The present invention relates to solid state light-emissive display apparatus utilizing a quantum size effect and method of manufacturing the same.
The display apparatuses using liquid crystals are lately in wide spread use, but these are not the best in such properties as energy-saving or brightness, since a liquid crystal display apparatus uses backlight in principle. For this reason, the research and development are widely proceeding for a solid state light-emissive display apparatus, aiming to realize high brightness, energy-saving, flat type, and high reliability rather more than liquid crystal.
As an existing solid state light-emissive display apparatus, there is EL(Electro Luminescence) display apparatus. EL display apparatus is composed of pixels each of which has a semiconductor layer including light emission center atoms and insulator layers sandwiching said semiconductor layer. As a light emission center atom, such elements that emit visible fluorescence, for example, Mn or rare earth elements are used, and as a semiconductor layer, such semiconductors that have larger band gap energy than visible light, for example, ZnS or else are used, and as insulator layers, such insulators that have a property which prevents dielectric breakdown of said semiconductor layers, for example, thin films of SiO2 or Si3N4 are used.
EL display apparatus emits light as following, electrons in a semiconductor are accelerated by high electric field imposed through insulation layers, the accelerated electrons collide to light emission center atoms to be excited, and the excited light emission center atoms emit fluorescence light. Therefore it is the specific feature of EL display apparatus that electric energy directly converts to light energy.
However, there are problems such that light emission efficiency is low and dielectric breakdown tends to occur, because considerably high electric field (106 V/cm or higher) is necessary to accelerate the electrons to such a high energy state (hot electron state) to emit EL light against the energy dispersion by phonon scattering. There are also such EL display apparatuses using organic materials as the semiconductor layer, but they also have problems such that emission efficiency easily becomes lower as organic materials are unstable and readily deteriorate.
There are also FED (Field Emission Device) display apparatuses as the display apparatuses to generate fluorescence by colliding and exciting light emission center atoms by accelerated electron (ballistic electron). However, an FED display apparatus has its problems such that, though it can emit light at relatively low electric field, it requires vacuum space and hence it can not be made to a flat and all-solid state type, since it emits out electrons into vacuum by using a field-emission type electron gun and accelerates them in vacuum.
Taking into consideration the afore-mentioned problems, the object of the present invention is to provide a solid state light-emissive display apparatus which has much superior properties to existing display apparatuses in brightness, efficiency, reliability, and a thin type. And also the other object of the present invention is to provide a method of manufacturing the said apparatus, which manufactures it at low cost.
In order to achieve the object mentioned above, there is provided a solid state light-emissive display apparatus according to the present invention, characterized in that it has light emitting pixels comprising of a luminous thin film composed of crystal fine particles of nm(nanometer) size coated with insulator and fluorescent fine particles of nm size in a form of laminating of two said each particle layers or in a form of mixed layer of said two particles, and a lower electrode and a transparent upper electrode sandwiching said luminous thin film, whereby to obtain luminous display by impressing alternating voltage or direct current voltage between said upper and lower electrodes.
In the solid state light-emissive display apparatus according to the present invention, said crystal fine particle of nm size coated with insulator is characterized in that it consists of a semiconductor or a metal single crystal fine particle of nm size and insulator film of nm thickness coating the surface of said single crystal fine particle.
In the solid state light-emissive display apparatus according to the present invention, said crystal fine particle of nm is preferably an intrinsic or impurity doped Si single crystal fine particle of nm size, and said insulator film is a SiO2 film of nm thickness coating the surface of said Si single crystal fine particle.
Also preferably, said fluorescent fine particle of nm size is a semiconductor fine particle having a band gap energy corresponding to an energy ranging from ultraviolet light to visible light. Said fluorescent fine particle of nm size may have a donor or/and an acceptor. Also said fluorescent fine particle of nm size may be a semiconductor fine particle involving luminous atoms or luminous atom ions.
According to the above mentioned makeup, the voltage impressed between the lower and the upper electrodes is distributed to the insulator films coating the crystal fine particles of nm size in the luminous thin film, the electrons injected from the lower electrode are accelerated by the electric field distributed to the insulator film, pass through said insulator film by tunneling or resonant tunneling, and pass through the single crystal fine particle of nm size without being scattered by phonons (Refer to JP 2001-332168, for example). The electrons repeat the above mentioned process for each adjacent crystal fine particle of nm size coated with insulator as a result to obtain high kinetic energy, and collide with the fluorescent fine particles of nm size. If the kinetic energy of the colliding electron is higher than the band gap energy of the fluorescent fine particle, a free electron and a hole are generated in the fluorescent fine particle, and a free exciton is generated from these free electron and hole.
Since the fluorescent fine particle is of nm size, said electron and hole are enclosed in space of nm size, the concentration of said free exciton is raised, and hence the luminous intensity by extinction of said free excitons is increased.
Also, in case that the fluorescent fine particle has a donor or/and an acceptor, the generated electron and hole form a bound exciton via a donor or/and an acceptor. Since the fluorescent fine particle is of nm size, the electron and the hole are enclosed in space of nm size, hence the concentration of bound exciton is raised, and the luminous intensity by extinction of said bound excitons is increased.
Also, in the case of fluorescent fine particle including luminous atoms or luminous atom ions, since the electrons having high kinetic energy are generated in large quantity by crystal fine particles coated with insulator, luminous atoms or luminous atom ions in fluorescent fine particles are excited in large quantity, and luminous intensity is increased.
Thus, according to the present invention, since electrons can be accelerated without energy loss and exciton concentration can be high, the luminous efficiency and brightness are high. Also, since the luminous thin film is thin and can emit light by itself, the apparatus of this invention can be made extremely thin. Also, since the applied voltage is low, reliability is high.
And, the solid state light-emissive display apparatus according to the present invention is characterized in that the upper and the lower electrodes are configurated in a form of matrix configuration, and the intersected region of the upper and the lower electrode is used as a light emitting pixel by simple matrix driven with these electrodes.
According to the makeup mentioned above, an image display apparatus of high efficiency, high brightness, thin type, and high reliability can be provided.
Further, the solid state light-emissive display apparatus of the present invention is characterized in that wirings for scanning and wirings for signals are provided in a form of matrix electrode configuration, a thin film transistor is provided at each intersection of said scanning and signal wirings, the gate electrode of said thin film transistor is connected to scanning wiring, the drain electrode of said thin film transistor is connected to signal wiring, the source electrode of said thin film transistor is connected to an electrode of a light emitting pixel, a luminous thin film is sandwiched by said electrode and upper electrode of said light emitting pixel, wherein each light emitting pixel can be actively driven by said each thin film transistor selected by said scanning and signal wirings.
According to the makeup mentioned above, since the optical distinction ratio between adjacent pixels can be made high, an image display apparatus of high efficiency, high brightness, thin type, and high reliability, and extremely high resolution can be provided.
Next, in order to achieve the other object mentioned above, there is provided in accordance with the present invention a method of manufacturing the solid state light-emissive apparatus characterized in that it comprises the steps of: forming Si single crystal fine particles of nm size being floating in an atmosphere by pyrolyzing SiH4 gas, and conveying said floating Si single crystal fine particles into O2 gas atmosphere, whereby the surface of said Si single crystal fine particles to be coated with SiO2 film of nm thickness.
According to the makeup described above, since the Si single crystal fine particles are formed in a state of floating and SiO2 film is formed on the surface of said floating Si single crystal fine particles in a state of floating, Si single crystal fine particles do not contact mutually not to be combined with each other, and hence mutually isolated Si single crystal fine particles coated with SiO2 film can be provided.
By using above mentioned particles, a solid state light-emissive apparatus can be manufactured by dissolving the crystal fine particles of nm size coated with insulator and the fluorescent fine particles of nm size into respective solvents, soaking a substrate and then taking it out in turn with respective solvents, whereby to laminate the layers of the crystal fine particle of nm size coated with insulator and the layers of fluorescent fine particle of nm size.
According to the makeup above mentioned, a mono-layer which consists of the crystal fine particles coated with insulator being densely aggregated on the substrate, is obtained by one time processing of soaking a substrate into the solvent dissolving the crystal fine particles of nm size coated with insulator and taking out there-from, and the desired thickness of the layer is obtained by repeating the above processing. Then, a mono-layer which consists of the fluorescent fine particles of nm size being densely aligned on the layer of the crystal fine particles of nm size coated with insulator on the substrate, is obtained by one time processing of soaking the substrate into the solvent dissolving fluorescent fine particles of nm size and taking out there-from, and the desired thickness of the layer is obtained by repeating the above processing. As the result, the luminous thin film can be provided, in which the crystal fine particle layer of the desired film thickness and the fluorescent fine particle layer of the desired film thickness are laminated.
According to the above mentioned method, since those fine particles can be densely packed with only a few gaps between those fine particles in the luminous thin film, it can emit light at high efficiency. And, since no expensive apparatus is needed for the manufacturing, it costs are low.
And the luminous thin film of the solid state light-emissive apparatus according to the present invention can be also manufactured by dissolving the crystal fine particles of nm size coated with insulator and the fluorescent fine particles of nm size into common solvent, by soaking a substrate into the solvent and then taking it out from the solvent, whereby to make a mixed layer of the crystal fine particles of nm size coated with insulator and the fluorescent fine particles of nm size.
According to the above mentioned makeup, a mono layer which consists of the crystal fine particles coated with insulator and the fluorescent fine particles of nm size being densely and mutually aligned on the substrate, is obtained by one time processing of soaking a substrate into the solvent and taking it out there-from, and the desired thickness of the layer is obtained by repeating the above processing.
According to the above mentioned method, since those fine particles can be densely packed with only a few gaps between those fine particles in the luminous thin film, it can emit light at high efficiency. And, since no expensive apparatus is needed for the manufacturing, costs are low. The afore mentioned crystal fine particles of nm size coated with insulator preferably consists of a single crystal fine particle of a semiconductor or a metal of nm size coated with insulator film of nm thickness.
Also, the single crystal fine particle of nm size is preferably an intrinsic or impurity-doped Si single crystal fine particle of nm size, and the insulator film is preferably a SiO2 film of nm thickness.
Said fluorescent fine particle of nm size may be a semiconductor fine particle having a band gap energy corresponding to an energy ranging from ultraviolet light to visible light. Also, a fluorescent fine particle of nm size may have a donor or/and an acceptor. Still further, a fluorescent fine particle of nm size may be a semiconductor fine particle involving luminous atoms or luminous atom ions.
The present invention will better be understood from the following detailed description and the drawings attached hereto showing certain illustrative forms of embodiment of the present invention; in this connection, it should be noted that such forms of embodiment illustrated in the accompanying drawings hereof are intended in no way to limit the present invention but to facilitate an explanation and an understanding thereof, in which drawings:
Hereinafter, a detailed explanation is given in respect to embodiment of the present invention, references being made to figures. In the drawing figures, it should be noted that the same reference characters are used to designate substantially the same or corresponding components.
In
In
In
An explanation is next made in respect to luminescence mechanism of said luminous part.
Voltage is applied between the lower electrode 2 and the upper electrode 4 so as to be positively high at the upper electrode 4. The voltage is distributed to respective insulators 5b of crystal fine particles coated with insulators 5 constituting the layer 6, that is, SiO2 film 5b of SiO2 coated Si single crystal fine particles 5. The electrons 9 withdrawn from the lower electrode 2 are accelerated by the electric field distributed to SiO2 films 5b, and pass through SiO2 films 5b by tunneling or resonant tunneling transporting phenomenon, since the thickness of SiO2 film 5b is thin. Since the diameter of a Si single crystal fine particle 5a is small, the electrons in Si single crystal fine particles 5a pass without being scattered by phonons because of quantum size effect, that is, without loss of kinetic energy. As shown in
As shown in
Thus, in accordance with the present invention, the generation efficiency of high energy electrons to excite fluorescent fine particles is quite high, and the exciton concentration is also quite high, therefore, high efficiency and high brightness luminescence can be obtained.
Also, since electrons 9 are not scattered by phonons in the process of acceleration, dielectric breakdown of crystal fine particle coated with insulators 5 does not tend to occur. Consequently, since it is possible to make the thickness of fluorescent thin film 3 extremely thin to raise the electric field intensity, a solid state light-emissive display apparatus which is extremely thin type and has high reliability can be obtained.
Also in case that a fluorescent fine particle 7 is doped with a donor or an acceptor, an exciton formed via a donor or an acceptor, namely a bound exciton 13 is formed. In case that a donor and an acceptor are doped, a bound exciton 13 is formed via a donor and an acceptor. In this case, too, since electrons 11 and holes 12 are enclosed inside fluorescent fine particles 7, that is, in the space of nm size, their coulomb interaction is very strong, and the formation probability of bound excitons 13 increases, whereby the bound exciton concentration increases. Since the bound exciton concentration is high in this way, luminescence intensity generated by extinction of bound excitons 13 increases. Also in this case, the luminescence wavelength corresponding to the depth of energy levels of a donor and an acceptor can be obtained. For example, ZnS doped with Al as a donor and Cu as an acceptor provides green light luminescence. Also, by using a semiconductor including luminous atoms or luminous atom ions for fluorescent fine particles 7, the accelerated electrons 9 excite the luminous atoms or luminous atom ions by collision excitation, whereby to generate fluorescence of specific wavelength when the luminous atoms or the luminous atom ions transit from the excited state to the ground state. For example, if Mn is included as luminous atoms in ZnS semiconductor, yellowish orange luminescence can be obtained.
According to the present invention, since electrons 9 can be accelerated at quite high efficiency, fluorescent fine particle layers 8 having luminous center atoms can be made to emit light of high brightness.
As described above, according to the present invention, electrons can be accelerated at quite high efficiency. Theoretically mentioned, since electrons can be accelerated without energy loss, it is possible to obtain luminescence with an applied voltage corresponding to the band gap energy of fluorescent fine particles. For example, if ZnS semiconductor is used as semiconductor of fluorescent fine particles, luminescence is obtained with the applied voltage of about 4V, because the band gap energy of ZnS is about 3.7 eV. Consequently, luminescence of high brightness is possible also by the makeup of
An explanation is next given in respect to a solid state light-emissive display apparatus of the present invention by simple matrix driving.
By making the cross-sectional regions of the lower electrode 2 and the upper electrode 4 as pixels, choosing an arbitrary one set from the plurality of the lower electrodes 2 and the plurality of the upper electrodes 4, and by applying a voltage between the lower electrodes 2 and the upper electrodes 4, the pixels at arbitrary positions are made luminous.
In accordance with the above mentioned, images and mobile images can be displayed. Since the luminous thin film explained in
An explanation is next given in respect to a solid state light-emissive display apparatus of the present invention by active driving.
Near matrix cross sectional region and on said scanning wiring 41 is set a gate electrode 46 of a thin film transistor protruding into the first insulation layer 42, a channel semiconductor layer 47 of a thin film transistor is set opposing to said gate electrode 46 on the first insulation layer 42, one end of said channel 47 is connected to the signal wiring 43 via a drain electrode 48, and the other end of said channel 47 is connected to the pixel electrode 45 via a source electrode 49.
In accordance with the above mentioned, images and mobile images can be displayed. As a luminous thin film explained in
Explanation is next given in respect to the method of manufacture of a solid state light-emissive display apparatus of the present invention.
The method of manufacture is first explained in respect to the making of the single crystal fine particles coated with insulator consisting of Si single crystal fine particles coated with SiO2 film.
By the method mentioned above, it is possible to produce SiO2-coated Si single crystal fine particles mutually separated without forming porous aggregate formed by mutual contact of said single crystal fine particles.
Explanation is next made in respect to the formation of luminous thin film by laminating of single crystal fine particles coated with insulator and fluorescent fine particles on a substrate.
The figure shows soaking the substrate 62 into the solvent 61 such as water and pulling up said substrate, wherein said substrate 62 has the lower electrodes 2 or the pixel electrodes 45 formed on it and in said solvent 61 single crystal fine particles coated with insulator 5 or fluorescent fine particles 7 are dissolved. The fine particles 63 which are single crystal fine particles coated with insulator 5 or fluorescent fine particles 7 in the solvent 61 are adhered to the substrate surface 62 so as to minimize the surface free energies such as the surface tension energy of the solvent 61, and the adsorption energy of fine particles 63 to the substrate 62, as the result, a mono layer 64 consisting of the fine particles 63 aligned mutually and densely on the substrate 62 is formed.
By the repeating of soaking and pulling up of the substrate 62, the fine particle layers 64 can be mutually and densely laminated to desired thickness corresponding to the repeating number.
In order to form the luminous thin film 3 of the makeup shown in
In order to form the luminous thin film 3 of the makeup shown in
In order to form the luminous thin film 3 of the makeup shown in
Since fine particles are aligned densely with few gaps in the luminous thin film thus formed, the electric field distribution is uniform, tunneling probability increases, and electrons can be accelerated at high efficiency. Also, brightness is high because fluorescent fine particles are densely aligned.
As will have been appreciated from the foregoing description, the present invention provides a solid state light-emissive display apparatus of dramatically higher brightness and efficiency, higher reliability, and of thinner type than existing display apparatuses. Also in accordance with the present invention, this solid state light-emissive display apparatus can be manufactured at low cost. Thus, if the apparatus of the present invention is used as the display apparatus of mobile phones or others, it is quite useful because of much lower power consumption, higher brightness, thinner type, and higher reliability than existing liquid crystal displays.
Number | Date | Country | Kind |
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2001-305857 | Oct 2001 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP02/10190 | 9/30/2002 | WO | 00 | 3/25/2004 |
Publishing Document | Publishing Date | Country | Kind |
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WO03/032690 | 4/17/2003 | WO | A |
Number | Name | Date | Kind |
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5229628 | Kobayashi et al. | Jul 1993 | A |
6143201 | Mano | Nov 2000 | A |
Number | Date | Country |
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05-206515 | Aug 1993 | JP |
09-7499 | Jan 1997 | JP |
09-92167 | Apr 1997 | JP |
2000-265166 | Sep 2000 | JP |
WO 0191155 | Nov 2001 | WO |
Number | Date | Country | |
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20040246408 A1 | Dec 2004 | US |