SENSOR MEMBER

There is provided a sensor member with a small risk of damage. A sensor member includes: a membrane; a protective film covering a part of the membrane; and an electrode portion connected to the membrane. The electrode portion 5 covers at least a part of the protective film.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a sensor member used for, for example, a pressure sensor or the like.

Description of the Related Art

As disclosed in JP 2005-249520 A, a film-shaped sensor including a strain-resistance film is known. In such a sensor, in order to protect the strain-resistance film, a protective film is formed to cover the strain-resistance film.

However, the protective film has a portion with poor adhesiveness, and there is a risk of occurrence of a peeling defect.

CITATION LIST

Patent Document 1: JP 2005-249520 A

BRIEF SUMMARY OF THE INVENTION

The present invention has been conceived in view of the foregoing circumstances, and an object of the present invention is to provide a sensor member with a small risk of damage.

In order to achieve the foregoing object, according to the present invention, there is provided a sensor member including: a membrane; a protective film covering a part of the membrane; and an electrode portion connected to the membrane. The electrode portion covers at least a part of the protective film.

Since an electrode is formed on the protective film by implementing such a configuration, a peeling defect such as peeling off from an end of the protective film or damage due to impact can be prevented.

Preferably, the electrode portion includes a mounting layer containing gold.

Since the mounting layer contains gold, the adhesiveness of the mounting layer to an Au wiring with good heat resistance is particularly good. Therefore, the electrode portion including such a mounting layer is improved in high-temperature resistance, and exhibits good adhesion to the wiring.

Preferably, the electrode portion includes a diffusion prevention layer consisting of a platinum group element.

Since the diffusion prevention layer contains a platinum group element that is chemically stable, interdiffusion between the membrane and the electrode portion can be effectively prevented.

Preferably, the electrode portion includes a contact layer contacting with the membrane.

The electrode portion including such a contact layer can effectively prevent interdiffusion between the membrane and the electrode portion. In addition, the electrode portion including the contact layer prevents a change in the property of the membrane under a high temperature environment, is improved in high-temperature resistance, and exhibits very good adhesion to the wiring even after being exposed to the high temperature environment.

Examples of an element contained in such a contact layer are Cr, Ti, Ni, Mo, and the like. Since such elements easily form alloys with other metal elements, such elements are effective in preventing a peeling defect of the films by ensuring adhesion strength between the films and between the layers.

Preferably, the protective film consists of an oxynitride.

Since such a protective film has high strength, the structural strength particularly at an end portion can be improved, and the reliability of the sensor member can be improved.

Preferably, the membrane includes a metal base member, an insulating film placed on the metal base member, and a strain-resistance film placed on the insulating film.

Such a membrane is suitable for use in a pressure sensor in a high temperature environment. In addition, since metal is used as a base material, the pressure sensor with high mechanical strength and high reliability can be realized. Incidentally, the sensor member may be used for physical quantity sensors other than the pressure sensor, such as an acceleration sensor, a torque sensor, and an inclination sensor.

Preferably, the electrode portion is disposed as an upper layer of the strain-resistance film to spread outward from the strain-resistance film.

Since the contacting area between the electrode portion and the protective film is increased, the strain-resistance film can be effectively protected from an external environment.

Preferably, the electrode portion is disposed as an upper layer of the strain-resistance film and inside the strain-resistance film.

Since the electrode portion is disposed in such a manner, a reduction in the size of the sensor member can be realized.

Preferably, the strain-resistance film includes a resistance portion that detects a pressure.

Such a sensor member is suitably used for the pressure sensor.

DETAILED DESCRIPTION OF THE INVENTIONS

Embodiments of the present invention will be described with reference to the drawings. The description will be made with reference to the drawings as necessary; however, the illustrated contents are merely schematic and exemplary for the understanding of the present invention, and the appearance, dimensional ratios, and the like may differ from the actual ones. In addition, hereinafter, the present invention will be specifically described based on the embodiments, but is not limited to these embodiments.

First Embodiment

An overall configuration of a sensor member2according to the present embodiment will be described. The sensor member2can be suitably used for, for example, a pressure sensor1illustrated inFIG.1.FIG.2is a cross-sectional view of the sensor member2illustrated inFIG.1, taken along line II-II. As illustrated inFIG.2, the sensor member2includes a membrane3, a protective film4, and an electrode portion5.

The membrane3includes a metal base member30; an insulating film31placed on the metal base member30; and a strain-resistance film32placed on the insulating film31. The metal base member30only needs to be able to hold the insulating film31and the strain-resistance film32, and is made of metal such as steel, aluminum alloy, stainless steel, or nickel alloy. The metal base member30may be configured to undergo deformation corresponding to pressure. As the metal base member30, the above-described metals can be used, and particularly, austenitic stainless steels such as SUS304 and SUS316, precipitation hardening stainless steels such as SUS630 and SUS631, and the like are preferably used from the viewpoint of durability at high temperatures or the like.

The shape of the metal base member30is not particularly limited. For example, the metal base member30may be formed in a hollow cylindrical shape having a space below. The metal base member30may be formed such that the insulating film31and the strain-resistance film32are formed on an end wall disposed at one end of the hollow cylinder. The sensor member2can measure a pressure of a fluid flowing through the hollow space of the metal base member30.

As illustrated inFIG.2, the insulating film31covers an upper surface of the metal base member30. In addition, the insulating film31is located between the metal base member30therebelow and the strain-resistance film32thereabove to ensure electrical insulation between the metal base member30and the strain-resistance film32.

Although not illustrated inFIG.1, the insulating film31is formed to cover substantially the entirety of the upper surface of the metal base member30. The insulating film31is composed of, for example, an insulating film made of silicon oxide, silicon nitride, silicon oxynitride, or the like. A thickness of the insulating film31is preferably 10 μm or less, further preferably 1 to 5 μm. The insulating film31can be formed on the upper surface of the metal base member30, for example, by a vapor deposition method such as CVD.

As illustrated inFIG.2, the strain-resistance film32is formed on the insulating film31, and constitutes a detection portion34illustrated inFIG.1. As illustrated inFIG.4, in the strain-resistance film32, pad connection portions36, a first resistance portion R1, a second resistance portion R2, a third resistance portion R3, and a fourth resistance portion R4are formed in a predetermined pattern by being connected by resistance wiring portions35. The first to fourth resistance portions R1, R2, R3, and R4generate strain corresponding to the deformation of the metal base member30, and are changed in resistance according to the deformation of the metal base member30. The first to fourth resistance portions R1to R4are connected by the resistance wiring portions35formed in the same strain-resistance film32, so as to constitute a Wheatstone bridge circuit as the detection portion34.

In addition, since the deformation amount of the metal base member30detected by the detection portion34changes depending on the pressure of the fluid or the like acting on the metal base member30, the detection portion34can detect the pressure acting on the metal base member30. Namely, the first to fourth resistance portions R1to R4of the sensor member2illustrated inFIG.1are provided at positions where the metal base member30is deformed and strained by pressure, and are configured such that the resistances change according to the strain amounts thereof. Incidentally, the pressure sensor1illustrated inFIG.1is connected to a circuit substrate (not illustrated) from pad portions55, and can receive an output of the detection portion34of the sensor member2or supply electric power from a power supply unit to the sensor member2.

The strain-resistance film32including the first to fourth resistance portions R1to R4can be produced, for example, by patterning a conductive thin film made of a predetermined material. The strain-resistance film32contains, for example, Cr and Al, preferably contains 50 to 99 at % of Cr and 1 to 50 at % of Al, and further preferably contains 70 to 90 at % of Cr and 5 to 30 at % of Al. Since the strain-resistance film32contains Cr and Al, the temperature coefficient of resistance (TCR) or temperature coefficient of sensitivity (TCS) under a high temperature environment is stable and highly accurate pressure detection can be performed. In addition, both a high gauge factor and good temperature stability can be achieved at a higher level by setting the amounts of Cr and Al within predetermined ranges.

The strain-resistance film32may contain an element other than Cr and Al, and for example, the strain-resistance film32may contain O or N. O or N contained in the strain-resistance film32, which is not completely removed and remains in a reaction chamber when the strain-resistance film32is formed, may be incorporated into the strain-resistance film32. In addition, O or N contained in the strain-resistance film32may be intentionally introduced into the strain-resistance film32by being used as an atmospheric gas during film formation or during annealing.

In addition, the strain-resistance film32may contain a metal element other than Cr and Al. The strain-resistance film32may contain a small amount of a metal or non-metal element other than Cr and Al, and heat treatment such as annealing may be performed, so that the gauge factor or temperature property is improved. Examples of the metal and non-metal elements other than Cr and Al contained in the strain-resistance film32include Ti, Nb, Ta, Ni, Zr, Hf, Si, Ge, C, P, Se, Te, Zn, Cu, Bi, Fe, Mo, W, As, Sn, Sb, Pb, B, Ge, In, Tl, Ru, Rh, Re, Os, Ir, Pt, Pd, Ag, Au, Co, Be, Mg, Ca, Sr, Ba, Mn, and rare earth elements.

The strain-resistance film32can be formed by a thin film method such as sputtering or vapor deposition. The first to fourth resistance portions R1to R4can be formed, for example, by patterning a thin film into a meandering shape. The thickness of the strain-resistance film32is not particularly limited, and is preferably 10 μm or less, further preferably 0.1 to 1 μm. Incidentally, as illustrated inFIG.2, the resistance wiring portions35are formed by patterning the strain-resistance film32.

As illustrated inFIG.2, the protective film4is formed on the membrane3(on the insulating film31and the strain-resistance film32). The protective film4includes a protective portion40covering the strain-resistance film32from above, and an outer edge portion41covering the insulating film31from above. The protective film4covers at least a part of the membrane3from above.

In the protective film4, openings42are formed in a predetermined pattern as illustrated inFIG.5. As illustrated inFIG.1, the protective film4covers the first to fourth resistance portions R1to R4and central portions35aof the resistance wiring portions35in the strain-resistance film32, but does not cover the pad connection portions36and side portions35bof the resistance wiring portions35. The pattern of the protective film4is not limited to this pattern, and may be a pattern in which side portions of the pad connection portions36are covered. As illustrated inFIG.2, the openings42are formed inside the protective portion40of the protective film4so as to be connected to upper surfaces of the central portions35aof the resistance wiring portions35of the strain-resistance film32.

The protective film4is composed of, for example, an insulating film similarly to the insulating film31. Examples of the insulating film constituting the protective film4include films made of an oxide, a nitride, and an oxynitride, and these films are preferably used from the viewpoint of improving the strength of the protective film4. More specifically, examples of the material constituting the protective film4include SiO2, SiON, Si3N4, AlO3, and ZrO2.

The protective film4can be formed on the strain-resistance film32and the insulating film31, for example, by CVD, sputtering, or the like; however, the method for forming the protective film4is not particularly limited. The thickness of the protective film4is not particularly limited, and is preferably 10 nm to 1000 nm, further preferably 100 nm to 300 nm.

As illustrated inFIGS.1and2, the electrode portion5is formed inside the opening42of the protective film4and on the protective film4(on the protective portion40). The electrode portion5includes an energized portion51electrically connected to the strain-resistance film32, and a skirt portion52covering the protective film4from above. The electrode portion5covers at least a part of the protective film4from above.

The electrode portion5is formed in a predetermined pattern including a wiring portion54and the pad portion55as illustrated inFIG.6. As illustrated inFIG.1, the electrode portions5are formed at four locations to correspond to the openings42of the protective film4. However, the number and disposition of the electrode portions5included in the sensor member2are not limited only to the example illustrated inFIG.1. In addition, the thickness of the electrode portions5is not particularly limited and is, for example, 50 to 500 nm, preferably 100 to 300 nm.

As illustrated inFIG.2, the energized portion51is a portion of the electrode portion5which is disposed inside an opening peripheral edge43of the protective film4when the sensor member2is viewed from above. A lower portion of the energized portion51is disposed in the inside of the opening42which is a region inside the opening peripheral edge43and lower than an upper end of the protective portion40, and a lower end of the energized portion51is in contact with the strain-resistance film32. In addition, an upper portion of the energized portion51is disposed in a region higher than the upper end of the protective portion40, and is connected to the skirt portion52.

The skirt portion52is a portion of the electrode portion5which is disposed outside the outer edge of the opening42when the sensor member2is viewed from above. As illustrated inFIG.2, the skirt portion52is provided on the protective portion40, and the skirt portion52is connected to the energized portion51on an inner side, the energized portion51being disposed in the opening42. As illustrated inFIG.1, the wiring portion54of the electrode portion5is wider than the opening42of the protective film4.

As illustrated inFIG.2, an end edge53of the skirt portion52is disposed above the protective portion40. In addition, the end edge53of the skirt portion52is disposed inside an end edge33of the strain-resistance film32.

A length L1of the skirt portion52from an inner side connected to the energized portion51to the end edge53is not particularly limited, but may be, for example, 0.001 times to 5 times a length L0at which the energized portion51is in contact with the central portion35aof the resistance wiring portion35of the strain-resistance film32. The length L1of the skirt portion52is shorter than a length L2of the side portion35bof the resistance wiring portion35of the strain-resistance film32, which is covered with the protective portion40.

FIG.3is an enlarged view of the sensor member2illustrated inFIG.2. As illustrated inFIG.3, the electrode portion5may include a contact layer50coverlaid on the strain-resistance film32; a diffusion prevention layer50boverlaid on the contact layer50c; and a mounting layer50aoverlaid on the diffusion prevention layer50b. The electrode portion5may have a multilayer film structure of three or more layers made of different materials. However, the electrode portion5is not limited only to a three-layered structure as illustrated inFIG.3, and the electrode portion5may have a laminated structure of one, two, or four or more layers.

As illustrated inFIG.3, the contact layer50clocated at a lowermost layer of the electrode portion5is in direct contact with the strain-resistance film32and the protective film4. The contact layer50cimproves the electrical property of the strain-resistance film32with an electrode by ensuring ohmic connection with the strain-resistance film32. In addition, the contact layer50cprevents a peeling defect of the films and the layers by ensuring adhesion strength between the electrode portion5and each of the strain-resistance film32and the protective film4.

The contact layer50ccan be formed by a vapor deposition method, sputtering, or the like. The thickness of the contact layer50cis not particularly limited and is, for example, 1 to 50 nm, preferably 5 to 20 nm. It is preferable that the contact layer50ccontains at least one of Cr, Ti, Ni, and Mo. Since these elements easily form alloys with other metals, the contact layer50ccontaining such elements can prevent a peeling defect between the films and the layers by ensuring adhesion strength between the contact layer50cand each of the strain-resistance film32and the diffusion prevention layer50b.

In addition, it is particularly preferable that the contact layer50ccontains Ti. Ti has the tendency of being difficult to diffuse into the mounting layer50acontaining Au or the like and being less likely to be deposited on an upper surface of the mounting layer50a. For this reason, the electrode portion5including the contact layer50ccontaining Ti exhibits suitable adhesiveness to the strain-resistance film32even after the electrode portion5is exposed to a high temperature environment.

Further, since it is difficult for Ti to diffuse into Cr, Ti constituting the contact layer50chas the property of being difficult to diffuse into the strain-resistance film32containing Cr and Al even under a high temperature environment. Therefore, even when the strain-resistance film32with an electrode including the contact layer50ccontaining Ti is used under a high temperature environment, the elements in the electrode portion5can be prevented from diffusing into the strain-resistance film32, and a degradation in the performance of the strain-resistance film32due to a change in composition can be prevented.

In addition, it is also preferable that the contact layer50ccontains a plurality of elements selected from Cr, Ti, Ni, and Mo. In addition, it is also preferable that the contact layer50cconsists of at least one of Cr, Ti, Ni, and Mo. Further, it is also particularly preferable that the contact layer50cconsists of Ti. In addition, it is also preferable that the contact layer50cconsists of a plurality of elements selected from Cr, Ti, Ni, and Mo.

Incidentally, when the contact layer50c, the diffusion prevention layer50b, and the mounting layer50aconsist of one or a plurality of specified elements, a case where an element other than the specified elements is inevitably or intentionally contained in these layers is not excluded. In that case, the content ratio of the other element is, for example, less than 10 at %, preferably less than 3 at %, and further preferably less than 1 at %.

As illustrated inFIG.3, the diffusion prevention layer50bis disposed between the contact layer50cand the mounting layer50ain the electrode portion5, and is sandwiched between the mounting layer50aand the contact layer50cin an up-down direction. The diffusion prevention layer50bprevents the elements contained in the film and layer such as the strain-resistance film32or the contact layer50cdisposed below the diffusion prevention layer50bfrom diffusing into the mounting layer50adisposed on the diffusion prevention layer50b, and prevents the elements from being deposited on the upper surface of the mounting layer50a. Incidentally, it is preferable that the diffusion prevention layer50bis disposed directly below the mounting layer50aeven when the strain-resistance film32or the electrode portion5has a multilayer structure of four or more layers.

The diffusion prevention layer50bcan be formed by a vapor deposition method, sputtering, or the like. The thickness of the diffusion prevention layer50bis not particularly limited and is, for example, 1 to 500 nm, preferably 5 to 50 nm. When the thickness of the diffusion prevention layer50bis too thin, a continuous film becomes difficult to form, and the diffusion prevention function may be weakened, and when the thickness is too thick, a problem such as film peeling may occur or a problem such as a decrease in productivity (throughput) due to an increase in film formation time may occur.

It is preferable that the diffusion prevention layer50bcontains a transition element belonging to a fifth or sixth period, from the viewpoint of preventing the elements contained in the strain-resistance film32, the contact layer50c, or the like from diffusing into the upper layer. Specifically, it is preferable that the diffusion prevention layer50bcontains one or a plurality of elements selected from Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, and Au.

In addition, it is further preferable that the diffusion prevention layer50bcontains a platinum group element. Specifically, it is preferable that the diffusion prevention layer50bcontains one or a plurality of elements selected from Ru, Rh, Pd, Os, Ir, and Pt. Since the platinum group elements have low reactivity and are chemically stable, the diffusion prevention layer50bcontaining a platinum group element exhibits a particularly suitable diffusion prevention effect even in a high temperature environment. Incidentally, among the platinum group elements, particularly, Pt has a track record of being used in other electrode fields, and has greater technological accumulation than other platinum group elements.

It is also preferable that the diffusion prevention layer50bconsists of a transition element belonging to the fifth or sixth period. In addition, it is also preferable that the diffusion prevention layer50bconsists of a platinum group element.

As illustrated inFIG.3, the mounting layer50alocated at an uppermost layer of the electrode portion5is exposed on the upper surface of the strain-resistance film32with an electrode. An external wiring (not illustrated) composed of a fine wire made of Au, Al, or the like is joined to the mounting layer50ain the pad portion55illustrated inFIG.1by wire bonding or the like. Incidentally, the pressure sensor1using the external wiring (not illustrated) composed of a fine wire made of Au or Al can be used even in a high temperature environment where the temperature is equal to or higher than the melting point of solder, and has good heat resistance. In addition, the pressure sensor1using an intermediate wiring72composed of a fine wire made of Au can be further improved in heat resistance than a pressure sensor using an external wiring composed of a fine wire made of Al.

The mounting layer50acan be formed by a vapor deposition method, sputtering, or the like. The thickness of the mounting layer50ais not particularly limited and is, for example, 10 to 400 nm, preferably 100 to 300 nm. When the thickness of the mounting layer50ais too thin, a continuous film becomes difficult to form, and adhesiveness to the external wiring deteriorates, which is a risk. When the thickness of the mounting layer50ais too thick, a problem such as film peeling may occur, or a problem such as a decrease in productivity (throughput) due to an increase in film formation time may occur.

It is preferable that the mounting layer50acontains at least one of Au, Al, and Ni from the viewpoint of heat resistance and joinability with the external wiring. In addition, from the viewpoint of further enhancing compatibility with a high temperature environment by enhancing heat resistance, it is further preferable that the mounting layer50acontains Au having low resistance and a high melting point even in a high temperature environment. In addition, in the case of using a fine wire made of Au as the material of the external wiring, since the mounting layer50acontains Au, the materials of both the intermediate wiring72and the mounting layer50aare Au. Accordingly, the adhesiveness of a joint portion between the external wiring and the mounting layer50ais improved.

In addition, it is preferable that the mounting layer50aconsists of at least one of Au, Al, and Ni, and is also particularly preferable that the mounting layer50aconsists of Au.

As illustrated inFIG.2, in the present embodiment, the sensor member2is configured such that the electrode portion5covers at least a part of the protective film4. An end of the protective film stacked on the strain-resistance film is more likely to peel off than other portions; however, since the electrode is formed on the protective film4by implementing such a configuration, a peeling defect such as peeling off from an end of the protective film4(for example, the opening peripheral edge43or the like) or damage due to impact can be prevented.

In addition, as illustrated inFIG.3, the electrode portion5may include the mounting layer50acontaining gold. Since the mounting layer50acontains gold, the adhesiveness of the mounting layer50ato the Au wiring with good heat resistance is particularly good. Therefore, the electrode portion5including the mounting layer50ais improved in high-temperature resistance, and exhibits good adhesion to the wiring.

In addition, the electrode portion5may include the diffusion prevention layer50bconsisting of a platinum group element. Since the diffusion prevention layer50bcontains a platinum group element that is chemically stable, interdiffusion between the membrane3and the electrode portion5can be effectively prevented.

In addition, the electrode portion5may include the contact layer50ccontacting to the membrane3. The electrode portion5including the contact layer50ccan effectively prevent interdiffusion between the membrane3and the electrode portion5. In addition, the electrode portion5including the contact layer50cprevents a change in the property of the membrane3under a high temperature environment, is improved in high-temperature resistance, and exhibits very good adhesion to the wiring even after being exposed to the high temperature environment.

Examples of the element contained in the contact layer50care Cr, Ti, Ni, Mo, and the like. Since such elements easily form alloys with other metal elements, such elements are effective in preventing a peeling defect of the films by ensuring contacting strength between the films and between the layers.

The protective film4may consist of an oxynitride. Since the protective film4has high strength, the structural strength particularly at an end portion can be improved, and the reliability of the sensor member2can be improved.

In addition, as illustrated inFIG.1, in the present embodiment, the strain-resistance film32includes the resistance portions R1to R4that detect a pressure. The sensor member2is suitably used for the pressure sensor1.

As illustrated inFIG.2, in the present embodiment, the membrane3includes the metal base member30; the insulating film31placed on the metal base member30; and the strain-resistance film32placed on the insulating film31. The membrane3is suitable for use in the pressure sensor in a high temperature environment. In addition, since metal is used as a base material, the pressure sensor with high mechanical strength and high reliability can be realized.

In addition, the electrode portion5is disposed as an upper layer of the strain-resistance film32and inside the strain-resistance film32. Since the electrode portion5is disposed in such a manner, a reduction in the size of the sensor member2can be realized.

Second Embodiment

A sensor member2aaccording to the present embodiment illustrated inFIG.7differs from that of the first embodiment only in the electrode portion5. The description of common portions will be omitted, and hereinafter, different portions will be mainly described in detail. Portions not described below are same as described in the first embodiment.

As illustrated inFIG.7, the skirt portion52is disposed on the protective film4. The end edge53of the skirt portion52is disposed above the outer edge portion41. The end edge53of the skirt portion52is disposed outside the end edge33of the strain-resistance film32.

As illustrated inFIG.7, the skirt portion52covers the protective portion40and covers at least a part of the outer edge portion41. The length L1of the skirt portion52from the inner side connected to the energized portion51to the end edge53is longer than the length L2of a protected portion of the strain-resistance film32, the protected portion being covered with the protective portion40.

The electrode portion5is disposed as an upper layer of the strain-resistance film32to spread outward from the strain-resistance film32. Since such disposition is implemented, the contacting area between the electrode portion5and the protective film4can be increased and the strain-resistance film32can be effectively protected from an external environment.

Incidentally, the above-described embodiments include, within the technical scope, various modes in which the design is changed or the configuration of each embodiment is replaced without departing from the concept of the claims.

For example, the metal base member30may be formed in a hollow cylindrical shape having a space below. The metal base member30may be formed such that the insulating film31and the strain-resistance film32are formed on an end wall disposed at one end of the hollow cylinder. A pressure of a fluid flowing through the hollow space of the metal base member30can be measured by using such a sensor member.

Incidentally, the sensor member may be used for a sensor other than the pressure sensor, and examples of the sensor using the sensor member2include physical quantity sensors such as an acceleration sensor, a torque sensor, and an inclination sensor.

EXPLANATIONS OF LETTERS OR NUMERALS