JP2788500B2 - Positive characteristic thin film thermistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a positive characteristic (hereinafter referred to as a PTC characteristic) thermistor (PTC characteristic) in which the electric resistance value increases remarkably above the Curie temperature.
More specifically, the present invention relates to a PTC thermistor in which a barium titanate-based composition is in a thin film state.

[Conventional technology]

Conventionally, a rare earth element such as Y or a transition metal element such as Nb or Ta is added to barium titanate, and the
In a semiconductor ceramic material fired at a temperature of 00 ° C., the electric resistance value suddenly increases at the Curie point, so-called
It is known to exhibit PTC characteristics. A heater, a temperature sensor, and the like utilizing this characteristic have been manufactured. Further, the Curie point can be shifted to a lower temperature side by partially replacing the Ba site with Sr. On the other hand, by replacing with Pb, the Curie point can be shifted to the high temperature side, and -30 ° C to 30 ° C.
It can be changed arbitrarily to some extent in the range of 0 ° C.

However, conventional PTC thermistors are available only in the form of thick films, and have responded to the demand for lower resistance by increasing the area. Therefore, if the thickness of the PTC thermistor can be reduced, a large area is not required, and the element can be reduced in size. In addition, since the operating voltage and the operating current can be set small with the reduction in resistance due to the thinning, a great expansion of practical applications can be expected.

Methods for thinning PTC thermistors include vapor deposition, sputtering, ion plating, plasma CVD, optical CVD, and thermal CV, which are commonly known as thin film production methods.
Although various methods such as the D method can be applied, the present inventors applied a sol-gel method using a metal alkoxide,
We have found that it is possible to reduce the thickness of the C thermistor, and made a proposal in Japanese Patent Application No. 63-282512.

[Problems to be solved by the invention]

However, when we try to obtain a barium titanate-based thin film from a metal alkoxide by the sol-gel method, the stability of the metal alkoxide in the solution is affected by, among other things, a very small amount of water, and the solubility deteriorates, causing precipitation. Admitted that there is a problem of generation. If a precipitate is formed, the composition ratio of the constituent metals changes, and if the precipitate is formed too much, PTC characteristics may not be obtained.

[Means for solving the problem]

In the present invention, a compound having chelating ability is used as an additive to increase the stability of the metal alkoxide. Presumably, the formation of a precipitate is suppressed by the metal alkoxide forming a chelate compound with the additive, so that it is possible to obtain PTC characteristics stably.

In particular, metals having low stability in the form of metal alkoxides, such as Ba and Sr, may be used as metal salts.

[Detailed Disclosure of the Invention]

That is, the present invention provides a positive characteristic comprising forming a barium titanate-based thin film from a solution or dispersion of a metal alkoxide or a solution or dispersion of a metal salt containing a compound having chelate-forming ability. A thin film thermistor, preferably containing a compound capable of forming a chelate, by applying a solution or dispersion of a metal alkoxide or a solution or dispersion of a metal salt on a substrate, and sintering the titanium-barium-based thin film. And a thin film thermistor having a positive characteristic formed by forming Ti, Ba, Sr, Si and X (X is Sb,
A thin film thermistor having a positive characteristic using at least one of Y, La, and Dy), and preferably, a compound having a chelate forming ability is a β-diketone or a polycarboxylic acid. It is an abstract.

 Hereinafter, the present invention will be described in detail.

The present invention, as described above, contains a compound capable of forming a chelate, from a solution or dispersion of a metal alkoxide or a solution or dispersion of a metal salt, by forming a barium titanate-based thin film from the positive characteristic thin film thermistor What you get.

In the present invention, the metal forming the barium titanate-based thin film is composed of Ti, Ba, Sr, Si, and X (X is at least one of Sb, Y, La, and Dy), and the composition ratio is Ti atom. When the number is 1 (hereinafter, the amount of metal used is 1
The values when Ba is 1 to 0.5 and Sr are 0 to 0.5
Preferably, Ti / (Ba + Sr) is in the range of 1.002 to 1.015, and Si = 0.0001 to 0.01, Sb, Y, La, and Dy = 0.0001 to 0.01. If desired, Mn
May be added from 0.0001 to 0.001.

By adding Sr complementarily to Ba, the Curie point can be shifted to a lower temperature side. Adding Ti in excess of 0.002 to 0.015 with respect to the sum of Ba and Sr and adding Si in 0.0001 to
Adding 0.01 makes it possible to control the particle size. Further, at least one element of Sb, Y, La, and Dy is set to 0.
By adding 0001 to 0.01, the resistance value at room temperature can be reduced. If desired, steep resistance temperature characteristics can be obtained when Mn is added in the range of 0.0001 to 0.001.

As each metal alkoxide used in the present invention, methoxide, ethoxide, propoxide, isopropoxide, butoxide and the like of the above-defined metal are used, and as the metal salt, an organic acid salt of the above-mentioned metal fatty acid or naphthenic acid is also used. Is used.

In the present invention, a compound having chelating ability is used. Examples of the compound having chelating ability include β-diketones, specifically acetylacetone, trifluoroacetylacetone, hexafluoroacetylacetone, 3-phenylacetylacetone, benzoyltriacetone. Fluoroacetone, furoyltrifluoroacetone,
Pivaloyltrifluoroacetone, thenoyltrifluoroacetone, dibenzoylmethane, dipivaloylmethane, heptafluorobutanoylpivaloylmethane, or a polycarboxylic acid; specifically, oxalic acid, ethylenediaminediacetic acid, ethylenediaminetetracarboxylic acid It is preferable to use acetic acid, diaminopropanoltetraacetic acid, diaminopropanetetraacetic acid, glycol ether diaminetetraacetic acid, iminodiacetic acid, hydroxyethyliminodiacetic acid, nitrilotriacetic acid, and nitrilotripropionic acid.

In the present invention, ethanol, propyl alcohol, isopropyl alcohol, alcohols such as butanol or acetone, chloroform, benzene, toluene, a solvent such as xylene, each of the above metal alkoxide or metal salt is added, and a compound having a chelate-forming ability is further added. 0.0001 to 10 mol, preferably 0.001 to 1 mol, is added as a starting material. Depending on the concentration of each metal alkoxide or metal salt or the amount of the additive, the metal alkoxide or metal salt in the liquid forms colloidal particles, and a dispersion of colloidal particles can be obtained. Does not impair.

The thinning of the barium titanate-based composition can be achieved by applying the solution or dispersion on a substrate, preferably by dip coating or spin coating. The thin film obtained at this time can be fired at a relatively low temperature, for example, at a temperature of about 500 to 1200 ° C. for about 0.5 to 20 hours, and becomes a semiconductor ceramic composed of a barium titanate-based composition.

In the present invention, the substrate is not particularly specified, but relatively inexpensively available Si substrate, SiO ₂ substrate,
An Al ₂ O ₃ substrate or the like is preferably used. When a back electrode is used, a Si substrate having a specific resistance of 0.1 Ωcm or less is suitable.

In the present invention, the minimum film thickness showing PTC characteristics is 0.0
The thickness is about 1 μm, and the maximum film thickness is about 30 μm due to practical limitations such as operability in thinning by the dip coating method or the spin coating method, but the characteristic is preferably 0.05 to 5 μm. In particular, when stable characteristics are to be obtained, a film thickness of 0.1 to 3 μm is most preferable.

(Embodiment)

Hereinafter, embodiments of the present invention, in particular, a specific example of forming a thermistor element will be described with reference to the drawings. As shown in FIG. 1, one side of a low-resistance Si substrate or SiO ₂ substrate 1 is made of Pt or
An electrode composed of the Au layer 2 is formed by vacuum deposition, ion plating, or the like. A thin film is formed on one surface of the substrate by applying a solution or a dispersion of a metal alkoxide or a metal salt containing a compound capable of forming a chelate prepared to a predetermined concentration by a dip coating method or a spin coating method and baking. Thus, a barium titanate-based thin film 3 as a positive temperature coefficient thermistor of the present invention, which is a ceramic semiconductor, is obtained. Further, an electrode 4 of Ni, Pt, Au or the like is formed thereon by the same means as described above to form a PTC thin film thermistor element.

〔Example〕

Further, specific embodiments will be described with reference to examples.

Example 1 Pt was added to a mirror-finished p-Si substrate (specific resistance 0.05 Ωcm).
It was formed by a 1 μm vacuum evaporation method. Then Ti / Ba / Sr / Si / S
Dissolve each isopropoxide in isopropyl alcohol so that b / Mn is 1 / 0.833 / 0.159 / 0.00496 / 0.00198 / 0.000397, and further add acetylacetone as an additive.
A solution in which 0.1 mol was added to Ti was subsequently applied onto Pt by a dip coating method. At a rate of 200 ° C / hr
After the temperature is raised to 800 ° C and left for about 1 hour, the temperature is lowered to room temperature at a rate of 100 ° C / hr. An electrode was formed on the obtained barium titanate-based thin film by Ni vapor deposition. The thickness of the barium titanate-based thin film was 0.1 μm.

By using acetylacetone, which is a compound capable of forming chelate, as an additive, no precipitate was formed in the solution preparation and application steps, and the PTC characteristics as shown in FIG. It was able to be obtained stably.

Example 2 Pt was added to a mirror-finished n-Si substrate (specific resistance 0.01 Ωcm).
It was formed by a 1 μm vacuum evaporation method. Subsequently, Ti / Ba / Sr / Si / La of isopropoxide of each metal was 1 / 0.833 / 0.159 / 0.0019
After dissolving in isopropyl alcohol at a ratio of 8 / 0.00198, 0.3 mol of trifluoroacetylacetone was added to Ti as an additive, and after 20 hours, the solution became a dispersion of colloid particles. This dispersion was applied on Pt by dip coating. The temperature was raised to 800 ° C at a rate of 200 ° C / hr, left for about 1 hour, and then left at 100 ° C / hr.
The temperature is lowered to room temperature. Pt was deposited on the obtained barium titanate-based thin film to form an electrode. The number of coating was three times, and the film thickness was 0.3 μm at that time.

No precipitate was found in the solution preparation and application steps, and even if this method was repeated 10 times, the PT as shown in FIG.
C characteristics could be obtained stably.

Example 3 Au was vapor-deposited at a thickness of 0.2 μm on a SiO ₂ substrate to form a conductive surface on the substrate. Then Ti / Sr / Si / Sb / Mn is 1 / 0.159 / 0.00496 / 0.0019
8 / 0.000397 to obtain isopropoxide and Ti
A solution obtained by dissolving barium stearate with / Ba of 1 / 0.833 in isopropyl alcohol and further adding 0.01 mol of ethylenediaminetetraacetic acid to Ti as an additive was applied on Au by dip coating. The temperature was raised to 800 ° C at a rate of 200 ° C / hr, left for about 1 hour, and then left at 100 ° C / hr.
The temperature is lowered to room temperature. Au was deposited on the obtained barium titanate-based thin film to form an electrode. At this time 10
By a single application, a barium titanate-based thin film having a thickness of 0.8 μm was obtained.

No precipitate was found in the solution preparation and application steps, and even if this method was repeated 10 times, the PT as shown in FIG.
C characteristics could be obtained stably.

(Comparative example)

Pt is applied to a mirror-finished p-Si substrate (resistivity 0.05Ωcm).
It was formed by a 1 μm vacuum evaporation method. Then Ti / Ba / Sr / Si / S
Each isopropoxide was dissolved in isopropyl alcohol so that b / Mn was 1 / 0.833 / 0.159 / 0.00496 / 0.00198 / 0.000397. The solution was applied on Pt by dip coating without adding a compound having chelating ability. This is heated to 800 ° C. at a rate of 200 ° C./hr, left for about 1 hour, and then cooled to room temperature at a rate of 100 ° C./hr. An electrode was formed on the obtained barium titanate-based thin film by Ni vapor deposition. The thickness of the barium titanate-based thin film was 0.1 μm.

A precipitate may be formed during the solution preparation and application steps, and depending on the amount of the precipitate, PTC characteristics may not often be obtained.

(Effects)

In Examples and Comparative Examples, the exposed portion of Pt or Au on which the barium titanate-based composition was not applied on the substrate was used as one electrode, and the upper electrode was used as the other electrode.
Resistance was measured as a function of temperature by using a sandwich electrode using i, Au or Pt, and PTC characteristics were evaluated. As is clear from FIG. 2 showing the results of Examples 1, 2 and 3, typical PTC characteristics were exhibited, and a PTC thin film thermistor could be obtained stably.

Unless a compound having chelate forming ability is added as shown in the comparative example, the characteristics may vary due to the influence of the environment in the solution preparation and coating steps, and PTC characteristics may not be obtained in many cases. There was a problem.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment of the present invention, and FIG.
FIG. 3 is a graph showing the relationship between the temperature and the resistance of the device according to the embodiment of the present invention. In FIG, 1 ...... Si or SiO ₂ substrate, 2 ...... Pt or Au layer, 3 ...... barium titanate-based thin film, 4 ...... Ni,
Shows a Pt or Au electrode.

Continuation of the front page (56) References JP-A-60-182701 (JP, A) JP-A-63-117914 (JP, A) JP-A-58-44339 (JP, A) JP-A-63-215545 (JP) , A) JP-A-2-281601 (JP, A) JP-B-37-8675 (JP, B1) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01C 7/02-7/22

Claims (4)

(57) [Claims] 1. A positive characteristic thin film formed by forming a barium titanate-based thin film from a solution or dispersion of a metal alkoxide or a solution or dispersion of a metal salt containing a compound capable of forming a chelate. Thermistor. 2. A titanium-barium-based thin film is formed by applying a metal alkoxide solution or dispersion or a metal salt solution or dispersion containing a compound capable of forming a chelate on a substrate and baking it. The PTC thin film thermistor according to claim 1. 3. As a metal of a metal alkoxide or a metal of a metal salt, Ti, Ba, Sr, Si and X (X is Sb, Y, La,
The positive characteristic thin film thermistor according to claim 1, wherein at least one of Dy is used. 4. The positive characteristic thin film thermistor according to claim 1, wherein the compound capable of forming a chelate is β-diketone or a polycarboxylic acid.