FMCp2 - 2

High thermal stability glass substrate
for high resolution display
Masahiro Hayashi, Tetsuya Murata, Yoshinari Kato, Takashi Murata,and Masahiko Ohji
Nippon Electric Glass, Co., Ltd. 2-7-1 Seiran, Otsu, Shiga 520-8639, Japan
Keywords : non-alkaline glass substrate, high resolution, active-matrix display

ABSTRACTA new glass substrate “OA-30” has been developed.
The high strain point of OA-30 leads to reduced thermalshrinkage of glass substrates during thermal treatment in
the Low temperature poly-silicon (LTPS) TFT process.
Low thermal shrinkage of OA-30 contributes to therealization of high resolution displays with LTPS TFTs.
1. INTRODUCTION
High resolution displays have been widely used formobile devices. LTPS is the most suitable TFT for displays
due to its high electron mobility. Since the processtemperature of LTPS TFT is higher than that of a-Si TFT,
conventional glass sometimes causes a patterning
mismatch from itsthermal shrinkage. As the weight of thedisplay for mobile devices needs to be lighter than that for
TV’s and monitors, thinner and lighter substrates arerequired. However, thinner glass substrate occasionallycauses breakage in the process due to its gravity sag,which would be a critical issue of lowering the productivityof the devices.
2. Properties of OA-30
The properties of OA-30 are shown in Table 1,compared with conventional the LCD glass substrates,
OA-11 and OA-10G [1]. The characteristics of OA-30 are ahigh strain point and a high Young’s modulus. The highstrain point and Young’s modulus realize high thermal andmechanical stability. Typical characteristics of glass aredescribed as follows.

3. Thermal stability
Figure 1 shows a schematic illustration of themeasurement method for thermal shrinkage [2]. Marking
lines were made by patterned Cr film. A glass sample
with marking lines was separated along the long side
into two pieces by laser scribing. One piece wassubjected to heat-treatment (Figure 2). After
heat-treatment, the treated piece was placed in touchwith the untreated one. The displacements of eachmarking line were measured and then shrinkage wascalculated by using the following equation:
Shrinkage [ppm] = (ı 'l1 [μm] + 'l2 [μm] ) / l0 [m] .
Here, l0 is the length between marking lines before
heat-treatment. 'l1 and 'l2 are the displacements ofeach marking line.
Figure 3 shows thermal shrinkage of OA-30, OA-11
and OA-10G after heat-treatment at 400-600°C for 60
min. The thermal shrinkage of OA-30 is less than 1/4 ofthat of OA-10G at 500°C and 1/6 of that of OA-10G at600°C. This comes from the high strain point of OA-30.
The result shows that OA-30 is much more stable indimension at high temperature, which is suitable for theLTPS process.

Table 1. Properties of OA-30, OA-11 and OA-10G.

Figure 1. Schematic illustration of the measurement
method for thermal shrinkage.

ISSN-L 1883-2490/21/0434 © 2014 ITE and SID

IDW ’14434

Figure 2. Profile of heat treatment for measurement ofthermal shrinkage.

Figure 4. Gravity sag for glass substrate.

Table 2. Calculated gravity sags of OA-30, OA-11 andOA-10G along thickness of glass substrate.

Figure 3. Thermal shrinkage of OA-30, OA-11 andOA-10G heat-treated at 400-600qC for an hour.

4. Mechanical stability
Table 2 shows the calculated gravity sag of OA-30,OA-11 and OA-10G along the thickness. The gravity sagof the glass substrate is calculated by using the equationin Figure 4, which indicates that the sag decreases withincreasing specific modulus, that is, the ratio of Young'smodulus to density (Young's modulus / density). The sagof OA-30 and OA-11 are lower than that of OA-10G. The
lower sag is achieved because of the high specificmodulus of OA-30 and OA-11. OA-30 and OA-11 exhibit asmall gravity sag. As glass size is increased or thickness isdecreased to meet the demand of LCD panels, the gravity
sag of the glass substrate increases. If the gravity sag is
too large, the risk of glass substrate fractures increases
during transportation. So OA-30 and OA-11 are expected
to increase device productivity by decreasing the risk ofglass breakage.

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IDW ’145. SUMMARY
Newly developed OA-30 would be a promising
substrate for LTPS process due to its high thermal andmechanical stability.
The high thermal stability realizes precise patterning atLTPSprocess
requiringhightemperatureheat-treatment. The high mechanical stability would
reduce the risk of breakage of glass substrate in the LCD
manufacturing process.
6. REFERENCES[1] Takahiro Kawaguchi et. al., IDW’09, pp.827-830.
[2] Tomoki Yanase et. al., IDW’08, pp.1837-1840.