Patent Application
20240255371
The present disclosure relates to a multilayer electrode provided on a strain resistance film, a strain resistance film with electrode, and a pressure sensor including the same.
As a strain resistance film used for a device such as a pressure sensor, a film containing Cr and Al has been proposed. Such a strain resistance film is reported to have excellent properties particularly at a high temperature.
In addition, an electrode layer for wiring with an external circuit is provided on such a strain resistance film. Such an electrode layer preferably has excellent bondability to both a strain resistance film and a wiring material, and for example, a multilayer electrode in which layers are layered has been proposed (see JP 2018-91848 A and the like).
However, an electrode layer for a strain resistance film according to the related-art has a disadvantage that adhesive force to wiring is reduced when exposed to a high temperature environment even when bondability at room temperature is excellent.
In addition, in a case of using a film containing Cr and Al as the strain resistance film, it is desirable to provide a multilayer electrode for a strain resistance film or the like that exhibits excellent adhesive force to wiring even after being exposed to a high temperature environment.
A multilayer electrode according to the present disclosure includes a contact layer capable of being superposed on a strain resistance film, a diffusion prevention layer superposed on the contact layer, and a mounting layer superposed on the diffusion prevention layer,
Hereinafter, the present disclosure will be described based on embodiments illustrated in the drawings.
In the pressure sensor 10, a fluid introduced into the flow path 12b is guided from the hollow portion of the stem 20 to an inner surface 22a of the membrane 22, and a fluid pressure acts on the membrane 22. The stem 20 is formed of, for example, 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 an axial core of the stem 20. The flange portion 21 is sandwiched between the connecting member 12 and a pressing member 14, and 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 to a pressure chamber or the like in which a fluid to be measured is sealed via the screw groove 12a. 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 communicate airtightly with the pressure chamber in which the fluid to be measured exists.
A circuit board 16 is attached to an upper surface of the pressing member 14. The circuit board 16 has a ring-shaped surrounding the periphery of the stem 20, and the shape of the circuit board 16 is not limited thereto. The circuit board 16 incorporates, for example, a circuit to which a detection signal from a strain resistance film with electrode 30 is transmitted.
As illustrated in
As illustrated in
The base insulating layer 52 is formed so as to cover substantially the entire outer surface 22b of the membrane 22, and is formed of, for example, silicon oxide, silicon nitride, silicon oxynitride, or the like. A 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 a vapor deposition method such as CVD.
Note that in a case where the outer surface 22b of the membrane 22 has insulating properties, 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, in a case where the membrane 22 is formed of an insulating material such as alumina, the strain resistance film 32 may be directly provided on the membrane 22.
As illustrated in
As illustrated in
The pressure sensor 10 illustrated in
The strain resistance film 32 including the first to fourth resistors R1 to R4 can be produced, for example, by patterning a conductive film formed of a predetermined material. The strain resistance film 32 contains Cr and Al, preferably contains 50 to 99 at % of Cr and 1 to 50 at % of Al, and more preferably contains 70 to 90 at % of Cr and 5 to 30 at % of Al. The strain resistance film 32 contains Cr and Al, such that a temperature coefficient of resistance (TCR) or a temperature coefficient of sensitivity (TCS) in a high temperature environment is stabilized, and highly accurate pressure detection becomes possible. In addition, when the amounts of Cr and Al are set to be within predetermined ranges, it is possible to achieve both a high gauge factor and excellent temperature stability at higher levels.
The strain resistance film 32 may contain elements other than Cr and Al, and for example, the strain resistance film 32 may contain O or N. O or N contained in the strain resistance film 32 may be an element remaining without being removed from a reaction chamber when the strain resistance film 32 is formed, and may be incorporated into the strain resistance film 32. In addition, O or N contained in the strain resistance film 32 may be intentionally introduced into the strain resistance film 32 by being used as an atmospheric gas during film formation or annealing.
In addition, the strain resistance film 32 may contain a metal element other than Cr and Al. The strain resistance film 32 contains a small amount of a metal other than Cr and Al or a nonmetallic element, and is subjected to a heat treatment such as annealing, such that the gauge factor and temperature properties may be improved. Examples of the metal other than Cr and Al or the nonmetallic element 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 a rare earth element.
The strain resistance 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 meander shape. A thickness of the strain resistance film 32 is not particularly limited, and is preferably 10 μm or less, and more preferably 0.1 to 1 μm. Note that, as illustrated in
As illustrated in
As illustrated in
Although not illustrated in
As illustrated in
As illustrated in
The contact layer 36a can be formed by a thin film method such as sputtering or vapor deposition. A thickness of the contact layer 36a is not particularly limited, and 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. Since these elements easily form an alloy with other metals, the contact layer 36a containing such elements can secure adhesion strength between the strain resistance film 32 and the diffusion prevention layer 36b, and can prevent peeling failures between the film and the layer.
In addition, it is particularly preferable that the contact layer 36a contains Ti. Ti is less likely to diffuse into the mounting layer 36c containing Au or the like, and tends to be less likely to be deposited on an upper surface of the mounting layer 36c. Therefore, the multilayer electrode 36 including the contact layer 36a containing Ti exhibits suitable adhesion to the intermediate wiring 72 even after the multilayer electrode 36 is exposed to a high temperature environment. In addition, it is particularly preferable that the contact layer 36a contains Ti.
Further, since Ti hardly diffuses into Cr, Ti constituting the contact layer 36a has a property of hardly diffusing into the strain resistance film 32 containing Cr and Al even in a high temperature environment. Therefore, the strain resistance film with electrode 30 including the contact layer 36a containing Ti can prevent diffusion of an element in the multilayer electrode 36 into the strain resistance film 32 even when used in a high temperature environment, and can prevent performance deterioration of the strain resistance film 32 due to a change in composition.
In addition, the contact layer 36a preferably contains elements among Cr, Ti, Ni, and Mo. In addition, it is preferable that the contact layer 36a is formed of at least one of Cr, Ti, Ni, and Mo. Further, it is particularly preferable that the contact layer 36a is formed of Ti. In addition, it is preferable that the contact layer 36a is formed of elements among Cr, Ti, Ni, and Mo.
Note that, in a case where the contact layer 36a, the diffusion prevention layer 36b, and the mounting layer 36c are formed of one or more designated elements, it is not excluded that elements other than the designated elements are inevitably or intentionally contained in these layers. In this case, a content ratio of the other elements is, for example, less than 10 at %, preferably less than 3 at %, and more preferably less than 1 at %.
As illustrated in
The diffusion prevention layer 36b can be formed by a thin film method such as sputtering or vapor deposition. A thickness of the diffusion prevention layer 36b is not particularly limited, and is, for example, 1 to 500 nm, and preferably 5 to 50 nm. When the thickness of the diffusion prevention layer 36b is too thin, it becomes difficult to form a continuous film, and a diffusion prevention function may be weakened, and when the thickness is too thick, a problem of film peeling may occur, or a problem of a decrease in productivity (throughput) due to an increase in film deposition time may occur.
The diffusion prevention layer 36b preferably contains a transition element belonging to the fifth or sixth period from the viewpoint of preventing diffusion of an element contained in the strain resistance film 32, the contact layer 36a, or the like into the upper layer. 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.
In addition, the diffusion prevention layer 36b preferably further contains a platinum group element. Specifically, the diffusion prevention layer 36b preferably contains one or more elements selected from Ru, Rh, Pd, Os, Ir, and Pt. Since the platinum group element has low reactivity and is chemically stable, the diffusion prevention layer 36b containing the platinum group element exhibits a particularly suitable diffusion prevention effect even in a high temperature environment. Note that, among platinum group elements, particularly Pt has a track record of being used in other electrode fields, and has technical accumulation from other platinum group elements.
The diffusion prevention layer 36b is also preferably formed of a transition element belonging to the fifth or sixth period. In addition, the diffusion prevention layer 36b is also preferably formed of a platinum group element.
As illustrated in
The mounting layer 36c can be formed by a thin film method such as sputtering or vapor deposition. A thickness of the mounting layer 36c is not particularly limited, and is, for example, 10 to 400 nm, and preferably 100 to 300 nm. When the thickness of the mounting layer 36c is too thin, it becomes difficult to form a continuous film, and the adhesion to the intermediate wiring 72 may be deteriorated. When the thickness of the mounting layer 36c is too thick, a problem of film peeling may occur, or a problem of a decrease in productivity (throughput) due to an increase in film deposition time may occur.
The mounting layer 36c preferably contains at least one of Au, Al, and Ni from the viewpoint of heat resistance and bondability with the intermediate wiring 72. In addition, from the viewpoint of enhancing the heat resistance and further enhancing the responsiveness to a high temperature environment, it is more preferable that the mounting layer 36c contains Au having low resistance and a high melting point even in a high temperature environment. In addition, in a case where a thin wire of Au is used as the material of the intermediate wiring 72, the mounting layer 36c contains Au, such that the intermediate wiring 72 and the mounting layer 36c are both formed of Au. As a result, the adhesion of the bonding portion between the intermediate wiring 72 and the mounting layer 36c is improved.
In addition, the mounting layer 36c is preferably formed of at least one of Au, Al, and Ni, and particularly preferably formed of Au.
Next, a method for manufacturing the pressure sensor 10 illustrated in
In order to form the strain resistance film with electrode 30, first, the base insulating layer 52 is formed with a predetermined thickness on the outer surface 22b of the membrane 22 so as to cover the membrane 22 by a thin film method such as CVD or sputtering (see
Next, as illustrated in
Next, as illustrated in
As illustrated in
As described above, the strain resistance film 32 and the multilayer electrode 36 are formed in thin films on the base insulating layer 52 formed on the outer surface 22b of the membrane 22, such that the strain resistance film with electrode 30 illustrated in
A heat treatment is performed at an appropriate temperature after formation of the strain resistance film 32 and the multilayer electrode 36, such that properties such as a gauge factor of the strain resistance film 32 can be enhanced. In addition, a heat treatment is performed after the formation of the multilayer electrode 36, such that bondability between the strain resistance film 32 and each layer inside the multilayer electrode 36 and the multilayer electrode 36 can be enhanced.
Note that, like a strain resistance film with electrode 130 illustrated in
Finally, as illustrated in
The multilayer electrode 36 illustrated in
Hereinafter, the multilayer electrode 36 and the strain resistance film with electrode 30 described above will be described in more detail with reference to examples, but the present disclosure is not limited to only examples.
On a strain resistance film 32 containing 70 to 95 at % of Cr and 5 to 30 at % of Al, a contact layer 36a formed of Ti, a diffusion prevention layer 36b formed of Pt, and a mounting layer 36c formed of Au were sequentially formed to have thicknesses of 5 nm, 20 nm, and 200 nm, respectively, as illustrated in
Each of samples was prepared in the same manner as that of the sample 1, except that a thickness of a contact layer 36a was 20 nm in the sample 2, a thickness of a diffusion prevention layer 36b was 5 nm in the sample 3, and a thickness of a mounting layer 36c was 100 nm in the sample 4 (see Table 1).
Each of samples was prepared in the same manner as that of the sample 1, except that a contact layer 36a was formed of Cr in the sample 5, a contact layer 36a was formed of Ni in the sample 6, and a diffusion prevention layer 36b was formed of W in the sample 7 (see Table 1).
A sample 8 was prepared in the same manner as that of the sample 1, except that a layer corresponding to the diffusion prevention layer 36b was formed of Ni.
Samples 9 to 15 were different from the sample 1 in that the multilayer electrode had a two-layer structure of a mounting layer 36c and a contact layer 36a, and did not include a diffusion prevention layer 36b. The sample 9 includes a contact layer 36a formed of Ti and having a thickness of 5 nm, and the sample 10 includes a contact layer 36a formed of Ti and having a thickness of 20 nm. The sample 11 includes a contact layer 36a formed of Cr and having a thickness of 5 nm, and the sample 12 includes a contact layer 36a formed of Cr and having a thickness of 20 nm. The sample 13 includes a contact layer 36a formed of Ni and having a thickness of 5 nm, and the sample 14 includes a contact layer 36a formed of Ni and having a thickness of 20 nm. The sample 15 has a contact layer 36a formed of Mo and having a thickness of 20 nm. Each of the samples 9 to 15 has a mounting layer 36c formed of Au and having a thickness of 200 nm.
100 samples of each sample were prepared, and an adhesion non-defect rate of wire bonding with an Au thin wire was evaluated. In the evaluation, 25 samples were divided into 4 groups, and the heat treatment conditions performed after the formation of the multilayer electrode 36 and before the wire bonding were set to be different for each group. The first group was not subjected to the heat treatment, the second group was subjected to the heat treatment at 350 degrees for 2 hours, the third group was subjected to the heat treatment at 400 degrees for 2 hours, and the fourth group was subjected to the heat treatment of 500 degrees for 2 hours. Conditions and evaluation results of each sample are shown in Table 1.
“⊙” (double circle), “∘” (circle), “Δ” (trigona), and “x” (cross) in Table 1 represent the adhesion non-defect rates of the wire bonding of each sample, “⊙” represents the non-defect rate of the top ¼ of the total, and “∘” represents the non-defect rate of less than the top ¼ and ½ or more of the total. In addition, “Δ” indicates that the non-defect rate of less than ½ and ¾ or more of the total, and “x” indicates that the non-defect rate of less than ¾ of the total.
The samples 1 to 7 in Table 1 showed excellent adhesion non-defect rates of wire bonding even in the samples after a heat treatment at a high temperature. Note that, in the sample 7 including the diffusion prevention layer 36b formed of W, wire bonding adhesion failures due to film peeling occurred under the condition of not performing a heat treatment (AsDepo), but other samples after a high temperature heat treatment showed an excellent adhesion non-defect rate. From this result, it is found that the diffusion prevention layer 36b formed of W which is a transition element belonging to the fifth or sixth period but is not a platinum group element can prevent film peeling by an appropriate heat treatment, and exhibits an excellent adhesion non-defect rate of wire bonding.
The samples 1 to 6 in Table 1 show excellent adhesion non-defect rates of wire bonding under any heat treatment condition, and it can be understood that Pt is particularly preferable as an element constituting the diffusion prevention layer 36b. In addition, comparison between the sample 1 and the samples 5 and 6 shows that the sample 1 in which the contact layer 36a is formed of Ti exhibits a better adhesion non-defect rate of wire bonding than the samples 5 and 6 in which the contact layer 36a is formed of Cr or Ni.
The sample 8 in Table 1 shows an excellent adhesion non-defect rate under the condition where the heat treatment is not performed (AsDepo), but it is found that the adhesion non-defect rate deteriorates as the heat treatment condition becomes higher. In particular, in the samples subjected to the heat treatment at 400° C. and 500° C., many defects in which the wire bonding did not adhere to the surface of the multilayer electrode 36 occurred. In the sample 8 in which the layer corresponding to the diffusion prevention layer 36b is formed of Ni which is not a transition element belonging to the fifth or sixth period, it is considered that a sufficient diffusion prevention effect was not obtained in the sample after a heat treatment at 400° C. and 500° C. was performed.
The samples 9 to 15 in Table 1 show an excellent adhesion non-defect rate under the condition where the heat treatment is not performed (AsDepo), but it is found that the adhesion non-defect rate deteriorates as the heat treatment condition becomes higher. In these samples without the diffusion prevention layer 36b, it is considered that elements of the strain resistance film 32 or the contact layer 36a were deposited on the surface of the mounting layer 36c by a heat treatment at a high temperature, and defects frequently occurred in which thin wires of wire bonding did not adhere to the surface of the multilayer electrode.
In addition,
Here, it can be understood that in
<Other Reasons why Ti is Preferred as Contact Layer 36a>
In
From
It can be understood from
In
Although the multilayer electrode 36, the strain resistance film with electrode 30, and the pressure sensor 10 according to the present disclosure have been described above with reference to the embodiments and examples, the present disclosure is not limited only to these embodiments and examples. It goes without saying that the present disclosure includes many other embodiments and modifications in addition to the embodiments and examples described above. For example, the pressure sensor 10 is not limited to the pressure sensor including the stem 20 as illustrated in
As understood from the description described above, the present specification discloses the following.
A multilayer electrode according to the present disclosure includes a contact layer capable of being superposed on a strain resistance film, a diffusion prevention layer superposed on the contact layer, and a mounting layer superposed on the diffusion prevention layer,
The multilayer electrode according to the present disclosure includes at least three layers of a contact layer, a diffusion prevention layer, and a mounting layer. The contact layer can be superposed on the strain resistance film. The diffusion prevention layer containing a transition element belonging to the fifth or sixth period prevents the elements contained in the contact layer and the superposed strain resistance film from interdiffusing into the mounting layer. In the multilayer electrode including such a diffusion prevention layer, the reaction of the interdiffused elements at the interface of the mounting layer is suppressed, such that high temperature resistance is improved, and excellent adhesive force to the wiring is exhibited even after the multilayer electrode is exposed to a high temperature environment.
For example, the diffusion prevention layer may contain a platinum group element.
When the diffusion prevention layer contains a chemically stable platinum group element, interdiffusion between the films and between the layers in the superposed strain resistance film and the multilayer electrode can be effectively prevented. In addition, the reaction of the interdiffused elements at the interface of the mounting layer can also be effectively suppressed.
In addition, the contact layer may contain, for example, at least one of Cr, Ti, Ni, and Mo.
In addition, the contact layer may contain, for example, Ti.
Since the elements contained in such a contact layer easily form an alloy with another metal element, it is effective for securing adhesion strength between films and between layers to prevent film peeling failures. In addition, in particular, Ti has a property of being relatively difficult to diffuse into the strain resistance film in a case where the superposed strain resistance film contains Cr and Al, and interdiffusion into the mounting layer is effectively prevented by the diffusion prevention layer containing the transition element belonging to the fifth or sixth period. Further, Ti is less likely to diffuse into the surface of the mounting layer containing Au or the like, and is less likely to be deposited on the upper surface of the mounting layer. Therefore, the multilayer electrode including such a contact layer can effectively prevent interdiffusion between the respective films and between the respective layers in the superposed strain resistance film and the multilayer electrode. In addition, the multilayer electrode including such a contact layer prevents a change in properties of the superposed strain resistance film in a high temperature environment, improves high temperature resistance, and exhibits significantly excellent adhesive force to wiring even after being exposed to the high temperature environment.
In addition, the mounting layer may contain, for example, Au.
When the mounting layer contains Au, the adhesion of the mounting layer to the Au wiring having excellent heat resistance is particularly excellent. Therefore, the multilayer electrode including such a mounting layer has improved high temperature resistance and exhibits excellent adhesive force to wiring.
In addition, the strain resistance film with electrode according to the present disclosure includes a strain resistance film containing Cr and Al, a multilayer electrode according to any one of the above, which is provided on the strain resistance film by superposing the contact layer on the strain resistance film, and the strain resistance film.
In addition, the pressure sensor according to the present disclosure includes a strain resistance film containing Cr and Al, a multilayer electrode according to any one of the above, which is provided on the strain resistance film by superposing the contact layer on the strain resistance film, the strain resistance film, and a membrane provided with the strain resistance film.
That is, the multilayer electrode is provided on the strain resistance film and is used as a strain resistance film with electrode. In addition, such a multilayer electrode and a strain resistance film are provided on a membrane or the like to constitute a pressure sensor exhibiting, for example, excellent resistance even in a high temperature environment.
In addition, for example, the strain resistance film may contain 50 to 99 at % of Cr and 1 to 50 at % of Al.
Such a strain resistance film has a stable high gauge factor in a wide temperature range, and the diffusion prevention layer of the multilayer electrode effectively prevents interdiffusion of Cr having a high content ratio in the strain resistance film into the mounting layer, thereby realizing a multilayer electrode that exhibits excellent adhesive force.
The present application is a continuation application of PCT application No. PCT/JP2021/037202 filed on Oct. 7, 2021. The disclosures of these applications are hereby incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2021/037202 | Oct 2021 | WO |
| Child | 18623315 | US |
