Strong microcavity resonance enhanced infrared detector and preparation method thereof

Abstract

The application provides a strong microcavity resonance enhanced infrared detector and a preparation method thereof, and belongs to the technical field of infrared detectors. The strong microcavity resonance enhanced infrared detector comprises a readout circuit located at a bottom layer; a distributed Bragg reflector located above the readout circuit, which has a plurality of indium columns with a length direction along a thickness direction of the distributed Bragg reflector; an infrared photosensitive chip located above the distributed Bragg reflector, which is interconnected with the readout circuit through the indium columns; and a passivation layer located above the infrared photosensitive chip; wherein a resonance cavity is formed between an upper surface of the distributed Bragg reflector and a lower surface of the passivation layer to perform resonance enhancement on target infrared light to be detected. The application can improve the quantum efficiency of the infrared detector, improve the effective conduction rate and reliability of the flip-chip welding of the indium columns, and improve the performance of the infrared detector.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of infrared detector, and particularly relates to a strong micro-cavity resonance enhanced infrared detector and a preparation method thereof. BACKGROUND

[0002] Infrared focal plane detector is an advanced imaging sensor with both infrared information acquisition and information processing functions. It has important and wide applications in military and civilian fields such as space-to-ground observation, photoelectric countermeasure, robot vision, search and tracking, medical and industrial thermal imaging, and missile precision guidance. Because of its irreplaceable position and role, major industrial powers in the world have listed the preparation technology of infrared focal plane detector as a key development high-tech project.

[0003] Quantum efficiency is an important indicator for measuring the performance of a detector, and the quantum efficiency of current long-wave and very long-wave infrared detectors is generally low. How to improve the quantum efficiency of infrared detectors has become a hot spot in the current industry. Infrared detectors are mainly divided into two types: uncooled infrared detectors and cooled infrared detectors. In order to improve the quantum efficiency of infrared detectors, some people have proposed a method of making a pair of mirrors on a photodetector to form a resonant cavity structure to improve the quantum efficiency of the detector. For example, Y.H.Zhang et al. proposed in Appl. Phys. Lett. (Applied Physics Letters) Vol. 82 (2003) 1129 that the interface formed by the detector and the air is used as the top mirror, and the bottom mirror is composed of the bottom electrode layer and the multi-period non-doped arsenic layer below it. This resonant cavity structure effectively improves the quantum efficiency, but the reflectivity of the bottom mirror is not large enough, which limits the further improvement of the quantum efficiency. However, for cooled infrared detectors, there is no related report on how to effectively improve the quantum efficiency. Figure 1 As shown in FIG. 1, the existing cooled infrared detector generally connects the infrared photosensitive chip 10 to the readout circuit 30 through the indium column 20, and the micro-cavity structure is made on the infrared photosensitive chip 10, which makes the overall structure of the device complex, and the micro-cavity structure may cause excessive stress on the infrared photosensitive chip under ultra-low temperature, resulting in performance degradation or even cracking.

[0004] At present, the infrared photosensitive chip generally adopts an infrared focal plane array (IRFPA) form, the pixels of the IRFPA gradually develop from the order of ten thousand to the order of one hundred thousand, one million, or even ten million, and the pixel density increases, which makes the preparation of the IRFPA more difficult and requires higher technology. This is because, when the pixel density of the IRFPA is higher and higher, the bump connecting the IRFPA and the readout circuit is smaller and smaller, and the density is higher and higher, and the spacing between the bumps of adjacent pixels is closer and closer. In this case, the flip-chip interconnection process of the infrared photosensitive chip and the readout circuit becomes a major technical bottleneck, specifically, in the bump manufacturing process, the flip-chip process, the material surface flatness, and other aspects. If any link has a problem, the sensitive material and the readout circuit may generate overpressure in the local area when interconnected, which may cause the bump to deform excessively, expand too much horizontally, and even exceed the pixel area, resulting in the short circuit between adjacent pixels, and such short-circuited pixels will eventually form blind pixels (or bad pixels).

[0005] In summary, the existing infrared detector has the following problems:

[0006] (1) Low quantum efficiency;

[0007] (2) When preparing a high-pixel infrared detector, the horizontal deformation or collapse of the indium column during flip-chip interconnection is prone to cause short circuits between pixels to form blind pixels or bad pixels. SUMMARY

[0008] The present application provides a strong microcavity resonance enhanced infrared detector and a preparation method thereof, which is used to solve the problem that the quantum efficiency of the current conventional cryogenic infrared detector is generally low, and the horizontal deformation or collapse of the indium column during flip-chip interconnection is prone to cause short circuits between pixels to form blind pixels or bad pixels.

[0009] To solve the above technical problems, the strong microcavity resonance enhanced infrared detector provided by the present application comprises:

[0010] a readout circuit located on the bottom layer;

[0011] a distributed Bragg reflector located above the readout circuit, the inside of the distributed Bragg reflector having a plurality of indium columns with the length direction distributed along the thickness direction of the distributed Bragg reflector;

[0012] an infrared photosensitive chip located above the distributed Bragg reflector, which is interconnected with the readout circuit through the indium column; and

[0013] a passivation layer located above the infrared photosensitive chip;

[0014] The upper surface of the distributed Bragg reflector and the lower surface of the passivation layer form a resonant cavity to resonantly enhance the target infrared light to be detected.

[0015] Further, the length of the resonant cavity is an integer multiple of the half wavelength of the target infrared light.

[0016] In some embodiments, the length of the resonant cavity is 1 or 2 times the half wavelength of the target infrared light.

[0017] In some embodiments, the distributed Bragg reflector comprises at least one first material layer and at least one second material layer alternately arranged, the refractive index of the first material layer being different from that of the second material layer.

[0018] In some embodiments, the material of the first material layer is Ge, and the material of the second material layer is ZnS.

[0019] The material of the passivation layer is ZnSe or GdTe.

[0020] The application provides a preparation method of the strong microcavity resonant enhancement infrared detector, further comprising the following steps:

[0021] S1, preparing a distributed Bragg reflector on a readout circuit;

[0022] S2, etching the distributed Bragg reflector to obtain a plurality of indium column holes with the length direction along the thickness direction of the distributed Bragg reflector;

[0023] S3, fabricating an indium column along the indium column hole on the readout circuit;

[0024] S4, preparing an infrared photosensitive chip and a passivation layer on the upper surface of the infrared photosensitive chip;

[0025] S5, flip-chip connecting the readout circuit and the infrared photosensitive chip, so that the upper surface of the distributed Bragg reflector and the lower surface of the passivation layer form a resonant cavity, and the length of the resonant cavity is an integer multiple of the half wavelength of the target infrared light to be detected.

[0026] The S1 comprises:

[0027] The first material and the second material are alternately used for film plating on the readout circuit to obtain at least one first material layer and at least one second material layer alternately arranged, as the distributed Bragg reflector; wherein the refractive index of the first material layer is different from that of the second material layer.

[0028] Further, the length of the resonant cavity is 1 or 2 times the half wavelength of the target infrared light in S5.

[0029] Further, the material of the first material layer is Ge, the material of the second material layer is ZnS, and the material of the passivation layer is ZnSe or GdTe.

[0030] The strong microcavity resonance enhanced infrared detector and the preparation method thereof have the following beneficial effects:

[0031] (1) By preparing the distributed Bragg reflector on the readout circuit and the passivation layer on the infrared photosensitive chip, a resonance cavity is formed between the distributed Bragg reflector and the passivation layer, so that the target infrared light to be detected is resonantly enhanced, and the quantum efficiency of the infrared detector, especially the quantum efficiency of the refrigeration type infrared detector, can be significantly improved.

[0032] (2) Since the dielectric film layer of the insulating distributed Bragg reflector is added between the adjacent indium columns, each bump of the readout circuit is isolated from other bumps, so that when the bump is expanded to the surrounding under pressure during flip-chip bonding, the adjacent indium columns will not be connected together to cause short circuit due to the isolation of the dielectric film layer, so that blind elements are not formed, and the distributed Bragg reflector can limit the degree of depression of the indium column to a certain extent during flip-chip bonding, thereby improving the effective conduction rate and reliability of the flip-chip bonding of the indium column, improving the production yield of the infrared detector and the performance of the infrared detector. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0034] Figure 1 is a structural schematic diagram of the existing refrigeration type infrared detector;

[0035] Figure 2 is a structural schematic diagram of the strong microcavity resonance enhanced infrared detector provided by the present application;

[0036] Figure 3 is a structural schematic diagram of the distributed Bragg reflector provided by the embodiment of the present application;

[0037] Figure 4 is a flow chart of the preparation method of the strong microcavity resonance enhanced infrared detector provided by the present application.

[0038] Explanation of reference signs:

[0039] 1, readout circuit; 2, distributed Bragg reflector; 3, infrared photosensitive chip; 4, passivation layer; 5, indium column; 21, first material layer; 22, second material layer. DETAILED DESCRIPTION

[0040] The embodiments of the present application will be further described in conjunction with the drawings and examples. The following detailed description of the examples and drawings is provided for the purpose of illustrating the principles of the present application, and is not intended to limit the scope of the present application, which can be realized in a variety of ways. The present application can be implemented in many different forms and should not be limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0041] The present application provides these embodiments is to make the present application and complete, and to the person skilled in the art fully express the scope of the present application. It should be noted that: unless otherwise specified, the relative arrangement of components and steps, the composition of materials, numerical expressions and values set forth in these examples should be interpreted as merely exemplary, and not as limiting.

[0042] It should be noted that, in the description of the present application, unless otherwise specified, the meaning of "a plurality of" is greater than or equal to two; the orientation or position relationship indicated by the terms "upper", "lower", "left", "right", "inner", "outer" and the like is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0043] In addition, "first", "second" and similar words used in the present application do not indicate any order, number or importance, but are only used to distinguish different parts. "Vertical" is not strictly vertical, but within the allowable range of error. "Parallel" is not strictly parallel, but within the allowable range of error. "Include" or "contain" and similar words mean that the elements before the word cover the elements listed after the word, and do not exclude the possibility of also covering other elements.

[0044] It should also be noted that, in the description of the present application, unless otherwise specified and limited, the terms "mounting", "connecting", "connection" should be interpreted broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be directly connected, or indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances. When it is described that a specific device is located between a first device and a second device, there can be an intermediate device between the specific device and the first device or the second device, or there can be no intermediate device.

[0045] All terms used in the present invention take the same meaning as understood by those of ordinary skill in the art to which the present invention pertains, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries should be interpreted to have meanings consistent with their meanings in the context of the relevant art, and should not be interpreted in an idealized or overly formalized sense, unless otherwise explicitly defined herein.

[0046] Techniques, methods, and devices known to those of ordinary skill in the relevant art can not be discussed in detail, but should be considered part of the specification where appropriate.

[0047] Figure 2 A schematic structural diagram of a strong microcavity resonance enhanced infrared detector provided by the present invention is shown in FIG. 1, which includes: Figure 2

[0048] a readout circuit 1 located at the bottom layer;

[0049] a Distributed Bragg Reflector (DBR) 2 located above the readout circuit 1, the inside of the DBR 2 having a plurality of indium pillars 5 distributed along the length direction of the thickness direction of the DBR 2;

[0050] an infrared photosensitive chip 3 located above the DBR 2, which is interconnected with the readout circuit 1 through the indium pillars 5; preferably, the infrared photosensitive chip 3 is an IRFPA;

[0051] a passivation layer 4 located above the infrared photosensitive chip 3, further, the passivation layer 4 has a semi-transmission and semi-reflection characteristic to the target infrared light to be detected, its upper surface is at least semi-transmissive to the target infrared light, and its lower surface is at least semi-reflective to the target infrared light; preferably, the material of the passivation layer is ZnSe or GdTe;

[0052] wherein the upper surface of the DBR 2 and the lower surface of the passivation layer 4 form a resonance cavity to resonate and enhance the target infrared light to be detected.

[0053] ​In the strong microcavity resonance enhanced infrared detector provided by the application, the passivation layer 4 on the upper side of the infrared photosensitive chip 3 and the distributed Bragg reflector 2 form a resonance cavity, the radiant energy of the target infrared light to be detected is first partially absorbed by the infrared photosensitive chip 3, the remaining energy is transmitted through the infrared photosensitive chip 3 and then repeatedly reflected in the resonance cavity between the distributed Bragg reflector 2 and the upper passivation layer 4, and then is absorbed by the infrared photosensitive chip 3 again, so that the target infrared light can be resonantly enhanced, and the quantum efficiency of the infrared detector, especially the quantum efficiency of the refrigeration type infrared detector, can be significantly improved. In addition, the dielectric film layer of the distributed Bragg reflector 2 is added between the adjacent indium columns 5, so that each bump of the readout circuit 1 is isolated from other bumps. When the bumps are expanded to the surrounding under pressure during flip-chip welding, the adjacent indium columns 5 will not be connected together to cause short circuit due to the isolation of the dielectric film layer, so that blind elements are not formed. The distributed Bragg reflector 2 can limit the degree of depression of the indium column 5 during flip-chip welding to a certain extent, so that the effective conduction rate and reliability of flip-chip welding of the indium column 5 can be improved, and the preparation yield of the infrared detector and the performance of the infrared detector can be improved.

[0054] Further, the resonance mode of the resonance cavity in the infrared detector provided by the application satisfies the F-P equation, and the length of the resonance cavity is an integer multiple of the half wavelength of the target infrared light, and is specifically shown in the following formula (1):

[0055]

[0056] Wherein, L is the length of the resonance cavity, λ is the wavelength of the target infrared light, and m is an integer, which is the order of the emission mode. Therefore, by adjusting the period of the DBR reflector (distributed Bragg reflector 2), the height of the indium column and the thickness of the infrared photosensitive chip and other parameters, the length of the resonance cavity can be adjusted to meet the resonance enhancement condition.

[0057] Preferably, the length of the resonance cavity is 1 or 2 times the half wavelength of the target infrared light.

[0058] Figure 3 As shown in the structure schematic diagram of the distributed Bragg reflector provided by the embodiment of the application, Figure 3 As shown in the structure schematic diagram of the distributed Bragg reflector provided by the embodiment of the application,

[0059] Preferably, the material of the first material layer 21 is Ge, and the material of the second material layer 22 is ZnS.

[0060] Corresponding to the strong microcavity resonance enhanced infrared detector provided by the application, the embodiment of the application further provides a preparation method of the strong microcavity resonance enhanced infrared detector, Figure 4 The flow chart of the preparation method of the strong microcavity resonance enhanced infrared detector provided by the application is shown in the figure, Figure 4 The method comprises the following steps:

[0061] S1, preparing a distributed Bragg reflector 2 on a readout circuit 1;

[0062] Further, the step S1 specifically comprises alternately coating a first material and a second material on the readout circuit 1 to obtain at least one first material layer 21 and at least one second material layer 22 alternately, as the distributed Bragg reflector 2; wherein the refractive index of the first material to the target infrared light to be detected is different from the refractive index of the second material to the target infrared light. Preferably, the material of the first material layer 21 is Ge, and the material of the second material layer 22 is ZnS.

[0063] S2, etching the distributed Bragg reflector 2 to obtain a plurality of indium column holes with the length direction along the thickness direction of the distributed Bragg reflector 2;

[0064] S3, manufacturing an indium column 5 along the indium column hole on the readout circuit 1;

[0065] S4, preparing an infrared photosensitive chip 3, and preparing a passivation layer 4 on the upper surface of the infrared photosensitive chip 3; preferably, the material of the passivation layer is ZnSe or GdTe;

[0066] S5, flip-chip interconnecting the readout circuit 1 and the infrared photosensitive chip 3, so as to form a resonant cavity between the upper surface of the distributed Bragg reflector 2 and the lower surface of the passivation layer 4, and the length of the resonant cavity is an integer multiple of the half wavelength of the target infrared light to be detected.

[0067] For example, taking 10 μm central wavelength as an example, by controlling the height of the indium column and the alternating period of the first material layer 21 and the second material layer 22 of the distributed Bragg reflector 2, the distance from the upper surface of the distributed Bragg reflector 2 to the lower surface of the passivation layer 4 (the length L of the resonant cavity) is 5 μm (when m is 1) or 10 μm (when m is 2).

[0068] Preferably, the length of the resonant cavity is 1 or 2 times the half wavelength of the target infrared light when flip-chip bonding the readout circuit 1 and the infrared light sensitive chip 3 in S5. Taking the central wavelength of 10 μm as an example, the refractive index of Ge is 4 and the refractive index of ZnS is 2.2, so the design thickness of the Ge layer in the distributed Bragg reflector 2 is 0.625 μm and the thickness of the ZnS layer is 1.136 μm before S1 is performed. The distributed Bragg reflector 2 with high reflectivity can be obtained by alternatingly coating Ge and ZnS, and the parameters of the distributed Bragg reflector 2 with high reflectivity and suitable for being prepared on the readout circuit 1 can be obtained by taking m = 1 or 2 in formula (1), and the distributed Bragg reflector 2 is prepared according to the parameters in S1.

[0069] The infrared detector and the preparation method thereof provided by the application can meet the resonance enhancement condition to improve the light absorption rate of the detector, can ensure the reliability of the flip-chip indium column, can improve the quantum efficiency of the infrared detector, can improve the effective conduction rate and the reliability of the flip-chip indium column, and can improve the performance of the infrared detector.

[0070] So far, the embodiments of the application have been described in detail. In order to avoid obscuring the concept of the application, some details known in the art are not described. Those skilled in the art can fully understand how to implement the technical solutions disclosed herein according to the above description.

[0071] Although some specific embodiments of the application have been described in detail above, those skilled in the art should understand that the above examples are only for illustration, but not for limiting the scope of the application. Those skilled in the art should understand that the above embodiments can be modified or some technical features can be replaced equivalently without departing from the scope and spirit of the application. In particular, the technical features mentioned in each embodiment can be combined in any way as long as there is no structural conflict.

Claims

1. A strong microcavity resonance enhanced infrared detector, characterized in that, include: The readout circuit (1) is located at the bottom layer; A distributed Bragg reflector (2) is located above the readout circuit (1), and the interior of the distributed Bragg reflector (2) has a plurality of indium pillars (5) whose length direction is distributed along the thickness direction of the distributed Bragg reflector (2). An infrared photosensitive chip (3) is located above the distributed Bragg reflector (2) and is interconnected with the readout circuit (1) via the indium pillar (5); and A passivation layer (4) is located above the infrared photosensitive chip (3); The upper surface of the distributed Bragg reflector (2) and the lower surface of the passivation layer (4) form a resonant cavity to resonate and enhance the infrared light of the target to be detected.

2. The enhanced infrared detector with strong microcavity resonance according to claim 1, characterized in that, The length of the resonant cavity is an integer multiple of half the wavelength of the target infrared light.

3. The high-intensity microcavity resonance enhanced infrared detector according to claim 2, characterized in that, The length of the resonant cavity is one or two times the half wavelength of the target infrared light.

4. The enhanced infrared detector with strong microcavity resonance according to claim 1, characterized in that, The distributed Bragg reflector (2) includes at least one first material layer (21) and at least one second material layer (22) that alternate with each other, wherein the refractive index of the first material layer (21) is different from the refractive index of the second material layer (22).

5. The high-intensity microcavity resonance enhanced infrared detector according to claim 4, characterized in that, The material of the first material layer (21) is Ge, and the material of the second material layer (22) is ZnS.

6. The high-intensity microcavity resonance enhanced infrared detector according to claim 1, characterized in that, The material of the passivation layer (4) is ZnSe or GdTe.

7. A method for fabricating a strong microcavity resonance enhanced infrared detector, characterized in that, Includes the following steps: S1. Fabricate a distributed Bragg reflector (2) on the readout circuit (1); S2. Etch the distributed Bragg reflector (2) to obtain a number of indium pillar holes whose length direction is distributed along the thickness direction of the distributed Bragg reflector (2); S3. An indium pillar (5) is made along the indium pillar hole on the readout circuit (1); S4. Prepare an infrared photosensitive chip (3) and prepare a passivation layer (4) on the surface of the infrared photosensitive chip (3). S5. The readout circuit (1) and the infrared photosensitive chip (3) are flip-chip interconnected, so that the upper surface of the distributed Bragg reflector (2) and the lower surface of the passivation layer (4) form a resonant cavity, and the length of the resonant cavity is an integer multiple of half the wavelength of the infrared light of the target to be detected.

8. The preparation method according to claim 7, characterized in that, S1 includes: The first material and the second material are alternately coated on the readout circuit (1) to obtain at least one first material layer (21) and at least one second material layer (22) that alternate with each other, as a distributed Bragg reflector (2); wherein the refractive index of the first material layer is different from the refractive index of the second material layer.

9. The preparation method according to claim 8, characterized in that, In S5, the length of the resonant cavity is made to be 1 or 2 times the half wavelength of the target infrared light.

10. The preparation method according to claim 8, characterized in that, The material of the first material layer (21) is Ge, the material of the second material layer (22) is ZnS, and the material of the passivation layer (4) is ZnSe or GdTe.

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