Thin-film thermistor, electronic device, and method for manufacturing thin-film thermistor

Abstract

This thin-film thermistor has an insulating substrate, a temperature-sensitive layer positioned on a first surface of the insulating substrate, and an electrode layer including two comb-form electrodes connected to the temperature-sensitive layer. The temperature-sensitive layer contains a metal oxide containing manganese, cobalt, and zinc and has a film strain of 0.40% or less. The metal oxide may be expressed as MnxCoyZnzO(1–w–x–y–z) (11 atm% ≤ x ≤ 19 atm%, 18 atm% ≤ y ≤ 36 atm%, 0.1 atm% ≤ z ≤ 13 atm%).

Description

Thin film thermistor, electronic device, and method for manufacturing thin film thermistor

[0001] The present disclosure relates to a thin film thermistor, an electronic device, and a method for manufacturing a thin film thermistor.

[0002] Electronic devices and the like are sometimes equipped with elements that measure temperature for purposes such as temperature control and monitoring of operation. Thermistors are known as such elements. Thin-film thermistors, which are suitable for miniaturizing thermistors, have a temperature-sensitive layer whose resistivity changes with temperature. Highly sensitive thermistors have a large B constant, which represents the change in resistivity relative to temperature. JP-A-6-251906 discloses a composition made of oxides of manganese, cobalt, and zinc as a material for a temperature-sensitive layer with a large B constant.

[0003] One aspect of the present disclosure is a thin film thermistor comprising: [1] an insulating substrate; a temperature-sensitive layer located on a first surface of the insulating substrate; and an electrode layer including two electrodes connected to the temperature-sensitive layer, wherein the temperature-sensitive layer contains a metal oxide containing manganese, cobalt, and zinc, and the film strain is 0.40% or less. [2] The metal oxide is Mn ｘ Co ｙ Zn ｚ O （１－ｗ－ｘ－ｙ－ｚ）(11 atm%≦x≦19 atm%, 18 atm%≦y≦36 atm%, 0.1 atm%≦z≦13 atm%). [3] The thin film thermistor of [1] or [2], wherein the temperature-sensitive layer has a cubic spinel crystal structure, and the lattice constant of the cubic spinel crystal structure is 8.22 Å or more and 8.33 Å or less. [4] The thin film thermistor of any of [1] to [3], wherein the insulating substrate has an amorphous silicon dioxide layer along the first surface, and the thickness of the amorphous silicon dioxide layer is 0.1 μm or more. [5] The thin film thermistor of any of [1] to [4], wherein the temperature-sensitive layer has a B-constant of 3500 K or more and 7000 K or less in the temperature range of 25° C. or more and 50° C. or less, and a resistivity at 25° C. of 20 kΩ cm or less. [6] An electronic device comprising the thin film thermistor according to any one of [1] to [5]. [7] A method for manufacturing a thin film thermistor having an insulating substrate, a temperature-sensitive layer located on a first surface of the insulating substrate, and an electrode layer including two electrodes connected to the temperature-sensitive layer, wherein the surface of the insulating substrate has an amorphous silicon dioxide layer, and the temperature-sensitive layer is formed on the insulating substrate by sputtering using a target containing manganese, cobalt, and zinc and introducing a gas containing oxygen, or by sputtering using a target containing manganese, cobalt, and zinc and at least one of the manganese, cobalt, and zinc is an oxide, and the film formation is carried out at a temperature in the range of 300°C to 680°C.

[0004] FIG. 1 is a plan view showing the structure of a piezoelectric device, which is an example of an electronic device having a thin film thermistor of this embodiment; FIG. 2 is a view explaining the bonding positions of bonding members; FIG. 3 is a view explaining the bonding positions of bonding members; FIG. 4 is a cross-sectional view of an electronic device; FIG. 5 is a perspective view showing an example of a thin film thermistor; FIG. 6 is a plan view showing another example of a thin film thermistor; FIG. 7 is a flowchart showing a first example of the procedure for a method of manufacturing a thin film thermistor; FIG. 8 is a flowchart showing a second example of the procedure for a method of manufacturing a thin film thermistor; and FIG. 9 is a table showing measurement results for the characteristics of a thin film thermistor.

[0005] 1 is a plan view showing the internal structure of a piezoelectric device 1, which is an example of an electronic device having a thin film thermistor 10 according to this embodiment, with a cover 40 removed.

[0006] The piezoelectric device 1 includes a package 30, a piezoelectric vibration element 20, and a thin-film thermistor 10. The package 30 has a recess 30a in the center of the top surface. The piezoelectric vibration element 20 is located within the recess 30a.

[0007] The package 30 is a housing made of, for example, a ceramic material, a semiconductor material, a glass material, or a combination thereof. Conductor signal lines are provided inside and on the surface of the above-mentioned material of the package 30. The signal lines may be related to power supply and grounding. The signal lines may be made of, for example, molybdenum, copper, silver, tungsten, or the like. Nickel plating, gold plating, or the like may be laminated on the surface of some or all of the signal lines. Electrode pads 311 and 312 are located at one end of the recess 30a in the X direction, which is the longitudinal direction of the recess 30a, and are aligned in the Y direction perpendicular to the X direction. The electrode pads 311 and 312 may be printed with gold or the like on the surface of the recess 30a.

[0008] The piezoelectric vibration element 20 may be, for example, a quartz crystal resonator. The piezoelectric vibration element 20 has mounting electrodes 211 and 212 aligned in a direction perpendicular to the longitudinal direction at one end of a quartz crystal blank 201. The mounting electrode 211 is connected to an excitation electrode 221 located on the upper surface of the piezoelectric vibration element 20. The mounting electrode 212 is connected to an excitation electrode (not shown) located on the lower surface of the piezoelectric vibration element 20 so as to overlap the excitation electrode 221 in a plan view. The quartz crystal blank 201 may have both flat upper and lower surfaces, or may have a structure in which at least one surface is partially thick or thin.

[0009] The piezoelectric vibration element 20 may be positioned such that its longitudinal direction is parallel to the X-direction of the package 30. The mounting electrodes 211, 212 are connected to electrode pads 311, 312 located within the recess 30a via a bonding member 320. The piezoelectric vibration element 20 does not need to be in contact with the package 30 at any point other than the mounting electrodes 211, 212. In other words, the piezoelectric vibration element 20 may be in a cantilevered state. When a voltage is applied between the excitation electrodes, the crystal blank 201 vibrates, and a voltage generated between the excitation electrodes in response to the vibration of the crystal blank 201 is output to the outside via the mounting electrodes 211, 212 and the electrode pads 311, 312.

[0010] The bonding member 320 is a heat-cured conductive adhesive. The conductive adhesive may be, for example, a silver paste containing silver particles. The conductive adhesive may be applied to the electrode pads 311, 312 in a substantially elliptical area. This allows the bonding member 320 to extend within the planar view area of ​​the electrode pads 311, 312 and the mounting electrodes 211, 212, depending on the wettability of the electrode pads 311, 312 and the mounting electrodes 211, 212, without extending beyond the planar view area of ​​the electrode pads 311, 312 and the mounting electrodes 211, 212.

[0011] A recessed portion 30b is located below the piezoelectric vibration element 20 on a portion of the bottom surface of the recess 30a. The thin-film thermistor 10 may be located within the recessed portion 30b. The thin-film thermistor 10 may be connected to the electrode pads 331, 332 within the recessed portion 30b via a bonding member 340. The bonding member 340 may be a heat-cured conductive adhesive. The conductive adhesive may be applied in a substantially elliptical shape to the electrode pads 331, 332 and heat-cured in a state where it spreads out to a range that does not extend beyond the planar view of the electrode pads 331, 332 depending on the wettability of the electrode pads 331, 332, etc. The bonding member 340 may be made of the same component as the bonding member 320, or the bonding members 320, 340 may be different from each other.

[0012] 2A to 2C are diagrams illustrating the bonding position of the bonding member 340. The illustrations show the area of ​​the recess 30b with the lid 40 removed. As described above, the electrode pads 331 and 332 are bonded to the thin-film thermistor 10 by the bonding member 340. As shown in FIG. 2A , the bonding member 340 may extend beyond the area of ​​the thin-film thermistor 10 on the long side of the thin-film thermistor 10 in a plan view, e.g., on the +Y side. Accordingly, the bonding member 340 also adheres to the side of the thin-film thermistor 10, i.e., the side of the insulating substrate 11 (see FIG. 4A ) whose normal direction is within the XY plane. This reduces peeling of the thin-film thermistor 10 from the electrode pads 331 and 332.

[0013] As shown in FIG. 2B , the bonding member 340 may extend beyond the thin-film thermistor 10 on the short sides of the thin-film thermistor 10, for example, on the ±X sides. Alternatively, as shown in FIG. 2C , the bonding member 340 may extend beyond the thin-film thermistor 10 at only a portion, particularly one, of the multiple locations within the recess 30b. Also, in FIGS. 2A to 2C , the bonding member 340 may extend beyond the thin-film thermistor 10 at both the X-direction end and the Y-direction end. As described below, if the insulating substrate 11 of the thin-film thermistor 10 is a combination of a silicon substrate 111 and an insulating film 112, when conductive bonding members 340 are attached to two locations on the silicon substrate 111, current flows between the two locations, changing the resistance of the thin-film thermistor 10. Therefore, in this case, the resistance of the thin-film thermistor 10 must be adjusted taking into account the current flowing through the silicon substrate 111 between the electrode pads 331 and 332.

[0014] 3 is a cross-sectional view taken along the cross-sectional line iii in FIG. 1. The electrode pads 331, 332 and the thin-film thermistor 10 are located in a recess 30b on the bottom surface of the recess 30a. The recess 30b and the thin-film thermistor 10 may be located on the opposite side of the package 30 from the electrode pads 311, 312 in the X direction. In this case, the longitudinal direction of the package 30 and the longitudinal direction of the recess 30b and the thin-film thermistor 10 may be the same direction (X direction).

[0015] The recess 30a including the recessed portion 30b is sealed by bonding a lid 40 to the upper end of the package 30, i.e., the upper surface of the sidewall of the recess 30a. The lid 40 is a flat plate of a metal conductor, and may be, for example, a metal containing iron, copper, nickel, cobalt, molybdenum, or tungsten, or an alloy thereof, such as Kovar. The bonding material used for sealing with the lid 40 may be capable of bonding by heating within a temperature range that does not adversely affect the characteristics of the thin-film thermistor 10 sealed therein. For example, the lid 40 may be bonded using a brazing material or the like. A frame-shaped metallization layer may be located between the upper end of the package 30 and the lid 40. The metallization layer may be a plated layer or a conductive layer that is applied and baked.

[0016] Fig. 4A is a perspective view showing an example of the thin-film thermistor 10 of this embodiment. Fig. 4B is a plan view showing another example of the thin-film thermistor. As shown in the example of Fig. 4A, the thin-film thermistor 10 has an insulating substrate 11, a temperature-sensitive layer 12, and an electrode layer 13, which are stacked in this order toward the +Z direction. A portion of the electrode layer 13 and a portion of the temperature-sensitive layer 12 may be covered with a protective film 14. Note that the shapes shown in Figs. 4A and 4B are for illustrative purposes only, and the thickness ratios between each layer in the Z direction and the ratios between the thickness and width in the X and Y directions may not reflect the respective ratios of an actual product.

[0017] The insulating substrate 11 may include, for example, a silicon substrate 111 and an insulating film 112. The insulating film 112 is located on the +Z side of the silicon substrate 111, i.e., along the first surface in contact with the temperature-sensitive layer 12. The insulating film 112 may be, for example, an amorphous silicon dioxide layer. The insulating film 112 may have a thickness of 0.1 μm or more, which is an appropriate thickness that maintains insulation and prevents cracks from occurring due to warping of the insulating substrate 11 during transportation after the insulating substrate 11 has been ground to reduce its thickness. It is known that an amorphous layer produces a halo-shaped diffraction image on the side of smaller diffraction angles in X-ray diffraction, for example. That is, whether or not a substrate contains an amorphous silicon dioxide layer can be identified by whether or not a peak with a distribution shape corresponding to this halo is present in the spectral intensity corresponding to the diffraction angle in X-ray diffraction. The silicon substrate 111 may be a crystalline substrate or an amorphous substrate. The thickness of the silicon substrate 111 may be, for example, approximately 50 μm. That is, it is sufficient that the insulating substrate 11 has insulating properties at least in a portion of an appropriate thickness from the contact surface with the temperature-sensitive layer 12 .

[0018] Alternatively, the insulating substrate 11 may be entirely insulating. In this case, the insulating substrate 11 may be, for example, quartz glass, crystal, sapphire, alumina, or the like. Even when the insulating substrate 11 is entirely insulating, it may further have an amorphous silicon dioxide layer on the +Z side, i.e., between the insulating substrate 11 and the temperature-sensitive layer 12. Having the temperature-sensitive layer 12 on the amorphous silicon dioxide layer may improve the crystallinity of the temperature-sensitive layer 12.

[0019] Furthermore, the thin-film thermistor 10 may have high thermal conductivity so that the temperature of the thin-film thermistor 10 can quickly follow temperature changes in the package 30. For example, the insulating substrate 11 may have high thermal conductivity. The thermal conductivity of quartz glass is approximately 1.4 W / mK, while the thermal conductivity of amorphous silicon is approximately 3.3 W / mK. In comparison, the thermal conductivity of crystalline silicon is as high as approximately 135 W / mK. Therefore, the insulating substrate 11 may have a silicon substrate 111 that is a crystalline silicon substrate, with an amorphous silicon dioxide layer on its surface as the insulating film 112.

[0020] Such an insulating substrate 11 may be, for example, a crystalline silicon substrate whose surface has been thermally oxidized. The insulating substrate 11, obtained by thermally oxidizing the surface of a crystalline silicon substrate, has insulating films 112 on both sides of the silicon substrate 111. In one embodiment, the insulating layer on the -Z side, which does not contact the temperature-sensitive layer 12, may be removed by grinding, polishing, or the like. That is, the insulating substrate 11 may have a structure in which no insulating layer exists on the side that does not contact the temperature-sensitive layer 12. In this case, as described above, the initial thickness of the silicon substrate 111 may be determined so that the thickness of the insulating substrate 11 after grinding or polishing is appropriate. However, even in this case, a silicon dioxide layer formed by natural oxidation may be located on the side of the silicon substrate 111 that does not contact the temperature-sensitive layer 12. An insulating substrate 11 having such a structure exhibits high temperature tracking capability relative to the temperature of the package 30 when the side that does not contact the temperature-sensitive layer 12 is mounted and fixed to the package 30.

[0021] If the side of the thin-film thermistor 10 with the temperature-sensitive layer 12 and electrode layer 13 is mounted and fixed to the package 30 using a conductive adhesive or the like, heat is easily transferred to the temperature-sensitive layer 12 via the electrode layer 13, which is directly fixed to the package 30. Therefore, high temperature tracking is achieved even when the insulating substrate 11 is an insulating substrate rather than a crystalline silicon substrate with a thermally oxidized surface. Furthermore, even if the side of the thin-film thermistor 10 without the temperature-sensitive layer 12 and electrode layer 13 is mounted and fixed to the package 30 using a conductive adhesive or the like, if the insulating substrate 11 is a crystalline silicon substrate with a thermally oxidized surface, the temperature of the entire thin-film thermistor 10 becomes uniform more quickly, resulting in higher temperature tracking and allowing the temperature of the temperature-sensitive layer 12 to quickly respond to changes in the ambient temperature. However, in this mounting and fixing method, a conductive adhesive must also be applied to the side of the insulating substrate to electrically connect the electrode pads 331 and 332 of the package 30 to the connection electrodes 131 and 132 of the thin-film thermistor 10, respectively. Alternatively, a separate mounting method such as wire bonding must be added.

[0022] The temperature-sensitive layer 12 is a thin film whose resistivity changes depending on the temperature. The thickness of the temperature-sensitive layer 12 is, for example, several hundred nanometers or less, and may be 100 nanometers or less. On the other hand, the thickness of the temperature-sensitive layer 12 may be 20 nm or more. The temperature-sensitive layer 12 contains a metal oxide containing at least manganese (Mn), cobalt (Co), zinc (Zn), and oxygen (O). That is, the atomic composition of the temperature-sensitive layer 12 is Mn ｘ Co ｙ Zn ｚ O （１－ｗ－ｘ－ｙ－ｚ） The temperature-sensitive layer 12 may have a cubic spinel crystal structure. The temperature-sensitive layer 12 may contain other 3d transition metals such as iron (Fe) or 4d transition metals such as yttrium (Y). The temperature-sensitive layer 12 may also contain other components that may be mixed in during manufacturing, such as carbon (C), nitrogen (N), hydrogen (H), and argon (Ar). In addition to or instead of this, the temperature-sensitive layer 12 may contain H ２ , H ２ O, CO ２ , N ２ , C ２ H ４ , C ３ H ８ The temperature-sensitive layer 12 may also contain trace amounts of functional groups, such as hydroxyl groups (OH) and carbonyl groups (CO).

[0023] To reduce peeling between the temperature-sensitive layer 12 and the electrode layer 13, the surface unevenness of the temperature-sensitive layer 12 may be within an appropriate range. The unevenness of the temperature-sensitive layer 12 is measured at any cross section along the ±Z direction of the thin-film thermistor 10. For example, the unevenness of the temperature-sensitive layer 12 may be expressed as a value [%] obtained by dividing the difference Sz in the Z component between the position furthest on the +Z side and the position furthest on the −Z side by the thickness of the temperature-sensitive layer 12 at a magnification of, for example, 500,000 times, of the field of view of a scanning transmission electron microscope (STEM) that includes the interface between the temperature-sensitive layer 12 and the electrode layer 13. The thickness of the temperature-sensitive layer 12 may be determined by X-ray reflectivity measurement (XRR). The unevenness of the temperature-sensitive layer 12 may be, for example, 5% or more, 8% or more, or 15% or more. On the other hand, the unevenness of the temperature-sensitive layer 12 may be 50% or less, 30% or less, or 20% or less.

[0024] The electrode layer 13 includes connection electrodes 131 and 132 at both ends and two comb-shaped electrodes 133 and 134. The upper surfaces of the connection electrodes 131 and 132 on the +Z side protrude from the protective film 14, allowing connection to the outside. The connection electrodes 131 and 132 may have an underlayer of, for example, nickel (Ni) or chromium (Cr) coated with gold (Au). To reduce peeling between the electrode layer 13 and the protective film 14, the unevenness of the electrode layer 13 may be affected by the unevenness of the temperature-sensitive layer 12. The unevenness of the electrode layer 13 is measured at any cross section along the ±Z direction of the thin-film thermistor 10. For example, the unevenness of the electrode layer 13 may be expressed as a value [%] obtained by dividing the difference Sz in the Z component between the position furthest on the +Z side and the position furthest on the −Z side by the thickness of the electrode layer 13 at a magnification of, for example, 500,000 times, the field of view of the electrode layer 13 that includes the surface of the electrode layer 13 on the protective film 14 side using a scanning transmission electron microscope (STEM). The thickness of the electrode layer 13 may be measured using an STEM cross section at a magnification of, for example, 500,000 times, a field of view that includes the entire thickness of the electrode layer 13. Furthermore, if the electrode layer 13 is substantially trapezoidal, measurement may be performed on a cross section that excludes the inclined portion from the measurement area. The unevenness of the electrode layer 13 may be such that, for example, the ratio calculated by dividing the size of the unevenness by the average electrode thickness measured between the thickest and thinnest points on the STEM cross section may be 14% or more, 18% or more, or 19% or more. On the other hand, the unevenness of the electrode layer 13 may be such that the ratio is 50% or less, 40% or less, or 30% or less.

[0025] The comb-shaped electrode 133 is connected to the connection electrode 131 and the temperature-sensitive layer 12, and the comb-shaped electrode 134 is connected to the connection electrode 132 and the temperature-sensitive layer 12. The shapes and thicknesses of the connection electrodes 131, 132 may be determined as appropriate. The comb-shaped electrode 133 has a current collecting portion 135 and multiple comb-tooth electrodes 137. The comb-shaped electrode 134 has a current collecting portion 136 and multiple comb-tooth electrodes 138. The current collecting portions 135, 136 may extend in the X direction at different positions in the Y direction. The +X side end of the current collecting portion 135 may be connected to the connection electrode 131. The −X side end of the current collecting portion 136 may be connected to the connection electrode 132.

[0026] The multiple comb-tooth electrodes 137 may extend in the -Y direction from the current collector 135 located on the +Y side of the temperature-sensitive layer 12, at a right angle to the current collector 135. The multiple comb-tooth electrodes 138 may extend in the +Y direction from the current collector 136 located on the -Y side of the temperature-sensitive layer 12, at a right angle to the current collector 136. The comb-tooth electrodes 137 of the comb-tooth electrode 133 and the comb-tooth electrodes 138 of the comb-tooth electrode 134 are arranged alternately at appropriate intervals in the X direction. The number of comb-tooth electrodes 137 and the number of comb-tooth electrodes 138 may be the same or may differ by one. Alternatively, the number of comb-tooth electrodes 137 and the number of comb-tooth electrodes 138 may be the same, but the length of just one comb tooth may differ.

[0027] The thickness of the comb-tooth electrodes 133, 134 may be 20 nm or more and 200 nm or less. The overall length of the comb-tooth electrodes 133, 134 is adjusted appropriately depending on the resistivity of the temperature-sensitive layer 12. Here, the overall length is the sum of the lengths of the multiple comb-tooth electrodes 137, 138 in the Y direction. The lengths of the comb-tooth electrodes 137, 138 may be equal. Alternatively, from the perspective of adjusting the overall length, the number of teeth of the comb-tooth electrodes 137, 138 may differ by one, or some of the comb-tooth electrodes 137 or 138, for example, one of the teeth may be different in length from the others, for example, shorter. When all the comb-tooth electrodes 137, 138 have the same length, the overall length is the value obtained by multiplying the comb tooth length, which is the length of each comb-tooth electrode 137, 138 in the Y direction, by the total number of teeth of the comb-tooth electrodes 137, 138. The total length of the comb-tooth electrodes 133, 134 may be, for example, 1,000 μm or more and 80,000 μm or less, or 4,000 μm or more and 10,000 μm or less. Furthermore, if the distance between the tip of the comb-tooth electrode 137 and the current collecting portion 136 and the distance between the tip of the comb-tooth electrode 138 and the current collecting portion 135 are each defined as d2, the distance d2 may be greater than d1, or d2 = d1, where d1 is the distance between the comb-tooth electrodes 137 and 138 adjacent to each other in the X direction. When d2 = d1, the cross-sectional area of ​​the current path in the temperature-sensitive layer 12 that flows between the comb-tooth electrodes 133, 134 at the distance d1 = d2 is larger than the total length of the comb-tooth electrodes 133, 134. In other words, as the current path in the temperature-sensitive layer 12 increases, the effective overall length of the comb-tooth electrodes 133 and 134 increases by (N-2), which is the sum of the width d3 of each comb-tooth electrode 137, 138 in the X direction and twice the distance d1 (the total number N of comb-tooth electrodes 137, 138 minus the two electrodes at both ends), i.e., (d3 + d1 × 2) × (N-2). When the comb-tooth electrodes 133 and 134 each have a large number of comb-tooth electrodes 137, 138, the cross-sectional area of ​​the current path equivalent to the current path between the comb-tooth electrodes 137 and 138 increases particularly effectively. Therefore, the overall length of the comb-tooth electrodes 137, 138 in the Y direction can be uniformly shortened. Furthermore, the number of comb-tooth electrodes 137, 138 required for the resistance value of the thin-film thermistor 10 can be reduced.Therefore, even if a film with a higher resistivity is used for the temperature-sensitive layer 12, the thin film thermistor 10 can be designed with a more compact comb-tooth region than conventional ones.

[0028] The cross-sectional shape of the current collecting parts 135, 136 parallel to the YZ plane may be substantially rectangular. Alternatively, the shape of the current collecting parts 135, 136 may be substantially trapezoidal. These shapes increase the contact area between the current collecting parts 135, 136 and the protective film 14, thereby reducing the possibility of the protective film 14 peeling off.

[0029] The comb-shaped electrodes 133, 134 may contain some or all of, for example, palladium (Pd), gold (Au), platinum (Pt), and titanium (Ti). From the perspective of reducing peeling, it is preferable for the electrode layer 13 to have a linear expansion coefficient close to that of the temperature-sensitive layer 12. For example, if the linear expansion coefficient of the temperature-sensitive layer 12 is between that of platinum (Pt) and that of gold (Au), but is closer to that of gold (Au), a higher thickness ratio of gold (Au) than that of platinum (Pt) and titanium (Ti) in the comb-shaped electrodes 133, 134 can reduce stress generated during heating. For example, the ratio of the total thickness of the platinum (Pt) layer and the titanium (Ti) layer to the thickness of the gold (Au) layer may be 1% to 60%. This thickness ratio reduces peeling of the comb-shaped electrodes 133, 134 from the temperature-sensitive layer 12.

[0030] The cross-sectional shape of each of the comb-tooth electrodes 137, 138 in the comb-tooth electrodes 133, 134 parallel to the XZ plane or the YZ plane may also be substantially rectangular. Alternatively, the cross-sectional shape of the comb-tooth electrodes 137, 138 may be substantially trapezoidal. With such a shape, the contact area between the comb-tooth electrodes 133, 134 and the protective film 14 increases. As a result, the possibility of peeling off of the protective film 14 is reduced.

[0031] The comb-tooth electrodes 133, 134 may be entirely covered with the protective film 14. When the comb-tooth electrodes 133, 134 are covered with the protective film 14, the upper layer of the comb-tooth electrodes 133, 134 located on the +Z side may be made of titanium (Ti). When the upper layer of the comb-tooth electrodes 133, 134 is made of titanium (Ti), the adhesion between the comb-tooth electrodes 133, 134 and the protective film 14 is improved. When the protective film 14 is made of silicon dioxide, titanium (Ti) tends to react with oxygen in the silicon dioxide to form titanium oxide. Therefore, the bond between titanium oxide and silicon dioxide is strengthened, reducing the possibility that the protective film 14 will peel off from the comb-tooth electrodes 133, 134 due to heat.

[0032] The protective film 14 is an insulating film and may be made of silicon nitride, silicon dioxide, or the like. While FIGS. 4A and 4B show the comb-shaped electrodes 133 and 134 covered with the optically transparent protective film 14, the protective film 14 does not need to be optically transparent. The thickness of the protective film 14 may be 10 nm or more and 500 nm or less. The protective film 14 can reduce thermal warping of the insulating substrate 11. Furthermore, even if conductive adhesive or the like protrudes from the electrode pads and spreads onto portions of the comb-shaped electrodes 137 and 138 when mounting the thin-film thermistor 10 in the package 30, the presence of the protective film 14 can reduce the risk of short-circuiting. The unevenness of the protective film 14 on the +Z side may be affected by the unevenness of the temperature-sensitive layer 12 and the electrode layer 13. The unevenness of the protective film 14 is measured at any cross section along the ±Z direction of the thin-film thermistor 10. For example, the thickness of the protective film 14 may be expressed as a value [%] obtained by dividing the difference Sz in the Z component between the position furthest on the +Z side and the position furthest on the −Z side at a magnification of, for example, 500,000 times, the field of view of the surface of the protective film 14 in a scanning transmission electron microscope (STEM), by the thickness of the protective film 14. The unevenness of the protective film 14 may be calculated by dividing the size of the unevenness by the average electrode thickness measured at the thickest and thinnest points on the STEM cross section, and the ratio may be, for example, 5% or more, 10% or more, or 15% or more. On the other hand, the unevenness of the protective film 14 may be 50% or less, 30% or less, or 20% or less.

[0033] As shown in the plan view of Figure 4B, another example of a thin-film thermistor 10a has an electrode layer 13a on a temperature-sensitive layer 12. The electrode layer 13a includes connection electrodes 131a and 132a at both ends and two comb-shaped electrodes 133a and 134a. The connection electrodes 131a and 132a have the same positional relationship with respect to the temperature-sensitive layer 12, structure, and function as the connection electrodes 131 and 132 described above, so a detailed description will be omitted. Also, the protective film 14 is not shown in this plan view.

[0034] The comb-shaped electrode 133a is connected to the connection electrode 131a and the temperature-sensitive layer 12, and the comb-shaped electrode 134a is connected to the connection electrode 132a and the temperature-sensitive layer 12. The comb-shaped electrode 133a has a current collecting portion 135a and a comb-shaped electrode 137a. The current collecting portion 135a may be located closer to the center of the thin-film thermistor 10a than the connection electrode 131a in the X direction, i.e., on the -X side, in a plan view, and extend in the Y direction parallel to the connection electrode 131a. The current collecting portion 136a may be located closer to the center of the thin-film thermistor 10a than the connection electrode 132a in the X direction, i.e., on the +X side, in a plan view, and extend in the Y direction parallel to the connection electrode 132a.

[0035] A plurality of comb-tooth electrodes 137a may extend in parallel in the −X direction from the current collecting portion 135a. A plurality of comb-tooth electrodes 138a may extend in parallel in the +X direction from the current collecting portion 136a. The comb-tooth electrodes 137a and 138a extend in the X direction alternately at appropriate intervals in the Y direction.

[0036] The cross-sectional shape of the current collecting portions 135a, 136a parallel to the YZ plane may be substantially trapezoidal. Alternatively, the cross-sectional shape of the current collecting portions 135a, 136a may be substantially rectangular. This shape increases the contact area between the current collecting portions 135a, 136a and the protective film 14, reducing the possibility of peeling of the protective film 14. The length S2 of the current collecting portions 135a, 136a in the Y direction on the side connected to the connection electrodes 131a, 132a may satisfy, for example, 0.1 × S1 ≦ S2 ≦ 6 × S1, or S1 = S2, where S1 is the length S1 of the connection electrodes 131a, 132a in the Y direction. On the side connected to the comb-tooth electrodes 137a, 138a of the current collecting portions 135a, 136a, the tip of the comb tooth of the comb-tooth electrode 137a located furthest to the +Y side may face the current collecting portion 136a in the −X direction, unlike the shape shown in FIG. 4A . Furthermore, the tip of the comb tooth of the comb-tooth electrode 138a located furthest on the -Y side may face the current collecting portion 135a in the +X direction. This structure reduces the disturbance in the voltage distribution in the temperature-sensitive layer 12 near the tips of the comb teeth located at both ends in the Y direction of the thin-film thermistor 10, thereby making the resistance value of the temperature-sensitive layer 12 more stable. Therefore, the length S3 of the side of the current collecting portions 135a, 136a connected to the comb-tooth electrodes 137a, 138a may be equal to or greater than the overall width of the comb-tooth electrodes 137a, 138a in the Y direction. Here, the overall width is expressed as (the distance between adjacent comb teeth + the width of the comb-tooth electrode) x the total number of comb teeth.

[0037] The width of the comb-tooth electrodes 137a, 138a in the Y direction may be 0.3 μm or more and 10.0 μm or less. The total length of the comb-tooth electrodes 133a, 134a may be 1,000 μm or more and 40,000 μm or less, or 4,000 μm or more and 10,000 μm or less. Here, the total length is the sum of the lengths of the multiple comb-tooth electrodes 137a, 138a in the X direction. The lengths of the comb-tooth electrodes 137a, 138a may be equal. Alternatively, the lengths of the comb-tooth electrodes 137a, 138a may differ by one tooth. Alternatively, the lengths of the comb-tooth electrodes 137a, 138a may differ by a length shorter than one tooth. The total length is calculated by multiplying the comb tooth length, which is the length of each comb-tooth electrode 137a, 138a in the X direction, by the total number of comb-tooth electrodes 137a, 138a. Furthermore, if the distance between the tip of comb-tooth electrode 137a and final current portion 136a and the distance between the tip of comb-tooth electrode 138a and final current portion 135a are each defined as d2, then distance d2 may be d2 > d1 or d2 = d1, relative to the distance d1 between adjacent comb-tooth electrodes 137a and 138a in the X direction. When d2 = d1, the cross-sectional area of ​​the current path in temperature-sensitive layer 12 that flows between comb-tooth electrodes 133a, 134a at distance d1 = d2 increases compared to the overall length of comb-tooth electrodes 133a, 134a. In other words, as the current path in the temperature-sensitive layer 12 increases, the effective overall length of the comb-tooth electrodes 137a and 138a increases by (N-2), which is the sum of the width d3 of each comb tooth in the Y direction and twice the distance d1, minus the two teeth at both ends, from the total number N of comb teeth, and by two teeth, which is the sum of the width of each comb tooth and the distance d1, i.e., (d3 + d1 × 2) × (N-2) + (d3 + d1) × 2. In a comb-tooth configuration with a large number of comb-tooth electrodes 137a and 138a, the cross-sectional area of ​​the current path equivalent to the current path between the comb-tooth electrodes 137a and 138a increases particularly effectively. Therefore, the overall length of the comb-tooth electrodes 137a and 138a in the X direction can be uniformly shortened. Furthermore, it is possible to reduce the number of comb-tooth electrodes 137a and comb-tooth electrodes 138a required for the resistance value of the thin film thermistor 10. Therefore, even if a film with a higher resistivity is used for the temperature-sensitive layer 12, the thin film thermistor 10 can be designed with a more compact comb-tooth region than before.The number of comb-tooth electrodes 137a, 138a may be different from the number shown in the figure. For example, the total number of comb-tooth electrodes 137a, 138a may be 2 or more and 1,000 or less, or 20 or more and 300 or less. The resistance value of the thin-film thermistor 10 is determined depending on the total number of comb-tooth electrodes 137a, 138a. To obtain a desired resistance value of the thin-film thermistor 10, the total number can be appropriately designed depending on the resistivity of the temperature-sensitive layer 12. The cross-section of the comb-tooth electrodes 137a, 138a perpendicular to the X-axis may be approximately trapezoidal. In this case, the width of the side of the comb-tooth electrodes 137a, 138a that contacts the temperature-sensitive layer 12 is larger than the width of the side opposite the temperature-sensitive layer, thereby reducing peeling of the comb-tooth electrodes 137a, 138a from the temperature-sensitive layer 12.

[0038] Furthermore, the distance between each tip of comb-tooth electrode 137a and current collecting portion 134a may be equal to each other, and this distance may also be equal to the distance between each tip of comb-tooth electrode 138a and current collecting portion 133a. Regarding comb-tooth electrodes 133a, 134a and current collecting portions 135a, 136a, configurations, structures, materials, etc. not described above may be the same as those described for comb-tooth electrodes 133, 134 and current collecting portions 135, 136.

[0039] In this thin-film thermistor 10, the temperature-sensitive layer 12 electrically connecting the interdigital electrodes 133 and 134 must have a resistivity that changes with temperature with good sensitivity and precision. For example, the B constant, i.e., the logarithmic ratio of the resistivity ratio Rb / Ra to the rate of change (1 / Tb-1 / Ta) of temperature Tb [K] from temperature Ta [K] (ln(Rb / Ra)) / ((1 / Tb)-(1 / Ta))), is desirably within an appropriate range. For example, in the range of 25°C to 50°C, the thin-film thermistor 10 may have a B constant of 3500 K or more, or 4000 K or more. Furthermore, the B constant may be 7000 K or less, or 6000 K or less. The activation energy of the resistivity may be 0.3 eV to 0.6 eV.

[0040] In such a thin-film thermistor 10, zinc (Zn) is expected to be included in the temperature-sensitive layer 12 as in the prior art to increase the B constant. However, when a film containing zinc (Zn) is subjected to heat treatment after deposition, the lattice constant of the film shortens, making the thin-film thermistor 10 prone to peeling at the interface with the substrate. Through research, the inventors discovered that the occurrence of peeling can be reduced by appropriately combining the crystallinity of the insulating substrate 11 with the crystallinity of the temperature-sensitive layer 12. By appropriately combining the crystallinity of the insulating substrate 11 with the crystallinity of the temperature-sensitive layer 12, the film strain of the temperature-sensitive layer 12 is reduced. Film strain is strain caused by non-uniform deformation of the lattice associated with the crystal structure, i.e., lattice strain. Such film strain may be determined by the half-width of the peak in X-ray diffraction. The half-width may be obtained, for example, by fitting a diffraction intensity profile to a predetermined function using the Whole Pattern Fitting (WPF) method. In one embodiment, the film strain of the temperature-sensitive layer 12 is set to 0.40% or less, thereby reducing peeling without decreasing the B constant. The lower limit of the film strain of the temperature-sensitive layer 12 may be within a range that is feasible in manufacturing.

[0041] The crystallinity of the temperature-sensitive layer 12 can be adjusted, for example, by the deposition temperature of the temperature-sensitive layer 12 and the composition ratio of each component. In one embodiment, the atomic composition of the temperature-sensitive layer 12 may be, for example, 11 atm%≦x≦19 atm%, 18 atm%≦y≦36 atm%, and 0.1 atm%≦z≦13 atm%. "Atm%" represents the atomic composition percentage. The atomic composition percentage z of zinc (Zn) may be 10 atm% or less, 5 atm% or less, 3 atm% or less, or 2 atm% or less. For example, the atomic composition percentage z may be approximately 1.0 atm%. As described below, by making the atomic composition percentage z of zinc smaller than x and y, the resistivity of the film can be reduced, allowing the thin-film thermistor 10 to be miniaturized. The atomic composition percentage w represents the amount of other transition metals, rare earth elements, and carbon (C), nitrogen (N), hydrogen (H), argon (Ar), and other elements that may be present during the manufacturing process. The amount of the elements may be in the range of 0 atm%≦w≦5 atm%. ２ O ４Cobalt (Co), manganese (Mn), and zinc (Zn) occupy the A site, while manganese (Mn) and cobalt (Co) occupy the B site. Zinc (Zn) is thought to occupy the A site as a divalent ion. Manganese (Mn) and cobalt (Co) are also thought to occupy the A site as divalent ions and the B site as trivalent ions (Reference: Eiji Muromachi, "Inorganic Chemistry of Oxides: Crystal Structure and Phase Equilibrium (Materials Textbook Series)," Uchida Rokakuho, 2018). The ionic radius of divalent zinc (Zn) is smaller than that of divalent manganese (Mn). Therefore, increasing the amount of zinc (Zn) and decreasing the amount of manganese (Mn) reduces the lattice constant, increasing the film resistivity. This, in turn, increases film strain, making the film more susceptible to thermal peeling and reducing thermal stability. By setting the lattice constant to 8.22 Å or more and 8.33 Å or less to reduce exfoliation of amorphous silicon dioxide, hopping conduction of carriers flowing between manganese Mn ions becomes easier. This leads to simultaneous achievement of three properties: film resistivity of 20 kΩ cm or less, thermal stability, and sensitivity. The lattice constant may be calculated from peaks obtained by XRD measurement, or may be determined from a TEM diffraction pattern.

[0042] On the other hand, the surface of the insulating substrate 11 may be adjusted to appropriately adjust the crystallinity of the temperature-sensitive layer 12 of the insulating substrate 11. In particular, when the surface of the insulating substrate 11 has high crystallinity, the temperature-sensitive layer 12, which has a thickness of several hundred nanometers or less, tends to be more easily constrained by the crystalline structure and crystalline planes of the substrate, resulting in a film with large film strain and therefore prone to peeling. Therefore, in one embodiment, the thin-film thermistor 10 may have an amorphous silicon dioxide layer on the surface of the insulating substrate 11. This reduces the film strain of the temperature-sensitive layer 12, reducing the occurrence of peeling while allowing the temperature-sensitive layer 12 to achieve a high B constant, particularly a value of 3500 K or higher. Furthermore, to ensure compatibility with the amorphous silicon dioxide layer, the composition of manganese, cobalt, zinc, oxygen, and other impurities may be adjusted, or the film formation temperature may be adjusted, to determine the crystalline structure of the film so that the lattice constant is 8.22 Å or more and 8.33 Å or less.

[0043] 5A and 5B are flowcharts showing the steps of a method for manufacturing a thin-film thermistor 10. In the first example manufacturing process shown in FIG. 5A, an insulating substrate 11 having an insulating film 112, which is an amorphous silicon dioxide layer, on its surface is first obtained (P1). This insulating substrate 11 may be obtained, for example, by thermally oxidizing the surface of a silicon substrate. The obtained insulating substrate 11 is placed in a chamber of a sputtering device. Note that to reduce the possibility of the substrate cracking during transportation, the thickness of the substrate may be adjusted by grinding to several hundred μm, for example, 525 μm, in (P8) described below.

[0044] Manganese, cobalt, and zinc are set as targets in the chamber of the sputtering device (P2). Alternatively, the set targets may contain an alloy of two or more of manganese, cobalt, and zinc. A gas containing oxygen is introduced into the chamber of the sputtering device (P3). Components other than oxygen may be various inert gases typically used in sputtering. The oxygen concentration may be, for example, about 20%.

[0045] The sputtering device is operated to apply a voltage to perform sputtering, thereby forming a temperature-sensitive layer 12 containing each component of the target and oxygen on the surface of the insulating substrate 11 (P4). The applied voltage and the frequency of the AC voltage in RF sputtering may vary depending on the target. At this time, the deposition temperature of the temperature-sensitive layer 12 is set within a range of 300°C to 680°C. During deposition, the sputtering device may be capable of rotating the insulating substrate 11 around an axis perpendicular to the surface on which the temperature-sensitive layer 12 is formed.

[0046] An electrode layer 13 including comb-shaped electrodes 133 is formed on the formed temperature-sensitive layer 12 (P5). Each electrode of the electrode layer 13 may be formed by any method. For example, an electrode pattern may be formed on the temperature-sensitive layer 12 using photoresist, a metal thin film may be formed by vapor deposition or sputtering, and then lift-off may be performed to form each electrode. Alternatively, each electrode may be formed by printing or coating directly on the temperature-sensitive layer 12.

[0047] A protective film 14 is formed (P6). As described above, the protective film 14 may be a silicon dioxide film or a silicon nitride film. The silicon dioxide film may be obtained by, for example, CVD (chemical vapor deposition), sputtering, or evaporation. Alternatively, the protective film 14 may be obtained by other methods.

[0048] The connection pads 131 and 132 are formed (P7). A photoresist pattern may be formed in which the resist is left on the protective film 14 except where the connection pads 131 and 132 are to be formed, and no resist is left in the locations where the connection pads 131 and 132 are to be formed. After that, the protective film 14 located at the window positions of the photoresist pattern may be removed by dry etching, and a metal thin film for the connection pads may be formed by vapor deposition or sputtering. The resist is removed by lift-off, and the connection pads 131 and 132 are obtained.

[0049] The thickness of the substrate is reduced (P8). After a protective tape is attached to the surface of the substrate on which the temperature-sensitive layer 12 is formed, the rear surface opposite to the surface on which the temperature-sensitive layer 12 is formed may be ground by back grinding.

[0050] The substrate is cut (P9). For example, the substrate may be cut by stealth dicing. Specifically, while the protective tape is attached in step P8, a laser is irradiated from the back side of the substrate to create a cut, and then protective tape is attached to the back side of the substrate, which is expanded and divided along the cut. Alternatively, the substrate may be cut to the desired size by blade dicing. The thin-film thermistor obtained in this manner may be mounted on the target piezoelectric device 1 or the like (P10).

[0051] 5B, in the manufacturing process of the second example, process P2 of the manufacturing process of the first example is changed to process P2a, and process P3 is changed to process P3a. The other processes are the same in the first and second examples, so detailed explanations will be omitted.

[0052] After step P1, three types of targets, each of which is an oxide of at least one of manganese, cobalt, and zinc, are set as targets in the chamber of the sputtering apparatus (P2a). All of the three types of targets set may be oxides. Alternatively, the set targets may include an alloy containing two or more of manganese, cobalt, and zinc, and this alloy may be a metal oxide. Next, a gas is introduced into the chamber (P3a). The gas may be a commonly used inert gas such as argon. Unlike the above-mentioned step P3, the gas does not necessarily contain oxygen. Then, the process proceeds to step P4.

[0053] The thin-film thermistor 10 manufactured in the above manner has a film strain of the temperature-sensitive layer 12 in the range of 0.40 or less. Meanwhile, the B constant of the thin-film thermistor 10 is 3500 K or more. Furthermore, in this embodiment, the resistivity of the thin-film thermistor 10 between 25°C and 50°C does not change significantly before and after heat treatment. For example, the change in the B constant between 25°C and 50°C before and after heat treatment may be 2% or less.

[0054] As described above, the thin-film thermistor 10 of this embodiment includes an insulating substrate 11, a temperature-sensitive layer 12 located above the +Z side surface of the insulating substrate 11, and an electrode layer 13 including two comb-shaped electrodes 133, 134 connected to the temperature-sensitive layer 12. The temperature-sensitive layer 12 contains a metal oxide including manganese, cobalt, and zinc, and has a film strain of 0.40% or less. Thus, the thin-film thermistor 10 contains zinc and has small film strain. This strengthens the adhesion between the temperature-sensitive layer 12 and the insulating substrate 11, making them less likely to peel. Furthermore, the thin-film thermistor 10 can achieve a sensitivity with a B-constant of 4000 K or higher. Therefore, the thin-film thermistor 10 can achieve both a stable structure and high sensitivity.

[0055] The metal oxide is Mn ｘ Co ｙ Zn ｚ O （１－ｗ－ｘ－ｙ－ｚ）(11 atm%≦x≦19 atm%, 18 atm%≦y≦36 atm%, 0.1 atm%≦z≦13 atm%). When the temperature-sensitive layer 12 has such a component ratio, the thin-film thermistor 10 has a stable structure and its film distortion falls within a preferred range.

[0056] The temperature-sensitive layer 12 may have a cubic spinel crystal structure, and the lattice constant of the crystal structure may be 8.22 Å or more and 8.33 Å or less. By having the lattice constant in this range, the resistivity of the temperature-sensitive layer 12 can be reduced, the heat resistance of the temperature-sensitive layer 12 can be increased, and changes in the B constant due to heat treatment can be reduced.

[0057] The insulating substrate 11 may also have an insulating film 112 made of an amorphous silicon dioxide layer on the surface on the +Z side. The thickness of this insulating film 112 may be 0.1 μm or more. If the crystal orientation of the insulating substrate 11 is too uniform, the crystal structure of the thin temperature-sensitive layer 12 is constrained by this crystal orientation, resulting in increased film distortion. By having the insulating substrate 11 have an amorphous silicon dioxide layer as the insulating film 112 on the surface that contacts the temperature-sensitive layer 12, the above-mentioned constraints on the crystal structure of the temperature-sensitive layer 12 are reduced. This stabilizes the bond between the temperature-sensitive layer 12 and the insulating substrate 11 and improves the heat resistance of the temperature-sensitive layer 12. This results in a more stable structure for the thin-film thermistor 10.

[0058] The temperature-sensitive layer 12 may also have a B-constant of 3500 K or more and 7000 K or less in the temperature range of 25° C. or more and 50° C. or less, and a resistivity of 20 kΩcm or less at 25° C. Furthermore, the resistivity of 10 kΩcm or less at 25° C. As described above, the temperature-sensitive layer 12 contains zinc and has small film strain, and thus has these characteristics, so that the thin-film thermistor 10 simultaneously achieves three properties: low resistance, stable structure, and high sensitivity.

[0059] The electronic device of this embodiment may also include the above-described thin film thermistor 10. This allows the electronic device to acquire temperature information using a thermistor with high sensitivity and a stable structure.

[0060] In addition, in the method for manufacturing a thin-film thermistor according to this embodiment, the insulating substrate 11 has an insulating film 112, which is an amorphous silicon dioxide layer, on its surface. The temperature-sensitive layer 12 is then formed on the insulating substrate 11, particularly on the insulating film 112, by sputtering using a target containing manganese, cobalt, and zinc and introducing an oxygen-containing gas, or by sputtering using a target containing manganese, cobalt, and zinc, with at least one of the manganese, cobalt, and zinc being an oxide. The film formation is performed at a temperature in the range of 300°C to 680°C. This manufacturing method allows for the production of a thin-film thermistor 10 with small film distortion and a large B constant, without requiring complex procedures. In other words, a thin-film thermistor 10 with both a stable structure and high sensitivity is obtained.

[0061] The above embodiment is merely an example, and various modifications are possible. For example, the resistivity of the temperature-sensitive layer 12 of the thin-film thermistor 10 does not necessarily have to be less than 20 kΩcm. Also, the B constant may be greater than 7000 K.

[0062] Furthermore, the amorphous silicon dioxide layer in the insulating substrate 11 does not have to be obtained by subjecting the surface of a silicon substrate to thermal oxidation treatment.

[0063] The temperature-sensitive layer 12 may also have a structure that deviates from the cubic spinel crystal structure.

[0064] Although the above example shows a piezoelectric device 1 equipped with a thin-film thermistor 10, the thin-film thermistor 10 may also be used in other electronic devices. Examples of electronic devices include a heat sensor that detects heat generated by an IC (integrated circuit) or a cutting tool. The specific details of the structure, configuration, materials, size, etc. shown in the above embodiment may be modified as appropriate without departing from the spirit of this disclosure. The scope of the present invention includes the scope of the invention set forth in the claims and their equivalents.

[0065] [Example] Figure 6 is a table showing the measurement results of the characteristics of the thin film thermistor 10 manufactured using the above-mentioned manufacturing method. Manufacturing parameters include the film formation temperature, film thickness, annealing temperature, and component ratio. As described above, the characteristics evaluated are the B constant, resistivity, and film strain. Furthermore, as a characteristic of the spinel crystal structure, the lattice constant can be obtained from the spacing between multiple peaks obtained by X-ray diffraction. In the X-ray diffraction, X-rays were incident on the temperature-sensitive layer at an incident angle of 0.5 degrees. The B constant was calculated using the following equation 1 using the resistance values ​​(Ra, Rb) when the temperature Ta was 25°C and the temperature Tb was 50°C.

[0066] B=ln(Rb / Ra) / (1 / (273.15+Tb)-1 / (273.15+Ta))... (Formula 1)

[0067] The resistance value was obtained by measuring the current value when a voltage of 1.5 V was applied using a two-terminal method with a digital multimeter (3457A MULTIMETER manufactured by Hewlett-Packard) connected to a four-probe cable (SR4-SS manufactured by Asteratec Co., Ltd.) with a probe spacing of 1 mm and an RCF coefficient of 8.3. The resistivity of the temperature-sensitive layer was determined by multiplying this resistance value by the film thickness of the temperature-sensitive layer, the RCF coefficient, and 0.0903. Here, 0.0903 is a coefficient used to convert the resistance value measured by the two-terminal method to the resistance value measured by the four-terminal method relative to the RCF coefficient. Temperature control at 25°C and 50°C was performed by placing the substrate on a temperature-control plate (Cool Plate SCP-85 manufactured by AS ONE Corporation).

[0068] As described above, the unevenness of the temperature-sensitive layer is measured at any cross section along the ±Z direction of the thin-film thermistor. Using a scanning transmission electron microscope (STEM), the difference Sz in the Z component between the position furthest on the +Z side and the position furthest on the −Z side at the interface is measured at a magnification of, for example, 500,000 times, within a field of view that includes the interface between the temperature-sensitive layer and the electrode layer. The magnitude of the unevenness is expressed as the value [%] obtained by dividing the difference Sz by the measured thickness of the temperature-sensitive layer. The film thickness of the temperature-sensitive layer is determined by X-ray reflectometry (XRR). The unevenness of the electrode layer and the protective layer is measured using the same procedure as the unevenness of the temperature-sensitive layer, except for the setting of the field of view. The thickness of the electrode layer is measured using a STEM cross section at a magnification of, for example, 500,000 times, within a field of view that includes the entire thickness of the electrode layer. The film thickness of the protective layer is measured using a STEM cross section at a magnification of, for example, 500,000 times, within a field of view that includes the entire thickness of the protective layer.

[0069] In the peelability test, a thin-film thermistor with a comb-shaped electrode formed on a temperature-sensitive film as shown in Figure 4B was used. A UV-curable backgrind surface protection tape was attached to the temperature-sensitive film, and ultraviolet light was irradiated. After that, when the protection tape was peeled off, it was visually confirmed whether the temperature-sensitive film peeled off from the insulating substrate. Lintec's Adwill E series protection tape was used.

[0070] For the thin-film thermistors of each example and comparative example, a thermosensitive film was fabricated on a substrate having an amorphous silicon dioxide layer formed by thermal oxidation using a combination of DC sputtering and RF sputtering. Sputtering involved the use of 2-inch targets of manganese, cobalt, and zinc, respectively, and the deposition was performed under argon gas containing 20% ​​oxygen, with the component ratios described for each example. The electrode structure shown in Figure 4B was formed on the thermosensitive film. Specifically, the electrode length, which is the length of one comb tooth, was 159 μm, and there were a total of 34 comb-tooth electrodes. The distance d2 between the tip of the comb-tooth electrode and the current collecting portion was 5 μm. The cross section of the comb-tooth electrode along its width direction was approximately trapezoidal, with the width on the thermosensitive layer side being 2000 to 2250 nm and the width on the protective film side being 1950 to 2000 nm. The current collecting portion is approximately rectangular in plan view, with a length in the X direction of 35 μm, and lengths in the Y direction of 233 μm (length S3) and 210 μm (length S2). The electrode pad has a length S1 in the Y direction of 210 μm and a length in the X direction of 60 μm. An electrode layer is formed having comb-tooth electrodes with a distance d1 between adjacent comb-tooth electrodes of 5 μm, and a silicon dioxide protective film is further formed to cover the comb-tooth electrodes. Multiple thin-film thermistors formed on the substrate were thinned to a thickness of 50 μm by back-grinding, and then individually diced into thin-film thermistors measuring 0.3 mm x 0.4 mm in plan view by stealth dicing.

[0071] In Comparative Example 1, the temperature-sensitive layer was formed at room temperature (25°C). In Comparative Example 2, the temperature-sensitive layer was formed at room temperature and then annealed in air at 700°C. It can be seen that in Comparative Example 1, the film resistivity was low, but the B constant was low and the film strain was large. On the other hand, in Comparative Example 2, the B constant was improved, but the film strain was large, meaning that the temperature-sensitive layer was prone to peeling from the substrate, as shown by the results of the peeling test. As a result, the thin-film thermistor had low heat resistance and the B constant changed significantly after heating. Furthermore, annealing increased the resistivity of the temperature-sensitive layer at 25°C. Furthermore, the unevenness of the temperature-sensitive layer was small, at around 2.0%, and the electrode layer peeled off from the temperature-sensitive layer during annealing by heating.

[0072] On the other hand, in Examples 1 to 4, the film formation temperature was set within the range of 300-680°C. This resulted in a B-constant of 3500K or higher and a film strain of 0.40 or less. Accordingly, as shown by the results of the peeling test, the temperature-sensitive layer was less likely to peel off from the insulating substrate. Specifically, the following applies: (1) The lattice constant was 8.22 Å to 8.33 Å. (2) The resistivity was 10 kΩcm or less. (3) The change in the B-constant due to heating, expressed as the rate of change ΔB / Ba × 100 [%] of the difference between the B-constant Ba before heating and the B-constant Bb after heating at 300°C for 40 minutes, is 4% or less. These factors improved the thermal resistance of the thin-film thermistor. Furthermore, in Examples 1 and 4, the temperature-sensitive layer had an unevenness of 5% or more. This affected the peeling of the electrode layer from the temperature-sensitive layer.

[0073] Furthermore, in Examples 1, 2, and 4, the zinc component ratio was reduced compared to Example 3, to 10 atm% or less, approximately 1 atm%. This allowed the lattice constant to be increased to a certain extent, further reducing the resistivity of the film. By reducing the resistivity of the film, it became possible to simplify the pattern of the comb-tooth electrodes, and the thin-film thermistor could also be made smaller. It was also found that the thermal resistance was improved. Note that if the temperature-sensitive layer contains components other than manganese, cobalt, zinc, and oxygen, the lattice constant may also change due to the influence of these other components.

[0074] Thus, the thin film thermistor of this embodiment is able to achieve both good sensitivity, as indicated by a B-constant of 3500 K or higher, particularly 4000 K or higher, and reduced peeling due to a film strain of 0.40 or lower. Furthermore, the thin film thermistor has higher heat resistance than conventional thin film thermistors, and can also have a lower resistivity at 25° C. The above tendency was also obtained when an insulating substrate having an amorphous silicon dioxide layer on the surface of a quartz glass substrate was used instead of the insulating substrate having an amorphous silicon dioxide layer on the surface of a silicon substrate as described above.

[0075] The present disclosure can be utilized in thin film thermistors, electronic devices, and methods for manufacturing thin film thermistors.

[0076] REFERENCE SIGNS LIST 1 Piezoelectric device 10 Thin film thermistor 11 Insulating substrate 111 Silicon substrate 112 Insulating film 12 Temperature sensitive layer 13 Electrode layer 131, 132 Connection electrodes 133, 134 Comb-shaped electrodes 14 Protective film 20 Piezoelectric vibration element 201 Crystal blank 211, 212 Mounting electrode 221 Excitation electrode 30 Package 30a Recess 30b Cavity 311, 312 Electrode pads 320, 340 Bonding member 331, 332 Electrode pads 40 Lid

Claims

1. A thin film thermistor having an insulating substrate, a temperature-sensitive layer located on a first surface of the insulating substrate, and an electrode layer including two electrodes connected to the temperature-sensitive layer, wherein the temperature-sensitive layer contains a metal oxide including manganese, cobalt, and zinc and has a film strain of 0.40% or less.

2. The metal oxide is Mn ｘ Co ｙ Zn ｚ O （１－ｗ－ｘ－ｙ－ｚ） The thin film thermistor according to claim 1, which is represented by (11 atm% ≤ x ≤ 19 atm%, 18 atm% ≤ y ≤ 36 atm%, 0.1 atm% ≤ z ≤ 13 atm%).

3. The thin film thermistor according to claim 1 or 2, wherein the metal oxide has a cubic spinel crystal structure and a lattice constant of the cubic spinel crystal structure is 8.22 Å or more and 8.33 Å or less.

4. The thin film thermistor according to any one of claims 1 to 3, wherein the insulating substrate has an amorphous silicon dioxide layer along the first surface, and a thickness of the amorphous silicon dioxide layer is 0.1 µm or more.

5. The thin film thermistor according to any one of claims 1 to 4, wherein in a temperature range of 25°C or more and 50°C or less, the B constant is 3500 K or more and 7000 K or less, and a resistivity at 25°C is 20 kΩcm or less.

6. An electronic device including the thin film thermistor according to any one of claims 1 to 5.

7. A method for manufacturing a thin film thermistor having an insulating substrate, a temperature-sensitive layer located on a first surface of the insulating substrate, and an electrode layer including two electrodes connected to the temperature-sensitive layer, wherein the surface of the insulating substrate has an amorphous silicon dioxide layer, and the temperature-sensitive layer is formed on the insulating substrate by sputtering including manganese, cobalt, and zinc in a target and introducing a gas containing oxygen, or by sputtering including manganese, cobalt, and zinc in a target and at least one of the manganese, cobalt, and zinc being an oxide, and the film formation is performed in a range of 300°C or more and 680°C or less.

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