Flexible substrate, method of fabricating the same, and thin film transistor using the same
View Patent ↗A flexible substrate for a TFT includes a metal substrate having a predetermined coefficient of thermal expansion, and a buffer layer on the metal substrate, the buffer layer including a silicon oxide or a silicon nitride, wherein the predetermined coefficient of thermal expansion of the metal substrate satisfies an equation as follows, α f + 0.162 × ( 1 - v f ) E f ≤ α s ≤ α f + 0.889 × ( 1 - v f ) E f E f representing Young's modulus of the buffer layer, v f representing Poisson's ratio of the buffer layer, α f representing a coefficient of thermal expansion of the buffer layer, and α s representing the predetermined coefficient of thermal expansion of the metal substrate.
1. A flexible substrate, comprising:
a metal substrate having a predetermined coefficient of thermal expansion; and
a buffer layer on the metal substrate, the buffer layer including a silicon oxide or a silicon nitride,
wherein the predetermined coefficient of thermal expansion of the metal substrate satisfies an equation as follows,
α
f
+
0.162
×
(
1
-
v
f
)
E
f
≤
α
s
≤
α
f
+
0.889
×
(
1
-
v
f
)
E
f
E f representing Young's modulus of the buffer layer, V f representing Poisson's ratio of the buffer layer, o f representing a coefficient of thermal expansion of the buffer layer, and α s representing the predetermined coefficient of thermal expansion of the metal substrate.
2. The flexible substrate as claimed in claim 1 , wherein the buffer layer includes a silicon oxide, and the predetermined coefficient of thermal expansion of the metal substrate is from about 2.86 ppm/° C. to about 11.48 ppm/° C.
3. The flexible substrate as claimed in claim 1 , wherein the buffer layer includes a silicon nitride, and the predetermined coefficient of thermal expansion of the metal substrate is from about 3.19 ppm/° C. to about 8.01 ppm/° C.
4. The flexible substrate as claimed in claim 1 , wherein the predetermined coefficient of thermal expansion of the metal substrate satisfies an equation as follows:
α
f
+
0.270
×
(
1
-
v
f
)
E
f
≤
α
s
≤
α
f
+
0.741
×
(
1
-
v
f
)
E
f
5. The flexible substrate as claimed in claim 4 , wherein the buffer layer includes a silicon oxide, and the predetermined coefficient of thermal expansion of the metal substrate is from about 4.14 ppm/° C. to about 9.72 ppm/° C.
6. The flexible substrate as claimed in claim 4 , wherein the buffer layer includes a silicon nitride, and the predetermined coefficient of thermal expansion of the metal substrate is from about 3.79 ppm/° C. to about 7.05 ppm/° C.
7. A method of fabricating a flexible substrate, comprising:
forming a metal substrate having a predetermined coefficient of thermal expansion; and
forming a buffer layer on the metal substrate, the buffer layer including a silicon oxide or a silicon nitride,
wherein the predetermined coefficient of thermal expansion of the metal substrate satisfies an equation as follows:
α
f
+
0.162
×
(
1
-
v
f
)
E
f
≤
α
s
≤
α
f
+
0.889
×
(
1
-
v
f
)
E
f
E f representing Young's modulus of the buffer layer, V f representing Poisson's ratio of the buffer layer, α f representing a coefficient of thermal expansion of the buffer layer, and α s representing the predetermined coefficient of thermal expansion of the metal substrate.
8. The method as claimed in claim 7 , wherein the buffer layer is formed of a silicon oxide and the metal substrate has a coefficient of thermal expansion ranging from about 2.86 ppm/° C. to about 11.48 ppm/° C.
9. The method as claimed in claim 7 , wherein the buffer layer is formed of a silicon nitride and the metal substrate has a coefficient of thermal expansion ranging from about 3.19 ppm/° C. to about 8.01 ppm/° C.
10. The method as claimed in claim 7 , wherein the predetermined coefficient of thermal expansion of the metal substrate satisfies an equation as follows:
α
f
+
0.270
×
(
1
-
v
f
)
E
f
≤
α
s
≤
α
f
+
0.741
×
(
1
-
v
f
)
E
f
.
11. The method as claimed in claim 10 , wherein the buffer layer is formed of a silicon oxide and the metal substrate has a coefficient of thermal expansion ranging from about 4.14 ppm/° C. to about 9.72 ppm/° C.
12. The method as claimed in claim 10 , wherein the buffer layer is formed of a silicon nitride and the metal substrate has a coefficient of thermal expansion ranging from about 3.79 ppm/° C. to about 7.05 ppm/° C.
13. The method as claimed in claim 7 , wherein the buffer layer is formed on the metal substrate at a temperature of about 300° C. to about 400° C.
14. A thin film transistor (TFT), comprising:
a metal substrate having a predetermined coefficient of thermal expansion; and
a buffer layer on the metal substrate, the buffer layer including a silicon oxide or a silicon nitride;
a semiconductor layer on the buffer layer, the semiconductor layer including a source region, a drain region, and a channel region;
a gate electrode on the semiconductor layer, the gate electrode overlapping the channel region of the semiconductor layer;
a gate insulating layer between the semiconductor layer and the gate electrode;
a source electrode electrically connected with the source region of the semiconductor layer; and
a drain electrode electrically connected with the drain region of the semiconductor layer,
wherein the predetermined coefficient of thermal expansion of the metal substrate satisfies an equation as follows,
α
f
+
0.162
×
(
1
-
v
f
)
E
f
≤
α
s
≤
α
f
+
0.889
×
(
1
-
v
f
)
E
f
E f representing Young's modulus of the buffer layer, V f representing Poisson's ratio of the buffer layer, α f representing a coefficient of thermal expansion of the buffer layer, and α s representing the predetermined coefficient of thermal expansion of the metal substrate.
15. The TFT as claimed in claim 14 , wherein the buffer layer includes a silicon oxide, and the predetermined coefficient of thermal expansion of the metal substrate is from about 2.86 ppm/° C. to about 11.48 ppm/° C.
16. The TFT as claimed in claim 14 , wherein the buffer layer includes a silicon nitride, and the predetermined coefficient of thermal expansion of the metal substrate is from about 3.19 ppm/° C. to about 8.01 ppm/° C.
17. The TFT as claimed in claim 14 , wherein the predetermined coefficient of thermal expansion of the metal substrate satisfies an equation as follows:
α
f
+
0.270
×
(
1
-
v
f
)
E
f
≤
α
s
≤
α
f
+
0.741
×
(
1
-
v
f
)
E
f
.
18. The TFT as claimed in claim 17 , wherein the buffer layer includes a silicon oxide, and the predetermined coefficient of thermal expansion of the metal substrate is from about 4.14 ppm/° C. to about 9.72 ppm/° C.
19. The TFT as claimed in claim 17 , wherein the buffer layer includes a silicon nitride, and the predetermined coefficient of thermal expansion of the metal substrate is from about 3.79 ppm/° C. to about 7.05 ppm/° C.
20. The flexible substrate as claimed in claim 1 , wherein:
the buffer layer is silicon oxide having a Young's modulus of the silicon oxide of about 70GPa, a Poisson's ratio of about 0.17, and a coefficient of thermal expansion α f of about 0.94 ppm/° C., and
the predetermined coefficient of thermal expansion of the metal substrate is from about 2.86 ppm/° C. to about 11.48 ppm/° C.
21. The flexible substrate as claimed in claim 20 , wherein the metal substrate is Fe-42Ni alloy.
22. The flexible substrate as claimed in claim 1 , wherein the buffer layer is silicon nitride having a Young's modulus of the silicon nitride of about 120 to 140GPa, a Poisson's ratio of about 0.23, and a coefficient of thermal expansion α f of about 2.3 ppm/° C., and
the predetermined coefficient of thermal expansion of the metal substrate is from about 3.19 ppm/° C. to about 8.01 ppm/° C.
23. The flexible substrate as claimed in claim 22 , wherein the metal substrate is Fe-42Ni alloy.