U.S. patent application number 11/726551 was filed with the patent office on 2007-07-19 for method of repairing a light-emitting device and method of manufacturing a light-emitting device.
This patent application is currently assigned to Semiconductor Energy Laboratory Co., Ltd.. Invention is credited to Shunpei Yamazaki.
Application Number | 20070166843 11/726551 |
Document ID | / |
Family ID | 19009886 |
Filed Date | 2007-07-19 |
United States Patent
Application |
20070166843 |
Kind Code |
A1 |
Yamazaki; Shunpei |
July 19, 2007 |
Method of repairing a light-emitting device and method of
manufacturing a light-emitting device
Abstract
A method of repairing a light-emitting device capable of
performing high quality image display even if pinholes are formed
when forming an organic compound layer is provided. Device
contamination can be prevented during repair. By applying a reverse
bias voltage to an organic light emitting element during fixed
periods of time, the electric current flowing in the EL element
during application of the reverse bias voltage is reduced. Further,
by forming a cathode so as to contain as little as possible of the
high mobility ions Li and Na, contamination of the device when the
reverse bias is applied can he prevented. It is preferable to use
AlMg and MgAg for this type of cathode.
Inventors: |
Yamazaki; Shunpei;
(Kanagawa, JP) |
Correspondence
Address: |
COOK, ALEX, MCFARRON, MANZO, CUMMINGS & MEHLER LTD
SUITE 2850
200 WEST ADAMS STREET
CHICAGO
IL
60606
US
|
Assignee: |
Semiconductor Energy Laboratory
Co., Ltd.
|
Family ID: |
19009886 |
Appl. No.: |
11/726551 |
Filed: |
March 22, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10873592 |
Jun 22, 2004 |
7195499 |
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11726551 |
Mar 22, 2007 |
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10158658 |
May 30, 2002 |
6777249 |
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10873592 |
Jun 22, 2004 |
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Current U.S.
Class: |
438/4 |
Current CPC
Class: |
H01L 51/5221 20130101;
H01L 27/32 20130101; G09G 2300/0426 20130101; H01L 51/52 20130101;
G09G 2330/08 20130101; G09G 2320/043 20130101; H01L 2251/568
20130101; G09G 3/3216 20130101; G09G 2300/0809 20130101; G09G 3/006
20130101; G09G 2310/0251 20130101; G09G 2310/0256 20130101; G09G
2300/0842 20130101; G09G 2310/061 20130101; G09G 3/3233 20130101;
H01L 27/3244 20130101; G09G 2300/0861 20130101 |
Class at
Publication: |
438/004 |
International
Class: |
H01L 21/00 20060101
H01L021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 1, 2001 |
JP |
2001-167512 |
Claims
1-42. (canceled)
43. A method of repairing a light-emitting device comprising a
light emitting element having an anode, a cathode, and a compound
layer interposed therbetween, wherein the cathode contains Mg, and
at least one of Al and Ag, the repairing method comprising:
applying a reverse bias voltage between the anode and the
cathode.
44-87. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method of repairing a
light-emitting device, and to a method of manufacturing a
light-emitting device using the repairing method in an intermediate
process step. More specifically, the present invention relates to a
method of repairing a light-emitting device by applying a reverse
bias to organic light emitting,elements, and to a method of
manufacturing a light-emitting device using the repairing
method.
[0003] The term "light-emitting device" is a generic term referring
to organic light emitting displays in which organic light emitting
elements formed on a substrate are enclosed between the substrate
and a covering material, and to modules in which ICs are mounted in
the organic light emitting displays.
[0004] 2. Description of the Related Art
[0005] Organic light emitting elements are self light emitting, and
therefore have high visibility. In addition to organic light
emitting elements being optimal for making devices thinner because
a backlight like that used in liquid crystal display devices (LCDs)
is not needed, there is no limit on the angle of view.
Light-emitting devices using organic light emitting elements have
therefore been in the spotlight in recent years as electro-optical
devices that can replace CRTs and LCDs.
[0006] Organic light emitting elements have a layer containing an
organic compound (hereafter referred to as an organic compound
layer) in which luminescence (electroluminescence) is generated by
the addition of an electric field, an anode layer, and a cathode
layer. Two types of luminescence exist, light emission when
returning to a base state from a singlet excited state
(fluorescence) and light emission when returning to a base state
from a triplet excited state (phosphorescence), and it is possible
to apply the repairing method of the present invention to
light-emitting devices using either type of light emission.
[0007] Note that, in this specification, all layers formed between
an anode and a cathode are defined as the organic compound layer.
Specifically, light emitting layers, hole injecting layers,
electron injecting layers, hole transporting layers, electron
transporting layers, and the like are included in the term organic
compound layer. Organic light emitting elements basically have a
structure in which an anode, a light emitting layer, and a cathode
are laminated in the order. Other structures also exist in addition
to this structure, such as one in which an anode, a hole injecting
layer, a light emitting layer, and a cathode are laminated in the
order, and one in which an anode, a hole injecting layer, a light
emitting layer, an electron transporting layer, and a cathode are
laminated in the order.
[0008] Further, making a light emitting element emit light is
referred to as driving the light emitting element in this
specification. Light emitting elements formed by an anode, an
organic compound layer, and a cathode are referred to as organic
light emitting elements in this specification.
[0009] Organic light emitting elements have high rectification
characteristics, and electric current flows in the organic compound
if the electric potential of the anode is higher than the electric
potential of the cathode. Light is emitted due to recombination of
the carrier. Conversely, if the anode is at a lower electric
potential than the cathode, almost no electric current will flow in
the organic compound layer. From this diode structure, organic
light emitting elements are also referred to as organic light
emitting diodes (OLEDs).
[0010] In making organic light emitting elements, generally one
electrode, either the anode of the cathode, is formed, after which
the organic compound layer is formed so as to contact the
electrode. The remaining electrode is then formed so as to contact
the organic compound layer.
[0011] The main methods of forming the organic compound layer are a
film formation method by evaporation, and a film formation method
by spin coating. Whichever method is used, care is taken when
performing film formation. Substrates are washed before film
formation so that refuse and the like does not adhere to the
substrate during film formation of the electrodes and the organic
compound layer, and management of the cleanliness of a clean room
within which film formation takes place is performed
thoroughly.
[0012] However, even if every effort is made for cleanliness, there
are cases in which refuse and the like adhere to the electrodes or
other films, forming holes (pinholes) in the organic compound
layer. FIG. 12A shows a simple cross sectional diagram of an
organic light emitting element 200 for a case in which there is a
short circuit between two electrodes 201 and 202. If a pinhole is
opened in an organic compound layer 203, then the two electrodes
201 and 202 are connected in the pinhole when forming the electrode
202 on the organic compound layer 203, thus forming a short circuit
in some cases. Note that portions in which two layers formed
sandwiching a light emitting layer therebetween are connected
through pinholes formed in the light emitting layer are hereafter
referred to as defect portions 204.
[0013] The voltage-current characteristics of an organic light
emitting element that does not have a defect portion are shown in
FIG. 13A, and the voltage-current characteristics of an organic
light emitting element that has a short circuit in a defect portion
are shown in FIG. 13B.
[0014] Comparing FIGS. 13A and 13B, it can be seen that the
electric current flowing in the organic light emitting element 200
when a reverse bias voltage is applied to the organic light
emitting element 200 is larger for the case of FIG. 13B.
[0015] This is because the two electrodes are shorted in the defect
portion 204 for the case of FIG. 13B, and current therefore flows
in the defect portion 204, differing from FIG. 13A.
[0016] If the two electrodes 201 and 202 are shorted in the defect
portion 204, then the brightness of light emitted from the organic
compound layer drops. The electric current flowing in an organic
light emitting element having a defect portion when a forward bias
voltage is applied is shown schematically in FIG. 12B.
[0017] It can be considered that the defect portion 204 has a
resistance R.sub.SC therein, and thereby the two electrodes of the
organic light emitting element 200 are connected for cases in which
the two electrodes 201 and 202 are shorted in the defect portion
204. Consequently, if the electric current flowing in the defect
portion 204 is taken as I.sub.SC, and the electric current flowing
in the organic compound layer 203 is taken as I.sub.dio when an
electric current I.sub.ori flows from one electrode of the organic
light emitting element, then the electric current I.sub.ori
satisfies the equation I.sub.ori=I.sub.SC+I.sub.dio.
[0018] If I.sub.ori is taken as fixed in the aforementioned
equation I.sub.ori=I.sub.SC+I.sub.dio, then the current I.sub.dio
actually flowing in the organic compound layer 203 becomes smaller
in organic light emitting elements having defect portions. If the
resistance R.sub.SC in the defect portion 204 becomes smaller, then
I.sub.SC increases, and therefore this tendency becomes more
conspicuous and the rectification properties of the organic light
emitting element 200 collapse.
[0019] If the current I.sub.dio flowing in the organic compound
layer 203 becomes smaller, then the brightness of light emitted
from the organic light emitting element 200 drops. That is, if
there is a short circuit in the defect portion, then the brightness
of light emitted from the organic light emitting element when a
forward bias voltage is applied becomes lower compared to a case in
which there is no short circuit.
[0020] Further, even if the organic compound lager is formed by
laminating together a plurality of layers, if a pinhole is formed
in the light emitting layer, then the hole injecting layer or the
hole transporting layer will be connected to the electron injecting
layer or the electron transporting layer through the pinhole.
Portions in which the hole injecting layer or the hole transporting
layer is connected to the electron injecting layer or the electron
transporting layer also become the source of lowered brightness in
light emitted from the organic light emitting element because a
reverse bias electric current flows, similarly to that in the
defect portion in which the electrodes are shorted. Note that, all
portions in which two layers, formed sandwiching a light emitting
layer therebetween, are connected through a pinhole formed in the
light emitting layer are hereafter referred to generically as
defect portions. The defect portions are portions in which an anode
and a cathode are electrically short-circuited.
[0021] In addition, if there is a short circuit in the defect
portion, then not only will the brightness of light emitted from
the organic light emitting element drop, but the degradation of the
organic compound layer in the vicinity of the defect portion will
be promoted because electric current always flows in the defect
portion.
SUMMARY OF THE INVENTION
[0022] In view of the above problems, an object of the present
invention is to propose a method of repairing a defect portion.
[0023] The applicants of the present invention consider that even
if a defect portion is formed in an organic light emitting element,
a drop in the electric current flowing in an organic compound layer
when a forward bias voltage is applied can be prevented, provided
that the resistance in the defect portion is increased.
[0024] A method of increasing the resistance R.sub.SC in the defect
portion by applying a reverse bias voltage to the organic light
emitting element, causing a reverse bias electric current I.sub.rev
to flow, is proposed.
[0025] If the reverse bias electric current I.sub.rev flows in the
organic light emitting element, then almost all of this current
flows in the defect portion that has a short circuit, and almost
none flows in the organic compound layer. If an electric current
I.sub.SC flowing in the defect portion becomes larger, then the
temperature of the defect portion increases, and therefore the
defect portion burns out, is gasified and vaporizes, or is oxidized
or carbonized and becomes an insulator. A certain change occurs in
the defect portion, and as a result, the resistance R.sub.SC
therefore becomes larger. Note that, in this specification, the
defect portion, after the resistance R.sub.SC has been increased by
the flow of a reverse bias electric current, is referred to as a
denatured layer.
[0026] If the resistance R.sub.SC becomes larger, then the electric
current flowing in the denatured layer becomes smaller when a
forward bias voltage is applied to the organic light emitting
element. Instead, the electric current flowing in the organic
compound layer becomes larger, and the brightness of emitted light
increases.
[0027] Further, degradation of the organic compound layer existing
in the vicinity of the defect portion is easily promoted because
current always flows in the defect portion. However, the denatured
layer has a high resistance R.sub.SC, and therefore current does
not easily flow. The promotion of degradation of the organic
compound layer existing in the vicinity of the denatured layer can
thus be prevented.
[0028] Materials for cathodes of the organic light emitting
elements used in the present invention are considered next. It is
preferable that a material having a low work function be used for
the cathode because electron injection is performed there. Li and
Mg are included in such materials, and their influence on the light
emitting element was investigated.
[0029] The C-V (capacitance-voltage) characteristics were
investigated using a test piece having a MOS (metal oxide silicon)
structure. The ratio between a MOS capacitance C and an insulating
film capacitance C.sub.ox depends upon voltage. When a clean MOS
transistor having no impurities was used, C/C.sub.ox showed an
ideal C-V characteristic unambiguously determined in response to
voltage. Cases in which there is a shift from this ideal C-V
characteristic show that the MOS transistor is contaminated by
ionic impurities.
[0030] The initial characteristics, and the characteristics after
applying a 1.7 MV/cm bias to the MOS transistor at a temperature of
150.degree. C. for one hour were measured. A process in which a
bias is applied while adding thermal shock is referred to as BT
(bias temperature) processing. Taking Si as a base level, positive
bias application processing (+BT processing) and negative bias
application processing (-BT processing) were performed.
[0031] Measurement of the C-V characteristics was performed while
increasing the electrode electric potential from -10V to +10V, and
then decreasing the electrode electric potential from +10V to -10V,
taking Si as the base level.
[0032] For the MOS structure, a silicon oxide film having a 50 nm
film thickness was formed on a silicon substrate, and in addition,
AlMg, MgAg, or AlLi was formed as an electrode on the silicon oxide
film. Note that, for the measurements, the weight ratios were as
follows: AlMg, Al:Mg=95:5; MgAg, Mg:Ag=90:10; and AlLi,
Al:Li=90:110.
[0033] A case of using AlMg as the electrode (FIG. 17) and a case
of using MgAg as the electrode (FIG. 18) show ideal characteristics
in which C/C.sub.ox is unambiguously determined by voltage for both
the initial characteristics, and the characteristics after
performing BT processing. This shows that the diffusion of Mg is at
a level that can be ignored even after imposing the thermal
shock.
[0034] However, for a case in which AlLi was used as the electrode
(FIG. 19), the resulting C-V characteristics show a large shift
compared to the ideal values. In particular, a characteristic 600
showed a large variation with respect to the ideal value after
performing positive bias application BT processing (+BT
processing). It is thought that this is because Li.sup.+ elutes
from the electrode and diffuses due to electrical repulsion when
the AlLi electrode has a positive electric potential. A hysteresis
can also be seen in the C-V characteristics for the initial
characteristics, and for the characteristics after performing
negative bias application processing (-BT processing). This may be
due to a very small amount of Li.sup.+ that elutes by the
application of a positive voltage during measurement.
[0035] The results thus show that electrodes to which high
diffusion Li is added are not preferable for the structure of the
present invention in which the cathode is given a positive electric
potential when applying a reverse bias to the organic light
emitting elements.
[0036] If a reverse bias is applied and Li.sup.+ contained in the
cathode elutes, then the device will become contaminated while the
defect portion is being repaired by the reverse bias application.
The Li.sup.+ that elutes from the cathode has high mobility, and
therefore may penetrate an interlayer insulating film, reach a TFT,
and contaminate a channel layer. The TFT performance thus
degrades.
[0037] Of course, structures in which high mobility Na, not only
Li, is contained in the cathode are also not preferable for a
similar reason. The less the amount of Li and Ni contained in the
cathode becomes, the better.
[0038] Further, it can be seen that it is preferable to use
electrodes that contain low diffusion Mg. For example, the use of
AlMg and MgAg is extremely effective.
[0039] The organic compound layer in the light emitting element of
the present invention can be formed using known organic compound
materials. The organic compound layer may also be formed having an
inorganic material as a portion of the organic compound layer. For
example, by forming the organic compound layer using as a portion a
layer that contains a low work function alkaline metal element, or
an alkaline earth metal element, an increase in the injection
characteristics of electrons from the cathode can be achieved. In
addition, light emitting elements having superior characteristics
can be formed by including an organic material capable of
increasing the transportability of the injected carrier in the
organic compound layer. Note that there are no particular
limitations placed on the type of inorganic materials capable of
being included in the organic compound layer, nor are there
limitations placed on the arrangement of layers containing
inorganic materials within the organic compound layer. Known
inorganic materials can be freely disposed.
[0040] Note that it is also possible to use the present invention
in passive type light-emitting devices, not only in active matrix
type light-emitting devices.
[0041] Hereinbelow, a description is given on the structure of the
present invention.
[0042] According to the present invention, there is provided a
method of repairing a light-emitting device containing an organic
light emitting element having an anode, a cathode, and an organic
compound layer sandwiched between the anode and the cathode,
characterized in that: [0043] the concentration of at least one of
Li and Na contained in the cathode is equal to or less than
1.times.10.sup.18 atoms/cm.sup.3,
[0044] the repairing method comprising: [0045] applying a reverse
bias voltage between the anode and the cathode.
[0046] According to the present invention, there is provided a
method of repairing a light-emitting device containing an organic
light emitting element having an anode, a cathode, and an organic
compound layer sandwiched between the anode and the cathode,
characterized in that: [0047] the concentration of at least one of
Li and Na contained in the cathode is equal to or less than
1.times.10.sup.18 atoms/cm.sup.3,
[0048] the repairing method comprising: [0049] applying a reverse
bias voltage between the anode and the cathode, thus making an
electric current flow in portions at which the anode and the
cathode are electrically short-circuited, causing the
short-circuited portions to emit heat; and [0050] making the
portions that emit heat into higher resistance portions, or
insulating portions.
[0051] According to the present invention, there is provided a
method of repairing a light-emitting device containing an organic
light emitting element having an anode, a cathode, and an organic
compound layer sandwiched between the anode and the cathode,
characterized in that: [0052] the concentration of at least one of
Li and Na contained in the cathode is equal to or less than
1.times.10.sup.18 atoms/cm.sup.3; and [0053] the organic compound
layer has a hole injecting layer, a hole transporting layer, an
electron injecting layer or an electron transporting layer, and a
light emitting layer,
[0054] the repairing method comprising: [0055] applying a reverse
bias voltage between the anode and the cathode, thus making an
electric current flow in portions at which a layer on the light
emitting layer and a layer under the light emitting layer are
electrically short-circuited, causing the short-circuited portions
to emit heat; and [0056] making the portions that emit heat into
higher resistance portions, or insulating portions.
[0057] According to the present invention, there is provided a
method of repairing a light-emitting device containing an organic
light emitting element having an anode, a cathode, and an organic
compound layer sandwiched between the anode and the cathode,
characterized in that: [0058] the concentration of at least one of
Li and Na contained in the cathode is equal to or less than
1.times.10.sup.18 atoms/cm.sup.3,
[0059] the repairing method comprising: [0060] applying a reverse
bias voltage between the anode and the cathode, thus making at
least one of the anode and the cathode penetrate into the organic
compound layer, causing an electric current to flow in portions at
which the anode and the cathode are in electrical contact.
[0061] According to the present invention, there is provided a
method of repairing a light-emitting device, characterized in that
there is the electrical current flowing in portions at which the
anode and the cathode are in electrical contact, causing heat to be
emitted, and-making the portions that emit heat into higher
resistance portions, or insulating portions.
[0062] According to the present invention, there is provided a
method of repairing a light-emitting device containing an organic
light emitting element having an anode, a cathode, and an organic
compound layer sandwiched between the anode and the cathode,
characterized in that: [0063] the concentration of at least one of
Li and Na contained in the cathode is equal to or less than
1.times.10.sup.18 atoms/cm.sup.3, and the organic compound layer
has a hole injecting layer, a hole transporting layer, an electron
injecting layer or an electron transporting layer, and a light
emitting layer;
[0064] the repairing method comprising: [0065] applying a reverse
bias voltage between the anode and the cathode, thus making a layer
on the light emitting layer or a layer under the light emitting
layer penetrate into the light emitting layer, causing an electric
current to flow in portions at which the layer on the light
emitting layer and the layer under the light emitting layer are in
electrical contact.
[0066] According to the present invention, there is provided a
method of repairing a light-emitting device, characterized in that
there is the electrical current flowing in portions at which the
layer on the light emitting layer and the layer under the light
emitting layer are in electrical contact, causing heat to be
emitted, and making the portions that emit heat into higher
resistance portions, or insulating portions.
[0067] According to the present invention, there is provided a
method of repairing a light-emitting device, characterized in that
the cathode is an alloy containing at least one of Be, Mg, Ca, Sr
and Ba.
[0068] According to the present invention, there is provided a
method of repairing a light-emitting device, characterized in that
the cathode is an alloy containing magnesium.
[0069] According to the present invention, there is provided a
method of repairing a light-emitting device, characterized in that
the cathode is AlMg, MgAg or MgAgAl.
[0070] According to the present invention, there is provided a
method of repairing a light-emitting device containing an organic
light emitting element having an anode, a cathode, and an organic
compound layer sandwiched between the anode and the cathode,
characterized in that: [0071] the cathode contains Mg, and at least
one of Al and Ag, the repairing method comprising: [0072] applying
a reverse bias voltage between the anode and the cathode.
[0073] According to the present invention, there is provided a
method of repairing a light-emitting device containing an organic
light emitting element having an anode, a cathode, and an organic
compound layer sandwiched between the anode and the cathode,
characterized in that: [0074] the cathode contains Mg, and at least
one of Al and Ag,
[0075] the repairing method comprising: [0076] applying a reverse
bias voltage between the anode and the cathode, thus causing an
electric current to flow in portions at which the anode and the
cathode are electrically short-circuited, causing the
short-circuited portions to emit heat; and [0077] making the
portions that emit heat into higher resistance portions, or
insulating portions.
[0078] According to the present invention, there is provided a
method of repairing a light-emitting device containing an organic
light emitting element having an anode, a cathode, and an organic
compound layer sandwiched between the anode and the cathode,
characterized in that: [0079] the cathode contains Mg, and at least
one of Al and Ag; and [0080] the organic compound layer has a hole
injecting layer, a hole transporting layer, an electron injecting
layer or an electron transporting layer, and a light emitting
layer,
[0081] the repairing method comprising: [0082] applying a reverse
bias voltage between the anode and the cathode, thus making an
electric current flow in portions at which a layer on the light
emitting layer and a layer under the light emitting layer are
electrically short-circuited, causing the short-circuited portions
to emit heat; and [0083] making the portions that emit heat into
higher resistance portions, or insulating portions.
[0084] According to the present invention, there is provided a
method of repairing a light-emitting device containing an organic
light emitting element having an anode, a cathode, and an organic
compound layer sandwiched between the anode and the cathode,
characterized in that: [0085] the cathode contains Mg, and at least
one of Al and Ag,
[0086] the repairing method comprising: [0087] applying a reverse
bias voltage between the anode and the cathode, thus making at
least one of the anode and the cathode penetrate into the organic
compound layer, causing an electric current to flow in portions at
which the anode and the cathode are in electrical contact.
[0088] According to the present invention, there is provided a
method of repairing a light-emitting device, characterized in that
there is the electrical current flowing in portions at which the
anode and the cathode are in electrical contact, causing heat to be
emitted, and making the portions that emit heat into higher
resistance portions, or insulating portions.
[0089] According to the present invention, there is provided a
method of repairing a light-emitting device containing an organic
light emitting element having an anode, a cathode, and an organic
compound layer sandwiched between the anode and the cathode,
characterized in that: [0090] the cathode contains Mg, and at least
one of Al and Ag; and [0091] the organic compound layer has a hole
injecting layer, a hole transporting layer, an electron injecting
layer or an electron transporting layer, and a light emitting
layer,
[0092] the repairing method comprising: [0093] applying a reverse
bias voltage between the anode and the cathode, thus making a layer
on the light emitting layer or a layer under the light emitting
layer penetrate into the light emitting layer, causing an electric
current to flow in portions at which the layer on the light
emitting layer and the layer under the light emitting layer are in
electrical contact.
[0094] According to the present invention, there is provided a
method of repairing a light-emitting device, characterized in that
there is the electrical current flowing in portions at which the
layer on the light emitting layer and the layer under the light
emitting layer are in electrical contact, causing heat to be
emitted, and making the portions that emit heat into higher
resistance portions, or insulating portions.
[0095] According to the present invention, there is provided a
method of repairing a light-emitting device, characterized in that
the concentration of at least one of Li and Na contained in the
cathode is equal to or less than 1.times.10.sup.18
atoms/cm.sup.3.
[0096] According to the present invention, there is provided a
method of repairing a light-emitting device, characterized in that
the amount of Mg contained in the cathode is equal to or more than
1.times.10.sup.20 atoms/cm.sup.3.
[0097] According to the present invention, there is provided a
method of repairing a light-emitting device, characterized in that
the reverse bias voltage is applied during fixed periods of
time.
[0098] According to the present invention, there is provided a
method of repairing a light-emitting device, characterized in that
the reverse bias voltage is gradually increased during the
application until it settles within .+-.15% of the height at which
an avalanche current begins to flow within the organic compound
layer.
[0099] According to the present invention, there is provided a
method of repairing a light-emitting device, characterized in that
the organic light emitting elements are arranged in a matrix shape,
and a thin film transistor is connected to each of the organic
light emitting elements.
[0100] According to the present invention, there is provided a
method of manufacturing a light-emitting device containing an
organic light emitting element having an anode, a cathode, and an
organic compound layer sandwiched between the anode and the
cathode, characterized by comprising: [0101] forming the cathode
such that the concentration of at least one of Li and Na contained
in the cathode is equal to or less than 1.times.10.sup.18
atoms/cm.sup.3; and then [0102] applying a reverse bias voltage
between the anode and the cathode.
[0103] According to the present invention, there is provided a
method of manufacturing a light-emitting device containing an
organic light emitting element having an anode, a cathode, and an
organic compound layer sandwiched between the anode and the
cathode, characterized by comprising: [0104] forming the cathode
such that the concentration of at least one of Li and Na contained
in the cathode is equal to or less than 1.times.10.sup.18
atoms/cm.sup.3; and then [0105] applying a reverse bias voltage
between the anode and the cathode, thus making an electric current
flow in portions at which the anode and the cathode are
electrically short-circuited, causing the short-circuited portions
to emit heat, and making the portions that emit heat into higher
resistance portions, or insulating portions.
[0106] According to the present invention, there is provided a
method of manufacturing a light-emitting device containing an
organic light emitting element having an anode, a cathode, and an
organic compound layer sandwiched between the anode and the
cathode, characterizing by comprising: [0107] forming the cathode
from an alloy containing Mg and at least one of Al and Ag; and then
[0108] applying a reverse bias voltage between the anode and the
cathode.
[0109] According to the present invention, there is provided a
method of manufacturing a light-emitting device containing an
organic light emitting element having an anode, a cathode, and an
organic compound layer sandwiched between the anode and the
cathode, characterizing by comprising: [0110] forming the cathode
from an alloy containing Mg and at least one of Al and Ag; and then
[0111] applying a reverse bias voltage between the anode and the
cathode, thus making an electric current flow in portions at which
the anode and the cathode are electrically short-circuited, causing
the short-circuited portions to emit heat, and making the portions
that emit heat into higher resistance portions, or insulating
portions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0112] In the accompanying drawings:
[0113] FIGS. 1A and 1B are diagrams schematically showing electric
current flowing in an organic light emitting element when a reverse
bias voltage is applied to the organic light emitting element;
[0114] FIGS. 2A and 2B are diagrams schematically showing changes
in the voltage-current characteristics of an organic light emitting
element during repair processing, and showing electric current
flowing in the organic light emitting element when a forward bias
is applied to the organic light emitting element after repair,
respectively;
[0115] FIG. 3 is a circuit diagram of a pixel of Embodiment 1;
[0116] FIGS. 4A and 4B are diagrams showing a circuit diagram of a
pixel portion of Embodiment 1, and operation of the pixel portion
during repair, respectively;
[0117] FIG. 5 is a circuit diagram of a pixel of Embodiment 2;
[0118] FIGS. 6A and 6B are diagrams showing a circuit diagram of a
pixel portion of Embodiment 2, and operation of the pixel portion
during repair, respectively;
[0119] FIG. 7 is a circuit diagram of a pixel of Embodiment 3;
[0120] FIGS. 8A and 8B are diagrams showing a circuit diagram of a
pixel portion of Embodiment 3, and operation of the pixel portion
during repair, respectively;
[0121] FIGS. 9A and 9B are diagrams showing the structure of
organic light emitting elements of Embodiment 4;
[0122] FIGS. 10A and 10B are diagrams showing the structure of
organic light emitting elements of Embodiment 4;
[0123] FIGS. 11A to 11H are electronic equipment having
light-emitting devices which use the repairing method of Embodiment
10 of the present invention;
[0124] FIGS. 12A and 12B are diagrams showing schematically a cross
sectional diagram of an organic light emitting element having a
defect portion, and electric current flowing when a forward bias
current flows in the organic light emitting element,
respectively;
[0125] FIGS. 13A and 13B are diagrams showing the voltage-current
characteristics of an organic light emitting element;
[0126] FIG. 14 is a cross sectional diagram of a light-emitting
device of Embodiment 5;
[0127] FIG. 15 is a cross sectional diagram of a light-emitting
device of Embodiment 6;
[0128] FIG. 16 is a cross sectional diagram of a light-emitting
device of Embodiment 7;
[0129] FIG. 17 is a diagram showing a MOS structure in which AlMg
is used as an electrode, and the capacitance-voltage
characteristics of the MOS structure;
[0130] FIG. 18 is a diagram showing a MOS structure in which MgAg
is used as an electrode, and the capacitance-voltage
characteristics of the MOS structure;
[0131] FIG. 19 is a diagram showing a MOS structure in which AlLi
is used as an electrode, and the capacitance-voltage
characteristics of the MOS structure; and
[0132] FIGS. 20A and 20B are diagrams of a case of using the
repairing method of he present invention for a passive type
light-emitting device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiment Mode
[0133] A repairing method of the present invention is explained
using FIGS. 1A and 1B. FIG. 1A is a diagram that schematically
shows the flow of electric current when a reverse bias voltage is
applied to an organic light emitting element having a defect
portion.
[0134] A ground voltage GND and a reverse bias voltage V.sub.rev
are alternately applied to the organic light emitting element. A
timing chart for the alternate application of the ground voltage
GND and the reverse bias voltage V.sub.rev is shown in FIG. 1B.
Note that, although the ground voltage GND and the reverse bias
voltage V.sub.rev are applied alternately in the embodiment mode,
the present invention is not limited to this structure. Other
structures may also be used provided that a reverse bias electric
current is made to flow in the organic light emitting element. A
forward bias voltage and the reverse bias voltage V.sub.rev may
therefore also be applied alternately to the organic-light emitting
element.
[0135] Further, although the reverse bias voltage is applied to the
organic light emitting element for fixed time periods in the
embodiment mode, the present invention is not limited by this. A
direct current (DC) reverse bias voltage may also be applied to the
organic light emitting element.
[0136] The reverse bias voltage is gradually increased in the
embodiment mode until the avalanche phenomenon occurs, and an
avalanche current flows in the organic light emitting element. The
voltage at which the avalanche current begins to flow in the
organic light emitting element is referred to as an avalanche
voltage in this specification. However, the present invention is
not limited to this structure. It is possible for a designer to
suitably determine the size of the voltage applied to the organic
light emitting element. The size of the voltage applied to the
organic light emitting element may be one capable of causing the
defect portion to be denatured, and one at which damage to the
organic light emitting element and degradation of an organic
compound layer do not occur.
[0137] Further, a structure in which a DC reverse bias voltage is
gradually increased may also be used.
[0138] In addition, a constant reverse bias voltage may also be
applied to the organic light emitting element for fixed periods of
time, and may be applied by DC.
[0139] It is possible to prevent degradation if the reverse bias
voltage is applied to the organic light emitting element for fixed
periods of time resulting from the generation of heat in the
organic compound layer in the vicinity of the defect portion due to
the applied reverse bias voltage.
[0140] Further, by gradually increasing the size of the reverse
bias voltage, it becomes easy to identify an optimal height of the
reverse bias voltage for repairing the organic light emitting
element.
[0141] If the reverse bias voltage V.sub.rev is applied to the
organic light emitting element, then a reverse bias electric
current I.sub.rev will flow. The reverse bias electric current
I.sub.rev satisfies the equation I.sub.rev=I.sub.dio+I.sub.SC,
where I.sub.dio is the electric current flowing in an organic
compound layer 103, and I.sub.SC is the electric current flowing in
a defect portion 104. Note that there is almost no current flowing
in the organic compound layer, and therefore the reverse bias
electric current I.sub.rev.apprxeq.I.sub.SC.
[0142] The temperature of the defect portion 104 increases if the
electric current I.sub.rev flows in the defect portion 104, and
therefore the defect portion burns out, is gasified and vaporizes,
or is oxidized or carbonized and becomes an insulator, thus
becoming a denatured layer. A resistance R.sub.SC therefore becomes
larger.
[0143] Changes in the voltage-current characteristics of an organic
light emitting element having the defect portion 104 are shown in
FIG. 2A over time when using the repairing method of the present
invention. The graph of the voltage-current characteristics changes
in the direction shown by the arrows in the figure over time. Note
that V.sub.av denotes an avalanche voltage. The electric current
flowing in the organic light emitting element when the reverse bias
voltage is applied becomes smaller as time passes, and therefore
the electric current I.sub.SC flowing in the defect portion becomes
less along with an increase in the resistance R.sub.SC of the
defect portion.
[0144] The flow of electric current when a forward bias voltage is
applied to the organic light emitting element is shown
schematically in FIG. 2B. If the electric current I.sub.SC flowing
in the defect portion becomes smaller, then in practice the
electric current I.sub.dio flowing in the organic compound layer
becomes larger, and the brightness of light emission becomes
higher, when the forward bias voltage is applied to the organic
light emitting element.
[0145] Note that the organic light emitting element has a structure
in which the organic compound layer is sandwiched between an anode
and a cathode. Known materials may be freely used for the anode and
the organic compound lager. However, it is necessary to be careful
such that the high mobility components, for example, Na and Li, are
not mixed into the cathode in the present invention. If the amount
of Li and Na contained in the cathode exceeds 1.times.10.sup.18
atoms/cm.sup.3, then Li and Na diffuse and impart an influence on
TFT performance. Problems such as degradation or instability in the
TFT characteristics become very evident. It is therefore necessary
that the amounts of Na and Li contained in the cathode are each
kept equal to or less than 1.times.10.sup.18 atoms/cm.sup.3.
[0146] An alloy containing low work function magnesium is used for
the cathode in the present invention. It is preferable, for
example, to use alloys such as AlMg and MgAg. The amount of Mg
contained in the cathode can be freely determined while considering
the work function of the cathode. However, if the amount of Mg
contained in the cathode is less than 1.times.10.sup.20
atoms/cm.sup.3, then the work function becomes high, and the
efficiency of light emission falls. Consequently, it is preferable
that the amount of Mg contained in the cathode be at least equal
to, or greater than, 1.times.10.sup.20 atoms/cm.sup.3.
[0147] Even if pinholes are formed due to the influence of refuse
or the like during film formation of an organic compound layer,
therefore forming short circuits between two layers formed
sandwiching a light emitting layer, use of the method of the
present invention can change the short-circuited defect portion
into a denatured portion, increasing its resistance. In addition,
the actual amount of electric current flowing in the organic
compound layer when a forward bias voltage is applied to the
organic light emitting element can be increased. The brightness of
light emission can therefore be increased when the same voltage is
applied, even if a defect portion exists, in accordance with the
repairing method of the present invention.
[0148] Furthermore, an electric current always flows in the defect
portion, and degradation of the organic compound layer existing in
the vicinity of the defect portion is easily promoted. However, the
denatured layer has a high resistance R.sub.sc. It thus becomes
more difficult for current to flow, and promotion of degradation of
the organic compound layer existing in the vicinity of the
denatured layer can be prevented.
[0149] Further, the cathode of the organic light emitting element
has the low diffusion elements Mg, Al, and Ag, as its main
constituents, and it therefore becomes possible to prevent device
contamination accompanying application of the reverse bias
voltage.
Embodiments
[0150] Embodiments of the present invention are explained
below.
Embodiment 1
[0151] An example of using the repairing method of the present
invention in an active matrix type light-emitting device having two
thin film transistors (TFTs) in every pixel is explained in
Embodiment 1.
[0152] FIG. 3 shows a circuit diagram of a pixel of a
light-emitting device using the repairing method of the present
invention. Each pixel has a source signal line Si (where i is an
integer from 1 to x), an electric power source supply line Vi
(where i is an integer from 1 to x), and a gate signal line Gj
(where j is an integer from 1 to y).
[0153] Further, each pixel has a switching TFT 301, a driver TFT
302, an organic light emitting element 303, and a capacitor
304.
[0154] A gate electrode of the switching TFT 301 is connected to
the gate signal line Gi. Further, one of a source region and a
drain region of the switching TFT 301 is connected to the source
signal line Si, and the other one is connected to a gate electrode
of the driver TFT 302.
[0155] A source region of the driver TFT 302 is connected to the
electric power source supply line Vi, and a drain region of the
driver TFT 302 is connected to one of two electrodes on the organic
light emitting element 303. Among the two electrodes of the organic
light emitting element 303, the electrode not connected to the
drain region of the driver TFT 302 is connected to an opposing
electric power source 307.
[0156] Note that, of the two organic light emitting element 303
electrodes, the one connected to the drain region of the driver TFT
302 is referred to as a pixel electrode, and the one connected to
the opposing electric power source 307 is referred to as an
opposing electrode.
[0157] The capacitor 304 is formed between the gate electrode of
the driver TFT 302 and the electric power source supply line
Vi.
[0158] A pixel portion of a light-emitting device having a
plurality of the pixels of FIG. 3 is shown in FIG. 4A. The pixel
portion 306 has the source signal lines S1 to Sx, the electric
power source supply lines V1 to Vx, and the gate signal lines G1 to
Gy. A plurality of the pixels 305 are formed in a matrix shape in
the pixel portion 306.
[0159] TFT operation in each pixel when repairing defect portions
in the organic light emitting elements 303, and the size of the
voltage input to the electric power source supply line Vi and the
opposing electrode are shown in FIG. 4B. The switching TFTs 301 and
the driver TFTs 302 of each pixel are both placed in an on state
when repairing the defect portions in the organic light emitting
elements 303. A predetermined reverse bias electric current flows
in the organic light emitting elements at fixed intervals of time
by fixing the voltage of the electric power source supply line Vi
and changing the opposing electrode voltage at the fixed periods of
time.
[0160] Repair of defects in the organic light emitting elements may
be performed once for all of the pixels 305 in the pixel portion
306, may be performed line by line for single lines of pixels, or
may be performed for each pixel individually.
[0161] Of the two electrodes on the organic light emitting elements
in Embodiment 1, the cathode is formed using an alloy containing
magnesium, alloys such as AlMg and MgAg, for example. Na and Li,
high mobility components, are kept from being mixed into the
cathode, and the amounts of Na and Li contained in the cathode are
both set to equal to or less than 1.times.10.sup.18
atoms/cm.sup.3.
[0162] In accordance with the circuit of Embodiment 1, the reverse
bias can be applied to the organic light emitting elements by
suitably regulating the voltages applied to the switching TFT, the
driver TFT, the electric power source supply line, and the opposing
electric power source. The reverse bias can be applied without
device contamination because processing is strictly managed so that
Li and Na are not contained in the organic light emitting element
cathodes.
Embodiment 2
[0163] An example of using the repairing method of the present
invention in an active matrix type light-emitting device having
three thin film transistors (TFTs) in every pixel is explained in
Embodiment 2.
[0164] FIG. 5 shows a circuit diagram of a pixel of a light
emitting element using the repairing method of the present
invention. Each pixel has a source signal line Si (where i is an
integer from 1 to x), an electric power source supply line Vi
(where i is an integer from 1 to x), a write in gate signal line
Gaj (where j is an integer from 1 to y), and an erasure gate signal
line Gej (where j is an integer from 1 to y).
[0165] Further, each pixel has a switching TFT 501a, an erasure TFT
501b, a driver TFT 502, an organic light emitting element 503, and
a capacitor 504.
[0166] A gate electrode of the switching TFT 501a is connected to
the write in gate signal line Gaj. Further, one of a source region
and a drain region of the switching TFT 501a is connected to the
source signal line Si, and the other one is connected to a gate
electrode of the driver TFT 502.
[0167] A gate electrode of the erasure TFT 501b is connected to the
erasure gate signal line Gej. Further, one of a source region and a
drain region of the erasure TFT 501b is connected to the electric
power source supply line Vi, and the other one is connected to a
gate electrode of the driver TFT 502.
[0168] A source region of the driver TFT 502 is connected to the
electric power source supply line Vi, and a drain region of the
driver TFT 502 is connected to one of two electrodes on the organic
light emitting element 503. Of the two electrodes on the organic
light emitting element 503, the one not connected to the drain
region of the driver TFT 502 is connected to an opposing electric
power source 507.
[0169] Note that, of the two electrodes on the organic light
emitting element 503, the electrode connected to the drain region
of the driver TFT 502 is referred to as a pixel electrode, and the
electrode connected to the opposing electric power source 507 is
referred to as an opposing electrode.
[0170] Further, the capacitor 504 is formed between the gate
electrode of the driver TFT 502 and the electric power source
supply line Vi.
[0171] A pixel portion of a light-emitting device having a
plurality of the pixels of FIG. 5 is shown in FIG. 6A. The pixel
portion 506 has the source signal lines S1 to Sx, the electric
power source supply lines V1 to Vx, the write in gate signal lines
Ga1 to Gay, and the erasure gate signal lines Ge1 to Gey. A
plurality of the pixels 505 are formed in a matrix shape in the
pixel portion 506.
[0172] TFT operation in each pixel when repairing defect portions
in the organic light emitting elements 503, and the size of the
voltage input to the electric power source supply line Vi and the
opposing electrode are shown in FIG. 6B. The switching TFTs 501a
and the driver TFTs 502 of each pixel are both placed in an on
state when repairing the defect portions in the organic light
emitting elements 503. Further, the erasure TFT 501b of each pixel
is placed in an off state. A predetermined reverse bias electric
current flows in the organic light emitting elements 503 at fixed
intervals of time by fixing the voltage of the electric power
source supply line Vi and changing the opposing electrode voltage
at the fixed periods of time.
[0173] Repair of defects in the organic light emitting elements 503
may be performed once for all of the pixels 505 in the pixel
portion 506, may be performed line by line for single lines of
pixels, or may be performed for each pixel individually.
[0174] Note that the cathodes of the organic light emitting
elements are formed using an alloy containing magnesium, alloys
such as AlMg and MgAg, for example, so that alkaline elements do
not elute when the reverse bias is applied. Na and Li, high
mobility components, are kept from being mixed into the cathode,
and the amounts of Na and Li contained in the cathode are both set
to equal to or less than 1.times.10.sup.18 atoms/cm.sup.3.
[0175] In accordance with the circuit of Embodiment 2, the reverse
bias can also be applied to the organic light emitting
elements.
Embodiment 3
[0176] An example of using the repairing method of the present
invention in an active matrix type light-emitting device having
three thin film transistors (TFTs) in every pixel is explained in
Embodiment 3.
[0177] FIG. 7 shows a circuit diagram of a pixel of a
light-emitting device using the repairing method of the present
invention. Each pixel has a source signal line Si (where i is an
integer from 1 to x), an electric power source supply line Vi
(where i is an integer from 1 to x), and a gate signal line Gj
(where j is an integer from 1 to y).
[0178] Further, each pixel has a switching TFT 401, a driver TFT
402, an organic light emitting element 403, a capacitor 404, and a
reverse bias application TFT 408.
[0179] A gate electrode of the switching TFT 401 is connected to
the gate signal line Gi. Further, one of a source region and a
drain region of the switching TFT 401 is connected to the source
signal line Si, and the other one is connected to a gate electrode
of the driver TFT 402.
[0180] A source region of the driver TFT 402 is connected to the
electric power source supply line Vi, and a drain region of the
driver TFT 402 is connected to one of two electrodes on the organic
light emitting element 403. Among the two electrodes of the organic
light emitting element 403, the electrode not connected to the
drain region of the driver TFT 402 is connected to an opposing
electric power source 407.
[0181] Note that, of the two organic light emitting element 403
electrodes, the one connected to the drain region of the driver TFT
402 is referred to as a pixel electrode, and the one connected to
the opposing electric power source 407 is referred to as an
opposing electrode.
[0182] A gate electrode of the reverse bias application TFT 408 is
connected to the electric power source supply line Vi. Further, one
of a source region and a drain region of the reverse bias
application TFT 408 is connected to the electric power source
supply line Vi, and the other one is connected to the pixel
electrode of the organic light emitting element.
[0183] The capacitor 404 is formed between the gate electrode of
the driver TFT 402 and the electric power source supply line
Vi.
[0184] A pixel portion of a light-emitting device having a
plurality of the pixels of FIG. 7 is shown in FIG. 8A. The pixel
portion 406 has the source signal lines S1 to Sx, the electric
power source supply lines V1 to Vx, and the gate signal lines G1 to
Gy. A plurality of the pixels 405 are formed in a matrix shape in
the pixel portion 406.
[0185] TFT operation in each pixel when repairing defect portions
in the organic light emitting elements 403, and the size of the
voltage input to the electric power source supply line Vi and the
opposing electrode are shown in FIG. 8B. The switching TFTs 401 and
the driver TFTs 402 of each pixel are both placed in an off state
when repairing the defect portions in the organic light emitting
elements 403. A forward direction voltage is then applied by
placing the reverse bias application TFTs 408, which have
rectification characteristics, in an on state. An electric current
flows in the reverse bias TFTs by doing so, and a reverse bias is
applied to the organic light emitting elements. A predetermined
reverse bias electric current flows in the organic light emitting
elements at fixed intervals of time by fixing the voltage of the
electric power source supply line Vi and changing the opposing
electrode voltage at the fixed periods of time.
[0186] Repair of defects in the organic light emitting elements may
be performed once for all of the pixels, or may be performed line
by line for single lines of pixels.
[0187] Note that the cathodes of the organic light emitting
elements are formed using an alloy containing magnesium, alloys
such as AlMg and MgAg, for example, so that alkaline elements do
not elute when the reverse bias is applied. Na and Li, high
mobility components, are kept from being mixed into the cathode,
and the amounts of Na and Li contained in the cathode are both set
to equal to or less than 1.times.10.sup.18 atoms/cm.sup.3.
[0188] The circuit of Embodiment 3 can easily apply a reverse bias
to the organic light emitting elements by adjusting the electric
potential of the electric power source supply line and the electric
potential of the opposing electric power source.
Embodiment 4
[0189] This embodiment describes a case of applying a repairing
method of the present invention to an organic light emitting
element whose organic compound layer comprises a plurality of
layers.
[0190] FIG. 9A shows the structure of the organic light emitting
element. First, a hole injection layer is formed by spin coating to
a thickness of 30 nm from PEDOT that is a polythiophene derivative
on an anode formed from a compound of indium oxide and tin oxide
(ITO). Next, an MTDATA layer with a thickness of 20 nm and an
.alpha.-NPD layer with a thickness of 10 nm are formed by
evaporation as a hole transporting layer. On the hole transporting
layer, a light emitting layer is formed from a luminous material,
Alq.sub.3, that is a singlet compound by evaporation to a thickness
of 50 nm. Then a cathode is formed by depositing AlMg through
evaporation to a thickness of 100 nm to complete the organic light
emitting element.
[0191] If a pin hole is opened and a defect portion is formed in
the light emitting layer of the organic light emitting element
structured as above, the AlMg that is the cathode is undesirably
brought into contact with the .alpha.-NPD layer that is the hole
transporting layer in the defect portion.
[0192] When a reverse bias current is caused to flow in the organic
light emitting element having the defect portion at given time
intervals, the temperature in the defect portion is raised so that
the defect portion is burnt out, vaporized, or oxidized or
carbonized to be transformed into an insulator. As a result, the
defect portion is changed into the transmuted portion to increase
the resistance thereof. Therefore degradation of a part of the
organic compound layer that surrounds the transmuted portion is not
accelerated.
[0193] Light emitted from this organic light emitting element
utilizes singlet excitation energy from the singlet compound.
[0194] FIG. 9B shows the structure of another organic light
emitting element. First, a hole injection layer is formed by
evaporation to a thickness of 20 nm from copper phthalocyanine on
an anode formed from a compound of indium oxide and tin oxide.
Next, a hole transporting layer is formed from .alpha.-NPD by
evaporation to a thickness of 10 nm. On the hole transporting
layer, a light emitting layer is formed from light emitting
materials, Ir(ppy).sub.3 and CBP, that are triplet compounds by
evaporation to a thickness of 20 nm. An electron transporting layer
is formed on the light emitting layer by forming a BCP layer with a
thickness of 10 nm and an Alq.sub.3 layer with a thickness of 40 nm
through evaporation. Then a cathode is formed by depositing AlMg
through evaporation to a thickness of 100 nm to complete the
organic light emitting element.
[0195] If a pin hole is opened and a defect portion is formed in
the light emitting layer of the organic light emitting element
structured as above, the BCP lager that is the electron
transporting layer is undesirably brought into contact with the
.alpha.-NPD layer that is the hole transporting layer in the defect
portion.
[0196] When a reverse bias current is caused to flow in the organic
light emitting element having the defect portion at given time
intervals, the temperature in the defect portion is raised so that
the defect portion is burnt out, vaporized, or oxidized or
carbonized to be transformed into an insulator. As a result, the
defect portion is changed into the transmuted portion to increase
the resistance thereof. Therefore degradation of a part of the
organic compound layer that surrounds the transmuted portion is not
accelerated.
[0197] Light emitted from this organic light emitting element
utilizes triplet excitation energy from the triplet compounds.
[0198] FIG. 10A shows the structure of still another organic light
emitting, element. First, a hole injection layer is formed by spin
coating to a thickness of 30 nm from PEDOT that is a polythiophene
derivative on an anode formed from a compound of indium oxide and
tin oxide (ITO). On the hole injection layer, a light emitting
layer is formed from a light emitting material, Alq.sub.3, that is
a singlet compound by evaporation to a thickness of 50 nm. Then a
cathode is formed by depositing AlMg through evaporation to a
thickness of 100 nm to complete the light emitting element.
[0199] If a pin hole is opened and a defect portion is formed in
the light emitting layer of the organic light emitting element
structured as above, the AlMg that is the cathode is undesirably
brought into contact with the PEDOT layer that is the hole
injection layer in the defect portion.
[0200] When a reverse bias current is caused to flow in the organic
light emitting element having the defect portion at given time
intervals, the temperature in the defect portion is raised so that
the defect portion is burnt out, vaporized, or oxidized or
carbonized to be transformed into an insulator. As a result, the
defect portion is changed into the transmuted portion to increase
the resistance thereof. Therefore, degradation of a part of the
organic compound layer that surrounds the transmuted portion is not
accelerated.
[0201] Light emitted from this organic light emitting element
utilizes singlet excitation energy from the singlet compound.
[0202] FIG. 10B shows the structure of yet still another organic
light emitting element. First, a cathode is formed by evaporation
from AlMg to a thickness of 100 nm. On the cathode, a light
emitting layer is formed from a light emitting material, Alq.sub.3,
that is a singlet compound by evaporation to a thickness of 50 nm.
Next, a hole injection layer is formed by spin coating to a
thickness of 30 nm from PEDOT that is a polythiophene derivative.
An Au film with a thickness of 5 nm is formed thereon. The Au film
is provided to prevent degradation of a surface of the organic
compound layer in later steps. Then an anode is formed on the Au
film from a compound of indium oxide and tin oxide (ITO) to
complete the organic light emitting element.
[0203] If a pin hole is opened and a defect portion is formed in
the light emitting layer of the organic light emitting element
structured as above, the AlMg that is the cathode is undesirably
brought into contact with the PEDOT layer that is the hole
injection layer in the defect portion.
[0204] Light emitted from this organic light emitting element
utilizes singlet excitation energy from the singlet compound.
[0205] With the above structure, the present invention can increase
the amount of current actually flowing through the organic compound
layer upon application of a forward bias voltage to the organic
light emitting element even if a pin hole is formed in the organic
compound layer during formation of the layer due to dusts or the
like and two layers sandwiching a light emitting layer
short-circuit, because the method can raise the resistance of the
defect portion where the short circuit takes place by changing the
defect portion into the transmuted portion. Therefore the repairing
method of the present invention can raise the luminance of emitted
light with application of the same level of voltage despite the
presence of the defect portion.
[0206] Furthermore, the invention can prevent accelerated
degradation in a part of the organic compound layer that surrounds
the defect portion by changing the defect portion into the
transmuted portion to increase the resistance thereof.
[0207] A carbide generated by carbonization of a light emitting
material is high in insulating property and is stable as a
substance. For that reason, the repairing method of the present
invention is particularly effective when an organic compound
material is formed in lamination in the defect portion, for
example, when the defect portion is formed in a light emitting
layer (Alq.sub.3), and the hole injection lager (PEDOT) is
laminated in contact with the light emitting layer (Alq.sub.3).
[0208] This embodiment may be combined freely with Embodiments 1 to
3.
Embodiment 5
[0209] In this embodiment, materials of a light emitting element by
which phosphorescence from a triplet exciton can be employed for
emitting a light. As a result, the power consumption of the organic
light emitting element can be reduced, the lifetime of the organic
light emitting element can be elongated and the weight of the
organic light emitting element can be lightened.
[0210] The following is a report where the external light emitting
quantum efficiency is improved by using the triplet exciton (T.
Tsutsui, C. Adachi, S. Saito, Photochemical Processes in Organized
Molecular Systems, ed. K. Honda, (Elsevier Sci. Pub., Tokyo, 1991)
p. 437).
[0211] The molecular formula of an EL material (coumarin pigment)
reported by the above article is represented as follows.
##STR1##
[0212] (M. A. Baldo, D. F. O'Brien, Y. You, A. Shoustikov, S.
Sibley, M. E. Thompson, S. R. Forrest, Nature 395 (1998) p.151)
[0213] The molecular formula of an EL material (Pt complex)
reported by the above article is represented as follows.
##STR2##
[0214] (M. A. Baldo, S. Lamansky, P. E. Burrows, M. E. Thompson, S.
R. Forrest, Appl. Phys. Lett., 75 (1999) p. 4.) (T. Tsutsui, M. J.
Yang, M. Yahiro, K. Nakamura, T. Watanabe T. Tsuji, Y Fukuda, T.
Wakimoto, S. Mayaguchi, Jpn, Appl. Phys., 38 (12B) (1999)
L1502)
[0215] The molecular formula of an EL material (Ir complex)
reported by the above article is represented as follows.
##STR3##
[0216] As described above, if phosphorescence from a triplet
exciton can be put to practical use, it can realize the external
light emitting quantum efficiency three to four times as high as
that in the case of using fluorescence from a singlet exciton in
principle.
[0217] The structure according to this embodiment can be freely
implemented in combination of any structures of the Embodiments 1
to 4.
Embodiment 6
[0218] This embodiment gives descriptions on a sectional view of a
light-emitting device to which a repairing method of the present
invention is applied.
[0219] In FIG. 14, an n-channel TFT 503 is formed by using a
switching TFT 721 formed on a substrate 700.
[0220] The switching TFT 721 in this embodiment has a double gate
structure in which two channel regions are formed. However, the TFT
may take a single gate structure having one channel region or a
triple gate structure having three channel regions.
[0221] A driving circuit formed on the substrate 700 has an
n-channel TFT 723 and a p-channel TFT 724. Although the TFTs of the
driving circuit are of single gate structure in this embodiment,
the TFTs may take the double gate structure or the triple gate
structure.
[0222] Wiring lines 701 and 703 function as source wiring lines of
the CMOS circuit whereas 702 functions as a drain wiring line
thereof. A wiring line 704 functions as a wiring line that
electrically connects a source wiring line 708 to a source region
of the switching TFT. A wiring line 705 functions as a wiring line
that electrically connects a drain wiring line 709 to a drain
region of the switching TFT.
[0223] A p-channel TFT is used for a driving TFT 722. The driving
TFT 722 in this embodiment is of single gate structure but it may
have the double gate structure or the triple gate structure.
[0224] A wiring line 706 is a source wiring line of the driving TFT
(corresponds to a current supply line). A wiring line 707 is an
electrode that is laid on a pixel electrode 710 of the driving TFT
to be electrically connected to the pixel electrode 710.
[0225] The pixel electrode 710 is formed from a transparent
conductive film and serves as an anode of an organic light emitting
element. The transparent conductive film is obtained from a
compound of indium oxide and tin oxide or a compound of indium
oxide and zinc oxide, or from zinc oxide, tin oxide, or indium
oxide alone. The transparent conductive film may be doped with
gallium. The pixel electrode 710 is formed on a flat interlayer
insulating film 711 before forming the above wiring lines. In this
embodiment, the film 711 is a planarization film made of resin and
it is very important to level the level differences caused by the
TFTs with the planarization film 711. An organic compound layer to
be formed later is so thin that the existence of level differences
can cause light emission defect. Accordingly the surface has to be
leveled before forming the pixel electrode so that the organic
compound layer is formed on as flat a surface as possible.
[0226] After the wiring lines 701 to 707 are formed, a bank 712 is
formed as shown in FIG. 14. The bank 712 is formed by patterning an
insulating film containing silicon, or an organic resin film, which
has a thickness of 100 to 400 nm.
[0227] An organic compound layer 713 is formed on the pixel
electrode 710. Although only one pixel is shown in FIG. 14, formed
in this embodiment are organic compound layers for red light (R),
organic compound layers for green light (G), and organic compound
layers for blue light (B). A low molecular weight organic compound
layer is formed by evaporation in this embodiment. Specifically, a
laminate structure is formed, in which a copper phthalocyanine
(CuPc) film with a thickness of 20 nm is formed as a hole injection
layer 713a and a tris-8-quinolinolate aluminum complex (Alq.sub.3)
film with a thickness of 70 nm is formed as a light emitting layer
713b on the hole injection layer. The color of emitted light can be
controlled by choosing which fluorescent pigment, such as
quinacridon, perylene, or DCM1, is used to dope Alq.sub.3.
[0228] The material given in the above is merely an example of
organic compound materials that can be used for the organic
compound layer and there is no need to be limited thereto. The
organic compound layer (meaning a layer for light emission and for
carrier transportation to emit light) may have a charge carrier
transporting layer or a charge carrier injection layer, or both, in
addition to the light emitting layer. For instance, a high
molecular weight organic compound material may be employed for the
organic compound layer though used in the example shown in this
embodiment is a low molecular weight organic compound material.
Inorganic materials such as silicon carbide may be used for the
charge carrier transporting layer and the charge carrier injection
layer. Known organic materials and known inorganic materials can be
used.
[0229] On the organic compound layer 713, a cathode 714 is formed
from a conductive film. In this embodiment, an alloy film of
aluminum and magnesium is used as the conductive film. A known MgAg
film (an alloy film of magnesium and silver) may of course be used.
An appropriate cathode material is a conductive film made of an
element belonging to Group 2 in the periodic table, or a conductive
film doped with a Group 2 element. For example, at least one
element among these Be, Mg, Ca, Sr and Ba should be added.
[0230] When the cathode have two film laminated structure,
magnesium is formed in contact with the organic compound layer, and
aluminum is formed on the magnesium, the voltage starting emitting
light of the organic light emitting layer can be lowered.
[0231] It is preferable to form magnesium into 100 nm thickness and
also aluminum into 100 nm thickness.
[0232] Formation of the cathode 714 completes an organic light
emitting element 719. The organic light emitting element 719 here
means a capacitor comprising the pixel electrode (anode) 710, the
organic compound layer 713, and the cathode 714.
[0233] It is effective to provide a passivation film 716 so as to
cover the organic light emitting element 719 completely. The
passivation film 716 is an insulating film, examples of which
include a carbon film, a silicon nitride film, and a silicon
oxynitride film. A single layer or a laminate of these insulating
films is used for the passivation film.
[0234] It is preferable to use as the passivation film a film that
can cover a wide area.
[0235] A carbon film, a DLC (diamond-like carbon) film, in
particular, is effective. The DLC film can be formed in a
temperature range between room temperature and 100.degree. C., and
therefore is easy to form above the organic compound layer 713 that
has a low heat resistance. Furthermore, the DLC film is highly
effective in blocking oxygen and can prevent oxidization of the
organic compound layer 713. Therefore the organic compound layer
713 can be saved from being oxidized before a sealing step to be
carried out subsequently.
[0236] A seal 717 is provided on the passivation film 716 and a
cover member 718 is bonded. A UV-curable resin can be used as the
seal 717. It is effective to place a substance having a hygroscopic
effect or a substance having an antioxidizing effect inside the
seal 717. The cover member 718 used in this embodiment is a glass
substrate, a quartz substrate, or a plastic substrate (including a
plastic film) with carbon films (preferably diamond-like carbon
films) formed on its front and back.
[0237] Thus completed is a light-emitting device structured as
shown in FIG. 14. It is effective to use a multi-chamber type (or
in-line type) film forming apparatus to successively process the
steps subsequent to formation of the bank 712 up through formation
of the passivation film 716 without exposing the device to the air.
The successive processing for avoiding exposure to the air may
further be extended to include the step of bonding the cover member
718.
[0238] The TFTs in this embodiment are each characterized in that:
a gate electrode is formed from a conductive film having two
layers; almost no difference in concentration is found between low
concentration impurity regions that are formed between a channel
region and a drain region, thereby forming a gentle concentration
gradient; and the low concentration impurity regions are classified
into one that overlaps with the underlying gate electrode (this one
is called a GOLD region) and one that does not overlap the gate
electrode (this one is called an LDD region). The edges of a gate
insulating film, namely, a region above the region that does not
overlap the gate electrode and above a high concentration impurity
region are tapered.
[0239] In the light-emitting device of this embodiment, if there is
a pin hole in the light emitting layer 713b, it causes a defect
portion where the hole injection layer 713a and the cathode 714 are
brought into contact through the pin hole. The defect portion can
be changed into a transmuted portion 715 by the repairing method of
the present invention, resulting in a raise in resistance.
Therefore the other part of the pixel than the pin hole can have
increased luminance and degradation of a part of the organic
compound layer that surrounds the pin hole is not accelerated.
[0240] This embodiment shows the structure of the pixel portion and
of the driving circuit only. However, the manufacturing process
according to this embodiment can also form logic circuits such as a
signal divider circuit, a D/A converter, an operation amplifier,
and a .gamma. correction circuit on the same insulator which holds
the pixel portion and the driving circuit. Additionally, a memory
and a microprocessor may be formed.
[0241] The structure of this embodiment can be combined with any of
Embodiments 1, 2, 3, and 8.
Embodiment 7
[0242] This embodiment gives descriptions on a sectional view of a
light-emitting device to which a repairing method of the present
invention is applied.
[0243] In FIG. 15, an p-channel TFT 200 and an n-channel TFT 201 of
a driving circuit are formed on the same substrate on which a
driving TFT 203, a switching TFT 204, and a capacitor storage 205
are formed to constitute a pixel portion.
[0244] The p-channel TFT 200 of the driving circuit is comprised
of: a conductive layer 220 having a second taper shape and
functioning as a gate electrode; a channel region 206; a third
impurity region 207a to function as a source region or a drain
region; a fourth impurity region (A) 207b serving as an LDD region
that does not overlap the gate electrode 220; and a fourth impurity
region (B) 207c serving as an LDD region that partially overlaps
the gate electrode 220.
[0245] The n-channel TFT 201 of the driving circuit is
comprised-of: a conductive layer 221 having a second taper shape
and functioning as a gate electrode; a channel region 208; a first
impurity region 209a to function as a source region or a drain
region; a second impurity region (A) 209b serving as an LDD region
that does not overlap the gate electrode 221; and a second impurity
region (B) 209c serving as an LDD region that partially overlaps
the gate electrode 221. While the channel length is 2 to 7 .mu.m,
the length of a portion where the second impurity region (B) 209c
overlaps the gate electrode 221 is set to 0.1 to 0.3 .mu.m. The
length of this L.sub.OV region is controlled by adjusting the
thickness of the gate electrode 221 and the angle of the tapered
portion. With this LDD region formed in the n-channel TFT, the high
electric field generated in the vicinity of the drain region is
eased to prevent creation of hot carriers and thus prevent
degradation of the TFT.
[0246] Similarly, the driving TFT 203 is comprised of: a conductive
layer 223 having a second taper shape and functioning as a gate
electrode; a channel region 212: a third impurity region 213a to
function as a source region or a drain region; a fourth impurity
region (A) 213b serving as an LDD region that does not overlap the
gate electrode 223; and a fourth impurity region (B) 213c serving
as an LDD region that partially overlaps the gate electrode
223.
[0247] Logic circuits such as a shift register circuit and a buffer
circuit, and a sampling circuit having an analog switch constitute
the driving circuit. In FIG. 15, the TFTs of these circuits have a
single gate structure in which one gate electrode is placed between
a source and a drain that form a pair. However, the TFTs may have a
multi-gate structure in which a plurality of electrodes are placed
between the source and the drain that form a pair.
[0248] The drain region of the driving TFT 203 is connected to a
pixel electrode 271 through a wiring line 231 on an interlayer
insulating film 159. An organic compound layer 272 is formed from a
known organic compound material so as to contact with the pixel
electrode 271. A cathode 273 is formed so as to contact with the
organic compound layer 272.
[0249] The switching TFT 204 is comprised of: a conductive layer
224 having a second taper shape and functioning as a gate
electrode; channel regions 214a and 214b; first impurity regions
215a and 217 to function as source regions or drain regions; a
second impurity region (A) 215b serving as an LDD region that does
not overlap the gate electrode 224; and a second impurity region
(B) 215c serving as an LDD region that partially overlaps the gate
electrode 224. The length of a portion where the second impurity
region (B) 215c overlaps the gate electrode 224 is set to 0.1 to
0.3 .mu.m. The capacitor storage is comprised of: a semiconductor
layer extended from the first impurity region 217 and having a
second impurity region (A) 219b, a second impurity region (B) 219c,
and a region 218 that is not doped with any impurity element for
setting the conductivity type of the region; an insulating layer of
the same layer as a gate insulating film having a third shape; and
a capacitor wiring line 225 that is formed form a conductive layer
having a second taper shape.
[0250] In the light-emitting device of this embodiment, if there is
a pin hole in the organic compound layer 272, it causes a defect
portion where the pixel electrode 271 and the cathode 273 are
brought into contact through the pin hole. The defect portion can
be changed into a transmuted portion 274 by the repairing method of
the present invention, resulting in a raise in resistance.
Therefore the other part of the pixel than the pin hole can have
increased luminance and degradation of a part of the organic
compound layer that surrounds the pin hole is not accelerated.
[0251] The structure of this embodiment can be combined with any of
Embodiments 1, 2, 3, and 8.
Embodiment 8
[0252] An outline of a cross sectional structure of a
light-emitting device using the repair method of the present
invention is explained in this embodiment.
[0253] Reference numeral 811 denotes a substrate in FIG. 16, and
reference numeral 812 denotes an insulating film which becomes a
base (hereafter referred to as a base film). A light transmitting
substrate, typically a glass substrate, a quartz substrate, a glass
ceramic substrate, or a crystalline glass substrate can be used as
the substrate 811. However, the substrate used must be one able to
withstand the highest process temperature during the manufacturing
processes.
[0254] Further, the base film 812 is particularly effective when
using a substrate containing mobile ions or a substrate which has
conductivity, but the base film 812 need not be formed on a quartz
substrate. An insulating film containing silicon may be used as the
base film 812. Note that the term insulating film containing
silicon specifically indicates an insulating film such as a silicon
oxide film, a silicon nitride film, and a silicon oxynitride film
(denoted as SiOxNy, where x and y are arbitrary integers)
containing oxygen or nitrogen at predetermined ratios with respect
to silicon.
[0255] Reference numeral 8201 denotes a switching TFT, reference
numeral 8202 denotes a driver TFT, and both are formed by n-channel
TFT and p-channel TFTs respectively. When the direction of light
emitted is toward the substrate lower side (surface where TFTs and
the organic compound layer are not formed), the above structure is
preferable. However, the present invention is not limited to this
structure. The switching TFT and the driver TFT may be either
n-channel TFTs or p-channel TFTs.
[0256] The switching TFT 8201 has an active layer containing a
source region 813, a drain region 814, LDD regions 815a to 815d, a
separation region 816, and an active layer including channel
regions 817a and 817b, a gate insulating film 818, gate electrodes
819a and 819b, a first interlayer insulating film 820, a source
signal line 821 and a drain wiring 822. Note that the gate
insulating film 818 and the first interlayer insulating film 820
may be common among all TFTs on the substrate, or may differ
depending upon the circuit or the element.
[0257] Furthermore, the switching TFT 8201 shown in FIG. 16 is
electrically connected to the gate electrodes 817a and 817b,
becoming namely a double gate structure. Not only the double gate
structure, but also a multi-gate structure (a structure containing
an active layer having two or more channel regions connected in
series) such as a triple gate structure, may of course also be
used.
[0258] The multi-gate structure is extremely effective in reducing
the off current, and provided that the off current of the switching
TFT is sufficiently lowered, a capacitor connected to the gate
electrode of the driver TFT 8202 can be have its capacitance
reduced to the minimum necessary. Namely, the surface area of the
capacitor can be made smaller, and therefore using the multi-gate
structure is also effective in expanding the effective light
emitting surface area of the organic light emitting elements.
[0259] In addition, the LDD regions 815a to 815d are formed so as
not to overlap the gate electrodes 819a and 819b through the gate
insulating film 818 in the switching TFT 8201. This type of
structure is extremely effective in reducing the off current.
Furthermore, the length (width) of the LDD regions 815a to 815d may
be set from 0.5 to 3.5 .mu.m, typically between 2.0 and 2.5
.mu.m.
[0260] Note that forming an offset region (a region which is a
semiconductor layer having the same composition as the channel
region and to which the gate voltage is not applied) between the
channel region and the LDD region is additionally preferable in
that the off current is lowered. Further, when using a multi-gate
structure having two or more gate electrodes, the separation region
816 (a region to which the same impurity element, at the same
concentration, as that added to the source region or the drain
region, is added) is effective in reducing the off current.
[0261] Next, the driver TFT 8202 is formed having an active layer
containing a source region 826, a drain region 827, and a channel
region 829; the gate insulating film 818; a gate electrode 830, the
first interlayer insulating film 820; a source wiring 831; and a
drain wiring 832. The driver TFT 8202 is a p-channel TFT in
Embodiment 8.
[0262] Further, the drain region 814 of the switching TFT 8201 is
connected to the gate electrode 830 of the driver TFT 8202.
Although not shown in the figure, specifically the gate electrode
830 of the driver TFT 8202 is electrically connected to the drain
region 814 of the switching TFT 8201 through the drain wiring (also
referred to as a connection wiring) 822. The source wiring 831 of
the driver TFT 8202 is connected to an power source supply line
(not shown in the figure).
[0263] The driver TFT 8202 is an element for controlling the amount
of electric current injected to the organic light emitting element,
and a relatively large amount of current flows. It is therefore
preferable to design the channel width W to be larger than the
channel width of the switching TFT. Further, it is preferable to
design the channel length L such that an excess of electric current
does not flow in the driver TFT 8202. It is preferable to have from
0.5 to 2 .mu.A (more preferably between 1 and 1.5 .mu.A) per
pixel.
[0264] In addition, by making the film thickness of the active
lagers (particularly the channel region) of the driver TFT 8202
thicker (preferably from 50 to 100 nm, even better between 60 and
80 nm), deterioration of the TFT may be suppressed. Conversely, it
is also effective to make the film thickness of the active layer
(particularly the channel region) thinner (preferably from 20 to 50
nm, even better between 25 and 40 nm), from the standpoint of
making the off current smaller, for the case of the switching TFT
8201.
[0265] The structures of the TFTs formed within the pixel are
explained above, but a driver circuit is also formed simultaneously
at this point. A CMOS circuit, which becomes a basic unit for
forming the driver circuit, is shown in FIG. 16.
[0266] A TFT having a structure in which hot carrier injection is
reduced without an excessive drop in the operating speed is used as
an n-channel TFT 8204 of the CMOS circuit in FIG. 16. Note that the
term driver circuit indicates a source signal line driver circuit
and a gate signal line driver circuit here. It is also possible to
form other logic circuit (such as a level shifter, an A/D
converter, and a signal division circuit).
[0267] An active layer of the n-channel TFT 8204 of the CMOS
circuit contains a source region 835, a drain region 836, an LDD
region 837, and a channel region 838. The LDD region 837 overlaps
with a gate electrode 839 through the gate insulating film 818.
[0268] Formation of the LDD region 837 on only the drain region 836
side is so as not to have drop the operating speed. Further, it is
not necessary to be very concerned about the off current with the
n-channel TFT 8204, and it is good to place more importance on the
operating speed. Thus, it is desirable that the LDD region 837 is
made to completely overlap the gate electrode to decrease a
resistance component to a minimum. It is therefore preferable to
eliminate so-called offset.
[0269] Furthermore, there is almost no need to be concerned with
degradation of a p-channel TFT 8205 of the CMOS circuit, due to hot
carrier injection, and therefore no LDD region need be formed in
particular. Its active layer therefore contains a source region
840, a drain region 841, and a channel region 842, and a gate
insulating film 818 and a gate electrode 843 are formed on the
active layer. It is also possible, of course, to take measures
against hot carrier injection by forming an LDD region similar to
that of the n-channel TFT 8204.
[0270] The reference numerals 861 to 865 are a mask to form the
channel region 842, 838, 817a, 817b, and 829.
[0271] Further, the n-channel TFT 8204 and the p-channel TFT 8205
have source wirings 844 and 845, respectively, on their source
regions, through the first interlayer insulating film 820. In
addition, the drain regions of the n-channel TFT 8204 and the
p-channel TFT 8205 are mutually connected electrically by a drain
wiring 846.
[0272] Next, reference numeral 847 denotes a first passivation
film, and its film thickness may be set from 10 nm to 1 .mu.m
(preferably between 200 and 500 nm). An insulating film containing
silicon (in particular, it is preferable to use an oxidized silicon
nitride film or a silicon nitride film) can be used as the
passivation film material. The passivation film 847 possesses a
role of protecting the TFTs from alkaline metals and moisture.
Further, reference numeral 848 denotes a second interlayer
insulating film, which has a function as a leveling film for
performing leveling of a step due to the TFTs. An organic resin
film is preferable as the second interlayer insulating film 848,
and one such as polyimide, polyamide, acrylic, or BCB
(benzocyclobutene) may be used. These organic resin films have the
advantages of easily forming a good, level surface, having a low
specific dielectric constant. The organic compound layer is
extremely sensitive to unevenness, and therefore it is preferable
to mostly absorb the TFT step by the second interlayer insulating
film 848. In addition, it is preferable to form the low specific
dielectric constant material thickly in order to reduce the
parasitic capacitance formed between the gate signal wiring, the
data signal wiring and the cathode of the organic light emitting
element. The thickness, therefore, is preferably from 0.5 to 5
.mu.m (more preferably between 1.5 and 2.5 .mu.m).
[0273] Further, reference numeral 849 denotes a pixel electrode
(organic light emitting element anode) made from a transparent
conducting film. After forming a contact hole (opening) in the
second interlayer insulating film 848 and in the first passivation
film 847, the pixel electrode 849 is formed so as to be connected
to the drain wiring 832 of the driver TFT 8202.
[0274] A third interlayer insulating film 850 is formed on the
pixel electrode 849 from a silicon oxide film, a silicon oxynitride
film, or an organic resin film, with a thickness of from 0.3 to 1
.mu.m. An open portion is formed in the third interlayer insulating
film 850 over the pixel electrode 849 by etching, and the edge of
the open portion is etched so as to become a tapered shape. The
taper angle may be set from 10 to 60.degree., (preferably between
30 and 50.degree.).
[0275] An organic compound layer 851 is formed on the third
interlayer insulating film 850. A single layer structure or a
lamination structure can be used for the organic compound layer
851, but the lamination structure has a better light emitting
efficiency. In general, a hole injecting layer, a hole transporting
layer, a light emitting layer, and an electron transporting layer
are formed in order on the pixel electrode, but a structure having
a hole transporting layer, a light emitting layer, and an electron
transporting layer, or a structure having a hole injecting layer, a
hole transporting layer, a light emitting layer, an electron
transporting lager, and an electron injecting layer may also be
used. Any known structure may be used by the present invention, and
doping of such as a fluorescing pigment into the organic compound
layer may also be performed.
[0276] The structure of FIG. 16 is an example of a case of forming
three types of organic light emitting elements corresponding to R,
G, and B. Note that although only one pixel is shown in FIG. 16,
pixels having an identical structure are formed corresponding to
red, green and blue colors, respectively, and that color display
can thus be performed. It is possible to implement the present
invention without concern as to the method of color display.
[0277] A cathode 852 of the organic light emitting element is
formed on the organic compound layer 851. A material containing a
low work coefficient-material such as magnesium (Mg), lithium (Li),
or calcium (Ca), is used as the cathode 852. Preferably, an
electrode made from MgAg (a material made from Mg and Ag at a
mixture of Mg:Ag=10:1) or an electrode made from AlMg (a material
made from Mg and Al at a mixture of Mg:Al=5:95) are used. In
addition, a MgAgAl electrode can be given as other examples.
[0278] The organic compound light emitting element 8206 is formed
by the pixel electrode (anode) 849, the organic compound layer 851,
and the cathode 852.
[0279] The lamination body comprising the organic compound layer
851 must be formed separately for each pixel, but the organic
compound layer 851 is extremely weak with respect to moisture, and
consequently a normal photolithography technique cannot be used. It
is therefore preferable to use a physical mask material such as a
metal mask, and to selectively form the layers by a gas phase
method such as vacuum evaporation, sputtering, or plasma CVD.
[0280] Note that it is also possible to use a method such as ink
jet printing, screen printing or spin coating as the method of
selectively forming the organic compound layer. However, the
cathode cannot be formed in succession with these methods at
present, and therefore it is preferable to use the other methods
stated above.
[0281] Further, reference numeral 853 denotes a protecting
electrode, which protects the cathode 852 from external moisture
and the like at the same time is an electrode for connecting to the
cathode 852 of each pixel. It is preferable to use a low resistance
material containing aluminum (Al), copper (Cu), or silver (Ag) as
the protecting electrode 853. The protecting electrode 853 can also
be expected to have a heat radiating effect which relieves the
amount of heat generated by the organic compound layer.
[0282] Reference numeral 854 denotes a second passivation film,
which may be formed with a film thickness of 10 nm to 1 .mu.m
(preferably between 200 and 500 nm). The aim of forming the second
passivation film 854 is mainly for protecting the organic compound
layer 851 from moisture, but it is also effective to give the
second passivation film 854 a heat radiating effect. Note that the
organic compound layer is weak with respect to heat, as stated
above, and therefore it is preferable to perform film formation at
as low a temperature, as possible (preferably within a temperature
range from room temperature to 120.degree. C.). Plasma CVD,
sputtering, vacuum evaporation, ion plating, and solution coating
(spin coating) can therefore be considered as preferable film
formation methods.
[0283] Note that it goes without saying that all of the TFTs shown
in FIG. 16 may have a polysilicon film as their active layer in the
present invention.
[0284] When the pinhole is formed in the organic compound layer 860
in the light-emitting device, the defective portion that the pixel
electrode 849 and the cathode 852 are connecting through the
pinhole is formed. By the repair method of the present invention,
resistance can be higher by changing the defective portion to the
denatured portion 860. Therefore, the brightness in the portion
other than the pinhole of the pixel are raised, and the
deterioration of the organic compound layer surrounding of the
pinhole can be prevented the promotion.
[0285] Note that it is possible to implement this embodiment
combination with Embodiments 1, 2, 3, and 8.
Embodiment 9
[0286] A light-emitting device using an organic compound element is
self-luminous and therefore is superior in visibility in bright
surroundings compared to liquid crystal display devices and has
wider viewing angle. Accordingly, it can be used for display units
of various electric equipment.
[0287] Given as examples of electric equipment employing a
light-emitting device to which a repairing method of the present
invention is applied are: a video camera; a digital camera; a
goggle type display (head mounted display): a navigation system; an
audio reproducing device (car audio, an audio component, and the
like); a notebook computer; a game machine; a portable information
terminal (a mobile computer, a portable telephone, a portable game
machine, an electronic book, etc.); and an image reproducing device
(specifically, a device capable of processing data in a recording
medium such as a digital versatile disk (DVD) and having a display
device that can display the image of the data). The light-emitting
device having an organic compound element is desirable particularly
for a portable information terminal since its screen is often
viewed obliquely and is required to have a wide viewing angle.
Specific examples of the electric equipment are shown in FIGS. 11A
to 11H.
[0288] FIG. 11A shows a display device, which comprises a casing
2001, a supporting base 2002, a display unit 2003, speaker units
2004, a video input terminal 2005, etc. The light-emitting device
to which the repairing method of the present invention is applied
can be used for the display unit 2003. The light-emitting device
having an organic light emitting element is self-luminous and does
not need a backlight, so that it can make a thinner display unit
than liquid display devices can. The term display device includes
every display device for displaying information such as one for a
personal computer, one for receiving TV broadcasting, and one for
advertisement.
[0289] FIG. 11B shows a digital still camera, which comprises a
main body 2101, a display unit 2102, an image receiving unit 2103,
operation keys 2104, an external connection port 2105, a shutter
2106, etc. The light-emitting device to which the repairing method
of the present invention is applied can be used for the display
unit 2102.
[0290] FIG. 11C shows a notebook computer, which comprises a main
body 2201, a casing 2202, a display unit 2203, a keyboard 2204, an
external connection port 2205, a pointing mouse 2206, etc. The
light-emitting device to which the repairing method of the present
invention is applied can be used for the display unit 2203.
[0291] FIG. 11D shows a mobile computer, which comprises a main
body 2301, a display unit 2302, a switch 2303, operation keys 2304,
an infrared ray port 2305, etc. The light-emitting device to which
the repairing method of the present invention is applied can be
used for the display unit 2302.
[0292] FIG. 11E shows a portable image reproducing device equipped
with a recording medium (a DVD player, to be specific). The device
comprises a main body 2401, a casing 2402, a display unit A 2403, a
display unit B 2404, a recording medium (DVD) reading unit 2405,
operation keys 2406, speaker units 2407, etc. The display unit A
2403 mainly displays image information whereas the display unit B
2404 mainly displays text information. The light-emitting device to
which the repairing method of the present invention is applied can
be used for the display units A 2403 and B 2404. The term image
reproducing device equipped with a recording medium includes video
game machines.
[0293] FIG. 11F shows a goggle type display (head mounted display),
which comprises a main body 2501, display units 2502, and arm units
2503. The light-emitting device to which the repairing method of
the present invention is applied can be used for the display units
2502.
[0294] FIG. 11G shows a video camera, which comprises a main body
2601, a display unit 2602, a casing 2603, an external connection
port 2604, a remote control receiving unit 2605, an image receiving
unit 2606, a battery 2607, an audio input unit 2608, operation keys
2609, etc. The light-emitting device to which the repairing method
of the present invention is applied can be used for the display
unit 2602.
[0295] FIG. 11H shows a portable telephone, which comprises a main
body 2701, a casing 2702, a display unit 2703, an audio input unit
2704, an audio output unit 2705, operation keys 2706, an external
connection port 2707, an antenna 2708, etc. The light-emitting
device to which the repairing method of the present invention is
applied can be used for the display unit 2703. If the display unit
2703 displays white characters on a black background, power
consumption of the portable telephone can be reduced.
[0296] If the luminance of light emitted from organic compound
materials is increased in future, the light-emitting device having
an organic light emitting element can be used also in a front or
rear projector in which light bearing outputted image information
is magnified by a lens or the like to be projected on a screen.
[0297] The electric equipment given in the above often displays
information distributed through electronic communication lines such
as Internet and CATV (cable television), especially, animation
information with increasing frequency. The light-emitting device
having an organic light emitting element is suitable for displaying
animation information since organic light emitting materials have
fast response speed.
[0298] In the light-emitting device, portions that emit light
consume power. Therefore it is desirable to display information
such that as small portions as possible emit light. Accordingly, if
the light-emitting device is used for a display unit that mainly
displays text information such as a portable information terminal,
in particular, a portable telephone, and an audio reproducing
device, it is desirable to assign light emitting portions to
display text information while portions that do not emit light
serve as the background.
[0299] As described above, the application range of the
light-emitting device to which the repairing method of the present
invention is applied is very wide and electric equipment of every
field can employ the device. The electric equipment in this
embodiment may use any of the structures shown in Embodiments 1 to
7.
Embodiment 10
[0300] A case of applying the repairing method of the present
invention to a passive type (simple matrix type) light-emitting
device is explained in Embodiment 10.
[0301] The structure of a passive type light-emitting device is
shown in FIG. 20A. Reference numeral 905 denotes a pixel portion,
and the pixel portion 905 has a plurality of pixels 906. Each pixel
has one of a plurality of data lines 903, and one of a plurality of
scanning lines 904. An organic compound layer is formed between the
data lines and the scanning lines 904, and the data lines 903 and
the scanning lines 904 becomes electrodes, thus forming organic
light emitting elements 907.
[0302] Signals input to the data lines 903 are controlled in a data
line driver circuit 901, and signals input to the scanning lines
904 are controlled in a scanning line driver circuit 902.
[0303] The voltage size for the signals input to the scanning lines
904 and the data lines 903 when the repairing method of the present
invention is used are shown in FIG. 20B. A predetermined reverse
bias electric current flows in the organic light emitting elements
907 during fixed periods of time by fixing the voltage of each of
the scanning lines 904, and changing the voltage of the data lines
at the fixed periods of time.
[0304] Note that repair of defects in the organic light emitting
elements 907 may be performed once for all of the pixels 906 in the
pixel portion 905, may be performed line by line for single lines
of pixels, or may be performed for each pixel individually.
[0305] Even if pinholes are formed due to the influence of refuse
or the like during film formation of the organic compound layer,
thus forming short circuits between two layers formed sandwiching
the organic compound layer, use of the method of the present
invention can increase the resistance of a short-circuited defect
portion. In addition, the actual amount of electric current flowing
in the organic compound layer when a forward bias voltage is
applied to the organic light emitting element can be increased. The
brightness of light emission can therefore be increased when the
same voltage is applied, even if a defect portion exists, in
accordance with the repairing method of the present invention.
[0306] Furthermore, electric current always flows in the defect
portion, and degradation of the organic compound layer existing in
the vicinity of the defect portion is easily promoted. However, a
denatured layer has a high resistance R.sub.sc. It thus becomes
more difficult for current to flow, and promotion of degradation of
the organic compound layer existing in the vicinity of the
denatured layer can be prevented.
[0307] It is possible to implement Embodiment 10 by freely
combining it with Embodiments 4, 5, and 9.
[0308] In accordance with the aforementioned structures, the
present invention can increase the resistance of short-circuited
defect portions even if pinholes are formed due to the influence of
refuse and the like during organic compound film formation, thus
forming short circuits between two layers formed sandwiching an
organic compound layer. In addition, the actual electric current
flowing in the organic compound layer when a forward bias voltage
is applied to organic light emitting elements can be increased. The
brightness of light emission can therefore be increased when the
same voltage is applied, even if the defect portion exists, in
accordance with the repairing method of the present invention.
[0309] Further, electric current always flows in the defect
portion, and therefore degradation of the organic compound layer
existing in the vicinity of the defect portion is easily promoted.
However, a denatured layer has a high resistance R.sub.SC, and
therefore electric current does not easily flow, and the promotion
of degradation in the organic compound layer existing in the
vicinity of the denatured layer can be prevented.
[0310] In addition, contamination of devices such as organic light
emitting elements and TFTs when a reverse bias is applied to the
organic light emitting elements can be prevented by forming the
cathodes of the organic light emitting elements such that they
contain as little Na and Li as possible.
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