Micro-bridge structure, preparation method thereof and uncooled infrared micro-bolometer

Abstract

The invention provides a micro-bridge structure and a preparation method thereof, and an uncooled infrared micro-bolometer, the micro-bridge structure comprises a plurality of pixels, each pixel comprises a substrate, a bridge leg and a bridge surface, the bridge leg of a single pixel and the bridge leg of at least one adjacent pixel are arranged in a staggered layer manner, and the projection parts of the bridge legs on the substrate are overlapped. The bridge legs of two adjacent pixels are arranged at different heights to form a staggered layer arrangement structure, the design space of the bridge legs is expanded, the bridge floor layout of a single pixel is not influenced, and the problem that the layout space of the pixels is limited is solved, so that the length of the bridge legs can be greatly increased, the microbridge thermal conductivity problem can be improved without increasing the number of layers of the microbridge structure, and the service life of the microbridge is prolonged. And the stability of the structure of the uncooled infrared micro-bolometer and the reliability of the uncooled infrared detector are effectively ensured.

Description

Technical Field

[0001] The invention belongs to the field of infrared detection technology, and in particular relates to a microbridge structure and a preparation method thereof, and an uncooled infrared microbolometer. Background Art

[0002] The pixel structure of the uncooled infrared microbolometer is a suspended microbridge structure, which is generally composed of a reflector layer, anchor columns, bridge legs, bridge deck and absorption surface. Currently, there are single-layer microbridge structures with only one suspended structure, double-layer microbridge structures with bridge legs and bridge deck in two layers, and double-layer microbridge structures with bridge legs and bridge deck in one layer and an absorption layer added on top.

[0003] However, when the pixel size is reduced, the design space of the microbridge structure is limited, the microbridge leg length is insufficient, and the thermal conductivity of the microbridge cannot be further reduced, which will lead to a decrease in the performance of the uncooled infrared detector. If the problem of excessive thermal conductivity is solved by increasing the number of layers of the pixel microbridge, the stability of the microbridge structure will deteriorate and the reliability of the detector will be reduced. Summary of the invention

[0004] The purpose of the present invention is to provide a microbridge structure which can at least solve some of the defects in the prior art.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A microbridge structure comprises a plurality of picture elements, wherein the picture elements comprise a substrate, bridge legs and a bridge deck, wherein the bridge legs of a single picture element are arranged in staggered layers with the bridge legs of at least one adjacent picture element and their projections on the substrate partially overlap.

[0007] Furthermore, the plurality of picture elements are arranged in an array, and the bridge legs of two adjacent picture elements in each row or column of picture elements are arranged in staggered layers.

[0008] Furthermore, the bridge legs of two spaced-apart picture elements in each row or column are located at the same height.

[0009] Furthermore, the bridge leg is suspended above the substrate by a first anchor column, and the bridge deck is suspended above the bridge leg by a second anchor column; two adjacent pixels in which the bridge legs are staggered include a first pixel and a second pixel, a bridge leg portion of the first pixel spans between the substrate and the bridge leg of the second pixel, and a bridge leg portion of the second pixel spans between the bridge deck and the bridge leg of the first pixel.

[0010] Furthermore, the bridge legs of a single pixel extend simultaneously to above the substrates of two adjacent pixels.

[0011] Furthermore, the bridge leg comprises two cantilever beams which are not in contact with each other, and half of the area of ​​the two cantilever beams of a single pixel is located above the substrate of the pixel, and the other half of the area is located above the substrates of two adjacent pixels.

[0012] Furthermore, the bridge deck of a single pixel is located above the substrate of the pixel.

[0013] Furthermore, the bridge decks of the pixels are located at the same height.

[0014] In addition, the present invention also provides a method for preparing a microbridge structure, comprising the following steps:

[0015] S1, preparing a substrate;

[0016] S2, forming a sacrificial layer on the substrate, and forming a first anchor column and a bridge leg supported by the first anchor column based on the sacrificial layer, wherein the bridge legs of two pixels arranged in a staggered manner are manufactured step by step by setting sacrificial layers with different numbers of layers;

[0017] S3, forming a second anchor column and a bridge deck supported by the second anchor column based on the sacrificial layer;

[0018] S4. Release the sacrificial layer to obtain a microbridge structure.

[0019] The present invention also provides an uncooled infrared microbolometer, comprising the above-mentioned microbridge structure.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The microbridge structure provided by the present invention places the bridge legs of its two adjacent pixels at different heights to form a staggered structural design, which expands the design space of the bridge legs without affecting the bridge deck layout of a single pixel, solves the problem of limited pixel layout space, and can greatly increase the length of the bridge legs. The thermal conductivity problem of the microbridge can be improved without increasing the number of microbridge structure layers, effectively ensuring the stability of the uncooled infrared microbolometer structure and the reliability of the uncooled infrared detector.

[0022] The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a cross-sectional schematic diagram of the microbridge structure of the present invention;

[0024] Figure 2 is a three-dimensional schematic diagram of the microbridge structure of the present invention;

[0025] Figure 3 It is a process flow chart for preparing the microbridge structure of the present invention.

[0026] Explanation of the accompanying drawings: 1. first pixel; 2. second pixel; 3. reflector layer; 4. bridge leg; 5. first anchor column; 6. second anchor column; 7. bridge deck; 8. first sacrificial layer; 9. second sacrificial layer; 10. third sacrificial layer; 11. electrode. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] In the description of the present invention, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0029] In the description of the present invention, it should be noted that, unless otherwise clearly stipulated and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, a conflicting connection or an integral connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0030] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features; in the description of the present invention, unless otherwise specified, "multiple" and "several" mean two or more.

[0031] This embodiment provides a microbridge structure, including a plurality of pixels, wherein the pixels include a substrate, a bridge leg 4 and a bridge deck 7, wherein the bridge leg 4 and the bridge deck 7 are both suspended above the substrate through anchor support; in the design of the plurality of pixels, the bridge leg 4 of a single pixel and the bridge leg 4 of at least one adjacent pixel are arranged in a staggered manner and the projections on the substrate overlap. In this embodiment, the bridge legs 4 of two adjacent pixels are designed to be arranged in a staggered manner at different heights, so that for these two pixels, the bridge leg 4 of a single pixel not only occupies its own pixel space, but also occupies the spatial position of the adjacent pixel, thereby expanding the layout space of the bridge leg 4 of a single pixel, increasing the length of the bridge leg 4, and realizing the long bridge leg design of a small pixel, thereby reducing the thermal conductivity of the microbridge structure.

[0032] In some embodiments, for the arrangement of multiple pixels, the multiple pixels are designed to be arranged in an array. Preferably, in this array arrangement structure, the bridge legs 4 of two adjacent pixels in each row or column of pixels are arranged in staggered layers, and there are two types of pixels in this array arrangement structure, which can be defined as a first pixel 1 and a second pixel 2. The bridge legs of the two pixels are of different heights and the two pixels are arranged alternately, thereby forming an imaging array, so that the bridge leg layout of a single pixel occupies its own pixel area and part of the area of ​​the pixels around it.

[0033] Preferably, the bridge legs 4 of two spaced-apart picture elements in each row or column are located at the same height, where spaced-apart refers to being spaced one picture element apart. Specifically, for the alternatingly arranged first picture elements 1 and second picture elements 2, the bridge legs of each first picture element 1 are located at the same height, and the bridge legs of each second picture element 2 are located at the same height.

[0034] The microbridge structure in this embodiment can be a microbridge structure in which the bridge deck 7 and the bridge leg 4 of a single pixel are placed on the same layer, in which case the bridge deck and the bridge leg layers between adjacent pixels can be arranged in staggered layers, or a double-layer microbridge structure in which the bridge deck 7 and the bridge leg 4 of a single pixel are placed in two layers. This embodiment is specifically described by taking the microbridge structure in which the bridge deck 7 and the bridge leg 4 of a single pixel are placed in two layers as an example.

[0035] Specifically, Figure 1 and Figure 2As shown, in a single pixel, the bridge leg 4 is suspended above the substrate by the first anchor column 5, and the bridge deck 7 is suspended above the bridge leg 4 by the second anchor column 6. For the arrangement of multiple pixels of the microbridge structure in which the bridge deck 7 and the bridge leg 4 are arranged in two layers, the multiple pixels are designed as two types of pixels, which can be defined as the first pixel 1 and the second pixel 2. The bridge legs of the two pixels have different heights and are arranged alternately. Specifically, the bridge leg 4 of the first pixel 1 is partially spanned between the substrate and the bridge leg 4 of the second pixel 2, and the bridge leg 4 of the second pixel 2 is partially spanned between the bridge deck 7 and the bridge leg 4 of the first pixel 1. As a result, the bridge legs 4 of the first pixel 1 and the second pixel 2 form a staggered arrangement, and the staggered arrangement of the bridge legs 4 will not affect the layout of the bridge deck 7 of the first pixel 1 and the second pixel 2.

[0036] Optionally, the bridge leg 4 of a single pixel can be extended to the substrate of two adjacent pixels at the same time, so that the bridge leg of a single pixel not only occupies its own pixel space, but also occupies part of the space of two adjacent pixels, further increasing the length of the bridge leg of a single pixel; for example, Figure 1 In the micro-bridge structure shown, when the bridge leg 4 of a single pixel occupies half the area of ​​the adjacent pixel, for the first pixel 1, its bridge leg 4 layout occupies its own pixel area and half the area of ​​the second pixel 2 on its right and half the area of ​​the second pixel 2 in the adjacent pixel unit on its left, that is, the bridge leg layout area of ​​the first pixel 1 is increased from one pixel area to two pixel areas. Similarly, the bridge leg 4 layout area of ​​the second pixel 2 is also increased from one pixel area to two pixel areas, thereby greatly increasing the length of the bridge leg of a single pixel.

[0037] In some embodiments, Figure 1 and Figure 2 As shown, the bridge leg 4 includes two cantilever beams (i.e. Figure 1 4a and 4b), the two cantilever beams of a single pixel are both suspended above the substrate through the support of the first anchor column 5; the two ends of the bridge deck 7 are respectively supported above the two cantilever beams through the second anchor column 6. Specifically, half of the area of ​​the two cantilever beams of a single pixel is located above the substrate of the pixel, that is, this half of the area is located in its own pixel space, and the other half of the area is located above the substrates of two adjacent pixels, that is, the other half of the area is located in the adjacent pixel space. The cantilever beams are in a multi-winding structure along the direction parallel to the substrate surface to increase the length of the cantilever beam. The multi-winding structure can be, but is not limited to, multi-S-shaped, multi-bow-shaped, etc. Preferably, the two cantilever beams of the bridge leg 4 in a single pixel are designed to be arranged side by side and in a symmetrical structure.

[0038] Optionally, the bridge deck 7 of a single pixel is located above the substrate of the pixel, and the bridge decks 7 of each pixel are located at the same height; specifically, a readout circuit is provided in the substrate, and the bridge deck 7 of a single pixel is electrically connected to the readout circuit in the substrate of the pixel through the second anchor column 6, the bridge leg 4 and the first anchor column 5 of the pixel.

[0039] The preparation process of the microbridge structure with two layers of bridge deck 7 and bridge leg 4 of the above-mentioned single pixel is as follows: Figure 3 As shown, the specific steps include:

[0040] S1. Prepare a substrate (not shown in the figure).

[0041] Specifically, the substrate has a built-in readout circuit, and the electrode 11 and the reflector layer 3 are formed on the substrate. The electrode 11 and the reflector layer 3 can be prepared by thin film deposition and photolithography patterning processes.

[0042] S2. Form a sacrificial layer on the substrate, and form a first anchor column 5 and a bridge leg 4 supported by the first anchor column 5 based on the sacrificial layer, wherein the bridge leg 4 of two pixels arranged in a staggered manner is manufactured step by step by setting sacrificial layers with different numbers of layers.

[0043] The specific process of making the bridge legs of the two pixels (i.e., the first pixel 1 and the second pixel 2) arranged in the above staggered manner is as follows:

[0044] S21 , spin-coating a first sacrificial layer 8 on the electrode 11 of the substrate and the reflector layer 3 , and etching the first sacrificial layer 8 at the electrically conductive portion of the substrate of the first pixel 1 (ie, the electrode 11 ) to form a first anchor column 5 for the first pixel 1 .

[0045] The material of the first sacrificial layer 8 may be but is not limited to polyimide, and the thickness of the first sacrificial layer 8 is between 0.2-1.5 μm.

[0046] S22 , forming a bridge leg 4 supported by the first anchor column 5 of the first pixel 1 on the surface of the first sacrificial layer 8 , and the bridge leg 4 of the first pixel 1 spans to the surface of the first sacrificial layer 8 of the adjacent second pixel 2 .

[0047] Specifically, the bridge leg 4 of the first pixel 1 is prepared by thin film deposition and photolithography patterning process. The structure of the bridge leg 4 is a multiple coiled structure design. The bridge leg 4 is composed of a supporting layer, an electrically conductive metal layer and a passivation layer. The materials of the supporting layer and the passivation layer are generally silicon oxide and silicon nitride. The metal layer is generally titanium, titanium nitride, copper, aluminum, silver, etc.

[0048] S23, spin-coating the second sacrificial layer 9 on the surface of the first sacrificial layer 8, the second sacrificial layer 9 covers the first anchor column 5 and the bridge leg 4 of the first pixel 1, and etching the first sacrificial layer 8 and the second sacrificial layer 9 at the electrically conductive position of the substrate of the second pixel 2 (i.e., the electrode 11) to form the first anchor column 5 of the second pixel 2.

[0049] Specifically, the second sacrificial layer 9 is the same as the first sacrificial layer 8 , and its material can be polyimide, with a thickness of 0.2-1.5 μm.

[0050] S24 , forming a bridge leg 4 supported by the first anchor column 5 of the second pixel 2 on the surface of the second sacrificial layer 9 , and the bridge leg 4 of the second pixel 2 spans to the surface of the second sacrificial layer 9 of the adjacent first pixel 1 .

[0051] Specifically, the bridge leg 4 of the second pixel 2 is also prepared by thin film deposition and photolithography patterning process, and its structure and material are consistent with the bridge leg 4 of the first pixel 1, ensuring the uniformity of the micro-bridge structure imaging array.

[0052] S3. Forming a second anchor column 6 and a bridge deck 7 supported by the second anchor column 6 based on the sacrificial layer.

[0053] Specifically, a third sacrificial layer 10 is spin-coated on the surface of the second sacrificial layer 9, and the sacrificial layer is etched to the bridge leg 4 of the first pixel 1 and the second pixel 2 to form a second anchor column 6; then a bridge deck 7 supported by the second anchor column 6 is formed on the surface of the third sacrificial layer 10.

[0054] Specifically, the third sacrificial layer 10 is the same as the first sacrificial layer 8, and its material can be polyimide with a thickness of 0.2-1.5 μm. Since the bridge legs 4 of the first pixel 1 and the second pixel 2 are at different heights, the second anchor pillars 6 of different heights can be prepared by step-by-step photolithography and etching.

[0055] Specifically, the bridge deck 7 can be prepared by multiple thin film deposition, photolithography, etching and cleaning processes, and the bridge deck 7 of the first pixel 1 and the second pixel 2 has the same structure and material. The material of the bridge deck 7 generally includes several combinations of silicon nitride, silicon oxide, vanadium oxide, titanium, titanium nitride, germanium silicon, amorphous silicon, aluminum, copper, gold, etc.

[0056] S4, releasing the above-mentioned sacrificial layers (i.e., the first sacrificial layer 8, the second sacrificial layer 9, and the third sacrificial layer 10) through a sacrificial layer release process, that is, forming Figure 1 The microbridge structure of the suspended structure is shown.

[0057] In addition, this embodiment also provides an uncooled infrared microbolometer, including the above-mentioned microbridge structure.

[0058] In summary, the microbridge structure provided by the present invention places the bridge legs of its two adjacent pixels at different heights to form a staggered structural design, which expands the design space of the bridge legs without affecting the bridge deck layout of a single pixel, solving the problem of limited pixel layout space, thereby being able to greatly increase the length of the bridge legs and improve the microbridge thermal conductivity problem without increasing the number of microbridge structure layers. The array structure stability and performance of the uncooled infrared microbolometer using the microbridge structure will also be significantly improved.

[0059] The above examples are merely illustrative of the present invention and do not constitute a limitation on the protection scope of the present invention. All designs that are the same or similar to the present invention fall within the protection scope of the present invention.

Claims

1. A microbridge structure, comprising a plurality of pixels, wherein the pixels include a substrate, a bridge leg and a bridge deck, characterized in that: The bridge leg of a single picture element is arranged in a staggered layer with the bridge leg of at least one adjacent picture element, and their projections on the substrate partially overlap.

2. The microbridge structure according to claim 1, characterized in that: The plurality of picture elements are arranged in an array, and the bridge legs of two adjacent picture elements in each row or column of picture elements are arranged in staggered layers.

3. The microbridge structure according to claim 2, characterized in that: The bridge legs of two alternate picture elements in each row or column are located at the same height.

4. The microbridge structure according to any one of claims 1 to 3, characterized in that: The bridge leg is suspended above the substrate by a first anchor column, and the bridge deck is suspended above the bridge leg by a second anchor column; two adjacent pixels in which the bridge legs are staggered include a first pixel and a second pixel, a bridge leg portion of the first pixel spans between the substrate and the bridge leg of the second pixel, and a bridge leg portion of the second pixel spans between the bridge deck and the bridge leg of the first pixel.

5. The microbridge structure according to claim 4, characterized in that: The bridge legs of a single picture element simultaneously extend above the substrates of two adjacent picture elements.

6. The microbridge structure according to claim 5, characterized in that: The bridge leg comprises two cantilever beams which are not in contact with each other. Half of the area of ​​the two cantilever beams of a single pixel is located above the substrate of the pixel, and the other half of the area is located above the substrates of two adjacent pixels.

7. The microbridge structure according to claim 4, characterized in that: The bridge deck of a single pixel is located above the substrate of the pixel.

8. The microbridge structure according to claim 4, characterized in that: The bridge decks of the pixels are located at the same height.

9. A method for preparing a microbridge structure according to any one of claims 1 to 8, characterized in that: The steps include: S1, preparing a substrate; S2, forming a sacrificial layer on the substrate, and forming a first anchor column and a bridge leg supported by the first anchor column based on the sacrificial layer, wherein the bridge legs of two pixels arranged in a staggered manner are manufactured step by step by setting sacrificial layers with different numbers of layers; S3, forming a second anchor column and a bridge deck supported by the second anchor column based on the sacrificial layer; S4. Release the sacrificial layer to obtain a microbridge structure.

10. An uncooled infrared microbolometer, characterized in that: The microbridge structure comprises the microbridge structure described in any one of claims 1 to 8.

Images