JP7549984B2 - Stacked electrode, strain-resistant film with electrode, and pressure sensor - Google Patents

Description

The present invention relates to a laminated electrode provided on a strain-resistance film, a strain-resistance film with electrodes, and a pressure sensor having these.

A strain-resistance film containing Cr and Al has been proposed for use in devices such as pressure sensors. Such strain-resistance films have been reported to have excellent properties, especially at high temperatures.

In addition, an electrode layer for wiring to an external circuit is provided on such a strain resistive film. It is preferable that such an electrode layer has good adhesion to both the strain resistive film and the wiring material. For example, a laminated electrode in which multiple layers are stacked has been proposed (see Patent Document 1, etc.).

JP 2018-91848 A

However, the inventors of the present invention encountered the problem that, even if the electrode layer for a conventional strain-resistant film has good bonding properties at room temperature, the adhesion to the wiring decreases when exposed to a high-temperature environment.

The present invention was made in consideration of the above-mentioned circumstances, and its purpose is to provide a laminated electrode for a strain-resistant film that exhibits good adhesion to wiring even after exposure to a high-temperature environment when a strain-resistant film containing Cr and Al is used.

The laminated electrode according to the present invention is a laminated electrode provided on a strain resistive film,
The strain-resistance film includes Cr and Al,
the laminated electrode has a contact layer overlapping the strain resistive film, a diffusion prevention layer overlapping the contact layer, and a mounting layer overlapping the diffusion prevention layer,
The diffusion prevention layer contains a transition element belonging to the fifth or sixth period.

The laminated electrode according to the present invention is formed on a strain-resistant film containing Cr and Al, and has at least three layers: a contact layer, a diffusion prevention layer, and a mounting layer. The diffusion prevention layer, which contains a transition element belonging to the fifth or sixth period, prevents elements contained in the contact layer and the strain-resistant film from interdiffusing into the mounting layer. A laminated electrode having such a diffusion prevention layer has improved high-temperature resistance and exhibits good adhesion to wiring even after exposure to a high-temperature environment by suppressing the reaction of the interdiffused elements at the mounting layer interface.

For example, the strain-resistant film may contain 50 to 99 at% Cr and 1 to 50 at% Al.

This type of strain-resistant film has a stable, high gauge factor over a wide temperature range, and the anti-diffusion layer of the laminated electrode effectively prevents interdiffusion of Cr, which has a high content in the strain-resistant film, into the mounting layer, resulting in a laminated electrode with good adhesion.

For example, the diffusion prevention layer may contain a platinum group element.

By containing a chemically stable platinum group element, the diffusion prevention layer can effectively prevent interdiffusion between the films and layers in the strain resistive film and laminated electrode. In addition, reactions of interdiffused elements at the mounting layer interface can also be effectively suppressed.

Furthermore, for example, the contact layer may contain at least one of Cr, Ti, Ni, and Mo.
For example, the contact layer may contain Ti.

The elements contained in such a contact layer are likely to form alloys with other metal elements, and are therefore effective in ensuring inter-film and inter-layer adhesion strength and preventing film peeling failure. In particular, Ti is relatively difficult to diffuse into a strain-resistant film containing Cr and Al, and the diffusion prevention layer containing a transition element belonging to the fifth or sixth period effectively prevents interdiffusion into the mounting layer. Furthermore, Ti is also difficult to diffuse into a mounting layer containing Au, etc., and is unlikely to precipitate on the upper surface of the mounting layer. Therefore, a laminated electrode having such a contact layer can effectively prevent interdiffusion between the films and layers in the strain-resistant film and the laminated electrode. In addition, a laminated electrode having such a contact layer prevents changes in the characteristics of the strain-resistant film in a high-temperature environment, improves high-temperature resistance, and exerts very good adhesion to wiring even after exposure to a high-temperature environment.

Also, for example, the mounting layer may contain Au.

By containing Au in the mounting layer, the adhesion of the mounting layer to the heat-resistant Au wiring is particularly good. Therefore, a laminated electrode having such a mounting layer has improved high-temperature resistance and exhibits good adhesion to the wiring.

Moreover, an electrode-attached strain-resistance film according to the present invention comprises any one of the laminated electrodes described above and the strain-resistance film.
A pressure sensor according to the present invention includes any one of the laminated electrodes described above,
The strain-resistance film;
and a membrane on which the strain resistive film is provided.

The laminated electrode is provided on a strain resistance film and used as an electrode-equipped strain resistance film. In addition, such a laminated electrode and strain resistance film are provided on a membrane or the like to form, for example, a pressure sensor that exhibits excellent resistance even in high-temperature environments.

FIG. 1 is a schematic cross-sectional view of a pressure sensor according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of a portion indicated by II in FIG. FIG. 3 is a schematic diagram showing an example of a pattern arrangement of the strain-resistance film with electrodes included in the pressure sensor shown in FIG. FIG. 4 is a graph showing the difference in the diffusion state of elements depending on whether or not there is a diffusion prevention layer. FIG. 5 is a micrograph showing that the diffusion of Cr is prevented by the diffusion prevention layer. FIG. 6 is a graph showing the change in gauge factor due to the change in composition of the strain-resistance film. FIG. 7 is a schematic diagram showing another example of a pattern arrangement of the strain-resistance film with electrodes included in the pressure sensor shown in FIG.

The present invention will now be described based on the embodiments shown in the drawings.

Figure 1 is a schematic cross-sectional view of a pressure sensor 10 using a laminated electrode 36 (see Figure 2) according to one embodiment of the present invention. As shown in Figure 1, the pressure sensor 10 has a membrane 22 that deforms in response to pressure. In this embodiment, the membrane 22 is composed of an end wall formed at one end of a hollow cylindrical stem 20. The other end of the stem 20 is an open end of the hollow portion, and the hollow portion of the stem 20 is connected to the flow path 12b of the connection member 12.

In the pressure sensor 10, the fluid introduced into the flow path 12b is guided from the hollow portion of the stem 20 to the inner surface 22a of the membrane 22, so that the fluid pressure acts on the membrane 22. The stem 20 is made of a metal such as stainless steel.

A flange portion 21 is formed around the open end of the stem 20 so as to protrude outward from the axis of the stem 20. The flange portion 21 is sandwiched between the connection member 12 and the holding member 14, so that the flow path 12b leading to the inner surface 22a of the membrane 22 is sealed.

The connecting member 12 has a screw groove 12a for fixing the pressure sensor 10. The pressure sensor 10 is fixed via the screw groove 12a to a pressure chamber in which the fluid to be measured is sealed. As a result, the flow path 12b formed inside the connecting member 12 and the inner surface 22a of the membrane 22 in the stem 20 are airtightly connected to the pressure chamber in which the fluid to be measured exists.

A circuit board 16 is attached to the upper surface of the retaining member 14. The circuit board 16 has a ring shape that surrounds the stem 20, but the shape of the circuit board 16 is not limited to this. The circuit board 16 includes, for example, a built-in circuit that transmits a detection signal from the electrode-equipped strain-resistance film 30.

As shown in FIG. 1, an electrode-equipped strain-resistance film 30 is provided on the outer surface 22b of the membrane 22. The electrode-equipped strain-resistance film 30 and the circuit board 16 are connected by intermediate wiring 72, for example, by wire bonding.

Figure 2 is a schematic cross-sectional view showing an enlarged portion of the electrode-attached strain-resistance film 30 included in the pressure sensor 10 shown in Figure 1. As shown in Figure 2, the electrode-attached strain-resistance film 30 has a strain-resistance film 32 and a laminated electrode for the strain-resistance film (hereinafter also simply referred to as a "laminated electrode") 36.

As shown in FIG. 2, the strain-resistant film 32 is provided on the outer surface 22b of the membrane 22 via an underlying insulating layer 52.

The base insulating layer 52 is formed so as to cover almost the entire outer surface 22b of the membrane 22, and is composed of, for example, silicon oxide, silicon nitride, silicon oxynitride, etc. The thickness of the base insulating layer 52 is preferably 10 μm or less, and more preferably 1 to 5 μm. The base insulating layer 52 can be formed on the outer surface 22b of the membrane 22 by, for example, a deposition method such as CVD.

If the outer surface 22b of the membrane 22 is insulating, the strain resistance film 32 may be formed directly on the outer surface 22b of the membrane 22 without forming the base insulating layer 52. For example, if the membrane 22 is made of an insulating material such as alumina, the strain resistance film 32 may be provided directly on the membrane 22.

As shown in FIG. 2, in the electrode-equipped strain-resistance film 30, the laminated electrode 36 is provided on the strain-resistance film 32. FIG. 3 is a schematic plan view of the electrode-equipped strain-resistance film 30 shown in FIGS. 1 and 2, seen from above, and shows the pattern arrangement of the electrode-equipped strain-resistance film 30.

As shown in FIG. 3, the first resistor R1, the second resistor R2, the third resistor R3 and the fourth resistor R4 are formed in a predetermined pattern on the strain resistive film 32. The first to fourth resistors R1, R2, R3 and R4 generate strain in response to the deformation of the membrane 22, and their resistance values change in response to the deformation of the membrane 22. These first to fourth resistors R1 to R4 are connected by electrical wiring 34 to form a Wheatstone bridge circuit.

The pressure sensor 10 shown in FIG. 1 detects the fluid pressure acting on the membrane 22 from the output of a Wheatstone bridge circuit consisting of the first to fourth resistors R1 to R4 shown in FIG. 3. That is, the first to fourth resistors R1 to R4 are provided at positions where the membrane 22 shown in FIGS. 1 and 2 is deformed and distorted by fluid pressure, and are configured so that the resistance value changes according to the amount of distortion.

The strain-resistance film 32 having the first to fourth resistors R1 to R4 can be fabricated, for example, by patterning a conductive thin film of a predetermined material. The strain-resistance film 32 contains Cr and Al, preferably 50 to 99 at% Cr and 1 to 50 at% Al, and more preferably 70 to 90 at% Cr and 5 to 30 at% Al. By containing Cr and Al, the strain-resistance film 32 stabilizes the TCR (Temperature coefficient of Resistance) and TCS (Temperature coefficient of sensitivity) in a high-temperature environment, enabling highly accurate pressure detection. In addition, by setting the content of Cr and Al within a predetermined range, a high gauge factor and good temperature stability can be achieved at a higher level.

The strain resistive film 32 may contain elements other than Cr and Al. For example, the strain resistive film 32 may contain O or N. The O or N contained in the strain resistive film 32 may be those that were not completely removed from the reaction chamber when the strain resistive film 32 was formed and that were then incorporated into the strain resistive film 32. The O or N contained in the strain resistive film 32 may also be those that were intentionally introduced into the strain resistive film 32 by being used as an atmospheric gas during film formation or annealing.

The strain-resistance film 32 may also contain metal elements other than Cr and Al. The strain-resistance film 32 may contain trace amounts of metals and nonmetallic elements other than Cr and Al, and may improve the gauge factor and temperature characteristics by heat treatment such as annealing. Examples of metals and nonmetallic elements other than Cr and Al contained in the strain-resistance film 32 include 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 resistive film 32 can be formed by a thin film method such as sputtering or vapor deposition. The first to fourth resistors R1 to R4 can be formed, for example, by patterning a thin film into a meandering shape. The thickness of the strain resistive film 32 is not particularly limited, but is preferably 10 μm or less, and more preferably 0.1 to 1 μm. The electrical wiring 34 may be formed by patterning the strain resistive film 32 as shown in FIG. 3, or may be formed from a conductive film or layer different from that of the strain resistive film 32 (see FIG. 7).

As shown in FIG. 2, the laminated electrode 36 is disposed on top of the strain resistive film 32. As shown in FIG. 2, the laminated electrode 36 is formed on a portion of the upper surface of the strain resistive film 32.

As shown in FIG. 3, the laminated electrodes 36 are formed independently at four locations on the strain resistive film 32. Each laminated electrode 36 is electrically connected to any two of the first to fourth resistors R1 to R4 via electrical wiring 34. The laminated electrodes 36 are provided at locations on the strain resistive film 32 where the first to fourth resistors R1 to R4 are not formed.

Although not shown in FIG. 3, one end of the intermediate wiring 72 shown in FIG. 1 and FIG. 2 is connected to each of the laminated electrodes 36 shown in FIG. 3. In other words, the output of the Wheatstone bridge circuit formed by the first to fourth resistors R1 to R4 is transmitted to the circuit board 16 shown in FIG. 1 via the laminated electrode 36 and the intermediate wiring 72 (see FIG. 1 and FIG. 2).

As shown in FIG. 2, the laminated electrode 36 has a contact layer 36a that overlaps the strain resistive film, a diffusion prevention layer 36b that overlaps the contact layer 36a, and a mounting layer 36c that overlaps the diffusion prevention layer 36b. The laminated electrode 36 has a multilayer film structure of three or more layers formed of different materials. However, the laminated electrode 36 is not limited to the three-layer structure shown in FIG. 2, and the laminated electrode 36 may have a laminated structure of four or more layers.

As shown in FIG. 2, the contact layer 36a, which is the lowest layer of the laminated electrode 36, is in direct contact with the strain resistive film 32. The contact layer 36a ensures an ohmic connection with the strain resistive film 32, improving the electrical characteristics of the electrode-attached strain resistive film 30. The contact layer 36a also ensures the adhesive strength between the strain resistive film 32 and the laminated electrode 36, preventing peeling of the films and layers.

The contact layer 36a can be formed by a thin film method such as sputtering or vapor deposition. The thickness of the contact layer 36a is not particularly limited, but is, for example, 1 to 50 nm, and preferably 5 to 20 nm. The contact layer 36a preferably contains at least one of Cr, Ti, Ni, and Mo. These elements are easy to form alloys with other metals, so the contact layer 36a containing such elements can ensure the adhesive strength with the strain resistive film 32 and the diffusion prevention layer 36b, and prevent peeling failure between the films and layers.

It is particularly preferable that the contact layer 36a contains Ti. Ti is less likely to diffuse into the mounting layer 36c containing Au, etc., and is less likely to precipitate on the upper surface of the mounting layer 36c. Therefore, the laminated electrode 36 having the contact layer 36a containing Ti exhibits suitable adhesion to the intermediate wiring 72 even after the laminated electrode 36 is exposed to a high-temperature environment. It is particularly preferable that the contact layer 36a contains Ti.

Furthermore, since Ti does not easily diffuse into Cr, the Ti constituting the contact layer 36a has the property of not easily diffusing into the strain-resistance film 32 containing Cr and Al even in a high-temperature environment. Therefore, the electrode-attached strain-resistance film 30 having the contact layer 36a containing Ti can prevent the elements in the laminated electrode 36 from diffusing into the strain-resistance film 32 even when used in a high-temperature environment, and can prevent the performance degradation of the strain-resistance film 32 due to composition changes.

It is also preferable that the contact layer 36a contains a plurality of elements selected from the group consisting of Cr, Ti, Ni, and Mo. It is also preferable that the contact layer 36a is made of at least one of the group consisting of Cr, Ti, Ni, and Mo. It is particularly preferable that the contact layer 36a is made of Ti. It is also preferable that the contact layer 36a is made of a plurality of elements selected from the group consisting of Cr, Ti, Ni, and Mo.

When the contact layer 36a, the diffusion prevention layer 36b, and the mounting layer 36c are said to be made of one or more specified elements, this does not exclude the inevitable or intentional inclusion of other elements in these layers other than the specified elements. In such cases, the content of the other elements is, for example, less than 10 at%, preferably less than 3 at%, and more preferably less than 1 at%.

As shown in FIG. 2, the diffusion prevention layer 36b is disposed between the contact layer 36a and the mounting layer 36c in the laminated electrode 36, and is sandwiched between the mounting layer 36c and the contact layer 36a in the vertical direction. The diffusion prevention layer 36b prevents elements contained in the films and layers disposed below the diffusion prevention layer 36b, such as the strain resistance film 32 and the contact layer 36a, from diffusing into the mounting layer 36c disposed above the diffusion prevention layer 36b, and also prevents them from precipitating on the upper surface of the mounting layer 36c. Note that the diffusion prevention layer 36b is preferably disposed directly below the mounting layer 36c even when the strain resistance film 32 and the laminated electrode 36 have a multi-layer structure of four or more layers.

The diffusion prevention layer 36b can be formed by a thin film method such as sputtering or vapor deposition. The thickness of the diffusion prevention layer 36b is not particularly limited, but is, for example, 1 to 500 nm, and preferably 5 to 50 nm. If the diffusion prevention layer 36b is too thin, it may be difficult to form a continuous film, and the diffusion prevention function may be weakened, while if the thickness is too thick, problems may occur with film peeling or reduced productivity (throughput) due to increased film formation time.

The diffusion prevention layer 36b preferably contains a transition element belonging to the fifth or sixth period from the viewpoint of preventing the diffusion of elements contained in the strain resistive film 32, the contact layer 36a, etc., into upper layers. Specifically, the diffusion prevention layer 36b preferably contains one or more 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.

Moreover, it is more preferable that the diffusion prevention layer 36b contains a platinum group element. Specifically, it is preferable that the diffusion prevention layer 36b contains one or more elements selected from Ru, Rh, Pd, Os, Ir, and Pt. Platinum group elements are less reactive and chemically stable, so the diffusion prevention layer 36b containing a platinum group element exhibits a particularly favorable diffusion prevention effect even in high-temperature environments. Among the platinum group elements, Pt in particular has a track record of being used in other electrode fields, and has more technological expertise than other platinum group elements.

The diffusion prevention layer 36b is preferably made of a transition element belonging to the fifth or sixth period. The diffusion prevention layer 36b is also preferably made of a platinum group element.

As shown in FIG. 2, the mounting layer 36c, which is the uppermost layer of the laminated electrode 36, is exposed on the upper surface of the electrode-attached strain-resistance film 30. An intermediate wiring 72 made of thin wires such as Au or Al is joined to the mounting layer 36c by wire bonding or the like. Note that a pressure sensor 10 using intermediate wiring 72 made of thin wires of Au or Al can be used in high-temperature environments above the melting point of solder, and has good heat resistance. Furthermore, a pressure sensor 10 using intermediate wiring 72 made of thin Au wires can have improved heat resistance compared to a pressure sensor using intermediate wiring 72 made of thin Al wires.

The mounting layer 36c can be formed by a thin film method such as sputtering or vapor deposition. The thickness of the mounting layer 36c is not particularly limited, but is, for example, 10 to 400 nm, and preferably 100 to 300 nm. If the mounting layer 36c is too thin, it becomes difficult to form a continuous film, and there is a risk of reduced adhesion to the intermediate wiring 72. If the mounting layer 36c is too thick, problems such as film peeling may occur, or the productivity (throughput) may decrease due to increased film formation time.

From the viewpoint of heat resistance and bonding with the intermediate wiring 72, it is preferable that the mounting layer 36c contains at least one of Au, Al, and Ni. Furthermore, from the viewpoint of improving heat resistance and further improving compatibility with high-temperature environments, it is even more preferable that the mounting layer 36c contains Au, which has low resistance and a high melting point even in high-temperature environments. Furthermore, when a thin Au wire is used as the material for the intermediate wiring 72, the mounting layer 36c contains Au, so that both the intermediate wiring 72 and the mounting layer 36c are made of Au. This improves the adhesion of the joint between the intermediate wiring 72 and the mounting layer 36c.

Mounting layer 36c is also preferably made of at least one of Au, Al, and Ni, and is particularly preferably made of Au.

Next, a method for manufacturing the pressure sensor 10 shown in FIG. 1 will be described. In the pressure sensor 10, first, the stem 20 is prepared. The material of the stem 20 is, for example, SUS316. Next, as shown in FIG. 2, a strain-resistance film 30 with electrodes is formed on the outer surface 22b of the membrane 22 of the stem 20.

To form the electrode-attached strain-resistance film 30, first, a base insulating layer 52 is formed to a predetermined thickness on the outer surface 22b of the membrane 22 by a thin-film method such as CVD or sputtering so as to cover the membrane 22 (see FIG. 2). Examples of the base insulating layer 52 include a silicon oxide film or a silicon nitride film.

Next, as shown in FIG. 2, a strain resistive film 32 is formed on the surface of the base insulating layer 52. The strain resistive film 32 is formed by a thin film method such as vapor deposition or sputtering. The shape of the strain resistive film 32, which includes the first to fourth resistors R1 to R4 and the electrical wiring 34, is formed by patterning using photolithography or the like.

Next, as shown in FIG. 2, a laminated electrode 36 is formed on the strain resistive film 32. When forming the laminated electrode 36, conductive thin films are formed on the strain resistive film 32 in the following order: contact layer 36a, diffusion prevention layer 36b, and mounting layer 36c. The contact layer 36a, diffusion prevention layer 36b, and mounting layer 36c of the laminated electrode 36 are formed by a thin film method such as sputtering or vapor deposition.

The contact layer 36a, the diffusion prevention layer 36b, and the mounting layer 36c included in the laminated electrode 36 are formed only at predetermined positions on the strain resistive film 32, as shown in FIG. 3. The patterning of each layer included in the laminated electrode 36 can be performed by photolithography, as with the strain resistive film 32, but other methods may also be used.

In this way, the strain-resistance film 32 and the laminated electrode 36 are formed as thin films on the base insulating layer 52 formed on the outer surface 22b of the membrane 22, thereby forming the strain-resistance film 30 with electrodes shown in FIG. 3. In manufacturing the strain-resistance film 30 with electrodes, a heat treatment such as annealing (e.g., 350 to 800°C) may be performed after the strain-resistance film 32 and the laminated electrode 36 are formed.

By performing heat treatment at an appropriate temperature after the formation of the strain resistive film 32 and the laminated electrode 36, it is possible to improve the characteristics of the strain resistive film 32, such as the gauge factor. In addition, by performing heat treatment after the formation of the laminated electrode 36, it is possible to improve the bonding between the strain resistive film 32 and the laminated electrode 36, and between each layer inside the laminated electrode 36.

As shown in FIG. 7, the electrical wiring 134 may be formed on the strain resistive film 32 at the same time as the laminated electrode 36 or a part of the layer included in the laminated electrode 36 is formed. In this case, the electrical wiring 134 has the same material and properties as the laminated electrode 36 or a part of it. By making the electrical wiring 134 from the same material as the laminated electrode 36 or a part of it, the problem of the resistance value of the electrical wiring 134 being affected by strain can be prevented compared to when a part of the strain resistive film 32 constitutes the electrical wiring 34 (see FIG. 3). In addition, the electrical wiring 134 of the same material and structure as the laminated electrode 36 has good bonding to the strain resistive film 32, and can prevent peeling defects. However, the electrical wiring 134 may be formed on the base insulating layer 52.

Finally, as shown in FIG. 1, the circuit board 16 is fixed to the stem 20 on which the electrode-equipped strain-resistance film 30 is formed, and intermediate wiring 72 is formed to connect the circuit board 16 and the electrode-equipped strain-resistance film 30, thereby obtaining the pressure sensor 10. The intermediate wiring 72 is formed by wire bonding using thin Au wires, etc.

The laminated electrode 36 shown in FIG. 3 has at least three layers: a contact layer 36a, a diffusion prevention layer 36b, and a mounting layer 36c, and the diffusion prevention layer 36b contains a transition element belonging to the fifth or sixth period. The laminated electrode 36 having such a diffusion prevention layer 36b prevents elements contained in the contact layer 36a and the strain resistance film 32 from interdiffusing into the mounting layer 36c, and the reaction of the interdiffused elements at the interface of the mounting layer 36c is suppressed, thereby improving high temperature resistance. In addition, the laminated electrode 36 has good adhesion to the intermediate wiring 72 even after exposure to a high temperature environment due to the diffusion prevention effect of the diffusion prevention layer 36b.

The laminated electrode 36 and the electrode-attached strain-resistance film 30 will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

<Sample 1>
A contact layer 36a made of Ti with a thickness of 5 nm, a diffusion prevention layer 36b made of Pt with a thickness of 20 nm, and a mounting layer 36c made of Au with a thickness of 200 nm were formed in this order on a strain-resistant film 32 containing 70 to 95 at % Cr and 5 to 30 at % Al, as shown in Fig. 2, to form a laminated electrode 36, thereby producing sample 1. The strain-resistant film 32 and each layer of the laminated electrode 36 were formed by sputtering (see Table 1).

<Samples 2 to 4>
Each sample is similar to sample 1, except that sample 2 has a contact layer 36a with a thickness of 20 nm, sample 3 has a diffusion prevention layer 36b with a thickness of 5 nm, and sample 4 has a mounting layer 36c with a thickness of 100 nm (see Table 1).

<Samples 5 to 7>
Sample 5 has contact layer 36a made of Cr, sample 6 has contact layer 36a made of Ni, and sample 7 has diffusion prevention layer 36b made of W. Except for this, each sample is similar to sample 1 (see Table 1).

<Sample 8>
Sample 8 is similar to sample 1, except that the layer corresponding to the diffusion prevention layer 36b is made of Ni.

<Samples 9 to 15>
Samples 9 to 15 are different from Sample 1 in that the laminated electrode has a two-layer structure of a mounting layer 36c and a contact layer 36a, and does not have a diffusion prevention layer 36b. Sample 9 has a contact layer 36a made of Ti with a thickness of 5 nm, and Sample 10 has a contact layer 36a made of Ti with a thickness of 20 nm. Sample 11 has a contact layer 36a made of Cr with a thickness of 5 nm, and Sample 12 has a contact layer 36a made of Cr with a thickness of 20 nm. Sample 13 has a contact layer 36a made of Ni with a thickness of 5 nm, and Sample 14 has a contact layer 36a made of Ni with a thickness of 20 nm. Sample 15 has a contact layer 36a made of Mo with a thickness of 20 nm. All of Samples 9 to 15 have a mounting layer 36c made of Au with a thickness of 200 nm.

<Evaluation of Samples 1 to 15>
100 samples of each specimen were prepared, and the success rate of wire bonding with Au fine wires was evaluated. In the evaluation, the specimens were divided into four groups of 25 samples each, and the heat treatment conditions performed after the formation of the laminated electrode 36 and before wire bonding were different for each group. The first group was not heat-treated, the second group was heat-treated at 350 degrees for 2 hours, the third group was heat-treated at 400 degrees for 2 hours, and the fourth group was heat-treated at 500 degrees for 2 hours. The conditions of each specimen and the evaluation results are shown in Table 1.

In Table 1, "◎", "〇", "△", and "×" represent the wire bonding attachment success rate for each sample, with "◎" indicating a success rate that was in the top quarter of the overall rate, "〇" indicating a success rate that was less than the top quarter and more than half the overall rate. "△" indicates a success rate that was less than half the overall rate but more than three-quarters the above rate, and "×" indicating a success rate that was less than the top three-quarters the overall rate.

Samples 1 to 7 in Table 1 showed good wire bonding attachment success rates even after high-temperature heat treatment. Note that sample 7, which has a diffusion prevention layer 36b made of W, experienced wire bonding adhesion failure due to film peeling when not heat-treated (AsDepo), but other samples after high-temperature heat treatment showed good attachment success rates. These results show that the diffusion prevention layer 36b made of W, a transition element belonging to the fifth or sixth period but not a platinum group element, can prevent film peeling with appropriate heat treatment and shows good wire bonding attachment success rates.

Samples 1 to 6 in Table 1 show good wire bonding attachment success rates under all heat treatment conditions, and it can be seen that Pt is particularly preferable as the element that constitutes the diffusion prevention layer 36b. Furthermore, by comparing sample 1 with samples 5 and 6, it can be seen that sample 1, whose contact layer 36a is made of Ti, shows a better wire bonding attachment success rate than samples 5 and 6, whose contact layer 36a is made of Cr or Ni.

Sample 8 in Table 1 shows a good adhesion success rate when no heat treatment (AsDepo) was performed, but it can be seen that the adhesion success rate worsens as the heat treatment temperature increases. In particular, in samples after heat treatment at 400°C and 500°C, many defects occurred in which the wire bonding did not adhere to the surface of the laminated electrode 36. In sample 8, in which the layer corresponding to the diffusion prevention layer 36b is made of Ni, which is not a transition element belonging to the 5th or 6th period, it is believed that a sufficient diffusion prevention effect was not obtained in samples after heat treatment at 400°C and 500°C.

Samples 9 to 15 in Table 1 show a good adhesion success rate when no heat treatment (AsDepo) was performed, but it can be seen that the adhesion success rate worsens as the heat treatment temperature increases. In these samples without the diffusion prevention layer 36b, it is believed that elements of the strain resistive film 32 and contact layer 36a precipitate on the surface of the mounting layer 36c due to the high-temperature heat treatment, causing many defects in which the thin wires of the wire bonding do not adhere to the surface of the laminated electrode.

<Differences in results between Sample 1 and Sample 5>
FIG. 4(a) shows a sample with a three-layer structure prepared by forming a thin film of Ti (5 nm thick) and a thin film of Au (200 nm thick) on a thin film (300 nm thick) containing 70 to 95 at % Cr and 5 to 30 at % Al, and then subjecting the sample to a heat treatment at 350° C. for 2 hours. After that, the elements in the vicinity of the top surface of the sample were analyzed by XPS (ESCA).

Figure 4(b) shows a sample with a three-layer structure prepared by forming a thin film of Cr (5 nm thick) and a thin film of Au (200 nm thick) on a thin film (300 nm thick) containing 70-95 at% Cr and 5-30 at% Al, and after heat treatment at 350°C for 2 hours, the elements near the top surface of the sample were analyzed by XPS (ESCA). Note that the horizontal axis in Figures 4(a) and 4(b) is the sputtering time (min), and the vertical axis is the intensity.

Here, in FIG. 4(a), it can be seen that there is almost no Ti in the lower layer on the sample surface and there is a lot of Au, whereas in FIG. 4(b), there is a lot of Cr and oxygen on the sample surface and little Au. Comparing FIG. 4(a) and FIG. 4(b), it can be seen that Ti is less likely to diffuse into Au than Cr, and the problem of segregation on the surface of the Au layer after heat treatment is less likely to occur. This is also thought to correspond to the fact that, in the results shown in Table 1, sample 1, whose contact layer 36a is made of Ti, showed a better wire bonding attachment success rate than sample 5, whose contact layer 36a is made of Cr.

<Other reasons why Ti is preferable for the contact layer 36a>
Fig. 5 shows a sample with a three-layer structure prepared by forming a thin film of Ti (5 nm) and a thin film of Au (200 nm) on a thin film of Cr, and then performing a heat treatment at 350°C for 2 hours, after which the cross section of the sample was subjected to elemental analysis by SEM-EDS. Fig. 5(a) shows the location of Ti in white, and Fig. 5(b) shows the location of Cr in white.

From Figure 5(a), it can be seen that Ti, which is abundant in the vertical center of the sample, spreads slightly toward the upper Au layer to form a mixed region, whereas it hardly spreads into the lower Cr layer, forming a sharp boundary. Also, from a comparison of Figures 5(a) and 5(b), it can be seen that there is almost no Cr in the vertical center of the sample where Ti is abundant.

From Figure 5, it can be seen that Ti and Cr are unlikely to diffuse into each other, and it is believed that using Ti as the material for the contact layer 36a can prevent the composition of the strain resistive film 32 from changing in a high-temperature environment.

<Preferable Cr and Al content of strain-sensitive resistive film>
6 shows the relationship between the difference in composition of the strain resistive film 32 and the change in the gauge factor of the strain resistive film 32 for the electrode-attached strain resistive film 30 shown in FIG. 2 and FIG. 3. The electrode-attached strain resistive film 30 used for the evaluation was prepared by forming the strain resistive film 32 containing Cr and Al by sputtering on a Si wafer with a thermal oxide film, and then forming the contact layer 36a (Ti, 5 nm), the diffusion prevention layer 36b (Pt, 20 nm), and the mounting layer 36c (Au, 200 nm) by electron beam deposition to form the laminated electrode 36. As described below, six samples of the electrode-attached strain resistive film 30 with different compositions of the strain resistive film 32 were prepared, and the gauge factor of each sample was measured by a cantilever bending test. The composition of the strain resistive film 32 was adjusted by changing the Cr/Al ratio of the sputtering target.
<Sample 1> Al: 5 at %, Cr: 95 at %
<Sample 2> Al: 15 at%, Cr: 85 at%
<Sample 3> Al: 30 at%, Cr: 70 at%
<Sample 4> Al: 45 at%, Cr: 55 at%
<Sample 5> Al: 60 at%, Cr: 40 at%
<Sample 6> Al: 80 at%, Cr: 20 at%

The horizontal axis of FIG. 6 is the Al composition (at%), and the vertical axis is the gauge factor (K-factor). As shown in FIG. 6, it can be seen that the electrode-attached strain-resistant film 30 has a high gauge factor in the region where the Al content is lower than the Cr content. Therefore, from the viewpoint of increasing the gauge factor, it can be seen that the strain-resistant film 32 preferably contains 50 to 99 at% Cr and 1 to 50 at% Al, and more preferably contains 70 to 95 at% Cr and 5 to 30 at% Al.

The laminated electrode 36, the strain-resistance film 30 with electrodes, and the pressure sensor 10 according to the present invention have been described above with reference to embodiments and examples, but the present invention is not limited to these embodiments and examples. It goes without saying that the present invention includes many other embodiments and modifications in addition to the above-mentioned embodiments and examples. For example, the pressure sensor 10 is not limited to only those having a stem 20 as shown in FIG. 1, but may be one in which the strain-resistance film 30 with electrodes is formed on a flat substrate. Examples of the material of the substrate include Si and alumina (Al ₂ O ₃ ).

REFERENCE SIGNS LIST 10...Pressure sensor 12...Connecting member 12a...Thread groove 12b...Flow path 14...Retaining member 16...Circuit board 20...Stem 21...Flange portion 22...Membrane 22a...Inner surface 22b...Outer surface 30...Strain resistance film with electrode 32...Strain resistance film R1...First resistor R2...Second resistor R3...Third resistor R4...Fourth resistor 34...Electrical wiring 36...Laminated electrode for strain resistance film (laminate electrode)
36a: contact layer; 36b: diffusion prevention layer; 36c: mounting layer; 52: base insulating layer; 72: intermediate wiring

Claims (6)

A laminated electrode provided on a strain-resistance film,
The strain-resistance film includes Cr and Al,
the laminated electrode has a contact layer overlapping the strain resistive film, a diffusion prevention layer overlapping the contact layer, and a mounting layer overlapping the diffusion prevention layer,
the contact layer includes at least one of Ti, Ni, and Mo;
The diffusion prevention layer is a laminated electrode made of a platinum group element . The laminated electrode according to claim 1, characterized in that the strain-resistance film contains 50 to 99 at% Cr and 1 to 50 at% Al. 3. The laminated electrode according to claim 1, wherein the contact layer contains Ti. 4. The laminated electrode according to claim 1, wherein the mounting layer contains Au. A laminated electrode according to any one of claims 1 to 4 ,
A strain-resistance film with an electrode comprising the strain-resistance film. The laminated electrode according to any one of claims 1 to 4 ,
The strain-resistance film;
A pressure sensor having a membrane on which the strain resistive film is provided.