JP6691414B2 - Stress sensor - Google Patents

Description

  The present invention relates to a stress sensor.

  Conventionally, a sensor that detects pressure, stress, or the like using a diaphragm is known. For example, Patent Document 1 discloses a pressure sensor that detects the pressure applied to the diaphragm based on the deflection of the diaphragm.

JP, 2005-143713, A

  However, a stress sensor using a diaphragm may not necessarily have high stress detection capability.

  An object of the present invention made in view of the above point is to provide a stress sensor capable of improving the detection capability.

The stress sensor according to the embodiment of the present invention,
A diaphragm,
A sensitive film disposed on the surface of the diaphragm and partially having a penetrating region;
In the diaphragm, a detection unit located in a stress change region where a stress change occurs due to the penetrating region ,
The sensitive film is located inside the outer peripheral portion of the diaphragm,
At least a part of the detection unit is located inside the penetrating region .

  The stress sensor according to the embodiment of the present invention can improve the detection capability.

It is a top view which shows schematic structure of the stress sensor which concerns on the 1st Embodiment of this invention. It is sectional drawing which followed the LL line of the stress sensor shown in FIG. FIG. 3 is an enlarged view of a range A shown in FIG. 2 when gas molecules are adsorbed on a sensitive film. It is a top view which shows the modification of the stress sensor which concerns on the 1st Embodiment of this invention. It is a top view which shows schematic structure of the stress sensor which concerns on the 2nd Embodiment of this invention. It is a top view which shows the modification of the stress sensor which concerns on the 2nd Embodiment of this invention. It is sectional drawing which shows the schematic structure of the SOI substrate used for manufacture of the stress sensor which concerns on the 1st and 2nd embodiment of this invention. It is sectional drawing for demonstrating the manufacturing process of the stress sensor which concerns on the 1st and 2nd embodiment of this invention. It is sectional drawing for demonstrating the manufacturing process of the stress sensor which concerns on the 1st and 2nd embodiment of this invention. It is sectional drawing for demonstrating the manufacturing process of the stress sensor which concerns on the 1st and 2nd embodiment of this invention. It is sectional drawing for demonstrating the manufacturing process of the stress sensor which concerns on the 1st and 2nd embodiment of this invention. It is sectional drawing for demonstrating the manufacturing process of the stress sensor which concerns on the 1st and 2nd embodiment of this invention. It is sectional drawing for demonstrating the manufacturing process of the stress sensor which concerns on the 1st and 2nd embodiment of this invention.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In addition, in the embodiment according to the present invention, it is assumed that the diaphragm is deformed by the adsorption of the substance to the film (sensitive film) arranged on the surface of the diaphragm, and the stress is generated in the diaphragm. Also, the drawings used in the following description are schematic.

(First embodiment)
FIG. 1 is a top view showing a schematic configuration of a stress sensor 1 according to a first embodiment of the present invention, and FIG. 2 is a sectional view taken along line LL of the stress sensor 1 shown in FIG. . In the present specification, it is assumed that the z-axis positive direction is the upper side and the z-axis negative direction is the lower side.

  The stress sensor 1 includes a diaphragm 10, a sensitive film 20 having a penetrating region 30, and four piezoresistive elements (detection units) 40, 41, 42, 43. The sensitive film 20 is disposed on the upper surface of the diaphragm 10. The stress sensor 1 detects the specific substance by the sensitive film 20 adsorbing the specific substance in the fluid. Gas is blown onto the stress sensor 1 from the upper surface side, for example. The stress sensor 1 can detect whether or not the sprayed gas contains a specific gas molecule to be detected. The stress sensor 1 is manufactured using, for example, an SOI (Silicon on Insulator) substrate. An example of a method of manufacturing the stress sensor 1 will be described later.

  The diaphragm 10 is a deformable member. The diaphragm 10 is, for example, a thin substrate. The diaphragm 10 can be, for example, an n-type Si substrate. As shown in FIG. 1, the diaphragm 10 may have a rectangular shape when viewed from the upper surface side. The diaphragm 10 is integrally formed with a substrate that is thicker than the diaphragm 10 around the diaphragm 10. When the sensitive film 20 arranged on the upper surface of the diaphragm 10 is deformed, the diaphragm 10 is deformed according to the degree of deformation of the sensitive film 20.

  The sensitive film 20 partially has a through region 30. In the present embodiment, the sensitive film 20 has a circular shape and has a through region 30 in the central portion. When a substance to be detected is adsorbed on the surface of the sensitive film 20, the sensitive film 20 expands and contracts and deforms due to physical contact with the substance, a chemical reaction with the substance, or the like. For the sensitive film 20, a material corresponding to the substance to be detected is used. The thicknesses of the diaphragm 10 and the sensitive film 20 can be appropriately selected in consideration of the material used for the sensitive film 20, the substance to be detected, and the like. As an example, the material of the sensitive film 20 may be polystyrene, chloroprene rubber, polymethylmethacrylate, nitrocellulose, or the like.

  As shown in FIG. 1, the penetrating region 30 has a circular shape when viewed from the upper surface side. In the present embodiment, the penetrating region 30 is located in the central portion of the sensitive film 20. In the stress sensor 1, due to the presence of the penetrating region 30, the stress generated in the diaphragm 10 when the substance to be detected is adsorbed by the sensitive film 20 increases near the boundary 31 of the penetrating region 30. The details of this principle will be described later.

  The resistance value of each of the piezoresistive elements 40 to 43 changes according to the stress received by itself. The piezoresistive elements 40 to 43 are, for example, p-type Si. The piezoresistive elements 40 to 43 may be formed by diffusing boron (B) when the diaphragm 10 is n-type Si. The piezoresistive elements 40 to 43 are arranged on the diaphragm 10. In the present specification, "disposed on the diaphragm 10" means a state in which it is disposed on the upper surface of the flat plate-shaped diaphragm 10 and a state in which it is embedded in the diaphragm 10 on the upper surface side of the diaphragm 10 as shown in FIG. Including. The piezoresistive elements 40 to 43 are located in the stress change region on the diaphragm 10. Here, the stress change region is a region in which the stress largely changes due to the deformation of the diaphragm 10 caused by the presence of the penetrating region 30 when a substance to be detected is adsorbed on the sensitive film 20. The stress change region includes, for example, the boundary 31 of the penetrating region 30 and the vicinity of the boundary 31. The vicinity of the boundary 31 includes an area inside and an area outside the penetrating area 30 with the boundary 31 as a reference in a top view. The stress change region is shown as a region D as an example in FIG. 3 described later. In the present embodiment, as shown in FIG. 1, the four piezoresistive elements 40 to 43 are arranged at equal intervals along the boundary 31 in a region inside the penetrating region 30 with respect to the boundary 31 in a top view. There is. The piezoresistive elements 40 to 43 are strip-shaped, for example.

  The piezoresistive elements 40 to 43 form a Wheatstone bridge circuit. The stress sensor 1 detects the change in the resistance value of the piezoresistive elements 40 to 43 as an electric signal from the Wheatstone bridge circuit composed of the piezoresistive elements 40 to 43, and transfers it to the sensitive film 20 of the substance to be detected. Can be detected. Note that the Wheatstone bridge circuit does not necessarily have to be configured by using all of the four piezoresistive elements 40 to 43, and may be configured by using any one, two, or three of the piezoresistive elements 40 to 43. May be. Further, when the Wheatstone bridge circuit is configured using any one, two or three of the piezoresistive elements 40 to 43, the stress sensor 1 includes the piezoresistive elements of the number used in the Wheatstone bridge circuit. It may be provided on the diaphragm 10.

  In the piezoresistive elements 40 to 43, the portion located inside the penetrating region 30 may be larger than the portion located outside the penetrating region 30. In the present embodiment, the piezoresistive elements 40 to 43 are located only inside the penetrating region 30 in a top view, as shown in FIG. Note that the piezoresistive elements 40 to 43 are not limited to being located only inside the penetrating region 30, and the piezoresistive elements 40 to 43 may be located in the stress change region. Therefore, the piezoresistive elements 40 to 43 may be located at the boundary of the penetrating region 30 or outside the penetrating region 30. Although the piezoresistive elements 40 to 43 are located on the upper surface side of the diaphragm 10 in FIGS. 1 and 2, they may be located inside or on the lower surface side of the diaphragm 10.

  Further, in the present embodiment, the stress sensor 1 includes four piezoresistive elements 40 to 43, but the number of piezoresistive elements included in the stress sensor 1 is not limited to four. The stress sensor 1 may include any number of piezoresistive elements capable of detecting a substance to be detected.

  Further, instead of the piezoresistive element, another piezoelectric element may be used as a detection unit that detects the stress generated in the diaphragm 10.

  Next, the relationship between the penetration region 30 and the stress generated in the diaphragm 10 will be described with reference to FIG. FIG. 3 is an enlarged view of the range A shown in FIG. 2 when the gas molecules 2 are adsorbed on the sensitive film 20. The gas molecule 2 schematically shows the gas molecule to be detected using the stress sensor 1.

  As shown in FIG. 3, when the gas molecules 2 are adsorbed on the sensitive film 20, the sensitive film 20 is deformed. Along with the deformation of the sensitive film 20, the region of the diaphragm 10 where the sensitive film 20 is arranged also deforms. On the other hand, since the sensitive film 20 is not arranged in the penetrating region 30 of the diaphragm 10, the sensitive film 20 is unlikely to deform. Thus, the region C that is easily affected by the sensitive film 20 and the region B that is not easily affected by the sensitive film 20 are located inside (the region B in FIG. 3) and outside (the region C in FIG. 3) of the penetrating region 30 with the boundary 31 as a reference. It is formed.

  Specifically, the region C of the diaphragm 10 is deformed into a convex shape in which the central side of the sensitive film 20 rises upward. On the other hand, the region B of the diaphragm 10 is hardly affected by the deformation of the sensitive film 20, and thus is not easily deformed, and remains substantially parallel to the xy plane, for example. At this time, in the region D existing near the boundary between the regions C and B, the diaphragm 10 is largely deformed as shown in FIG. Therefore, in the region D, the degree of deformation of the diaphragm 10 becomes large, and the stress generated at that portion becomes large. Since the piezoresistive elements 40 to 43 are arranged in the region D where large stress is likely to occur, the deformation of the piezoresistive elements 40 to 43 when the substance to be detected is adsorbed on the sensitive film 20. growing. Therefore, the resistance values of the piezoresistive elements 40 to 43 also tend to change greatly.

  As described above, in the stress sensor 1 according to the first embodiment, when the substance to be detected is adsorbed on the sensitive film 20, the degree of deformation of the diaphragm 10 in the stress change region penetrates the sensitive film 20. It is larger than that without the region 30. Therefore, the stress generated in the stress change region also becomes larger. Therefore, the change in the resistance value of the piezoresistive elements 40 to 43 located near the boundary 31, which is the stress change region, becomes larger. Thereby, in the stress sensor 1, the ability to detect the stress generated in the diaphragm 10 when the substance to be detected is adsorbed by the sensitive film 20 can be improved. Therefore, in the stress sensor 1, it is possible to improve the detection ability of the substance to be detected.

(Modification of the first embodiment)
Next, a modified example of the stress sensor 1 according to the first embodiment will be described.

  FIG. 4 is a top view showing a modified example (stress sensor 1a) of the stress sensor 1 according to the first embodiment of the present invention. In addition, in each component shown in FIG. 4, the same components as those shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

  The stress sensor 1a includes a diaphragm 10, a sensitive film 20a having a penetrating region 30a, and piezoresistive elements (detection units) 40, 41, 42, 43. As shown in FIG. 4, the penetrating region 30a has a rectangular shape when viewed from the upper surface side, and the boundary 31a also has a rectangular shape. The piezoresistive elements 40 to 43 are arranged in the stress change region, like the stress sensor 1 according to the first embodiment. In this example, the piezoresistive elements 40 to 43 are arranged around the corners of the penetrating region 30a.

  Even with such a stress sensor 1a, the same effect as that of the stress sensor 1 according to the first embodiment can be obtained. The penetrating region may have any other shape than the circular shape and the rectangular shape.

(Second embodiment)
FIG. 5: is a top view which shows schematic structure of the stress sensor 1b which concerns on the 2nd Embodiment of this invention. In the components shown in FIG. 5, the same components as those shown in FIGS. 1 and 2 are designated by the same reference numerals, and the description thereof will be omitted.

  The stress sensor 1b includes a diaphragm 10b, a sensitive film 20b having a penetrating region 30, and piezoresistive elements 40, 41, 42, 43.

  The diaphragm 10b is a single crystal n-type Si substrate, and in FIG. 5, the surface parallel to the xy plane (the surface perpendicular to the z axis) shown in FIG. 5 is the Si (100) surface. In the diaphragm 10b, the x-axis direction is the [110] direction, the y-axis direction is the [1-10] direction, and the z-axis direction is the [001] direction. The diaphragm 10 has four notches 50 to 53 on its outer peripheral portion.

  The sensitive film 20b is disposed on the diaphragm 10b and has a through region 30 in the center thereof. Further, the sensitive film 20b has four notches 50 to 53 on its outer peripheral portion. In the present embodiment, the notches 50 to 53 of the diaphragm 10 and the sensitive film 20b are notched in the same shape. That is, as shown in FIG. 5, the cutout lines of the cutout portions 50 to 53 of the diaphragm 10b and the sensitive film 20b coincide with each other in a top view. However, the notches of the diaphragm 10 and the sensitive film 20b may have different shapes.

  In the present embodiment, the notches 50 to 53 have a wedge shape when viewed from the upper surface side, as shown in FIG. The wedge shape means a shape in which the width becomes smaller toward the tip. In this embodiment, the wedge shape is a triangle.

  The piezoresistive elements 40 to 43 are p-type Si, and are formed by diffusing boron (B) in the diaphragm 10b, which is an n-type Si substrate, for example. The piezoresistive elements 40 to 43 are arranged in the [-110] direction, the [-1-10] direction, the [1-10] direction, and the [110] direction (hereinafter collectively referred to as "<110> direction"). It

  Here, the piezoresistive coefficient (the proportional coefficient between the stress applied to the piezoresistive element and the resistance value of the piezoresistive element that changes due to the stress) depends on the crystal orientation. Furthermore, in the Si (100) plane, the piezoresistive coefficient of p-type Si becomes maximum in the <110> direction, and the <100> direction (the <100> direction is the [-100] direction, the [0-10] direction, It is the smallest in the directions including the [100] direction and the [010] direction. Therefore, the piezoresistive elements 40 to 43 are arranged in the direction in which the piezoresistive coefficient is maximized so that the resistance value that changes depending on the stress received is maximized. That is, the piezoresistive elements 40 to 43 are provided, for example, as shown in FIG. 5, along the direction along the x-axis or the y-axis, that is, along the <110> direction of the diaphragm 10b.

  Thus, by providing the notches 50 to 53 in the <100> direction of the diaphragm 10b, when the substance is adsorbed by the sensitive film 20b, the diaphragm 10b is mainly deformed along the <110> direction. become. Therefore, when the substance is adsorbed to the sensitive film 20b, the diaphragm 10b has a greater degree of deformation in the central portion (that is, in the vicinity of the penetrating region 30) than in the outer peripheral portion. As a result, the degree of deformation of the diaphragm 10 in the stress change region is increased, and the stress generated in the stress change region is also increased.

  Further, the piezoresistive elements 40 to 43 are arranged in the <110> direction where the piezoresistive coefficient of the stress change region is maximum. As a result, the resistance value that changes due to the stress applied to the piezoresistive elements 40 to 43 can be maximized, and the ability to detect the force generated in the diaphragm 10 can be improved. That is, the longitudinal direction of the piezoresistive elements 40 to 43 is provided along the <110> direction of the diaphragm 10b.

  In addition, in the stress sensor 1b, the sensitive film 20b is also provided with notches 50 to 53 on its outer peripheral portion. As a result, when the substance to be detected is sprayed onto the stress sensor 1 from the upper surface side, the substance not adsorbed on the sensitive film 20b passes through the notches 50 to 53. Therefore, according to the stress sensor 1b, it is possible to prevent the object not adsorbed on the sensitive film 20b from remaining on the upper surface of the stress sensor 1b.

  In addition, in the stress sensor 1b, the second sensitive film may be disposed on the lower surface of the diaphragm 10b on which the sensitive film 20b is not disposed. As a result, the substance to be detected that has passed through the notches 50 to 53 may flow into the lower surface side of the diaphragm 10b and be adsorbed to the second sensitive film. When the second sensitive film has a property of being deformed in the direction opposite to that of the sensitive film 20 on the upper surface side when adsorbing the substance to be detected, the degree of deformation of the diaphragm 10b becomes larger.

  Other configurations and effects of the stress sensor 1b according to the second embodiment are similar to those of the stress sensor 1 according to the first embodiment.

(Modification of the second embodiment)
Next, a modification of the stress sensor 1b according to the second embodiment will be described.

  FIG. 6 is a top view showing a modified example (stress sensor 1c) of the stress sensor according to the second embodiment of the present invention. In each component shown in FIG. 6, the same components as those shown in FIG. 5 are designated by the same reference numerals, and the description thereof will be omitted.

  The stress sensor 1c includes a diaphragm 10b, a sensitive film 20c having a penetrating region 30c, and piezoresistive elements 40, 41, 42, 43. As shown in FIG. 6, the penetrating region 30c has a rectangular shape when viewed from the upper surface side, and the boundary 31c also has a rectangular shape.

  Even with such a stress sensor 1c, the same effect as that of the stress sensor 1b according to the second embodiment can be obtained.

(Manufacturing process of the stress sensor according to the first and second embodiments)
Next, an example of a manufacturing process of the stress sensor according to the first and second embodiments of the present invention will be described with reference to FIGS. In addition, in each component shown in FIGS. 7 to 13, the same component is denoted by the same reference numeral.

(1) Preparation of SOI Substrate First, an SOI substrate used for manufacturing a stress sensor is prepared. FIG. 7 shows a schematic structure of an SOI substrate used for manufacturing the stress sensor according to the first and second embodiments of the present invention. As shown in FIG. 7, the SOI substrate 100 includes a first substrate 110, a SiO ₂ layer 111, and a second substrate 112. The first substrate 110 and the second substrate 112 are Si substrates. The first substrate 110 functions as a diaphragm and is thinner than the second substrate 112. In the SOI substrate 100, the SiO ₂ layer 111 is arranged on the second substrate 112, and the first substrate 110 is arranged on the SiO ₂ layer 111. The SOI substrate 100 is manufactured by, for example, a so-called bonding method. In the following, the first substrate 110 is n-type.

(2) Formation of Diffusion Wiring (Highly Doped Layer) Next, diffusion wiring is formed on the SOI substrate 100 shown in FIG. As shown in FIG. 8, after forming the mask pattern 200 on the first substrate 110, high-concentration boron (B) is injected into the opening of the mask pattern 200 by an ion implantation method to diffuse the diffusion wirings 41a, 41b, 43a. , 43b are formed.

(3) Formation of piezoresistive element (lowly doped layer) After removing the mask pattern 200 shown in FIG. 8, piezoresistive elements 40 to 43 are formed. As shown in FIG. 9, after forming the mask pattern 201 on the first substrate 110, low concentration boron (B) is injected into the opening of the mask pattern 201 by an ion implantation method to form the piezoresistive elements 40 to 43. Form.

(4) Formation of Metal Wiring The mask pattern 201 shown in FIG. 9 is removed, insulating layers 310a and 310b having a predetermined pattern are laminated, and then metal wiring such as aluminum is formed. As shown in FIG. 10A, a metal (eg, aluminum) is deposited on the entire surface of the first substrate 110 by sputtering to form a metal layer 300 (eg, aluminum layer). Next, as shown in FIG. 10B, a mask pattern 202 is formed on the metal layer 300. Then, as shown in FIG. 10C, the metal layer 300 not protected by the mask pattern 202 is etched to form metal wirings 300a and 300b. The piezoresistive elements 40 to 43 form a Wheatstone bridge circuit by the connection by the metal wiring 300a and the diffusion wiring 41a.

(5) Formation of Cutouts After removing the mask pattern 202 shown in FIG. 10C, cutouts 50 to 53 are formed in the case of the stress sensor according to the second embodiment. First, as shown in FIG. 11A, a mask pattern 203 is formed on the first substrate 110. Then, as shown in FIG. 11B, after forming the notches 50 to 53 by dry etching through the mask pattern 203, the mask pattern 203 is removed. At this time, the dry etching conditions are set in advance so that the SiO ₂ layer 111 serves as a stop layer. If the stress sensor does not have the cutout portion, this step may be skipped and the process may proceed to the next step.

(6) Formation of Diaphragm After turning the SOI substrate 100 upside down, the diaphragm is formed. As shown in FIG. 12A, after forming the mask pattern 204 on the second substrate 112, the second substrate 112 not protected by the mask pattern 204 is dry-etched to form the recess 400. At this time, dry etching conditions are set in advance so that the SiO ₂ layer 111 plays a role of a stop layer. Then, the dry etching conditions are changed, and the SiO ₂ layer 111 is removed to form the diaphragm 10A, as shown in FIG. 12B. Although various diaphragms have been described in the first and second embodiments, they are referred to as diaphragm 10A in FIG. 12 (b).

(7) Formation of Sensitive Film The mask pattern 204 shown in FIG. 12B is removed, the SOI substrate 100 is turned upside down, and then the sensitive film 20A is formed. As shown in FIG. 13, a sensitive film material is applied on the diaphragm 10A and then dried to form a sensitive film 20A. Although various sensitive films have been described in the first and second embodiments, they are referred to as sensitive films 20A in FIG.

  Although the first substrate 110 is n-type here, for example, when the first substrate 110 is p-type, (2) formation of the diffusion wiring (highly doped layer) and (3) piezo are performed. In the formation of the resistance element (low-doped layer), phosphorus (P) is implanted instead of boron (B).

  Although the present invention has been described based on the drawings and the embodiments, it should be noted that those skilled in the art can easily make various variations and modifications based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention. For example, the functions and the like included in each constituent unit and each step can be rearranged so as not to logically contradict, and a plurality of constituent units and steps can be combined into one or divided. Is.

1, 1a, 1b, 1c Stress sensor 2 Gas molecule 10, 10A, 10b Diaphragm 20, 20A, 20a, 20b, 20c Sensitive film 30, 30a, 30c Penetration region 31, 31a, 31c Boundary 40, 41, 42, 43 Piezo Resistance element (detection unit)
41a, 41b, 43a, 43b Diffusion wiring 50, 51, 52, 53 Notch portion 100 SOI substrate 110 First substrate 111 SiO ₂ layer 112 Second substrate 200, 201, 202, 203, 204 Mask pattern 300 Metal layer 300a, 300b Metal wiring 310a, 310b Insulating layer 400 Recess

Claims (9)

A diaphragm,
A sensitive film disposed on the surface of the diaphragm and partially having a penetrating region;
In the diaphragm, a detection unit located in a stress change region where a stress change occurs due to the penetrating region ,
The sensitive film is located inside the outer peripheral portion of the diaphragm,
At least a part of the detection unit is a stress sensor located inside the penetration region .   The stress sensor according to claim 1, wherein the sensitive film has a cutout portion on an outer peripheral portion thereof.   The stress sensor according to claim 2, wherein the cutout portion of the sensitive film has a wedge shape.   The stress sensor according to claim 1, wherein the diaphragm has a cutout portion on an outer peripheral portion thereof.   The stress sensor according to claim 4, wherein the cutout portion of the diaphragm has a wedge shape.   The stress sensor according to claim 4 or 5, further comprising a second sensitive film arranged on another surface of the diaphragm different from the surface on which the sensitive film is arranged.   The stress sensor according to any one of claims 1 to 6, wherein the stress change region is a region including a boundary of the penetrating region and a vicinity of the boundary. Wherein the detection unit includes a portion located inside the transmembrane region is greater than the portion located outside of the transmembrane region, the stress sensor according to any one of claims 1 to 7. The stress sensor according to claim 1, wherein the detection unit includes a piezoresistive element.

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