Low-thermal-conductivity micro-bolometer based on total stress beam and design method of low-thermal-conductivity micro-bolometer

Abstract

The invention discloses a low-thermal-conductivity micro-bolometer based on a total stress beam and a design method of the low-thermal-conductivity micro-bolometer. Each bridge comprises a bridge column connecting section and a bridge floor connecting section, the width of the bridge column connecting section changes in the y direction, the width of the bridge floor connecting section changes in the x direction, the width distribution of the bridge column connecting section changing in the y direction and the width distribution of the bridge floor connecting section changing in the x direction are optimized respectively, the thermal conductivity of the device is optimized to the maximum extent, and therefore the responsivity is increased; according to the method, the bending moment and the torque borne by the bridge are comprehensively considered, the unnecessary bridge area is reduced through theoretical analytical solution calculation, and the thermal conductivity of the bridge is greatly reduced to improve the response rate; furthermore, an algorithm for optimizing the single-layer material bridge is expanded and corrected to a double-layer composite beam structure or even a multi-layer composite beam structure, so that the design method disclosed by the invention can be used in an actual application scene.

Description

Technical Field

[0001] The present invention relates to the field of infrared sensors, and in particular to a low thermal conductivity microbolometer based on a fully stressed beam and a design method thereof. Background Art

[0002] In recent years, thanks to the development of infrared detection technology towards ultra-high response rate and miniaturization, the bridge of the bridge microbolometer will become thinner and longer to achieve lower thermal conductivity. The bridge of the single-layer bridge microbolometer serves as a thermal conductor and support, and the bridge deck serves as an absorption layer. The curved bridge design will lead to a loss of mechanical support performance and a reduction in the absorption area. Although in recent years some research teams have achieved the effect of functional separation by making double-layer umbrella-shaped microbolometers, that is, the upper layer is made into an umbrella-shaped absorption layer, and the lower layer is separately arranged with slender bridges as a thermal conductive structure, the process complexity of this design has been significantly increased, and the above problems have not been fundamentally solved. The optimization method also needs to follow the mechanical properties of the device itself. For the design of equal-width bridges at various positions in traditional microbolometers, this method has the following shortcomings:

[0003] Because commonly used bridges of uniform width experience uneven load distribution, some sections of the bridge are susceptible to fracture due to higher loads, while other sections may still experience loads well below their mechanical limits. Currently, there is a lack of research focused on systematically optimizing bridge stress widths, so understanding the mechanical model of microbolometer beams and mastering the relevant theory is essential. Summary of the Invention

[0004] In view of the above problems existing in the prior art, the present invention proposes a low thermal conductivity microbolometer based on a fully stressed beam and a design method thereof.

[0005] An object of the present invention is to provide a design method for a low thermal conductivity microbolometer based on a fully stressed beam.

[0006] The design method of the low thermal conductivity microbolometer based on the full stress beam of the present invention comprises the following steps:

[0007] 1) Low thermal conductivity microbolometer composition:

[0008] The low thermal conductivity microbolometer includes a substrate, a bridge column, a bridge and a bridge deck; two bridge columns are arranged perpendicular to the substrate on the substrate; the tops of the bridge columns are provided with a bridge and a bridge deck connected as one body with the same density and height, the bridge deck is located in the center and is connected to the tops of the corresponding bridge columns by a single or multiple bridges;

[0009] Each bridge consists of a column connecting section and a deck connecting section. The starting end of the column connecting section is connected to the bridge column, the end of the deck connecting section is connected to the bridge deck, and the end of the deck connecting section is connected to the bridge deck. The cross-sectional dimension of the bridge deck is much larger than the width of the bridge. The length of the bridge is much larger than the width and thickness of the bridge.

[0010] 2) Establish a coordinate system:

[0011] An orthogonal coordinate system is established, with the z-axis direction being the positive force direction, the axis of the bridge column being on the z-axis, the substrate being on the xy plane, and the plane where the bridge and the bridge deck are located being on the xy plane;

[0012] The length of the bridge column connection section is along the y direction, with a length of L1. The width of the bridge column connection section varies along the y direction, with a width distribution of b(y). The length of the bridge deck connection section is along the x direction, with a length of L2. The width of the bridge deck connection section varies along the x direction, with a width distribution of b(x). The width distribution of the bridge column connection section along the y direction and the width distribution of the bridge deck connection section along the x direction are optimized separately to maximize the thermal conductivity of the device, thereby increasing the responsiveness.

[0013] In the subsequent mechanical analysis, the bridge column connection section, bridge deck connection section and bridge deck were separated into independent free bodies;

[0014] 3) Analysis of the first principal stress and normal stress of the bridge:

[0015]

[0016] In formula (1), σ1 is the first principal stress, σ x and σ y are the normal stresses along the x and y directions, τ xy is the shear stress along the xy plane, and M is the bending moment; due to bending, the entire bridge is subjected to normal stress along the x or y direction along its length or In formula (3), b is the width of the bridge; k1 is the first empirical constant of torsion related to the ratio b / h; in formula (4), I represents the moment of inertia; z represents the distance from the point to be solved to the neutral layer of a single-layer bridge made of uniform material. During the bending process, the outer layer of the material is stretched and the inner layer is squeezed. There must be a transition layer on its cross section that is neither stretched nor compressed, and the stress is almost zero. This transition layer is called the neutral layer of the material. h represents the height of the bridge deck and the bridge. In formula (4), When , is the normal stress σ along the x and y directions x and σ y Absolute maximum value;

[0017] 4) Shear stress analysis of bridges:

[0018] τ xymax =τ xymax-torsion +τxy-bend (5)

[0019]

[0020] In formula (5), τ xymax represents the maximum shear stress along the xy plane, τ xymax-rorsion represents the maximum shear stress along the xy plane caused by torsion, T is the torque, τ xy-bend is the shear stress parallel to the xy plane caused by bending; for slender bridge structures whose length is much greater than the thickness and width, the three-dimensional structure is converted into a one-dimensional structure along the length direction of the bridge. Only the maximum stress distribution is considered in this section, so for τ in formula (1) xy Use τ xymax Instead, because the above calculation σ x or σ y The absolute maximum value is used to calculate the maximum value of the first principal stress σ1 in this model; the shear stresses in the yz and xz directions caused by torsion are ignored; and for this slender bridge, the cross-section of the bridge deck is large, and the moment of inertia of the bridge deck is more than 10 times the moment of inertia of the bridge, so the normal stress σ in the y direction is ignored in the bridge deck connection section. y and the shear stress τ parallel to the xy plane due to bending xy-bend , ignoring the normal stress σ in the x-direction in the bridge column connection section x and the shear stress τ parallel to the xy plane due to bending xy-bend , simplifying formula (5) to obtain:

[0021] τ xymax =τ xymax-torsion

[0022] 5) Bending moment and torque analysis of bridges:

[0023] M(x)=M Gx +V G x (7)

[0024] T DG =M Dy

[0025] M(y)=M Dy +V D y (8)

[0026] T BD =M Dx

[0027] M Dy =M Gy , M Bx =M Dx(9) Equations (7) and (8) are the bending moment equations and torque equations for the bridge deck connection section and the bridge column connection section, respectively. Equation (9) is the bending moment boundary condition, where M(x) is the bending moment distribution of the bridge deck connection section along the x direction, M(y) is the bending moment distribution of the bridge column connection section along the y direction, and T DG and T BD are the torques of the bridge deck connection section and the bridge column connection section respectively; M ij is the bending moment at point i along direction j, i = G or D, point G is the end of the bridge deck connection section, point d is the connection between the bridge deck connection section and the bridge column connection section, point B is the beginning of the bridge column connection section, j = x or y, V k is the shear force at point k, k = G or D; BD is the bridge deck connection section, DG is the bridge deck connection section;

[0028] 6) Introduce the deflection equation:

[0029] For this statically uncertain structure, the torsion angle deflection equation is introduced to solve;

[0030]

[0031] θ tx =θ bx , θ ty =θ by (12) Equation (10) is the expression for the torsion angle. In Equation (10), θ tx and θ ty are the torsion angles of the end point G of the bridge deck connection along the x-direction and the y-direction respectively. Equation (11) is the expression of the bending angle. In Equation (11), θ bx and θ by are the bending angles in the x-direction and y-direction of the end point G of the bridge deck connection segment, E is the Young's modulus of the supporting layer material, and k2 is the second torsion empirical constant related to b / h; Equation (12) is the constraint condition: for the xy plane, the deflection angles at the end point G of the bridge deck connection segment and the starting point B of the bridge column connection segment are approximately regarded as 0; the torsion of the bridge column connection segment and the bending of the bridge deck connection segment contribute to the deflection angle of the end point G of the bridge deck connection segment along the x-direction; the bending of the bridge column connection segment and the torsion of the bridge deck connection segment contribute to the deflection angle of the end point G of the bridge deck connection segment along the y-direction; for the x-direction, the torsion angle of the bridge column connection segment is equal to the bending angle of the bridge deck connection segment; for the y-direction, the bending angle of the bridge column connection segment is equal to the torsion angle of the bridge deck connection segment; this relationship is solved by combining the expressions of torsion angle (10) and bending angle (11) to obtain the bending moment M Gx and bending moment M Dy , and then according to equations (7) to (9), solve the torque and bending moment distribution at each location on the bridge leg;

[0032] 7) Based on mechanical analysis, the following force balance equation and bending moment balance equation are obtained:

[0033] V G +V G′ =PA,M G +M G′ =0 (13)

[0034]

[0035] Where P is the distributed load on the microbolometer, P = kρgh, the area of ​​the bridge deck is A, kg represents the maximum acceleration of the structure, □ is the acceleration due to gravity, ρ and h represent the density and height of the bridge deck and bridge, respectively, and k is the coefficient of gravity acceleration. According to the symmetry of the structure, we can get Where G′ is the point symmetric to point G about the bridge surface;

[0036] For the bridge deck connection section, at the end point G of the bridge deck connection section, the bending moment M caused by the fixed structure is considered. G and shear force V G In the moment equilibrium equation, the last two terms of equations (14) and (15) are ignored because the load on the bridge is relatively small.

[0037] One term, the simplified moment equilibrium equations (16) and (17) are obtained:

[0038]

[0039] 8) Solve the width distribution:

[0040] Combining the constraint condition (12) with the bending moment and torque equations (7) and (8) and the simplified bending moment equilibrium equation and force equilibrium equations (13), (16) and (17), all parametric equations are substituted into the parameter values ​​of the structure, and the analytical solution of the width distribution of the bridge is calculated by solving the equations simultaneously.

[0041] In step 8), all the above equations are combined. For studying material fracture, only the maximum value of the first principal stress needs to be considered. The analytical solution of the bridge width distribution is obtained when the maximum value of the first principal stress in the one-dimensional bridge model is equal at all locations (let the left side of equation (1) be a constant). Let where σ allow is the safety factor of the bridge material and yield strength σ Y The product of .

[0042] Furthermore, in practical applications, since the microbolometer reads signals through voltage, metal electrodes are usually deposited on the bridge to form a composite beam structure with the upper layer being the electrode layer and the lower layer being the support layer, which affects the stress state of the original single-layer material. The present invention introduces the parameters of the multilayer material into the model optimization. In this invention, the lower support layer is made of silicon nitride or silicon oxide inorganic materials, and the upper electrode layer is made of platinum or gold, which has good ductility. Since the brittleness of the support layer is higher than that of the electrode layer, and the tensile fracture strength of the support layer is often lower than the compressive fracture strength, it is analyzed here whether the first principal stress of the support layer is higher than the designed allowable tensile stress. According to the integral result of the moment of inertia of the composite beam, the calculation formula is as follows:

[0043]

[0044] h0 is the distance from the bridge surface to the neutral layer, h1 and h2 are the heights of the upper and lower layers respectively; G1 and G2 are the shear moduli of the upper and lower layers respectively, E1 and E2 are the elastic moduli of the upper and lower layers respectively, k′1 is the first empirical value of the torsional constant of the composite beam; I1 and I2 are the moments of inertia of the upper and lower layers respectively; b co is the width of the composite beam, τ′ xymax-torsion is the maximum shear stress caused by torsion in the composite beam, y max is the maximum distance from the support layer surface to the neutral layer; Equations (21) to (23) are the normal stress σ of the composite beam respectively. co , torsion angle θ co_t and bending angle θ co_b k′2 is the second empirical value of the composite beam torsional constant. Substituting these corrections into the above constraint equation (12), the moment and torque equations, and the simplified moment and force equilibrium equations yields an analytical solution to the width distribution of the double-layer composite beam. The specific width distribution of the composite beam is determined based on the first maximum principal stress of the layer with the poorer yield strength.

[0045] For composite beams made of multiple layers (three or more layers), the material mechanics formulas for composite beams are used for calculations. Specifically, the Young's modulus and shear modulus of various materials are used to correct for the moment of inertia, torsional moment of inertia, bending moment, torque, bending angle, and torsion angle. For multi-beam bridge structures, such as the dual-beam bridge structures targeted by this invention, these conditions also need to be modified for mechanical analysis.

[0046] In step 1), the cross-sectional dimensions of the bridge deck are at least 10 times greater than the width of the bridge. The length of the bridge is at least 10 times greater than the width and thickness of the bridge. The substrate is silicon with a thickness of 250 to 400 μm. The bridge columns, deck, and bridge are made of silicon nitride, silicon oxide, or aluminum oxide, with a thickness of 150 to 300 nm. The electrodes are made of platinum, nickel, gold, titanium, or ITO, with a thickness of 50 to 150 nm.

[0047] Another object of the present invention is to provide a low thermal conductivity microbolometer based on a fully stressed beam.

[0048] The low thermal conductivity microbolometer based on the fully stressed beam of the present invention includes: the low thermal conductivity microbolometer includes a substrate, a bridge column, a bridge and a bridge deck; two bridge columns perpendicular to the substrate are arranged on the substrate; the top of the bridge column is provided with a bridge and a bridge deck connected as a whole with the same density and height, the bridge deck is located in the center, and is connected to the top of the corresponding bridge column by a single or multiple bridges; each bridge includes a bridge column connecting section and a bridge deck connecting section, the starting end of the bridge column connecting section is connected to the bridge column, the end is connected to the bridge deck connecting section, and the end of the bridge deck connecting section is connected to the bridge deck; the cross-sectional size of the bridge deck is much larger than the width of the bridge; the length of the bridge is much larger than the width and thickness of the bridge; an orthogonal coordinate system is established, the z-axis direction is the positive force direction, the axis of the bridge column is located on the z-axis, the substrate is located in the xy plane, and the plane where the bridge and the bridge deck are located is located in the xy plane; the length direction of the bridge column connecting section is along the y direction, the length is L1, and the bridge column connecting section The width varies along the y direction; the length direction of the bridge deck connection section is along the x direction, the length is L2, and the width of the bridge deck connection section varies along the x direction; the width distribution of the bridge column connection section along the y direction and the width distribution of the bridge deck connection section along the x direction are optimized respectively, so as to maximize the thermal conductivity of the device and thus increase the responsiveness; the first principal stress, normal stress and shear stress of the bridge are analyzed, and the normal stress in the y direction and the shear stress parallel to the xy plane caused by bending are ignored in the bridge deck connection section, and the normal stress in the x direction and the shear stress parallel to the xy plane caused by bending are ignored in the bridge column connection section; the torsion angle deflection equation is used as the constraint condition, and the bending moment and torque equations as well as the bending moment equilibrium equation and the force equilibrium equation are solved simultaneously. Only the maximum value of the first principal stress needs to be considered, and the analytical solution of the equal bridge width distribution at all the first principal stress maximum values ​​in the one-dimensional bridge model is solved to obtain the width distribution of the bridge.

[0049] Advantages of the present invention:

[0050] The present invention comprehensively considers the bending moment and torque acting on the bridge, reduces unnecessary bridge area through theoretical analytical calculations, and significantly reduces the thermal conductivity of the bridge to improve the response rate; the algorithm for optimizing single-layer material bridges is expanded and modified to double-layer composite beam structures or even multi-layer composite beam structures, so that the algorithm of the present invention can be used in actual application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 Schematic diagram of the bridge structure of a traditional microbolometer;

[0052] Figure 2 A top view of a bridge structure of an embodiment of a low thermal conductivity microbolometer based on a fully stressed beam of the present invention;

[0053] Figure 3 A cross-sectional view of a bridge showing an embodiment of the low thermal conductivity microbolometer based on a fully stressed beam of the present invention. DETAILED DESCRIPTION

[0054] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings.

[0055] Figure 1 It is a bridge structure in the prior art, wherein the widths of the bridges 2 connecting the bridge decks 1 are consistent.

[0056] Example 1

[0057] In this embodiment, a single-layer beam structure is used, with silicon nitride used as the single layer material for the bridge and deck. Calculating the above parameters by entering them into the model reveals that the standard deviation of the first maximum principal stress across the entire bridge leg does not exceed 5.92 and 4.997 MPa, essentially achieving a state of uniform stress throughout. The material parameters for the single-layer beam structure are shown in Table 1 below:

[0058] Table 1 Parameters of single-layer beam structure materials

[0059]

[0060] The design method of the low thermal conductivity microbolometer based on the fully stressed beam of this embodiment includes the following steps:

[0061] 1) Low thermal conductivity microbolometer composition:

[0062] The low thermal conductivity microbolometer includes a substrate, a bridge column, a bridge and a bridge deck; two bridge columns are arranged perpendicular to the substrate on the substrate; the tops of the bridge columns are provided with a bridge and a bridge deck connected as one body with the same density and height, with the bridge deck located in the center and connected to the tops of the corresponding bridge columns by two bridges;

[0063] like Figure 2 As shown in the figure, each bridge includes a column connection section BD and a deck connection section DG. The starting end of the column connection section is connected to the bridge column, the end is connected to the deck connection section, and the end of the deck connection section is connected to the bridge deck. The cross-sectional size of the bridge deck is much larger than the width of the bridge. The lengths of the column connection section and the deck connection section are 64.5μm and 81.2μm respectively, and the thickness is 150

[0064] nm; the substrate is made of silicon with a thickness of 300 μm;

[0065] 2) Establish a coordinate system:

[0066] An orthogonal coordinate system is established, with the z-axis direction being the positive force direction, the axis of the bridge column being on the z-axis, the substrate being on the xy plane, and the plane where the bridge and the bridge deck are located being on the xy plane;

[0067] The length of the bridge column connection section is along the y direction, with a length of L1. The width of the bridge column connection section varies along the y direction, with a width distribution of b(y). The length of the bridge deck connection section is along the x direction, with a length of L2. The width of the bridge deck connection section varies along the x direction, with a width distribution of b(x). The width distribution of the bridge column connection section along the y direction and the width distribution of the bridge deck connection section along the x direction are optimized separately to maximize the thermal conductivity of the device, thereby increasing the responsiveness.

[0068] In the subsequent mechanical analysis, the bridge column connection section, bridge deck connection section and bridge deck were separated into independent free bodies;

[0069] 3) Analysis of the first principal stress and normal stress of the bridge:

[0070]

[0071] In formula (1), σ1 is the first principal stress, σ x and σ y are the normal stresses along the x and y directions, τ xy is the shear stress along the xy plane, and M is the bending moment. Due to bending, the entire bridge is subjected to a normal stress σ along the x or y direction along its length. x or σ y In formula (3), b is the width of the bridge; k1 is the first empirical constant of torsion related to the ratio b / h; in formula (4), I represents the moment of inertia; z represents the distance from the point to be solved to the neutral layer of a single-layer bridge of uniform material. During the bending process, the outer layer of the material is stretched and the inner layer is squeezed. There must be a transition layer on its cross section that is neither stretched nor compressed, and the stress is almost zero. This transition layer is called the neutral layer of the material; in formula (4), z is taken as When , is the normal stress σ along the x and y directions x or σ y Absolute maximum value;

[0072] 4) Shear stress analysis of bridges:

[0073] τ xymax =τ xymax-torsion +τ xy-bend (5)

[0074]

[0075] In formula (5), τ xymax represents the maximum shear stress along the xy plane, τ xymax-torsion represents the maximum shear stress along the xy plane caused by torsion, T is the torque, τ xy-bendDue to the shear stress parallel to the xy plane caused by bending; for slender bridge structures whose length is much greater than the thickness and width, the three-dimensional structure is converted into a one-dimensional structure along the long direction of the bridge. Only the maximum stress distribution is considered in this section, so for τ in formula (1) xy Use τ xymax Instead, because the above calculation σ x or σ y The absolute maximum value is used to calculate the maximum value of the first principal stress σ1 in this model. The shear stresses in the yz and xz directions caused by torsion are ignored. In addition, for this slender rectangular beam, the cross section of the bridge deck is large, and the moment of inertia of the bridge deck is more than 10 times that of the bridge. Therefore, the normal stress σ in the y direction is ignored in the bridge deck connection section. y and the shear stress τ parallel to the xy plane due to bending xy-bend , ignoring the normal stress σ in the x-direction in the bridge column connection section x and the shear stress τ parallel to the xy plane due to bending xy-bend , simplifying formula (5) to obtain:

[0076] τ xymax =τ xymax-torsion

[0077] 5) Bending moment and torque analysis of bridges:

[0078] M(x)=M Gx +V G x (7)

[0079] T DG =M Dy

[0080] M(y)=M Dy +V D y (8)

[0081] T BD =M Dx

[0082] M Dy =M Gy , M Bx =M Dx (9) Equations (7) and (8) are the bending moment equations and torque equations for the bridge deck connection section and the bridge column connection section, respectively. Equation (9) is the bending moment boundary condition, where M(x) is the bending moment distribution of the bridge deck connection section along the x direction, M(y) is the bending moment distribution of the bridge column connection section along the y direction, and T DG and T BD are the torques of the bridge deck connection section and the bridge column connection section respectively; M ijis the bending moment at point i along direction j, i = G or D, point G is the end of the bridge deck connection section, point D is the connection between the bridge deck connection section and the bridge column connection section, point B is the beginning of the bridge column connection section, j = x or y, V k is the shear force at point k, k = G or D; BD is the bridge deck connection section, DG is the bridge deck connection section;

[0083] 6) Introduce the deflection equation:

[0084] For this statically uncertain structure, the torsion angle deflection equation is introduced to solve;

[0085]

[0086] θ tx =θ bx , θ ty =θ by (12) ((10) is the expression for the torsion angle, where θ tx and θ ty are the torsion angles of the end point G of the bridge deck connection along the x-direction and the y-direction respectively. Equation (11) is the expression of the bending angle. In Equation (11), θ bx and θ by are the bending angles in the x-direction and y-direction of the end point G of the bridge deck connection segment, E is the Young's modulus of the supporting layer material, and k2 is the second torsion empirical constant related to b / h; Equation (12) is the constraint condition: for the xy plane, the deflection angles at the end point G of the bridge deck connection segment and the starting point B of the bridge column connection segment are approximately regarded as 0; the torsion of the bridge column connection segment and the bending of the bridge deck connection segment contribute to the deflection angle of the end point G of the bridge deck connection segment along the x-direction; the bending of the bridge column connection segment and the torsion of the bridge deck connection segment contribute to the deflection angle of the end point G of the bridge deck connection segment along the y-direction; for the x-direction, the torsion angle of the bridge column connection segment is equal to the bending angle of the bridge deck connection segment; for the y-direction, the bending angle of the bridge column connection segment is equal to the torsion angle of the bridge deck connection segment; this relationship is solved by combining the expressions of torsion angle (10) and bending angle (11) to obtain the bending moment M Gx and bending moment M Dy , and then according to equations (7) to (9), solve the torque and bending moment distribution at each location on the bridge leg;

[0087] 7) According to mechanical analysis, the following moment equilibrium equation and force equilibrium equation are obtained:

[0088] V G +V G′ =PA,M G +M G′ =0 (13)

[0089]

[0090] Where P is the distributed load on the microbolometer, P = kρgh, the area of ​​the bridge deck is A, kg represents the maximum acceleration of the structure, g is the acceleration due to gravity, ρ and h represent the density and height of the bridge deck and bridge, respectively, and k is the coefficient of gravity acceleration, where k = 5000. Based on the symmetry of the structure, we get Where G′ is the point symmetrical to point G about the bridge deck; for the bridge deck connection section, at the end point G of the bridge deck connection section, the bending moment M caused by the fixed structure is considered. G and shear force V G ; In the moment equilibrium equation, since the load on the bridge is relatively small, equation (14) is ignored. and the last term of (15), we obtain the simplified moment equilibrium equations (16) and (17):

[0091]

[0092] 8) Solve the width distribution:

[0093] With the constraint condition (12), all the above equations are combined. For studying material fracture, only the maximum value of the first principal stress needs to be considered. The analytical solution of the bridge width distribution is obtained when the maximum value of the first principal stress is equal at all locations in the one-dimensional bridge model (let the left side of equation (1) be a constant). In the solution process, let where σ allow is the safety factor of the bridge material and yield strength σ Y The product of .

[0094] Example 2

[0095] This embodiment uses a composite beam structure with two layers of materials. The two layers of the bridge are made of metal Pt as the upper electrode layer and silicon nitride as the lower support layer. The thickness of the electrode layer is 50nm. The parameters of the composite beam structure materials are shown in Table 2 below:

[0096] Table 2 Parameters of double-layer composite bridge leg materials

[0097]

[0098] According to the integral result of the moment of inertia of the composite beam, the calculation formula is as follows:

[0099]

[0100]

[0101] h0 is the distance from the bridge surface to the neutral layer, h1 and h2 are the heights of the upper and lower layers, respectively, and the width of the bridge is b. G1 and G2 are the shear moduli of the upper and lower layers, respectively, E1 and E2 are the elastic moduli of the upper and lower layers, respectively, k′1 is the first empirical value of the torsion constant of a rectangular bridge; I1 and I2 are the moments of inertia of the upper and lower layers, respectively; b co is the width of the composite beam, τ′ xymax-torsion is the maximum shear stress caused by torsion in the double-layer composite beam, y max is the maximum distance from the support layer surface to the neutral layer; Equations (21) to (23) are the normal stress σ of the bridge respectively. co , torsion angle θ co_t and bending angle θ co_b k′² is the second empirical value of the torsional constant for rectangular beams in Equation (22). Substituting these corrections into the constraints (Equation (12)) and the bending moment and torque equations above yields an analytical solution for the bridge distribution of a two-layer composite material. The specific bridge width is determined based on the first maximum principal stress in the layer with the poorer yield strength.

[0102] By substituting the above parameters into the calculation, it was found that the standard deviation of the first maximum principal stress of the entire bridge did not exceed 5.92 and 4.997 MPa, basically achieving a state of equal stress everywhere.

[0103] Finally, it should be noted that the purpose of disclosing the embodiments is to facilitate a further understanding of the present invention. However, those skilled in the art will appreciate that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the contents disclosed in the embodiments; the scope of protection claimed by the present invention shall be determined by the scope defined in the claims.

Claims

1. A design method for a low thermal conductivity microbolometer based on a fully stressed beam, characterized in that: The design method comprises the following steps: 1) Low thermal conductivity microbolometer composition: The low thermal conductivity microbolometer includes a substrate, a bridge column, a bridge and a bridge deck; two bridge columns are arranged perpendicular to the substrate on the substrate; the tops of the bridge columns are provided with a bridge and a bridge deck connected as one body with the same density and height, the bridge deck is located in the center and is connected to the tops of the corresponding bridge columns by a single or multiple bridges; Each bridge consists of a column connecting section and a deck connecting section. The starting end of the column connecting section is connected to the bridge column, the end of the deck connecting section is connected to the bridge deck, and the end of the deck connecting section is connected to the bridge deck. The cross-sectional dimension of the bridge deck is much larger than the width of the bridge. The length of the bridge is much larger than the width and thickness of the bridge. 2) Establish a coordinate system: An orthogonal coordinate system is established, where the axis of the bridge column is located on the z-axis, the substrate is located on the xy plane, and the plane where the bridge and the bridge deck are located is located on the xy plane; The length of the bridge column connection section is along the y direction, and the width of the bridge column connection section varies along the y direction; the length of the bridge deck connection section is along the x direction, and the width of the bridge deck connection section varies along the x direction. The width distribution of the bridge column connection section along the y direction and the width distribution of the bridge deck connection section along the x direction are optimized separately to maximize the thermal conductivity of the device and thus increase the responsiveness. In the subsequent mechanical analysis, the bridge column connection section, bridge deck connection section and bridge deck were separated into independent free bodies; 3) Conduct mechanical analysis of the bridge based on the first principal stress, normal stress formula, and shear stress formula; For slender bridge structures whose length is much greater than their thickness and width, the three-dimensional structure is converted into a one-dimensional structure along the length of the bridge. Only the maximum stress distribution in this section is considered, and the maximum value of the first principal stress is calculated in this model. The shear stresses in the yz and xz directions caused by torsion are ignored. In addition, for such slender bridges, the cross-section of the bridge deck is large, and the moment of inertia of the bridge deck is more than 10 times the moment of inertia of the bridge. The normal stress in the y direction and the shear stress parallel to the xy plane caused by bending are ignored in the bridge deck connection section, and the normal stress in the x direction and the shear stress parallel to the xy plane caused by bending are ignored in the bridge column connection section, simplifying the shear stress formula. 4) Analyze the bending moment and torque of the bridge based on the bending moment equation and torque equation: The torque of the bridge deck connection section is equal to the bending moment of the connection point between the bridge column connection section and the bridge deck connection section in the y direction, and the torque of the bridge column connection section is equal to the bending moment of the connection point between the bridge column connection section and the bridge deck connection section in the x direction; 5) For statically indeterminate structures, the torsion angle deflection equation is introduced to solve; For the xy plane, the deflection angles at the end of the deck connection and the beginning of the column connection are approximately considered to be 0; the torsion of the column connection and the bending of the deck connection contribute to the deflection angle of the end of the deck connection along the x direction; the bending of the column connection and the torsion of the deck connection contribute to the deflection angle of the end of the deck connection along the y direction; for the x direction, the torsion angle of the column connection is equal to the bending angle of the deck connection; for the y direction, the bending angle of the column connection is equal to the torsion angle of the deck connection; this relationship is solved by combining the torsion angle and the bending angle expression, and finally the torque and bending moment distribution at each location on the bridge leg is solved; 6) Based on mechanical analysis, the force balance equation and the moment balance equation for the end of the bridge deck connection section are obtained as boundary conditions; 7) Solve the width distribution: Combining the constraint condition formula with the bending moment and torque equations as well as the bending moment equilibrium equation and the force equilibrium equation, all parametric equations are substituted into the parameter values ​​of the structure. By solving the equations simultaneously, the analytical solution of the width distribution of the bridge is calculated.

2. The design method according to claim 1, wherein: In step 1), the bridge columns, bridge deck and bridge are made of silicon nitride, silicon oxide or aluminum oxide.

3. The design method according to claim 1, wherein: In step 8), to study the material fracture, only the maximum value of the first principal stress needs to be considered, and the analytical solution of the equal bridge width distribution of the maximum value of the first principal stress in the one-dimensional bridge model is solved.

4. The design method according to claim 1, wherein: According to the mechanical analysis of the double-layer composite beam, the maximum shear stress, torsion angle, bending angle, moment of inertia and normal stress are corrected, and these corrections are substituted into the corresponding constraint equations, the bending moment equation, the torque equation, and the simplified bending moment equilibrium equation and force equilibrium equation to obtain the analytical solution of the width distribution of the double-layer composite beam.

5. The design method according to claim 4, wherein: For composite beams composed of more than three layers of materials, the composite beam material mechanics formula is used for calculation, and the Young's modulus and shear modulus of the three or more layers of materials are used for correction in the calculation of moment of inertia, torsional moment of inertia, bending moment, torque, bending angle and torsion angle.

6. A low thermal conductivity microbolometer based on a fully stressed beam, characterized in that: The low thermal conductivity microbolometer includes: the low thermal conductivity microbolometer includes a substrate, a bridge column, a bridge and a bridge deck; two bridge columns perpendicular to the substrate are set on the substrate; the top of the bridge column is provided with a bridge and a bridge deck connected as a whole with the same density and height, the bridge deck is located in the center, and is connected to the top of the corresponding bridge column by a single or multiple bridges; each bridge includes a bridge column connecting section and a bridge deck connecting section, the starting end of the bridge column connecting section is connected to the bridge column, the end is connected to the bridge deck connecting section, and the end of the bridge deck connecting section is connected to the bridge deck; the cross-sectional size of the bridge deck is much larger than the width of the bridge; the length of the bridge is much larger than the width and thickness of the bridge; an orthogonal coordinate system is established, the z-axis direction is the positive force direction, the axis of the bridge column is located on the z-axis, the substrate is located in the xy plane, and the plane where the bridge and the bridge deck are located is located in the xy plane; the length direction of the bridge column connecting section is along the y direction, and the width of the bridge column connecting section is along the y direction. direction changes; the length direction of the bridge deck connection section is along the x direction, and the width of the bridge deck connection section changes along the x direction; the width distribution of the bridge column connection section along the y direction and the width distribution of the bridge deck connection section along the x direction are optimized respectively, so as to maximize the thermal conductivity of the device and thus increase the responsiveness; the first principal stress, normal stress and shear stress of the bridge are analyzed, and the normal stress in the y direction and the shear stress parallel to the xy plane caused by bending are ignored in the bridge deck connection section, and the normal stress in the x direction and the shear stress parallel to the xy plane caused by bending are ignored in the bridge column connection section; the torsion angle deflection equation is used as the constraint condition, and the bending moment and torque equations as well as the bending moment equilibrium equation and the force equilibrium equation are solved simultaneously. Only the maximum value of the first principal stress needs to be considered, and the analytical solution of the equal bridge width distribution at all the maximum values ​​of the first principal stress in the one-dimensional bridge model is solved to obtain the width distribution of the bridge.

7. The low thermal conductivity microbolometer according to claim 6, wherein: The bridge columns, bridge deck and bridge are made of silicon nitride, silicon oxide or aluminum oxide.

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