A photoelectric detector mounting method and system based on Newton rings

Abstract

The present invention discloses a method and system for mounting a photodetector based on Newton's rings, relating to the technical field of photodetector manufacturing. The Newton's ring-based photodetector mounting method includes the following steps: utilizing the Newton's rings formed between a convex lens and the photosensitive surface of the photodetector for alignment, thereby mounting the convex lens on the photodetector. This method achieves low-cost, more convenient, and faster alignment of the convex lens with the center of the photosensitive surface of the photodetector.

Description

Technical Field

[0001] The present invention relates to the technical field of photoelectric detector preparation, and in particular to a photoelectric detector mounting method and system based on Newton rings. Background Art

[0002] Currently, the primary packaging format for photodetectors used in traditional high-speed optical communications or quantum secure communications is a coaxial pigtail package. This type of package typically employs active alignment (also known as active coupling), whereby the peak value of the photoresponse current is used during the coupling process to determine whether the pigtail is aligned with the center of the photosensitive surface.

[0003] However, for the applications of SPAD (Single Photon Avalanche Diode) photodetectors or detection arrays in spatial single-photon detection, such as ranging, quantum imaging, lidar, biomedicine and integrated circuit testing, lens mounting is required to increase the duty cycle. If active alignment is still used to complete the mounting of the lens and the photosensitive surface, there will be more complex modifications to the existing traditional packaging equipment hardware.

[0004] In addition, due to reasons such as the diffusion process, the diffusion morphology of the low-concentration area after two diffusions may not be uniform everywhere, or the edge curvature of the active area may not be ideal. A large alignment bias voltage that has not been optimized may amplify the uneven electric field distribution in the active area, thereby causing alignment failure. If a passive coupling method using alignment marks is used, due to individual differences in lenses, it is difficult to ensure that the crown of the lens perfectly coincides with the geometric center of the photosensitive surface. Summary of the Invention

[0005] In response to the defects in the prior art, the first aspect of the present invention provides a photodetector mounting method based on Newton rings, which has a low implementation cost and can more conveniently and quickly align the convex lens and the center of the photosensitive surface of the photodetector.

[0006] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0007] A method for mounting a photoelectric detector based on Newton rings, the method comprising the following steps:

[0008] The convex lens is mounted on the photodetector by using the Newton rings formed between the convex lens and the photosensitive surface of the photodetector for alignment.

[0009] In some embodiments, the alignment using Newton's rings formed between the convex lens and the photosensitive surface of the photodetector includes:

[0010] irradiating the convex lens with a light source to form Newton rings through the antireflection film on the photosensitive surface;

[0011] The convex lens is moved to align the interference center of the Newton rings with the geometric center of the photosensitive surface.

[0012] In some embodiments, the convex lens is illuminated by a light source provided on a welding machine, and the convex lens is moved by the welding machine;

[0013] The generated Newton's rings are observed using a collection device arranged near the light source to determine whether the interference center of the Newton's rings is aligned with the geometric center of the photosensitive surface.

[0014] In some embodiments, the acquisition device is a camera.

[0015] In some embodiments, the light source is a visible light source with adjustable wavelength.

[0016] In some embodiments, the present invention further comprises:

[0017] By adjusting the distance between the convex lens and the photosensitive surface, the curvature radius of the convex lens, the refractive index of the medium, the wavelength of the incident light wave and / or the thickness of the anti-reflection film, a Newton ring interference morphology that is easy to observe can be selected.

[0018] In some embodiments, the distance between the convex lens and the photosensitive surface is 150 nm, the curvature radius of the convex lens is 1 mm, the refractive index of the medium is 1, the wavelength of the incident light wave is 600 nm, and the thickness of the antireflection film is 0.2 μm.

[0019] A second aspect of the present invention provides a photoelectric detector mounting system based on Newton rings, which has a low implementation cost and can more conveniently and quickly align the convex lens and the center of the photosensitive surface of the photoelectric detector.

[0020] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0021] A photoelectric detector mounting system based on Newton rings, comprising:

[0022] A welding machine, which is used to carry the convex lens and the photodetector to be mounted and can drive the convex lens to move;

[0023] a light source, which is provided on the welding machine and is used to illuminate the convex lens so as to form Newton rings through the photosensitive surface of the photodetector;

[0024] A collection device is provided close to the light source and is used to observe the generated Newton rings.

[0025] In some embodiments, the acquisition device is a camera.

[0026] In some embodiments, the light source is a visible light source with adjustable wavelength.

[0027] Compared with the prior art, the advantages of the present invention are:

[0028] The Newton's ring-based photodetector mounting method disclosed herein utilizes the Newton's rings formed between a convex lens and the photodetector's photosensitive surface for alignment, allowing the convex lens to be mounted on the photodetector. This method is cost-effective and allows for quick and easy alignment of the convex lens with the center of the photodetector's photosensitive surface. It can effectively reduce dark counts caused by a light-delayed avalanche caused by photogenerated carriers being generated outside the active region, thereby improving the performance of SPADs in related applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a flow chart of a method for mounting a photoelectric detector based on Newton rings according to an embodiment of the present invention;

[0030] Figure 2 is a schematic diagram of a Newton's ring forming apparatus;

[0031] Figure 3 It is a Newton's ring figure with a dark spot in the center;

[0032] Figure 4 It is a Newton ring figure with a bright spot in the center;

[0033] Figure 5 It is the cross-section and surface pattern of the photodetector chip. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of this application.

[0035] An embodiment of the present invention discloses a method for mounting a photoelectric detector based on Newton rings, the method comprising the following steps:

[0036] The convex lens is mounted on the photodetector by using the Newton rings formed between the convex lens and the photosensitive surface of the photodetector for alignment.

[0037] The idea of the present invention is to use the Newton rings formed by thin film interference to assist alignment. Figure 1 As shown, it includes the following steps:

[0038] S1. Illuminate the convex lens with a light source to form Newton rings through the antireflection film on the photosensitive surface.

[0039] It is worth mentioning that Newton's rings, also known as "Newton's circles". In optics, Newton's rings are a thin film interference phenomenon. Figure 2 As shown in the figure, a convex lens with a curvature radius of R is placed with the convex surface facing downwards and parallel to a flat glass. When it is illuminated by sunlight or white light, some bright and dark colored rings can be seen; when it is illuminated by monochromatic light almost vertically, some bright and dark monochrome circles appear, such as Figure 3 and Figure 4 shown.

[0040] These circles are spaced at varying distances, becoming narrower as the distance from the center increases. They are interference fringes formed by the interference of light rays transmitted through the sphere and reflected from the plane. When the refractive index of the medium is n, the wedge thickness between the convex lens and the flat plate is d, and the distance between the lens and the flat plate is e, and considering half-wave loss, the optical path difference of the light reflected from the upper and lower surfaces of the dielectric film is:

[0041]

[0042] Among them, when Δ=kλ(k=1,2,3,...), the interference is enhanced and bright fringes are formed; when When , the interference weakens and dark fringes are formed. Figure 2 The geometric relationship The radius of the k-level (k=1, 2, 3, ...) bright ring can be calculated as:

[0043]

[0044] The radius of the k-level (k=1,2,3,...) dark ring is:

[0045]

[0046] At a certain point P, the intensity distribution of two equal-amplitude coherent lights after superposition is:

[0047]

[0048] It can be seen that the interference result is related to the curvature radius R of the lens, the refractive index n of the medium, the wavelength λ of the incident light wave and the thickness of the air film (d+e):

[0049] When (k=1,2,3,...) the film thickness is:

[0050]

[0051] When , the center of Newton's rings should be a bright spot;

[0052] When (k=1,2,3,...) the film thickness is:

[0053]

[0054] In either case, the center of the interference pattern is the lowest point on the convex lens surface.

[0055] S2. Move the convex lens to align the interference center of the Newton rings with the geometric center of the photosensitive surface.

[0056] After the Newton rings are formed in step S1, the interference center of the Newton rings can be aligned with the geometric center of the photosensitive surface by moving the convex lens.

[0057] In a specific implementation, a convex lens can be illuminated by a light source installed on a welding machine, and the convex lens can be moved by the welding machine. Then, a collection device installed near the light source can be used to observe the generated Newton's rings and determine whether the interference center of the Newton's rings is aligned with the geometric center of the photosensitive surface. Preferably, the collection device can be a camera.

[0058] That is, when installing the convex lens, place the coupling welding machine directly above the photodetector near the observation camera and install a light source. The light is then emitted perpendicular to the surface, and the Newton's rings formed by the interference of the light through the lens are observed. At the same time, the distance between the convex lens and the photosensitive surface, the radius of curvature of the convex lens, the refractive index of the medium, the wavelength of the incident light wave, and / or the thickness of the anti-reflection film are adjusted to select the Newton's ring interference morphology that is easy to observe. Adjust the position of the convex lens so that the center of the Newton's ring interference coincides with the center of the photosensitive surface and the ring shape is standard. This completes the alignment of the lens and the center of the photodetector.

[0059] It is worth noting that for SPADs, the dark count rate under the premise of meeting a certain PDE is the core indicator of single-photon performance, which determines the degree of extractability of single-photon avalanche signals. Therefore, reducing the dark count rate is a key technology for achieving high-performance SPADs. Once the lens coupling deviation is large, in addition to causing a decrease in coupling efficiency and thus affecting the PDE under the same overbias, it will also introduce a charge persistence effect. That is, after photogenerated carriers are generated in areas outside the depletion region of the absorption layer, the longitudinal electric field components in these areas are insufficient, resulting in the carriers being unable to immediately cross the valence band step at the InGaAs / InP material interface. Instead, under the action of the transverse electric field components, they drift laterally for a certain period of time to reach the depletion region and cause an avalanche. This delayed lightless avalanche will greatly increase the probability of SPAD triggering false counts in applications.

[0060] In the present invention, the Newton rings formed between the convex lens and the photosensitive surface of the photodetector are used for alignment to ensure that the geometric centers of the lens and the photosensitive surface are perfectly aligned, which is also the key to improving the single-photon performance of SPAD photoelectric detection devices and detection arrays in related applications.

[0061] The following is a specific example:

[0062] See also Figure 5 Figure 2 shows a cross-section and surface pattern of a photodetector chip. Metal refers to the P-type contact metal ring surrounding the photosensitive surface of a front-illuminated SPAD. P-Pad refers to the metal pad extending from the metal ring to facilitate bonding and packaging. Together, they form the anode of the SPAD.

[0063] The existing photosensitive surface size is Φ80μm, the P-type contact metal ring width is 10μm, the P-type Pad metal thickness is 0.3μm, the anti-reflection film thickness is 0.2μm, and the passivation film thickness is 0.5μm; the medium (air) refractive index n=1, the curvature radius R=1mm, the light source wavelength λ=600nm, and the distance between the lens and the photodetector plane e=150nm (i.e. λ / 4).

[0064] According to formula (5), the center of the Newton rings is a bright spot. According to formula (3), the radius of the k-level dark ring, r = sqrt(2k-1)*17.32μm. When k = 3, r ≈ 38.73μm, which is close to the radius of the photosensitive surface (40μm). At this time, the edge of the photosensitive surface is partially covered by the metal ring, so it is necessary to calculate whether the part of the metal ring that protrudes above the photosensitive surface has contacted the lens surface. According to formula (1), when k = 3, (e + d) = 1.5λ = 900nm, which is much larger than the 300nm raised by the metal ring. At this time, d = 750nm and e = 150nm. Therefore, this alignment scheme is feasible.

[0065] Furthermore, the metal ring body is 100 nm higher than the photosensitive surface, and accordingly, the radius r of the k = 4 dark ring in this local area is expanded to approximately 48 μm, close to the 50 μm radius of the metal ring's outer ring, thus also being used for alignment. The interference pattern on the metal pad is negligible.

[0066] In summary, the Newton's ring-based photodetector mounting method of the present invention utilizes the Newton's rings formed between a convex lens and the photosensitive surface of a photodetector for alignment, thereby mounting the convex lens to the photodetector. This method is cost-effective and allows for more convenient and rapid alignment of the convex lens with the center of the photosensitive surface of the photodetector. It can effectively reduce dark counts caused by the delayed avalanche of light when photogenerated carriers are generated at the periphery of the active region, thereby improving the performance of SPADs in related applications.

[0067] An embodiment of the present invention further provides a photoelectric detector mounting system based on Newton rings, which includes a welding machine, a light source and an acquisition device.

[0068] The welding machine is used to carry the convex lens and photodetector to be mounted and can drive the convex lens to move. A light source is mounted on the welding machine to illuminate the convex lens, thereby forming Newton rings on the photosensitive surface of the photodetector. A collection device is located near the light source to observe the generated Newton rings.

[0069] In some embodiments, the acquisition device is a camera.

[0070] In some embodiments, the light source is a visible light source with adjustable wavelength.

[0071] In summary, the Newton ring-based photodetector mounting system of the present invention includes a welding machine, a light source and a collection device. The welding machine is used to carry the convex lens and the photodetector to be mounted, and can drive the convex lens to move. The light source is arranged on the welding machine, and is used to illuminate the convex lens to form Newton rings through the photosensitive surface of the photodetector. The collection device is arranged close to the light source, and is used to observe the generated Newton rings. It uses the Newton rings formed between the convex lens and the photosensitive surface of the photodetector for alignment to mount the convex lens on the photodetector, which has a low cost and can more conveniently and quickly align the convex lens and the center of the photosensitive surface of the photodetector. It can effectively reduce the dark counts caused by the lightless delay avalanche caused by the generation position of photogenerated carriers at the periphery of the active area, thereby improving the performance of SPAD in related applications.

[0072] The above are only specific implementations of the embodiments of the present invention, but the scope of protection of the embodiments of the present invention is not limited to them. Any person skilled in the art can easily conceive of various equivalent modifications or replacements within the technical scope disclosed in the embodiments of the present invention, and such modifications or replacements should be included in the scope of protection of the embodiments of the present invention. Therefore, the scope of protection of the embodiments of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for mounting a photoelectric detector based on Newton rings, characterized in that: The method comprises the following steps: The convex lens is mounted on the photodetector by using the Newton rings formed between the convex lens and the photosensitive surface of the photodetector for alignment; The alignment using Newton's rings formed between the convex lens and the photosensitive surface of the photodetector includes: irradiating the convex lens with a light source to form Newton rings through the antireflection film on the photosensitive surface; The convex lens is moved to align the interference center of the Newton rings with the geometric center of the photosensitive surface.

2. The method for mounting a photoelectric detector based on Newton rings according to claim 1, wherein: The convex lens is illuminated by a light source provided on the welding machine, and the convex lens is moved by the welding machine; The generated Newton's rings are observed using a collection device arranged near the light source to determine whether the interference center of the Newton's rings is aligned with the geometric center of the photosensitive surface.

3. The method for mounting a photoelectric detector based on Newton rings according to claim 2, wherein: The acquisition device is a camera.

4. A method for mounting a photoelectric detector based on Newton rings according to claim 1 or 2, characterized in that: The light source is a visible light source with adjustable wavelength.

5. The method for mounting a photoelectric detector based on Newton rings according to claim 4, characterized in that: Also includes: By adjusting the distance between the convex lens and the photosensitive surface, the curvature radius of the convex lens, the refractive index of the medium, the wavelength of the incident light wave and / or the thickness of the anti-reflection film, a Newton ring interference morphology that is easy to observe can be selected.

6. The method for mounting a photoelectric detector based on Newton rings according to claim 5, characterized in that: The distance between the convex lens and the photosensitive surface is 150 nm, the curvature radius of the convex lens is 1 mm, the refractive index of the medium is 1, the wavelength of the incident light wave is 600 nm, and the thickness of the antireflection film is 0.2 μm.

7. A photoelectric detector mounting system based on Newton rings, characterized in that: include: A welding machine, which is used to carry the convex lens and the photodetector to be mounted and can drive the convex lens to move; a light source, which is provided on the welding machine and is used to illuminate the convex lens so as to form Newton rings through the photosensitive surface of the photodetector; A collection device is provided close to the light source and is used to observe the generated Newton rings.

8. The Newton ring-based photoelectric detector mounting system according to claim 7, characterized in that: The acquisition device is a camera.

9. The Newton ring-based photoelectric detector mounting system according to claim 7, characterized in that: The light source is a visible light source with adjustable wavelength.

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