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This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/LED.2018.2845114, IEEE Electron
Device Letters
9
Abstract—Polymethyl methacrylate (PMMA) /
poly(vinylalcohol) (PVA) bilayer polymer dielectrics were
used to fabricate ultra-thin free-substrate n-type
PTCDI-C13 organic thin-film transistors (OTFTs). PVA can
help peel the entire device from the supporting layer, while
PMMA improves the performance of the n-type OTFTs. As a
result, we were able to achieve a current on/off ratio
exceeding 10
7
for an ultra-thin (~590 nm) substrate-free
PTCDI-C13 OTFT. The electron mobility achieved as high
as 0.54 cm
2
V
-1
s
-1
. These n-type OTFTs can successfully
adhere to a 3D curved surface with nearly unaltered
mobility and current on/off ratio and a strong resistance to
crumpling. These results show that ultrathin flexible
n-channel OTFTs have promising potential for applications
in flexible and conformal electronic devices.
Index Terms—N-channel organic thin-film transistors
(OTFTs); ultra-thin; flexible; conformal.
I. INTRODUCTION
lexible organic thin-film transistors (OTFTs) have attracted
a great deal of interest due to their unique advantages such
as low cost, low process temperature, mechanical flexibility,
and light weight, which give them strong potential for flexible
electronic applications, including flexible displays, sensors,
and radio frequency identification (RFID) tags, etc[1-5]. The
flexibility of OTFTs is mainly limited by the substrate
thickness (d), which determines the strain (ε) for a given
bending radius (r) according to ε = d/2r[6]. An effective
method to enhance flexibility is to fabricate free-substrate
organic electronic devices[7-10], this method dramatically
decreases the thickness of the whole device. Decreased
thickness is favorable for ultrathin device fabrication and
allows good device flexibility [7]. Additionally, an ultrathin
device with good flexibility also has good mechanical
robustness and good adhesion to curved surfaces for potential
applications in future portable and wearable electronics[11-14].
Recently, a few outstanding studies have shown the fabrication
of the ultrathin flexible OTFTs by applying a free-substrate
______________________________
This work is supported by National Natural Science Foundation of
China (61574032,51703020,51732003,51322305), 111 Project
(B13013), Project funded by China Postdoctoral Science
Foundation(2016M601361), Fundamental Research Funds for the
Central Universities (2412017QD008).
The authors are with the Centre for Advanced Optoelectronic
Functional Materials Research and Key Laboratory of UV-Emitting
Materials and Technology (Northeast Normal University), Ministry of
Education, Changchun 130024, P. R. China.
Qingxin Tang and Yanhong Tong is the corresponding author
(tangqx@nenu.edu.cn).
device configuration. For example, Tokito’s group achieved
350-nm free-substrate DNTT OTFTs with a mobility of 0.37
cm
2
V
-1
s
-1
, and their electrical characteristics did not show
change under 50% compressive strain [9]. Liu’s group
fabricated free-substrate OTFTs with high bending stability via
water-floatation delamination [7]. The mobility of the OTFTs
reached 0.53 cm
2
V
-1
s
-1
and the OTFTs still exhibited good
field-effect performance when adhered on the edge of a knife.
Currently, almost all reports of ultrathin flexible OTFTs have
utilized p-channel materials, mainly due to the lack of
n-channel organic materials with air stability and good
performance [15,16]. However, the development of ultrathin
flexible OTFTs based on n-channel organic materials is
extremely important for the fabrication of wearable and
portable complementary electronic circuits.
In this work, we present the construction of free-substrate
flexible n-type PTCDI-C13 OTFTs with PMMA and PVA
bilayer polymer dielectrics. The n-type OTFTs can be
mechanically peeled from the supporting substrate using 3M
tape, to fabricate an ultrathin free-substrate device. Compared
with solution-assisted delamination, dry delamination prevents
contamination of the solution in the organic semiconductor
material, which is especially important for water-sensitive
n-type organic materials. These resulting device thickness is
only ~590 nm. The ultrathin flexible PTCDI-C13 OTFTs can
adhere to a 3D curved surface. Moreover, the ultrathin OTFTs
exhibit a mobility as high as 0.51 cm
2
V
−1
s
−1
, a current on/off
ratio exceeding 10
7
on a 0.65 cm glass hemisphere, and good
operational stability, demonstrating their potential for
applications in conformal electronics. It is also worth
mentioning that the ultrathin n-type OTFTs still exhibit good
field-effect mobility after crumpling 10 times. The PTCDI-C13
OTFTs with good adhesion to curved surfaces and excellent
mechanical robustness show potential for applications in
portable and wearable organic electronics.
II. EXPERIMENTAL DETAILS
Heavily doped silicon wafers were used as substrates for the
fabrication of ultrathin OTFTs. The substrates were cleaned
and subsequently modified by a self-assembled
octadecyltrichlorosilane (OTS) layer (Acros, 95%). This layer
weakens the interactions between layers and allows the device
to be peeled off the substrate. A typical bottom-gate top-contact
configuration was employed for the OTFTvfabrication. First,
30-nm-thick gold (Au) was thermally deposited as the
bottom-gate electrode. Second, an aqueous solution of PVA
was spin-coated on the substrate, and then, a PMMA solution in
Ultrathin free-substrate n-type PTCDI-C13
transistors with bilayer polymer dielectrics
Meiling Liu, Haiting Wang, Yanhong Tong, Xiaoli Zhao, Qingxin Tang, and Yichun Liu
F
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