Structure and manufacturing method for photo coupler single chip

Abstract

This invention provides an optically coupled single-chip structure and its manufacturing method. The optically coupled single-chip structure includes an epitaxial substrate, a light-emitting unit, an electrical isolation layer, and a light-receiving unit. The light-emitting unit is disposed on the epitaxial substrate, the electrical isolation layer is disposed on the light-emitting unit, and the light-receiving unit is disposed on the electrical isolation layer. After the light-emitting unit generates an optical signal in response to an input signal, the optical signal is directly absorbed by the light-receiving unit through the electrical isolation layer and then converted into an output signal.

Description

[Technical Field]

[0001] This invention relates to an optical coupling element and its manufacturing method, and more particularly to an optical coupling single-chip structure having both a light-emitting unit and a light-receiving unit on a single chip and its manufacturing method. [Previous Technology]

[0002] An optocoupler is an electronic component that uses light to transmit electrical signals. It typically consists of two chips with different functions: a light-emitting diode (LED) and a photodetector unit, such as a phototransistor or photodiode, to achieve electrical isolation and signal transmission. This design eliminates the direct electrical connection between the input and output circuits, thus providing high-voltage isolation and noise suppression.

[0003] As shown in Figure 1, conventional optical coupling elements 1 can generally be divided into left-right arranged packaging structures and top-bottom arranged packaging structures. For optical coupling elements 1 with left-right arranged packaging structures, the light-emitting diode 10 and the photodetector 20 are respectively arranged in left-right relative positions inside the optical coupling element 1. On the other hand, for optical coupling elements 1 with top-bottom arranged packaging structures, the light-emitting diode 10 and the photodetector 20 are respectively arranged in top-bottom relative positions inside the optical coupling element 1. However, regardless of whether the optical coupling element 1 has a left-right arranged or top-bottom arranged packaging structure, the light-emitting diode 10 and the photodetector 20 are two separate and independent chips. In the path of optical signal transmission, the light must pass through the air or packaging medium outside the light-emitting diode 10 before it can be received by the photodetector 20. As a result, the external quantum efficiency of the light-emitting diode will be significantly reduced.

[0004] On the other hand, from the perspective of the physical structure arrangement, the two independent chips, the light-emitting diode 10 and the photodetector unit 20, must be separately mounted onto the lead frame 30 before they can be combined into a final component. Therefore, conventional optocouplers must arrange the spatial layout of two independent chips and the lead frame, which will occupy a considerable volume after combination. In addition, there are problems such as cumbersome manufacturing process and high cost. The aforementioned problems encountered by conventional optocouplers regarding the optical signal transmission path, excessive component size, and high cost urgently need to be improved. [Summary of the Invention]

[0005] The main objective of this invention is to provide an innovative optically coupled single-chip structure and its manufacturing method, which can not only increase the external quantum efficiency of the light-emitting diode, but also reduce the overall volume of the optically coupled element to achieve thinner packaging element, reduce process time and cost.

[0006] To achieve the above objectives, the present invention provides an optically coupled single-chip structure, wherein the optically coupled single-chip structure includes an epitaxial substrate, a light-emitting unit, an electrical isolation layer, and a light-receiving unit. The light-emitting unit is disposed on the epitaxial substrate, the electrical isolation layer is disposed on the light-emitting unit, and the light-receiving unit is disposed on the electrical isolation layer. After the light-emitting unit generates an optical signal in response to an input signal, the optical signal is directly absorbed by the light-receiving unit through the electrical isolation layer and then converted into an output signal.

[0007] In one embodiment of the optically coupled single-crystal structure of the present invention, the difference in lattice constant of each material of the light-emitting unit, the light-receiving unit and the electrical insulating layer is no greater than 0.4 Å.

[0008] In one embodiment of the optically coupled single-chip structure of the present invention, the material band gap (Eg) of the light-emitting unit is not less than the material band gap of the light-receiving unit.

[0009] In one embodiment of the optically coupled single-chip structure of the present invention, the material bandgap of the electrical isolation layer is at least 0.1 eV greater than the material bandgap of the light-emitting unit.

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

[0011] In one embodiment of the optically coupled single-chip structure of the present invention, the electrical isolation layer includes 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 less than 10 17 / cm 3.

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

[0013] To achieve the above objectives, the present invention provides an optically coupled single-chip structure, wherein the optically coupled single-chip structure includes an epitaxial substrate, a light-receiving unit, an electrical isolation layer, and a light-emitting unit. The light-receiving unit is disposed on the epitaxial substrate, the electrical isolation layer is disposed on the light-receiving unit, and the light-emitting unit is disposed on the electrical isolation layer. The light-emitting unit can generate an optical signal in response to an input signal, and the optical signal is directly absorbed by the light-receiving unit through the electrical isolation layer and then converted into an output signal.

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

[0015] To achieve the above objectives, the present invention provides a method for manufacturing an optically coupled single-chip structure, comprising the following steps: First, an epitaxial substrate is provided. Next, a light-emitting unit is provided and disposed on the epitaxial substrate. Next, an electrical isolation layer is provided and disposed on the light-emitting unit. Then, a light-receiving unit is provided and disposed on the electrical isolation layer. The light-emitting unit can generate an optical signal in response to an input signal, and the optical signal is directly absorbed by the light-receiving unit through the electrical isolation layer and then converted into an output signal.

[0016] In one embodiment of the optically coupled single-chip structure manufacturing method of the present invention, the steps of providing a light-emitting unit, providing an electrical isolation layer, and providing a light-receiving unit are all epitaxially manufactured on an epitaxial substrate by metal-organic chemical vapor deposition.

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

[0018] Other objects of the present invention, as well as the technical means and embodiments of the present invention, will be understood by those skilled in the art after referring to the drawings and the embodiments described below.

Implementation Method

[0020] The present invention will be explained below through embodiments. These embodiments are not intended to limit the implementation of the invention to any specific environment, application, or special method as described in the embodiments. Therefore, the descriptions of the embodiments are for illustrative purposes only and are not intended to limit the invention. It should be noted that in the following embodiments and drawings, elements not directly related to the present invention have been omitted and are not shown, and the dimensional relationships between the elements in the drawings are for ease of understanding only and are not intended to limit the actual scale.

[0021] This invention discloses an optically coupled single-chip structure and its manufacturing method. Referring to Figure 2, firstly, an epitaxial substrate 100 is provided. This epitaxial substrate can be 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 sequentially epitaxially formed on the epitaxial substrate 100 using metal-organic chemical vapor deposition (MOCVD). It should be noted that another vertical structure of the optically coupled single-chip structure of this invention can also arrange the light-emitting unit below the light-receiving unit, that is, the light-receiving unit and the electrical insulating layer are sequentially epitaxially formed on the epitaxial substrate, and finally the light-emitting unit is formed. This vertical structure is also within the scope of the optically coupled single-chip structure of this invention. However, for the sake of brevity, the structure shown in Figure 2 will be used as an example for the following description.

[0022] It should be noted that, in order to achieve the simultaneous epitaxial formation of the aforementioned three functional units, including the light-emitting unit 200, the electrical insulating layer 300, and the light-receiving unit 400, on the same epitaxial substrate, the materials for each layer of these three functional units must be selected with substantially similar lattice constants, and the differences should not be too large. Specifically, the difference in lattice constants between the materials of each layer should not exceed 0.4 Å, so as to facilitate the smooth epitaxial growth of each layer of material on a wafer. On the other hand, as shown in the embodiment in FIG2, since the light-emitting unit 200 in this optically coupled single-chip structure is in direct contact with the epitaxial substrate 100, when the device is operating, the waste heat generated by the light-emitting unit 200 due to light emission can be directly dissipated through the epitaxial substrate 100, thereby improving the device performance.

[0023] Furthermore, as can be clearly seen from Figure 2, unlike conventional optical coupling elements, one of the technical features of the optical coupling element disclosed in this invention is that the element is a single-chip structure. That is, as shown in Figure 2, a light-emitting unit 200 and a light-receiving unit 400 are sequentially formed on a wafer by epitaxial growth. The two different functional units, the light-emitting unit 200 and the light-receiving unit 400, are electrically isolated from each other by an electrical insulating layer 300, which overcomes the problems of conventional technology such as large device size, high manufacturing cost, and poor photoelectric efficiency.

[0024] Please refer to Figure 3, which details the structure and composition of each layer of the light-emitting unit 200, the electrically insulating layer 300, and the light-receiving unit 400 in a specific embodiment of the optically coupled single-chip structure of the present invention. A gallium arsenide buffer layer may be disposed between the epitaxial substrate 100 and the light-emitting unit 200 for lattice adjustment required for subsequent epitaxial growth. The light-emitting unit 200 may be, but is not limited to, a III-V group epitaxial composite layer, which sequentially comprises 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 may be a ternary compound semiconductor layer, for example, an N-type indium gallium phosphide (InGaP) heavily doped epitaxial layer, serving as an N-type contact layer. Similarly, the P-type doped epitaxial layer 230 can be a ternary compound semiconductor layer, such as a heavily doped P-type indium gallium phosphide (InGaP) epitaxial layer, serving as a P-type contact layer. The multiple quantum wells 220 can be made of aluminum gallium arsenide (AlGaAs) ternary material as a barrier layer and gallium arsenide (GaAs) as a quantum well layer. Furthermore, an intrinsic spacer layer can be disposed outside the barrier layer and the quantum well layer, for example, undoped aluminum gallium arsenide (AlGaAs) can be chosen as the spacer layer to prevent dopant from diffusing into the quantum well structure and improve the confinement efficiency of electrons and holes in the quantum well.

[0025] Furthermore, preferably, a distributed Bragg reflector (DBR), such as an aluminum gallium arsenide / aluminum arsenide (AlGaAs / AlAs) stack, can be selectively arranged between the N-type doped epitaxial layer 210 and the multiple quantum wells 220 to prevent photons from escaping towards the substrate, thereby increasing the number of photons reflected upwards and improving the light extraction efficiency of the light-emitting diode. In addition, an N-type doped layer, such as an N-type aluminum gallium arsenide (AlGaAs) layer, is disposed between the N-type doped epitaxial layer 210 and the multiple quantum wells 220 to provide a high free electron concentration, assisting in the efficient injection of electrons into the MQW structure. A P-type doped layer, such as a P-type aluminum gallium arsenide (AlGaAs) layer, is disposed between the P-type doped epitaxial layer 230 and the multiple quantum wells 220 to provide a high free hole concentration, injecting holes into the MQW structure and forming a potential barrier corresponding to the N-type aluminum gallium arsenide (AlGaAs) layer, promoting the efficient recombination of electrons and holes.

[0026] Please refer to Figure 3. The following describes the structure and composition of the light-receiving unit 400 in a specific embodiment of the optically coupled single-chip structure of the present invention. As shown in Figure 3, the light-receiving unit 400 of the present invention is a typical photodiode structure, which can convert the light signal emitted by the light-emitting unit into an electrical signal. Its structure generally 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 can be an N-type indium gallium phosphide (InGaP) heavily doped epitaxial layer, providing a high free electron concentration as an N-type contact layer. Similarly, the P-type heavily doped layer 430 can be a P-type indium gallium phosphide (InGaP) heavily doped epitaxial layer, serving as a P-type contact layer, providing a high free hole concentration to help holes be injected into the intrinsic layer 420. Furthermore, in this embodiment, the intrinsic layer 420 can be an undoped or lightly doped gallium arsenide (GaAs) layer, which serves as the active region of the photodiode. Photons emitted by the light-emitting unit are absorbed in this region, generating electron-hole pairs. The thickness design of the intrinsic layer can adjust the light absorption and quantum efficiency.

[0027] Furthermore, in a specific embodiment, a spacer layer may be further provided between the intrinsic layer 420 and the N-type heavily doped layer 410 and the P-type heavily doped layer 430. For example, undoped aluminum gallium arsenide (AlGaAs) may be selected as the spacer layer to prevent impurities doped on both sides of the intrinsic layer 420 from diffusing into the active region. Additionally, an N-type doped layer, such as an N-type aluminum gallium arsenide (AlGaAs) layer, is provided between the aforementioned spacer layer and the intrinsic layer 420. A P-type doped layer, such as a P-type aluminum gallium arsenide (AlGaAs) layer, is provided between the aforementioned spacer layer and the intrinsic layer 420 to provide a high free hole concentration.

[0028] Please continue referring to Figure 3. In order for the two different functional units, the light-emitting unit 200 and the light-receiving unit 400, to work normally without interference, after the light-emitting unit 200 is epitaxially epitaxially formed on the epitaxial substrate 100, an electrical isolation layer 300 must first be set on the light-emitting unit 200 for electrical isolation. In the embodiment of the present invention, this electrical isolation layer 300 can be an N-type / P-type reverse bias interface layer, that is, an electrical isolation effect is formed by using a PN diode under reverse bias. Specifically, a P-type indium gallium phosphide (InGaP) light-doped layer is first epitaxially formed on the light-emitting unit 200, and then an N-type indium gallium phosphide (InGaP) light-doped layer is formed to form an N-type / P-type indium gallium phosphide (InGaP) reverse bias interface layer to achieve the electrical isolation effect. In a preferred embodiment, the doping concentration of this N-type / P-type indium gallium phosphide reverse bias interface layer is less than 10¹⁷ / cm³, which increases the width of the depletion region with a lower doping concentration, further enhancing the electrical isolation effect. Furthermore, preferably, undoped aluminum gallium arsenide (AlGaAs) can be epitaxially formed between the electrical isolation layer 300 and the light-emitting unit 200 and the light-receiving unit 400 as spacer layers.

[0029] It should be noted that the aforementioned description of the structure and composition of each layer of the light-emitting unit 200, the electrical insulating layer 300, and the light-receiving unit 400 is merely an example and is not intended to limit the present invention. Any variations that can be made by those skilled in the art after understanding the foregoing description are within the scope of the present invention. However, when selecting the material composition of each of the aforementioned units, it should be noted that the energy band gap (Eg) of each layer of the light-emitting unit is not less than the energy band gap of each layer of the light-receiving unit. That is, even if the wavelength of the light emitted by the light-emitting unit is less than the wavelength of the light absorbed by the light-receiving unit, the light signal emitted by the light-emitting unit can be smoothly absorbed by the light-receiving unit and further converted and output as an electrical signal. On the other hand, in order to ensure that the electrical barrier layer does not absorb the light emitted by the light-emitting unit, that is, to make the electrical barrier layer appear "transparent" to the light-emitting unit, the band gap of the electrical barrier layer is preferably at least 0.1 eV larger than the band gap of the light-emitting unit, so that most of the light emitted by the light-emitting unit is received by the light-receiving unit.

[0030] Please refer to Figure 4, which shows a schematic diagram of the electrode design of the optically coupled single-chip structure in an embodiment of the present invention. One pair of positive and negative electrodes (including a positive electrode 240 and a negative electrode 250) of the light-emitting unit 200 and one pair of positive and negative electrodes (including a positive electrode 440 and a 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 penetrates the light-receiving unit 400 and the electrical isolation layer 300 and is 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, and 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 heavily doped P-type layer 430, and the negative electrode 450 of the light-receiving unit 400 penetrates the heavily doped P-type layer 430 and the intrinsic layer 420 and is electrically connected to the heavily doped N-type layer 410. It should be noted that the portions of the electrodes that penetrate the epitaxial layer must be isolated from the epitaxial layer by an insulating layer to prevent short circuits. Furthermore, according to the foregoing, when the optically coupled single-chip structure of this invention consists of an epitaxial substrate, a light-receiving unit, an electrical insulating layer, and a light-emitting unit from bottom to top, the electrode design must be adjusted accordingly. That is, one pair of positive and negative electrodes from the light-receiving unit is disposed on the light-emitting unit and electrically connected to the light-receiving unit after penetrating the light-emitting unit. Those skilled in the art can easily deduce this from the foregoing, so it will not be elaborated further below.

[0031] Furthermore, this electrode layout design can be customized to meet component requirements, and can be designed as wire-bonded electrodes or flip-chip electrodes to achieve further thinning. In a preferred embodiment, refer to Figure 5, which shows a top view of the electrode layout of the optically coupled single-chip structure of the present invention. Figure 5 shows that the present invention increases the coverage area of ​​the positive electrode 440 of the light-receiving unit, so as to reflect and recover light emitted by the light-emitting unit that is about to dissipate but has not been absorbed by the light-receiving unit 400 back into the light-emitting unit 400, thereby improving component efficiency. Also, in the aforementioned embodiment, the epitaxial substrate is an intrinsically semi-insulating substrate. If a conductive substrate is selected in other embodiments, the aforementioned layout of four electrodes on the same side can be changed to a design where three electrodes are located on one side and the other electrode is disposed on a conductive substrate.

[0032] In summary, the optically coupled single-chip structure of the present invention simultaneously forms a light-emitting unit, an electrically insulating layer, and a light-receiving unit on a wafer via epitaxy. Therefore, the light emitted from the epitaxial layer of the light-emitting diode passes directly through the electrically insulating layer after passing through a material with a similar refractive index, and is then absorbed by the light-receiving unit, greatly improving 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 can generate an optical signal in response to an external input signal, and then be directly absorbed by the light-receiving unit in the optically coupled single-chip element through the electrically insulating layer and converted into an output signal. This overcomes the problem that the light transmission path of traditional optically coupled elements must pass through the outside of the light-emitting unit before being received by the light-receiving unit, resulting in reduced light efficiency. At the same time, the volume of the single-chip structure is also greatly reduced, allowing the device to further meet the requirements of thinness, while reducing process time and manufacturing costs.

[0033] Please refer to Figure 6, which shows a schematic flowchart of the steps for manufacturing the optically coupled monolithic chip structure of the present invention. First, in step S01, an epitaxial substrate is provided. Second, in step S02, a light-emitting unit is provided, which may be a light-emitting diode. Next, in step S03, an electrical insulating layer is provided on the light-emitting unit. In step S04, a light-receiving unit is provided on the electrical insulating layer to form an optically coupled monolithic chip structure having both a light-emitting unit and a light-receiving unit on a single structure. Detailed descriptions of each unit can be found in the foregoing description and will not be repeated here.

[0034] The above embodiments are only used to illustrate the implementation of the present invention and explain the technical features of the present invention, and are not intended to limit the scope of protection of the present invention. Any changes or equivalent arrangements that can be easily made by those skilled in the art are within the scope of the present invention, and the scope of protection of the present invention shall be determined by the scope of the patent application. [Simplified Explanation of the Diagram]

[0019] Figure 1 is a cross-sectional schematic diagram of two conventional optical coupling elements; Figures 2 to 4 are cross-sectional schematic diagrams of manufacturing the optical coupling single-chip structure of the present invention; Figure 5 is a top view schematic diagram of the electrode layout of the optical coupling single-chip structure of the present invention; and Figure 6 is a schematic diagram of the manufacturing process steps of the optical coupling single-chip structure of the present invention.

Claims

1. A photocoupled single-chip structure, comprising: an epitaxial substrate; a light-emitting unit epitaxially grown on the epitaxial substrate; an electrical isolation layer epitaxially grown on the light-emitting unit; and a light-receiving unit epitaxially grown on the electrical isolation layer, wherein, The light-emitting unit can generate an optical signal in response to an input signal. The optical signal is then directly absorbed by the light-receiving unit through the electrical isolation layer and converted into an output signal.

2. The optically coupled single-chip structure as described in claim 1, wherein the difference in lattice constant of the materials of the light-emitting unit, the light-receiving unit and the electrical insulating layer is not greater than 0.4 Å.

3. The optically coupled single-chip structure as described in claim 1, wherein the energy band gap (Eg) of the light-emitting unit is not less than the energy band gap of the light-receiving unit.

4. The optically coupled single-chip structure as described in claim 1, wherein the material bandgap of the electrical isolation layer is at least 0.1 eV greater than the material bandgap of the light-emitting unit.

5. The optically coupled single-chip structure as described in claim 1, wherein the epitaxial substrate is a gallium arsenide (GaAs) substrate.

6. The optically coupled single-chip structure as described in claim 5, wherein the electrical isolation layer includes an N-type / P-type indium gallium phosphide (InGaP) reverse bias interface layer, the doping concentration of the N-type / P-type indium gallium phosphide reverse bias interface layer being less than 10¹⁷ / cm³.

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

8. A photocoupled single-chip structure, comprising: an epitaxial substrate; a light-receiving unit epitaxially grown on the epitaxial substrate; an electrical isolation layer epitaxially grown on the light-receiving unit; and a light-emitting unit epitaxially grown on the electrical isolation layer, wherein, The light-emitting unit can generate an optical signal in response to an input signal. The optical signal is then directly absorbed by the light-receiving unit through the electrical isolation layer and converted into an output signal.

9. The optically coupled monocrystalline structure as described in claim 8, wherein the difference in lattice constant of the materials of the light-emitting unit, the light-receiving unit and the electrical insulating layer is not greater than 0.4 Å.

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

11. A method for manufacturing an optically coupled single-chip structure, comprising: providing an epitaxial substrate; providing a light-emitting unit epitaxially grown on the epitaxial substrate; providing an electrical isolation layer epitaxially grown on the light-emitting unit; and providing a light-receiving unit epitaxially grown on the electrical isolation layer, wherein, The light-emitting unit can generate an optical signal in response to an input signal. The optical signal is then directly absorbed by the light-receiving unit through the electrical isolation layer and converted into an output signal.

12. The manufacturing method as described in claim 11, wherein the steps of epitaxially growing a light-emitting unit, epitaxially growing an electrical insulating layer, and epitaxially growing a light-receiving unit are all epitaxially manufactured on the epitaxial substrate by metal-organic chemical vapor deposition.

13. The manufacturing method as claimed in claim 11 further includes the step of forming a pair of positive and negative electrodes that are individually electrically connected to the light-emitting unit and the light-receiving unit, wherein the pair of positive and negative electrodes of the light-emitting unit passes through the light-receiving unit.

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