Power device, high-voltage-resistant field limiting ring terminal thereof and preparation method of high-voltage-resistant field limiting ring terminal

Abstract

The invention discloses a power device and a high-voltage-resistant field limiting ring terminal and a preparation method thereof, the power device comprises N straightaway regions and N terminal regions, the terminal regions and the straightaway regions are sequentially and correspondingly connected at intervals to form the field limiting ring terminal, N is greater than 2, and N is greater than 1. The curvature radius of the center point of at least one terminal area in the N terminal areas is a preset first curvature radius, the curvature radius of the end points of the terminal areas is a preset second curvature radius, and the first curvature radius is smaller than the second curvature radius; the curvature radius between the center point and the end point on the terminal area gradually changes from the first curvature radius to the second curvature radius. By adopting the field limiting ring terminal with the gradually changed curvature radius or curvature, the structure of the field limiting ring terminal of the power device can be optimized, the overall average curvature is reduced, and the curvature effect is reduced, so that the weak points of the device are reduced, and the withstand voltage of the device is improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductors, and in particular to a power device and a high-voltage field limiting ring terminal thereof, and a preparation method thereof. Background Art

[0002] Semiconductor power devices are key components in modern electronic devices. With the development of technology, the performance requirements for power devices are constantly increasing, especially in terms of withstand voltage, on-resistance, switching speed, reliability, etc. In order to meet these requirements, field limiting ring terminal technology, as an important terminal structure design, is widely used in semiconductor power devices to improve their withstand voltage characteristics and overall performance.

[0003] Field-limiting ring terminal technology is a key technology for improving the withstand voltage of power semiconductor devices. By setting a series of field-limiting ring terminals around the active area of ​​the device, the terminal corners of the field-limiting ring terminal structure of conventional power devices are quarter arcs, which will produce a curvature effect. The radius of curvature at the arc is R. At the junction of the arc and the straight edge area, the terminal curvature radius suddenly changes from R to 0 of the straight edge, causing the electric field strength to increase, resulting in early breakdown here, and reducing the breakdown voltage of the semiconductor power device. Therefore, in order to improve the withstand voltage, the method of increasing the edge chamfer curvature radius (reducing the curvature) is generally adopted, but this will greatly increase the area of ​​the terminal withstand voltage area and reduce the area of ​​the device active area. Summary of the invention

[0004] The embodiment of the present invention provides a power device and a high-voltage field limiting ring terminal and a preparation method thereof, so as to solve the problem in the prior art that the breakdown voltage of the semiconductor power device is reduced due to the increase of electric field strength caused by the sudden change of curvature radius, thereby reducing the voltage resistance of the semiconductor power device.

[0005] Based on the above purpose, in one embodiment, a high withstand voltage field limiting ring terminal of a power device is provided, comprising N straight area regions and N terminal areas, each of the terminal areas is sequentially connected with each of the straight area regions at intervals and correspondingly to form a field limiting ring terminal, N>2, a curvature radius of a center point of at least one of the N terminal areas is a preset first curvature radius, a curvature radius of an end point of the terminal area is a preset second curvature radius, the first curvature radius is smaller than the second curvature radius, and a curvature radius from the center point to the end point on the terminal area gradually changes from the first curvature radius to the second curvature radius; Alternatively, the curvature of the center point of at least one of the N terminal areas is a preset first curvature, the curvature of the endpoint of the terminal area is a preset second curvature, the second curvature is greater than the first curvature, and the curvature between the center point and the endpoint of the terminal area gradually changes from the first curvature to the second curvature.

[0006] In one embodiment, the second radius of curvature is infinite, or the second curvature is zero.

[0007] In one embodiment, taking one of the endpoints on the terminal area as the coordinate origin, the calculation expression of the curvature of any point between the endpoint and the center point on the terminal area is: Q= , Wherein, Q is the curvature of any point between the end point and the center point on the terminal area, a is the lateral distance between the center point of the terminal area and the end point of the terminal area, X is the distance between any point and the coordinate origin, and R is the first curvature radius, or, is the first curvature.

[0008] In one embodiment, a method for preparing a high withstand voltage field limiting ring terminal of a power device is provided, the preparation method comprising: Providing a semiconductor substrate; coating a photoresist on the semiconductor substrate; Using a preset mask plate, transferring a preset gradient window pattern on the mask plate to the photoresist to obtain a photoresist with a gradient window, wherein the radius of curvature of the center point of the gradient window pattern on the mask plate is a preset first radius of curvature, the radius of curvature of the endpoints of the gradient window pattern is a preset second radius of curvature, the first radius of curvature is smaller than the second radius of curvature, and the radius of curvature from the center point to the endpoints on the gradient window gradually changes from the first radius of curvature to the second radius of curvature, or the curvature of the center point of the gradient window pattern is a preset first curvature, the endpoints of the gradient window pattern are preset second curvature, the first curvature is larger than the second curvature, and the curvature from the center point to the endpoints on the gradient window gradually changes from the first curvature to the second curvature; Ion implantation is performed into the photoresist with the gradient window, and the photoresist is removed to obtain the high withstand voltage field limiting ring terminal region.

[0009] In one embodiment, the second radius of curvature is infinite, or the second curvature is zero.

[0010] In one embodiment, taking one of the endpoints on the gradient window graph as the coordinate origin, the calculation expression of the curvature of any point between the endpoint and the center point on the gradient window graph is: Q= , Wherein, Q is the curvature of any point between the end point and the center point on the terminal area, a is the lateral distance between the center point of the gradient window graphic and the end point of the gradient window graphic, X is the distance between the any point and the coordinate origin, R is the first curvature radius, or, is the first curvature.

[0011] In one embodiment, a power device is provided, comprising an active area structure, a high-voltage field limiting ring terminal arranged at the periphery of the active area structure, the high-voltage field limiting ring terminal comprising N straight areas and N terminal areas, each of the terminal areas being sequentially connected to each of the straight areas at intervals and correspondingly to form a field limiting ring terminal, N>2, a curvature radius of a center point of at least one of the N terminal areas being a preset first curvature radius, a curvature radius of an end point of the terminal area being a preset second curvature radius, the first curvature radius being smaller than the second curvature radius, and a curvature radius from the center point to the end point on the terminal area gradually changing from the first curvature radius to the second curvature radius; Alternatively, the curvature of the center point of at least one of the N terminal areas is a preset first curvature, the curvature of the endpoint of the terminal area is a preset second curvature, the second curvature is greater than the first curvature, and the curvature between the center point and the endpoint of the terminal area gradually changes from the first curvature to the second curvature.

[0012] In one embodiment, the high-voltage field limiting ring terminal includes four terminal regions, and each of the terminal regions is a terminal region with a gradually changing radius of curvature or a gradually changing curvature.

[0013] In one embodiment, the second radius of curvature is infinite, or the second curvature is zero.

[0014] In one embodiment, taking one of the endpoints on the terminal area as the coordinate origin, the calculation expression of the curvature of any point between the endpoint and the center point on the terminal area is: Q= , Wherein, Q is the curvature of any point between the end point and the center point on the terminal area, a is the lateral distance between the center point of the terminal area and the end point of the terminal area, X is the distance between any point and the coordinate origin, and R is the first curvature radius, or, is the first curvature.

[0015] The above-mentioned power device and its high withstand voltage field limiting ring terminal and preparation method optimize the field limiting ring terminal structure of the power device by setting the curvature radius of the terminal area to a gradual curvature radius, or by setting the curvature of the terminal area to a gradual curvature. Due to the curvature effect, the electric field is large where the curvature is large, and the electric field is related to the breakdown voltage. The larger the electric field, the easier it is to break down, and the lower the withstand voltage, so the place with a large curvature is the weak point of the device. By gradually changing the terminal curvature from the first curvature to the second curvature, the overall average curvature can be reduced, the curvature effect can be reduced, and thus the weak points of the device can be reduced and the withstand voltage of the device can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0017] Figure 1 A schematic diagram of a high withstand voltage field limiting ring region and its first curvature radius in one embodiment of the present invention; Figure 2 is a schematic diagram of calculating the lateral distance a between the center point and the end point of the terminal area in one embodiment of the present invention; Figure 3 is a schematic diagram of a semiconductor substrate provided in one embodiment of the present invention; Figure 4 is a schematic diagram of coating photoresist on a semiconductor substrate in one embodiment of the present invention; Figure 5 A schematic diagram of an exposure and photolithography process using a mask in one embodiment of the present invention; Figure 6 A schematic diagram of a gradual window pattern left on a photoresist in one embodiment of the present invention; Figure 7 is a schematic diagram of ion implantation in one embodiment of the present invention; Figure 8 It is a schematic diagram after removing the photoresist in one embodiment of the present invention; Fig. 9 It is a schematic diagram of a terminal area prepared in one embodiment of the present invention; Fig.10 This is a diagram of a high-voltage field-limiting ring terminal structure in which all four terminal regions have a gradient curvature radius or a gradient curvature in one embodiment of the present invention. Explanation of the accompanying drawings: 1. semiconductor substrate; 2. photoresist; 3. exposure light; 4. gradient window pattern; 5. implanted ions; 6. field limiting ring terminal region; 7. mask. DETAILED DESCRIPTION

[0018] 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 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.

[0019] It should be understood that the present invention can be implemented in different forms and should not be construed as being limited to the embodiments set forth herein. On the contrary, providing these embodiments will make the disclosure thorough and complete and fully convey the scope of the present invention to those skilled in the art. In the accompanying drawings, the sizes and relative sizes of layers and regions may be exaggerated for clarity. The same reference numerals throughout represent the same elements.

[0020] It should be understood that when an element or layer is referred to as being "on, adjacent to, connected to or coupled to other elements or layers, it may be directly on, adjacent to, connected to or coupled to other elements or layers, or there may be intervening elements or layers. In contrast, when an element is referred to as being "directly on, directly adjacent to, directly connected to or directly coupled to other elements or layers, there may be no intervening elements or layers. It should be understood that, although the terms first, second, third, etc. may be used to describe various elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or part from another element, component, region, layer or part. Therefore, without departing from the teachings of the present invention, the first element, component, region, layer or part discussed below may be represented as a second element, component, region, layer or part.

[0021] Spatially relative terms such as "under," "beneath," "below," "under," "above," "above," and the like may be used herein for ease of description to describe the relationship of an element or feature shown in the figures to other elements or features. It should be understood that the spatially relative terms are intended to include different orientations of the device in use and operation in addition to the orientations shown in the figures. For example, if the device in the accompanying drawings is flipped, then the elements or features described as "under other elements" or "under" or "under" will be oriented as "above" the other elements or features. Thus, the exemplary terms "under" and "under" may include both upper and lower orientations. The device may be otherwise oriented (rotated 90 degrees or other orientations) and the spatial descriptors used herein are interpreted accordingly.

[0022] The purpose of the terms used herein is only to describe specific embodiments and is not intended to be limiting of the present invention. When used herein, the singular forms "one", "an" and "said / the" are also intended to include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "consisting of" and / or "comprising", when used in this specification, determine the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0023] In order to fully understand the present invention, detailed structures and steps will be presented in the following description to illustrate the technical solutions proposed by the present invention. The preferred embodiments of the present invention are described in detail below, but in addition to these detailed descriptions, the present invention may also have other implementations.

[0024] In one embodiment, a high withstand voltage field limiting ring terminal of a power device is provided, such as Figure 1 As shown, it includes N straight areas and N terminal areas, each of the terminal areas is connected to each of the straight areas in sequence and at intervals to form a field limiting ring terminal, N>2, the curvature radius of the center point of at least one of the N terminal areas is a preset first curvature radius, the curvature radius of the end point of the terminal area is a preset second curvature radius, the first curvature radius is smaller than the second curvature radius, and the curvature radius from the center point to the end point on the terminal area gradually changes from the first curvature radius to the second curvature radius; Alternatively, the curvature of the center point of at least one of the N terminal areas is a preset first curvature, the curvature of the endpoint of the terminal area is a preset second curvature, the second curvature is greater than the first curvature, and the curvature between the center point and the endpoint of the terminal area gradually changes from the first curvature to the second curvature.

[0025] Among them, Figure 1 As shown, R1 is a preset first curvature radius, R1 is smaller than the second curvature radius, and R1 is a curvature radius of a field limiting ring terminal of a common arc structure. A normal power device has four terminal regions, and the curvature radius or the terminal region with a gradual curvature in this embodiment can be one, two, three or four. When there is one terminal region with a gradual curvature radius or a gradual curvature, the voltage resistance of the power device can be improved to a certain extent. When it is increased to two, the voltage resistance is further improved. When it is increased to three, the voltage resistance is further improved. When all four are terminal regions with a gradual curvature radius or a gradual curvature, the voltage resistance can be improved to the greatest extent.

[0026] The field limiting ring terminal of this embodiment can reduce the average curvature of the terminal area, reduce the curvature effect, reduce the electric field strength, and thus improve the withstand voltage by setting the curvature radius or curvature of the terminal area to a gradual curvature radius or curvature.

[0027] In one embodiment, the second radius of curvature is infinite, or the second curvature is zero.

[0028] Since the second radius of curvature is a straight edge, the second radius of curvature is infinite, or, since the radius of curvature and the curvature are inversely proportional to each other, the second curvature is zero.

[0029] In one embodiment, taking one of the endpoints on the terminal area as the coordinate origin, the calculation expression of the curvature of any point between the endpoint and the center point on the terminal area is: Q= , Wherein, Q is the curvature of any point between the end point and the center point on the terminal area, a is the lateral distance between the center point of the terminal area and the end point of the terminal area, X is the distance between any point and the coordinate origin, and R is the first curvature radius, or, is the first curvature.

[0030] Among them, Figure 2 As shown, the terminal region is an R * R The radius of curvature at the center point E of the terminal area is R, and the distance BE from the center point E to the vertex B of the square is RR, the distance CE from the vertex C of the square to the center point E is R -( RR), where CE, EF and CF form an isosceles right triangle CEF, and the side length EF of the isosceles right triangle is R -R+ R, EF is the lateral distance a of the terminal area from the first curvature radius to the second curvature radius, or the lateral distance a of the terminal area from the first curvature to the second curvature. Substituting the value of a into the calculation expression of the curvature of any point between the end point and the center point, we can get: Q= .

[0031] In one embodiment, a method for preparing a high withstand voltage field limiting ring terminal of a power device is provided, the preparation method comprising the following steps: S401, providing a semiconductor substrate 1; The semiconductor substrate 1 provided is as follows: Figure 3As shown, the semiconductor substrate 1 can be made of existing common N-type silicon (Si) material or silicon carbide (SiC) material, etc. The specific semiconductor material can be selected according to the requirements of the product.

[0032] S402, coating a layer of photoresist 2 on the semiconductor substrate 1; Wherein, the coated photoresist 2 is as follows Figure 4 As shown, photoresist, also known as photoresist, is a photosensitive material that undergoes chemical changes under the irradiation of light, thereby causing a change in the dissolution rate. It is one of the key materials in the processing of semiconductors and microelectronic devices.

[0033] S403, using a preset mask plate 7, transferring the preset gradient window pattern 4 on the mask plate 7 to the photoresist 2 to obtain a photoresist having a gradient window pattern 4; the radius of curvature of the center point of the gradient window pattern 4 on the mask plate 7 is a preset first radius of curvature, the radius of curvature of the endpoints of the gradient window pattern 4 is a preset second radius of curvature, the first radius of curvature is smaller than the second radius of curvature, and the radius of curvature from the center point to the endpoints on the gradient window pattern 4 gradually changes from the first radius of curvature to the second radius of curvature, or the curvature of the center point of the gradient window pattern 4 is a preset first curvature, the endpoints of the gradient window pattern 4 are a preset second curvature, the first curvature is larger than the second curvature, and the curvature from the center point to the endpoints on the gradient window pattern 4 gradually changes from the first curvature to the second curvature; Among them, the mask plate 7 with the gradient window pattern 4 is as follows: Figure 5 As shown, through the exposure operation, the gradient window pattern 4 on the mask 7 is transferred to the photoresist 2. The gradient window pattern 4 is an opaque area. Since the transparent area on the mask 7 allows light to pass through, while the opaque area blocks the light, when the light 3 passes through the mask 7 and irradiates the photoresist 2 on the semiconductor substrate, an exposure area corresponding to the gradient window pattern 4 on the mask 7 will be formed on the photoresist 2. Then, a photolithography process is performed. Since the photoresist in the exposure area will be dissolved, leaving the gradient window pattern 4 on the mask 7, the gradient window pattern can be transferred to the photoresist, as shown in FIG. Figure 6 shown.

[0034] S404 , implanting ions 5 into the photoresist having the gradient window 4 , removing the photoresist 2 , and obtaining the high withstand voltage field limiting ring terminal region 6 .

[0035] When ion implantation is performed, the implanted ions 5 are P-type ions, such as Figure 7 As shown, after removing the photoresist 2, as Figure 8 As shown, the high withstand voltage field limiting ring terminal region can be obtained, such as Fig. 9 shown.

[0036] The preparation method of the high voltage-resistant field limiting ring terminal area of ​​the present embodiment is the same as the existing preparation process flow, except that the window pattern preset on the mask is changed from the existing quarter arc to a window pattern with a gradual curvature radius or a gradual curvature. Without adding additional process steps, the voltage resistance and reliability of the field limiting ring terminal area can be improved.

[0037] In one embodiment, the second radius of curvature is infinite, or the second curvature is zero.

[0038] In one embodiment, taking one of the endpoints on the terminal area as the coordinate origin, the calculation expression of the curvature of any point between the endpoint and the center point on the terminal area is: Q= , Wherein, Q is the curvature of any point between the end point and the center point on the terminal area, a is the lateral distance between the center point of the terminal area and the end point of the terminal area, X is the distance between any point and the coordinate origin, and R is the first curvature radius, or, is the first curvature.

[0039] Among them, the above embodiments and Figure 1 The specific calculation method of the lateral distance a of the transition from the first curvature radius to the second curvature radius of the terminal area, or the lateral distance a of the transition from the first curvature to the second curvature of the terminal area remains unchanged, and is still R -R+ R.

[0040] In one embodiment, a power device is provided, comprising an active area structure, a high-voltage field limiting ring terminal arranged at the periphery of the active area structure, the high-voltage field limiting ring terminal comprising N straight areas and N terminal areas, each of the terminal areas being sequentially connected to each of the straight areas at intervals and correspondingly to form a field limiting ring terminal, N>2, a curvature radius of a center point of at least one of the N terminal areas being a preset first curvature radius, a curvature radius of an end point of the terminal area being a preset second curvature radius, the first curvature radius being smaller than the second curvature radius, and a curvature radius from the center point to the end point on the terminal area gradually changing from the first curvature radius to the second curvature radius; Alternatively, the curvature of the center point of at least one of the N terminal areas is a preset first curvature, the curvature of the endpoint of the terminal area is a preset second curvature, the second curvature is greater than the first curvature, and the curvature between the center point and the endpoint of the terminal area gradually changes from the first curvature to the second curvature.

[0041] In one embodiment, if Fig.10 As shown, the high-voltage field limiting ring terminal includes four terminal regions, and each of the terminal regions is a terminal region with a gradually changing radius of curvature or a gradually changing curvature.

[0042] Among them, when the four terminal areas of the field limiting ring terminal of the power device are all terminal areas with a gradual curvature radius or a gradual curvature, the voltage resistance of the power device will be improved compared with the above-mentioned field limiting ring terminals with only one, only two, or only three gradual curvature radius or a gradual curvature, and the terminal areas with all gradual curvature radius or a gradual curvature have the best voltage resistance and the highest reliability.

[0043] In this embodiment, the high withstand voltage field limiting ring terminal is as follows Fig.10 As shown, the semiconductor at the terminal of the field limiting ring can be an N-type semiconductor or a P-type semiconductor.

[0044] In one embodiment, the second radius of curvature is infinite, or the second curvature is zero.

[0045] In one embodiment, taking one of the endpoints on the terminal area as the coordinate origin, the calculation expression of the curvature of any point between the endpoint and the center point on the terminal area is: Q= , Wherein, Q is the curvature of any point between the end point and the center point on the terminal area, a is the lateral distance between the center point of the terminal area and the end point of the terminal area, X is the distance between any point and the coordinate origin, and R is the first curvature radius, or, is the first curvature.

[0046] Among them, the above embodiments and Figure 1 The specific calculation method of the lateral distance a of the transition from the first curvature radius to the second curvature radius of the terminal area, or the lateral distance a of the transition from the first curvature to the second curvature of the terminal area remains unchanged, and is still R -R+ R.

[0047] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A high withstand voltage field limiting ring terminal for a power device, characterized in that: The invention comprises N straight areas and N terminal areas, wherein each terminal area is connected to each straight area in sequence and at intervals to form a field limiting ring terminal, N>2, the curvature radius of the center point of at least one terminal area among the N terminal areas is a preset first curvature radius, the curvature radius of the end point of the terminal area is a preset second curvature radius, the first curvature radius is smaller than the second curvature radius, and the curvature radius from the center point to the end point on the terminal area gradually changes from the first curvature radius to the second curvature radius; Alternatively, the curvature of the center point of at least one of the N terminal areas is a preset first curvature, the curvature of the endpoint of the terminal area is a preset second curvature, the second curvature is greater than the first curvature, and the curvature between the center point and the endpoint of the terminal area gradually changes from the first curvature to the second curvature.

2. The high withstand voltage field limiting ring terminal of a power device according to claim 1, characterized in that: The second radius of curvature is infinite, or the second curvature is zero.

3. The high withstand voltage field limiting ring terminal of a power device according to claim 1, characterized in that: Taking one of the endpoints on the terminal area as the coordinate origin, the calculation expression of the curvature of any point between the endpoint and the center point on the terminal area is: Q= ， Wherein, Q is the curvature of any point between the end point and the center point on the terminal area, a is the lateral distance between the center point of the terminal area and the end point of the terminal area, X is the distance between any point and the coordinate origin, and R is the first curvature radius, or, is the first curvature.

4. A method for preparing a high-voltage field-limiting ring terminal of a power device, characterized in that: The preparation method comprises: Providing a semiconductor substrate; coating a photoresist on the semiconductor substrate; Using a preset mask plate, transferring a preset gradient window pattern on the mask plate to the photoresist to obtain a photoresist with a gradient window, wherein the radius of curvature of the center point of the gradient window pattern on the mask plate is a preset first radius of curvature, the radius of curvature of the endpoints of the gradient window pattern is a preset second radius of curvature, the first radius of curvature is smaller than the second radius of curvature, and the radius of curvature from the center point to the endpoints on the gradient window gradually changes from the first radius of curvature to the second radius of curvature, or the curvature of the center point of the gradient window pattern is a preset first curvature, the endpoints of the gradient window pattern are preset second curvature, the first curvature is larger than the second curvature, and the curvature from the center point to the endpoints on the gradient window gradually changes from the first curvature to the second curvature; Ion implantation is performed into the photoresist with the gradient window, and the photoresist is removed to obtain the high withstand voltage field limiting ring terminal region.

5. The method for preparing a high withstand voltage field limiting ring terminal of a power device according to claim 4, characterized in that: The second radius of curvature is infinite, or the second curvature is zero.

6. The method for preparing a high withstand voltage field limiting ring terminal of a power device according to claim 4, characterized in that: Taking one of the endpoints on the gradient window graph as the coordinate origin, the calculation expression of the curvature of any point between the endpoint and the center point on the gradient window graph is: Q= ， Wherein, Q is the curvature of any point between the end point and the center point on the terminal area, a is the lateral distance between the center point of the gradient window graphic and the end point of the gradient window graphic, X is the distance between the any point and the coordinate origin, R is the first curvature radius, or, is the first curvature.

7. A power device, characterized in that: The invention comprises an active area structure, and a high-voltage field-limiting ring terminal arranged at the periphery of the active area structure, wherein the high-voltage field-limiting ring terminal comprises N straight areas and N terminal areas, and each of the terminal areas is sequentially connected with each of the straight areas at intervals to form a field-limiting ring terminal, wherein N>2, the curvature radius of the center point of at least one of the N terminal areas is a preset first curvature radius, the curvature radius of the end point of the terminal area is a preset second curvature radius, the first curvature radius is smaller than the second curvature radius, and the curvature radius from the center point to the end point on the terminal area gradually changes from the first curvature radius to the second curvature radius; Alternatively, the curvature of the center point of at least one of the N terminal areas is a preset first curvature, the curvature of the endpoint of the terminal area is a preset second curvature, the second curvature is greater than the first curvature, and the curvature between the center point and the endpoint of the terminal area gradually changes from the first curvature to the second curvature.

8. A power device according to claim 7, characterized in that: The high-voltage field limiting ring terminal includes four terminal regions, and each of the terminal regions is a terminal region with a gradually changing radius of curvature or a gradually changing curvature.

9. A power device according to claim 7, characterized in that: The second radius of curvature is infinite, or the second curvature is zero.

10. A power device according to claim 7, characterized in that: Taking one of the endpoints on the terminal area as the coordinate origin, the calculation expression of the curvature of any point between the endpoint and the center point on the terminal area is: Q= ， Wherein, Q is the curvature of any point between the end point and the center point on the terminal area, a is the lateral distance between the center point of the terminal area and the end point of the terminal area, X is the distance between any point and the coordinate origin, and R is the first curvature radius, or, is the first curvature.

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