A photodetector integrating linear mode and Geiger mode and its working method

Abstract

The present invention provides a photodetector integrating linear mode and Geiger mode and a working method thereof, which includes a Geiger mode detector chip located in the upper layer and a linear mode detector chip located in the lower layer. The Geiger mode detector chip and the linear mode detector chip are bonded and integrated through flip-chip bonding in the N electrode region; the Geiger mode detector chip uses a multi-element photon counter MPPC, and the linear mode detector chip uses a large photosensitive area avalanche photodiode LAAPD. Through the detection process itself, different working modes are adaptively selected, and the respective advantages of different working modes are utilized to eliminate the "time blind area" and "space blind area" while optimizing resource consumption and system efficiency as much as possible.

Description

Technical Field

[0001] The present invention relates to the technical field of optoelectronic detection, and particularly to an optoelectronic detector integrating linear mode and Geiger mode and its working method. Background Art

[0002] Time-of-flight (ToF) imaging sensor chips operating in Geiger mode, such as single-photon avalanche diode (SPAD) arrays and multi-pixel photon counters (MPPC or SiPM), are a rapidly emerging optoelectronic imaging technology. Due to the strict limitation of the transmitting end power by regulations related to eye safety, compared with the relatively short detection distance of traditional linear-mode avalanche photodiodes (APD), the greatest advantage of these Geiger-mode sensors lies in their ability to quickly generate depth images of the environment at relatively long distances by utilizing their single-photon-level detection sensitivity. Therefore, such low-light sensors are considered a key enabling technology for future autonomous driving systems.

[0003] However, while the self-sustaining avalanche unique to the Geiger mode brings high gain and high sensitivity, it also introduces a recovery time at the nanosecond level (measured data from Hamamatsu: the recovery time required for a SPAD with a photosensitive surface size of 10μm is 10ns, and the duration is proportional to the photosensitive surface size). This greatly limits the time resolution of SAPDs, that is, the ability to capture and track fast-moving objects. This defect has been alleviated by the gradual application of SiPMs, but the "time blind zone" remains at the same order of magnitude and there is no fundamental improvement. In addition, the continuous input of strong light from high-reflectivity objects at close range causes the Geiger-mode sensor to be transiently filled and thus unable to be used, and the detection times of the transmitted and returned light are too close, which also makes it impossible for SPADs to distinguish signal light from stray light, resulting in signal distortion. These introduced "space blind zones" will also pose a great safety hazard for application scenarios with frequent emergencies. In reality, autonomous driving usually employs a detection scheme integrating multiple sensors to ensure its safety redundancy, so this has to sacrifice a certain volume, spatial arrangement, energy consumption, and system solution efficiency, etc.

[0004] In view of this, the present invention proposes an optoelectronic detector integrating linear mode and Geiger mode and its working method. Summary of the Invention

[0005] The object of the present invention is to propose a high-dynamic-range detector integrating linear mode and Geiger mode; through the detection process itself, adaptively select different working modes, utilize the respective advantages of different working modes, and while eliminating the "time blind zone" and "space blind zone", optimize the resource consumption and system efficiency as much as possible.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] An optoelectronic detector integrating linear mode and Geiger mode, comprising a Geiger mode detector chip located in the upper layer and a linear mode detector chip located in the lower layer. The Geiger mode detector chip and the linear mode detector chip are bonded and integrated through flip-chip bonding in the N electrode region. The Geiger mode detector chip uses a multi-element photon counter MPPC, and the linear mode detector chip uses a large photosensitive area avalanche photodiode LAAPD.

[0008] Preferably, both the multi-element photon counter MPPC and the large photosensitive area avalanche photodiode LAAPD are of InGaAs / InP material system. The absorption layer thickness of the multi-element photon counter MPPC is 0.5 - 1.5 μm, and the absorption layer thickness of the large photosensitive area avalanche photodiode LAAPD is 2 - 4 μm.

[0009] Preferably, the N electrode metal of the multi-element photon counter MPPC and the large photosensitive area avalanche photodiode LAAPD is a multi-layer metal structure, and the multi-layer metal structure includes Ti / Pt / Au, Ni / Pt / Au or AuGe / Ni / Au. Among them, Ti / Pt / Au means the bottom layer metal is Ti, the middle layer metal is Pt, and the outer layer metal is Au; Ni / Pt / Au means the bottom layer metal is Ni, the middle layer metal is Pt, and the outer layer metal is Au; AuGe / Ni / Au means the bottom layer metal is AuGe, the middle layer metal is Ni, and the outer layer metal is Au.

[0010] Preferably, the preparation method of the optoelectronic detector includes:

[0011] S1. Prepare two kinds of chips, namely the multi-element photon counter MPPC and the large photosensitive area avalanche photodiode LAAPD respectively.

[0012] S2. According to the selected integration method, prepare the under-bump metal layer UBM on the N electrode regions of the two kinds of chips by evaporation or sputtering respectively, and perform photolithography, indium pillar evaporation and stripping on the surfaces of the under-bump metal layers UBM of the two kinds of chips respectively to complete the preparation of the indium pillars.

[0013] S3. Perform dicing on the wafer-level multi-element photon counter MPPC and the large photosensitive area avalanche photodiode LAAPD after the indium pillar arrays are prepared, and perform appearance inspection and screening on the diced chips. Then, bond the selected qualified MPPC chips and LAAPD chips through indium pillars by flip-chip bonding.

[0014] S4. Lead out signal leads to the ceramic base at the electrodes, and inject and cure optical glue in the gap between the two kinds of chips.

[0015] S5. According to the selected integration method, a microlens array is separately fabricated to align and mount the multi-element photon counter MPPC using the microlens array.

[0016] Preferably, the integration method includes a face-to-face integration method and a stack-up integration method;

[0017] In the face-to-face integration method, both the multi-element photon counter MPPC and the large photosensitive area avalanche photodiode LAAPD adopt coplanar electrodes, and the two chips are integrated in a face-to-face manner with the N electrode regions;

[0018] In the stack-up integration method, the multi-element photon counter MPPC adopts non-coplanar electrodes, the large photosensitive area avalanche photodiode LAAPD adopts coplanar electrodes, and the two chips are integrated in a face-to-face manner with the N electrode regions.

[0019] Preferably, the height of the indium pillar is 4 - 10 μm, and the diameter of the indium pillar is 8 - 15 μm.

[0020] Preferably, S5 is specifically as follows: when the selected integration method is the stack-up integration method, a microlens array is separately fabricated, and the microlens array is moved by a suction nozzle until the geometric center of the photosensitive surface of each pixel of the multi-element photon counter MPPC coincides with the crown of each lens, and then the gap between the microlens array and the device is filled and reinforced with an insulating optical adhesive.

[0021] Preferably, the microlens array is replaced with a diffraction grating or a photonic crystal lens to align and mount the multi-element photon counter MPPC.

[0022] Preferably, the microlens array is fabricated based on a wide-bandgap material substrate through a process flow including thinning, double-sided polishing, photolithography, hot melt reflow, etching, and optical antireflection coating, and the wide-bandgap material substrate includes an InP substrate or a GaP substrate.

[0023] A working method of an optoelectronic detector integrating linear mode and Geiger mode, the method is specifically as follows:

[0024] The optical signal is first received by the upper multi-element photon counter MPPC;

[0025] If the optical signal is a weak optical signal reflected back from a long distance, it is received by the multi-element photon counter MPPC and converted into an electrical analog signal, and directly sent to an amplifier circuit for subsequent processing, and will not be received by the lower large photosensitive area avalanche photodiode LAAPD;

[0026] If the optical signal is a strong light signal reflected back at a short distance, after the multi-element photon counter MPPC receives it, multiple pixels enter the dead time zone. When the amplitude of the superimposed signal generated reaches a preset value, the lower-layer large photosensitive area avalanche photodiode LAAPD is triggered to start working, and the multi-element photon counter MPPC stops working, completing the switching of the strong light detection mode; the remaining strong light energy that penetrates the upper-layer multi-element photon counter MPPC is absorbed by the absorption layer of the lower-layer large photosensitive area avalanche photodiode LAAPD;

[0027] The large photosensitive area avalanche photodiode LAAPD operates in the linear region to track high-speed moving targets that produce short-distance reflections, so as to eliminate blind spots;

[0028] When the large photosensitive area avalanche photodiode LAAPD does not detect a strong light signal, the upper-layer MPPC is triggered to start working again, completing the switching of the weak light detection mode.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] Through the detection process itself, the present invention adaptively selects different working modes, utilizes the respective advantages of different working modes, eliminates the "time blind spot" and "space blind spot" while optimizing resource consumption and system efficiency as much as possible. Compared with the single-mode detector applications in the prior art, the present application can eliminate blind spots; compared with the fusion schemes of multiple detectors in the prior art, the present application can save space and energy consumption and has a higher system efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a photodetector integrating the linear mode and Geiger mode in a face-to-face integration manner according to the present invention;

[0032] Figure 2 It is a photodetector integrating the linear mode and Geiger mode in a stacked integration manner according to the present invention;

[0033] Figure 3 It is a flowchart of the preparation method of the photodetector integrating the linear mode and Geiger mode according to the present invention;

[0034] Figure 4 It is a schematic diagram of the adaptive working principle for eliminating blind spots according to the present invention.

[0035] In the figure, 1 - multi-element photon counter MPPC; 2 - large photosensitive area avalanche photodiode LAAPD; 3 - N electrode region of MPPC; 4 - N electrode region of LAAPD; 5 - first signal; 6 - common N-pole signal; 7 - second signal; 8 - microlens array. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The following combines the attached Figures 1-4, a specific description of the technical solution of the present invention will be given.

[0037] The present invention proposes a photodetector integrating linear mode and Geiger mode. Referring to the attached Figures 1-2 , it includes a Geiger mode detector chip located in the upper layer and a linear mode detector chip located in the lower layer. The Geiger mode detector chip and the linear mode detector chip are bonded and integrated by flip-chip bonding in the N electrode region; the Geiger mode detector chip uses a multi-element photon counter MPPC 1, and the linear mode detector chip uses a large photosensitive area avalanche photodiode LAAPD 2.

[0038] In this embodiment, both the multi-element photon counter MPPC 1 and the large photosensitive area avalanche photodiode LAAPD 2 are of InGaAs / InP material system; the absorption layer thickness of the multi-element photon counter MPPC1 is 0.5 - 1.5 μm, and the absorption layer thickness of the large photosensitive area avalanche photodiode LAAPD 2 is 2 - 4 μm.

[0039] In this embodiment, the N electrode metal of the multi-element photon counter MPPC 1 and the large photosensitive area avalanche photodiode LAAPD 2 is a multi-layer metal structure, and the multi-layer metal structure includes Ti / Pt / Au, Ni / Pt / Au or AuGe / Ni / Au. Among them, Ti / Pt / Au means the bottom layer metal is Ti, the middle layer metal is Pt, and the outer layer metal is Au; Ni / Pt / Au means the bottom layer metal is Ni, the middle layer metal is Pt, and the outer layer metal is Au; AuGe / Ni / Au means the bottom layer metal is AuGe, the middle layer metal is Ni, and the outer layer metal is Au.

[0040] In this embodiment, the preparation method of the photodetector includes:

[0041] S1. Prepare two types of chips, namely a multi-element photon counter MPPC and a large photosensitive area avalanche photodiode LAAPD, respectively;

[0042] S2. According to the selected integration method, prepare an under-bump metal layer UBM in the N electrode region 3 of the multi-element photon counter MPPC and the N electrode region 4 of the large photosensitive area avalanche photodiode LAAPD by evaporation or sputtering respectively, and perform photolithography, indium pillar evaporation and stripping on the surface of the under-bump metal layer UBM of the two chips respectively to complete the preparation of the indium pillars;

[0043] S3. Perform dicing (dicing is a standard process in the industry and will not be elaborated here) on the wafer-level multi-element photon counter MPPC and the large photosensitive area avalanche photodiode LAAPD after the indium pillar array is prepared, and perform appearance inspection and screening on the diced chips. Then, flip-chip bond the selected qualified MPPC chips and LAAPD chips through indium pillars.

[0044] S4. Lead signal leads to the ceramic base at the electrodes, and inject and cure optical glue into the gap between the two chips; the signal leads include the first signal 5, the common N-pole signal 6, and the second signal 7.

[0045] S5. According to the selected integration method, separately fabricate a microlens array 8 for aligning and mounting the multi-element photon counter MPPC using the microlens array 8.

[0046] In this embodiment, the integration methods include the face-to-face integration method and the stacked integration method.

[0047] In the face-to-face integration method, both the multi-element photon counter MPPC and the large photosensitive area avalanche photodiode LAAPD use coplanar electrodes, and the two chips are integrated in a face-to-face manner with the N-electrode regions.

[0048] In the stacked integration method, the multi-element photon counter MPPC uses non-coplanar electrodes, the large photosensitive area avalanche photodiode LAAPD uses coplanar electrodes, and the two chips are integrated in a face-to-face manner with the N-electrode regions.

[0049] In this embodiment, the height of the indium pillar is 4 - 10 μm, and the diameter of the indium pillar is 8 - 15 μm; for good flip-chip bonding.

[0050] In this embodiment, if Figure 1 the face-to-face integration method can use the integrated one-piece microlens array on the MPPC substrate to expand the effective light-receiving area, then no additional independent microlens array is required; otherwise, if Figure 2 the stacked integration method requires adding an independent microlens array 8 to expand the effective light-receiving area. Therefore, S5 is specifically: when the selected integration method is the stacked integration method, separately fabricate the microlens array 8, and use a suction nozzle to move the microlens array 8 so that the geometric center of the photosensitive surface of each lens crown coincides with the geometric center of each pixel (cell) of the multi-element photon counter MPPC, and then fill and reinforce the gap between the microlens array 8 and the device with insulating optical glue. This step can be completed using a standard flip-chip bonding device.

[0051] In this embodiment, the microlens array 8 is replaced with a diffraction grating or a photonic crystal lens for aligning and mounting the multi-element photon counter MPPC.

[0052] In this embodiment, the microlens array 8 is fabricated based on a wide-bandgap material substrate wafer through a process flow including thinning, double-sided polishing, photolithography, hot melt reflow, etching, and optical antireflection coating. The wide-bandgap material substrate wafer includes an InP substrate wafer or a GaP substrate wafer.

[0053] The present invention also provides a working method for a photodetector integrating linear mode and Geiger mode. Specifically, the method is as follows:

[0054] The optical signal is first received by the upper-layer multi-photon counter MPPC.

[0055] If the optical signal is a weak optical signal reflected from a long distance, it is fully received by the multi-photon counter MPPC and converted into an electrical analog signal, which is directly sent to the amplifier circuit for subsequent processing without being received by the lower-layer large photosensitive area avalanche photodiode LAAPD.

[0056] If the optical signal is a strong optical signal reflected from a short distance, after being received by the multi-photon counter MPPC, multiple pixels enter the dead time zone. When the superimposed signal amplitude generated reaches a preset value, it triggers the lower-layer large photosensitive area avalanche photodiode LAAPD to start working, and the multi-photon counter MPPC stops working. The system preferentially processes potential near-range hazards, and the strong light detection mode switching is completed. Optionally, the transmitter can correspondingly increase the repetition frequency. Since the relatively thin absorption layer of the upper-layer multi-photon counter MPPC is not sufficient to completely absorb, the remaining strong light energy penetrates and reaches the lower layer, and is finally fully absorbed by the relatively thick absorption layer of the lower-layer large photosensitive area avalanche photodiode LAAPD.

[0057] The LAAPD operates in the linear region and has no recovery time limit, so it can work at a relatively high sampling frequency, thus being capable of tracking high-speed moving targets that produce near-range reflections to eliminate blind spots.

[0058] When the large photosensitive area avalanche photodiode LAAPD does not detect a strong optical signal, it triggers the upper-layer MPPC to start working again, and the weak light detection mode switching is completed.

[0059] The above are the preferred embodiments of the present invention. All changes made according to the technical solutions of the present invention, when the functions and effects generated do not exceed the scope of the technical solutions of the present invention, fall within the protection scope of the present invention.

Claims

1. A photodetector integrating linear mode and Geiger mode, characterized in that: It includes a Geiger mode detector chip located at the upper layer and a linear mode detector chip located at the lower layer, wherein the Geiger mode detector chip and the linear mode detector chip are bonded and integrated by flip-chip bonding in the N-electrode region; the Geiger mode detector chip adopts a multi-element photon counter MPPC, and the linear mode detector chip adopts a large photosensitive surface avalanche photodiode LAAPD; The working method of the photoelectric detector integrating linear mode and Geiger mode is specifically as follows: The optical signal is first received by the upper-layer multi-photon counter MPPC; If the optical signal is a weak light signal reflected from a long distance, it will be received by the multi-photon counter MPPC and converted into an electrical analog signal, and directly sent to the amplifier circuit for subsequent processing, and will not be received by the large photosensitive surface avalanche photodiode LAAPD at the lower layer; If the light signal is a strong light signal reflected from a short distance, after the multi-element photon counter MPPC receives it, multiple pixels enter the dead time zone, and the generated superimposed signal amplitude reaches the preset value, triggering the lower large photosensitive surface avalanche photodiode LAAPD to start working, the multi-element photon counter MPPC stops working, and the strong light detection mode is switched; the remaining strong light energy penetrating the upper multi-element photon counter MPPC is absorbed by the lower large photosensitive surface avalanche photodiode LAAPD absorption layer; The large photosensitive surface avalanche photodiode LAAPD works in the linear region to track high-speed moving targets that produce close-range reflections to eliminate blind spots; When the large photosensitive surface avalanche photodiode LAAPD fails to detect a strong light signal, the upper MPPC is triggered to restart working, and the weak light detection mode is switched.

2. The photodetector integrating linear mode and Geiger mode according to claim 1, characterized in that: The multi-photon counter MPPC and the large photosensitive surface avalanche photodiode LAAPD are both made of InGaAs / InP material system; the absorption layer thickness of the multi-photon counter MPPC is 0.5-1.5 μm, and the absorption layer thickness of the large photosensitive surface avalanche photodiode LAAPD is 2-4 μm.

3. The photodetector integrating linear mode and Geiger mode according to claim 1, characterized in that: The N-electrode metal of the multi-element photon counter MPPC and the large photosensitive surface avalanche photodiode LAAPD is a multi-layer metal structure, and the multi-layer metal structure includes Ti / Pt / Au, Ni / Pt / Au or AuGe / Ni / Au, wherein Ti / Pt / Au means that the bottom metal is Ti, the middle metal is Pt, and the outer metal is Au; Ni / Pt / Au means that the bottom metal is Ni, the middle metal is Pt, and the outer metal is Au; AuGe / Ni / Au means that the bottom metal is AuGe, the middle metal is Ni, and the outer metal is Au.

4. The photodetector integrating linear mode and Geiger mode according to claim 1, characterized in that: The preparation method of the photodetector comprises: S1, prepare two chips, namely, multi-element photon counter MPPC and large photosensitive surface avalanche photodiode LAAPD; S2. According to the selected integration method, an under-ball metal layer (UBM) is prepared by evaporation or sputtering in the N-electrode region of the two chips respectively, and photolithography, indium column evaporation and stripping are performed on the surface of the under-ball metal layer (UBM) of the two chips respectively to complete the preparation of the indium column; S3, the wafer-level multi-element photon counter MPPC and the large photosensitive surface avalanche photodiode LAAPD prepared by the indium pillar array are divided and split respectively, and the appearance of the split chips is inspected and screened, and then the selected qualified MPPC chips and LAAPD chips are flip-chip bonded through the indium pillars; S4, lead the signal lead wire to the ceramic base at the electrode, and inject and cure the optical glue in the gap between the two chips; S5. According to the selected integration method, a microlens array is separately manufactured to align and mount the multi-photon counter MPPC using the microlens array.

5. The photodetector integrating linear mode and Geiger mode according to claim 4, characterized in that: The integration methods include face-to-face integration and stacked integration. In the face-to-face integration method, both the multi-electrode photon counter MPPC and the large photosensitive surface avalanche photodiode LAAPD use coplanar electrodes, and the two chips are integrated in a face-to-face manner with the N-electrode regions; In the stacked integration method, the multi-electrode counter MPPC adopts skew electrodes, the large photosensitive surface avalanche photodiode LAAPD adopts coplanar electrodes, and the two chips are integrated in a face-to-face manner with the N-electrode regions.

6. The photodetector integrating linear mode and Geiger mode according to claim 4, characterized in that: The height of the indium column is 4-10 μm, and the diameter of the indium column is 8-15 μm.

7. The photodetector integrating linear mode and Geiger mode according to claim 4, characterized in that: Specifically, S5 is as follows: when the selected integration method is a stacked integration method, a microlens array is manufactured separately, and a suction nozzle is used to move the microlens array until each lens crown coincides with the geometric center of the photosensitive surface of each pixel of the multi-photon counter MPPC, and then the gap between the microlens array and the device is filled and reinforced with insulating optical glue.

8. The photodetector integrating linear mode and Geiger mode according to claim 7, characterized in that: The microlens array is replaced with a diffraction grating or a photonic crystal lens to align and mount the multi-photon counter MPPC.

9. The photodetector integrating linear mode and Geiger mode according to claim 7, characterized in that: The microlens array is manufactured based on a wide energy band material substrate through a process flow including thinning, double-sided grinding and polishing, photolithography, hot melt reflow, etching, and optical anti-reflection film coating. The wide energy band material substrate includes an InP substrate or a GaP substrate.

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