A monolithic integrated opto-coupler and method of manufacture
By integrating the optical emitter and optical receiver on the same GaN-based epitaxial wafer, the problems of large size and high power consumption of existing optocouplers are solved, realizing a miniaturized, low-power, and highly reliable optocoupler suitable for mass production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NANJING UNIV OF POSTS & TELECOMM
- Filing Date
- 2022-01-27
- Publication Date
- 2026-05-29
AI Technical Summary
Existing optocouplers are fabricated using different process platforms and are packaged off-chip, resulting in problems such as large size and high power consumption.
Using monolithic integration technology, the optical transmitter and optical receiver are fabricated on the same GaN-based epitaxial wafer. Physical and electrical separation is achieved through isolation trenches, and the high electron mobility and high thermal conductivity of GaN epitaxial materials are utilized in conjunction with MEMS processes for fabrication.
It achieves miniaturization, low power consumption, high speed and high reliability of optocouplers, reduces processing difficulty and production cost, and is suitable for mass production.
Smart Images
Figure CN114582912B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a monolithic integrated optocoupler and its fabrication method, belonging to the field of integrated optoelectronic technology. Background Technology
[0002] Optocouplers transmit electrical signals through light as a medium and provide good isolation between input and output electrical signals. They are widely used in electrical insulation, level conversion, drive circuits, pulse amplification, solid-state relays, communication equipment, and microelectromechanical interfaces.
[0003] Currently, the various components of an optocoupler (mainly including light emitting and receiving devices) are fabricated using different process platforms and then assembled in off-chip packaging. By utilizing suitable material systems and advanced fabrication processes, the various components of an optocoupler can be fabricated on a single chip, achieving monolithic integration of the optocoupler. This offers significant advantages such as smaller size, lower power consumption, higher speed, higher reliability, and mass production capabilities, representing a crucial trend in the future development of optocouplers and possessing significant economic and application value. Summary of the Invention
[0004] The purpose of this invention is to provide a monolithic integrated optocoupler and its fabrication method, in order to solve the defects of existing technologies that are fabricated through different process platforms and assembled in the form of off-chip packaging, resulting in large size and high power consumption.
[0005] A monolithic integrated optocoupler includes a visible light LED and a photosensitive VMOSFET disposed on the same GaN-based epitaxial wafer;
[0006] The visible light LED serves as a light emitter, used to convert electrical signals into light signals. The visible light LED and the photosensitive VMOSFET are located on the same substrate and are physically and electrically separated by an isolation trench.
[0007] Furthermore, the GaN-based epitaxial wafer comprises, from bottom to top, a substrate material, AlN, AlGaN, N-type GaN, GaN multiple quantum wells, and P-type GaN.
[0008] Furthermore, below the positive electrode of the visible light LED are, in sequence, a P-type GaN layer, a multiple quantum well layer, a first N-type GaN layer, a first AlGaN layer, and a first AlN layer; the negative electrode of the visible light LED is in direct contact with the first N-type GaN layer, the positive electrode is located on the side closer to the photosensitive VMOSFET, and the negative electrode is located on the side farther away from the photosensitive VMOSFET.
[0009] Furthermore, the photosensitive VMOSFET includes a source, a drain, a gate, a second N-type GaN layer, and a third N-type GaN layer, with the gate located between the source and the drain; the source is connected to the second N-type GaN layer, and the drain is connected to the third N-type GaN layer; the epitaxial layers below the second N-type GaN layer and the third N-type GaN layer are sequentially provided with a second AlGaN layer, a second AlN layer, a sapphire substrate, and a visible light reflective layer.
[0010] Furthermore, the channel shape of the photosensitive VMOSFET is V-shaped, with the bottom of the V-shape located inside the second AlGaN layer. A gate dielectric layer covers the V-shaped channel, and the gate is located above the gate dielectric layer.
[0011] Furthermore, the visible light reflective layer is a metallic Ag reflective layer or a distributed Bragg reflective layer.
[0012] Furthermore, a silicon substrate is disposed below the visible light LED and the photosensitive VMOSFET. The center of the silicon substrate is hollowed out to form a suspended thin film structure, and a cavity is formed below the thin film structure. The silicon substrate is bonded by a visible light reflector.
[0013] A method for fabricating a monolithic integrated optocoupler, the method comprising:
[0014] A layer of photoresist is coated on a GaN-based epitaxial wafer and photolithography is performed to expose the P-type GaN layer region that needs to be etched. Then, ICP dry etching is performed until the N-type GaN layer is reached and then stopped.
[0015] Then, a layer of photoresist is coated and photolithography is performed to expose the area where the isolation trench needs to be made. Next, ICP dry etching is performed until the substrate is reached.
[0016] A layer of photoresist is coated and photolithography is performed to expose the etching window of the photosensitive VMOSFET channel region. Then, ICP dry etching is performed to form a V-shaped trench. The bottom of the V-shaped trench is located inside the second AlGaN layer. Then, the sidewalls of the V-shaped trench are smoothed.
[0017] A high-quality gate dielectric layer is grown by plasma-enhanced chemical vapor deposition or atomic layer deposition and etched into shape after photolithography.
[0018] A layer of photoresist is coated, and the photoresist on the source and drain of the photosensitive VMOSFET and the negative electrode of the visible light LED is removed by photolithography.
[0019] Remove the photoresist and the metal layer on the photoresist, and strip to form the source and drain of the photosensitive VMOSFET and the negative electrode of the visible light LED;
[0020] A layer of photoresist is coated, and the photoresist on the gate of the photosensitive VMOSFET and the positive electrode of the visible light LED is removed by photolithography.
[0021] Remove the photoresist and the metal layer on the photoresist, and strip to form the gate of the photosensitive VMOSFET and the positive electrode of the visible light LED;
[0022] The silicon substrate beneath the visible light LED and photosensitive VMOSFET is removed, while the silicon substrate around the device is retained as a support to form a suspended thin film structure. Then, the back of the device is bonded to a visible light reflector to form a monolithic integrated optocoupler.
[0023] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:
[0024] The optocoupler of the present invention has all its components fabricated on the same chip, which realizes monolithic integration and brings significant advantages such as small size, low power consumption, high speed, high reliability, and mass production.
[0025] The optocoupler of the present invention uses a silicon-based GaN epitaxial wafer. The GaN material epitaxially has excellent properties such as high electron mobility, high thermal conductivity, high temperature resistance, corrosion resistance and radiation resistance, and can be used to fabricate high-performance optoelectronic devices and electronic devices at the same time.
[0026] The optocoupler of the present invention has a silicon substrate that can be processed using mature MEMS process lines, which is of great significance for mass production and reducing production costs.
[0027] The photosensitive VMOSFET of the present invention does not require complex ion implantation technology for fabrication, and no epitaxial material growth is introduced during the processing. At the same time, it is fully compatible with the fabrication process of visible light LEDs, which reduces the processing difficulty of optocouplers. Attached Figure Description
[0028] Figure 1 This is a schematic diagram illustrating the principle of the present invention;
[0029] Figure 2 This is a schematic diagram of the structure of the epitaxial wafer of the present invention;
[0030] Figure 3 This is a top view of the monolithic integrated optocoupler of the present invention;
[0031] Figure 4 This is a cross-sectional view along the A-A' direction when silicon is selected as the substrate material in this invention;
[0032] Figure 5 This is a B-B' cross-sectional view when silicon is selected as the substrate material in this invention;
[0033] Figure 6This is a cross-sectional view along line A-A' when sapphire is selected as the substrate material in this invention;
[0034] Figure 7 This is a cross-sectional view along the B-B' direction when sapphire is selected as the substrate material in this invention.
[0035] In the figure: 1. Visible LED; 2. Photosensitive VMOSFET; 3. Substrate material; 4. AlN; 5. AlGaN; 6. N-type GaN; 7. InGaN / GaN multiple quantum wells; 8. P-type GaN; 9. P-type GaN layer; 10. Multiple quantum well layer; 11. First N-type GaN layer; 12. First AlGaN layer; 13. First AlN layer; 14. Negative electrode; 15. Positive electrode; 16. Source; 17. Drain; 18. Gate; 19. Second N-type GaN layer; 20. Third N-type GaN layer; 21. Second AlGaN layer; 22. Second AlN layer; 23. Gate dielectric layer; 24. Silicon substrate; 25. Cavity; 26. Visible light reflector; 27. Sapphire substrate; 28. Visible light reflector layer. Detailed Implementation
[0036] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.
[0037] See Figure 1-7 This invention proposes a monolithic integrated optocoupler, comprising a visible light LED 1 and a photosensitive VMOSFET 2, both components being fabricated on the same GaN-based epitaxial wafer;
[0038] The visible light LED 1 serves as a light emitter, used to convert electrical signals into light signals.
[0039] The photosensitive VMOSFET 2 serves as a light receiver, used to convert light signals into electrical signals.
[0040] In this embodiment, the monolithic integrated optocoupler uses a GaN-based epitaxial wafer; the epitaxial materials used in this invention, from bottom to top, are substrate material 3, AlN 4, AlGaN 5, N-type GaN 6, InGaN / GaN multiple quantum well 7, and P-type GaN 8; substrate material 3 can be silicon or sapphire.
[0041] The visible light LED 1 and the photosensitive VMOSFET 2 are located on the same substrate and are physically and electrically separated by an isolation trench.
[0042] In this embodiment, when silicon is selected as the substrate material 3, the visible light LED 1 is arranged below the positive electrode as follows: a P-type GaN layer 9, a multiple quantum well layer 10, a first N-type GaN layer 11, a first AlGaN layer 12, and a first AlN layer 13; the negative electrode 14 is in direct contact with the first N-type GaN layer 11, and the contact type is ohmic contact; the positive electrode 15 is located on the side closer to the photosensitive VMOSFET 2, and the negative electrode 14 is located on the side farther away from the photosensitive VMOSFET 2;
[0043] The photosensitive VMOSFET 2 includes three electrodes: a source 16, a drain 17, and a gate 18, with the gate 18 located between the source 16 and the drain 17. The source 16 is connected to the second N-type GaN layer 19, and the drain 17 is connected to the third N-type GaN layer 20. The epitaxial layers below the second N-type GaN layer 19 and the third N-type GaN layer 20 are, in sequence, a second AlGaN layer 21 and a second AlN layer 22.
[0044] The photosensitive VMOSFET 2 has a V-shaped channel, with the bottom of the V-shape located inside the second AlGaN layer 21. A gate dielectric layer 23 covers the V-shaped channel, and the gate 18 is located above the gate dielectric layer 23. To prevent the silicon substrate 24 from absorbing light, the silicon substrate 24 below the visible light LED 1 and the photosensitive VMOSFET 2 is partially hollowed out to form a suspended thin film structure, and a cavity 25 is formed below the thin film structure. To increase the optical coupling path from the visible light LED 1 to the photosensitive VMOSFET 2, the back silicon substrate 24 is bonded to the visible light reflector 26.
[0045] In this embodiment, when sapphire is selected as the substrate material 3, the visible light LED 1 is arranged below the positive electrode as follows: a P-type GaN layer 9, a multi-quantum well layer 10, a first N-type GaN layer 11, a first AlGaN layer 12 and a first AlN layer 13, a sapphire substrate 27 and a visible light reflective layer 28; the negative electrode 14 is in direct contact with the first N-type GaN layer 11, and the contact type is ohmic contact; the positive electrode 15 is located on the side closer to the photosensitive VMOSFET 2, and the negative electrode 14 is located on the side farther away from the photosensitive VMOSFET 2;
[0046] In this embodiment, the photosensitive VMOSFET 2 includes three electrodes: a source 16, a drain 17, and a gate 18, with the gate 18 located between the source 16 and the drain 17. The source 16 is connected to the second N-type GaN layer 19, and the drain 17 is connected to the third N-type GaN layer 20. Below the second N-type GaN layer 19 and the third N-type GaN layer 20 are, in sequence, a second AlGaN layer 21, a second AlN layer 22, a sapphire substrate 27, and a visible light reflective layer 28. The channel shape of the photosensitive VMOSFET 2 is V-shaped, with the bottom of the V-shape located inside the second AlGaN layer 21. A gate dielectric layer 23 covers the V-shaped channel, and the gate 18 is located above the gate dielectric layer 23. To increase the optical coupling path from the visible light LED 1 to the photosensitive VMOSFET 2, a visible light reflective layer 28 is covered on the sapphire substrate 27 on the back side. Specifically, a metal Ag reflective layer or a distributed Bragg reflective layer can be selected.
[0047] In this embodiment, the positive electrode 15 of the visible light LED 1 is made of the same material as the gate 18 of the photosensitive VMOSFET 2, which can be an alloy material such as Ni / Au, and has an ohmic contact with the P-type GaN; the negative electrode 14 of the visible light LED is made of the same material as the source 16 and drain 17 of the photosensitive VMOSFET 2, which can be an alloy material such as Ti / Al, and has an ohmic contact with the N-type GaN.
[0048] The photosensitive VMOSFET 2 utilizes the difference in doping concentration and band gap between N-type GaN and AlGaN to achieve enhancement-mode operation, meaning that a positive voltage needs to be applied to the gate to turn on the channel.
[0049] The working principle of this invention is as follows: An input electrical signal is applied to the two electrodes of the visible light LED 1. The visible light LED 1 converts the input electrical signal into an output optical signal. The output optical signal is coupled to the trench of the photosensitive VMOSFET 2, causing an increase in the channel conductivity, thereby increasing the output current of the photosensitive VMOSFET 2. The strength of the electrical signal applied across the visible light LED 1 can be deduced from the change in output current, and the waveform of the output current is basically consistent with the waveform of the input electrical signal. Therefore, the entire chip system can realize the conversion between electricity and light and electricity from input to output. With the help of the optical path, the input and output signals are electrically isolated.
[0050] The present invention provides a method for fabricating a monolithic integrated optocoupler as follows:
[0051] Step 1: Coat a layer of photoresist on the GaN-based epitaxial wafer and perform photolithography to expose the P-type GaN layer region to be etched. Then perform ICP dry etching until the N-type GaN layer is reached.
[0052] Step 2: Coat a layer of photoresist and perform photolithography to expose the area where the isolation trench needs to be made. Then perform ICP dry etching until the substrate is reached.
[0053] Step 3: Coat a layer of photoresist and perform photolithography to expose the etching window of the VMOSFET 2 channel region. Then perform ICP dry etching to form a V-shaped trench. The bottom of the V-shaped trench is located inside the second AlGaN layer 21. Then smooth the sidewalls of the V-shaped trench.
[0054] Step 4: A high-quality gate dielectric layer 23 is grown by plasma-enhanced chemical vapor deposition (PECVD) or atomic layer deposition (ALD) and etched into shape after photolithography;
[0055] Step 5: Coat a layer of photoresist, and use photolithography to remove the photoresist above the source 16 and drain 17 of the photosensitive VMOSFET and the negative electrode 14 of the visible light LED1;
[0056] Step 6: Electron beam evaporates the metal electrode material, removes the photoresist and the metal layer on the photoresist, and peels off the source 16 and drain 17 of the photosensitive VMOSFET and the negative electrode of the visible light LED.
[0057] Step 7: Apply a layer of photoresist, and use photolithography to remove the photoresist above the gate 18 of the photosensitive VMOSFET 2 and the positive electrode 15 of the visible light LED 1;
[0058] Step 8: Electron beam evaporates the metal electrode material, removes the photoresist and the metal layer on the photoresist, and peels off the gate 18 of the photosensitive VMOSFET 2 and the positive electrode 15 of the visible light LED 1;
[0059] Step 9: When silicon is selected as the substrate material 3, the silicon substrate 24 under the visible light LED 1 and the photosensitive VMOSFET 2 is removed by deep reactive silicon ion etching (DRIE), and the silicon substrate 24 around the device is retained as a support to form a suspended thin film structure. Then the back of the device is bonded to the visible light reflector 26 to obtain a monolithic integrated optocoupler.
[0060] When sapphire is selected as the substrate material 3, a layer of metallic Ag or a distributed Bragg reflector layer is deposited on the bottom of the sapphire substrate 27.
[0061] The criteria for distinguishing whether it is this structure are as follows: This invention discloses a monolithic integrated optocoupler, comprising a visible light LED 1 and a photosensitive VMOSFET 2. Both components are fabricated on the same GaN-based epitaxial wafer. The epitaxial materials, from bottom to top, are substrate material 3, AlN 4, AlGaN 5, N-type GaN 6, InGaN / GaN multiple quantum well 7, and P-type GaN 8. The positive electrode 15 of the visible light LED is located near the photosensitive VMOSFET 2 and is physically separated by an isolation trench. The negative electrode 14 is located away from the photosensitive VMOSFET 2. The source 16 and drain 17 of the photosensitive VMOSFET 2 are in direct contact with the first N-type GaN layer 11. The channel shape of the photosensitive VMOSFET 2 is V-shaped, with the bottom of the V-shape located inside the second AlGaN layer 21. A gate dielectric layer 23 covers the V-shaped channel, and the gate 18 is located above the gate dielectric layer 23. To increase the size of the visible light LED... The optical coupling from the visible light LED 1 to the photosensitive VMOSFET 2 channel is such that when the substrate material 3 is silicon, the silicon substrate 24 below the visible light LED 1 and the photosensitive VMOSFET 2 is partially hollowed out to form a suspended thin film structure, and the back silicon substrate 24 is bonded to a visible light reflector 26. When the substrate material is sapphire, a visible light reflector layer 28 is covered on the back sapphire substrate 27.
[0062] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A monolithic integrated optocoupler, characterized in that, It includes a visible light LED (1) and a photosensitive VMOSFET (2) disposed on the same GaN-based epitaxial wafer; The visible light LED (1) serves as a light emitter to convert electrical signals into light signals. The visible light LED (1) and the photosensitive VMOSFET (2) are located on the same substrate and are physically and electrically separated by an isolation trench. Below the positive electrode (15) of the visible light LED (1) are, in sequence, a P-type GaN layer (9), a multi-quantum well layer (10), a first N-type GaN layer (11), a first AlGaN layer (12), and a first AlN layer (13); the negative electrode (14) of the visible light LED (1) is in direct contact with the first N-type GaN layer (11), the positive electrode (15) is located on the side closer to the photosensitive VMOSFET (2), and the negative electrode (14) is located on the side farther away from the photosensitive VMOSFET (2); The photosensitive VMOSFET (2) includes a source (16), a drain (17), a gate (18), a second N-type GaN layer (19), and a third N-type GaN layer (20). The gate (18) is located between the source (16) and the drain (17). The source (16) is connected to the second N-type GaN layer (19), and the drain (17) is connected to the third N-type GaN layer (20). The epitaxial layers below the second N-type GaN layer (19) and the third N-type GaN layer (20) are respectively provided with a second AlGaN layer (21), a second AlN layer (22), a substrate (27), and a visible light reflective layer. The photosensitive VMOSFET (2) has a V-shaped channel with the bottom of the V-shape located inside the second AlGaN layer (21). A gate dielectric layer (23) covers the V-shaped channel, and the gate dielectric layer (23) is located above the gate (18).
2. The monolithic integrated optocoupler according to claim 1, characterized in that, The GaN-based epitaxial wafer comprises, from bottom to top, a substrate material (3), AlN (4), AlGaN (5), N-type GaN (6), GaN multiple quantum wells (7), and P-type GaN (8).
3. The monolithic integrated optocoupler according to claim 1, characterized in that, The visible light reflective layer (28) is selected as a metallic Ag reflective layer or a distributed Bragg reflective layer.
4. The monolithic integrated optocoupler according to claim 1, characterized in that, A silicon substrate (24) is provided below the visible light LED 1 and the photosensitive VMOSFET (2). The center of the silicon substrate (24) is hollowed out to form a suspended thin film structure and a cavity (25) is formed below the thin film structure. The silicon substrate (24) is bonded to the visible light reflector.
5. A method for fabricating a monolithic integrated optocoupler according to any one of claims 1-4, characterized in that, The method includes: A layer of photoresist is coated on a GaN-based epitaxial wafer and photolithography is performed to expose the P-type GaN layer region that needs to be etched. Then, ICP dry etching is performed until the N-type GaN layer is reached and then stopped. Then, a layer of photoresist is coated and photolithography is performed to expose the area where the isolation trench needs to be made. Next, ICP dry etching is performed until the substrate is reached. A layer of photoresist is coated and photolithography is performed to expose the etching window of the photosensitive VMOSFET channel region. Then, ICP dry etching is performed to form a V-shaped trench. The bottom of the V-shaped trench is located inside the second AlGaN layer. Then, the sidewalls of the V-shaped trench are smoothed. A high-quality gate dielectric layer is grown by plasma-enhanced chemical vapor deposition or atomic layer deposition and etched into shape after photolithography. A layer of photoresist is coated, and the photoresist on the source and drain of the photosensitive VMOSFET and the negative electrode of the visible light LED is removed by photolithography. Remove the photoresist and the metal layer on the photoresist, and strip to form the source and drain of the photosensitive VMOSFET and the negative electrode of the visible light LED; A layer of photoresist is coated, and the photoresist on the gate of the photosensitive VMOSFET and the positive electrode of the visible light LED is removed by photolithography. Remove the photoresist and the metal layer on the photoresist, and strip to form the gate of the photosensitive VMOSFET and the positive electrode of the visible light LED; The silicon substrate beneath the visible light LED and photosensitive VMOSFET is removed, while the silicon substrate around the device is retained as a support to form a suspended thin film structure. Then, the back of the device is bonded to a visible light reflector to form a monolithic integrated optocoupler.