Communication sheets using printed organic nonvolatile memories
Tsuyoshi Sekitani1, Yoshiaki Noguchi1, Shintaro Nakano1, Koichiro Zaitsu1, Yusaku Kato1,Makoto Takamiya2, Takayasu Sakurai3, and Takao Someya1*
1

Quantum-Phase Electronics Center, School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan
2
3VDEC, The University of Tokyo, Tokyo 153-8904, Japan

Center for Collaborative Research, The University of Tokyo, Tokyo 153-8904, Japan

Abstracts
Human-scale communication sheets have been
manufactured using printing processes with integrating
an organic nonvolatile FeRAM with nondestructive readcapability and plastic MEMS switches. The
communication route is dynamically formed by MEMS
switches and stored by the memory. The “1”-“0” ratioof the memory exceeds 103 after 104 cycles in air.

1. Introduction:
Ambient electronics is expected to open up a newcontinent of applications. This paper reports acommunication sheet which can build infrastructure for theambient electronics together with the wireless powertransmission sheet previously published in IEDM [1,2].
Combining relatively long-distance wired communicationand mm-scale wireless communication, the sheet offers a
new communication method that enables multiple
electronic objects scattered over the sheet to communicate
contactlessly with each otherby establishingcommunication paths easily without cumbersome physicalconnections (Fig. 1). Since the information transmitted overthe sheet is confined in small space close to ad hoc routed
paths, the system provides more secure communication
against tapping compared with ordinary wireless LAN andis free from issues related with radio frequency band
allocation which has been already tight.
The communication route is dynamically formed using
printed plastic MEMS switches. In order to store therouting information, a nonvolatile memory cell array basedon printing processes is developed, which is ferroelectric
random access memory (FeRAM) [3]. Each cell consists of
one organic ferroelectric memory transistor and two organic
transistors (Fig. 2). Although all previously reported
organic nonvolatile memory cells utilized a one-transistor(1T) structure [4,5], this is the first demonstration of anonvolatile, nondestructive memory using a three-transistor(3T) structure, which maintains a time-continuous current
and/or voltage. This feature is well suited for programming
actuators such as MEMS switches distributed over large
area. Moreover, the 3T structure nonvolatile memory cells
can significantly reduce the chance of a false writing,compared with 1T structure cells.
The effective communication area is 21 × 21 cm2. The
sheet contains a two-dimensional array of 8 × 8
communication cells. The “1”-“0” current ratio of organic

Fig. 1: Communication sheet. (a) An image of the manufactured large-area communication sheet. The whole surface ofthe table is covered with multiple prototype communication sheets. (b) A principle of the communication sheet.

1-4244-0439-X/07/$25.00 © 2007 IEEE221

Fig. 2: Circuit diagram. (a) This communication sheet comprises communication coils, MEMS switches, and organic
nonvolatile memories. The periodicity is 25.4 mm. (b) Each memory cell comprises an access transistor (ATr), a memorytransistor (MTr), and an erase transistor (ETr).

Fig. 3: Communication sheet comprising communication coils, MEMS switches, global wiring, and organic
nonvolatile memories. (a) Device assembly. Coil: The inductance and resistance of the coil are 27 µH and 25 Ω,respectively. MEMS: (A) Electrodes for electrostatic attraction as the common and control electrodes of the MEMS
switches. (B) and (C) Electrodes for the transmission of the communication signal. Memory: (b) A cross-sectional
illustration. A circuit diagram in Fig. 2 (b).
nonvolatile memory exceeds 105. The retention time ismore than 15 days in air.
The thickness and weight of the entire sheet are 1 mm and100 g, respectively.

2. Device manufacturing process:Each cell of the organic nonvolatile memory array(Fig. 3) comprises three organic transistors; an accesstransistor, a memory transistor, and an erase transistor. All
the metal wires and electrodes are patterned by inkjet using
silver nanoparticles. Polyimide is inkjetted to form gate
dielectric layers for access and erase transistors, while222

Fig. 4: Organic nonvolatile memory. Transistor characteristics of stand-alone (a) ATr and (b) MTr. (c) Transfer
characteristics of the memory cell with a 3T structure. The “1” state is attained after applying voltages of VWLA = VWLE =–40 V, VBL = +40 V, and VWLM = –60 V, while the “0”state is attained after applying voltages of VWLA = VWLE = –40 V, VBL= –40 V, and VWLM = +60 V. Read-out is performed by applying VWLA = +60 V to –60 V, VWLE = –40 V, and VBL = –10 V,
while VWLM = 0 V. All the measurements are performed in air. A 3T memory cell exhibits a large “1”-“0” current ratio
exceeding 105 in air.

Fig. 5: Memory characteristics and plastic MEMS switch driven by an organic memory. (a) Retention characteristics
in air: Transfer curves of the memory cell after storage in air for 15 days. (b) Fatigue characteristics in air and a nitrogenenvironment: Transfer curves after 104 writing and erasing cycles. (c) Plastic MEMS switch driven by an organic memory.
Voltages (VM) through an organic memory cell when the memory is “1” or “0” in air. Measurements are performed at thevoltages of VWLA = –40 V and VBL = –40 V, while VWLM = VWLE = 0 V. When 9 V are applied to the control electrode ofthe MEMS switch, the resistance decreases to 23 Ω.
poly(vinylidenefluoride/trifluoroethylene) [P(VDF/TrFE)][6] is used to form a ferroelectric gate dielectric layer for
memory transistors. The surface of P(VDF-TrFE) is coatedwith fluoride parylene. Pentacene channel layers depositedin a vacuum and source/drain electrodes are directly formed
by inkjet to build the top contact devices.
All the transistors are coated with organic/metallic
encapsulation layers and annealed for a threshold control.
The channel length is 30 µm for all the transistors, while
the width of the access, memory, and erase transistors are
16.5 mm, 45 mm, and 300 µm, respectively.
The MEMS switch is formed by using inkjet printing
and NC mechanical punching system㩷 [1]. The electrodes

for communication and those for control and common are
patterned on a 25-µm-thick polyimide membrane.
The global wiring sheet comprises 9 copper lines withthe thickness of 18 µm for interconnection between MEMSswitches. The resistance is less than 1 Ω.
The communication coil comprises square copper coilswith an outer diameter of 25 mm. Both the width andspacing of the copper lines are 100 µm. The number ofturns is 53. The inductance and resistance are 27 µH and 25Ω, respectively.
The assembly (Fig. 3): A plastic MEMS switch arraylaminated together with the communication coil sheet and223

Fig. 6: Communication. (a) Schematic illustration of the communication system. (b) Transmission loss from “VS” to “VR”
as a function of frequency. (c) When a signal of VS is applied from the “sender” end, a signal of VR is observed at the“receiver” end when the MEMS switch is ON (“1”). The frequency is 2 MHz. The received signal is less than 1 mV when
the MEMS switch is OFF (“0”). (d) The communication sheet works cooperatively with the wireless power transmission
sheet. The power sheet under the communication sheet can transmit power to two robots with LEDs wirelessly.

the global wiring sheet comprising copper lines for theinterconnections between the MEMS switches.

3. Device characteristics:
The pentacene transistors for access and erase transistors
exhibit mobility of 1 cm2/Vs and an on/off ratio of 105. A
memory transistor exhibits large hysteresis at VGS = 0 V.
The memory with a 3T structure (Figs. 4 and 5): A 3T
memory cell exhibits a large “1”-“0” current ratio of 105 inair. The current ratio exceeds 103 after it is stored in air for
15 days owing to the organic/metallic hybrid encapsulation[7]. Furthermore, the memory retains a high ratio of above
103 after 104 write cycles in air. The time for “0” to “1” is40 ms, while the time for ”1” to “0” is 10 ms. With thedecrease in the thickness of P(VDF-TrFE), thewriting/erasing voltages decrease to 20 V.
A plastic MEMS switch (Fig. 5 (c)) is driven by anorganic nonvolatile memory cell. An organic memory cell
can supply stable voltages above 10 V to the controlelectrode of the MEMS switch when the memory is inwrite-state. When 9 V is applied to the control electrodes,
the resistance changes from >106 Ω to 20 Ω. Maximum
frequency response of the MEMS switch is 1 KHz.
The communication (Fig. 6): An organic memory cell
can supply continuously stable voltages of above 10 V tothe control electrode of the MEMS switch when thememory is in the “1”. The communication signal istransmitted at 2 MHz, which is the resonance frequency ofthe system. The on/off ratio of the MEMS switch in thecommunication signal exceeds 103. The communicationsheet can cooperatively work with the power transmission
sheet.

Acknowledgment: This study was partially supported bySpecial Coordination Funds for Promoting and Technology,
the Ministry of Education, Culture, Sports, Science andTechnology and JST/CREST. We also thank TorayEngineering Co., Ltd. for providing high-performance
P(VDF-TrFE), Kyocera Chemical Cooperation for ahigh-purity polyimide precursors (KEMITITE CT4112),and Daisankasei Co., Ltd. for a high-purity parylene(diX-SR).
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Kato, K. Hizu, H. Kawaguchi, T. Sakurai, and T.
Someya, 2006 IEDM 11.1.
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