Strain-resistive film and pressure sensor

Abstract

To provide a strain resistance film capable of reducing changes in properties associated with changes in composition, and to provide a pressure sensor including the same.SOLUTION: A strain resistance film is represented by a general formula Cr100-x-yAlxNy, where x and y represent composition ranges that satisfy 25<x≤50 and 0.1<y≤20, respectively.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a strain-resistance film whose resistance value changes in response to strain, and a pressure sensor using the same. [Background technology]

[0002] It has been reported that materials containing Cr, Al, and N have a high gauge factor in the relatively high temperature range of -50°C to 300°C, and are promising as strain-resistance films. In particular, Patent Document 1 reports that such strain-resistance films can obtain favorable characteristics not only in terms of the gauge factor but also in terms of the temperature coefficient of sensitivity (TCS) by containing Al in a composition range of 4 at% to 25 at%.

[0003] On the other hand, strain-resistive films containing Cr, Al, and N can be fabricated by thin-film methods, but it is not easy to reduce the compositional variation in such strain-resistive films. In other words, if an appropriate composition range that allows a certain degree of compositional variation can be found, a strain-resistive film with good productivity can be realized. At the same time, if the strain-resistive film has a high linearity in the relationship between temperature and resistance value, the temperature characteristics of the strain-resistive film can be calibrated in a low temperature range, which improves productivity by shortening the fabrication time. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-91848 A Summary of the Invention [Problem to be solved by the invention]

[0005] In this situation, the inventors of the present invention discovered a strain-resistance film capable of reducing the change in characteristics that accompanies a change in composition in a material containing Cr, Al, and N, and completed the present invention.

[0006] The present invention has been made in view of such a situation, and an object thereof is to provide a strain resistance film capable of reducing characteristic changes accompanying compositional changes and a pressure sensor using the same.

Means for Solving the Problems

[0007] The strain resistance film according to the present invention is General formula Cr 100-x-y Al x N y represented by, and the respective composition ranges of x and y are 25 < x ≤ 50 and 0.1 < y ≤ 20.

[0008] The strain resistance film according to the present invention is a strain resistance film represented by the general formula Cr 100-x-y Al x N y By setting 25 < x ≤ 50 and 0.1 < y ≤ 20 in the strain resistance film represented by, it has been found that characteristic changes accompanying compositional changes can be reduced, and at the same time, the relationship between the resistance value and temperature has very good linearity. In particular, by increasing the content of Al compared to conventional strain resistance films, characteristic changes accompanying compositional changes can be reduced compared to conventional strain resistance films. Further, such a strain resistance film can allow compositional variations during manufacturing within an appropriate range and has good productivity. Furthermore, due to the latter's good linearity, rapid calibration of the temperature resistance characteristics of the strain resistance film is possible in the low temperature region, so that productivity can be improved by shortening the calibration time.

[0009] Also, for example, the strain resistance film according to the present invention may have an absolute value of the temperature coefficient of resistance (TCR) of 2000 ppm / °C or less in a temperature range of -50°C or higher and 450°C or lower.

[0010] Since such a strain resistance film has a resistance value change per unit temperature change within a predetermined range, for example, when used as a pressure sensor, the temperature correction error can be reduced.

[0011] Also, for example, the strain resistance film according to the present invention may have an absolute value of the temperature coefficient of sensitivity (TCS) of 2000 ppm / °C or less in a temperature range of -50°C or higher and 450°C or lower.

[0012] Such a strain-sensitive resistive film has a sensitivity change per unit temperature change within a predetermined range, and therefore can reduce temperature correction errors when used as a pressure sensor, for example.

[0013] Also, for example, the strain-resistance film according to the present invention may contain O in an amount of 10 at % or less based on the total amount of Cr, Al, N, and O.

[0014] By controlling the O content to 10 at % or less, the gauge factor can be increased, for example, in a temperature range of -50°C or more and 450°C or less.

[0015] A pressure sensor according to the present invention includes any one of the strain resistive films described above, and an electrode portion electrically connected to the strain resistive film.

[0016] In addition, for example, when temperature calibration of resistance is performed in the low temperature range, the relationship between the temperature calibration line of resistance and the resistance temperature line of the strain resistance film is determined by the coefficient of determination R 2 may be 0.8 or more.

[0017] Such a strain-sensitive resistive film has a particularly good linear relationship between the resistance value and the temperature, so that the temperature resistance characteristic can be calibrated quickly and with high accuracy.

[0018] The pressure sensor according to the present invention has a strain-resistance film in which the characteristic change due to the composition change is reduced compared to the conventional strain-resistance film, and therefore has good productivity. In addition, since the characteristic variation of the strain-resistance film is suppressed, it is possible to obtain a pressure detection value with higher accuracy than the conventional one. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic cross-sectional view of a pressure sensor according to one embodiment of the present invention. [Diagram 2] FIG. 2 is an enlarged cross-sectional view of a portion indicated by II in FIG. [Diagram 3]FIG. 3 is a conceptual diagram illustrating a strain-resistance film according to an embodiment of the present invention. [Figure 4] FIG. 4 is a graph showing the relationship between the Al content and the TCR. [Diagram 5] FIG. 5 is a graph showing the relationship between the Al content and the gauge factor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, the present invention will be described based on the embodiments shown in the drawings.

[0021] 1 is a schematic cross-sectional view of a pressure sensor 10 using a strain-resistance film 32 according to one embodiment of the present invention. As shown in FIG. 1, the pressure sensor 10 has a membrane 22 that deforms in response to pressure. In FIG. 1, the membrane 22 is configured as an end wall formed at one end of a hollow cylindrical stem 20, but it can also be configured as a flat Si substrate 122 (see FIG. 3) as in the embodiment. 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 a flow path 12b of the connection member 12.

[0022] 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. However, the shape corresponding to the stem 20 may be obtained by processing a silicon substrate by etching, or by joining a flat silicon substrate to another member.

[0023] 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 pressing member 14 so as to seal the flow path 12b leading to the inner surface 22a of the membrane 22.

[0024] 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.

[0025] A circuit board 16 is attached to the upper surface of the pressing member 14. The circuit board 16 has a ring-like shape that surrounds the stem 20, but the shape of the circuit board 16 is not limited to this. The circuit board 16 has built-in circuits, for example, that transmit detection signals from the strain resistive film 32.

[0026] 1, a strain resistive film 32 and the like are provided on an outer surface 22b of the membrane 22. The strain resistive film 32 and the circuit board 16 are electrically connected via intermediate wiring 72 or the like formed by wire bonding or the like.

[0027] FIG. 2 is a schematic cross-sectional view showing an enlarged view of a part of the strain-resistance film 32 and its surrounding area included in the pressure sensor 10 shown in FIG.

[0028] As shown in FIG. 2, the strain resistive film 32 is provided on the outer surface 22b of the membrane 22 with an underlying insulating layer 52 interposed therebetween.

[0029] 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, a silicon oxide such as SiO2, a silicon nitride, a silicon oxynitride, or the like. 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.

[0030] In addition, when the outer surface 22b of the membrane 22 has insulating properties, the underlying insulating layer 52 may be omitted, and the strain resistance film 32 may be formed directly on the outer surface 22b of the membrane 22. For example, when 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.

[0031] As shown in FIG. 2, the electrode portion 36 is provided on the strain resistance film 32. Although not shown, for example, resistors constituting a Wheatstone bridge circuit are formed on the strain resistance film 32 in a predetermined pattern. Since the resistance value of the resistors formed on the strain resistance film 32 changes according to the deformation of the membrane 22, the strain generated in the membrane 22 and the fluid pressure acting on the membrane 22 are detected from the output of the Wheatstone bridge circuit. The strain resistance film 32 having resistors can be manufactured by microfabricating (patterning) a thin film formed to a predetermined thickness.

[0032] Here, the strain resistance film 32 is represented by the general formula Cr 100-x-y Al x N y where 25 < x ≤ 50 and 0.1 < y ≤ 20 for each composition region of x and y. It has been found that by setting the strain resistance film 32 to such a composition, changes in characteristics due to composition changes can be reduced. In particular, by setting the content of N within a predetermined range and making the content of Al greater than 25% in atomic ratio, changes in characteristics due to composition changes can be reduced compared to conventional strain resistance films (see FIG. 4). Therefore, such a strain resistance film 32 can tolerate composition variations during manufacturing within an appropriate range and has good productivity.

[0033] Also, the strain resistance film 32 can ensure an appropriate gauge factor by setting the content of N within a predetermined range and making the content of Al 50% or less in atomic ratio (see FIG. 5).

[0034] The strain resistive film 32 may have an absolute value of a temperature coefficient of resistance (TCR) of 2000 ppm / ° C. or less in a temperature range of −50° C. to 450° C. Such a strain resistive film 32 has a small rate of change in resistance value associated with temperature change in a wide range from low to high temperatures, and is therefore suitable for use as the strain resistive film 32 of the pressure sensor 10 used in a wide temperature range, whereby temperature correction errors can be reduced and highly accurate detection can be performed.

[0035] The strain resistive film 32 may have an absolute value of a temperature coefficient of sensitivity (TCS) of 2000 ppm / ° C. or less in a temperature range of −50° C. to 450° C. Such a strain resistive film 32 has a small rate of change in sensitivity due to temperature change in a wide range from low temperature to high temperature, and is therefore suitable for use as the strain resistive film 32 of the pressure sensor 10 used in a wide temperature range, whereby temperature correction errors can be reduced and highly accurate detection can be performed.

[0036] The strain-resistance film 32 may contain O as an inevitable impurity in an amount of 10 at % or less with respect to the total amount of Cr, Al, N, and O. By containing O as an inevitable impurity in an amount of 10 at % or less, the strain-resistance film 32 can increase the gauge factor in a temperature range of, for example, −50° C. or more and 450° C. or less.

[0037] The strain resistive film 32 can be formed by a thin film method such as sputtering or deposition using a DC sputtering device or an RF sputtering device. The thickness of the strain resistive film 32 is not particularly limited, but can be, for example, 1 nm to 1000 nm, and is preferably about 50 nm to 500 nm. The O and N contained in the strain resistive film 32 may be those that remain in the reaction chamber when the strain resistive film 32 is formed and are not completely removed, and are then taken into the strain resistive film 32. The O and N contained in the strain resistive film 32 may be those that are intentionally introduced into the strain resistive film 32 while controlling the amount of introduction, for example, by using them as atmospheric gases during film formation or annealing.

[0038] The strain resistive film 32 may contain trace amounts of metals and nonmetallic elements other than Cr and Al. Examples of metals and nonmetallic elements other than Cr and Al contained in the strain resistive 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 characteristics of the strain resistive film 32, such as the gauge factor, the temperature coefficient of sensitivity, and the temperature coefficient of resistance, may change depending on the presence or absence of these trace elements and the heat treatment conditions such as annealing.

[0039] The heat treatment temperature during the manufacture of the strain resistive film 32 is not particularly limited, but may be, for example, 50°C to 550°C, and is preferably 350°C to 550°C.

[0040] As shown in Fig. 2, the electrode portion 36 is provided on top of the strain resistive film 32 and is electrically connected to the strain resistive film 32. As shown in Fig. 2, the electrode portion 36 is formed on a part of the upper surface of the strain resistive film 32. The output of the Wheatstone bridge circuit of the strain resistive film 32 is transmitted to the circuit board 16 shown in Fig. 1 via the electrode portion 36 and intermediate wiring 72. Examples of materials for the electrode portion 36 include conductive metals and alloys, and more specifically, examples of materials include Cr, Ti, Ni, Mo, and platinum group elements. The electrode portion 36 may also have a multi-layer structure made of different materials.

[0041] 2 can be formed by a thin-film method such as sputtering or vapor deposition, like the strain-resistant film 32. However, the base insulating layer 52 and the electrode portion 36 may be formed by a method other than the thin-film method, and for example, the base insulating layer 52 made of a SiO2 film may be provided on the surface of the Si substrate by heating the surface of the Si substrate to form a thermal oxide film.

[0042] The strain-resistance film and pressure sensor according to the present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0043] Example 1 As an example 1, the general formula Cr 100-x-y Al x N y Eight samples (samples 1 to 8) with different Al (x values) were prepared for the strain resistive film represented by the formula: Composition analysis, measurement of temperature coefficient of resistance (TCR), and measurement of temperature coefficient of sensitivity (TCS) were performed for each sample.

[0044] Sample preparation FIG. 3 is a schematic diagram showing the structure of the samples (samples 1 to 8) prepared in Example 1. In Example 1, a Si substrate 122 was heated to form a SiO2 film 152, which is a thermal oxide film, on the surface of the Si substrate 122, and then a strain resistive film 132 was formed on the surface of the SiO2 film 152 using a DC sputtering device. Furthermore, the formed strain resistive film 132 was annealed (heat treated) at 350° C., and resistors constituting a Wheatstone bridge circuit were formed in the strain resistive film 132 by microfabrication. Finally, an electrode layer was formed on the surface of the strain resistive film 132 by electron deposition, and a sample for measuring the temperature coefficient of resistance (TCR) and the temperature coefficient of sensitivity (TCS) was obtained.

[0045] In forming the strain-resistance film 132 for each sample, eight samples with different Al contents (x values) were fabricated by changing the number of Cr targets and Al targets used in the DC sputtering device and the potential of each target. Sputtering was performed in an atmosphere of Ar gas and a small amount of N gas. The thickness of the strain-resistance film 132 was 300 nm.

[0046] Composition analysis The composition of the strain resistive film 132 of each of Samples 1 to 8 was analyzed by XRF (X-ray fluorescence) method.

[0047] Temperature Coefficient of Resistance (TCR) Measurement The resistance value of each sample (sample 1 to sample 8) was measured while changing the environmental temperature from -50°C to 450°C, and the relationship between the resistance value and temperature for each sample was linearly approximated by the least squares method to obtain a slope, from which the TCR (ppm / °C) was calculated. The reference temperature for the calculated TCR was 25°C.

[0048] Quantitative evaluation of linearity For each sample (sample 1 to sample 8), the resistance value was measured while changing the environmental temperature from -50°C to 450°C, and the temperature calibration line (R Cal ) and calculate the resistance temperature line (R Meas ) coefficient of determination R 2 was calculated using the following formula (1).

number

[0049] Temperature Coefficient of Resistance (TCS) Measurement For each sample (sample 1 to sample 8), the gauge factor (k-factor) was measured while changing the environmental temperature from -50°C to 450°C, and the relationship between the gauge factor and temperature for each sample was linearly approximated by the least squares method to obtain the slope, from which the TCS (ppm / °C) was calculated. The reference temperature for the calculated TCS was 25°C.

[0050] Composition analysis results of each sample, coefficient of determination R 2 The measurement results of the temperature coefficient of resistance (TCR) and temperature coefficient of sensitivity (TCS) are shown in Table 1. [Table 1]

[0051] As shown in Table 1, all of samples 1 to 8 contain O as an unavoidable impurity in an amount of 10 at% or less relative to the total amount of Cr, Al, N, and O, and are represented by the general formula Cr 100-x-y Al x N yA strain resistance film 132 represented by [the formula] and with 0.1 < y ≤ 20 was obtained.

[0052] Samples 1 to 4 have a relatively low Al content in the strain resistance film 132 and 0 ≤ x ≤ 25. In contrast, Samples 5 to 8 have a relatively high Al content in the strain resistance film 132 and 25 < x ≤ 50.

[0053] FIG. 4 is a graph in which each sample shown in Table 1 is plotted with the TCR shown in Table 1 on the vertical axis and the Al content on the horizontal axis. As shown in FIG. 4, in Samples 1 to 4 where 0 ≤ x ≤ 25 and the Al content is relatively low, the slope of the TCR with respect to the unit composition change of Al (horizontal axis) is large, and the absolute value of the slope calculated by linearly approximating each plot by the least squares method is 105 (see Table 1). In contrast, in Samples 5 to 8 where 25 < x ≤ 50 and the Al content is relatively high, the slope of the TCR with respect to the unit composition change of Al (horizontal axis) is small, and the absolute value of the slope calculated by linearly approximating each plot by the least squares method is 16 (see Table 1).

[0054] Thus, in the strain resistance film 132 where 25 < x ≤ 50, the absolute value of the slope of the TCR, which is the change in the TCR accompanying the unit composition change of Al, is less than one-sixth of that of the strain resistance film 132 where 0 ≤ x ≤ 25, and it was confirmed that the characteristic change accompanying the composition change can be significantly suppressed. Regarding the TCR value itself, for all of Samples 1 to 8, the absolute value was 2000 ppm / °C or less. On the other hand, as shown in Table 1, among the strain resistance films 132 where 0 ≤ x ≤ 25, there was one like Sample 2 whose absolute value of TCS exceeded 2000 ppm / °C, but for the strain resistance films 132 related to Samples 5 to 8 where 25 < x ≤ 50, the absolute value of all TCS was 2000 ppm / °C or less.

[0055] Also, the value of the coefficient of determination R 2 calculated in the temperature range from -50°C to 450°C is 、AIn Samples 5 to 8 (25 < x ≤ 50) with a relatively high content of l, it was 0.8 or more in each sample, and it was confirmed that the strain resistance film for each sample had high linearity in the relationship between temperature and resistance value.

[0056] Example 2 In Example 2, in the same manner as in Example 1, for the strain resistance film 132 represented by the general formula Cr 100-x-y Al x N y nine samples with different Al (x value) were prepared, and the composition (Al content) of the strain resistance film 132 and the gauge factor (k-factor) at 25°C were measured. FIG. 5 is a graph plotting the measurement results of each sample, with the gauge factor on the vertical axis and the Al content on the horizontal axis.

[0057] As shown in FIG. 5, for samples with x ≤ 50, they have a gauge factor value sufficiently larger than 2.6, which is a value for general metals, and it was confirmed that they can be suitably used as the strain resistance film 132. On the other hand, when the Al content exceeds 50 at%, it can be seen that the gauge factor is less than 3 and the sensitivity of the strain resistance film 132 decreases.

[0058] As described above, the pressure sensor 10, strain resistance films 32 and 132 according to the present invention have been described with reference to the embodiments and examples. However, the present invention is not limited to only these embodiments and examples. Needless to say, the present invention includes many other embodiments and modifications in addition to the above-described embodiments and examples. For example, the pressure sensor 10 is not limited to only those having a stem 20 as shown in FIG. 1, and may be one produced by etching a substrate, or one produced by joining a member formed with strain resistance films 32 and 132 on a flat substrate to other members. The material of the substrate may be any of metal, semiconductor, and insulator. Specifically, in addition to Si mentioned in the examples, alumina (Al2O3) etc. may also be mentioned.

Description of Reference Numerals

[0059] 10... Pressure sensor 12... Connection member 12a...Thread groove 12b...Flow path 14…Restraining member 16...Circuit board 20…Stem 21...Flange section 22…Membrane 22a…Inner surface 22b…External surface 32, 132...Distortion resistive film 36...Electrode part 52...Base insulation layer 72...Intermediate wiring 152...SiO2 film 122...Si substrate

Claims

1. General formula Cr 100-x-y A x N y The strain-resistance film is represented by the formula: where x and y are in the composition ranges of 25<x≦50 and 0.1<y≦20, respectively.

2. 2. The strain-resistance film according to claim 1, wherein the absolute value of the temperature coefficient of resistance (TCR) is 2000 ppm / ° C. or less in the temperature range of −50° C. to 450° C.

3. 3. The strain-sensitive resistive film according to claim 1, wherein the absolute value of the temperature coefficient of sensitivity (TCS) is 2000 ppm / ° C. or less in the temperature range of −50° C. to 450° C.

4. 4. The distortion-resistant film according to claim 1, further comprising O in an amount of 10 at % or less based on the total amount of Cr, Al, N, and O.

5. A strain-resistance film according to any one of claims 1 to 4, and an electrode portion electrically connected to the strain resistive film.

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