JP6311341B2 - Capacitance type pressure sensor and input device - Google Patents

Description

  The present invention relates to a capacitive pressure sensor and an input device. In particular, the present invention relates to a capacitive pressure sensor in a touch mode in which a diaphragm bent by pressure contacts a facing surface to detect pressure. The present invention also relates to an input device using the pressure sensor.

  In a general capacitive pressure sensor, a conductive diaphragm (movable electrode) and a fixed electrode are opposed to each other with a gap therebetween, and a change in capacitance between the diaphragm deflected by pressure and the fixed electrode. The pressure is detected from. However, when this pressure sensor is a micro device manufactured by MEMS technology using a glass substrate or a silicon substrate, if a large pressure is applied to the diaphragm, the diaphragm may be greatly bent and damaged.

  Therefore, a dielectric film is provided on the surface of the fixed electrode, and the diaphragm bent by pressure is brought into contact with the dielectric film so that the capacitance between the diaphragm and the fixed electrode changes due to the change in the contact area. A pressure sensor has been proposed. Such a pressure sensor may be referred to as a touch mode capacitive pressure sensor.

  In the capacitance type pressure sensor, it is a very important issue to stabilize the shape of the diaphragm which is the pressure receiving portion. The pressure sensor measures the change in capacitance caused by the deformation of the diaphragm due to external pressure, whereas when the diaphragm deforms unexpectedly due to causes other than external pressure, such as buckling or fatigue, The output characteristics of the pressure sensor change due to the deformation of the diaphragm. As a result, the sensitivity of the pressure sensor deteriorates or malfunction of the pressure sensor occurs. Therefore, stabilizing the shape of the diaphragm is an important issue in the pressure sensor.

  1A, 1B, and 1C are schematic diagrams illustrating initial deformation due to buckling or fatigue of the diaphragm. In the pressure sensor 11 shown here, the upper surface of the fixed electrode substrate 12 is covered with a dielectric film 13, and a recess 14 is formed on the upper surface of the dielectric film 13. An upper substrate 15 is laminated on the upper surface of the dielectric film 13, and the upper substrate 15 covers the upper surface opening of the recess 14. A region of the upper substrate 15 positioned above the recess 14 is a diaphragm 16 that senses pressure and deforms.

  In the capacitive pressure sensor 11, it is preferable that the diaphragm 16 is formed flat, or formed so as to bulge slightly upward. However, when the diaphragm 16 is mechanically deteriorated due to a pressure endurance test or a long-term use, the diaphragm 16 is buckled or fatigued as shown in FIG. 1 (A), FIG. 1 (B) or FIG. 1 (C). It may be deformed. FIG. 1A shows a first-order deformation mode in which the center portion of the diaphragm 16 is deformed so as to swell downward. FIG. 1B shows a secondary deformation mode in which a part of the diaphragm 16 is deformed so as to bulge upward and another part is deformed so as to bulge downward. FIG. 1C shows a third-order deformation mode. When initial deformation as shown in FIG. 1 (A), FIG. 1 (B) or FIG. 1 (C) occurs in the diaphragm 16, the electrostatic capacitance (initial value) between the diaphragm 16 (movable electrode) and the fixed electrode substrate 12. (Capacity) increases or measurement accuracy deteriorates.

  In order to solve such a problem, in the pressure sensor disclosed in Patent Document 1, the diaphragm is formed of a multilayer film, and internal stresses generated in each layer of the multilayer film are canceled with each other, whereby the initial shape of the diaphragm is changed. It is stabilized.

  However, the method using a multilayer film as in Patent Document 1 has a problem that it takes time to manufacture the diaphragm and the manufacturing cost of the pressure sensor is high. Further, in order to stabilize the measurement accuracy of the pressure sensor, it is not sufficient to stabilize the initial shape of the diaphragm. In other words, in order to obtain measurement sensitivity for a wide range of pressures from low pressure to high pressure with a small area diaphragm, durability against a mechanical load such as a pressure durability test is also required. In a capacitance type pressure sensor, it is desired to obtain measurement sensitivity with respect to a pressure of 0 Pa to several MPa. In reality, however, the diaphragm is deformed as shown in FIG. The output characteristics of the battery sometimes changed. As a result, in the conventional pressure sensor, it is difficult to achieve both the ease of deformation of the diaphragm at low pressure (high sensitivity characteristics) and the durability against high pressure.

JP 2000-133818 A

  An object of the present invention is to provide a capacitive pressure sensor in which initial deformation of the diaphragm is unlikely to occur.

A first capacitive pressure sensor according to the present invention includes a fixed electrode substrate, a dielectric film having a recess on one of the upper surface and the lower surface, and covering the upper surface of the fixed electrode substrate, and an upper surface of the dielectric film. possess a substrate on which is provided, the upper formed by the recessed portion facing the region of the substrate, an elastically deformable diaphragm, a compression stress layer formed on at least a portion of the upper surface of the diaphragm, When the compressive stress film is viewed from a direction perpendicular to the top surface of the fixed electrode substrate, the compressive stress film is formed in a radially symmetrical manner around its center, and the radially extending branches of the compressive stress film are formed on the center side. The width of the end portion on the front end side is narrower than the width of the end portion .
An embodiment of the first capacitive pressure sensor according to the present invention is characterized in that the width of the branch is gradually narrowed away from the center of the compressive stress film.

In the first capacitive pressure sensor according to the present invention, the compressive stress film is formed on at least a part of the upper surface of the diaphragm. Therefore, even if the diaphragm is deformed due to buckling or fatigue, the compressive stress film is used. This corrects the shape of the diaphragm. Therefore, the shape of the diaphragm can be maintained in a desired shape, and the output characteristics of the pressure sensor can be maintained. Further, since the compressive stress film is formed on the upper surface of the diaphragm, the strength of the diaphragm is increased. Furthermore, in the first capacitive pressure sensor according to the present invention and the above-described embodiment, the rotationally symmetrical radial compressive stress film having a narrow width on the tip side is provided, so that the diaphragm is deformed almost uniformly in each direction. In addition, since the area ratio of the compressive stress film gradually decreases according to the radial distance measured from the center of the diaphragm, the initial deformation of the diaphragm and the deformation when subjected to pressure become smooth.

In another embodiment of the first capacitive pressure sensor according to the present invention, when viewed from a direction perpendicular to the upper surface of the fixed electrode substrate, the center of the compressive stress film overlaps the center of the diaphragm. It is characterized by being. According to such an embodiment, since the compressive stress film is formed in the middle of the diaphragm, the diaphragm is less likely to deform unevenly depending on the direction.

Yet another embodiment of the first capacitive pressure sensor according to the present invention is characterized in that an area of the compressive stress film is smaller than an area of the diaphragm. In such an embodiment, since the compressive stress film is not formed on the outer peripheral portion of the diaphragm, the elastic deformation of the diaphragm due to the pressure is hardly hindered, and the sensitivity of the pressure sensor is improved.

  Still another embodiment of the first capacitive pressure sensor according to the present invention is such that, when viewed from a direction perpendicular to the upper surface of the fixed electrode substrate, the concave portion is circular and the compressive stress film is also circular. It is characterized by that. According to this embodiment, the diaphragm can be uniformly deformed in each direction.

  Yet another embodiment of the first capacitive pressure sensor according to the present invention is characterized in that the compressive stress film is formed of an elastic body. According to this embodiment, the diaphragm can be protected by the compressive stress film when the diaphragm is pushed with a pen tip or the like.

A second capacitive pressure sensor according to the present invention includes a fixed electrode substrate, a dielectric film having a recess on one of the upper surface and the lower surface, and covering the upper surface of the fixed electrode substrate, and the upper surface of the dielectric film. An upper substrate provided on the upper substrate, an elastically deformable diaphragm formed by a region of the upper substrate facing the recess, and a tensile stress film formed on at least a part of the lower surface of the diaphragm, When viewed from a direction perpendicular to the upper surface of the fixed electrode substrate, the tensile stress film is formed in a radially symmetrical manner around its center, and the radially extending branches of the tensile stress film are formed on the center side. The width of the end portion on the front end side is narrower than the width of the end portion.

In the second capacitive pressure sensor according to the present invention, since the tensile stress film is formed on at least a part of the lower surface of the diaphragm, the tensile stress film even if the diaphragm is deformed due to buckling or fatigue. This corrects the shape of the diaphragm. Therefore, the shape of the diaphragm can be maintained in a desired shape, and the output characteristics of the pressure sensor can be maintained. Further, since the tensile stress film is formed on the lower surface of the diaphragm, the strength of the diaphragm is increased. Further, in the second capacitive pressure sensor according to the present invention, the rotationally symmetrical radial compressive stress film having a narrow width on the tip side is provided, so that the diaphragm can be deformed almost uniformly in each direction. At the same time, the area ratio of the compressive stress film gradually decreases according to the radial distance measured from the center of the diaphragm, so that the initial deformation of the diaphragm and the deformation when subjected to pressure become smooth.

Each of the first and second capacitive pressure sensors according to the present invention can be used for a pressure detector or an input device.

  The means for solving the above-described problems in the present invention has a feature in which the above-described constituent elements are appropriately combined, and the present invention enables many variations by combining such constituent elements. . In particular, an embodiment similar to the first capacitive pressure sensor is possible for the second and third capacitive pressure sensors.

1A, 1B, and 1C are schematic cross-sectional views showing various modes of buckling deformation that occur in a capacitive pressure sensor. FIG. 2A is a perspective view showing the capacitive pressure sensor according to the first embodiment of the present invention. FIG. 2B is a partially exploded perspective view of the pressure sensor shown in FIG. FIG. 3A is a plan view of the pressure sensor shown in FIG. FIG. 3B is a cross-sectional view of the pressure sensor shown in FIG. FIG. 4 is a diagram showing the relationship between the magnitude of the load applied to the pressure sensor and the capacitance generated in the pressure sensor. FIG. 5 is a diagram showing a shape when the diaphragm is actually deformed. FIG. 6 is a plan view showing a modification of the pressure sensor according to Embodiment 1 of the present invention. FIG. 7 is a plan view showing another modification of the pressure sensor according to Embodiment 1 of the present invention. FIG. 8A is a plan view of a capacitive pressure sensor according to Embodiment 2 of the present invention. FIG. 8B is a cross-sectional view of the pressure sensor shown in FIG. FIG. 9A is a plan view of a capacitive pressure sensor according to Embodiment 3 of the present invention. FIG. 9B is a cross-sectional view of the pressure sensor shown in FIG. FIG. 10A is a diagram showing measured values of stress generated in the dielectric film when the dielectric film is formed by the plasma TEOS method while changing the RF power. FIG. 10B is a schematic diagram showing the state of the dielectric film 33 and the upper substrate 35 when the RF power is low. FIG. 10C is a schematic diagram showing the state of the dielectric film 33 and the upper substrate 35 when the RF power is high. FIG. 11A is a partially exploded perspective view showing a pressure detector according to Embodiment 4 of the present invention. FIG. 11B is a cross-sectional view of the pressure detector shown in FIG. FIG. 12 is a schematic cross-sectional view of an input device according to Embodiment 5 of the present invention.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments, and various design changes can be made without departing from the gist of the present invention.

(Embodiment 1)
Hereinafter, the structure of the capacitive pressure sensor 31 according to the first embodiment of the present invention will be described with reference to FIGS. 2A is a perspective view of the pressure sensor 31, and FIG. 2B is a partially exploded perspective view of the pressure sensor 31. FIG. FIG. 3A is a plan view of the diaphragm 36. FIG. 3B is a schematic cross-sectional view of the pressure sensor 31 in a cross section that passes through the center of the diaphragm 36. FIG. 4 is a diagram illustrating the load-capacitance characteristics of the pressure sensor.

In the pressure sensor 31, the upper surface of the fixed electrode substrate 32 is covered with a dielectric film 33. As the fixed electrode substrate 32, a Si substrate or a glass substrate is used. The dielectric film 33 is made of, for example, SiO ₂ or SiN. The dielectric film 33 has a disk-shaped recess 34 (concave portion) at the center of the upper surface thereof. The bottom surface of the recess 34 is covered with a dielectric film 33.

  On the upper surface of the dielectric film 33, a thin upper substrate 35 made of a conductive material such as low-resistance Si is laminated. The upper substrate 35 covers the upper surface opening of the recess 34. A portion of the upper substrate 35 located outside the recess 34 (hereinafter referred to as an outer peripheral portion 37) is fixed to the upper surface of the dielectric film 33. A circular portion of the upper substrate 35 that floats above the recess 34 is a pressure-sensitive diaphragm 36 (movable electrode) that is elastically deformed by a load or pressure. An electrode pad 39 a that is electrically connected to the diaphragm 36 is provided on the upper surface of the upper substrate 35. The electrode pad 39a is formed of a metal thin film.

  Although not shown, the fixed electrode substrate 32 is provided with a fixed electrode. For example, when the fixed electrode substrate 32 is a Si substrate, the back surface of the fixed electrode substrate 32 may be a fixed electrode. Alternatively, a fixed electrode made of an impurity diffusion layer may be provided on the upper surface of the fixed electrode substrate 32, and the electrode pad 39 b provided on the upper surface of the upper substrate 35 may be electrically connected to the fixed electrode through the through hole 40 provided in the dielectric film 33. .

  A compressive stress film 38 is provided at the center of the upper surface of the diaphragm 36. The compressive stress film 38 is a circular thin film, and the entire lower surface thereof is bonded to the upper surface of the diaphragm 36. The compressive stress film 38 generates compressive stress inside even when no load is applied from the outside of the pressure sensor 31 (initial state). The compressive stress film 38 is disposed so that the center of the compressive stress film 38 and the center of the diaphragm 36 (or the recess 34) coincide with each other when viewed from a direction perpendicular to the upper surface of the fixed electrode substrate 32.

  The pressure sensor 31 is a touch mode capacitive pressure sensor. FIG. 4 shows the relationship (load-capacitance characteristics) between the load W [gF] applied to the diaphragm 36 of the pressure sensor 31 and the capacitance C [pF] generated between the fixed electrode substrate 32 and the diaphragm 36. It is a figure shown typically. FIG. 4 shows the deformation state of the diaphragm 36 at several points on the curve indicating the load-capacitance characteristics.

  When a load W is applied to the diaphragm 36 of the pressure sensor 31, the diaphragm 36 bends according to the load W and contacts the dielectric film 33 with a certain load Wa. A section (non-contact area) where the load is 0 to Wa in FIG. 4 is a state where the diaphragm 36 is not in contact with the dielectric film 33. A section (contact start region) where the load is from Wa to Wb represents a state from when the diaphragm 36 contacts the dielectric film 33 until it reliably contacts with a certain area. In the section (operation region) where the load is from Wb to Wc, the area of the portion where the diaphragm 36 is in contact with the dielectric film 33 gradually increases as the load increases. The section where the load is greater than or equal to Wc (saturation region) is a region where almost the entire surface of the diaphragm 36 is in contact with the dielectric film 33 and the contact area hardly increases even when the load increases.

  According to the load-capacitance characteristics of FIG. 4, the change in the capacitance C is very small in the non-contact region where the diaphragm 36 is not in contact, but gradually the rate of change (increase rate) of the capacitance C in the contact start region. ) Becomes larger. Although the linearity is improved in the operation region, the rate of change of the capacitance C gradually decreases, and the capacitance C hardly increases in the saturation region. In particular, when the load exceeds Wd, the capacitance C becomes a saturation value Cd and does not change.

In such a pressure sensor 31 in the touch mode, the contact area between the diaphragm 36 and the dielectric film 33 is S, the thickness of the dielectric film 33 is d, the relative dielectric constant of the dielectric film 33 is εr, and the dielectric in vacuum If the rate is εo, the capacitance C between the diaphragm 36 and the dielectric film 33 can be expressed by the following formula 1.
C = Co + εo · εr · (S / d) (Formula 1)
Here, Co is a capacitance in a non-contact region.

  In the pressure sensor 31, a compressive stress film 38 is formed on the upper surface of the diaphragm 36, and compressive stress is generated in the compressive stress film 38 in an initial state. Since the compressive force is applied to the compressive stress film 38 from the diaphragm 36 at the joint surface between the compressive stress film 38 and the diaphragm 36 and is contracted in the film direction, a compressive stress is generated inside. Therefore, the compressive stress film 38 tends to spread against the compressive stress. On the contrary, the diaphragm 36 is expanded in the film direction by the reaction force from the compressive stress film 38 at the joint surface between the diaphragm 36 and the compressive stress film 38, and therefore tends to contract against the reaction force (tensile force). As a result, the compressive stress film 38 tends to spread and the diaphragm 36 tends to shrink, so that the diaphragm 36 and the compressive stress film 38 are curved to be slightly convex upward in the initial state. Therefore, even if the diaphragm 36 is deformed in a defective mode due to buckling or fatigue as shown in FIG. 1, a force for forcibly returning the diaphragm 36 to be convex upward acts, The shape in the initial state (the state excluding the load) can be stabilized, and the output characteristics of the pressure sensor 31 can be stabilized. In the pressure endurance test or the like, fatigue is accumulated in the diaphragm 36 due to the deformation, but since the deformation of the compressive stress film 38 itself is not repeated, the compressive stress of the compressive stress film 38 is continuously maintained. .

  Further, since the pressure sensor 31 is a touch mode capacitance pressure sensor, even when a large pressure is applied to the diaphragm 36, the diaphragm 36 is prevented from being damaged by contacting the dielectric film 33. it can. In addition, since the compressive stress film 38 is formed on the diaphragm 36, the mechanical strength of the diaphragm 36 is increased. Further, if the compressive stress film 38 provided on the upper surface of the diaphragm 36 is made of an elastic body (for example, a polymer material such as polyimide), the compressive stress film 38 functions as a buffer material, and a hard load applying member ( For example, even when the diaphragm 36 is pressed by the tip of the touch pen), mechanical deterioration (wear, cracking, chipping) of the diaphragm 36 is less likely to occur.

  The compressive stress film 38 is desirably formed as thin as possible as compared with the diaphragm 36. This is because by reducing the thickness of the compressive stress film 38, it is difficult to reduce the sensitivity of the pressure sensor 31 in the low pressure region.

  The compressive stress film 38 is formed so that the center of the compressive stress film 38 and the center of the diaphragm 36 coincide as described above. That is, in the case of this embodiment, the disk-shaped compressive stress film 38 is concentric with the disk-shaped diaphragm 36 (or the recess 34) when viewed from the direction perpendicular to the upper surface of the fixed electrode substrate 32. Has been placed. Thus, if the compressive stress film 38 is concentric with the diaphragm 36 and is positioned in the middle of the diaphragm 36, the diaphragm 36 is unlikely to deform unevenly depending on the direction, and the deterioration of the diaphragm 36 also proceeds concentrically. . Therefore, even when the deterioration of the diaphragm 36 proceeds, the diaphragm 36 isotropically deforms, so that the characteristic fluctuation of the pressure sensor 31 can be reduced.

  The compressive stress film 38 may have a larger area than the diaphragm 36, and the compressive stress film 38 may extend to the upper surface of the outer peripheral portion 37. However, the ring-shaped portion at the edge of the diaphragm 36 is the most deformed portion, and the spring characteristic of this ring-shaped portion affects the sensitivity of the pressure sensor 31. Therefore, if the compressive stress film 38 is larger than the diaphragm 36, The sensitivity of the pressure sensor 31 decreases. Therefore, in the pressure sensor 31, it is desirable that the area of the compressive stress film 38 is smaller than the area of the diaphragm 36, and the compressive stress film 38 is smaller than the diaphragm 36. If the compressive stress film 38 is made smaller than the diaphragm 36 and the compressive stress film 38 is not provided in the ring-shaped portion of the edge of the diaphragm 36, the sensitivity reduction of the pressure sensor 31 can be reduced.

  In particular, it is desirable that the compressive stress film 38 has a shape similar to that of the diaphragm 36 and has a scale of 1/2 or less of the diaphragm 36. In other words, it is desirable that the radius and width of the compressive stress film 38 be ½ or less of the radius and width of the diaphragm 36. FIG. 5 shows the actual deformation of the diaphragm 36. Sample No. 1 in FIG. 5 shows a state in which the diaphragm 36 is deformed upwardly. Sample No. 2 shows a state in which a part is deformed upward and the other part is deformed downward (secondary deformation mode). Sample No. 3 represents a state in which the diaphragm 36 is deformed in a convex downward direction (primary deformation mode). As can be seen from the deformation of each mode in FIG. 5, the change in the shape of the diaphragm 36 is noticeable mainly in the region where the radius is R / 2 (where R is the radius of the diaphragm 36). By forming the compressive stress film 38 in the range, the deformation of the diaphragm 36 can be effectively corrected by the small compressive stress film 38. Since the area where the compressive stress film 38 of the diaphragm 36 is not formed (the area outside the compressive stress film 38) is widened, the diaphragm 36 is easily elastically deformed, and the influence on the sensitivity of the pressure sensor 31 is minimized. However, the deformation of the diaphragm 36 can be corrected.

  The compressive stress film 38 can have a compressive stress by using the film forming conditions of the compressive stress film 38. That is, the difference between the film forming environment of the compressive stress film 38 and the normal operating environment of the pressure sensor 31 may be used so that the compressive stress remains in the compressive stress film 38 under the normal operating environment. For example, it is assumed that when the compressive stress film 38 is formed on the upper surface of the diaphragm 36 in a high temperature environment, neither the diaphragm 36 nor the compressive stress film 38 has internal stress. It is assumed that when the pressure sensor 31 is taken out from the film forming apparatus and the pressure sensor 31 is returned to a normal temperature environment, the thermal contraction rate of the diaphragm 36 is larger than the thermal contraction rate of the compressive stress film 38. In this case, the compressive stress film 38 having a small thermal contraction rate receives a compressive force from the diaphragm 36, and the compressive stress remains inside. The diaphragm 36 having a large heat shrinkage rate receives resistance against shrinkage, that is, tensile force, from the compressive stress film 38, and thus tensile stress remains in the diaphragm 36. Therefore, the compressive stress film 38 tends to spread outward against the compressive stress, and the diaphragm 36 tends to shrink inward against the tensile stress, so that the diaphragm 36 and the compressive stress film 38 are convex upward. To bend. In short, since the diaphragm 36 is greatly contracted and the compressive stress film 38 is contracted small, the diaphragm 36 and the compressive stress film 38 are curved so as to be convex upward.

The material of the compressive stress film 38 may be any material that can be formed on the upper substrate 35 and can have compressive stress. For example, the compressive stress film 38 can be formed using SiO ₂ , SiN, polysilicon or other semiconductor, Ti or other metal material, polyimide or other polymer material. Further, when the compressive stress film 38 is pushed by a hard load application member (for example, a touch pen), if the compressive stress film 38 is formed of an elastic body such as polyimide, the diaphragm 36 is protected by the compressive stress film 38. it can.

  In addition, since what is provided in the upper surface of the diaphragm 36 will be effective if it is the compressive-stress film 38, the strength of the compressive stress in the compressive-stress film 38 is not ask | required.

(Modification of Embodiment 1)
FIG. 6 is a plan view showing a modification of the first embodiment of the present invention. The compressive stress film 38 provided on the diaphragm 36 may have a polygonal shape, for example, a rectangular shape or a hexagonal shape as in this modification. In particular, it is desirable that the compressive stress film 38 has a regular polygonal shape that is rotationally symmetric about the center.

  FIG. 7 is a plan view showing another modification of the first embodiment of the present invention. In this modification, a radial compressive stress film 38 is provided on the upper surface of the diaphragm 36. In particular, the compressive stress film 38 is desirably radially symmetric about the center. In the case of the disk-like compressive stress film 38, when the elastic modulus of the compressive stress film 38 is large, when the compressive stress film 38 is pressed, the diaphragm 36 may be bent suddenly in the radial direction at the edge of the compressive stress film 38. . On the other hand, if the radial compressive stress film 38 is formed as in this modification, the compressive stress film 38 is gradually increased from the center of the diaphragm 36 toward the outer peripheral side in a portion where the compressive stress film 38 is radial. (The area ratio of the compressive stress film 38 in the ring-shaped region around the center of the diaphragm 36) gradually decreases. As a result, the compressive force applied to the diaphragm 36 is smoothly reduced from the center toward the outer peripheral side, the diaphragm 36 is smoothly deformed, and the characteristics of the pressure sensor 31 are stabilized.

(Embodiment 2)
FIG. 8A is a plan view showing a capacitive pressure sensor 51 according to Embodiment 2 of the present invention. FIG. 8B is a cross-sectional view of the pressure sensor 51. In this embodiment, the tensile stress film 52 is formed on at least a part of the lower surface of the diaphragm 36. Since other parts are the same as those in the first embodiment, the same parts as those in the embodiment are denoted by the same reference numerals as those in the first embodiment, and description thereof will be omitted (the same applies hereinafter).

  In the pressure sensor 51 of the second embodiment, a tensile stress film 52 is formed on the lower surface of the diaphragm 36. Since tensile stress remains inside the tensile stress film 52, the tensile stress film 52 tries to shrink itself in the film direction against the tensile stress, and at the same time, the diaphragm 36 also tries to shrink. Since the lower surface of the diaphragm 36 is contracted by the tensile stress film 52, compressive stress is generated inside. Accordingly, the tensile stress film 52 tends to shrink in the film direction, and the diaphragm 36 tends to spread against the force from the tensile stress film 52 to shrink. As a result, the diaphragm 36 and the tensile stress film 52 are deformed so as to protrude upward in the initial state.

  If the tensile stress film 52 is provided on the lower surface of the diaphragm 36, the tensile stress film 52 is confined in the recess 34, so that the tensile stress film 52 is protected from humidity and gas (particularly corrosive gas). . Therefore, it is possible to prevent buckling deformation of the diaphragm 36 while stabilizing the stress state of the diaphragm 36 and the tensile stress film 52.

(Embodiment 3)
FIG. 9A is a plan view showing a capacitive pressure sensor 61 according to Embodiment 3 of the present invention. FIG. 9B is a cross-sectional view of the pressure sensor 61. In this embodiment, at least a part of the dielectric film 33 bonded to the lower surface of the diaphragm 36 has a tensile stress. In the dielectric film 33, only the thin film portion 62 bonded to the lower surface of the diaphragm 36 may have tensile stress, but the entire dielectric film 33 has tensile stress in consideration of the manufacturing process. May be. Even in such an embodiment, the diaphragm 36 is deformed so as to protrude upward in the initial state by the same action as in the second embodiment. Furthermore, in this embodiment, since it is not necessary to provide the compressive stress film 38 and the tensile stress film 52, the manufacturing process of the pressure sensor is simplified and the manufacturing cost is reduced.

In order to apply tensile stress to the dielectric film 33, when the dielectric film 33 is formed by MEMS technology, the film formation temperature and the RF power are controlled to control the film thickness after the dielectric film 33 is formed. The stress state can be controlled. For example, when the dielectric film 33 is formed on the lower surface of the upper substrate 35 by the plasma TEOS method with the lower surface of the upper substrate 35 facing upward, the stress generated in the dielectric film 33 is changed by changing the RF power. Can be controlled. In the plasma TEOS method, TEOS (tetraethylorthosilicate: Si (OC ₂ H ₅ ) ₄ ) is deposited on the lower surface (upward surface) of the upper substrate 35 by a CVD apparatus. At this time, TEOS is decomposed into the following chemical formula to form a SiO ₂ film. As a result, a dielectric film 33 made of SiO ₂ is formed on the lower surface of the upper substrate 35.
Si (OC ₂ H ₅ ) ₄ → SiO ₂ + by-product

FIG. 10A shows the results of actual measurement of the RF power and the stress generated in the SiO ₂ film by changing the RF power under a certain condition to form a SiO ₂ film (dielectric film) by the plasma TEOS method. . As shown in FIG. 10A, when the SiO ₂ film is formed using TEOS, tensile stress is generated in the SiO ₂ film when the RF power is low. As a result, the upper substrate 35 on which the dielectric film 33 (SiO ₂ film) is formed is initially deformed so as to be convex on the upper substrate side as shown in FIG. Further, when the RF power is gradually increased, the tensile stress of the SiO ₂ film gradually decreases along with it, and the compressive stress gradually increases after exceeding the zero internal stress state. As a result, when the RF power is high, the upper substrate 35 on which the dielectric film 33 is formed is initially deformed so as to be convex on the dielectric film side as shown in FIG. Therefore, when the dielectric film 33 is formed on the upper substrate 35 by the power TEOS method, if the dielectric film 33 is formed with a small RF power, the film can be formed with a tensile stress. It becomes possible.

  Needless to say, in the second and third embodiments, the same modifications and technical descriptions as those in the first embodiment are applied.

(Embodiment 4)
FIG. 11A is a partially exploded perspective view showing a pressure detector 71 according to Embodiment 4 of the present invention. FIG. 11B is a cross-sectional view of the pressure detector 71. In the pressure detector 71, a pressure sensor 72 according to the present invention is housed in a ceramic casing 73. The pressure sensor 72 is fixed to the bottom surface of the casing 73 by a bonding layer 74 such as Au. The casing 73 is provided with a through-hole electrode 75 a penetrating vertically, and the upper end of the through-hole electrode 75 a is connected to the bonding layer 74. Since the bonding layer 74 is electrically connected to the fixed electrode of the pressure sensor 72, the fixed electrode of the pressure sensor 72 is drawn to the lower surface of the casing 73 through the through-hole electrode 75a. In the vicinity of the fixed position of the pressure sensor 72, a stepped portion 76 that is one step higher is provided on the bottom surface of the casing 73. The step portion 76 is provided with a through-hole electrode 75 b penetrating vertically, and the electrode pad 39 a of the pressure sensor 72 and the upper surface of the through-hole electrode 75 b are connected by a bonding wire 77. Therefore, the diaphragm is drawn to the lower surface of the casing 73 through the through-hole electrode 75b. The upper surface of the casing 73 is covered with a lid 78, and the diaphragm portion of the pressure sensor 72 is exposed from the opening 79 of the lid 78.

  Such a pressure detector 71 can be used for detecting a load or pressure applied to the diaphragm of the pressure sensor 72. For example, it can be used as a pressure detector 71 for detecting pen pressure.

(Embodiment 5)
FIG. 12 is a cross-sectional view showing the structure of a plate-type input device 81 according to Embodiment 5 of the present invention, such as a touch panel. This input device 81 has a large number of sensor portions 82 having the same structure as the pressure sensor according to the present invention arranged in an array (for example, a rectangular shape or a honeycomb shape). Note that each sensor unit 82 is electrically independent, and the pressure applied to each sensor unit 82 can be detected independently. According to such an input device 81, a point pressed with a finger or the like as in a touch panel can be detected, and the pressing strength of each point can also be detected.

31, 51, 61 Pressure sensor 32 Fixed electrode substrate 33 Dielectric film 34 Recess 35 Upper substrate 36 Diaphragm 38 Compressive stress film 52 Tensile stress film 62 Thin film portion 71 Pressure detector 72 Pressure sensor

Claims (9)

A fixed electrode substrate;
A dielectric film having a recess on one of the upper surface and the lower surface, and covering the upper surface of the fixed electrode substrate;
An upper substrate provided on the dielectric film;
An elastically deformable diaphragm formed by a region of the upper substrate facing the recess;
A compressive stress film formed on at least a part of the upper surface of the diaphragm;
Have
The compressive stress film is formed radially in a rotationally symmetrical manner when viewed from a direction perpendicular to the upper surface of the fixed electrode substrate,
The capacitance type pressure sensor according to claim 1, wherein the radially extending branches of the compressive stress film have a width at the end on the tip side that is narrower than a width at the end on the center side.   2. The capacitive pressure sensor according to claim 1, wherein a width of the branch is gradually narrowed as the distance from the center of the compressive stress film is increased.   2. The capacitive pressure sensor according to claim 1, wherein the center of the compressive stress film overlaps the center of the diaphragm when viewed from a direction perpendicular to the upper surface of the fixed electrode substrate.   The capacitive pressure sensor according to claim 1, wherein an area of the compressive stress film is smaller than an area of the diaphragm.   2. The capacitive pressure sensor according to claim 1, wherein when viewed from a direction perpendicular to the upper surface of the fixed electrode substrate, the concave portion is circular and the compressive stress film is also circular.   The capacitive pressure sensor according to claim 1, wherein the compressive stress film is formed of an elastic body. A fixed electrode substrate;
A dielectric film having a recess on one of the upper surface and the lower surface, and covering the upper surface of the fixed electrode substrate;
An upper substrate provided on the dielectric film;
An elastically deformable diaphragm formed by a region of the upper substrate facing the recess;
A tensile stress film formed on at least a part of the lower surface of the diaphragm;
Have
The tensile stress film is formed radially in a rotationally symmetric manner around its center when viewed from a direction perpendicular to the upper surface of the fixed electrode substrate.
The capacitance-type pressure sensor according to claim 1, wherein the radially extending branches of the tensile stress film have a width at the end on the tip side that is narrower than a width at the end on the center side.   A pressure detector in which the capacitive pressure sensor according to claim 1 or 7 is housed in a casing.   An input device on which the capacitive pressure sensor according to claim 1 is mounted.

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