JP2009231305A - Display and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve light-emitting efficiency as a display and to reduce display irregularities. <P>SOLUTION: The display has a plurality of pixels formed in a matrix shape. The display includes a substrate 30, a plurality of pixel electrodes 32 and counter electrodes 37. Each pixel has one pixel electrode 32, the counter electrode 37 and a plurality of granular light-emitting diodes 22, and the plurality of granular light-emitting diodes 22 are sprinkled at random on the one pixel electrode 32. Each of the plurality of granular light-emitting diodes 22 incldues a crystalline semiconductor composed of a nitride of group III-V. The crystalline semiconductor includes a polyhedron whose outer peripheral surface is composed of a plurality of flat crystal lattice planes. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a display device and a method for manufacturing the display device, and more particularly to a display device including a light emitter composed of a plurality of fine particles dispersed on a substrate and a method for manufacturing the display device.

  Patent Document 1 discloses a light emitting element and a display device that have high luminous efficiency and can be enlarged at low cost.

  As shown in the cross-sectional view of FIG. 19, the light-emitting element and the display device described in Patent Document 1 sandwich a light-emitting layer 303 between a pair of electrodes 302 and 304 on a substrate 301, and an AC voltage is supplied by an AC power source 304. Is applied to cause the light emitting layer 303 to emit light. The light emitting layer 303 has a structure in which light emitting particles 306 are dispersed in a binder 305 made of an organic material. Since it is only dispersed in the resin, it is easy to increase the area at low cost. FIG. 20 is a cross-sectional view illustrating a cross-sectional structure of the light emitting particles 306 included in the light emitting layer 303. As shown in FIG. 20, the luminescent particle 306 has a spherical first semiconductor part 307 (n-type) and a second semiconductor part 308 (p-type) covering the surface of the first semiconductor part 307. By being a spherical particle and having an n-type semiconductor and a p-type semiconductor in a layered structure, when an electric field is applied, electrons and holes collide with each other, and highly efficient light emission can be obtained.

In addition, Non-Patent Document 1 is cited as a document that can be related to the present invention.
JP 2006-127884 A Applied Physics, Vol. 68, No. 2 (1999), pages 152 to 155, Takashi Mukai, Shuji Nakamura, “White and Ultraviolet Light Emitting Diodes”

  The inventor further studied improvement in luminous efficiency and reduction in display unevenness as a display device. As a result, the particles sandwiched between the pixel electrode and the counter electrode are composed of a crystalline semiconductor having a polyhedral shape whose outer peripheral surface is composed of a plurality of flat crystal lattice planes. The inventors found that extremely high luminous efficiency can be achieved as compared with a certain case, and completed the present invention.

The display device of the present invention includes:
A substrate,
A plurality of pixel electrodes provided on the substrate;
A plurality of particulate light emitting diodes randomly distributed on each of the plurality of pixel electrodes;
A counter electrode covering the plurality of particulate light emitting diodes;
With
Each of the plurality of particulate light emitting diodes is made of a crystalline semiconductor made of a group III-V nitride,
A first conductive type first semiconductor, an active layer, and a second conductive type second semiconductor,
The active layer is formed in a part of the periphery of the first semiconductor;
The second semiconductor covers the periphery of the active layer;
The first semiconductor is electrically connected to either the pixel electrode or the counter electrode,
The second semiconductor is electrically connected to the other of the pixel electrode and the counter electrode,
The crystalline semiconductor has a polyhedral shape whose outer peripheral surface is composed of a plurality of flat crystal lattice planes.

The first manufacturing method of the display device of the present invention is as follows.
A step (A) of randomly dispersing the plurality of particulate light emitting diodes on each of the plurality of pixel electrodes;
(B) filling a part of the plurality of particulate light emitting diodes in the dielectric layer by forming a dielectric layer on each of the plurality of pixel electrodes dispersed with the plurality of particulate light emitting diodes; ,
Etching the surface of each particulate light emitting diode not covered with the dielectric layer to expose a part of the first semiconductor, and forming a counter electrode on the exposed first semiconductor Step (E),
In order.

The second manufacturing method of the display device of the present invention is as follows.
A step of filling the part of the plurality of particulate light emitting diodes in the dielectric layer by randomly dispersing the particulate light emitting diodes in the dielectric layer of the dummy substrate provided with a dielectric layer on the surface thereof (B1),
Etching the surface of each particulate light emitting diode not covered with the dielectric layer to expose the first semiconductor (B2);
Providing a pixel electrode on the exposed first semiconductor, and electrically connecting the pixel electrode and the first semiconductor (C2);
A peeling step (D2) for peeling the dummy substrate from the dielectric layer;
A step (E1) of forming a counter electrode on the second semiconductor of the particulate light emitting diode on the surface side exposed by peeling, and electrically connecting the counter electrode and the second semiconductor;
In order.

  In the display device of the present invention, a large number of particulate light emitting diodes are dispersed on the pixel electrode, and light is emitted by charge injection from the pixel electrode and the counter electrode electrically connected to each particulate light emitting diode. Such a crystalline semiconductor constituting the particulate light emitting diode has a polyhedral shape whose outer peripheral surface is composed of a plurality of flat crystal lattice planes. High efficiency can be realized. The display device manufacturing method of the present invention realizes electrical connection between a large number of particulate light emitting diodes and pixel electrodes and counter electrodes in a simple process, facilitating charge injection from the electrodes to the particulate light emitting diodes. Thus, a display device that is highly efficient, low in cost, has little display unevenness, and can be easily enlarged is realized.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is an enlarged plan view of a pixel of a display device of the present invention.

  FIG. 2 is a cross-sectional view of the display device of the present invention in which a part of the plan view of FIG. 1 is enlarged.

  FIG. 3 is a block diagram of a film forming apparatus for obtaining a particulate light emitting diode used in a display device according to the present invention.

  FIG. 4 is a cross-sectional view of the particulate light emitting diode produced by the film forming apparatus shown in FIG.

  FIG. 5 is a cross-sectional view showing each step in the method for manufacturing a display device according to the present invention.

  As shown in FIGS. 1 and 2, the display device of the present invention is randomly distributed on the substrate 30, the plurality of pixel electrodes 32 provided on the substrate 30, and the plurality of pixel electrodes 32. A plurality of particulate light emitting diodes 22 and a counter electrode 37 covering the plurality of particulate light emitting diodes 22 are provided.

  Each of the plurality of particulate light emitting diodes 22 is made of a crystalline semiconductor made of a group III-group V nitride. The outer peripheral surface of this crystalline semiconductor consists of a plurality of flat crystal lattice planes.

  Further, the crystalline semiconductor includes a first conductive type first semiconductor 21n (n-type), an active layer 21i, and a second conductive type second semiconductor 22p (p-type). The active layer 21i is formed in a part of the periphery of the first semiconductor 21n. The second semiconductor 21p covers the periphery of the active layer 21i. The first semiconductor 21n is electrically connected to the counter electrode 37. The second semiconductor 21p is electrically connected to the pixel electrode 32.

  As the substrate 30, glass or plastic, or a metal sheet such as stainless steel having an insulating layer provided on the surface can be used. The substrate 30 may be an active matrix substrate provided with TFTs 31 as shown in FIG.

  The plurality of pixel electrodes 32 are made of a material that can make ohmic contact with the second semiconductor 21p. As an example, when the second semiconductor 21p is p-type GaN, the material of the pixel electrode 32 is preferably ITO or gold.

  Examples of the material of the counter electrode 37 that covers the particulate light emitting diode include materials that are in ohmic contact with the first semiconductor 21n, such as Ti, Al, Ag, and Hf. The counter electrode 37 may be composed of a two-layer electrode such as Ti / Al. At least one of the pixel electrode 32 and the counter electrode 37 is transparent or translucent.

  The crystalline semiconductor made of a group III-V nitride constituting the particulate light emitting diode 22 is a single crystal or a polycrystal made of a small number of grains made of gallium nitride, indium nitride, aluminum nitride, or a mixed crystal thereof. .

  The crystalline semiconductor has a polyhedral shape. A plurality of outer peripheral surfaces constituting the polyhedron are not artificial surfaces such as polished surfaces, but are formed by flat crystal lattice planes. For example, in FIG. 1 and FIG. 2, the particulate light emitting diode 22 has a hexagonal prism shape in which the side surface is an m-plane and the bottom surface is a C-plane. The shape of the light emitting diode 22 is not limited to this, and may be, for example, a trapezoidal shape, a hexagonal pyramid shape, or a tetrapot shape. However, even if there are parts other than the flat crystal lattice plane in a part of a large number of particulate light emitting diodes or in a small number of parts of the polyhedron, the influence on the light emission characteristics is small. Generally, it only needs to be configured.

  Furthermore, by manufacturing the display device of the present invention, which will be described later, by dispersing and mounting minute particulate light emitting diodes, it can be manufactured in a simple process even when the number of pixels is enormous.

  As shown in FIG. 2, the particulate light emitting diode 22 is fixed on the pixel electrode 32 with a conductive fixing layer 34 such as ITO or gold, and the pixel electrode 32 and the second conductive type (p-type) second semiconductor. 21p is electrically connected.

  Further, the first conductive type (n-type) first semiconductor 21 n is electrically connected to the counter electrode 37 with the dielectric layer 35 and the insulating layer 36 interposed therebetween.

  The TFT 31 is controlled by a signal supplied via the gate electrode 31g and the source electrode 31s. A current corresponding to video information is applied between the pixel electrode 32 and the counter electrode 31 through the TFT 31, and electrons and holes are recombined in the active layer 21i to emit light.

In the first semiconductor 21n and the second semiconductor 21p, the active layer 21i can be set to have a band structure and conductivity with high light emission efficiency similar to a normal light emitting diode. For example, the first semiconductor 21n is n-type GaN doped with Si, the second semiconductor 21p is p-type GaN doped with Mg, and the active layer 21i is non-doped GaN and In _x Ga _(1-x) N (0 <x <1 ) Are stacked in a multiple quantum well (MQW) structure.

  Since the active layer 21i functions as the light emitting layer of the display device, the band gap for visible light emission or ultraviolet light emission is preferably 1.9 eV or more, and the composition of the active layer may be changed to display the RGB three primary colors. Color conversion by body may be used. Although the number of TFTs 31 is one in FIG. 1, since the luminance of a light emitting diode is proportional to the current value, constant current driving by a plurality of transistors such as a current copier used in an organic EL can be employed. Further, instead of the active matrix type, a simple matrix type that can be created at a lower cost or a simple segment display may be used.

  The crystalline semiconductor constituting the particulate light-emitting diode 22 preferably includes a flat crystal lattice plane having a Miller index of {0001}, {1-100}, or {1-101}. As will be understood from the examples described later, the polyhedral crystal composed of these index planes can emit light with high efficiency and high luminance.

  Among these, the crystalline semiconductor is preferably a vertically long hexagonal columnar particle having a {1-100} plane as a side surface.

  At this time, the nonpolar plane {1-100} plane (m plane) having a very low defect density occupies most of the surface and emits light with high efficiency. In such a hexagonal column shape whose side surface is longer than the bottom surface, the hexagonal column is tilted as shown in FIGS. 1 and 2, and the probability that the side surface (second semiconductor 21p) of the hexagonal column shape is in contact with the pixel electrode 32 increases. The m-plane always emits light, variation in emission wavelength is suppressed, and high-efficiency light emission can be obtained even at a long wavelength due to the effect of the nonpolar plane.

  The crystalline semiconductor composing the particulate light emitting diode 22 is a particle obtained by heteroepitaxially growing a group III-V nitride on the surface of a single crystal core particle, and the thickness of the crystalline semiconductor is 1 micron or more. Also good. With the crystalline semiconductor having such a structure, a group III-V nitride film having a low dislocation density is obtained, and the light emission efficiency is increased.

  The core particle may be formed of at least one material selected from the group consisting of aluminum nitride, silicon carbide, aluminum oxide, zinc oxide, and beta gallium oxide. Core particles made of these materials have physical properties suitable for group III-V nitride crystal growth. The shape of the core particles may be a substantially spherical or polyhedral aluminum oxide with rounded corners. As such core particles, single crystal particles can be produced at low cost, and a crystalline semiconductor film with few defects can be formed on the surface thereof.

  In the display device of the present invention, as shown in FIG. 2, a part of the plurality of particulate light emitting diodes 22 including the second semiconductor 21p is embedded in the dielectric layer 35, and a part of the first semiconductor 21n is a dielectric layer. It may protrude from 35 and be electrically connected to the counter electrode 37. A large number of minute particulate light-emitting diodes 22 can be mounted in a batch by the method for manufacturing a display device of the present invention, which will be described later. That is, a mask for fixing a large number of particulate light-emitting diodes 22 and insulating the individual light-emitting diodes 22 and exposing the first semiconductor 21n by a dielectric layer 35 formed by a simple method by application such as printing. Can play a role.

  The dielectric layer 35 may include a phosphor that emits light having a wavelength different from that of the light when excited by the light emitted from the particulate light emitting diode 22. Thereby, the dielectric layer 35 can have a function of light conversion in addition to the above-described function.

When the standard deviation of the peak emission wavelength of the particulate light emitting diodes 22 in the display device of the present invention is σ nm, the number n of the particulate light emitting diodes 22 positioned on each pixel electrode is preferably larger than 16σ ² .

  The characteristics of individual particulate light emitting diodes vary widely, but since a large number of light emitting diodes (particulate light emitting diodes) are dispersed in one pixel and each particulate light emitting diode emits light, the emission color is made uniform.

  If the number of particulate light emitting diodes of about 25 is dispersed in one pixel, the color variation can be suppressed to an inconspicuous level. This will be described in detail in an experimental example.

Since not all of the particulate light emitting diodes arranged in one pixel emit light and a non-lighting failure may occur, it is preferable to disperse 25 or more particulate light emitting diodes per pixel. However, when the non-lighting failure occurs at a rate that cannot be ignored, it is preferable to spray so that the number n sufficiently exceeds 16σ ² .

  If the color unevenness can be made uniform in this way, the brightness unevenness can be corrected under the driving conditions. Even if the number of lights varies slightly, if you measure the image variation in advance with a camera, etc., and correct the drive conditions with reference to the variation data, you can make the luminance unevenness almost invisible, and there are some non-lighting defects. There is no problem.

  The pixel size of a display for displaying a television image or the like is about 0.5 mm for a large domestic television. For this reason, in order to arrange 25 or more particulate light emitting diodes in one pixel, the size of the particulate light emitting diodes must be 100 μm or less. Since a gap of a certain degree is required, 50 μm or more and −60 μm or less are more desirable.

  Next, a method for manufacturing the display device of the present invention will be described with reference to FIGS.

  First, a plurality of particulate light emitting diodes 22 such as a cross section of the particulate light emitting diode of FIG. 4 (a plane parallel to the bottom surface of the hexagonal column) is prepared. Such a particulate light emitting diode 22 can be produced using, for example, a film forming apparatus as shown in FIG. A substrate 30 having a plurality of pixel electrodes 32 is prepared. Then, the following steps (A) to (E) shown in FIG. Step (A) of randomly dispersing a plurality of particulate light emitting diodes 22 on each of the plurality of pixel electrodes 32 (FIG. 5A). A step of filling a part of the plurality of particulate light emitting diodes 22 in the dielectric layer 25 by forming a dielectric layer 35 on each of the plurality of pixel electrodes 32 on which the plurality of particulate light emitting diodes 22 are dispersed (B (FIG. 5B). A step (C) of etching a surface of each particulate light emitting diode 22 not covered with the dielectric layer 35 to expose a part of the first semiconductor 21n (FIG. 5C). Step (D) of forming a counter electrode 37 on the exposed first semiconductor 21n (FIG. 5E).

  A method of preparing a large number of particulate light emitting diodes 22 can be prepared, for example, by crystal growth by a fluidized bed method as shown in the block diagram of the film forming apparatus in FIG.

  Hereinafter, crystal growth by the fluidized bed method will be described.

  The apparatus shown in FIG. 3 includes a reaction furnace 60 in which a porous plate 61 is disposed, and a heater 62 for heating the reaction furnace 60. The material of the porous plate is preferably a material that can withstand the reaction temperature and is difficult to attach a reaction product such as GaN. For example, quartz or silicon nitride is preferable. A pipe 64 a for flowing hydrogen or nitrogen as a carrier gas and a cylinder 64 b for storing ammonia as a reaction gas are connected in parallel to the reaction furnace 60 and vaporizers 63 a and 63 b through a mass flow 65. In the vaporizers 63a and 63b, an organic metal (MO) raw material such as trimethylgallium (TMGa) or trimethylindium (TMIn) used for crystal growth is vaporized, and hydrogen gas or nitrogen gas sent via the mass flow 65 is used. After being mixed with the gas, it is supplied to the reactor 60 through the mass flow 66.

In the fluidized bed method using such an apparatus, a powder consisting of a large number of core particles 67 is placed on the porous plate 61 in the reaction furnace 60, and then a gas is allowed to flow from the back of the porous plate 61. Fluidize. And by heating the reaction furnace 60 and powder with the heater 62, powder and gas are made to react and the surface of the core particle 67 is coat | covered with the reaction product. This fluidized bed method is described, for example, in Chemical Industrial Papers, Vol. 22, No. 2, pages 412 to 414, Shigeo Chiba et al., “AlN coating of Si ₃ N ₄ fine particles by fluidized bed CVD method”. . The core particle 67 is preferably a single crystal fine particle with good dispersibility. If the particle size is too small, the core particle 67 is aggregated and cannot be separated, so 0.1 micron or more is preferable. The material can be selected from materials that can be used as a gallium nitride substrate, such as aluminum oxide (alumina or sapphire), gallium nitride, silicon carbide, zinc oxide, and beta gallium oxide. Details in the case of preparing alumina fine particles as core particles will be described below.

A particulate light-emitting diode 22 as shown in the cross-sectional view of FIG. 4 is formed on the surface of the core particle 67 made of dried alumina fine particles. Specifically, first, the surface of the alumina particles is cleaned by flowing only hydrogen gas for several minutes at a reactor temperature of 1100 degrees. The temperature of the reactor is lowered to 510 ° C., and trimethylgallium, trimethylaluminum, and ammonia are reacted using hydrogen gas as a carrier gas to form an AlGaN buffer layer 21a (thickness 25 nm). Subsequently, the temperature of the furnace is raised to 1000 to 1100 ° C., and crystal growth is performed on the first semiconductor (n-type GaN layer) 21n doped with Si by mixing silane with trimethylgallium. Further, the carrier gas is changed to nitrogen, the temperature is lowered to about 800 degrees, and undoped GaN, trimethylgallium is mixed with trimethylindium, and In _x Ga _(1-x) N {0 <x <1} (hereinafter referred to as InGaN) (Abbreviated) are alternately formed every several nm to form an active layer 21i composed of three quantum well layers (MQW). On the MQW layer, trimethylgallium mixed with biscyclopentadienylmagnesium (Cp ₂ Mg) and ammonia are reacted to grow a second semiconductor (p-type GaN layer) 21p of about 400 nm, and in nitrogen at 800 ° C. The particulate light emitting diode 22 is created by annealing. Note that the ratio of MO to ammonia (III / V ratio) and the ratio of TMGa to TMIn when depositing InGaN are almost the same as the conditions of general GaN-based MOCVD. The thicknesses of the MQW and the p layer are substantially constant, but the size and shape of the particles can be changed depending on the conditions for forming the n layer that grows first. Since the aggregates of the particulate light emitting diodes produced by the fluidized bed vary, the shape and size are made uniform by classification means such as sedimentation.

  Note that the fluidized bed method used in the present embodiment as a method for crystal growth around the core particles is preferable because a large amount of fine particles can be uniformly and collectively processed. Any other method may be used as long as it can supply energy such as heat for promoting the reaction. For example, the particle levitation method may be an electrostatic levitation method, a magnetic field levitation method, a method of levitation using charging in plasma, or the particles may be moved on a heating plate or stirred. A method of performing MOCVD is also possible. In addition to vapor phase growth, liquid phase growth such as the sodium flux method, which has been studied for GaN growth, can also be performed by suspending core particles in the raw material melt and growing crystals on the fine particles.

  Next, a detailed example of steps A to E will be described with reference to FIG.

  A method of mounting the particulate light emitting diode 22 on the substrate will be described with reference to FIG. 1 which is a plan view in which pixels of the display device of the present invention are enlarged and FIGS. 5A to 5D.

  First, a glass substrate 30 on which an amorphous silicon TFT 31 and a pixel electrode 32 made of, for example, ITO shown in FIGS. 1 and 5A are prepared. A bank (ridge) 33 surrounding the pixel electrode 32 is formed on the glass substrate 30 with an acrylic photosensitive resin. The pixel pitch is, for example, 480 μm long × 160 μm wide, and the height of the ridge 33 can be set to 10 μm, for example. On the pixel electrode 32 surrounded by the ridge 33, for example, a paste in which gold nanoparticles dispersed from Harima Kasei Co., Ltd. are dispersed is dropped and dried to form a conductive fixing layer 34 having a thickness of 30 nm. Keep it. Instead of using the gold nano paste, an ITO nano paste having a close work function may be used. When a large number of particulate light-emitting diodes 22 formed by crystal growth by the fluidized bed method described above are blown with nitrogen gas or the like in the chamber and allowed to fall naturally on the conductive fixed layer 34, a pixel as shown in FIG. It is randomly distributed on the electrode 32 (FIG. 5A). A solution in which the particulate light emitting diodes 22 are dispersed in a solvent may be prepared, and this solution may be applied to the ridge 33 by a technique such as printing or ink jetting, and the solvent may be volatilized. Thereafter, when heated, the gold nanoparticles in the conductive fixed layer 134 are melted and fused with the second semiconductor (p-type GaN) 21p, which is the outermost layer in the particulate light emitting diode 122, and the pixel electrode 32 and the second semiconductor. 21p is electrically connected.

  FIG. 1 is a plan view of one pixel in a display device manufactured by the above-described process, and a cross-section at a dotted line in the drawing corresponds to FIG. In FIG. 1, a source wiring 31s and a gate wiring 31g connected to the TFT 31 are shown. As can be seen from FIG. 1, the positions of the particulate light emitting diodes 22 are irregular.

  Next, as shown in FIG. 5B, for example, an epoxy-based transparent resin material is spin-coated, and a dielectric layer 35 made of this material is formed. At this time, by dispersing phosphors emitting green and red by blue excitation such as SiAlON in the dielectric layer 35, green and red light emission can be obtained in addition to InGaN blue to realize full color. It is also possible to perform whitening. Alternatively, by using a particulate light emitting diode that emits light of other colors such as green with increased indium composition and red color of GaAlAs, RGB pixels can be painted separately to achieve full color, or high color rendering white It is also possible. The RGB pixels can be separately applied by a method similar to that for manufacturing a liquid crystal color filter. For example, three types of solutions in which particulate light-emitting diodes of each emission color are dispersed in a solvent are prepared and applied to the corresponding pixels by printing, or a transfer method using a dry film carrying the particulate light-emitting diodes. Etc. can also be used.

  The dielectric layer 35 may be formed by applying an inorganic dielectric paste in addition to the resin. For example, a paste in which nanoparticles of titanium oxide or zirconia are dispersed can be applied and dried. In this case, since the refractive indexes of titanium oxide and zirconia are 2.7 and 2.2, respectively, it is close to the refractive index 2.5 of GaN, and dielectrics are formed using resin (refractive index: 1.6 to 1.7). It is considered that the light extraction efficiency is improved even when the body layer 36 is formed.

In FIG. 5C, after the dielectric layer 35 is dried and cured, the resin thinly adhered on the surface of the particulate light emitting diode 22 is removed by an oxygen asher. The surface of the particulate light emitting diode 22 exposed from the dielectric layer 35 is etched until it reaches the first semiconductor (n-type GaN) 21n. Etching may be ordinary dry etching used in GaN-based devices. For example, it can be performed by plasma etching using a gas in which CH ₄ , H ₂ , Ar, and N ₂ are mixed at a ratio of 5: 15: 3: 3.

  Next, when the insulating layer 136 made of, for example, an acrylic resist material is spin-coated at a thickness of 2 microns, the protruding upper part of the particulate light emitting diode 122 becomes thin. When the surface of the insulating layer 136 is shaved by short-time exposure and development and oxygen asher, the second semiconductor 21p is filled with the insulating layer 136, and the first semiconductor 21n is exposed as shown in FIG. Finally, as shown in FIG. 5E, a counter electrode 37 (n electrode) made of, for example, a Ti / Al two-layer electrode (Ti thickness: 20 nm, Al thickness: 200 nm) is formed. The insulating layer 136 insulates the second semiconductor 21p and the counter electrode 37, and prevents current leakage from the counter electrode 37 (n electrode) to the second semiconductor 21p (p layer).

  According to the manufacturing method as described above, a large number of minute particulate light emitting diodes are mounted on a large number of pixel electrodes on a large screen in order to save the trouble of mounting the light emitting diodes one by one as in the past. This also makes it easy to reduce the mounting cost.

  As long as the second semiconductor 21p and the counter electrode 37 are insulated and current leakage from the counter electrode 37 (n electrode) to the second semiconductor 21p (p layer) is prevented, the process of FIG. The step of forming the layer 136 is not necessarily required.

  In this case, the counter electrode 37 is preferably formed in advance on a second substrate (not shown in FIG. 5). That is, the second substrate on which the counter electrode 37 is formed in advance is disposed on the first semiconductor 21n exposed from the dielectric layer 114, and the counter electrode 37 and the first semiconductor 21n are electrically connected. It is preferable to do.

  The control circuit of the display device according to the present invention will be described with reference to FIG.

  The display device according to the present embodiment includes a display unit 90 including a display panel created by the above manufacturing method. Specifically, the display unit 90 has a configuration in which a plurality of pixels shown in FIG. 1 are arranged in rows and columns (matrix). A voltage is applied to the particulate light emitting diode (element indicated by reference numeral “22” in FIG. 1) via the TFT of each pixel, and active matrix driving is executed.

  The driving circuit for display includes a gate driver 91 for supplying a scanning signal to the gate line and a source driver 92 for supplying an image signal to the source line, and the operation is controlled by the control circuit 93. That is, the control circuit 93 reads data including image data from the VRAM 94, supplies the scanning signal, the image signal, and the timing signal to the gate driver 91 and the source driver 92, and causes the display unit 90 to display the image.

  As the image signal, the current-brightness characteristic of the light-emitting device composed of light-emitting diodes is not a linear characteristic, so the halftone expression is a pulse width modulation that makes the drive current constant and changes the pulse width rather than controlling it with the current value. Is preferred. Specifically, subfield driving used in plasma displays may be applied. The total light emission time may be controlled by dividing each frame of 60 Hz into subframes having different lengths and controlling lighting and non-lighting in each subframe by turning on and off the TFTs. Of course, if the uniformity of the panel is improved and the controllability of the current-luminance characteristics is improved, the current value and the pulse width modulation may be combined.

(Embodiment 2)
Next, a second manufacturing method of the display device of the present invention will be described with reference to FIGS. FIG. 6 is a process diagram of the second manufacturing method of the display device of the present invention, and FIG. 7 is a plan view of the simple matrix type display device of the present invention corresponding to FIG.

  The second manufacturing method of the display device of the present invention includes the following steps (B1) to (E1).

  In the step (B1), the particulate light emitting diodes 22 are randomly dispersed in the dielectric layer 114 of the dummy substrate 113 having the dielectric layer provided on the surface, and a plurality of the particulate light emitting diodes 22 are disposed in the dielectric layer 114. This is a process of filling a part of (FIG. 6A).

  Step (B2) is a step of etching the surface of each particulate light-emitting diode that is not covered with the dielectric layer to expose the first semiconductor (FIG. 6B).

  Step (C1) is a step (FIG. 6C) for forming the insulating layer 115 filling the second semiconductor 21 p on the dielectric layer 114. In addition, although mentioned later, this process (C1) is not necessarily required.

  Step (C2) is a step of providing the pixel electrode 116 on the exposed first semiconductor 21n and electrically connecting the pixel electrode 116 and the first semiconductor 21n (FIG. 6D).

  Step (D1) is a step of attaching the substrate 118 to the surface of the dummy substrate 113 on the side of the dielectric layer 114 (FIG. 6E).

  Step (D2) is a peeling step for peeling the dummy substrate 113 from the dielectric layer 114 (FIG. 6F).

  In the step (E1), the counter electrode 119 is formed on the second semiconductor 21p of the particulate light emitting diode 22 on the surface side exposed by the peeling, and the counter electrode 119 and the second semiconductor 21p are electrically connected. (FIG. 6 (g)).

  Prior to the above steps, the particulate light emitting diode 22 is prepared, and the method of making the same may be the same as the manufacturing method of the first embodiment.

  The dummy substrate 113 in the step (B1) is preferably a film material that can be easily peeled off, such as PET or polyimide, and on which the dielectric layer 114 can be applied. For the dielectric layer 114, for example, a transparent epoxy resin or silicone resin used for sealing a light emitting diode can be used. If the light emitting diode 22 is sprayed before applying and drying a solution such as an epoxy resin, a part of the particulate light emitting diode 22 is embedded in the dielectric layer 114 as shown in FIG. The particulate light emitting diode 22 may be mixed in an epoxy resin solution dissolved in a solvent, applied onto the dummy substrate 113, and dried. At this time, the dielectric layer 114 has a film thickness corresponding to the solid content concentration, and if the thin film on the particulate light emitting diode 22 is removed by oxygen asher or the like, a part of the particulate light emitting diode 22 becomes the dielectric layer 114. Can be buried. In the step (B2), as in the first embodiment, the first semiconductor 21n is exposed by etching (FIG. 6B).

  Further, in step (C1) of FIG. 6C, a highly insulating resin material is applied by spin coating or the like to form the insulating layer 115 filling the second semiconductor 21p. When the thin film on the particulate light emitting diode is removed with an oxygen asher or the like, only the first semiconductor 21n is exposed.

  In the next step (C2), as shown in FIG. 6 (d), the pixel electrode 116 is directly formed by sputtering or vapor deposition, and patterned by ordinary fine processing, and the stripe-shaped column electrode as shown in FIG. To do. The material of the pixel electrode is preferably a metal that is in ohmic contact with the first semiconductor 21n. Ti, Al, Ag, Hf, or the like can be used, and a two-layer electrode such as Ti / Al may be used. Next, in step (D1) of FIG. 6E, the substrate 118 is bonded to the dummy substrate side with the adhesive layer 117 on the pixel electrode 116. As the substrate 118, glass, resin film, plate-like plastic, metal film coated with an insulating layer, or the like can be used. Lightweight general-purpose plastic can be used. In order to facilitate mounting with the driving circuit, the extraction electrode 120 may be formed on the end of the substrate 118 and may be electrically connected to the pixel electrode 116 with a conductive paste or the like.

  As a method different from that shown in FIG. 6D, the substrate on which the pixel electrode 116 is formed may be bonded using a conductive adhesive layer 117. In this case, the conductive adhesive layer 117 is sandwiched between the pixel electrode 116, the particulate light emitting diode 21n, and the insulating layer 115. As the conductive adhesive layer 117, a solvent-free silver paste or the like can be used.

  In this case, as long as the second semiconductor 21p and the counter electrode 37 are insulated and current leakage from the pixel electrode 116 (n electrode) to the second semiconductor 21p (p layer) is prevented, the process of FIG. That is, the step (C1) for forming the insulating layer 116 is not necessarily required.

  In the step (D2) of FIG. 6F, the dummy substrate 113 is carefully peeled off from the end to expose the second semiconductor 21p on the peeling surface side. At this time, in order to clean the surface of the second semiconductor 21p, it is preferable to slightly remove the surface of the dielectric layer 114 on the peeling surface side with an oxygen asher or the like. In the step (E1), the counter electrode 119 is formed by sputtering, vapor deposition, or the like (FIG. 6G).

  Then, as shown in FIG. 7, by processing the counter electrode 119 so as to be a row electrode orthogonal to the pixel electrode 116, a simple matrix panel in which the pixel electrode 116 and the counter electrode 119 intersect is completed.

  The counter electrode 119 is preferably a metal that is in ohmic contact with the second semiconductor 21p. For example, ITO or Ni / Au can be used. Since either the pixel electrode 116 or the counter electrode 119 must be transparent or translucent, it is preferable to use ITO or make the metal electrode thin.

  In order to ensure long-term reliability, it is preferable to apply the sealing layer 121 on the counter electrode 119 (p electrode) with a silicone resin or the like. A column driver 122 and a row driver 123 are connected to these electrodes as shown in FIG. 7, a pulse voltage is applied between the pixel electrode (column electrode) 116 and the counter electrode (row electrode) 119, and line sequential scanning is performed. When driven, an image display can be obtained.

  Although the plan view of FIG. 7 depicts a panel of 3 rows and 2 columns for simplicity, high luminance light emission can be obtained from a large number of particulate light emitting diodes. Fine display is possible.

  In this embodiment, a simple matrix display device is illustrated, but when a substrate provided with TFTs is used as the substrate 118, an active matrix display device can be similarly formed. In this embodiment, the pixel electrode 116 or the counter electrode 119 may be electrically connected to the first semiconductor 21n.

(Example)
First, as a core particle, an alumina fine particle Sumicorundum (registered trademark) powder of about 3 μm was obtained from Sumitomo Chemical Co., Ltd. These alumina fine particles are fine particles used for fillers made by gas phase chemical reaction and are single crystal fine particles with good dispersibility. If this is spread on a 2 inch wafer at a market price of 5500 yen / kg, , Equivalent to 0.13 yen / sheet, which is a low cost of tens of thousands of sapphire wafers. It can be said that such a large price difference is derived from a physical and industrial reason that a crystal having a larger diameter takes longer to grow. FIG. 10 is a SEM (scanning electron microscope) photograph of the core particle 1, which is a polyhedral shape with rounded corners and is substantially spherical.

  First, the core particle powder was immersed in phosphoric acid for 1 minute and rinsed repeatedly with pure water, and then the powder was taken out by centrifugation and dried in a vacuum dryer. It was confirmed by SEM that the shape of the core particles in FIG. 1 was maintained by this washing.

  Next, gallium nitride (GaN) was grown on the surface of the particles by the procedure described in the first embodiment.

  AlGaN having a thickness of about 25 nm was formed at 510 ° C. in the buffer layer on the core particle. Next, the temperature was raised to 1050 ° C. to form a Si-doped n-type GaN layer. Crystals having different sizes and shapes were prepared by changing the conditions of the dope concentration and the film thickness.

Next, the furnace temperature was lowered to 790 ° C., the carrier gas was changed to nitrogen, and an undoped GaN layer of 7 nm and an In _0.15 Ga _0.85 N layer of 3 nm were alternately stacked to form an active layer made of MQW. The carrier gas was returned to hydrogen again at 1100 ° C., and Mg-doped p-type GaN was grown to 400 nm. Since the film thickness and the indium concentration differ depending on the plane orientation, conditions such as the film formation time and the gas composition were set based on the numerical values on the C plane obtained in a prior experiment.

  At this time, the obtained semiconductor crystals were particles having different crystal shapes depending on reaction conditions (time, gas flow rate, dope concentration, etc.) and variations. In order to investigate the relationship between the shape and the emission characteristics, crystal grains grown to the InGaN MWQ layer (active layer) before attaching the p layer (second semiconductor) were taken out, and the emission characteristics by SEM observation and CL were observed. .

  FIG. 11 is an example of an SEM photograph of a large number of crystal grains grown up to the MQW layer, and a large number of crystals having different sizes and shapes can be seen.

  Of such crystal particles, SEM photographs of crystal particles having greatly different shapes are shown in FIGS.

  The particle 2 in FIG. 12 is a crystal having a typical shape. FIG. 12A is a photograph seen from above, and FIG. 12B is a photograph seen obliquely. Although the length of the white arrow 10 in FIG. 12A indicates 10 microns, it can be seen that the particles are trapezoidal polyhedrons having a diameter of 20 microns on the short axis and about 40 microns on the long axis. When the plane orientation was examined by EBSD (electron beam backscatter diffraction) or the like, the hexagonal plane 3 was the C plane {0001}, the side planes 4 to 7 were the m plane {1-100} perpendicular to the C plane, 8 and 9, which were surfaces inclined by 62 degrees, were {1-101}. As described above, all the planes were flat crystal lattice planes having an Miller index absolute value of 1 or less, and single crystal polyhedral crystals having a shape completely different (unsimilar) from the core particles were formed.

On the other hand, FIG. 13 shows a GaN crystal particle close to a spherical shape with a substantially uniform thin film on the core particle, as in Patent Document 1, and is a comparative example.

The particle 11 in FIG. 13 has a diameter close to that of the core particle 1 in FIG. However, it was confirmed by X-ray microanalysis that the particles 11 had an InGaN film.

FIG. 14 and FIG. 15 show emission characteristics obtained by irradiating the particles of FIGS. 12 and 13 with an electron beam having the same current density and measuring CL emission. The horizontal axis represents wavelength and the vertical axis represents emission intensity.

  In FIG. 14A, the emission characteristics corresponding to each of the CL plane 3, plane 4 and plane 8 of the particle of FIG. 3 are indicated by a solid line 200, a broken line 201, and a dotted line 202. Also shown in FIGS. 14 (b), 14 (c), and 14 (d). The solid line 200 has three peaks. The peak at a wavelength of less than 370 nm is the band edge emission peak of the underlying GaN, the peak near 420 nm is the emission peak of InGaN in the active layer, and the peak of less than 560 nm is the yellow band. It is a peak derived from a crystal defect or the like.

  The InGaN emission peak wavelengths of the solid line 200, the broken line 201, and the dotted line 202 are 420 nm, 390 nm, and 415 nm, respectively, and the intensities are the broken line 201 (plane 4 or m plane), the dotted line 202 (plane 8), and the solid line 200 (plane 3 pass). The C-plane) in the order of 45000 to 90000.

  On the other hand, in the solid line 203 in FIG. 15 showing the light emission of the spherical particles in FIG. 13 as a comparative example, the emission peak of InGaN is at 405 nm, the intensity value is about 7000, which is about 1/10 of the light emission characteristics of FIG. There was only strength.

  As a flat polyhedral crystal that emits light with high brightness, in addition to FIG. 12, particles having a shape close to a hexagonal pyramid, such as crystal 230 in FIG. 16, and crystals such as hexagonal columns, such as 232 and 233 in FIG. I was also able to create. The particles 230 in FIG. 16 were hexagonal pyramid-shaped single crystals, and the hexagonal bottom surface 230a was a C-plane, the side surface 230b was an m-plane, and the slope 230c was a (1-101) plane. The particles 232 and 233 in FIG. 17 were hexagonal columnar single crystals, and the side surfaces of the hexagonal column were the m-plane and the bottom surface was the C-plane.

  The difference in emission intensity between the polyhedral particles of FIGS. 12, 16, and 17 and the spherical particles of FIG. 13 shows not only the CL emission but also the PL emission excited by a He-Cd laser (wavelength 325 nm). It was. The PL efficiency of the polyhedral particles was higher than that of the blue light-emitting diode film formed on the wafer, and high luminous efficiency was obtained. In particular, the hexagonal columnar crystal as shown in FIG. 17 has a PL intensity more than twice that of the trapezoidal or amorphous crystal as shown in FIG. As can be seen from FIG. 17, the vertically long hexagonal columnar crystal whose side surface is longer than the bottom surface falls on the substrate when it falls on the m surface, so that the excitation light hits the m surface and the m surface shines. It will be. As shown by the results of CL measurement, the m-plane shows stronger light emission than the C-plane, and this corresponds to the fact that hexagonal columnar crystals with long side faces are the best efficiently. If a particulate light emitting diode in which p-GaN is formed on the MQW layer of these polyhedral particles is formed, the spherical crystal as shown in FIG. The low index plane polyhedral crystal of FIG. 17 shows stronger EL emission.

  From such experimental results, the present invention can produce a high-quality crystal by growing it into a crystal that forms a polyhedron whose main constituent surface is not a spherical particle, but a flat crystal lattice plane, It was clarified that high-efficiency light emission is possible.

In addition, it was confirmed by cross-sectional SEM and TEM observation that alumina as core particles was contained inside these crystals. According to the cross-sectional observation, the crystal grown around the core particle has a large number of fine grains in the range of about 1 micron from the surface of the core particle, but the outside thereof is a very large single or several single particles. It was a high quality film that was covered with crystals and had few dislocation defects. For example, it has been observed by TEM that there are only one or two dislocation defects in the crystals of FIG. 12 and FIG. 17, and it is about 10 ⁶ / cm ² or less in terms of dislocation density. That is, it can be said that if crystal growth is performed on the surface of the core particle with a film thickness of 1 micron or more, good quality crystal particles with very few defects can be obtained on the surface on which the active layer is formed.

Conventional, GaN on a sapphire wafer is extremely high dislocation density defect is generated from the substrate surface, the dislocations will extend in a direction perpendicular to the substrate, 10 ^{to 10} even if the film thickness to a thickness of several microns / cm There are about ^two . There is a large difference in crystal growth between crystal growth on a planar substrate such as a wafer and crystal growth on micron-sized alumina particles as in this embodiment. Therefore, if the size of the core particle is increased, for example, when crystal growth is performed on alumina particles having a large mm size, the surface is closer to the plane when viewed microscopically, and the aspect of crystal growth is closer to that on the wafer. It is done.

  A number of such particulate light emitting diodes made of a polyhedral crystalline semiconductor having a flat crystal lattice plane on the outer peripheral surface are mounted and light-emitted by the method shown in the process cross-sectional view of FIG. 6 of the second embodiment. It was. However, since the size of the particulate light emitting diodes produced in the fluidized bed varies, the sizes are aligned in advance by a classification method such as a sedimentation method so that the variation is several microns or less.

  The substrate was coated with a silicone resin for sealing a light emitting diode manufactured by Shin-Etsu Chemical Co., Ltd. on a dummy substrate 113 made of a PET film having a thickness of 0.1 mm, and a dielectric layer (thickness 3 μm) made of an epoxy resin was applied. Formed.

  Next, the blown nitrogen gas is blown onto the dish on which the powder of the particulate light emitting diode 22 is placed in the spraying chamber, whereby the soared particulate light emitting diode 22 is dropped onto the dummy substrate 113, and the particulate light emission is performed. After the diode 22 is dispersed on the dielectric layer with good dispersibility, it is lightly pressed with a glass plate, embedded in the silicone resin layer, and heated at 150 ° C. to cure the dielectric layer 114. The bottom half was fixed in a buried state.

  Next, the surface of the particulate light emitting diode 22 exposed from the dielectric layer 114 was etched by a dry etching apparatus using the gas species described in the embodiment until it reached the n-type GaN layer 21n.

  Then, an insulating layer 115 of a positive acrylic resist resin that is substantially transparent to visible light is spin-coated under a condition of a film thickness of 2 microns and dried. In this state, since the resist is thinly placed on the particulate light emitting diode 22, the surface of the particulate light emitting diode 22 is in the insulating layer 115 when underexposure with an exposure time of 1/5 of the normal condition is performed. It was confirmed with a microscope that it was exposed from After cleaning the surface of the particulate light emitting diode 22 with an oxygen asher, an n-electrode of Ti / Al (Ti thickness: 20 nm, Al thickness: 200 nm) was formed by sputtering and further patterned in a stripe shape.

  Next, as shown in FIG. 6 (e), a polyimide resin substrate 118 having a thickness of 0.1 mm coated with an adhesive layer 116 made of an adhesive resin was adhered to the dielectric layer 114. At this time, the extraction electrode 120 and the pixel electrode 116 (n electrode) formed on the edge of the polyimide substrate were made conductive with a conductive paste. After increasing the adhesive strength of the adhesive layer by heating, the dummy substrate 113 was peeled off.

  After the dielectric layer 114 was etched with oxygen plasma until the surface of the particulate light emitting diode 22 was exposed, a counter electrode 119 (p electrode) made of Ni / ITO (10 nm / 100 nm) was deposited by sputtering and patterned. Thus, the structure shown in FIG. 7 can be obtained. When the terminal of the DC power source is brought into contact with the extraction electrode 120 and the counter electrode 119 (p electrode), the particulate light emitting diode 112 emits light.

  The counter electrode 119 (p electrode) can be formed by applying a metal paste such as gold, but the vacuum film formation such as vapor deposition or sputtering has a higher contact resistance of the counter electrode 119 (p electrode). It becomes easy to lower.

  Through the steps as described above, the second semiconductor 21p (p layer), which is a constituent surface of the polyhedron of the semiconductor crystal, is used as the counter electrode 119 (p electrode), and the first semiconductor (n layer) is used as the pixel electrode 116 (n ), And by applying a voltage to the counter electrode 119 (p electrode) and the pixel electrode 116 (n electrode), a rectifying property such as the characteristic curve 240 of the current-voltage characteristic diagram of FIG. 18 is obtained. Light blue-violet light was emitted when forward voltage was applied.

The threshold voltage was less than 4 volts, and light was emitted with high luminance exceeding 10,000 cd / m ² at an applied voltage of about 7 volts. The scattering density of the particulate light emitting diodes 22 is about 100 / mm 2, and light emission occurs at an area ratio of about 10%, and the luminance at the light emitting point is converted to exceed 100,000 cd / m ² . The voltage is slightly higher than that of a commercially available InGaN-light emitting diode, but this can be improved by optimization such as reduction of the electrode contact resistance. Although the polarity of the particulate light-emitting diode 22 may be reversed inside and outside, it is preferable that the second semiconductor (p layer) is placed outside in order to facilitate activation by annealing of p-GaN.

  As described above, the light emitting device according to the present invention has a large number of particulate light emitting diodes mounted on the substrate in a lump, thereby drastically reducing the mounting cost and the substrate cost. In this case, the crystalline semiconductor constituting the particulate light-emitting diode has a polyhedral shape whose outer peripheral surface is composed of a plurality of flat crystal lattice planes. Thus, a light emitting device with high luminance and high efficiency can be realized. Further, by using low-cost single crystal fine particles as core particles, the wafer cost can be drastically reduced, and the cost can be further reduced.

  According to the light emitting device of this embodiment, a large number of light emitting diode elements (particulate light emitting diodes 22) can be manufactured at low cost and can be easily mounted on a large-area substrate. As a result, high-efficiency, low-cost, highly uniform display devices and lighting devices can be mass-produced. Further, the temperature required for mounting the particulate light emitting diode is low, and it is possible to realize a thin and light large screen display such as a flexible sheet display using a plastic substrate in addition to glass. Since the particulate light-emitting diode used in the present embodiment is made of an inorganic material, it is highly reliable and does not require advanced moisture-proof treatment. Further, since it is resistant to heat, a very high luminance can be obtained, and TFTs are not always essential, and the cost can be reduced by simple matrix driving.

The lower limit of the size of the particulate light-emitting diode 22 can be defined by the film thickness at which a high-quality crystal is obtained, but is also determined according to the process accuracy (about 0.1 μm) such as coating and etching of the dielectric layer. obtain. If the particulate light emitting diode is not sufficiently larger than the process accuracy, it is difficult to ensure a stable connection with the electrode. For example, the insulating layer insulates the first semiconductor and the second semiconductor, and considering the pressure resistance of the resin, a thickness of 1 micron is necessary, and the particle-shaped light emitting diode preferably has a diameter several times or more, It is desirable to be about 3 microns or more.

Example 3
Light emitting diodes tend to vary in characteristics, and even commercially available blue diodes that are mass-produced have not been resolved, and are sold in different ranks. Even when the display device of the present invention is mass-produced, it is assumed that the same variation remains in the characteristics of the individual particulate light emitting diodes. Therefore, how many particulate light emitting diodes should be caused to emit light in one pixel was determined by simulation as follows.

FIG. 8 is a characteristic graph showing the result of the simulation. The solid line 30 in the graph is
An emission spectrum of a blue light-emitting diode having a peak wavelength λi of In _0.22 Ga _0.78 N of 467 nm is shown. Both the alternate long and short dash line 141 and the dotted line 142 indicate the emission spectrum in which the peak wavelength λi is shifted from 467 nm without changing the shape of the emission spectrum. The color difference ΔE ^* ab when the emission spectrum was shifted was determined. The color difference is a quantity that quantitatively represents a difference between two colors, and is represented by a distance between two points in the uniform color space. However, since the data of the visibility coefficient that is the basis for obtaining L ^* a ^* b ^* is obtained only in increments of 0.5 nm, the steps smaller than 0.5 nm are interpolated by interpolation.

The color difference ΔE ^* ab expressed by the following equation 1 is an index that quantifies the color difference perceived by humans in the CIE1976L ^* a ^* b ^* color system used in printed materials.

ΔE ^* ab = [(ΔL ^* ) 2+ (Δa ^* ) 2+ (Δb ^* ) 2] 1/2 (Expression 1)

This number 1 is widely used as a standard for color matching of printed matter as the most standard color difference formula. According to the printing ink handbook, a color difference of 1.2 or less is regarded as a practical tolerance for side-by-side comparison. If the color difference is 1.2 or less, the difference in color between adjacent pixels is not noticed or allowed. When this reference is applied to the emission color of the light emitting diode and ΔE ^* ab is calculated, if the peak wavelength λi is shifted by about 0.5 nm with respect to the standard emission spectrum shown by the solid line 140 in FIG. 8, ΔE ^* ab Becomes 1.2. It can be seen that the current blue light emitting diode has a peak wavelength λi variation of about 5 nm, which far exceeds the allowable color difference. Therefore, in order to make the dispersion of peak wavelengths uniform among individual light emitting diodes, it is necessary to arrange a large number of particulate light emitting diodes in each pixel. However, increasing the number of particulate light emitting diodes increases costs and requires an increase in pixel size, so it is extremely important to determine an appropriate number.

Assuming that the emission wavelength distribution of the population of the particulate light emitting diodes follows a normal distribution, the standard deviation of the emission peak wavelength is σ nm, and the number of the particulate light emitting diodes scattered in the pixel is n. When the average value of these n particulate light emitting diodes (samples from the population) is Xa and the average value of the population is μ, the average value Xa is in the range of μ−cσ / n ^0.5 or more and μ + cσ / n ^0.5 or less. The probability of entering is 95% when c = 2, and 99% when c = 2.58.

It can be used as a standard of uniformity that the shift amount of the peak wavelength λi is included with a probability of 95% within a range of ± 0.5 nm corresponding to the allowable color difference. From this, the number n may be (cσ / 0.5 nm) ² or more. As a measure of uniformity, assuming a 95% probability, c = 2 and n ≧ 16σ ² . If the variation (± 2σ) of the blue light emitting diode is 5 nm, σ is 1.25 nm. Substituting for n ≧ 16σ ² results in n ≧ 25.

  Therefore, if the number of the particulate light emitting diodes of about 25 is dispersed in one pixel, the color variation can be suppressed to an inconspicuous level.

  The display device of the present invention has advantages such as high light emission efficiency, low voltage, and high durability that an inorganic light emitting diode such as gallium nitride has, and is thin and easy to enlarge. For this reason, it is used as a display device for a home-use large-screen wall-mounted television, a low power consumption, ultra-lightweight mobile display, and can be used for a traffic light.

The technical ideas derived from the above disclosure are as follows:
A display device having a plurality of pixels formed in a matrix,
The display device includes a substrate (30), a plurality of pixel electrodes (32), and a counter electrode (37).
Each pixel includes one pixel electrode (32), a portion of the counter electrode (37) overlapping the one pixel electrode in plan view, and a plurality of particulate light emitting diodes (22).
The plurality of particulate light emitting diodes (22) are randomly distributed on the one pixel electrode (32),
The plurality of particulate light emitting diodes (22) are sandwiched between the pixel electrode (32) and the counter electrode (37),
Each of the plurality of particulate light emitting diodes (22) is made of a crystalline semiconductor made of a group III-V nitride,
Each of the plurality of particulate light emitting diodes (22) includes a first conductive type first semiconductor (21n), an active layer (21i), and a second conductive type second semiconductor (21p),
The active layer (21i) is formed on a part of the periphery of the first semiconductor (21n),
The second semiconductor (21p) covers the periphery of the active layer (21i),
The first semiconductor (21n) is electrically connected to either the pixel electrode (32) or the counter electrode (37),
The second semiconductor is electrically connected to either the pixel electrode (32) or the counter electrode (37),
The display device, wherein the crystalline semiconductor is a polyhedron having an outer peripheral surface composed of a plurality of flat crystal lattice planes.

  In the case of active matrix driving (FIG. 1), there is generally one counter electrode. In the case of passive matrix driving (FIG. 7), there are generally a plurality of counter electrodes. In this case, each counter electrode has a strip shape.

The top view which expanded the pixel of the display apparatus of Embodiment 1 of this invention. Sectional drawing which expanded the pixel of the display apparatus of Embodiment 1 of this invention. The block diagram showing the manufacturing apparatus of the particulate light emitting diode of embodiment of this invention Sectional drawing of the particulate light emitting diode of Embodiment 1 of this invention FIGS. 4A to 4E are process cross-sectional views illustrating a method for manufacturing a display device according to a first embodiment of the invention. FIGS. 4A to 4G are process cross-sectional views illustrating a method for manufacturing a display device according to a second embodiment of the invention. The top view of the display apparatus of Embodiment 2 of this invention Emission spectrum graph of display device of the present invention Block diagram of display device of the present invention (A), (b) are electron micrographs of core particles in examples of the present invention. Photomicrograph of crystalline semiconductor of Example of the present invention (A), (b) is the electron micrograph of the crystalline semiconductor of the Example of this invention. Electron micrograph of a particulate semiconductor showing a comparative example of the example of the present invention (A) to (d) are emission spectrum graphs of crystalline semiconductors of examples of the present invention. Emission spectrum graph of particulate semiconductor crystal of comparative example of embodiment of the present invention The top view which shows the electron microscope image of the crystalline semiconductor in the Example of this invention The top view which shows the electron microscope image of the crystalline semiconductor in the Example of this invention The graph showing the voltage-current characteristic of the display apparatus of the Example of this invention Sectional drawing of the light emitting element and display apparatus of a prior art example Sectional drawing of the light emitting particle | grains of the light emitting element and display apparatus of a prior art example

Explanation of symbols

21n ... first semiconductor 21i ... active layer 21p ... second semiconductor 22 ... particulate light emitting diode 30 ... substrate 31 ... TFT
32 ... Pixel electrode 35 ... Dielectric layer 36 ... Insulating layer 37 ... Counter electrode 67 ... Core particle 113 ... Dummy substrate 114 ... Dielectric layer 115 ... Insulating layer 116... Pixel electrode (n electrode)
117: Adhesive layer 118: Substrate 119: Counter electrode (p electrode)
201-202 ... emission characteristics of polyhedral crystal grains 203 ... emission characteristics of spherical crystal grains 240 ... characteristic curves

Claims (14)

A substrate,
A plurality of pixel electrodes provided on the substrate;
A plurality of particulate light emitting diodes randomly distributed on each of the plurality of pixel electrodes;
A counter electrode covering the plurality of particulate light emitting diodes;
With
Each of the plurality of particulate light emitting diodes is made of a crystalline semiconductor made of a group III-V nitride,
Each of the plurality of particulate light emitting diodes includes a first conductivity type first semiconductor, an active layer, and a second conductivity type second semiconductor,
The active layer is formed in a part of the periphery of the first semiconductor;
The second semiconductor covers the periphery of the active layer;
The first semiconductor is electrically connected to either the pixel electrode or the counter electrode,
The second semiconductor is electrically connected to the other of the pixel electrode and the counter electrode,
The display device, wherein the crystalline semiconductor has a polyhedral shape whose outer peripheral surface is composed of a plurality of flat crystal lattice planes.   The display device according to claim 1, wherein the crystalline semiconductor has two or more kinds of crystal lattice planes of Miller indices {0001}, {1-100}, and {1-101}. The crystalline semiconductor has a {1-100} plane;
The display device according to claim 1, wherein the {1-100} plane is electrically connected to the pixel electrode.   The display device according to claim 3, wherein the crystalline semiconductor has a hexagonal column shape, and a side surface of the hexagonal column is a {1-100} plane.   2. The display device according to claim 1, wherein the crystalline semiconductor is a polyhedral shaped particle in which a crystal having a thickness of 1 μm or more is grown on a surface of a single crystal core particle.   The display device according to claim 5, wherein the core particle is made of at least one material selected from the group consisting of gallium nitride, aluminum nitride, silicon carbide, aluminum oxide, zinc oxide, and beta gallium oxide.   The display device according to claim 6, wherein a shape of the core particle is a substantially spherical or rounded polyhedral aluminum oxide. Having a dielectric layer on the pixel electrode;
A part or all of the second semiconductor is embedded in the dielectric layer;
The display device according to claim 1, wherein a part of the first semiconductor protrudes from the dielectric layer and is electrically connected to the counter electrode.   The display device according to claim 8, wherein the dielectric layer further includes a phosphor. The substrate is formed of plastic;
The display device according to claim 1, further comprising an adhesive layer between the substrate and the pixel electrode. ^2. The display device according to claim 1, wherein when the standard deviation of the peak emission wavelength of the particulate light emitting diode is σ nm, the number n of the particulate light emitting diodes positioned on each pixel electrode is larger than 16σ ² .   The display device according to claim 1, wherein the particulate light emitting diode on each pixel electrode is driven by a transistor formed on each pixel electrode. A manufacturing method of a display device according to claim 1,
The manufacturing method includes:
A step (A) of randomly dispersing the plurality of particulate light emitting diodes on each of the plurality of pixel electrodes;
(B) filling a part of the plurality of particulate light emitting diodes in the dielectric layer by forming a dielectric layer on each of the plurality of pixel electrodes dispersed with the plurality of particulate light emitting diodes; ,
Etching the surface of each particulate light emitting diode not covered with the dielectric layer to expose a part of the first semiconductor, and forming a counter electrode on the exposed first semiconductor Step (D) to perform,
A method for manufacturing a display device, comprising: A manufacturing method of a display device according to claim 1,
A step of randomly dispersing the particulate light emitting diodes in the dielectric layer of the dummy substrate having a dielectric layer provided on a surface thereof, and burying a part of the plurality of particulate light emitting diodes in the dielectric layer ( B1),
Etching the surface of each particulate light emitting diode not covered with the dielectric layer to expose the first semiconductor (B2);
Providing either one of a pixel electrode and a counter electrode on the exposed first semiconductor, and electrically connecting the one electrode and the first semiconductor (C2);
A step (D1) of attaching a substrate to the surface on the dielectric layer side of the dummy substrate;
A peeling step (D2) for peeling the dummy substrate from the dielectric layer; and the other electrode of the pixel electrode and the counter electrode is provided on the second semiconductor of the particulate light emitting diode on the surface side exposed by the peeling, Electrically connecting the electrode and the second semiconductor (E1)
A method for manufacturing a display device, comprising:

Images