A photodiode, photodetector receiving circuit

Abstract

The utility model relates to a photodiode, including the substrate, epitaxial layer, oxide layer, antireflection coating, light -proof layer and passivation layer that form successively, have the buried layer in the substrate, have the isolation ring, photosensitive part and contact ring in the epitaxial layer, the isolation ring and the contact ring form in the photosensitive part's outside, and the isolation ring penetrates the epitaxial layer, and contact with the substrate. The utility model is further related to a photodetector receiving circuit applied to digital isolated optocoupler. The utility model can improve the light absorption efficiency of photodiode, and reduce the probability that digital isolated optocoupler is misled on account of noise fluctuation.

Description

Technical Field

[0001] This utility model relates to the field of semiconductor manufacturing technology, and more specifically to a photodiode and a photodetector receiving circuit applied to a digitally isolated optocoupler. Background Technology

[0002] Digital isolation optocouplers, as a type of opto-isolation device, typically achieve electrical isolation between input and output through a process of converting electrical signals into optical signals and then back into electrical signals. A digital isolation optocoupler is generally composed of two chip packages: an infrared light-emitting diode (IR LED) and a photodetector (such as a receiver chip consisting of a photodiode and a transistor at the output end). Figure 1 This is a typical package pin diagram for a digitally isolated optocoupler, which includes unconnected pins 1 and 4, IR LED anode pin 2 (positive electrode on the input side), IR LED cathode pin 3 (negative electrode on the input side), ground pin 5, open collector output pin 6, optional pin 7 (base of the output transistor or no connection), and power supply pin 8.

[0003] To meet the high-speed transmission requirements of digitally isolated optocouplers (DIOPs), the photodiodes in DIOPs typically have a large photosensitive area. When optical signals are transmitted through the DIOP, they may affect non-light-receiving devices, increasing leakage current and thus affecting the normal operation of the devices. Furthermore, noise fluctuations at the input and power supply voltages of the DIOP may cause false turn-on at the output. Utility Model Content

[0004] To address the problems in the prior art, this invention provides a photodiode and a photodetector receiving circuit to improve the light absorption efficiency of the photodiode and reduce the probability of false signaling by the digital isolation optocoupler due to noise fluctuations.

[0005] The present invention provides a photodiode comprising a substrate, an epitaxial layer, an oxide layer, an anti-reflection coating, a light-shielding layer, and a passivation layer formed sequentially. The substrate has a buried layer, and the epitaxial layer has an isolation ring, a photosensitive portion, and a contact ring. The isolation ring and the contact ring are formed outside the photosensitive portion, and the isolation ring penetrates the epitaxial layer and contacts the substrate.

[0006] Furthermore, the substrate, the isolation ring, and the photosensitive portion are of a first semiconductor type, while the buried layer, the epitaxial layer, and the contact ring are of a second semiconductor type.

[0007] Furthermore, the photosensitive part is etched into a honeycomb shape using photolithography to form honeycomb holes.

[0008] This invention increases the receiving area and improves the light receiving efficiency by forming honeycomb holes in the photosensitive part and using the lateral PN junction for light reception.

[0009] This utility model also provides a photodetector receiving circuit for use in a digitally isolated optocoupler, including the aforementioned photodiode, as well as an amplifying transistor and a noise reduction resistor connected to the photodiode.

[0010] Furthermore, the cathode of the photodiode is connected to the input power supply, and the anode of the photodiode is connected to the base of the amplifying transistor; the collector of the amplifying transistor is connected to the output terminal, and the emitter of the amplifying transistor is grounded; the first end of the noise reduction resistor is connected to the base of the amplifying transistor, and the second end of the noise reduction resistor is grounded.

[0011] This invention reduces the probability of output mis-conduction caused by the small current generated by noise fluctuations at the input of the optocoupler and the power supply voltage by adding a noise reduction resistor between the connection point of the photodiode and the amplifier transistor and ground. Attached Figure Description

[0012] Figure 1 This is a typical package pin diagram of a digital isolated optocoupler.

[0013] Figure 2 This is a schematic diagram of the photodiode according to Embodiment 1 of this utility model.

[0014] Figure 3 It is along Figure 2 The diagram shows the cross-sectional structure of a photodiode, with the dashed lines indicating the cross-section.

[0015] Figures 4-12 This is a schematic diagram of the structure of the photodiode according to the preparation method of the photodiode in Embodiment 2 of this utility model at each step.

[0016] Figure 13 This is a schematic diagram of the photodetector receiving circuit according to Embodiment 3 of this utility model.

[0017] Figure label:

[0018] 10-Substrate; 11-Buried layer; 20-Epipolar layer; 21-Isolation ring; 22-Photosensitive part; 23-Honeycomb hole; 24-Contact ring; 30-Oxide layer; 40-Antireflective coating; 50-Light-shielding layer; 60-Passivation layer. Detailed Implementation

[0019] To make the objectives, solutions, and advantages of this utility model clearer, the specific structure and working principle of this utility model will be described in more detail below with reference to the accompanying drawings. The embodiments described are only for explaining this utility model and are not limited to these embodiments, nor are they intended to limit the scope of application of this utility model.

[0020] The purpose of the following content is to provide the public with a clearer understanding of this utility model. However, those skilled in the art can clearly understand this utility model even without the following detailed description.

[0021] Example 1

[0022] like Figure 2 and Figure 3 As shown, this embodiment provides a photodiode comprising a substrate 10, an epitaxial layer 20, an oxide layer 30, an anti-reflection coating 40, a light-shielding layer 50, and a passivation layer 60 formed sequentially. The substrate 10 has a buried layer 11 for isolation, and the epitaxial layer 20 has an isolation ring 21, a photosensitive portion 22, and a contact ring 24. The isolation ring 21 and the contact ring 24 are formed outside the photosensitive portion 22, and the isolation ring 21 penetrates the entire epitaxial layer 20 and contacts the substrate 10, thereby achieving electrical isolation between the photodiode and other devices.

[0023] In this embodiment, the substrate 10, isolation ring 21, and photosensitive portion 22 are of the first semiconductor type, and the buried layer 11, epitaxial layer 20, and contact ring 24 are of the second semiconductor type. The first semiconductor type and the second semiconductor type refer to one being an N-type semiconductor and the other being a P-type semiconductor.

[0024] In this embodiment, the photosensitive portion 22 of the epitaxial layer 20 is etched into a honeycomb shape using photolithography, including but not limited to circular, square, and trapezoidal shapes, to reduce light reflectivity. This forms honeycomb holes 23 along the longitudinal direction of the photosensitive portion 22, allowing light to be received using the side PN junctions, increasing the receiving area and improving light reception efficiency.

[0025] In this embodiment, the epitaxial layer 20 may be made of monocrystalline silicon.

[0026] In this embodiment, the oxide layer 30 may be silicon dioxide or other suitable oxide layer materials.

[0027] In this embodiment, the anti-reflective coating 40 may be silicon nitride or other suitable anti-reflective coating materials.

[0028] In this embodiment, the light-shielding layer 50 is a metal light-shielding layer, which can be made of aluminum or other suitable metal light-shielding materials.

[0029] In this embodiment, the passivation layer 60 may be made of silicon nitride or other suitable passivation layer materials.

[0030] Example 2

[0031] This embodiment provides a method for fabricating a photodiode, used to fabricate the photodiode in Embodiment 1, comprising the following steps:

[0032] Step S10, as follows Figure 4 As shown, a substrate 10 is provided, and a buried layer 11 is formed in the substrate 10. Specifically, step S10 includes:

[0033] Step S11: Select silicon or other suitable materials that are low-cost, have good electrical and thermal conductivity, and are easy to integrate with optoelectronics as the substrate 10 of the first semiconductor type;

[0034] Step S12: The substrate 10 is cleaned with strong acid, strong alkali and ultrapure water to ensure the cleanliness of the substrate 10.

[0035] Step S13: A second semiconductor type buried layer 11 is fabricated in the substrate 10 for isolation using photolithography and doping techniques.

[0036] Step S20, as follows Figure 5 As shown, an epitaxial layer 20 of a second semiconductor type is grown on the substrate 10 at high temperature.

[0037] In this embodiment, the epitaxial layer 20 is grown by chemical vapor deposition. The epitaxial layer 20 can be made of single-crystal silicon, and the thickness and resistivity need to be precisely controlled during growth.

[0038] Step S30, as follows Figure 6 As shown, a first semiconductor type isolation ring 21 is formed in the epitaxial layer 20. The isolation ring 21 extends through the entire epitaxial layer 20 and contacts the substrate 10, thereby electrically isolating the photodiode from other devices. In this embodiment, the isolation ring 21 is formed by implantation, diffusion, or etching.

[0039] Step S40, as follows Figure 7 As shown, pure oxygen is introduced at high temperature to grow an oxide layer 30 on the upper surface of the epitaxial layer 20. When the epitaxial layer 20 is made of monocrystalline silicon, the oxide layer 30 is a silicon dioxide thin film layer.

[0040] Step S50, as follows Figure 8As shown, photolithography is performed on the oxide layer 30 to create honeycomb-shaped windows, forming a photosensitive portion 22 with honeycomb holes 23. Ion implantation or diffusion of a first semiconductor type is then performed in other areas of the photosensitive portion 22 outside the honeycomb holes 23 for subsequent light reception. Due to the presence of the honeycomb holes 23, the photosensitive portion 22 can absorb light using the PN junctions on its sides, improving light reception efficiency.

[0041] Step S60, as follows Figure 9 As shown, ions of a second semiconductor type with a concentration higher than that of the epitaxial layer 20 are implanted into the epitaxial layer 20 to form a contact ring 24, thereby promoting good ohmic contact between the metal and silicon and reducing contact resistance.

[0042] Step S70, as follows Figure 10 As shown, an anti-reflective coating 40 is grown above the epitaxial layer 20 to reduce light reflection loss of the photosensitive part 22 and improve absorption efficiency. In this embodiment, the method for growing the anti-reflective coating 40 is plasma-enhanced chemical vapor deposition, and the material of the anti-reflective coating 40 is silicon nitride.

[0043] Step S80, as follows Figure 11 As shown, a light-shielding layer 50 is grown on the area above the anti-reflective coating 40, excluding the photosensitive part 22. The light-shielding layer 50 prevents other areas besides the photosensitive part 22 from being affected by light. The light-shielding layer 50 not only covers the photodiode area excluding the photosensitive part, but also covers the entire surface of the digital isolation optocoupler chip, preventing other devices from being affected by light, increasing leakage current, and thus affecting the normal operation of the devices. In this embodiment, the light-shielding layer 50 is a metal light-shielding layer, and aluminum or other suitable metal light-shielding materials can be used.

[0044] Step S90, as follows Figure 12 As shown, a passivation layer 60 is grown on the upper surface of the light-shielding layer 50. The passivation layer 60 covers not only the photodiode region mentioned above, but also the entire surface of the digital isolation optocoupler chip, serving to block the penetration of metal ions and moisture from the environment and prevent device performance degradation. In this embodiment, the passivation layer 60 may be made of silicon nitride or other suitable passivation layer materials.

[0045] Example 3

[0046] This embodiment provides a photodetector receiver chip applied to a digital isolation optocoupler, and its circuit diagram is shown below. Figure 13 As shown, it includes a photodiode PD, an amplifying transistor Q0 connected to the photodiode PD, and a noise reduction resistor RB. The photodiode PD is the same as the photodiode in Embodiment 1.

[0047] Specifically, the cathode of the photodiode PD is connected to the input power supply VCC, and the anode is connected to the base of the amplifying transistor Q0; the collector of the amplifying transistor Q0 is connected to the output terminal VO, and the emitter of the amplifying transistor Q0 is grounded; the first end of the noise reduction resistor RB is connected to the base of the amplifying transistor Q0 and to the port VB / NC, and the second end of the noise reduction resistor RB is grounded.

[0048] The photodiode PD is used to receive light signals from the light-emitting diode and convert the light signals into current signals IB. After being amplified by the amplifying transistor Q0, the IB outputs a current signal IO, thereby realizing photoelectric conversion.

[0049] The noise reduction resistor RB provides a low-impedance path to conduct the noise current to GND when there is a small current that may be generated by noise fluctuations at the input of the optocoupler and the power supply voltage, thereby reducing the possibility of misleading current at the output.

[0050] In other embodiments, the amplifying transistor is replaced with a Darlington transistor or a MOSFET. The former has stronger driving capability, while the latter is fully compatible with CMOS technology and has lower on-resistance.

[0051] Additionally, it should be noted that the photodetector receiving circuit in other embodiments can be replaced with other types of photodetector receiving circuits. The photodetector receiving circuit can be an integrated circuit chip or a plate circuit composed of various discrete components.

[0052] The above description is merely a preferred embodiment of this utility model and is not intended to limit the scope of this utility model. Various variations can be made to the above embodiments of this utility model. That is, all simple and equivalent changes and modifications made based on the claims and description of this utility model application fall within the protection scope of the claims of this utility model patent. Any aspects of this utility model not described in detail are conventional technical content.

Claims

1. A photodiode, characterized in that, The material comprises a substrate, an epitaxial layer, an oxide layer, an anti-reflective coating, a light-shielding layer, and a passivation layer formed sequentially. The substrate has a buried layer, and the epitaxial layer has an isolation ring, a photosensitive portion, and a contact ring. The isolation ring and the contact ring are formed outside the photosensitive portion, and the isolation ring penetrates the epitaxial layer and contacts the substrate.

2. The photodiode according to claim 1, characterized in that, The substrate, the isolation ring, and the photosensitive part are of a first semiconductor type, and the buried layer, the epitaxial layer, and the contact ring are of a second semiconductor type.

3. The photodiode according to claim 1, characterized in that, The photosensitive part is etched into a honeycomb shape using photolithography to form honeycomb holes.

4. A photodetector receiving circuit, applied to a digitally isolated optocoupler, characterized in that, It includes a photodiode as described in any one of claims 1 to 3, and an amplifying transistor and a noise reduction resistor connected to the photodiode.

5. The photodetector receiving circuit according to claim 4, characterized in that, The cathode of the photodiode is connected to the input power supply, and the anode of the photodiode is connected to the base of the amplifying transistor; the collector of the amplifying transistor is connected to the output terminal, and the emitter of the amplifying transistor is grounded; the first end of the noise reduction resistor is connected to the base of the amplifying transistor, and the second end of the noise reduction resistor is grounded.

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