JP6008426B2 - Thin film sensor - Google Patents

Description

  The present invention relates to a thin film sensor that detects pressure based on a change in electrical resistance when pressure acts on a metal thin film.

  Patent Document 1 listed below uses an alloy of copper, manganese, and nickel as the material of the thin film sensor, and appropriately adjusts the respective compositions to reduce the pressure detection error with respect to the temperature change. Further, in Patent Document 1, an alloy of chrome and gold is used as a material for the thin film sensor, and the shape of the sensing part of the thin film sensor is different in length and width ratio in one direction with respect to an arbitrary orthogonal axis. It describes that the pressure sensitivity error due to the strain of the thin film sensor is reduced by making the strain sensitivity in the longitudinal direction and the lateral direction substantially the same value by configuring it to be the same as the ratio of the length and width in the direction. . As an example of the sensing part of the latter thin film sensor, there is disclosed one having a shape in which a pair of semicircular arc shaped parts are combined (one-round thin film sensor).

Japanese Patent No. 4527236

  By the way, since this type of thin film sensor is extremely small, it can be mounted in a narrow gap, and can be suitably used for detecting pressure applied to the surface of the skirt portion of an engine piston. it can. However, since the piston skirt is relatively low in rigidity, it easily deforms during operation, and the thin film sensor mounted on the piston distorts following the deformation of the skirt, which is the base material. There is a problem in that the strain due to deformation (electric resistance change) and the strain due to deformation of the base material (electric resistance change) are superposed, and the pressure detection accuracy decreases. In order to accurately detect the pressure on the surface of a base material that is easily deformed, such as a piston skirt, a thin film sensor that can effectively eliminate the influence of distortion (electric resistance change) due to deformation of the base material is required. .

  In the one-round thin film sensor described in Patent Document 1, the vertical strain sensitivity and the lateral strain sensitivity are set to substantially the same value to reduce the pressure detection error due to the strain. If both strain sensitivities can be reduced to zero, pressure detection errors due to strain can be further reduced.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to enable accurate pressure detection by eliminating the influence of deformation of a base material on which a thin film sensor is mounted.

To achieve the above object, according to the first aspect of the invention, a thin film of a first alloy that is an alloy of copper, manganese, and nickel and a thin film of a second alloy that is an alloy of nickel and chromium bets are stacked, the stacked thin film, the ratio of one-way length and width for any orthogonal axes, Ri same der the ratio in the other direction of the length and width, said first alloy of such absolute value is substantially equal gauge factor is offset by a thin film and the second code of the thin film opposite alloys, Rukoto thickness ratio is set between the first alloy and the second alloy A featured thin film sensor is proposed.

  According to the invention described in claim 2, in addition to the structure of claim 1, the film thickness ratio between the first alloy and the second alloy is approximately 4: 1. A thin film sensor is proposed.

  According to a third aspect of the present invention, in addition to the configuration of the first or second aspect, the sensor includes a sensing unit that senses pressure and a lead portion that extends from the sensing unit, and at least the sensing unit includes the sensing unit. A thin film sensor is proposed which is formed by laminating a thin film of a first alloy and a thin film of the second alloy.

According to the configuration of claim 1, the thin film formed by laminating the first alloy and the second alloy has a ratio of the length and width in one direction to the arbitrary orthogonal axis, and the length and width in the other direction. Since the ratio is the same, the pressure detection error due to the distortion of the thin film sensor can be reduced by setting the vertical and horizontal strain sensitivity to substantially the same value. Moreover, the thin film sensor is formed by laminating a thin film of a first alloy that is an alloy of copper, manganese, and nickel and a thin film of a second alloy that is an alloy of nickel and chromium, and the thin film of the first alloy The longitudinal strain sensitivity of the thin film sensor is set by setting the film thickness ratio of the first alloy and the second alloy so that the gauge factors having the opposite signs and the absolute values substantially equal to each other cancel each other. In addition , the gauge factor , which is the lateral strain sensitivity , can be reduced to reduce the pressure detection error due to the distortion of the base material.

According to the second aspect of the present invention, since the film thickness ratio between the first alloy and the second alloy is approximately 4: 1, the gauge factor of the thin film sensor can be substantially zero. Pressure detection error due to distortion can be minimized.

  According to the third aspect of the present invention, at least the sensing part of the sensing part for sensing pressure and the lead part extending from the sensing part is formed by laminating the first alloy thin film and the second alloy thin film. Therefore, pressure detection accuracy can be ensured.

The figure which shows the planar shape of a single wire | line type thin film sensor and a round type thin film sensor. The figure which shows the measuring apparatus of the pressure sensitivity of a thin film sensor. The graph which shows the pressure sensitivity of a single layer type thin film sensor. The figure which shows the measuring apparatus of the temperature sensitivity of a thin film sensor. The graph which shows the temperature sensitivity of a single layer type thin film sensor. The figure which shows the measuring apparatus of the distortion sensitivity of a thin film sensor. The figure which shows the cross-sectional shape of a single wire | line type thin film sensor and a round type thin film sensor. The figure which shows the circuit which modeled the two-layer type thin film sensor. The graph which shows the change of the output characteristic at the time of changing the film thickness ratio of a two-layer type thin film sensor.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  First, the sensor alloy applied to the present invention will be described.

  As shown in Table 1, the sensor alloy (1) to the sensor alloy (4) are all Cu-Mn-Ni alloys, and the composition (% by weight) of the sensor alloy (1) is 87.8% of Cu. , Mn is 8.75%, Ni is 3.45%, and the sensor alloy (2) is Cu is 86.6%, Mn is 11.0%, Ni is 2.4%. ) Is 87.4% Cu, 9.6% Mn and 3.0% Ni, and the sensor alloy (4) is 86.0% Cu, 12.0% Mn and 2.0% Ni. %. The sensor alloy (5) is a Ni-Cr alloy, and the composition (% by weight) of Ni is 90% and Cr is 10%.

  FIG. 1A shows the shape of a single-wire thin film sensor Sa, and a pair of lead portions 11 are connected by a linear sensing portion 12. FIG. 1B shows the shape of a one-round thin film sensor Sb. A pair of lead portions 11 and 11 and a connection portion 13 and 13 combining two semicircles are two semicircular arc-shaped sensings. The units 12 and 12 are connected.

  FIG. 2 shows an apparatus for measuring pressure sensitivity of a thin film sensor. The measuring apparatus includes a pressure vessel 21 that houses the thin film sensor, a high-pressure pump 22 that pressurizes the inside of the pressure vessel 21, and a pressure inside the pressure vessel 21. A pressure sensor 23 for converting the output of the pressure sensor 23 to a voltage, a Wheatstone bridge 25 for converting the electrical resistance value of the thin film sensor to a voltage, an amplifier 26 for amplifying the output of the Wheatstone bridge 25, And a recording device 27 for recording data.

FIG. 3 shows the measurement results of pressure sensitivity for each sensor alloy. The pressure sensitivity of sensor alloy (1) to sensor alloy (4) is 18 to 21 × 10 ⁻⁶ [(Ω / Ω) / MPa]. Thus, the pressure sensitivity of the sensor alloy (5) is 12 to 17 × 10 ⁻⁶ [(Ω / Ω) / MPa], which is more than the pressure sensitivity of the sensor alloy (1) to the sensor alloy (4). Is slightly lower.

  FIG. 4 shows an apparatus for measuring temperature sensitivity of a thin film sensor. The measurement apparatus includes a heater 27 that houses the thin film sensor, a temperature sensor 28 that converts the temperature inside the heater 27 into a voltage, and the electrical resistance of the thin film sensor. It comprises a Wheatstone bridge 29 that converts a value into a voltage, an amplifier 30 that amplifies the output of the Wheatstone bridge 29, and a recording device 31 that records data.

FIG. 5 shows measurement results of temperature sensitivity for each sensor alloy. The temperature sensitivity of the sensor alloy (1) is 10 to 30 × 10 ⁻⁶ [(Ω / Ω) / ° C], and the sensor alloy (2) Has a temperature sensitivity of −12 to −36 × 10 ⁻⁶ [(Ω / Ω) / ° C], and the sensor alloy (3) has a temperature sensitivity of −20 to 8 × 10 ⁻⁶ [(Ω / Ω) / ° C. The temperature sensitivity of the sensor alloy (4) is −43 to −53 × 10 ⁻⁶ [(Ω / Ω) / ° C.], which varies individually. On the other hand, the temperature sensitivity of the sensor alloy (5) is 84 to 128 × 10 ⁻⁶ [(Ω / Ω) / ° C.], which is remarkably increased as the temperature rises.

  FIG. 6 shows a method for measuring the strain sensitivity of the thin film sensor. A thin wire portion 34 sandwiched between a pair of parallel beam portions 33, 33 of a U-shaped tester 32 has a single wire type thin film sensor Sa shown in FIG. 1 (A) and a round type shown in FIG. 1 (B). Two thin film sensors Sb are attached. The single-line type thin film sensor Sa and the one-round type thin film sensor Sb on the right side in the drawing are used for measuring the longitudinal strain sensitivity, and their axes are aligned in the vertical direction (y direction). Further, the single-line thin film sensor Sa and the one-round thin film sensor Sb on the left side in the figure are for measuring the lateral strain sensitivity, and their axes are aligned in the horizontal direction (x direction). Further, a commercially available biaxial strain gauge 35 is attached to the thin portion 34 of the tester 32 as a monitor of the amount of strain in the vertical and horizontal directions.

  In the single-line thin film sensor Sa, since the sensing unit 12 is formed of a straight line and has directionality, the strain sensitivity is represented by the longitudinal strain sensitivity Kl and the lateral strain sensitivity Kw. On the other hand, in the one-round thin film sensor Sb, since the sensing units 12 and 12 are formed of a pair of semicircular arcs and have no directionality, the longitudinal strain sensitivity Kl and the lateral strain sensitivity Kw have the same value. Hereinafter, the longitudinal strain sensitivity Kl and the lateral strain sensitivity Kw of the one-round thin film sensor Sb may be referred to as a gauge factor Kc.

  By applying loads F, F facing each other to the pair of beam portions 33, 33 and causing a bending moment M to act on the thin portion 34, the thin portion 34 is distorted in the vertical and horizontal directions, and a single-wire thin film sensor By comparing the output of Sa and the output of the round type thin film sensor Sb with the output of the biaxial strain gauge 35, the strain sensitivity of the single-line type thin film sensor Sa and the round type thin film sensor Sb is measured.

  Table 2 shows the measurement results of strain sensitivity. The strain sensitivity of the single-line thin film sensor Sa is such that when Cu—Mn—Ni sensor alloys (1) to (4) are used, the longitudinal strain sensitivity Kl is 0.50 to 0.70, and the lateral strain sensitivity Kw is − When the Ni-Cr sensor alloy (5) is used, the longitudinal strain sensitivity Kl is 2.4 to 2.5, and the lateral strain sensitivity Kw is -0.11 to -0. .13.

  In addition, the strain sensitivity of the one-round thin film sensor Sb is such that when Cu—Mn—Ni sensor alloys (1) to (4) are used, the longitudinal strain sensitivity Kl is −0.25 to −0.35, and the lateral strain sensitivity. When Kw is −0.25 to −0.35 and the Ni—Cr sensor alloy (5) is used, the longitudinal strain sensitivity Kl is 1.18 to 1.2, and the lateral strain sensitivity Kw is 1.18 to 1.2.

  As disclosed in the above-mentioned Patent Document 1, in order to eliminate the influence of the strain applied to the thin film sensor and detect the pressure with high accuracy, it is desirable to match the longitudinal strain sensitivity Kl and the lateral strain sensitivity Kw. In the single-line thin film sensor Sa, the longitudinal strain sensitivity Kl and the lateral strain sensitivity Kw are inconsistent regardless of which sensor alloy (1) to (5) is used, and the influence of the strain applied to the thin film sensor is affected. It turns out that it cannot be excluded.

  On the other hand, if the one-round type thin film sensor Sb is employed, the longitudinal strain sensitivity Kl and the lateral strain sensitivity Kw, that is, the gauge factor Kc is substantially reduced regardless of which sensor alloy (1) to (5) is used. It can be seen that the influence of distortion applied to the thin film sensor Sb can be considerably eliminated.

  However, if the gauge factor Kc of the one-round type thin film sensor Sb can be made zero, the influence of the strain applied to the thin film sensor Sb can be further eliminated and the pressure can be detected with higher accuracy. The present invention achieves the above-mentioned problem by forming a one-round thin film sensor Sb, which has conventionally been formed of a single layer of a sensor alloy, by using a two-layer sensor alloy.

  FIG. 7A shows a cross section of a conventional single-layer thin film sensor. A non-conductive insulating film 16, a sensor layer 17 made of a sensor alloy and a wear-resistant protective film 18 are formed on a base material 15. It is constructed by stacking. FIG. 7B shows a cross section of a single-layer thin film sensor of the present invention. Instead of the single sensor layer 17 of the single-layer thin film sensor, two layers comprising a first sensor layer 17A and a second sensor 17B. The sensor layer is provided. The first sensor layer 17A is made of a Cu—Mn—Ni alloy, the second sensor layer 17B is made of a Ni—Cr alloy, and the thickness of the first sensor layer 17A and the thickness of the second sensor layer 17B are in a predetermined ratio. Is set.

  The base material 15 may be a silicon wafer, or may be a member that detects pressure, such as a piston skirt. The two-layer structure may be applied to all of the pair of lead portions 11, 11, the sensing portions 12, 12 and the connecting portions 13, 13 of the one-round thin film sensor Sb shown in FIG. The lead parts 11 and 11 and the connection parts 13 and 13 do not necessarily have a two-layer structure, and may have a single-layer structure.

  Next, the reason why the distortion sensitivity can be reduced to zero by making the one-round thin film sensor Sb into a two-layer structure will be described.

If the sign is defined as
R: resistance value of a thin film sensor having a two-layer structure [Ω]
K: Strain sensitivity of a thin film sensor having a two-layer structure ε: Strain of a thin film sensor having a two-layer structure RA: Electric resistance value [Ω] of the first sensor layer 17A
ρA: Electric resistivity [Ω · m] of the first sensor layer 17A
tA: thickness of the first sensor layer 17A [m]
KA: strain sensitivity of first sensor layer 17A εA: strain of first sensor layer 17A RB: electric resistance value [Ω] of second sensor layer 17B
ρB: Electric resistivity [Ω · m] of the second sensor layer 17B
tB: thickness of the second sensor layer 17B [m]
KB: strain sensitivity of second sensor layer 17B εB: strain of second sensor layer 17B L: length of sensor layer [m]
W: Width of sensor layer [m]
The output of the thin film sensor due to strain is expressed as follows.

  As shown in FIG. 8, since the first sensor layer 17A and the second sensor layer 17B can be regarded as being electrically connected in parallel, the resistance value R of the thin film sensor is

で与えられる。

Given in.

  From equations (1) and (2)

が得られる。

Is obtained.

  Here, when (1) is modified and substituted for RA and RB, and (2) is modified and substituted for dR,

が得られる。

Is obtained.

  Since it can be considered that the strain of the first sensor layer 17A and the strain of the second sensor layer 17B are equal, that is, dε = dεA = dεB,

が得られる。

Is obtained.

  The change in resistance value R is

で与えられる。

Given in.

  Further, dLA = dLB, dWA = dWB, dρ = ρ, and W >> t to dt = t, and substituting equation (6) into equation (5),

が得られる。

Is obtained.

  In the equation (7), the electrical resistivity ρA of the first sensor layer 17A and the electrical resistivity ρB of the second sensor layer 17b are known as shown in Table 3.

  The strain sensitivity KA of the first sensor layer 17A and the strain sensitivity KB of the second sensor layer 17B can be measured as shown in Table 2. That is, Kl or Kw of the Cu-Mn-Ni alloy in the column of the round-type thin film sensor Sb in Table 2 corresponds to KA in the formula (7), and Ni-Cr in the column of the round-type thin film sensor Sb in Table 2 The K1 or Kw of the alloy corresponds to KB in the equation (7).

  Moreover, since the thickness tA of the first sensor layer 17A and the thickness tB of the second sensor layer 17B can be arbitrarily set, the ratio (film thickness ratio = tB / tA) is set to an appropriate value. The strain sensitivity K of the thin film sensor having the two-layer structure, that is, the one-round thin film sensor Sb can make the gauge factor Kc zero.

FIG. 9A shows measured values of the longitudinal strain sensitivity Kl (see ■) and lateral strain sensitivity Kw (see ●) of a single- layer thin film sensor having a two-layer structure when the film thickness ratio = tB / tA is changed. , shows the measurements of the two-layer structure gauge factor Kc is the strain sensitivity of the thin-film sensor Sb of the round type (see ▲), in good agreement with the calculated value shown by the solid line. From the figure, when the film thickness ratio = approximately 25%, for example, when the thickness tA of the first sensor layer 17A is 200 nm and the thickness tB of the second sensor layer 17B is 50 nm, the one-round thin film sensor Sb It can be seen that the gage factor Kc of is substantially zero.

  Table 4 shows the measured values of the longitudinal strain sensitivity Kl and the lateral strain sensitivity Kw of the one-round thin film sensor Sb, to which one layer structure of Cu—Mn—Ni alloy is applied and one layer structure of Ni—Cr alloy is applied. 1 and those to which a two-layer structure of a Cu—Mn—Ni alloy and a Ni—Cr alloy are applied are shown.

  The longitudinal strain sensitivity Kl and the lateral strain sensitivity Kw are equal to each other when the single layer structure of the Cu—Mn—Ni alloy and the single layer structure of the Ni—Cr alloy are applied. Cannot be zero. On the other hand, in the case of applying a two-layer structure in which the film thickness ratio of the Cu—Mn—Ni alloy and the Ni—Cr alloy is approximately 25%, the longitudinal strain sensitivity Kl and the lateral strain sensitivity Kw are both substantially zero. I understand.

  Next, the pressure sensitivity and the temperature sensitivity of the one-layer thin film sensor Sb having a two-layer structure will be described.

αP: Pressure sensitivity of thin film sensor having a two-layer structure [(Ω / Ω) / MPa]
αPA: Pressure sensitivity of first sensor layer 17A [(Ω / Ω) / MPa]
αPB: Pressure sensitivity of second sensor layer 17B [(Ω / Ω) / MPa]
αT: Temperature sensitivity of thin-film sensor with two-layer structure [(Ω / Ω) / ° C]
αTA: temperature sensitivity of first sensor layer 17A [(Ω / Ω) / ° C]
αTB: Temperature sensitivity of second sensor layer 17B [(Ω / Ω) / ° C]
In the same way as the equation (7) showing the strain sensitivity K of the thin film sensor having the two-layer structure, the equations showing the temperature sensitivity αP of the thin film sensor having the two-layer structure and the temperature sensitivity αT of the thin film sensor having the two-layer structure are defined. Each can be derived as follows.

  (8), the pressure sensitivity αPA of the first sensor layer 17A and the pressure sensitivity αPB of the second sensor layer 17B shown in FIG. 3, the electrical resistivity ρA of the first sensor layer 17A shown in Table 3, and the second sensor layer When the electric resistivity ρB of 17b is substituted and the film thickness ratio = tB / tA is changed, the graph of FIG. 9B is obtained. The measured value indicated by ▲ is in good agreement with the calculated value indicated by the solid line, and it can be seen that the pressure sensitivity αP of the thin film sensor having the two-layer structure is substantially constant regardless of the film thickness ratio = tB / tA.

  In Equation (9), the temperature sensitivity αTA of the first sensor layer 17A and the temperature sensitivity αTB of the second sensor layer 17B shown in FIG. 5 and the electric resistivity ρA and the second sensor layer of the first sensor layer 17A shown in Table 3 are shown. When the electric resistivity ρB of 17b is substituted and the film thickness ratio = tB / tA is changed, the graph of FIG. 9C is obtained. It can be seen that when the film thickness ratio = tB / tA = 25%, the temperature sensitivity αT can be made substantially zero by using the sensor alloy (4) indicated by ▼.

  The embodiments of the present invention have been described above, but various design changes can be made without departing from the scope of the present invention.

  For example, the thin film sensor of the present invention is not limited to the one-round thin film sensor Sb of the embodiment, and the ratio of the length and width in one direction to the arbitrary orthogonal axis is the length and width in the other direction. It is sufficient if it is the same as the ratio.

Sa Single-line type thin film sensor Sb Round circuit type thin film sensor 11 Lead part 12 Sensing part 15 Base material 16 Insulating film 17 Sensor layer 17A First sensor layer 17B Second sensor 18 Protective film

Claims (3)

A thin film of a first alloy, which is an alloy of copper, manganese and nickel, and a thin film of a second alloy, which is an alloy of nickel and chromium, are laminated, and the laminated thin films are aligned with respect to an arbitrary orthogonal axis. the ratio of the direction of length and width, Ri same der the ratio in the other direction of the length and width, the sign of the thin film and the second alloy of the first alloy are substantially equal absolute value in opposite as the gauge factor is canceled out, thin-film sensor, wherein Rukoto thickness ratio of the second alloy and said first alloy is set.   2. The thin film sensor according to claim 1, wherein a film thickness ratio between the first alloy and the second alloy is approximately 4: 1.   A pressure sensing section; and a lead section extending from the sensing section, wherein at least the sensing section is configured by laminating the first alloy thin film and the second alloy thin film. The thin film sensor according to claim 1 or 2.

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