Visible light communication emission device with improved response frequency

Abstract

A visible light communication emission device with improved response frequency is provided, comprising a substrate, wherein an inductance coil module is provided on the substrate, a LED chip matrix formed by series connection of a plurality of LED chips is provided on the inductance coil module, and the inductance coil module and the LED chip matrix are connected in series, wherein inductance value L of the inductance coil module is configured to be: L=1/(.sup.2C), with C representing capacity in the device provided by LED chips and representing frequency, wherein the inductance coil module comprises more than one inductance coil whose composition materials from inside to outside are successively Cr, Al, Cr, Ti, and Ag.

Claims

1. A visible light communication emission device with improved response frequency, comprising a substrate, wherein an inductance coil module is provided on the substrate, a LED chip matrix formed by series connection of a plurality of LED chips is provided on the inductance coil module, and the inductance coil module and the LED chip matrix are connected in series, wherein inductance value L of the inductance coil module is configured to be: L=1/(.sup.2C), with C representing capacity in the device provided by LED chips and representing frequency, wherein the inductance coil module comprises more than one inductance coil whose composition materials from inside to outside are successively Cr, Al, Cr, Ti, and Ag.

2. The visible light communication emission device according to claim 1, wherein the inductance coil is a spiral with a cross section of trapezoid having a lower baseline angle of 45 degree.

3. The visible light communication emission device according to claim 1, wherein the inductance coil module comprises four inductance coils which are configured to form a 22 matrix, in which each two inductance coils are first connected in series and then connected in parallel with the other two inductance coils.

4. The visible light communication emission device according to claim 1, wherein the LED chip comprises successively a buffer layer located on a protective layer of the substrate, an n-type layer to generate electrons, a multiple quantum well layer, a electron blocking layer, a p-type layer, a transparent conductive electrode layer, and a p-type electrode layer.

5. The visible light communication emission device according to claim 4, wherein the p-type electrode layer is a polycyclic p-type electrode layer comprising from its outside to inside a nanosilver p-electrode, a ZnO p-electrode, and a Al p-electrode.

6. The visible light communication emission device according to claim 5, wherein the Al p-electrode has a thickness of 2-5 nm.

7. The visible light communication emission device according to claim 1, wherein a protective layer of the substrate is provided between the inductance coil module and the LED chip matrix.

8. The visible light communication emission device according to claim 7, wherein the protective layer of the substrate is a Al.sub.2O.sub.3 protective layer.

9. The visible light communication emission device according to claim 1, wherein the substrate is a sapphire substrate.

Description

BRIEF DESCRIPTION TO THE DRAWINGS

(1) FIG. 1 shows a top view of the visible light communication emission device in an example according to the present invention.

(2) FIG. 2 shows a cross section view of the inductance coil in an example according to the present invention.

(3) FIG. 3 shows a schematic view of the structure of the inductance coil module in an example according to the present invention.

(4) FIG. 4 shows a cross section view of the structure of the visible light communication emission device in an example according to the present invention.

LIST OF REFERENCE NUMBERS

(5) 1: hole on the substrate for series connection of the spiral inductance coil with the chips on the front 2: patterned substrate 3: negative electrode area of the chip 4: positive electrode of the device 5: wire between the chips in series connection 6: light emitting positive electrode area of the chip 7: nanosilver p-electrode 8: transparent ZnO p-electrode 9: Al p-electrode 10: n-electrode of the chip 11: negative electrode of the emission device 12: wire connecting inductance coils in parallel 13: wire connecting inductance coils in series 15: spiral inductance coil

DETAILED DESCRIPTION OF THE INVENTION

(6) The present invention will be described in conjugation with embodiments and figures.

(7) FIG. 1 shows a visible light communication emission device with improved response frequency, comprising a substrate. An inductance coil module is provided on the substrate, a LED chip matrix formed by series connection of a plurality of LED chips is provided on the inductance coil module, and the inductance coil module and the LED chip matrix are connected in series. The inductance value L of the inductance coil module is configured to be: L=1/(.sup.2C), with C representing capacity in the device provided by LED chips and representing frequency. The inductance coil module comprises more than one inductance coil. The composition materials of the inductance coil from inside to outside are successively Cr, Al, Cr, Ti, and Ag.

(8) The inductance coil is made by multilayer materials that have high light transmittance, with the outmost layer being silver which has an extreme high reflectivity. Light emitted by the positive electrode area of the LED chip is reflected by the silver after reaching the substrate to arrive at the light emitting positive electrode area, which improves light extraction efficiency of the device.

(9) As shown in FIG. 1, the present example comprises sixteen LED chips which are connected in series with each other and configured to form a 44 matrix.

(10) Since a single chip has a voltage of 3V and a current of 5-30 mA, the device have a total voltage of 83V=24V. A single LED chip has a capacitance of about 2000 pF-4000 pF, therefore, in the case that sixteen chips are connected in series in the visible light communication emission device, the device has a total capacitance of about 100 pF-300 pF.

(11) After series connection of the LED chips with the inductance coil module, the circuit has a total impedance of:

(12) $.Math.Z.Math.={\sqrt{R^2+\left(L-\frac{1}{C}\right)}}^2$

(13) wherein R represents self-resistance of the device, C represents capacity in the device provided by LED chips, and L represents inductance in the present example used to match the total capacitance of the circuit.

(14) In the case that the spiral inductance is not connected in series in the circuit, when the circuit has a input single of U.sub.in=U.sub.0 sin(t), total current I in the circuit is:

(15) $I=\frac{U_{\mathrm{in}}}{{\sqrt{R^2+\left(0-\frac{1}{C}\right)}}^2}=\frac{U_{\mathrm{in}}}{\sqrt{R^2+\frac{1}{{\left(C\right)}^2}}}$

(16) The power absorbed by the capacitance is:

(17) $P_C=I^2{Z}_C={\left(\frac{U_{\mathrm{in}}}{\sqrt{R^2+\frac{1}{{\left(C\right)}^2}}}\right)}^2.Math.\left(-\frac{1}{C}\right)$

(18) It can be obtained that:

(19) $P_C=-\frac{U_{\mathrm{in}}^2}{{\mathrm{CR}}^2+\frac{1}{C}}$

(20) When the visible light communication emission device has a total capacitance of 100 pF-300 pF and working frequency of 1 MHz-100 MHz, the C has a magnitude of 10.sup.4-10.sup.2. In addition, in operation of the LED, the resistance R is only tens of ohms, thus P.sub.C can be simplified as P.sub.C=U.sub.in.sup.2C. With the frequency co changing from 1 MHz to 100 MHz, |P.sub.C| also becomes greater, which indicates increasing power absorbed by the capacitance. In other words, output signals suffer from attenuation with increasing of frequency. It is found by practice that, without series connection of a matching inductance, after the frequency reaches 40 MHz, increase of output signals of the visible light communication emission device will suffer from attenuation with increasing of frequency.

(21) In the case that the spiral inductance is connected in series in the circuit, when the circuit also has an input single of U.sub.in=U.sub.0 sin(t), total current in the circuit is:

(22) $I=\frac{U_{\mathrm{in}}}{{\sqrt{R^2+\left(L-\frac{1}{C}\right)}}^2}$

(23) The power absorbed by the capacitance is P.sub.c=I.sup.2Z.sub.c, which can be simplified to be:

(24) $P_C=-\frac{U_{\mathrm{in}}^2}{R^2+{\left(L-\frac{1}{C}\right)}^2}.Math.\frac{1}{C}$

(25) For the same reason, the absorption power of the newly added inductance is:

(26) $P_L=I^2{Z}_L=\frac{U_{\mathrm{in}}^2}{R^2+{\left(L-\frac{1}{C}\right)}^2}.Math.L$

(27) In a perfect match of the inductance and the capacitance, P.sub.C+P.sub.L=0. It can be obtained by simplification that L=1/(.sup.2C).

(28) Then the total power absorbed by the capacitance and the inductance is P=P.sub.L+P.sub.C=0. In other words, the inductance and the capacitance are perfectly matched, and exchanges energy with each other. The inputted power is totally absorbed by the resistance. At this point, there will be no loss in the circuit at corresponding frequency, which means attenuation of output signal is suppressed. The frequency will increase when the device suffers from attenuation, which improves the response frequency of the LED as a visible light communication emission device.

(29) Preferably, the inductance coil is a spiral. The spiral has a cross section of trapezoid. The trapezoid has a lower baseline angle of 45 degree.

(30) As shown in FIG. 2, by the 45 degree trapezoid structure, when the light emitted from the positive electrode area moves downwards, it will arrive at section ab in FIG. 2, after which Al refection layer in the section ab will reflect the light towards section cd, which will then reflect the light in a direction opposite to the incident angle to the light emitting positive electrode area. In this way, the amount of out emitting light in the positive electrode area is increased.

(31) As shown in FIG. 3, the inductance coil module comprises four inductance coils which are configured to form a 22 matrix. Each two inductance coils are first connected in series, and then connected in parallel with the other two inductance coils.

(32) In order to allow the inductance coils arranged under all of the chips, a 22 circuit formed by four 320 m320 m inductance coils are used in the present example, with each two inductance coils first connected in series and then connected in parallel with the other two inductance coils.

(33) Since a single LED chip has a capacitance of about 3000 pF, in series connection of sixteen LEDs, the circuit has a total capacitance of about 200 pF. In a match at 40 MHz, the inductance required for the match is 78 nH. In accordance with the Wheeler's equation, the inductance can be determined by:

(34) $L={}_0{N}^2\frac{K_1{d}_{\mathrm{avg}}}{1+K_2}$

(35) wherein .sub.0=410.sup.7H/m, N represents number of turns in the coil, K is a coefficient related to the arrangement (in a square circle, K.sub.1=2.34, K.sub.2=2.75), d.sub.avg=(d.sub.in+d.sub.out)/2, =(d.sub.in+d.sub.out)/(d.sub.outd.sub.in) is the inner width of the inductance as a square circle, and d.sub.out is the outer width of the inductance as a square circle.

(36) Therefore, in the case of a 22 inductance arrangement, the outer width of the inductance is 320 m while the inner width is 0. In order to obtain an inductance of 78 nH, the number of turns in the coil is required to be 25-26. Since there may be some difference between theoretical calculation and real situation, an inductance of 78 nH with 25 turns per coil is chosen. Since the inductance is made by processes such as exposing, imaging and etching, the width of a metal can only be provided in a limited precision, whose minimal size is generally 0.1 m. In the present example, the spiral coil has the outer width of 320 m, the inner width of 0 m, and the trapezoid has the height of 2.5 m, the width of the upper baseline of 0.4 m, the width of the lower baseline of 5.4 m, and the interval of 1 m.

(37) As shown in FIG. 4, the LED chip comprises successively a buffer layer located on a protective layer of the substrate, an n-type layer to generate electrons, a multiple quantum well layer, a electron blocking layer, a p-type layer, a transparent conductive electrode layer, and a p-type electrode layer.

(38) Preferably, the p-type electrode layer is a polycyclic p-type electrode layer comprising from its outside to inside a nanosilver p-electrode, a ZnO p-electrode, and a Al p-electrode.

(39) A preparation method for the polycyclic p-type electrode is provided comprising:

(40) (1) evaporate plating a layer of Al by a PECVD device, and forming a cyclic rectangular electrode by chemical etching;

(41) (2) evaporate plating a ZnO film by a MOCVD (Metalorganic Chemical Vapor Deposition) device, and forming a cyclic rectangular ZnO electrode by etching using dry or wet etching;

(42) (3) growing nanosilver as nanosilver particle structure by PECVD evaporate plating or MOCVD technology, so as to provide a nanosilver p-electrode.

(43) The term nanosilver is short for silver nanoparticle, which refers to a particle formed by silver atoms with a particle size of 1-100 nm.

(44) Preferably, a protective layer of the substrate is provided between the inductance coil module and the LED chip matrix.

(45) Preferably, the protective layer of the substrate is a Al.sub.2O.sub.3 protective layer.

(46) After forming a spiral inductance coil on the substrate, a layer of Al.sub.2O.sub.3 sapphire material is further evaporate plated, allowing the Al.sub.2O.sub.3 material cover middle portions between the spiral inductance coil, which not only increases insulativity between each coil of the spiral inductance coil, protecting the spiral inductance coil, but also patterns the substrate.

(47) Preferably, in the present example, the substrate is a sapphire substrate.