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.