Optically coupled single chip structure and method for manufacturing the same

Abstract

To provide an optical coupling single chip structure and a method for manufacturing the same.SOLUTION: The optical coupling single-chip structure includes an epitaxial growth substrate, a light emitting unit, an electrically insulating layer, and a light receiving unit. The light emitting unit is disposed on the epitaxial growth substrate. The electrically insulating layer is disposed on the light emitting unit. The light-receiving unit is disposed on the electrically insulating layer. The light emitting unit generates an optical signal in response to an input signal. The optical signal passes through the electrically insulating layer and is directly absorbed by the light-receiving unit and converted into an output signal.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an optical coupling element and a manufacturing method thereof, and more particularly to a structure of an optical coupling single chip having both a light emitting unit and a light receiving unit on a single chip, and a manufacturing method thereof. [Background technology]

[0002] An optocoupler is an electronic device that uses light to transmit electrical signals. It typically consists of two chips with different functions, namely a light-emitting diode and a light-detecting unit (e.g., phototransistor, photodiode, etc.), to achieve electrical isolation and signal transmission. This design eliminates direct electrical connection between the input and output circuits, providing high-voltage isolation and noise suppression.

[0003] As shown in FIG. 1, conventional optocouplers 1 generally have a left-right packaging structure and a top-bottom packaging structure. In an optocoupler 1 with a left-right packaging structure, the light-emitting diode 10 and the photodetector unit 20 are respectively arranged at left and right positions facing each other inside the optocoupler 1. On the other hand, in an optocoupler 1 with a top-bottom packaging structure, the light-emitting diode 10 and the photodetector unit 20 are respectively arranged at top-bottom positions facing each other inside the optocoupler 1. However, in an optocoupler 1 with a left-right or top-bottom packaging structure, the light-emitting diode 10 and the photodetector unit 20 are separate, independent chips. In the optical signal transmission path, the optical signal passes through the air or packaging medium outside the light-emitting diode 10 before being received by the photodetector unit 20, which significantly reduces the external quantum efficiency of the light-emitting diode.

[0004] Meanwhile, in terms of physical structural arrangement, the two independent chips, the light-emitting diode 10 and the photodetector unit 20, must be mounted on a lead frame 30, respectively, and then assembled into the final device. Therefore, conventional optical couplers require space on the lead frame to accommodate the two independent chips. After assembly, they occupy a considerable volume. Furthermore, conventional optical couplers have problems such as complex manufacturing processes and high costs. The problems currently faced by the above-mentioned conventional optical couplers, such as the optical signal transmission path problem, excessive device volume, and high costs, require urgent improvement. Summary of the Invention

[0005] The main objective of the present invention is to provide an innovative optically coupled single-chip structure and manufacturing method thereof, which not only improves the external quantum efficiency of light-emitting diodes, but also reduces the overall volume of the optically coupled device, enabling thinner packaged devices, and further reduces manufacturing time and costs.

[0006] To achieve the above object, the present invention provides an optically coupled single-chip structure, which includes an epitaxial growth substrate, a light-emitting unit, an electrical insulating layer, and a light-receiving unit. The light-emitting unit is disposed on the epitaxial growth substrate. The electrical insulating layer is disposed on the light-emitting unit. The light-receiving unit is disposed on the electrical insulating layer. The light-emitting unit generates an optical signal according to an input signal. The optical signal passes through the electrical insulating layer and is directly absorbed by the light-receiving unit and converted into an output signal.

[0007] In an embodiment of the optically coupled single-chip structure of the present invention, the difference in lattice constants of the materials of the light-emitting unit, the light-receiving unit, and the electrical insulating layer is 0.4 angstroms (Å) or less.

[0008] In the optically coupled single-chip structure embodiment of the present invention, the energy band gap (Eg) of the light-emitting unit is equal to or greater than the energy band gap of the light-receiving unit.

[0009] In an embodiment of the optically coupled single-chip structure of the present invention, the bandgap of the electrically insulating layer is at least 0.1 eV larger than the bandgap of the light-emitting unit.

[0010] In an embodiment of the optically coupled single-chip structure of the present invention, the epitaxial growth substrate is a gallium arsenide (GaAs) substrate.

[0011] In an embodiment of the optically coupled single-chip structure of the present invention, the electrically insulating layer comprises an N-type / P-type indium gallium phosphide (InGaP) reverse bias interface layer, and the doping concentration of the N-type / P-type indium gallium phosphide reverse bias interface layer is 10 17 / cm 3 is less than.

[0012] In an optically coupled single-chip structure embodiment of the present invention, the light-emitting unit has a pair of positive and negative electrodes, which are disposed on the light-receiving unit and electrically connected to the light-emitting unit through the light-receiving unit.

[0013] To achieve the above object, the present invention provides an optically coupled single-chip structure, which includes an epitaxial growth substrate, a light-receiving unit, an electrical insulating layer, and a light-emitting unit. The light-receiving unit is disposed on the epitaxial growth substrate. The electrical insulating layer is disposed on the light-receiving unit. The light-emitting unit is disposed on the electrical insulating layer. The light-emitting unit generates an optical signal in response to an input signal. The optical signal passes through the electrical insulating layer and is directly absorbed by the light-receiving unit and converted into an output signal.

[0014] In an optically coupled single-chip structure embodiment of the present invention, the light-receiving unit has a pair of positive and negative electrodes, which are disposed on the light-emitting unit and electrically connected to the light-receiving unit through the light-emitting unit.

[0015] To achieve the above object, the present invention provides a method for manufacturing an optically coupled single-chip structure, the method comprising the steps of: preparing an epitaxial growth substrate; forming a light-emitting unit on the epitaxial growth substrate; forming an electrical insulating layer on the light-emitting unit; and forming a light-receiving unit on the electrical insulating layer. The light-emitting unit generates an optical signal in response to an input signal. The optical signal passes through the electrical insulating layer and is directly absorbed by the light-receiving unit and converted into an output signal.

[0016] In an embodiment of the method for manufacturing an optically coupled single-chip structure of the present invention, the steps of forming the light-emitting unit, the electrical insulating layer, and the light-receiving unit are all performed by epitaxial growth on an epitaxial growth substrate using metalorganic chemical vapor deposition.

[0017] In an embodiment of the method for manufacturing an optically coupled single-chip structure of the present invention, the method further includes forming a pair of positive and negative electrodes electrically connected to the light-emitting unit and the light-receiving unit, respectively, wherein the positive and negative electrodes of the light-emitting unit pass through the light-receiving unit.

[0018] Those skilled in the art can understand other objects of the present invention, as well as the technical means and embodiments of the present invention, by referring to the drawings and the embodiments described below. [Brief explanation of the drawings]

[0019] [Figure 1] Cross-sectional view showing two types of conventional optical coupling elements [Figure 2] 1A and 1B are cross-sectional views corresponding to the manufacturing steps of the optically coupled single chip structure of the present invention. [Figure 3] 1A and 1B are cross-sectional views corresponding to the manufacturing steps of the optically coupled single chip structure of the present invention. [Figure 4] 1A and 1B are cross-sectional views corresponding to the manufacturing steps of the optically coupled single chip structure of the present invention. [Figure 5] FIG. 1 is a plan view showing the electrode layout of the optically coupled single-chip structure of the present invention. [Figure 6] 1 is a flowchart of the manufacturing process of the optically coupled single chip structure of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention will be described below through examples. Note that the examples of the present invention are merely examples of embodiments and are not intended to limit the present invention to the environments, applications, or specific aspects described in the examples. Therefore, the explanation of the examples is intended to explain the present invention, but does not limit the present invention. Note that components not directly related to the present invention are omitted and not shown in the embodiments and drawings. The dimensional relationships between the components in the drawings are intended to facilitate understanding and do not limit the actual dimensions.

[0021] The present invention discloses an optically coupled single-chip structure and a method for fabricating the same. As shown in FIG. 2, an epitaxial growth substrate 100 is first prepared. This epitaxial growth substrate is typically a gallium arsenide (GaAs) wafer, but is not limited thereto. Next, a light-emitting unit 200, an electrical insulating layer 300, and a light-receiving unit 400 are epitaxially grown on the epitaxial growth substrate 100 using metal-organic chemical vapor deposition (MOCVD). Another optically coupled single-chip vertical structure of the present invention is one in which the light-emitting unit is disposed below the light-receiving unit, i.e., the light-receiving unit and the electrical insulating layer are sequentially formed on the epitaxial growth substrate, and finally the light-emitting unit is formed. This vertical structure is also included within the scope of the optically coupled single-chip structure of the present invention. However, for simplicity, the following description will be made using the structure shown in FIG. 2 as an example.

[0022] Furthermore, since the three functional units, including the light-emitting unit 200, the electrical insulating layer 300, and the light-receiving unit 400, are formed on the same epitaxial growth substrate by epitaxial growth, the materials for each of these three functional units must have substantially similar lattice constants, and the difference in lattice constants should not be too large. Specifically, the difference in lattice constants between the materials for each layer should be 0.4 angstroms (Å) or less, so that each layer can be epitaxially grown smoothly on the wafer. In the embodiment shown in FIG. 2, in this optically coupled single-chip structure, the light-emitting unit 200 is in direct contact with the epitaxial growth substrate 100. Therefore, during device operation, waste heat generated by the light-emitting unit 200 is directly dissipated through the epitaxial growth substrate 100, thereby improving device performance.

[0023] Furthermore, as can be seen from Fig. 2, one technical feature of the optocoupler of the present invention, which differs from conventional optocouplers, is that the optocoupler has a single-chip structure. That is, as shown in Fig. 2, the light-emitting unit 200 and the light-receiving unit 400 are formed sequentially on a wafer by epitaxial growth. An electrical insulating layer 300 is provided between the light-emitting unit 200 and the light-receiving unit 400. Therefore, the present invention overcomes the problems of the prior art, such as excessively large device volume, high manufacturing costs, and insufficient device photoelectric efficiency.

[0024] Referring to FIG. 3 , the structures and compositions of the light-emitting unit 200, electrical insulating layer 300, and light-receiving unit 400 in a specific embodiment of the optically coupled single-chip structure of the present invention will be described in detail. A gallium arsenide buffer layer can be provided between the epitaxial growth substrate 100 and the light-emitting unit 200 to adjust the lattice during subsequent epitaxial growth. The light-emitting unit 200 is a III-V epitaxial composite layer, but is not limited thereto. This epitaxial composite layer includes, in order, an N-type doped epitaxial layer 210, a multiple quantum well (MQW) 220, and a P-type doped epitaxial layer 230. In this embodiment, the N-type doped epitaxial layer 210 is a ternary compound semiconductor layer, such as a heavily doped N-type indium gallium phosphide (InGaP) layer, and functions as an N-type contact layer. Similarly, the P-type doped epitaxial layer 230 is a ternary compound semiconductor layer, such as a P-type indium gallium phosphide (InGaP) heavily doped layer, and functions as a P-type contact layer. The multiple quantum well 220 uses an aluminum gallium arsenide (AlGaAs) ternary material as a barrier layer and gallium arsenide (GaAs) as a quantum well layer. An intrinsic spacer layer may also be provided outside the barrier layer and quantum well layer. For example, undoped aluminum gallium arsenide (AlGaAs) may be selected as the spacer layer to prevent doping impurities from diffusing into the quantum well structure and improve the confinement efficiency of electrons and holes in the quantum well.

[0025] Furthermore, it is preferable to selectively dispose a distributed Bragg reflector (DBR), such as an aluminum gallium arsenide / aluminum arsenide (AlGaAs / AlAs) stack, between the N-type doped epitaxial layer 210 and the multiple quantum well 220, thereby preventing photons from scattering toward the substrate, increasing the number of photons reflected upward, and improving the light extraction efficiency of the light-emitting diode. Alternatively, an additional N-type doped layer, such as an N-type aluminum gallium arsenide (AlGaAs) layer, may be disposed between the N-type doped epitaxial layer 210 and the multiple quantum well 220. This provides a high free electron concentration and helps electrons to be effectively injected into the MQW structure. A P-type doped layer, such as a P-type aluminum gallium arsenide (AlGaAs) layer, can be provided between the P-type doped epitaxial layer 230 and the multiple quantum well 220 to provide a high concentration of free holes, inject holes into the MQW structure, and form a corresponding barrier in the N-type aluminum gallium arsenide (AlGaAs) layer, thereby promoting effective recombination of electrons and holes.

[0026] Referring to FIG. 3, the structure and composition of a light-receiving unit 400 in an embodiment of the optically coupled single-chip structure of the present invention will be described. As shown in FIG. 3, the light-receiving unit 400 of the present invention has a typical photodiode structure and converts an optical signal output from a light-emitting unit into an electrical signal. The structure of the light-receiving unit mainly includes an N-type heavily doped layer 410, an intrinsic layer 420, and a P-type heavily doped layer 430. The N-type heavily doped layer 410 is an N-type indium gallium phosphide (InGaP) heavily doped epitaxial layer and functions as an N-type contact layer, providing a high free electron concentration. Similarly, the P-type heavily doped layer 430 is a P-type indium gallium phosphide (InGaP) heavily doped epitaxial layer and functions as a P-type contact layer, providing a high free hole concentration, and helping holes to be injected into the intrinsic layer 420. In this embodiment, the intrinsic layer 420 is an undoped or lightly doped gallium arsenide (GaAs) layer, which functions as the active region of the photodiode, absorbing photons emitted from the light-emitting unit and generating electron-hole pairs. The thickness of the intrinsic layer can be adjusted to adjust the light absorption and quantum efficiency.

[0027] In a specific embodiment, a spacer layer may be further provided between the intrinsic layer 420 and the N-type heavily doped layer 410 or the P-type heavily doped layer 430. For example, undoped aluminum gallium arsenide (AlGaAs) may be selected as the spacer layer. This prevents the doping impurities on both sides of the intrinsic layer 420 from diffusing into the active region. An N-type doped layer, for example, an N-type aluminum gallium arsenide (AlGaAs) layer, may also be provided between the spacer layer and the intrinsic layer 420. A P-type doped layer, for example, a P-type aluminum gallium arsenide (AlGaAs) layer may be provided between the spacer layer and the intrinsic layer 420, thereby providing a high free hole concentration.

[0028] As shown in FIG. 3 , after the epitaxial growth of the light-emitting unit 200 on the epitaxial growth substrate 100 is completed, an electrical insulating layer 300 is first formed on the light-emitting unit 200 to function as electrical insulation, in order to ensure that the two different functional units, the light-emitting unit 200 and the light-receiving unit 400, operate normally and do not interfere with each other. In an embodiment of the present invention, the electrical insulating layer 300 is an N-type / P-type reverse bias interface layer. That is, the electrical insulating effect is achieved by utilizing the principle of reverse bias of a PN diode. Specifically, a P-type lightly doped InGaP layer is first epitaxially grown on the light-emitting unit 200, and then an N-type / P-type InGaP reverse bias interface layer is formed on the N-type lightly doped InGaP layer, thereby achieving the electrical insulating effect. In a more preferred embodiment, the doping concentration of the N-type / P-type InGaP reverse bias interface layer is 10 17 / cm 3 The doping concentration is less than 100 . The width of the depletion region can be increased by a low doping concentration, thereby enhancing the effect of electrical isolation. Preferably, undoped aluminum gallium arsenide (AlGaAs) layers may be further epitaxially grown between the electrical isolation layer 300 and the light-emitting unit 200 and the light-receiving unit 400, respectively, to function as spacer layers.

[0029] The above-described structures and compositions of the light-emitting unit 200, electrical insulating layer 300, and light-receiving unit 400 are merely examples and do not limit the present invention. Those skilled in the art may make modifications after understanding the above, and these modifications are within the scope of the present invention. When selecting materials for each unit, the band gap (Eg) of each layer of the light-emitting unit must be equal to or greater than the band gap of each layer of the light-receiving unit. That is, the wavelength of light generated by the light-emitting unit is smaller than the wavelength of light absorbed by the light-receiving unit. After the light-emitting unit generates an optical signal, the optical signal is smoothly absorbed by the light-receiving unit and then converted and output as an electrical signal. When selecting materials for the electrical insulating layer, the band gap of the electrical insulating layer is preferably at least 0.1 eV larger than the band gap of the light-emitting unit so that the electrical insulating layer does not absorb the light output from the light-emitting unit, i.e., so that the electrical insulating layer is "transparent" to the light-emitting unit. This allows most of the light output from the light-emitting unit to be absorbed by the light-receiving unit.

[0030] 4 is a schematic diagram of the electrode design of an optically coupled single-chip structure according to an embodiment of the present invention. The pair of positive and negative electrodes (positive electrode 240, negative electrode 250) of the light-emitting unit 200 and the pair of positive and negative electrodes (positive electrode 440, negative electrode 450) of the light-receiving unit 400 are both disposed on one side of the light-receiving unit 400. The pair of positive and negative electrodes of the light-emitting unit 200 penetrate the light-receiving unit 400 and the electrical insulating layer 300 and are electrically connected to the light-emitting unit 200. That is, the positive electrode 240 is electrically connected to the P-type doped epitaxial layer 230. The negative electrode 250 is electrically connected to the N-type doped epitaxial layer 210. The positive electrode 440 of the light-receiving unit 400 is electrically connected to the P-type heavily doped layer 430. The negative electrode 450 of the light-receiving unit 400 is electrically connected to the N-type heavily doped layer 410 by penetrating the P-type heavily doped layer 430 and the intrinsic layer 420. The portions where the electrodes penetrate the epitaxial layer are insulated from the epitaxial layer by an insulating layer to prevent short circuits. Meanwhile, based on the above description, if the optically coupled single-chip structure of the present invention is arranged from bottom to top in the order of epitaxial growth substrate, light-receiving unit, electrical insulating layer, and light-emitting unit, the electrode design must be adjusted accordingly. That is, the pair of positive and negative electrodes of the light-receiving unit are installed on the light-emitting unit and are electrically connected to the light-receiving unit by penetrating the light-emitting unit. Those skilled in the art can easily deduce this from the above description, so a detailed explanation will be omitted.

[0031] Furthermore, this electrode layout can be designed as a wire-bonded electrode or a flip-chip electrode depending on the device requirements, thereby achieving a thinner device. A more preferred embodiment will be described with reference to FIG. 5. FIG. 5 is a plan view showing the electrode layout of the optically coupled single-chip structure of the present invention. As shown in FIG. 5, the present invention increases the coverage area of ​​the positive electrode 440 of the light-receiving unit, thereby reflecting light emitted from the light-emitting unit but not absorbed by the light-receiving unit 400 back into the light-receiving unit 400, thereby improving the device efficiency. In addition, in the above embodiment, the epitaxial growth substrate is an intrinsic semi-insulating substrate. In another embodiment, if the substrate is a conductive substrate, the layout in which four electrodes are arranged on the same side is changed to a layout in which three electrodes are arranged on one surface and the remaining electrode is arranged on the conductive substrate.

[0032] In summary, in the optically coupled single-chip structure of the present invention, a light-emitting unit, an electrical insulating layer, and a light-receiving unit are formed on a wafer by epitaxial growth. Therefore, light emitted from the epitaxial layer of the light-emitting diode passes through an internal material with a similar refractive index, then passes directly through the electrical insulating layer and is absorbed by the light-receiving unit. This significantly improves the external quantum efficiency of the light-emitting diode. That is, the light-emitting unit of the optically coupled single-chip structure of the present invention generates an optical signal in response to an external input signal. The optical signal then passes through the electrical insulating layer and is directly absorbed by the light-receiving unit of the optically coupled single-chip device and converted into an output signal. This overcomes the problem of conventional optically coupled devices, where light must pass outside the light-emitting unit along a transmission path before being received by the light-receiving unit, resulting in reduced optical efficiency. Furthermore, the volume of the single-chip structure of the present invention is significantly reduced, thereby enabling the device to be made thinner and reducing manufacturing process time and costs.

[0033] FIG. 6 is a flowchart of the manufacturing process for the optically coupled single-chip structure of the present invention. First, in step S01, an epitaxial growth substrate is prepared. Next, in step S02, a light-emitting unit is formed. This light-emitting unit is a light-emitting diode. Next, in step S03, an electrical insulating layer is formed on the light-emitting unit. In step S04, a light-receiving unit is formed on the electrical insulating layer. As a result, the optically coupled single-chip structure of the present invention has both a light-emitting unit and a light-receiving unit in a single structure. Detailed descriptions of each unit can be found in the above content and are omitted here.

[0034] The above examples are intended to explain embodiments of the present invention and to explain the characteristic configurations of the present invention. The present invention is not limited to the above examples. Modifications or equivalent arrangements that can be easily made by those skilled in the art are also within the scope of the present invention. The scope of protection of the rights of the present invention is based on the claims. [Explanation of symbols]

[0035] 1 Optical coupling element 10. Light-emitting diode 20 Optical detection unit 30 Lead Frame 100 Epitaxial growth substrate 200 light-emitting units 210 N-type doped epitaxial layer 220 Multiple quantum wells 230 P-type doped epitaxial layer 240 positive electrode 250 negative electrode 300 Electrical insulating layer 400 Light receiving unit 410 N-type heavily doped layer 420 Intrinsic layer 430 P-type heavily doped layer 440 positive electrode 450 negative electrode

Claims

1. An optically coupled single chip structure, an epitaxial growth substrate; a light-emitting unit disposed on the epitaxial growth substrate; an electrical insulating layer disposed on the light emitting unit; a light-receiving unit disposed on the electrically insulating layer; the light emitting unit generates a light signal in response to an input signal; The optically coupled single-chip structure, wherein the optical signal passes through the electrical insulating layer and is directly absorbed by the light-receiving unit and converted into an output signal.

2. 2. The optically coupled single-chip structure according to claim 1, wherein the difference in lattice constant between the materials of the light-emitting unit, the light-receiving unit, and the electrical insulating layer is 0.4 angstroms (Å) or less.

3. 2. The optically coupled single-chip structure according to claim 1, wherein the energy band gap (Eg) of the light-emitting unit is equal to or larger than the energy band gap of the light-receiving unit.

4. 2. The optically coupled single-chip structure of claim 1, wherein the band gap of the electrically insulating layer is at least 0.1 eV larger than the band gap of the light-emitting unit.

5. 2. The optically coupled single chip structure of claim 1, wherein the epitaxial growth substrate is a gallium arsenide (GaAs) substrate.

6. The electrically insulating layer comprises an N-type / P-type indium gallium phosphide (InGaP) reverse bias interface layer, and the doping concentration of the N-type / P-type indium gallium phosphide reverse bias interface layer is 10 １７ / cm ３ 6. The optically coupled single-chip structure according to claim 5, wherein the optically coupled single-chip structure is less than 1 / 2 .mu.m.

7. The light-emitting unit has a pair of positive and negative electrodes, The optically coupled single-chip structure according to claim 1 , wherein the positive and negative electrodes are disposed on the light-receiving unit and electrically connected to the light-emitting unit through the light-receiving unit.

8. An optically coupled single chip structure, an epitaxial growth substrate; a light-receiving unit disposed on the epitaxial growth substrate; an electrical insulating layer disposed on the light receiving unit; a light-emitting unit disposed on the electrically insulating layer; the light emitting unit generates a light signal in response to an input signal; The optically coupled single-chip structure, wherein the optical signal passes through the electrical insulating layer and is directly absorbed by the light-receiving unit and converted into an output signal.

9. 9. The optically coupled single-chip structure according to claim 8, wherein the difference in lattice constant between the materials of the light-emitting unit, the light-receiving unit, and the electrical insulating layer is 0.4 angstroms (Å) or less.

10. The light-receiving unit has a pair of positive and negative electrodes, The optically coupled single-chip structure according to claim 8 , wherein the positive and negative electrodes are disposed on the light-emitting unit and electrically connected to the light-receiving unit through the light-emitting unit.

11. 1. A method for manufacturing an optically coupled single chip structure, comprising: providing an epitaxial growth substrate; forming a light-emitting unit on the epitaxial growth substrate; forming an electrical insulating layer on the light-emitting unit; forming a light-receiving unit on the electrical insulating layer; the light emitting unit generates a light signal in response to an input signal; The manufacturing method, wherein the optical signal passes through the electrical insulating layer and is directly absorbed by the light receiving unit and converted into an output signal.

12. 12. The manufacturing method according to claim 11, wherein the steps of forming the light-emitting unit, forming the electrical insulating layer, and forming the light-receiving unit are all performed by epitaxial growth on an epitaxial growth substrate using metal organic chemical vapor deposition.

13. further comprising a step of forming a pair of positive and negative electrodes electrically connected to the light-emitting unit and the light-receiving unit, respectively; The manufacturing method according to claim 11 , wherein the positive and negative electrodes of the light-emitting unit penetrate the light-receiving unit.

Images