Author Keywords
Colorless polyimide, transparent electronics, aging test, aging
atmosphere, loss transmission
Introduction
As known, polyimide (PI) have extensive applications in the aerospace
industry, microelectronic and optoelectronic engineering, organic
light-emitting diode display (OLED), and separation membrane due to
their high-temperature resistance, outstanding mechanical properties,
chemical and radiation resistance, and excellent dielectric
properties.1-4 PI is also introduced into the OLED
device to prepare the flexible substrate for its bendable function. For
the past few years, the colorless polyimide (CPI) has been drawn much
attention for its application in transparent electronics, such as the
camera under panel (CUP) in the OLED display which require a high
transmittance (Tr%).5-7 However, the high temperature
(even to 450℃) process of the preparation of OLED device may have huge
challenges on the properties of CPI, so we designed a series of aging
test experiments to study the influence of high temperature and
atmosphere on the Tr% of CPI films with structure of
Glass/SiO2/CPI/SiO2, as showed in Figure
1a. The sample 10, sample 12 and sample 14 were aging with 430℃, 450℃
and 470℃ for 120 min in N2 atmosphere,
respectively.8-11The sample 8 was without any aging
test and sample 11 was aging with 450℃ for 120 min in N2atmosphere. Both the five samples (sample 8, sample 10, sample 11,
sample 12 and sample 14) were all with a structure of
Glass/SiO2/CPI/SiO2.12-14
As showed in Figure 1b, the transmittance of samples based on different
structures and aging test were also measured to research the influence
of high temperature on the yellow index (YI) of CPI. With the increasing
of aging temperate from 430℃ to 450℃ and 470℃, the Tr% of the film
decrease obvious, especially responding the wavelength from 400nm to
600nm., the films with aging all had a low Tr% than which without
aging. For the samples with structure of
Glass/SiO2/CPI/SiO2, the loss
transmission were 0.22%, 1.22% and 4.82% for the samples (sample 10,
sample 12 and sample 14) aging with 430℃, 450℃ and 470℃, in
N2 atmosphere comparing with the sample without aging
(sample 8). The author thought that the higher temperature may damage
the polymer distribution in the CPI film, and leading the transparency
of CPI films lower. Meanwhile, the influence of aging atmosphere on the
Tr% was also researched with nitrogen and air. The film aging with
nitrogen had a higher Tr% than that aging with air, which is caused by
the oxidation reaction of CPI films during the aging test. The loss
transmission were 1.22% and 1.42% for the films aging with nitrogen
and air atmosphere. The properly temperature and inert atmosphere were
selectively methods to keep a high Tr% of CPI films for preparing
transparent electronics device.