U.S. patent application number 13/087300 was filed with the patent office on 2012-02-09 for substrate for flexible display and method of manufacturing the substrate.
This patent application is currently assigned to SAMSUNG MOBILE DISPLAY CO., LTD.. Invention is credited to SUNG-GUK AN, DONG-UN JIN, HOON-KEE MIN, SANG-JOON SEO.
Application Number | 20120034451 13/087300 |
Document ID | / |
Family ID | 45556372 |
Filed Date | 2012-02-09 |
United States Patent
Application |
20120034451 |
Kind Code |
A1 |
SEO; SANG-JOON ; et
al. |
February 9, 2012 |
SUBSTRATE FOR FLEXIBLE DISPLAY AND METHOD OF MANUFACTURING THE
SUBSTRATE
Abstract
A substrate for a flexible display is disclosed. The substrate
has a film stress range that does not affect an electronic device
such as a thin film transistor, and includes a barrier layer having
excellent oxygen and moisture blocking characteristics, and a
method of manufacturing the substrate. The substrate includes: a
plastic substrate having a glass transition temperature from about
350.degree. C. to about 500.degree. C.; and a barrier layer
disposed on the plastic substrate, having a multi-layer structure,
wherein at least one silicon oxide layer and at least one silicon
nitride layer are alternately stacked on each other, and having a
film stress from about -200 MPa to about 200 MPa due to the at
least one silicon oxide layer and the at least one silicon nitride
layer.
Inventors: |
SEO; SANG-JOON;
(Yongin-city, KR) ; MIN; HOON-KEE; (Yongin-city,
KR) ; JIN; DONG-UN; (Yongin-city, KR) ; AN;
SUNG-GUK; (Yongin-city, KR) |
Assignee: |
SAMSUNG MOBILE DISPLAY CO.,
LTD.
Yongin-city
KR
|
Family ID: |
45556372 |
Appl. No.: |
13/087300 |
Filed: |
April 14, 2011 |
Current U.S.
Class: |
428/332 ;
427/255.7; 427/419.2; 428/448 |
Current CPC
Class: |
Y10T 428/26 20150115;
H01L 29/786 20130101; C23C 16/401 20130101; G02F 1/133305 20130101;
G02F 2201/501 20130101; C23C 16/345 20130101; H01L 29/6675
20130101 |
Class at
Publication: |
428/332 ;
428/448; 427/419.2; 427/255.7 |
International
Class: |
B32B 5/00 20060101
B32B005/00; C23C 16/34 20060101 C23C016/34; C23C 16/40 20060101
C23C016/40; B32B 9/04 20060101 B32B009/04; B05D 1/36 20060101
B05D001/36 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 3, 2010 |
KR |
10-2010-0074979 |
Claims
1. A flexible substrate, comprising: a plastic substrate having a
glass transition temperature from about 350.degree. C. to about
500.degree. C.; and a barrier layer disposed on the plastic
substrate, having a multi-layer structure, which comprises at least
one silicon oxide layer and at least one silicon nitride layer that
are alternately stacked on each other, the barrier layer having a
film stress from about -200 MPa to about 200 MPa.
2. The substrate of claim 1, wherein the barrier layer comprises: a
first silicon oxide layer; a silicon nitride layer stacked on the
first silicon oxide layer; and a second silicon oxide layer stacked
on the silicon nitride layer.
3. The substrate of claim 1, wherein the barrier layer comprises: a
first silicon oxide layer; a first silicon nitride layer stacked on
the first silicon oxide layer; a second silicon oxide layer stacked
on the first silicon nitride layer; a second silicon nitride layer
stacked on the second silicon oxide layer; and a third silicon
oxide layer stacked on the second silicon nitride layer.
4. The substrate of claim 1, wherein the barrier layer comprises: a
first silicon oxide layer; a first silicon nitride layer stacked on
the first silicon oxide layer; a second silicon oxide layer stacked
on the first silicon nitride layer; a second silicon nitride layer
stacked on the second silicon oxide layer; a third silicon oxide
layer stacked on the second silicon nitride layer; a third silicon
nitride layer stacked on the third silicon oxide layer; and a
fourth silicon oxide layer stacked on the third silicon nitride
layer.
5. The substrate of claim 1, wherein the at least one silicon oxide
layer has compressive film stress, and wherein the at least one
silicon nitride layer has tensile film stress.
6. The substrate of claim 1, wherein a film density of the at least
one silicon nitride layer is from about 2.5 g/cm.sup.3 to about 2.7
g/cm.sup.3.
7. The substrate of claim 1, wherein a hydrogen atom content in the
at least one silicon nitride layer is from about 13% to about
17%.
8. The substrate of claim 1, wherein a thickness of each of the at
least one silicon nitride layer is from about 200 .ANG. to about
1000 .ANG..
9. The substrate of claim 1, wherein a thickness of each of the at
least one silicon oxide layer is from about 1000 .ANG. to about
3000 .ANG..
10. The substrate of claim 1, wherein the plastic substrate
comprises polyimide.
11. A method of manufacturing a flexible substrate, the method
comprising: providing a plastic substrate having a glass transition
temperature from about 350.degree. C. to about 500.degree. C.; and
forming a barrier layer having a film stress from about -200 MPa to
about 200 MPa by alternately stacking at least one silicon oxide
layer and at least one silicon nitride layer on the plastic
substrate.
12. The method of claim 11, wherein the forming of the barrier
layer comprises forming the barrier layer using a high temperature
deposition technique at a temperature from about 350.degree. C. to
about 400.degree. C.
13. The method of claim 11, wherein the barrier layer comprises: a
first silicon oxide layer; a silicon nitride layer stacked on the
first silicon oxide layer; and a second silicon oxide layer stacked
on the silicon nitride layer.
14. The method of claim 11, wherein the barrier layer comprises: a
first silicon oxide layer; a first silicon nitride layer stacked on
the first silicon oxide layer; a second silicon oxide layer stacked
on the first silicon nitride layer; a second silicon nitride layer
stacked on the second silicon oxide layer; and a third silicon
oxide layer stacked on the second silicon nitride layer.
15. The method of claim 11, wherein the barrier layer comprises: a
first silicon oxide layer; a first silicon nitride layer stacked on
the first silicon oxide layer; a second silicon oxide layer stacked
on the first silicon nitride layer; a second silicon nitride layer
stacked on the second silicon oxide layer; a third silicon oxide
layer stacked on the second silicon nitride layer; a third silicon
nitride layer stacked on the third silicon oxide layer; and a
fourth silicon oxide layer stacked on the third silicon nitride
layer.
16. The method of claim 11, wherein the at least one silicon oxide
layer has compressive film stress, and wherein the at least one
silicon nitride layer has tensile film stress.
17. The method of claim 11, wherein a film density of the at least
one silicon nitride layer is from about 2.5 g/cm.sup.3 to about 2.7
g/cm.sup.3.
18. The method of claim 11, wherein a hydrogen atom content in the
at least one silicon nitride layer is from about 13% to about 17%.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATION
[0001] This application claims the benefit of Korean Patent
Application No. 10-2010-0074979, filed on Aug. 3, 2010, in the
Korean Intellectual Property Office, the disclosure of which is
incorporated herein in its entirety by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present disclosure relates to a substrate for a flexible
display, and a method of manufacturing the substrate.
[0004] 2. Description of the Related Art
[0005] Markets of liquid crystal display devices and organic light
emitting display devices are currently expanding to displays of
digital cameras, video cameras, and mobile devices, such as
personal digital assistants (PDAs) and mobile phones. The displays
of mobile devices need to be thin, light, and moreover,
unbreakable. In order to form a thin and light display, a method of
preparing a display by using a conventional glass substrate, and
then thinning the glass substrate mechanically or chemically has
been introduced, besides a method of preparing a display by using a
thin glass substrate. However such methods are complicated and the
glass substrate may easily break, and thus the methods are
difficult to be actually used. Also, for the mobile devices to be
easily carried and to be applied to display devices of various
shapes, the displays may be flexible to realize a curved surface.
However, it is difficult for the conventional glass substrate to
have flexibility.
[0006] Accordingly, there have been attempts to manufacture a
display device by using a plastic substrate, but the plastic
substrate has high level of moisture and oxygen penetration and is
not suitable for a high temperature process.
SUMMARY OF THE INVENTION
[0007] One aspect of the present invention provides a substrate for
a thin, flexible display, which has film stress range that does not
affect an electronic device, such as a thin film transistor, and
includes a barrier layer having excellent oxygen and moisture
blocking characteristics, and a method of manufacturing the
substrate.
[0008] According to the aspect of the present invention, the
substrate including: a plastic substrate having a glass transition
temperature from about 350.degree. C. to about 500.degree. C.; and
a barrier layer disposed on the plastic substrate, having a
multi-layer structure, wherein at least one silicon oxide layer and
at least one silicon nitride layer are alternately stacked on each
other, and having a film stress from about -200 MPa to about 200
MPa due to the at least one silicon oxide layer and the at least
one silicon nitride layer.
[0009] The barrier layer may include: a first silicon oxide layer;
a silicon nitride layer stacked on the first silicon oxide layer;
and a second silicon oxide layer stacked on the silicon nitride
layer.
[0010] The barrier layer may include: a first silicon oxide layer;
a first silicon nitride layer stacked on the first silicon oxide
layer; a second silicon oxide layer stacked on the first silicon
nitride layer; a second silicon nitride layer stacked on the second
silicon oxide layer; and a third silicon oxide layer stacked on the
second silicon nitride layer.
[0011] The barrier layer may include: a first silicon oxide layer;
a first silicon nitride layer stacked on the first silicon oxide
layer; a second silicon oxide layer stacked on the first silicon
nitride layer; a second silicon nitride layer stacked on the second
silicon oxide layer; a third silicon oxide layer stacked on the
second silicon nitride layer; a third silicon nitride layer stacked
on the third silicon oxide layer; and a fourth silicon oxide layer
stacked on the third silicon nitride layer.
[0012] The at least one silicon oxide layer included in the barrier
layer may have compressive film stress. The at least one silicon
nitride layer included in the barrier layer may have tensile film
stress.
[0013] The at least one silicon nitride layer may have a film
density from about 2.5 g/cm.sup.3 to about 2.7 g/cm.sup.3.
[0014] The at least one silicon nitride layer may have a hydrogen
atom content from about 13% to about 17%.
[0015] Each of the at least one silicon nitride layer may have a
thickness from about 200 .ANG. to about 1000 .ANG..
[0016] Each of the at least one silicon oxide layer may have a
thickness from about 1000 .ANG. to about 3000 .ANG..
[0017] The plastic substrate may include at least one of polyimide,
polycarbonate, polyphenylene sulfide, and poly(arylen ether
sulfone.
[0018] According to another aspect of the present invention, there
is provided a method of manufacturing a substrate for a flexible
substrate, the method including: providing a plastic substrate
having a glass transition temperature from about 350.degree. C. to
about 500.degree. C.; and forming a barrier layer having a film
stress from about -200 MPa to about 200 MPa by alternately stacking
at least one silicon oxide layer and at least one silicon nitride
layer on the plastic substrate.
[0019] The forming of the barrier layer may include high
temperature deposition at a temperature from about 350.degree. C.
to about 400.degree. C.
[0020] The barrier layer may include: a first silicon oxide layer;
a silicon nitride layer stacked on the first silicon oxide layer;
and a second silicon oxide layer stacked on the silicon nitride
layer.
[0021] The barrier layer may include: a first silicon oxide layer;
a first silicon nitride layer stacked on the first silicon oxide
layer; a second silicon oxide layer stacked on the first silicon
nitride layer; a second silicon nitride layer stacked on the second
silicon oxide layer; and a third silicon oxide layer stacked on the
second silicon nitride layer.
[0022] The barrier layer may include: a first silicon oxide layer;
a first silicon nitride layer stacked on the first silicon oxide
layer; a second silicon oxide layer stacked on the first silicon
nitride layer; a second silicon nitride layer stacked on the second
silicon oxide layer; a third silicon oxide layer stacked on the
second silicon nitride layer; a third silicon nitride layer stacked
on the third silicon oxide layer; and a fourth silicon oxide layer
stacked on the third silicon nitride layer.
[0023] The at least one silicon oxide layer included in the barrier
layer may have compressive film stress. The at least one silicon
nitride layer included in the barrier layer may have tensile film
stress.
[0024] The at least one silicon nitride layer may have a film
density from about 2.5 g/cm.sup.3 to about 2.7 g/cm.sup.3.
[0025] The at least one silicon nitride layer may have a hydrogen
atom content from about 13% to about 17%.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The above and other features and advantages of the present
invention will become more apparent by describing in detail
exemplary embodiments thereof with reference to the attached
drawings in which:
[0027] FIG. 1 is a cross-sectional view of a substrate for a
flexible display, according to an embodiment of the present
invention;
[0028] FIG. 2 is a cross-sectional view of a substrate for a
flexible display, according to another embodiment of the present
invention;
[0029] FIG. 3 is a cross-sectional view of a substrate for a
flexible display, according to another embodiment of the present
invention;
[0030] FIGS. 4 through 6 are diagrams for describing a method of
manufacturing a display device by using the substrate of FIG. 1,
according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0031] While the invention have numerous embodiments, only some of
such embodiments will be illustrated in the drawings and described
in detail in the written description. The present invention is not
limited to the particular embodiments, and there are changes,
modifications and substitutes that do not depart from the spirit
and technical scope of the present invention.
[0032] While terms of "first," "second," "third," etc., are used to
describe various components, such terms do not carry the meaning of
order. These terms are used only to distinguish one component from
another. Also, in the present specification, the terms of
"including" and "having," are intended to mean "comprising" so as
to indicate the possibility of existence of any additional
features, numbers, steps, actions, components, parts, or
combinations.
[0033] Now, various features of the present invention will be
described more fully with reference to the accompanying drawings,
in which exemplary embodiments of the invention are shown.
[0034] FIG. 1 is a cross-sectional view of a substrate 1000 for a
flexible display, according to an embodiment of the present
invention.
[0035] The substrate 1000 according to the current embodiment of
the present invention includes a plastic substrate 50, and a
barrier layer 100 disposed on the plastic substrate 50.
[0036] The plastic substrate 50 has flexibility enough to realize a
flexible display. Also, the plastic substrate 50 may have a thin
film structure for the flexibility.
[0037] The plastic substrate 50 may have a glass transition
temperature (Tg) from about 350.degree. C. to about 500.degree. C.
With this feature, the plastic substrate 50 can stably perform
functions of a substrate without being deformed even when the
barrier layer 100, a thin film transistor, and an electronic device
are formed on the plastic substrate 50 at high temperature. In
detail, the barrier layer 100 is formed at a temperature from about
350.degree. C. to about 400.degree. C. Accordingly, if the Tg of
the plastic substrate 50 is less than about 350.degree. C., the
plastic substrate 50 may change to a rubber having elasticity at
about 350.degree. C. and thus may be unable to perform the
functions of substrate. On the other hand, the plastic substrate 50
having the Tg exceeding about 500.degree. C. has bad
processability.
[0038] The plastic substrate 50 may be formed of a polymer having
high thermal resistance. For example, the plastic substrate 50 may
include at least one material selected from the group consisting of
polyethersulfone (PES), polyacrylate (PAR), polyetherimide (PEI),
polyethylene naphthalate (PEN), polyethylene terephthalate (PET),
polyphenylene sulfide (PPS), polyarylate, polyimide (PI),
polycarbonate (PC), cellulose triacetate (TAC), cellulose acetate
propionate (CAP), and poly(arylen ether sulfone) as a type of
engineering plastic. Specifically, PI has excellent mechanical
strength and has better thermal resistance than other polymers as
the Tg of PI is about 450.degree. C. Accordingly, even when the
barrier layer 100 is disposed on the plastic substrate 50 including
PI at high temperature, the plastic substrate 50 may stably perform
the functions of a substrate without drooping due to a weight of
the barrier layer 100. Also, the plastic substrate 50 including at
least one of the above polymers has high level of oxygen and
moisture penetration. Accordingly, when a thin film transistor and
an electronic device are directly formed on the plastic substrate
50, the thin film transistor and the electronic device may be
exposed to oxygen and moisture penetrating through the plastic
substrate 50, and thus lifetime of a display may be remarkably
reduced. The barrier layer 100 is provided for blocking the
moisture and oxygen formed on the plastic substrate 50.
[0039] In embodiments, the barrier layer 100 is formed on the
plastic substrate 50, and may have a multi-layer structure, wherein
at least one silicon oxide (SiO.sub.x) layer and at least one
silicon nitride (SiN.sub.x) layer are alternately stacked on each
other. The barrier layer 100 forms a flat surface on the plastic
substrate 50 and blocks unwanted substances, such as oxygen and
moisture, from penetrating through the plastic substrate 50. The
barrier layer 100 may be formed using a plasma enhanced chemical
vapor deposition (PECVD) method using plasma. However, forming the
barrier layer 100 is not limited thereto, and any deposition method
may be used, such as an atmospheric pressure CVD (APCVD) method or
a low pressure CVD (LPCVD) method. According to an embodiment of
the present invention, the barrier layer 100 is formed at high
temperature so that the barrier layer 100 is thin, has a uniform
stress, and has a high film density. Specifically, in embodiments,
since the plastic substrate 50 having a high Tg is used, the
barrier layer 100 may be formed at high temperature.
[0040] In embodiments, the barrier layer 100 is formed at a
temperature from about 350.degree. C. to about 400.degree. C.
Accordingly, the barrier layer 100 may be formed to have a uniform
film stress, a thin thickness, and a high film density to
effectively block moisture and oxygen. Characteristics of the
barrier layer 100 will now be described in detail.
[0041] Referring to FIG. 1, the barrier layer 100 according to the
current embodiment of the present invention includes a first
silicon oxide layer 101 formed on the plastic substrate 50, a first
silicon nitride layer 201 formed on the first silicon oxide layer
101, and a second silicon oxide layer 102 formed on the first
silicon nitride layer 201. Here, the first and second silicon oxide
layers 101 and 102 may each have a film stress from about -100 MPa
to about -300 MPa, and the first silicon nitride layer 201 may have
a film stress from about -50 MPa to about 200 MPa. The film stress
denotes a size of strength of a thin film layer per unit area, and
may be compressive film stress or tensile film stress. Here, the
compressive film stress is indicated with a negative integer, and
the tensile film stress is indicated with a positive integer. Also,
the compressive film stress may be power pushing a thin film to
bend the thin film downward. On the other hand, the tensile film
stress may be power pulling a thin film to bend the thin film
upward.
[0042] In embodiments, each of the first and second silicon oxide
layers 101 and 102 may have compressive film stress, and the first
silicon nitride layer 201 may have tensile film stress.
Accordingly, with the structure, in which the first silicon oxide
layer 101, the first silicon nitride layer 201, and the second
silicon oxide layer 102 are alternatively stacked and have
different types of film stresses, the barrier layer 100 becomes
strong against external shock or bending. Also, the substrate 1000
does not affect a thin film transistor and an electronic device
disposed on the barrier layer 100 in terms of stress.
[0043] The barrier layer 100 has a film stress from about -200 MPa
to about 200 MPa. When the film stress of the barrier layer 100 is
below about -200 MPa or above about 200 MPa, the substrate 1000
including the barrier layer 100 may bend upward or downward. In
this case, the substrate 1000 may be stuck in an equipment during
transference or operation. Also, when the film stress of the
barrier layer 100 is below about -200 MPa or above about 200 MPa,
dislocation may be generated at an interface between a top surface
of the barrier layer 100 and another thin film disposed on the top
surface of the barrier layer 100 due to an excessive stress. Such
dislocation deteriorates characteristics of the thin film
transistor and the electronic device disposed on the barrier layer
100. Besides, film quality of the other film disposed on the
barrier layer 100 may deteriorate, thereby deteriorating electric
characteristics of the electronic device or causing a defect in the
electronic device. Alternatively, the barrier layer 100 may have a
film stress of about 0 MPa, because the film stress of the barrier
layer 100 may be counterbalanced as the first and second silicon
oxide layers 101 and 102, and the first silicon nitride layer 201
have different film stresses. Accordingly, even when the barrier
layer 100 has the film stress of 0 MPa, each of the first and
second silicon oxide layers 101 and 102 and the first silicon
nitride layer 201 still has film stress.
[0044] Also, The thickness of the first silicon nitride layer 201
may be from about 200 .ANG. to about 1000 .ANG.. Here, the
thickness of the first silicon nitride layer 201 is about 200 .ANG.
or above since 200 .ANG. is a minimum thickness for forming a thin
film. The thickness of the first silicon nitride layer 201 is
limited to about 1000 .ANG. or below due to the following reason.
When the first silicon nitride layer 201 is formed at high
temperature, hydrogen atoms are separated and escape from the first
silicon nitride layer 201 as coherence between silicon atoms and
the hydrogen atoms decreases, and thus a hydrogen atom content in
the first silicon nitride layer 201 decreases. Accordingly, film
stress of the first silicon nitride layer 201 changes from
compressive film stress to tensile film stress. At this time, when
the thickness of the first silicon nitride layer 201 exceeds 1000
.ANG., the first silicon nitride layer 201 may break or be
detached.
[0045] In embodiments, each of the first and second silicon oxide
layers 101 and 102 may have a thickness from about 1000 .ANG. to
about 3000 .ANG.. When the thickness of each of the first and
second silicon oxide layers 101 and 102 is below about 1000 .ANG.,
the first and second silicon oxide layers 101 and 102 are difficult
to be formed, and when the thickness of each of the first and
second silicon oxide layers 101 and 102 is above about 3000 .ANG.,
a time taken to form the first and second silicon oxide layers 101
and 102 remarkably increases.
[0046] In embodiments, moisture and oxygen penetration may be
controlled by the hydrogen atom content in the first silicon
nitride layer 201 included in the barrier layer 100.
[0047] In embodiments, the first silicon nitride layer 201 is
formed at a temperature from about 350.degree. C. to about
400.degree. C. using the PECVD technique as follows. The plastic
substrate 50 on which a layer is deposited is put into a chamber,
and a process temperature is set to be from about 350.degree. C. to
about 400.degree. C. under a plasma atmosphere. The first silicon
nitride layer 201 is formed with silane (SiH.sub.4) and ammonia
(NH.sub.3). The silane is decomposed into silicon (Si) atoms and
hydrogen (H) atoms, and the ammonia is decomposed into nitrogen (N)
atoms and hydrogen atoms by plasma. These decomposed silicon,
hydrogen, and nitrogen atoms fall onto the plastic substrate 50,
and react to form silicon nitride at surface temperature of the
plastic substrate 50.
[0048] Here, the nitrogen atoms and the hydrogen atoms combine with
the silicon atoms. Since coherence between the silicon atoms and
the hydrogen atoms is weaker than coherence between the silicon
atoms and the nitrogen atoms, even when the silicon atoms and the
nitrogen atoms maintain the coherence, the silicon atoms and the
hydrogen atoms are separated from each other at high temperature.
As a result, the hydrogen atoms separated from the silicon atoms
form hydrogen molecules (H.sub.2) and disappear. Accordingly, when
the first silicon nitride layer 201 is formed at high temperature,
the hydrogen atom content in the first silicon nitride layer 201 is
low. Also, as the hydrogen atom content in the first silicon
nitride layer 201 decreases, i.e., as the coherence between the
nitrogen atoms and silicon atoms increases, the film stress of the
first silicon nitride layer 201 becomes more tensile. Also, as the
hydrogen atom content in the first silicon nitride layer 201
decreases, film density of the first silicon nitride layer 201
increases.
[0049] In embodiments, the hydrogen atom content in the first
silicon nitride layer 201 may be from about 13% to about 17%,
because the hydrogen atom content in the first silicon nitride
layer 201 depends on the temperature of forming silicon nitride.
Experimentally, when a silicon nitride layer is deposited at a
temperature from about 350.degree. C. to about 400.degree. C.,
hydrogen atom content in the silicon nitride layer is from about
13% to about 17%. Also, if the hydrogen atom content in the first
silicon nitride layer 201 is below about 13%, film density of the
first silicon nitride layer 201 may increase, but tensile film
stress of the first silicon nitride layer 201 increases above a
threshold value and thus a stress balance of the barrier layer 100
may break. On the other hand, if the hydrogen atom content in the
first silicon nitride layer 201 is above about 17%, the film
density of the first silicon nitride layer 201 may remarkably
decrease, and thus unwanted substances, such as oxygen and
moisture, may penetrate into the thin film transistor and the
electronic device.
[0050] In embodiments, he film density of the first silicon nitride
layer 201 may be from about 2.5 g/cm.sup.3 to about 2.7 g/cm.sup.3,
The film density of the first silicon nitride layer 201 depends on
the hydrogen atom content in the first silicon nitride layer 201.
When the hydrogen atom content in the first silicon nitride layer
201 is from about 13% to about 17%, the film density of the first
silicon nitride layer 201 may be from about 2.5 g/cm.sup.3 to about
2.7 g/cm.sup.3. If the film density of the first silicon nitride
layer 201 is below about 2.5 g/cm.sup.3, the function of the first
silicon nitride layer 201 for blocking impure elements, such as
oxygen and moisture, from penetrating into the thin film transistor
and the electronic device may remarkably deteriorate. On the other
hand, the film density of the first silicon nitride layer 201 is
difficult to exceed about 2.7 g/cm.sup.3 if the hydrogen atom
content is from about 13% to about 17%.
[0051] FIG. 2 is a cross-sectional view of a substrate 1000a for a
flexible display, according to another embodiment of the present
invention. Referring to FIG. 2, the substrate 1000a is similar to
the substrate 1000 as at least one silicon oxide layer and at least
one silicon nitride layer are alternately stacked on the plastic
substrate 50. However, barrier layer 100a of the substrate 1000
includes the first silicon oxide layer 101, the first silicon
nitride layer 201 disposed on the first silicon oxide layer 101,
the second silicon oxide layer 102 disposed on the first silicon
nitride layer 201, a second silicon nitride layer 202 disposed on
the second silicon oxide layer 102, and a third silicon oxide layer
103 disposed on the second silicon nitride layer 202. Here,
discussions of the barrier layer 100 of FIG. 1 are all applicable
to the barrier layer 100a. Specifically, the characteristics of the
barrier layer 100 of FIG. 1 are all applicable to the
characteristics of the barrier layer 100a, including thicknesses,
types of film stresses, contents of hydrogen atoms, film densities.
Also, the method of making the oxide layers 101, 102 and nitride
layer 202 of the embodiment of FIG. 1 and conditions of forming
these layers are also applicable to the embodiment of FIG. 2. Thus,
the discussions are not repeated.
[0052] FIG. 3 is a cross-sectional view of a substrate 1000b for a
flexible display, according to another embodiment of the present
invention. Referring to FIG. 3, the substrate 1000b is similar to
the substrates 1000 and 1000a as at least one silicon oxide layer
and at least one silicon nitride layer are alternately stacked on
the plastic substrate 50. However, barrier layer 100b of the
substrate 1000b includes the first silicon oxide layer 101, the
first silicon nitride layer 201 disposed on the first silicon oxide
layer 101, the second silicon oxide layer 102 disposed on the first
silicon nitride layer 201, the second silicon nitride layer 202
disposed on the second silicon oxide layer 102, the third silicon
oxide layer 103 disposed on the second silicon nitride layer 202, a
third silicon nitride layer 203 disposed on the third silicon oxide
layer 103, and a fourth silicon oxide layer 104 disposed on the
third silicon nitride layer 203. Here, discussions of the barrier
layer 100 of FIG. 1 are all applicable to the barrier layer 100b.
Specifically, the characteristics of the barrier layer 100 of FIG.
1 are all applicable to the characteristics of the barrier layer
100b, including thicknesses, types of film stresses, contents of
hydrogen atoms, film densities. Also, the method of making the
oxide layers 101, 102 and nitride layer 202 of the embodiment of
FIG. 1 and conditions of forming these layers are also applicable
to the embodiment of FIG. 3. Thus, the discussions are not
repeated.
[0053] FIGS. 4 through 6 are diagrams for describing a method of
manufacturing a display device by using the substrate 1000 of FIG.
1, according to an embodiment of the present invention.
Specifically, FIGS. 4 and 5 are diagrams for describing a method of
manufacturing the substrate 1000. For the convenience of
description, only the method used for the substrate 1000 is
described. However, the same method will also be applied to the
substrates 1000a and 1000b.
[0054] Referring to FIG. 4, first, the plastic substrate 50 is
prepared. The Tg of the plastic substrate 50 may be from about
350.degree. C. to about 500.degree. C. so that the plastic
substrate 50 stand high temperature treatments.
[0055] Referring to FIG. 5, the barrier layer 100 is formed on the
plastic substrate 50. Here, the barrier layer 100 is formed at a
temperature from about 350.degree. C. to about 400.degree. C.
according to a PECVD method. In detail, the barrier layer 100
includes the first silicon oxide layer 101 formed on the plastic
substrate 50, the first silicon nitride layer 201 formed on the
first silicon oxide layer 101, and the second silicon oxide layer
102 formed on the first silicon nitride layer 201. Here, the
thickness of each of the first and second silicon oxide layers 101
and 102 is from about 1000 .ANG. to about 3000 .ANG., and the
thickness of the first silicon nitride layer 201 is from about 200
.ANG. to about 1000 .ANG.. Each of the first and second silicon
oxide layers 101 and 102 has compressive film stress, and the first
silicon nitride layer 201 has tensile film stress. Also, the film
stress of the barrier layer 100 is from about -200 MPa to about 200
MPa. Here, if the film stress of the barrier layer 100 is outside
the above range, the substrate 1000 could bend, or dislocation
could occur in the interface between the barrier layer 100 and a
device that is formed on the barrier layer 100 due to the film
stress.
[0056] In embodiments, the first silicon nitride layer 201 included
in the barrier layer 100 may be formed at a temperature from about
350.degree. C. to about 400.degree. C. according to a PECVD method,
by using silane and ammonia. In embodiments, the first silicon
nitride layer 201 formed as described above has a hydrogen atom
content from about 13% to about 17%, and a film density from about
2.5 g/cm.sup.3 to about 2.7 g/cm.sup.3, In embodiments, when the
hydrogen atom content in the first silicon nitride layer 201 is
from about 13% to about 17%, the film density of the first silicon
nitride layer 201 may be from about 2.5 g/cm.sup.3 to about 2.7
g/cm.sup.3 and the first silicon nitride layer 201 may block
moisture and oxygen suitably to manufacture the display device.
[0057] Referring to FIG. 6, in embodiments, a semiconductor active
layer 10, including a source region 10s, a drain region 10d, and a
channel region 10c, is patterned and formed on the barrier layer
100, and a first insulation layer 11 is formed on the semiconductor
active layer 10. A gate electrode 20g corresponding to the
semiconductor active layer 10 is formed on the first insulation
layer 11, and a second insulation layer 12 is formed on the gate
electrode 20g. A contact hole (not shown) is formed in the first
and second insulation layers 11 and 12, and a source electrode 20s
and a drain electrode 20d are formed on the second insulation layer
12 and are electrically connected to the semiconductor active layer
10 through the contact hole, thereby completing the manufacture of
a thin film transistor. Also, although not illustrated in FIG. 6, a
flexible display may be manufactured by further forming a capacitor
and an electronic device such as an organic light emitting device
(OLED).
[0058] When the barrier layer is not formed at high temperature,
the silicon oxide layer and silicon nitride layer may need to be
thick so as to prevent moisture and oxygen from penetrating.
Alternatively, when the barrier layer is formed at a low
temperature, particles of the barrier layer are loose, and thus
film stress of the barrier layer is high and a hydrogen atom
content is high. Accordingly, film density of the barrier layer is
low. As a result, when the barrier layer is formed at low
temperature, the barrier layer may have a high film stress, and
thus a thin film transistor and an electronic device are adversely
affected, moisture and oxygen blocking characteristics are low.
However, according to embodiments of the present invention, these
can be resolved by forming the barrier layer at high temperature
and with the use of a plastic substrate having a high Tg.
[0059] FIG. 6 illustrates a top gate thin film transistor that can
be formed over a barrier layer according to embodiments of the
invention. However, alterntatively a bottom gate thin film
transistor can be formed similarly. Also, only one thin film
transistor is shown in FIG. 6, but this is only for convenience of
description, and a plurality of thin film transistors, a plurality
of capacitors, or a plurality of OLEDs may be included.
[0060] In addition, in FIG. 6, the substrate 1000 is used as a
lower substrate formed below the thin film transistor and the
electronic device, but the substrate 1000 may also be disposed in
an encapsulating member. In other words, the encapsulating member
including the substrate 1000 is separately formed, and the
encapsulating member is combined to an OLED, thereby easily
encapsulating the OLED.
[0061] Also, the substrate 1000 may be used for any one of various
flat display devices, such as organic light emitting display
devices and liquid crystal display devices.
[0062] According to a substrate for a flexible display and a method
of manufacturing the substrate according to one or more embodiments
of the present invention, a barrier layer is formed on a plastic
substrate at high temperature, and thus the substrate having a thin
thickness and film stress range that does not adversely affect a
thin film transistor and an electronic device may be provided.
[0063] Also, the barrier layer includes a silicon nitride layer
that has a low hydrogen atom content in the silicon nitride layer.
Thus, the silicon nitride layer has a high film density, thereby
highly efficiently blocking moisture and oxygen penetration.
[0064] While the present invention has been particularly shown and
described with reference to exemplary embodiments thereof, it will
be understood by those of ordinary skill in the art that various
changes in form and details may be made therein without departing
from the spirit and scope of the present invention as defined by
the following claims.
* * * * *