Low energy-cost TFT technologies using ultra-thin flexible glass substrate
Noriyoshi
1
Yamauchi ,
Taketsugu
2
Itoh
and Takashi
3
Noguchi
1Information,
Production and Systems, Waseda University, Kitakyushu, Japan
2Corning Holding Japan G.K., Tokyo, Japan
3Faculty of Engineering, University of the Ryukyu, Okinawa, Japan
Abstract
This paper proposes a novel flexible display technologies using ultra-thin glass substrate. Flexible thin glass
substrate as a panel material for TFTs are proposed for the energy saving. There are many attractive
applications for such TFTs on thin glass like highly functional systems, and rather simple paper displays and
printable displays. They are suitable as high performance mobile terminals. The Si based TFTs crystallized
using semiconductor blue laser have an advantage as a highly functional panel by improving the performance
with reducing the production cost. The device structure of organic TFTs on thin flexible glass is more suitable
for reducing drastically an energy cost in which the semiconductor layer may be coated by a spin coating
method.
Introduction
Device Fabrication
[1,2]
Energy
Fabrication energy
poly-Si TFT
Si MOSFETs
O-TFT (pentacene)
1062 kWh/m2
2179 kWh/m2
102 kWh/m2
Highest total energy of Si MOSFET due to high energy
impact by ion implantation steps
Fabrication energy of Poly-Si TFT is ~ ½ for Si MOSFETs
Estimated large consumption of crystallization step
using ELA (excimer laser annealing) for LTPS
Blue-Multi-Diode-Laser (BLDA) annealing technology is
[3]
available to replace ELA
Lowest energy of O-TFT (organic
TFT), ~ 1/10 for poly-Si TFT,
1/30 for Si MOSFETs
Poly-Si film by BLDA annealing on flexible glass. The crystallized
area in the bended glass is seen more transparent (white in color)[3].
Substrate Fabrication Energy
Comparison of Si Wafer and
Glass Substrate
Fabrication energy
Si Wafer
Glass substrate
2130 kWh/kg
~1/100 for Si wafer
Low substrate energy for glass
Estimated lower CO2 emission for glass substrate
Melting Energy for
Flexible Glass
Corning has developed a 50 mm thin glass
substrate
Applicable spooled glass for roll-to-roll process,
[3]
will be adopted present to flexible device
Predicted low melting energy for thin-flexible
glass because of small specific volume
Ag stripe patterns
Required melting energy
(kWh/kg)
Example of spooled glass with Ag stripe patterns[4]
Melting capability (ton/day)
This figure shows the viscosity curves for typical glass, [a] : fused quartz glass,
[b] : aluminosilicate glass, [c] : borosilicate glass, [d] : soda-lime glass and [e] :
lead glass[4]. Pink spots correspond to viscosity at annealing point (1013 Pa s)
and at strain point (1014.5 Pa s) for alumino-borosilicate glasses that are
widely adopted to glass substrate for LCD.
The capability of glass melting for LCD application is estimated about 4 million m2/year
at 2003[6], melting capability per day is calculated about 19 ton/day, when the furnace
can produce to alumino-silicate glass of 0.7mm in thickness. The melting energy for
glass at 19 ton/day is able to estimate 1.2 kWh/kg[7].
Can assume same viscosity for flexible alumino-borosilicate glass to alumino-silicate.
Theoretical energy of glass melting is less 700 kcal/kg, corresponds to 0.82 kWh.
[8]
 Estimated 52% energy loss from energy balance estimation , effective energy will be 1.71
kWh/kg[8].
Estimated 1.2 kWh/kg from practical melting capability for LCD glass industry.
Expected lower melting energy for thinner flexible glass compared to 0.7mm glass.
Conclusions
Flexible glass substrate is applicable many attractive applications for such TFTs like paper displays and printable
displays. O-TFT and LTPS using blue laser on thin glass can realize the flexible devices. The device structure on
thin glass is more suitable in term of energy saving.
References
[1] T. Chuman, Pioneer R&D, 17 2 (2007)p. 13.
[2] Y.-C. Chen et al, Proc. of ITC 2006, 6-3 (2006) p285.
[3] T. Noguchi et al, SID’12 Digest, P140L (2012) p. 1129.
[4] S. Garner et al, SID’12 Digest, 26.1(2012) p.342.
[5] M. Lindig, ,Glass (2004) p. 294.
[6] http://www.agc.co.jp/news/2003/0619.html
[7] M. Yamane et al, Glass Eng. Handbook (2005).
[8] K. Kroger, Glastech. Ber, 26 7 (1953) p. 202.