IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 64, NO. 5, MAY 2017 1991
A High-Reliability Gate Driver Integrated in
Flexible AMOLED Display by IZO TFTs
Wei-Jing Wu,
Member, IEEE
, Li-Rong Zhang, Zhi-Ping Xu, Lei Zhou, Hao Tao,
Jian-Hua Zou, Miao Xu, Lei Wang, and Jun-Biao Peng
Abstract
— This paper presents a new gate driver
integrated by IZO thin-film transistors (TFTs) with the etch
stop layer structure on the polyimide substrate, which con-
sists of nine TFTs and two capacitors. There are several
advantages for the proposed gate driver, such as simple
circuitry, full-swing output, low power, and good reliability.
The proposed gate driver has been successfully integrated
in a flexible active matrix organic light emitting display with
the resolution of 200 (RGB) × 600, in which the conventional
2T1C pixel circuit with bottom-emission structure is used.
It is shown that there are no distortion and good noise-
suppressed characteristics for the output signals even up
to 600 stages. In addition, the proposed gate driver has a
good stability, since no voltage fluctuation occurs under
720-h test. Moreover, the flexible panel works well after a
10000 times repetitive bending performed on a test bench,
which is mainly composed of a programmed logic controller
and dc motor. During the bending test, the minimum curva-
ture radius of flexible panel can reach to be about 5 mm.
IndexTerms
— Flexibleactivematrixorganiclightemitting
display (AMOLED), gate driver, IZO thin-film transistors
(TFTs).
I. INTRODUCTION
F
LEXIBLE displays on a plastic substrate have received
much attention due to their superior characteristics, such
as thinner thickness, lighter weight, and bendability [1], [2].
The flexible active matrix organic light emitting dis-
play (AMOLED) is a very promising display technology
due to its all solid-state process [3]–[7]. To realize flexi-
ble AMOLED displays, it is mainly required to fabricate a
uniform and stable thin-film transistors (TFTs) backplane on
the flexible substrate. Low-temperature polycrystalline-silicon
Manuscript received December 15, 2016; accepted
December 15, 2016. Date of publication January 4, 2017; date of
current version April 19, 2017. This work was supported in part by
the 973 Program under Grant 2015CB655004 founded by the Ministry
of Science and Technology, in part by the National Natural Science
Foundation of China under Grant 61574062 and Grant 61574061,
and in part by the Science and Technology Program of Guangdong
Province under Grant 2016B090906002, Grant 2016B090907001,
Grant 2015B090914003, and Grant 2015B090915001. The review of
this paper was arranged by Editor M. M. Hussain.
(Corresponding
author: Wei-Jing Wu.)
W.-J. Wu, Z.-P. Xu, M. Xu, L. Wang, and J.-B. Peng are with the State
Key Laboratory of Luminescent Materials and Devices, South China Uni-
versity of Technology, Guangzhou 510640, China (wuwj@scut.edu.cn).
L.-R. Zhang, L. Zhou, H. Tao, and J.-H. Zou are with Guangzhou New
Vision Opto-Electronic Technology Co., Ltd., Guangzhou 510530, China.
Color versions of one or more of the figures in this paper are available
online at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TED.2016.2641448
Fig. 1. (a) Display panel with source driver IC and gate driver IC.
(b) Flexible display panel with the integrated gate driver.
TFTs are widely used to drive OLED devices due to high
field-effect mobility [>50 cm
2
/(V · S)] and stable electrical
performance [8], [9]. However, there still exist the drawbacks
of poor uniformity over a large area and quite high process
temperature (400 °C–500 °C) during silicon crystallization.
In the recent years, metal oxide (MO) TFTs have attracted
considerable interest due to high mobility, low fabrication
temperature, good uniformity, good process compatibility with
a-Si:H TFTs, and the compatibility with transparent or flexible
applications [10]–[14]. Discrete flexible MO TFTs and their
simple circuits have been reported by several groups [15]–[20].
For active matrix displays, such as AMOLED or AMLCD,
source driver in the column direction and gate driver in the
row direction are needed. Conventionally, the source driver IC
and gate driver IC, packaged with tape automated bond or chip
on glass, are boned to display panel, as shown in Fig. 1(a).For
flexible displays, ICs are easy to strip from the plastic substrate
under the process of bending. Along with the development of
TFT technology, the gate driver is being tried to be integrated
on the same flexible display panel. However, source driver is
hard to be integrated by TFTs due to its complexity. Hence, the
flexible display panel can be freely bended in the row direction
with the integration of gate driver, as shown in Fig. 1(b).
As a result, integrating the gate driver in the flexible dis-
play can not only enhance the reliability but also lower the
fabrication cost. It is common that the gate driver is integrated
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