Display device

A display device including: an organic light emitting display unit formed on a first substrate, the organic light emitting display unit comprising first and second electrodes facing each other, and an organic emissive layer formed between the first and second electrodes; and a liquid crystal display unit formed on a second substrate facing the first substrate, the liquid crystal display unit configured to operate as a liquid crystal shutter in response to an electrical potential difference, wherein a resonance structure of the organic light emitting display unit enables the liquid crystal display unit to form an image in a color reflected from each pixel of the organic light emitting display unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 10-2011-0058636, filed on Jun. 16, 2011, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

The present disclosure relates to a display device, and more particularly, to a display device in which an organic light-emitting display unit and a reflective liquid crystal display unit are coupled to each other so as to maximize outdoor visibility.

2. Description of the Related Technology

In general, an organic light-emitting display device including a thin film transistor (TFT) is drawing attention since it can be applied to electric and electronic products, such as a digital camera, a video camera, a camcorder, a personal digital assistant (PDA), a smart phone, a thin film television set, an ultra-slim notebook, a tablet PC, a flexible display device, and the like.

The organic light-emitting display device is a self luminescent display device that forms a color by recombining and emitting holes and electrons that are injected into an anode and a cathode at an organic emissive layer (EML), and has a stack structure in which the EML is interposed between the anode and the cathode.

However, since such a stack structure may not obtain highly efficient emissive, the organic light-emitting display device selectively uses an intermediate layer such as a hole injection layer (HIL), a hole transport layer (HTL), an electron transport layer (ETL), and an electron injection layer (EIL) that are disposed between electrodes and the EML.

A liquid crystal display panel is a light receiving display device that does not emit light, but rather receives light incident from outside to display an image.

The liquid crystal display panel displays an image, a number, a character, and the like by injecting liquid crystals between a plurality of substrates, and changing an arrangement of liquid crystal molecules when power is supplied. The liquid crystal display panel may be classified in various ways according to a driving method, a display method, and a display form. In this regard, a thin film transistor (TFT) liquid crystal display panel is a panel in which transistors are uniformly arranged on a substrate.

In particular, a liquid crystal display panel of a semi-transmission structure has excellent visibility characteristics under sunlight. However, power consumption increases, reflectivity is reduced, and the manufacturing process is difficult due to a reduction in an aperture ratio.

The organic light-emitting display device has advantageously a high color recombination rate, high contrast, and wide viewing angles, compared to the liquid crystal display panel. However, the organic light-emitting display device has an outdoor visibility characteristic caused by a polarizing film, and thus visibility of the organic light-emitting display device deteriorates due to a reflected polarizing film. Therefore, the organic light-emitting display device needs a structure capable of securing visibility under sunlight.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

One or more embodiments provide display devices including a structure of a reflective liquid crystal display unit so as to maximize outdoor visibility of an organic light emitting display unit.

According to one aspect, there is provided a display device including: an organic light emitting display unit formed on a first substrate, the organic light emitting display unit comprising first and second electrodes facing each other, and an organic emissive layer formed between the first and second electrodes; and a liquid crystal display unit formed on a second substrate facing the first substrate, the liquid crystal display unit configured to operate as a liquid crystal shutter in response to an electrical potential difference, wherein a resonance structure of the organic light emitting display unit enables the liquid crystal display unit to form an image in a color reflected from each pixel of the organic light emitting display unit.

The pixels of the organic light emitting display unit and the pixels of the liquid crystal display unit may face each other and be equal in quantity.

The liquid crystal display unit may be a reflective type liquid crystal display unit, where one of the first and second electrodes formed on the first substrate is a reflective plate.

The organic light emitting display unit may include a thin film transistor and an organic light emitting diode, and has the resonance structure including a combination of a reflective electrode and a semi-transparent electrode, where the first electrode is an anode electrically connected to the thin film transistor, and the second electrode is a cathode facing the first electrode.

The first electrode may be the reflective electrode formed of a reflective metal.

The second electrode may be the semi-transparent electrode formed of a semi-transparent metal.

The organic emissive layer may include red, green, and blue emissive layers to emit red, green, and blue lights, respectively, where the red, green, and blue emissive layers form green, violet, and yellow colors, respectively, due to the resonance structure.

A spacer may be disposed between the first and second substrates to maintain a gap therebetween.

The display device may further include: a touch pattern layer formed on the exterior surface of the second substrate.

The liquid crystal display unit may be a color filterless type.

The liquid crystal display unit may maintain an off status at night or indoors, and an on status outdoors or at solar light.

The organic light emitting display unit and the liquid crystal display unit may have the same resolution.

A polarizing plate may be formed in the exterior surface of the second electrode, where the organic light emitting display unit and the liquid crystal display unit share the polarizing plate.

The organic light emitting display unit may include a thin film transistor and an organic light emitting diode.

The thin film transistor may include a semiconductor active layer formed on the first substrate and comprising source and drain regions and a channel region; a gate electrode stacked on the semiconductor active layer via an insulating layer; and source and drain electrodes respectively electrically connected to the source and drain regions via a contact hole.

The organic light emitting diode may include: the first electrode electrically connected to the source electrode or the drain electrode; the organic emissive layer formed on the first electrode; and the second electrode formed on the organic emissive layer.

DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS

While terms such as “first,” “second,” etc., may be used to describe various components, such components must not be limited to the above terms. The above terms are used only to distinguish one component from another.

Embodiments of the display module will be described below in more detail with reference to the accompanying drawings. Those components that are the same or are in correspondence are generally referred to with the same reference numeral regardless of the figure number, and redundant explanations are omitted.

FIG. 1is a cross-sectional view illustrating an embodiment of a display device100.

Referring toFIG. 1, the display device100includes an organic light emitting display unit101and a liquid crystal display unit102stacked on the organic light emitting display unit101.

The display device100includes a first substrate103. The first substrate103may be an insulation substrate formed of, for example, glass, plastic, or the like.

A buffer layer104is formed on the first substrate103. The buffer layer104may include an organic material, an inorganic material, or a combination of an organic material and an inorganic material alternately stacked on each other. The buffer layer104prevents moisture or impurities generated from the first substrate103from diffusing. The buffer layer104also adjusts a transfer speed of heat when a semiconductor active layer105is crystallized, thereby facilitating crystallization of a semiconductor.

The semiconductor active layer105of a predetermined pattern is formed on the buffer layer104. In embodiments where the semiconductor active layer105is formed of polysilicon, the polysilicon may be formed by forming amorphous silicon and crystallizing the amorphous silicon.

A variety of methods of crystallizing the amorphous silicon may be used, including a rapid thermal annealing (RTA) method, a solid phase crystallization (SPC) method, an excimer laser annealing (ELA) method, a metal induced crystallization (MIC) method, a metal induced lateral crystallization (MILC) method, a sequential lateral solidification (SLS) method, and the like.

A source region106and a drain region107are formed in the semiconductor active layer105by doping N-type or P-type impurity ions. A channel region108that is not doped with impurities is formed between the source region106and the drain region107.

A gate insulating layer109is deposited on a top portion of the semiconductor active layer105. The gate insulating layer109may be a single layer formed of SiO2, or a double layer formed of SiO2and SiNx.

A gate electrode110is formed on a predetermined region of a top portion of the gate insulating layer109. The gate electrode110is connected to a gate line (not shown) that applies a thin film transistor on/off signal. The gate electrode110can use a single or multiple metals, and may be a single layer such as Mo, MoW, Cr, Al, Al alloy, Mg, Al, Ni, W, Au, and the like or a multi layer of a mixture of these single layers.

An interlayer insulating layer111is formed on a top portion of the gate electrode110. A source electrode112is electrically connected to the source region106via a contact hole. A drain electrode113is electrically connected to the drain region107via a contact hole.

A protection layer114(a passivation layer and/or a planarization layer) formed of SiO2 and SiNx, or the like, is formed on top portions of the source electrode112and the drain electrode113. The protection layer114may be formed of an organic material such as benzocyclobutene (BCB) or acryl, or an inorganic material such as SiNx. The protection layer114may be a single layer, or a double or multi layer, and may have various modifications.

A first electrode115that operates as an anode is formed by partially etching the protection layer114. The first electrode115is electrically connected to one of the source electrode112and the drain electrode113.

The first electrode115operates as one of electrodes included in an organic light emitting device, and may be formed of various conductive materials. The first electrode115may be a transparent electrode or a reflective electrode.

In some embodiments, where the first electrode115is the transparent electrode, the first electrode115may be formed of ITO, IZO, ZnO, or In2O3. In embodiments where the first electrode115is the reflective electrode, the first electrode115may be formed by forming a reflective layer using silver (Ag), magnesium (Mg), aluminum (Al), platinum (Pt), lead (Pd), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir), chromium (Cr), or any compound thereof, and doping the reflective layer with ITO, IZO, ZnO, or In2O3.

The first electrode115may have a shape corresponding to an opening shape of each sub-pixel when the first electrode115is the transparent electrode or the reflective electrode.

An organic emissive layer116is formed in an exposed portion of the first electrode115. The organic emissive layer116may be formed of a low molecular or high molecular organic material.

In embodiments where the organic emissive layer116is formed of a low molecular weight organic material, a hole injection layer (HIL), a hole transport layer (HTL), an emissive layer (EML), an electron transport layer (ETL), an electron injection layer (EIL), and the like, may be stacked in a single or complex structure to form the organic emissive layer116.

In embodiments where the organic emissive layer116is formed of a low molecular weight organic material, the low molecular weight organic material includes copper phthalocyanine (CuPc), N,N′-Di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB), or tris-8-hydroxyquinoline aluminum (Alq3). In such embodiments, the EML116may be formed in various ways. The organic emissive layer116may be formed by resonance depositing these high molecular weight organic materials.

In embodiments where the organic emissive layer116is formed of the high molecular weight organic material, the organic emissive layer116may include the HTL and an emissive layer (EML). The HTL may be formed of PEDOT, and the EML may be formed of polyphenylene vinylene (PPV) or polyfluorene high molecular organic materials, and may be formed using a screen printing method or an inkjet printing method.

A second electrode117that operates as a cathode and faces the first electrode115is formed on a top portion of the organic emissive layer116.

The second electrode117may also be a transparent electrode or a reflective electrode.

In some embodiments, when the second electrode117is the transparent electrode, the second electrode117may include a layer formed of a material habing a low work function, such as Li, Ca, LiF/Ca, LiF/Al, Al, Ag, and Mg, and compounds thereof, and an auxiliary electrode or a bus electrode line formed of a transparent electrode material such as ITO, IZO, ZnO, or In2O3formed on the layer.

In embodiments where the second electrode117is the reflective electrode, the second electrode117may be formed by depositing Li, Ca, LiF/Ca, LiF/Al, Al, Ag, Mg, or compounds thereof onto the front surface of the second electrode117.

The second electrode117may be formed by depositing the transparent electrode or the reflective electrode onto the front surface of a display region. In other embodiments, the second electrode117may be formed in various patterns. The first electrode115and the second electrode117may be stacked in opposite directions.

As described above, an organic light emitting device emits red, green, and blue lights from red, green, and blue pixels according to a flow of current, and forms predetermined image information. The organic light emitting device includes the first electrode115that is connected to the source electrode112or the drain electrode113of a thin film transistor (TFT), the second electrode117that covers the entire region of a pixel, and the organic emissive layer116disposed between the first electrode115and the second electrode117. The first electrode115receives a positive power supply from the source electrode112or the drain electrode113. The second electrode117receives negative power supply.

The first electrode115and the second electrode117are insulated from each other via the organic emissive layer116. The first115and second117electrodes apply voltages of different polarities to the organic emissive layer116, and allow the organic emissive layer116to emit light. The first electrode115and the second electrode117may have opposite polarities.

Sub-pixels of the organic light emitting display unit101include at least one TFT or organic light emitting diode. However, the present invention is not limited to the structure of the TFT shown inFIG. 1, and the number and structure of the TFT may be modified in various ways.

The display device100includes a second substrate118that faces the first substrate103. The second substrate118is a transparent substrate, such as for example, a transparent glass substrate formed of, for example, soda lime glass. In other embodiments, the second substrate118may be a transparent plastic substrate.

A liquid crystal display TFT119is formed on the second substrate118. The structure of the TFT119may include a structure of a semiconductor active layer, a source electrode, a drain electrode, a gate electrode, a pixel electrode, an insulating layer, and an arrangement layer, which is widely known to one of ordinary skill in the art, and thus its description will not be provided here.

A liquid crystal layer120is formed between the first substrate103and the second substrate118. In some embodiments, the liquid crystal layer120may include liquid crystals having a negative type dielectric constant anisotropy, and may be perpendicularly arranged.

A spacer121is disposed between the first substrate103and the second substrate118to maintain a gap therebetween. Liquid crystals of the liquid crystal layer120are injected into a space partitioned by the spacer121by using a resonance injection method.

The second electrode117of the organic light emitting display unit101may be used as a common electrode of the liquid crystal display unit102that faces the TFT119.

Accordingly, a pixel electrode included in the TFT119receives a pixel signal and generates an electric potential difference between the pixel electrode and the second electrode117used as the common electrode when the liquid crystal display unit102operates. The electric potential difference allows the liquid crystals of the liquid crystal layer120injected between the first substrate103and the second substrate118to function as a liquid crystal shutter, and thus the liquid crystals rotate due to the negative type dielectric constant anisotropy, thereby forming an image.

In some embodiments, an additional common electrode may be formed instead of the second electrode117being used as the common electrode.

A polarizing plate122is formed on an exterior surface of the second substrate118. The polarizing plate122is commonly applied to the organic light emitting display unit101and the liquid crystal display unit102, and prevents external light from being reflected.

In addition, a touch pattern layer123may be further formed between the second substrate118and the polarizing plate122so as to implement a touch panel function.

A sealing member124is formed in a boundary where the first substrate103and the second substrate118are coupled to each other to prevent impurities or moisture from invading from the outside.

The organic light emitting display unit101and the liquid crystal display unit102must have the same resolution in such a way that the display device100mainly uses the organic light emitting display unit101at night or indoors in which external light has a weak intensity, and mainly uses the liquid crystal display unit102in the daytime or outdoors in which external light has a strong intensity.

Pixels patterned to the organic light emitting display unit101may correspond to pixels patterned to the liquid crystal display unit102.

The number or locations of pixels patterned to the organic light emitting display unit101must be identical to the number or locations pixels patterned to the liquid crystal display unit102in a perpendicular direction, in order to implement a full color of the display device100.

Furthermore, one of the first electrode115and the second electrode117of the organic light emitting display unit101must be used as a reflective plate in order to use the liquid crystal display unit102as a reflective display unit.

In some embodiments, the first electrode115is used as the reflective plate. Thus, if external light is incident into the display device100, the incident light can be exited from the first electrode115through the second substrate118. As described above, the liquid crystal display unit102is the reflective display unit, and thus no backlight unit is unnecessary.

In addition, the liquid crystal display unit102is a color filterless type display device that implements a color without a color filter layer. Because the reflective color characteristics of red, green, and blue pixels of the organic light emitting display unit101are used, the liquid crystal display unit102does not need the color filter layer. The organic light emitting display unit101has a resonance structure, and thus reflective light forms a specific color.

FIG. 2is a graph showing a reflection spectrum of an embodiment of a liquid crystal display unit.

InFIG. 2, the X axis indicates the wavelength band, and the Y axis indicates reflectivity.

Referring toFIG. 2, a curve R of a red pixel has a reflectivity higher than 80% (or 0.8) and a maximum absorptivity around a wavelength band of 620 nanometers, a curve G of a green pixel has a reflectivity higher than 80% (or 0.8) and a maximum absorptivity around a wavelength band of 520 nanometers, and a curve B of a blue pixel has a reflectivity higher than 80% (or 0.8) and a maximum absorptivity around a wavelength band of 440 nanometers.

A curve W indicates a reflection spectrum in a white pixel, and a curve NE indicates a reflection spectrum in a non-emissive unit.

FIGS. 3A and 3Billustrate pixels of an embodiment of the organic light emitting display unit101.

Referring toFIGS. 3A and 3B, when seen with the naked eye, the organic light emitting display unit101forms green reflective light in a red pixel301R, violet reflective light in a green pixel301G, and yellow reflective light in a blue pixel301B.

Such green, violet, and yellow reflective lights are due to the resonance structure of the red, green, and blue pixels of the organic light emitting display unit101. The red, green, and blue pixels have different thin film thicknesses.

The first electrode115and the second electrode117are configured as a combination of a reflective electrode and a semi-transparent electrode so as to implement a micro-cavity effect.

In top emissive type display embodiments implementing an image in a direction of the second substrate118, the first electrode115may be a reflective electrode formed of, such as, for example, a reflective metal such as Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, and compounds thereof, or may further include a ITO, IZO, ZnO, or In2O3layer on a top portion and/or a bottom portion of the reflective metal.

The second electrode117may be a semi-transparent metal, such as, for example, an Mg and Ag alloy or metal such as Ag, Al, Au, Pt, Cr, etc. or an alloy containing these metals. The second electrode117may have a thickness in such a way that a reflectivity higher than about 5% and transmittance of about 50% can be implemented.

Accordingly, although the organic light emitting display unit101does not operate, the first electrode115and the second electrode117have a resonance structure of a combination of the reflective electrode and the semi-transparent electrode, and have different thin film thicknesses of red, green, and blue pixels. When white light is incident, light of a green wavelength band is absorbed, light of red and blue wavelength bands is reflected and forms a violet color in the green pixel, a green color in the red pixel, and a yellow color in the blue pixel.

The operation of the display device100having the above structure will now be described.

When the display device100is used at night or indoors in which external light has a weak intensity, the liquid crystal display unit102maintains an off status, the organic light emitting display unit101operates, and thus voltages are applied to the first electrode115and the second electrode117, and the organic emissive layer116emits light, thereby forming an image. The polarizing plate122prevents external light from being reflected.

When the display device100is used at solar light or outdoors in which external light has a strong intensity, the liquid crystal display unit102operates, voltages are applied to the second electrode117and the liquid crystal display TFT119, such application gives rise to a status change in proportional to a voltage applied to liquid crystals of the liquid crystal layer120disposed between the first substrate103and the second substrate118, a uniform amount of light of light source incident from the outside transmits the liquid crystal layer120, the amount of light is modulated and reflected from the first electrode115, thereby forming an image.

Accordingly, although the organic light emitting display unit101remains in the off status, since the red, green, and blue pixels of the organic light emitting display unit101have a resonance structure, a desired color can be implemented by using the reflection light generated from the organic light emitting display unit101without a color filter.

In some embodiments, the organic light emitting display unit101and the liquid crystal display unit102may simultaneously operate at solar light or outdoors in which external light has a strong intensity.

For example, to form a yellow color, the yellow color is formed by emitting the red and blue pixels of the liquid crystal display unit102and mixing the emitted red and blue pixels. Simultaneously, the blue pixel of the organic light emitting display unit110does not emit light, and a color is reflected due to a resonance phenomenon and forms the yellow color. In this regard, a color image can be corrected by using color change algorithm.

Although the red, green, and blue pixels are described, the present invention is not limited thereto. In other embodiments, the red, green, and blue pixels can form one of red, green, and blue colors irrespective of a sequence thereof.

In addition, as long as a full color is implemented, a combination of different colors, other than a combination of the red, green, and blue colors, can be possible. As long as the full color is implemented, various modifications such as a combination of four pixels can also be possible.

As described above, embodiments of the display device can obtain the following effects.

Outdoor visibility of a reflective liquid crystal display unit can be obtained without a change in the characteristics such as the image quality of an organic light emitting display unit or power consumption thereof.

A polarizing film is used to prevent external light from being reflected in the organic light emitting display unit and serve as an operating polarizing film in a reflective liquid crystal display unit.

A color is formed by using the reflection color characteristic of pixels of the organic light emitting display unit without a color filter.

An aperture ratio of the reflective liquid crystal display unit is not reduced, thereby easily obtaining a reflection brightness.