO
6 (61-54%-92%-99.7%=
hct
a 0.1msi
M
0.01

Proposed SAC
Simulated
1234

5678

Number of parallel transistors (N)(d)
Fig. 8. Conventional and proposed transistor mismatch
reduction techniques.

831

IV.

FLEXIBLE WET SENSOR SHEET TO DETECT URINATIONIN DIAPERS [11]B. ESD Protection With Organic Schottky DiodeESD protection is essential in the FWSS because theelectrodes can directly come in contact with wet human skin.
ESD protection in organic transistors, however, is difficult
because they are fabricated on an insulating film . To solve theproblem, ESD protection with organic Schottky diodes using
copper phthalocyanine (CuPc) in Fig. 11 is proposed. With theESD protection, the ESD tolerance is above 2kV, which
successfully satisfies level 1 of IEC 61000-4-2.

A. Overview of Wet Sensor Sheet
An organic transistor based flexible wet sensor sheet(FWSS) with wireless power and data transmission using
13.56MHz magnetic resonance is developed to detect urinationin diapers [11]. Fig. 9 shows a photograph of the developed
78mm x 53mm FWSS. In its actual implementation, the FWSS
is embedded in the cotton of a diaper, although FWSS is placedon the surface of the diaper in Fig. 9 for clarity. The FWSS is apassive transponder that is wirelessly powered by a reader andsends sensor data to the reader. In the FWSS, organic circuits
fabricated on a 12.5µm-thick flexible polyimide film arestacked on 40mm square coil on 12.5µm-thick flexible PCB.
Fig. 10 shows a circuit schematic of the FWSS and reader. The
reader is expected to be attached to the pants near the diaper.
The reader wirelessly transmits power between the coils via
magnetic resonance at 13.56MHz. In this work, instead of
conventional electromagnetic induction, magnetic resonance isused to increase the distance between the reader and FWSS.

REFERENCES
[1]

53 mm

Diaper

40 mm
12.5∈m-thickflexible PCB(polyimide)mm
87

Organic circuitsSensor electrodes

Fig. 9. Flexible wet sensor sheet (FWSS).
Reader
FWSS with organic transistors
Magnetic resonance (13.56MHz) (Transponder)
Organic diodes

AAC
Wetsensors

Datareceiver

ESD

Sensor electrodes

Fig. 10. Block diagram of flexible wet sensor sheet.
ESD protection circuitwith organic diode
Cross section
Al (Cathode)
PadCircuit

1M

Photograph(top view)
mm
2

CuPc
Au (Anode)
Polyimide

2 mmFig. 11. ESD Protection with organic schottky diode.

832

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