Display device

Abstract

A display device is provided, comprising: a flexible substrate; a display element located on the flexible substrate and comprising a thin film transistor; a metal layer disposed at a lower portion of the flexible substrate; and an air layer formed between the flexible substrate and the metal layer.

Description

[0001] The Korean Patent Application No. 10-2018-0088583, filed on Jul. 30, 2018 in the Korean Intellectual Property Office, entitled “Display Device”, is hereby incorporated by reference in its entirety. Technical Field

[0002] Embodiments relate to a display device. Background Art

[0003] The display device is used to display images, and includes a liquid crystal display, an organic light emitting diode display, and the like.

[0004] Conventionally, a liquid crystal display device is mainly used, but recently, an organic light emitting diode display has received attention as a display device.

[0005] Liquid crystal displays generally include a substrate and a thin film transistor and a liquid crystal layer on the substrate. Organic light emitting diode displays include a substrate and a thin film transistor in the same manner as liquid crystal displays, but differ from liquid crystal displays in that they include an organic light emitting element that emits light itself instead of having a liquid crystal layer.

[0006] The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. Summary of the invention

[0007] An embodiment relates to a display device including: a flexible substrate; a display element located on the flexible substrate and including a thin film transistor; a metal layer disposed at a lower portion of the flexible substrate; and an air layer formed between the flexible substrate and the metal layer.

[0008] The display device may further include a supporting member disposed between the flexible substrate and the metal layer to support the metal layer.

[0009] The support member may be formed on a surface of the metal layer facing a surface of the flexible substrate.

[0010] The supporting member may include a film and a ball formed inside the film.

[0011] The convex portions and the concave portions may be formed to be continuous in the surface of the film.

[0012] An air layer may be formed between the flexible substrate and the support member and / or between the support member and the metal layer.

[0013] The film or ball may include a conductive material.

[0014] The display device may further include a barrier layer on the flexible substrate and a buffer layer on the barrier layer. The display element may be located on the buffer layer.

[0015] The buffer layer or the barrier layer may be formed of at least one of silicon oxide, silicon nitride, and aluminum oxide.

[0016] The thickness of the buffer layer can be approximately And the thickness of the barrier layer can be about

[0017] A thin film transistor may include a semiconductor layer and a gate electrode on the semiconductor layer.

[0018] The first insulating layer may be disposed between the semiconductor layer and the gate electrode.

[0019] One end of the metal layer may be connected to a ground electrode.

[0020] The flexible substrate may be made of polyimide.

[0021] The thickness of the flexible substrate may be in the range of 3 μm to 10 μm.

[0022] An embodiment also relates to a display device, comprising: a flexible substrate; a barrier layer located on the flexible substrate; a buffer layer located on the barrier layer; a display element located on the buffer layer and comprising a thin film transistor; and a high dielectric constant layer disposed between the display element and the flexible substrate.

[0023] The high dielectric constant layer may be disposed between the flexible substrate and the barrier layer.

[0024] The high dielectric constant layer may be disposed between the barrier layer and the buffer layer.

[0025] The thin film transistor may include a semiconductor layer and a gate electrode on the semiconductor layer, and a first insulating layer may be disposed between the semiconductor layer and the gate electrode.

[0026] The flexible substrate may be made of polyimide. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Features will become apparent to those skilled in the art by describing in detail example embodiments with reference to the accompanying drawings, in which:

[0028] Figure 1 A cross-sectional view showing a display device according to an example embodiment;

[0029] Figure 2 shows a rear view of a display device according to an example embodiment;

[0030] Figure 3 Shown along Figure 2A cross-sectional view taken along line III-III;

[0031] Figure 4 A cross-sectional view of a display device according to a comparative example and a corresponding circuit diagram thereof are shown;

[0032] Figure 5 Show Figure 3 A cross-sectional view and its corresponding circuit diagram;

[0033] Figure 6 It shows that according to Figure 4 and Figure 5 A diagram of the gate voltage versus frequency in the circuit diagram;

[0034] Figure 7 A cross-sectional view showing a display device according to an example embodiment;

[0035] Figure 8 A cross-sectional view showing a display device according to an example embodiment;

[0036] Fig.9A , Fig. 9B and Fig. 9C A rear view showing a display device according to an example embodiment; and

[0037] Fig.10 A cross-sectional view illustrating a display device according to example embodiments. DETAILED DESCRIPTION

[0038] Now, example embodiments will be described more fully below with reference to the accompanying drawings; however, example embodiments may be implemented in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey example implementations to those skilled in the art.

[0039] In the accompanying drawings, the sizes of layers and regions may be exaggerated for clarity of illustration. In addition, it will be understood that when a layer is referred to as being "between" two layers, the layer may be the only layer between the two layers, or one or more intermediate layers may also be present. The same reference numerals represent the same elements throughout.

[0040] It will be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, the element may be directly on the other element, or there may be intervening elements. Conversely, when an element is referred to as being "directly on" another element, there are no intervening elements. In addition, in the specification, the words "on..." or "above..." mean being located on or below an object part, and do not necessarily mean being located on the upper side of the object part based on the direction of gravity.

[0041] In addition, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.

[0042] Furthermore, in the specification, the phrase "in a plan view" means a situation when an object portion is viewed from above, and the phrase "in a cross-sectional view" means a situation when a section taken by vertically cutting the object portion is viewed from the side.

[0043] In the following, reference will be made to Figure 1 A display device according to example embodiments is described.

[0044] Figure 1 A cross-sectional view illustrating a display device according to example embodiments.

[0045] Reference Figure 1 , the display device according to the example embodiment has a structure in which a window 100, a display element 200 including a thin film transistor (hereinafter may also be simply referred to as a "transistor"), a substrate 300, an air layer 400, a support member 407, and a metal layer 500 are sequentially stacked.

[0046] The window 100 is provided at the upper part or the outer part of the display device to protect various components provided at the lower part of the window 100. The window 100 is formed of a transparent material to transmit the internal light generated inside the display device to the outside so that an image can be visually recognized from the outside. The window 100 may be formed of, for example, a transparent film, glass, or plastic.

[0047] The display element 200 may be arranged below the window 100 and used as a component for displaying an image on a display device. The display element 200 may include, for example, a thin film transistor in a pixel circuit and a display unit connected to the thin film transistor to display an image. The display unit may be implemented differently by using a liquid crystal layer, an organic light emitting element, etc. The thin film transistor may receive a voltage to drive the display unit, and at least two thin film transistors may be used to drive the organic light emitting element. According to an example embodiment, a plurality of (for example, 6 to 8) thin film transistors may be used. In addition, according to an example embodiment, the thin film transistor may include a driving transistor, a switching transistor, a compensation transistor, an initialization transistor, a light emitting control transistor, etc.

[0048] The substrate 300 may be disposed at a lower portion of the display element 200. The substrate 300 may be formed of a flexible material such as plastic or polyimide (PI).

[0049] The air layer 400 may be disposed at a lower portion of the substrate 300 , and the metal layer 500 may be located at a lower portion of the air layer 400 .

[0050] The metal layer 500 may be disposed at a distance from the substrate 300. In addition, the metal layer 500 may have a structure, for example, with a thickness small enough to bend with the substrate 300 and then return to its original state. The metal layer 500 may be, for example, a metal film. As described in further detail below, the metal layer 500 and the air layer 400 may be combined to provide an effective capacitance in which the air layer 400 serves as a dielectric.

[0051] The air layer 400 may be an empty space between the substrate 300 and the metal layer 500. The space of the air layer 400 may be provided by a support member 407, and the support member 407 may be formed at opposite ends of the metal layer 500, or may be formed at various positions to keep a distance between the metal layer 500 and the substrate 300. The air layer 400 may be a space other than the support member 407.

[0052] A single metal layer 500 may be formed, or a plurality of metal layers 500 may be formed, for example, spaced apart in a direction parallel to the extending direction of the substrate 300. Figure 2 and Figure 3 An example embodiment in which a plurality of metal layers 500 are formed is described.

[0053] Figure 2 showing a rear view of a display device according to an example embodiment, Figure 3 Shown along Figure 2 A cross-sectional view taken along line III-III.

[0054] Although Figure 2 The display device shown in FIG. 1 is applied to a portable electronic device, but according to example embodiments, it may be applied to various electronic devices such as a TV and a tablet PC.

[0055] Reference Figure 2 , the display device according to the example embodiment includes a substrate 300, a plurality of metal layers 500, and a plurality of support members 407 in a bottom view. The metal layers 500 are located on the rear side of the substrate 300, and the support members 407 are located on opposite ends of each metal layer 500.

[0056] In the present exemplary embodiment, the metal layer 500 is arranged at the left side of the substrate 300 in parallel with the edge of the substrate 300, and is arranged at the right side of the substrate 300 in parallel with the edge of the substrate 300 to face the left side thereof. In addition, the metal layer 500 is arranged at the lower end of the substrate 300 in parallel along the edge of the substrate 300. Here, the metal layers 500 are arranged at a certain distance apart, and the distance between the metal layers 500 may be constant or non-constant.

[0057] In addition, the metal layer 500 may not be formed in a space to which a specific function needs to be assigned in the lower portion of the substrate 300. For example, the camera region A is shown to show that the metal layer 500 is not formed at a location where the camera is set, and a similar arrangement may be provided for a region where various sensors such as a fingerprint sensor (not shown) and a light sensor (not shown) are formed.

[0058] exist Figure 2 In the example embodiment shown in , the metal layers 500 are arranged at opposite sides of the substrate 300, respectively forming four quadrilaterals of similar size. One square metal layer 500 (having similar lengths and widths to each other) is disposed at the uppermost side of each opposite side of the substrate 300, and three rectangular metal layers 500 having a width slightly shorter than the length are disposed below the square metal layer 500 at each opposite side of the substrate 300. In addition, three square metal layers 500 (having similar lengths and widths) are disposed at the lower end of the substrate 300.

[0059] The square metal layer 500 may be formed to be, for example, 0.5 cm×0.5 cm or less. Here, although the metal layer 500 is implemented as a quadrangle, it may be implemented in various shapes such as a circle or a triangle. In addition, the metal layer 500 may be formed to have the same size and shape.

[0060] The support members 407 are disposed at opposite ends of the metal layer 500 facing the substrate 300. Two support members 407 may be formed at opposite ends of each metal layer 500, and may be formed by solidifying frit glass or the like.

[0061] Two support members 407 located at opposite ends of the metal layer 500 may be spaced apart by a certain distance. The number of support members 407 may vary according to the size and shape of the metal layer 500 , and the distance between the support members 407 may vary according to the number of support members 407 .

[0062] The support member 407 may be formed in an elliptical shape having a long width in a width direction of the metal layer 500 , or may be formed in various shapes such as a circular shape and a cylindrical shape according to the size and shape of the metal layer 500 .

[0063] The support member 407 may attach the metal layer 500 to the substrate 300. In an implementation, the substrate 300 and the support member 407 and / or the support member 407 and the metal layer 500 may be attached to each other by an adhesive such as an anisotropic conductive film (ACF).

[0064] The support member 407 maintains a constant distance between the substrate 300 and the metal layer 500 , so that the air layer 400 is formed in a region of the metal layer 500 overlapping the substrate 300 excluding the support member 407 .

[0065] Figure 2 Only one example is shown, and the metal layer 500 and the support member 407 may be variously arranged under the substrate 300 in various sizes and shapes.

[0066] Will refer to Figure 3 A detailed description is given in a stacking order in a cross-sectional view of a display device according to example embodiments.

[0067] Figure 3 Shown along Figure 2 A cross-sectional view taken along line III-III.

[0068] The structure including the thin film transistor 210, the substrate 300, the air layer 400, the support member 407, and the metal layer 500 included in the display element 200 will be described. Figure 3 , and for clarity, omitted Figure 1 Other elements such as window 100 in the cross-sectional view of the display device.

[0069] In the present example embodiment, the display device includes a metal layer 500 , an air layer 400 , a support member 407 , a substrate 300 , a buffer layer 130 , and a thin film transistor 210 .

[0070] The thin film transistor 210 includes a gate electrode 121 , a semiconductor layer 160 , a first insulating layer 141 , a second insulating layer 142 , a third insulating layer 143 , a source electrode 153 , and a drain electrode 154 .

[0071] Reference Figure 3 , the metal layer 500 is disposed at the bottom of the substrate 300. The metal layer 500 is disposed at the center of the bottom of the substrate 300 and is formed to have a size smaller than that of the substrate 300. The metal layer 500 may be freely disposed at the lower left side or the lower right side of the substrate 300, and may be variously formed into various sizes and shapes according to the disposed position.

[0072] One end of the metal layer 500 may be connected to a ground layer (eg, a ground electrode) (not shown).

[0073] The metal layer 500 may be formed of, for example, a metal having high thermal conductivity such as aluminum (Al), copper (Cu), silver (Ag), tungsten (W), or gold (Au).

[0074] The support member 407 may be disposed at opposite ends of the metal layer 500 and formed between the substrate 300 and the metal layer 500. The support member 407 may be formed by curing frit, an adhesive material, or the like.

[0075] The air layer 400 is formed in the inner space between the substrate 300 and the metal layer 500. The air layer 400 may be an inner space of the support member 407 disposed at opposite ends of the metal layer 500. The volume of the air layer 400 may vary according to the size and shape of the metal layer 500.

[0076] The substrate 300 is disposed over the air layer 400 and the support member 407. The substrate 300 may be made of a flexible material such as plastic or polyimide (PI), and may be formed to have a thickness of, for example, 3 μm to 10 μm.

[0077] exist Figure 3 In the example embodiment shown in FIG. 1 , the barrier layer 120 is located on the substrate 300, and the buffer layer 130 is located on the barrier layer 120. The barrier layer 120 and the buffer layer 130 may include a silicon oxide (SiO x ), Silicon Nitride (SiN x ) or aluminum oxide (Al 2 O 3 ) and may also include an organic insulating material such as polyimide acrylic (added with epoxy resin). Here, the barrier layer 120 may be formed to have, for example, (0.5 μm) thickness, and the buffer layer 130 may be formed to have, for example (0.2μm) thickness.

[0078] The semiconductor layer 160 is located on the buffer layer 130. The semiconductor layer 160 includes a channel region 150, a source region 151, and a drain region 152. The semiconductor layer 160 may include a polycrystalline semiconductor such as polysilicon or an oxide semiconductor.

[0079] The first insulating layer 141 covering the semiconductor layer 160 is located on the semiconductor layer 160. The gate electrode 121 of the thin film transistor 210 is located on the first insulating layer 141. The second insulating layer 142 is located on the gate electrode 121 to cover the gate electrode 121, and the third insulating layer 143 is located on the second insulating layer 142 to cover the second insulating layer 142. The first insulating layer 141, the second insulating layer 142, and the third insulating layer 143 are made of silicon oxide (SiO x ), Silicon Nitride (SiN x ), aluminum oxide (Al 2 O 3 ) etc.

[0080] The source region 151 and the drain region 152 are connected to electrodes (not shown) of other thin film transistors or data lines (not shown) through contact holes formed through the first insulating layer 141 , the second insulating layer 142 , and the third insulating layer 143 .

[0081] Although referenced Figure 2 and Figure 3 The display device applied to the portable electronic device is described, but the display device according to the example embodiment may be applied not only to the portable electronic device but also to various other electronic devices.

[0082] In the following, reference will be made to Figure 4 , Figure 5 and Figure 6 A gate voltage that changes when a display device is driven is described in detail.

[0083] Figure 4 A cross-sectional view of a display device according to a comparative example and a corresponding circuit diagram thereof are shown, Figure 5 According to an example embodiment, Figure 3 sectional view and its corresponding circuit diagram.

[0084] Figure 6 It shows that according to Figure 4 and Figure 5 A graph of the gate voltage versus frequency in the circuit diagram.

[0085] First, refer to Figure 4 , the display device according to the comparative example includes a substrate 300', a barrier layer 120', a buffer layer 130' and a thin film transistor 210'. Here, the thin film transistor 210' includes a gate electrode 121', a semiconductor layer 160', a first insulating layer 141', a second insulating layer 142', a third insulating layer 143', a source electrode 153' and a drain electrode 154'. The semiconductor layer 160' includes a channel region 150', a source region 151' and a drain region 152'.

[0086] The substrate 300 ′ may be formed of a flexible material such as plastic or polyimide.

[0087] In a flexible substrate, when a thin film transistor is driven, the transistor may not be normally driven due to materials of a layer structure provided at an upper portion and a lower portion of the transistor, movement of charges, and the like.

[0088] In the following, reference will be made to Figure 4 A circuit diagram is used to describe the factors that affect transistor driving.

[0089] Figure 4 The circuit diagram shows the elements and connection wiring corresponding to the cross-sectional view of the display device according to the comparative example. The circuit diagram is intended to be based on the gate voltage (V') when the thin film transistor 210' is driven. gate ) are used to describe factors that affect the operation of transistor 210'.

[0090] Figure 4The circuit diagram of FIG. 1 shows a gate driver 1000', a resistor R', a capacitor Cf of a buffer layer 130', a capacitor Cb of a barrier layer 120', and a capacitor Cp of a substrate 300'. Here, the resistor R' represents the resistance of a wiring connected between the gate driver 1000' and the thin film transistor 210'. The resistor R' can be determined by the length and profile of the wiring and its resistivity.

[0091] exist Figure 4 In the circuit diagram of , a first end of the gate driver 1000' is connected to a ground power supply, and a second end of the gate driver 1000' is connected to a resistor R'. The resistor R' is connected between the gate driver 1000' and the capacitor Cf of the buffer layer 130'. The capacitor Cf of the buffer layer 130' is connected to the capacitor Cb of the barrier layer 120' and the capacitor Cp of the substrate 300'. A first end of the capacitor Cp of the substrate 300' may be connected to the capacitor Cb of the barrier layer 120', and a second end of the substrate 300' may be floated or connected to another component element (not shown).

[0092] The gate driver 1000' alternately applies a gate-on voltage and a gate-off voltage to a gate wiring connected to the gate electrode 121' in response to a gate control signal applied from a signal controller (not shown). When the gate-on voltage is applied, the thin film transistor 210' is turned on.

[0093] When the thin film transistor 210 ′ is turned on, the transistor 210 ′ is driven in response to a gate-on voltage, a voltage across the drain electrode 154 ′ and the source electrode 153 ′, and a threshold voltage of the transistor 210 ′.

[0094] After transistor 210' is turned on, the gate voltage V' gate It may be affected by a voltage applied from the gate driver 1000', a resistance R', a charge of the buffer layer 130', a charge of the blocking layer 120', a charge of the substrate 300', and a voltage and frequency of an external power source (not shown).

[0095] Hereinafter, capacitance of each layer derived from charges of the buffer layer 130 ′ disposed under the thin film transistor 210 ′, charges of the blocking layer 120 ′, and charges of the substrate 300 ′ will be mainly described.

[0096] The capacitance of the isolation region, such as the buffer layer 130', the barrier layer 120' and the substrate 300', varies according to the thickness of the isolation region, the dielectric constant of the isolation region and the area of ​​the conductive layer disposed above and below the isolation region. When the areas of the conductive layers are different, the smaller of the two areas of the conductive layer is related to the capacitance of its isolation region.

[0097] The capacitance of each layer can be expressed by express.

[0098] Specifically, the capacitance C of the buffer layer 130 ′ is f It can be expressed by Equation 1.

[0099] (Equation 1)

[0100]

[0101] Here, A represents the area of ​​the buffer layer 130 ′, and d f represents the thickness of the buffer layer 130', ε o ·ε f represents the dielectric constant of the buffer layer 130 ′.

[0102] The capacitance C of the barrier layer 120' b It can be expressed by Equation 2.

[0103] (Equation 2)

[0104]

[0105] Here, A represents the area of ​​the barrier layer 120 ′, and d b represents the thickness of the barrier layer 120', ε o ·ε b represents the dielectric constant of the barrier layer 120'.

[0106] The capacitance C of the substrate 300' p It can be expressed by Equation 3.

[0107] (Equation 3)

[0108]

[0109] Here, A represents the overlapping area between the substrate 300' and the barrier layer 120', d p represents the thickness of the substrate 300', ε o ·ε p represents the dielectric constant of the substrate 300 ′.

[0110] The capacitor Cf of the buffer layer 130 ′, the capacitor Cb of the barrier layer 120 ′, and the capacitor Cp of the substrate 300 ′ are connected in series.

[0111] Therefore, the following is Figure 4 The total capacitance C' of the lower structure of the thin film transistor 210' according to the comparative example total .

[0112] (Equation 4)

[0113]

[0114] In the following, reference will be made to Figure 5 Factors that affect the operation of a thin film transistor when it is driven in a display device according to example embodiments are described.

[0115] Figure 5 Show Figure 3 sectional view and its corresponding circuit diagram.

[0116] Reference Figure 5 ,like Figure 3 As described in , the display device according to example embodiments includes a substrate 300 , a barrier layer 120 , a buffer layer 130 , and a thin film transistor 210 .

[0117] Figure 5 The cross-sectional view is also included in Figure 4 The metal layer 500, the support member 407 and the air layer 400 do not exist in the cross-sectional view of FIG.

[0118] Figure 5 The circuit diagram shows elements and connection wiring corresponding to the cross-sectional view of the display device according to the example.

[0119] Figure 5 The circuit diagram shows the gate driver 1000 , a resistor R, a capacitor Cf of the buffer layer 130 , a capacitor Cb of the barrier layer 120 , a capacitor Cp of the substrate 300 , and a capacitor Ca of the air layer 400 .

[0120] exist Figure 5 In the circuit diagram of FIG. 1 , a first end of the gate driver 1000 is connected to a ground power source, and a second end of the gate driver 1000 is connected to a resistor R. The resistor R is connected between the gate driver 1000 and the capacitor Cf of the buffer layer 130. The capacitor Cf of the buffer layer 130 is connected to the capacitor Cb of the barrier layer 120, and the capacitor Cb of the barrier layer 120 is connected to a first end of the capacitor Cp of the substrate 300. A second end of the capacitor Cp of the substrate 300 is connected to a first end of the capacitor Ca of the air layer 400, and a second end of the capacitor Ca of the air layer 400 is connected to a ground layer, for example, the metal layer 500 may be connected to the ground layer via an external power source Vi.

[0121] In the display device according to the example embodiment, similar to Figure 4 , gate voltage V gate It may be affected by a voltage applied from the gate driver 1000 , a resistance R, charges of the buffer layer 130 , charges of the blocking layer 120 , charges of the substrate 300 , and a voltage and frequency of an external power source (not shown).

[0122] Hereinafter, capacitance of each layer derived from charges of the buffer layer 130 disposed under the thin film transistor 210 , charges of the blocking layer 120 , and charges of the substrate 300 will be mainly described.

[0123] Figure 5 The capacitance of the buffer layer 130, the barrier layer 120 and the substrate 300 in the cross-sectional view of FIG. Figure 4 The structure of the cross-sectional view is the same as that of the structure of the cross-sectional view, and the capacitance of the buffer layer 130, the barrier layer 120 and the substrate 300 is Figure 4 The capacitances are the same as those shown in the circuit.

[0124] However, unlike Figure 4 ,because Figure 5 Also includes an air layer 400, so Figure 5 reflects the dielectric constant of the air layer 400 of 1. However, Figure 4 The difference in Figure 5 The air layer 400 is also included in , and thus the dielectric constant of the air layer 400 is reflected as 1. The area and distance overlapped with the substrate 300 and the metal layer 500 do not have a large influence on the capacitance of the air layer 400, and the capacitance of the air layer 400 can be approximated to 1.

[0125] The capacitor Cf of the buffer layer 130 , the capacitor Cb of the barrier layer 120 , the capacitor Cp of the substrate 300 , and the capacitor Ca of the air layer 400 are connected in series.

[0126] Therefore, the following is Figure 5 The total capacitance C of the lower structure of the thin film transistor 210 according to the example total .

[0127] (Equation 5)

[0128]

[0129] Compare this with Equation 4 The total capacitance C' of the lower structure of transistor 210' total In comparison, it can be seen that Figure 5 (Right now, Figure 3 ) of the lower structure of the transistor 210 according to the example embodiment total The value is less than Figure 4 The total capacitance C' of the lower structure of transistor 210' total The value of .

[0130] Refer again Figure 4 When the thin film transistor 210' according to the comparative example is driven, the gate voltage V' gateIt is affected by the resistor R', the capacitor Cf of the buffer layer 130', the capacitor Cb of the barrier layer 120' and the capacitor Cp of the substrate 300'.

[0131] On the contrary, Figure 5 In the circuit diagram of FIG. 1 , when the thin film transistor 210 according to the example is driven, the gate voltage V gate In addition to being affected by the resistor R, the capacitor Cf of the buffer layer 130 , the capacitor Cb of the barrier layer 120 , and the capacitor Cp of the substrate 300 , the capacitor Ca of the air layer 400 is also affected.

[0132] Regarding the display quality of the display device, it is recognized that when power is not applied to the display device, no afterimage appears on the display device.

[0133] However, even when power is not applied, the current of the transistor does not become zero, and residual current occurs in the display device. When power is not applied, the time until the transistor is completely turned off can be estimated from the perspective of a time constant.

[0134] Reference Figure 4 and Figure 5 The circuit diagram can be inferred by applying an external voltage to a circuit in which a resistor R (R') and a capacitor C (Cf, Cb, Cp, and Ca) are connected in series until a gate voltage V gate (V' gate ) The time constant for which a resistor R and a capacitor C are connected in series can be estimated by RC.

[0135] Figure 4 The time constant of the circuit diagram is R'C' total In other words, R' represents the resistance of the wiring connected between the gate driver 1000' and the thin film transistor 210', and C' total denoted the total capacitance of the lower structure of the thin film transistor 210 ′ of the comparative example.

[0136] Figure 5 The time constant of the circuit diagram is RC total In other words, R represents the resistance of the wiring connected between the gate driver 1000 and the thin film transistor 210, and C total ⊥ represents the total capacitance of the lower structure of the thin film transistor 210 of the example.

[0137] Will Figure 4 R'C' total and Figure 5 RC total For comparison, Figure 4 and Figure 5 have the same resistance. However, due to Figure 5 Ctotal With ratio Figure 4 C' total Small capacitance, so it can be seen Figure 4 The time constant of is larger. As a result, Figure 4 In the display device of the comparative example, when power is not applied, the time for the gate voltage of the thin film transistor to be reduced to zero is longer, resulting in a longer afterimage.

[0138] In the following, reference will be made to Figure 6 To describe the change in gate voltage according to the frequency region.

[0139] Figure 6 It shows that according to Figure 4 and Figure 5 A graph of the gate voltage versus frequency in the circuit diagram.

[0140] Reference Figure 6 The dotted line shows Figure 4 The gate voltage V' of the display device of the comparative example gate The solid line shows the operation Figure 5 The gate voltage V of the display device of the example gate operation.

[0141] First, refer to Figure 5 , assuming that the capacitor Ca of the air layer 400 is connected to the ground layer through the external power supply Vi.

[0142] In the circuit diagram in which the resistor R and the capacitor C are connected in series, when the transistor is driven, the gate voltage V gate It can be represented in frequency band as follows.

[0143] (Equation 6)

[0144]

[0145] Refer again Figure 6 , when driving the transistor, the gate voltage V gate It operates as a high-pass filter according to the frequency. Here, the cut-off frequency (gate voltage V gate The 3dB value of (the 3dB value of the frequency) is called the first frequency or the second frequency.

[0146] Figure 5 The first frequency is 1 / (RC total ), Figure 4 The second frequency is 1 / (R'C' total ).

[0147] based on Figure 5 The first frequency 1 / (RC total ), gate voltage V gate At the first frequency 1 / (RCtotal ) increases linearly in proportion to the frequency ω in the small frequency band. The gate voltage V gate At the first frequency 1 / (RC total ) remains constant in a large frequency band. It can be seen that even based on Figure 4 The second frequency 1 / (R'C' total ), there is also effectively a high-pass filter.

[0148] According to the second frequency 1 / (R'C' total ) is less than the first frequency 1 / (RC total ). As a result, in the low frequency band, Figure 4 The gate voltage V applied in the comparative example gate Than Figure 5 The gate voltage V gate big.

[0149] The gate voltage V applied in the low frequency band gate In this case, the gate voltage V gate It will affect the driving of the transistor, thereby deteriorating the display quality by causing afterimages, for example. Figure 5 The first frequency according to the example 1 / (RC total ) is greater than Figure 4 The second frequency according to the comparative example 1 / (R'C' total ). A gate voltage V higher than that of the comparative example is applied in the low frequency band. gate The gate voltage V gate , and since the transistor is driven by a signal with relatively less noise, afterimage can be improved, thereby improving display quality.

[0150] A high level of cutoff frequency can be used to prevent noise in the low frequency signal band from passing through the gate voltage, thereby improving the afterimage of the display device. Figure 5 The display device according to the example can achieve this effect by forming an air layer 400 between the substrate 300 and the metal layer 500. Figures 1 to 3 and Figure 5 In addition to the structure shown in FIG. 4 , another structure may be provided to form the air layer 400 .

[0151] Figure 7 A display device capable of presenting the same effect according to an example embodiment is shown.

[0152] In the following, reference will be made to Figure 7 A display device capable of presenting the same effect according to an example embodiment will be described.

[0153] Figure 7 A cross-sectional view illustrating a display device according to example embodiments.

[0154] Reference Figure 7 , the display device according to example embodiments includes a metal layer 500 , an air layer 400 , a film 406 , a ball 408 , a substrate 300 , a barrier layer 120 , a buffer layer 130 , and a thin film transistor 210 .

[0155] The thin film transistor 210 includes a gate electrode 121 , a semiconductor layer 160 , a first insulating layer 141 , a second insulating layer 142 , a third insulating layer 143 , a source electrode 153 , and a drain electrode 154 .

[0156] This example embodiment is combined with Figure 3 Compared with the display device according to the example embodiment, Figure 7 The display device of FIG. 1 has the same structure in terms of the substrate 300 , the barrier layer 120 , the buffer layer 130 , and the thin film transistor 210 , and thus their descriptions will be omitted.

[0157] Reference Figure 7 The film 406 and the balls 408 are disposed at the bottom of the substrate 300 such that, for example, the film 406 includes a plurality of balls 408 therein to maintain a constant distance between the substrate 300 and the metal layer 500 together with the balls 408. Here, the film 406 and the balls 408 are examples of the support member 407.

[0158] exist Figure 7 In the example embodiment shown in , the film 406 includes unevenness or irregularities on opposite sides of the surface. The portion of the film 406 provided with the balls 408 is convex, and the remaining portion of the film 406 without the balls 408 is concave. Here, the film 406 may be a film in which both the convex and concave portions are continuous, or one side of the film 406 may be a flat surface filled with concave portions and the convex and concave portions may be formed on the other side thereof.

[0159] The film 406 may be made of a material having adhesiveness, and may be implemented as a conductive film, an insulating film, a protective film, etc. The ball 408 may be made of a material having conductivity, and may be implemented as a conductive ball, etc.

[0160] The film 406 may be variously formed to have a size corresponding to the substrate 300 , and the balls 408 may be formed to have various sizes within a range thinner than the total thickness of the film 406 .

[0161] The metal layer 500 is disposed below the film 406 and may be disposed such that the side edges of the film 406 and the side edges of the metal layer 500 are aligned along a line perpendicular to the substrate 300. The metal layer 500 may be formed to have a size similar to that of the film 406. However, when the metal layer 500 is smaller than the film 406 (e.g., the metal layer 500 is smaller in lateral dimension than the film 406), the metal layer 500 may be disposed at any position below the film 406.

[0162] One end of the metal layer 500 may be connected to a ground layer (eg, a ground electrode) (not shown).

[0163] The air layer 400 is formed in the concave portion between the lower portion of the substrate 300 and the film 406. The air layer 400 is also formed at the concave portion between the metal layer 500 and the film 406. The volume of the air layer 400 may vary depending on the size and shape of the metal layer 500.

[0164] In addition to the film 406 , a protective film, a plurality of conductive films, or the like may be formed between the substrate 300 and the metal layer 500 .

[0165] In the display device according to the example embodiment, the air layer 400 is formed under the substrate 300 so that the total capacitance C of the lower structure of the transistor 210 total Reduce.

[0166] As a result, due to the total capacitance C of the lower structure of transistor 210 total The gate voltage of the low frequency band including noise in the frequency region is reduced, and thus it is possible to filter out the gate voltage.

[0167] Furthermore, since charges under the transistor 210 do not move to the transistor 210 , the transistor 210 may operate normally, and a display device with improved afterimage and improved display quality may be implemented.

[0168] This effect is caused by a structure in which the air layer 400 and the metal layer 500 are sequentially formed below the substrate 300. Meanwhile, the degree of afterimage improvement may vary depending on the distance between the substrate 300 and the metal layer 500.

[0169] In the following, reference will be made to Figure 8 The afterimage effect according to the distance between the substrate 300 and the metal layer 500 will be described.

[0170] Figure 8 A cross-sectional view illustrating a display device according to example embodiments.

[0171] Reference Figure 8, the display device according to the example embodiment has a structure in which a display element 200 including a thin film transistor, a substrate 300, an air layer 400, a support member 407, and a metal layer 500 are sequentially stacked.

[0172] Figure 8 It is used to describe the afterimage index according to the distance between the substrate 300 and the metal layer 500, and Figure 8 and Figure 1 Compared with the cross-sectional view of the display device according to the example embodiment, Figure 8 It is an approximate structure except for the window 100 located at the upper portion thereof.

[0173] Due to Figure 8 The description and Figure 1 The descriptions are the same and therefore will be omitted.

[0174] Hereinafter, an afterimage index according to a distance between the substrate 300 and the metal layer 500 will be described in detail.

[0175] The air layer 400 is formed as an empty space between the substrate 300 and the metal layer 500. The space in which the air layer 400 is provided is supported by a support member 407, and the support member 407 may be formed at opposite ends of the metal layer 500 or at different positions to maintain a distance between the metal layer 500 and the substrate 300. Therefore, the air layer 400 is formed in the space except for the support member 407.

[0176] The influence of the layer structure below the transistor on the transistor is changed by the air layer 400 formed along the distance between the substrate 300 and the metal layer 500. This effect can be recognized by the afterimage index.

[0177] Here, the afterimage index indicates that an afterimage occurs on the display device through a driven transistor even when no voltage is applied to the transistor, and a higher afterimage is disadvantageous.

[0178] Hereinafter, an afterimage index according to a distance between the substrate 300 and the metal layer 500 will be described with reference to Table 1.

[0179] (Table 1)

[0180]

[0181]

[0182] The thickness of the substrate 300 may be formed in the range of, for example, 3 μm to 10 μm.

[0183] When the thickness of the substrate 300 is 3 μm and the distance between the substrate 300 and the metal layer 500 is greater than or equal to 1.0 μm and less than or equal to 1.6 μm, the afterimage index is 0.62.

[0184] When the thickness of the substrate 300 is 5 μm and the distance between the substrate 300 and the metal layer 500 is greater than or equal to 1.6 μm and less than or equal to 3.2 μm, the afterimage index is 0.50.

[0185] When the thickness of the substrate 300 is 10 μm and the distance between the substrate 300 and the metal layer 500 is greater than or equal to 3.2 μm, the afterimage index is 0.36.

[0186] As can be seen with reference to Table 1, the afterimage is improved as the distance between the substrate 300 and the metal layer 500 increases. The increased thickness of the substrate 300 also improves the afterimage.

[0187] In the recent trend of realizing a slim display device, the thickness of the substrate is also reduced. Therefore, the substrate 300 may be appropriately formed to have a thickness of 5 μm to 10 μm and the distance between the substrate 300 and the metal layer 500 may be ensured to be 1.6 μm to 3.2 μm, so as to improve the afterimage by appropriately adjusting the distance between the substrate 300 and the metal layer 500 while maintaining the appropriate thickness of the substrate 300.

[0188] As described above, in the display device according to the example embodiment, the air layer 400 and the metal layer 500 are sequentially formed at the lower portion of the substrate 300 to reduce the total capacitance of the lower portion of the transistor. As a result, since the capacitance under the transistor is reduced, the gate voltage of the low frequency band including noise in the frequency region can be filtered.

[0189] Furthermore, since charges under the transistor can be prevented from moving to the transistor, the transistor can operate normally, and a display device with improved afterimage and improved display quality can be realized.

[0190] In the following, reference will be made to Fig.9A , Fig. 9B and Fig. 9C A rear view of a display device according to an exemplary embodiment is further described to implement a display device with improved afterimage and display quality.

[0191] Fig.9A , Fig. 9B and Fig. 9C A rear view of a display device according to example embodiments is shown.

[0192] Reference Fig.9A , Fig. 9B and Fig. 9C, the display device according to the example embodiment includes a substrate 300, metal layers 500, and support members 407 in a bottom view. The metal layers 500 are located on the rear side of the substrate 300, and the support members 407 are located on opposite ends of each metal layer 500.

[0193] First, refer to Fig.9A , the respective metal layers 500 are arranged at the left and right sides of the substrate 300 in parallel with the edge of the substrate 300, at the upper end of the substrate 300 in parallel with the edge of the substrate 300, and at the lower end of the substrate 300 while maintaining a distance slightly away from the edge of the lower end of the substrate 300, so that the side surfaces of the metal layers 500 are disposed in contact with the left and right sides of the substrate 300. In addition, the two metal layers 500 are disposed between the metal layer 500 on the lower end of the substrate 300 and the side surface of the camera area A of the substrate 300.

[0194] One metal layer 500 is disposed on each of the upper end, the lower end, the left side, and the right side of the substrate 300, each of which has a rectangular shape having a length greater than a width. Two metal layers 500 are disposed between the metal layer 500 on the lower end of the substrate 300 and the side surface of the camera area A of the substrate 300. The two metal layers 500 disposed between the lower end of the substrate 300 and the side surface of the camera area A are rectangles having different sizes.

[0195] Here, although the metal layer 500 is implemented in a quadrangular shape, it may be implemented in various shapes such as a circular shape or a triangular shape.

[0196] Support members 407 are formed at opposite ends of each metal layer 500. The number of support members 407 may vary according to the size and shape of the metal layer 500, and the distance between the support members 407 may vary according to the number of support members 407.

[0197] Next, refer to Fig. 9B , one metal layer 500 is arranged at the upper side of the substrate 300 in parallel with the edge of the substrate 300 , and the other metal layer 500 is arranged at a position facing the upper end of the substrate 300 in parallel with the edge of the substrate 300 .

[0198] Similarly, two support members 407 are formed at opposite ends of each metal layer 500 .

[0199] Finally, refer to Fig. 9C The metal layer 500 is disposed to be spaced a certain distance downward from the camera region A of the substrate 300. One metal layer 500 may be formed mostly on the lower region of the substrate 300. Two support members 407 are formed on opposite ends of the metal layer 500.

[0200] The display device can be formed to improve afterimage by forming the air layer 400 by attaching the metal layer 500 to the lower portion of the substrate 300 as described above. The capacitance of the lower portion of the transistor can be reduced by stacking a substance having a high dielectric constant between the transistor and the substrate.

[0201] Hereinafter, a display device capable of improving an afterimage according to a layer structure formed of a material having a large dielectric constant according to another example embodiment will be described.

[0202] Fig.10 A cross-sectional view of a display device according to example embodiments is shown.

[0203] Fig.10 The display device according to example embodiments includes a substrate 300 , a first high dielectric constant layer 115 , a barrier layer 120 , a second high dielectric constant layer 125 , a buffer layer 130 , and a thin film transistor 210 .

[0204] The thin film transistor 210 includes a gate electrode 121 , a semiconductor layer 160 , source and drain electrodes 153 and 154 , a first insulating layer 141 , a second insulating layer 142 , and a third insulating layer 143 .

[0205] The substrate 300 is disposed at a lower portion of the display device. For example, the substrate 300 may be formed of a flexible material such as plastic or polyimide (PI).

[0206] The barrier layer 120 is located on the substrate 300, and the first high dielectric constant layer 115 is disposed between the substrate 300 and the barrier layer 120. The first high dielectric constant layer 115 may be made of germanium (Ge), carbon nanotubes (C), Teflon (Teflon) or polyethylene terephthalate (PET).

[0207] The barrier layer 120 on the first high dielectric constant layer 115 may include, for example, silicon oxide (SiO x ), Silicon Nitride (SiN x ) or aluminum oxide (Al 2 O 3 ) and may also include an organic insulating material such as polyimide acrylic (with epoxy resin added).

[0208] The second high dielectric constant layer 125 is located on the barrier layer 120. The second high dielectric constant layer 125 may be made of germanium (Ge), carbon nanotubes (C), Teflon (Teflon), or polyethylene terephthalate (PET).

[0209] The buffer layer 130 may be located on the second high dielectric constant layer 125 and may include, for example, silicon oxide (SiO x ), Silicon Nitride (SiN x) or aluminum oxide (Al 2 O 3 ) and may also include an organic insulating material such as polyimide acrylic (with epoxy resin added).

[0210] In a flexible substrate, when a thin film transistor is driven, the transistor may not be normally driven due to materials of a layer structure provided at an upper portion and a lower portion of the transistor, movement of charges, and the like.

[0211] therefore, Fig.10 The display device according to example embodiments includes the first high dielectric constant layer 115 and the second high dielectric constant layer 125 in the lower structure of the transistor to reduce this problem.

[0212] When the transistor is driven, the buffer layer 130 , the barrier layer 120 , and the substrate 300 disposed under the transistor may function as a capacitor according to charges of the buffer layer 130 , charges of the barrier layer 120 , and charges of the substrate 300 .

[0213] The insulating regions such as the buffer layer 130 , the barrier layer 120 , and the substrate 300 have different capacitances according to the thickness of the insulating regions and the dielectric constant of the insulating regions.

[0214] However, the material constituting the first high dielectric constant layer 115 and the second high dielectric constant layer 125 corresponds to a material having a high dielectric loss factor, that is, a material having a high resistivity.

[0215] Therefore, according to example embodiments, total capacitance is reduced by increasing resistivity of a lower structure of a transistor in a display device in which the substrate 300 , the first high dielectric constant layer 115 , the barrier layer 120 , the second high dielectric constant layer 125 , and the buffer layer 130 are sequentially stacked.

[0216] Here, if only the first high dielectric constant layer 115 or only the second high dielectric constant layer 125 exists, the total capacitance of the lower portion of the transistor can be reduced, and thus at least one of the first high dielectric constant layer 115 and the second high dielectric constant layer 125 can be omitted. In addition, the total capacitance of the lower portion of the transistor can be reduced by increasing the thickness of the buffer layer 130 or the barrier layer 120.

[0217] As a result, since the total capacitance under the transistor is reduced, the gate voltage of a low frequency band including noise in the frequency region can be filtered.

[0218] Furthermore, since charges under the transistor can be prevented from moving to the transistor, the transistor can operate normally, and a display device with improved afterimage and improved display quality can be realized.

[0219] By way of summary and review, a flexible substrate may be made of, for example, plastic or polyimide (PI) for use in flexible products. In a flexible display device, afterimages or display quality degradation such as noise signal transmission in a low frequency band when a gate voltage of a thin film transistor is in may be caused by using a flexible substrate such as a plastic substrate.

[0220] As described above, the embodiments relate to a display device including a flexible substrate.

[0221] Embodiments may provide a flexible display device having improved afterimage and improved display quality by adjusting the total capacitance of a lower structure of a transistor.

[0222] According to an example embodiment, an air layer and a metal layer are sequentially formed under the substrate, thereby reducing the total capacitance of the lower portion of the transistor. As a result, since the capacitance under the transistor is reduced, a signal of a low frequency band including noise in a frequency region can be filtered. In addition, since the charge under the transistor can be prevented from moving to the transistor, the transistor can operate normally, and a display device with improved afterimage and improved display quality can be realized.

[0223] Example embodiments have been disclosed herein, and although specific terms are employed, they are used and interpreted in a general and descriptive sense only, and not for purposes of limitation. In some cases, as will be apparent to one of ordinary skill in the art, features, characteristics, and / or elements described in conjunction with a specific embodiment may be used alone or in combination with features, characteristics, and / or elements described in conjunction with other embodiments as of the time of filing this application, unless otherwise specifically noted. Therefore, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the invention as set forth in the claims.

[0224] <symbol description>

[0225] 100: Window 1000, 1000': Gate driver

[0226] 120, 120': barrier layer 121, 121': gate electrode

[0227] 115: First high dielectric constant layer

[0228] 125: Second highest dielectric constant layer

[0229] 130, 130': buffer layer 141, 141': first insulating layer

[0230] 142, 142': second insulating layer

[0231] 143, 143': The third insulation layer

[0232] 150, 150': channel region 151, 151': source region

[0233] 152, 152': drain region 153, 153': source electrode

[0234] 154, 154': drain electrode 160, 160': semiconductor layer

[0235] 200: display element 210, 210': thin film transistor

[0236] 300, 300': base 400: air layer

[0237] 406: membrane 407: support member

[0238] 408: ball 500: metal layer

Claims

1. A display device, comprising: Flexible substrate; A display element, located on the flexible substrate and comprising a thin film transistor; A metal layer disposed at a lower portion of the flexible substrate; an air layer formed between the flexible substrate and the metal layer; as well as A supporting member is disposed between the flexible substrate and the metal layer to support the metal layer.

2. The display device according to claim 1, wherein: The supporting member includes a film and a ball formed inside the film.

3. The display device according to claim 2, wherein: The convex and concave portions are formed to be continuous in the surface of the film, The air layer is formed between the flexible substrate and the supporting member and / or between the supporting member and the metal layer.

4. The display device according to claim 1, further comprising: a barrier layer disposed on the flexible substrate; as well as a buffer layer, located on the barrier layer, Wherein, the display element is located on the buffer layer.

5. The display device according to claim 4, wherein: The thickness of the buffer layer is 2000Å, and the thickness of the barrier layer is 5000Å.

6. The display device according to claim 1, wherein: One end of the metal layer is connected to a ground electrode.

7. The display device according to claim 1, wherein: The flexible substrate includes polyimide.

8. The display device according to claim 1, wherein: The thickness of the flexible substrate is in the range of 3 μm to 10 μm.

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