JP2753653B2 - Moisture sensitive element - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moisture-sensitive element, and more particularly, to a capacitance-type moisture-sensitive element which has excellent heat resistance and has improved temperature characteristics over time.

[Prior art and its problems] Many conventional moisture-sensitive elements detect a change in electric resistance by using ceramic as a moisture-sensitive material, and those that detect a change in electric capacity by using a polymer film as a derivative. It is used.

Among them, those using ceramics have problems such as narrow humidity measurement range and slow response speed,
The one using the polymer film has a wide humidity measurement range of approximately 0 to 100% RH and a high response speed, and is highly practical.

A moisture-sensitive film using this polymer is generally formed by, for example, plasma polymerization while heating the substrate at the time of forming the film (Japanese Patent Application Laid-Open Nos. Sho 62-217153 and 63-217153). -177050, JP-A-2-114166 and others).

Although these plasma polymerized films exhibit excellent moisture-sensitive properties, they have problems such as deterioration of temperature properties when left under high temperature and high humidity, and deterioration of temperature properties over time.

The present invention has been made in view of the above-described conventional circumstances, and an object of the present invention is to provide a moisture-sensitive element having improved temperature characteristics and small change with time.

[Means for Solving the Problems] That is, the present invention provides an insulating substrate, a lower electrode formed on the substrate, a polymer moisture-sensitive derivative thin film formed on the lower electrode, In a moisture-sensitive element, which is formed by sequentially laminating an upper electrode made of a moisture-permeable metal film formed on a substrate, a moisture-sensitive derivative thin film is formed by a plasma polymerization method, and then, in a vacuum of 1 × 10 ⁻⁶ Torr or less. 250 ℃ ~ 500
It is a moisture-sensitive element characterized by being subjected to a heat treatment at a temperature of ℃.

As shown in FIG. 1 showing the structure of an example of a moisture-sensitive element according to the present invention, a lower electrode 2 formed on an insulating substrate 1 and a moisture-sensitive derivative thin film formed on the electrode 2 3 and
And an upper electrode 4 made of a moisture-permeable metal film formed on the thin film 3.

The method of manufacturing the moisture-sensitive element of the present invention is a method for manufacturing a vapor-deposited or sputtered substrate using a corrosion-resistant metal such as Ni, Ta, Cr, Al, NiCr, Au or the like as a lower electrode on a cleaned insulating substrate, such as glass or a polyimide film. To a thickness of 1000 to 5000 Å. Next, if necessary, an insulating layer is formed, and then a polymer moisture-sensitive derivative thin film is formed by a plasma polymerization method. As a method of forming the moisture-sensitive derivative thin film, an aromatic or aliphatic compound already developed by the present applicant may be formed by monomer plasma polymerization (JP-A-2-114166).

Next, the polymer film is subjected to a heat treatment at 250 ° C. or less in a vacuum of 1 × 10 ⁻⁶ Torr or less. For this temperature,
Desirably, the temperature is from 250 to 500 ° C. If the temperature is lower than 250 ° C., the effect of the specific improvement cannot be expected much. If the temperature is higher than 500 ° C., the thickness of the dielectric moisture-sensitive film is remarkably reduced, which is not suitable for practical use. Further, a temperature around 300 to 400 ° C. is more preferable. The heat treatment time is desirably 30 minutes or more. Heat treatment is 1
It may be performed only once, but may be performed in a plurality of cycles.
At this time, it is preferable that the number is about 10 times in view of the balance between the work efficiency and the film improvement. The heat treatment of the moisture-sensitive dielectric thin film may be performed after forming an upper electrode described later.

Next, after taking out the substrate into the atmosphere, an upper electrode made of a moisture-permeable metal film is formed by vacuum evaporation or sputtering. Since the upper electrode is directly exposed to the outside air, it has a corrosion-resistant metal such as NiCr, Cr, Ta, Ni, Au, Pd, Pt.
It is better to use etc.

Next, when the lead wires are soldered by silver paste or ultrasonic soldering or the like and a large number of sensors are formed on one insulating substrate, the insulating substrate is cut.

[Operation] In the present invention, heat treatment in a vacuum is performed as stabilization or modification of the moisture-sensitive dielectric thin film. In the polymer film after film formation, compounds that have not yet reached polymers and remain relatively low molecules, or polymers that remain chemically unstable There are many. Therefore, by applying heat to such a film, low-molecular compounds are evaporated and removed, and desorption of hydrogen from unstable polymers and the like occurs, cross-linking progresses, and it becomes chemically stable. Become. As a result, the moisture-sensitive dielectric thin film becomes a dense polymer film, and the change over time in temperature characteristics is reduced, and the temperature characteristics are also improved.

Example Next, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view of one embodiment of a moisture-sensitive element according to the present invention. A lower electrode 2 made of nichrome (NiCr) is formed on the upper surface of an insulating substrate 1 made of glass to a thickness of about 1000 angstroms by a vacuum deposition method or the like. The body thin film 3 is flatly formed to a thickness of about 1500 angstroms by a plasma polymerization method. The dielectric constant of the moisture-sensitive dielectric thin film 3 changes as a function of the amount of absorbed moisture.

The substrate 1, the lower electrode 2, and the moisture-sensitive dielectric thin film 3
Can be arbitrarily selected according to the purpose.

On the surface (upper surface) of the moisture-sensitive dielectric thin film 3 facing the lower electrode 2, the upper electrode 4 is formed by oblique deposition at an incident angle of 75 ° with respect to the normal to the upper surface of the moisture-sensitive dielectric thin film 3. It is formed at about 400 angstroms.

Such an upper electrode 4 can be formed by a vapor deposition device as shown in FIG.

That is, the material 21 before forming the upper electrode 4 is placed on the support base 23 above the inside of the bell jar 19, and a moisture-sensitive dielectric thin film is formed in the incident angle direction of a vapor deposition material described later. 3 are arranged in a positional relationship such that the direction A is 75 °. The illustration of the support members of the support base 23 is omitted.

On the other hand, below the raw material 21 in the bell jar 19, a nichrome wire 25 as a vapor deposition material wound around the heating filament 27 is arranged, and the bell jar 19 is connected to an exhaust device (not shown).

In such an oblique deposition apparatus, the inside of the bell jar 19 is evacuated to a degree of vacuum of about 5 × 10 ⁻⁶ Torr, and then the filament 27 is evacuated.
To heat and evaporate the nichrome wire 25 on the upper surface of the dielectric thin film 3.
Deposited obliquely at an incident angle of 75 °.

In this embodiment, after forming up to the upper electrode as described above, vacuum heat treatment is performed. For vacuum heating, the same bell jar as used when forming the upper electrode may be used, or another bell jar may be used. FIG. 3 is a schematic configuration diagram of a position used for vacuum heating, in which a support base 34 for holding a moisture-sensitive element material 33 and a tungsten filament 32 for heating are installed in a bell jar 31, and the moisture-sensitive element material 33 is a tungsten filament. It is heated by 32. Material 33 temperature is thermocouple
Measured by 35. Using such a device, 1 ×
The moisture was evacuated to 10 ⁻⁶ Torr or less, and the holding at room temperature and 350 ° C. for 30 minutes was repeated three times to obtain a moisture-sensitive element of the present invention.

In this embodiment, the heat treatment is performed after the formation of the upper electrode. However, the heat treatment may be performed after forming the moisture-sensitive film, and then the upper electrode may be formed.

Next, the time-dependent changes at 40 ° C. of the moisture-sensitive element obtained in this example and the humidity-sensitive element prepared in the same manner as in the example except that the vacuum heat treatment was not performed are shown in FIGS. 4 and 5, respectively. Show. The horizontal axis of these figures is the number of elapsed days (days), and the vertical axis is based on the 0% RH capacity value (C ₀ ) on day 0, and ｛(C _x −
C ₀ ) / C ₀ ｝ × 100 (C _x in the _equation is each measured capacity value), and is a change rate (%) (hereinafter, the change rate is a value calculated by the same equation). In the figure, □ is 0% RH, + is 10% RH, ◇
Indicates a case of 30% RH, Δ indicates a case of 60% RH, and X indicates a case of 90% RH. From both figures, it can be seen that the rate of change is more constant after 180 days after vacuum heat treatment, and the stability with time is superior.

FIGS. 6 and 7 show the high-temperature and high-humidity treatment (140 ° C., 90%) of the humidity-sensitive element of this example and a humidity-sensitive element prepared in the same manner as described above except that the vacuum heat treatment was not performed. R
H shows the moisture sensitivity before and after standing for 12 hours. In both figures, the horizontal axis is the measured humidity (% RH), the vertical axis is the rate of change (%, 0% RH before treatment), □ is the measurement result before high temperature and high humidity treatment, + is the measurement after treatment The results are shown respectively. As can be seen from both figures, in FIG. 6, which is a device subjected to the vacuum heat treatment, the same humidity sensitivity as before the treatment was obtained after the high-temperature and high-humidity treatment. It can be seen that it is stable without any change.

Further, FIGS. 8 and 9 show the moisture sensitivity characteristics of the device subjected to the vacuum heat treatment and the device not subjected to the vacuum heat treatment at 20 ° C. (indicated by □ in the figure) and 40 ° C. (indicated by + in the figure), respectively. The horizontal axis indicates the measured humidity (% RH), and the vertical axis indicates the rate of change (%, 20
C, 0% RH basis), FIG. 10 and FIG.
Figure 11 shows 0% RH (□), 10% RH (+), 30% RH for each element
(◇), 60% RH (△), 90% RH (×) shows the change over time of the temperature characteristics, the vertical axis plots the temperature characteristics at each measured humidity converted to% RH is there. FIGS. 8 and 9 show that the moisture-sensitive element of the present invention has the same rate of change at both 20 ° C. and 40 ° C., which is superior to the conventional element without heat treatment. I understand. From FIGS. 10 and 11, it can be seen that the element of the present invention is also improved in the change over time in temperature characteristics.

[Effects of the Invention] As described above, in the moisture-sensitive element of the present invention, the moisture-sensitive film is subjected to heat treatment at 250 to 500 ° C in a vacuum of 1 × 10 ^-6 Torr or less by a plasma polymerization method in a film forming method. Therefore, there is little change in characteristics after being left under high temperature and high humidity, and the heat resistance is excellent, and the change over time in temperature characteristics is also improved. In addition, the vacuum heat treatment can be performed in the same apparatus by using the existing film forming process, so that the working efficiency is not impaired.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of one embodiment of the present invention, FIG. 2 is a schematic diagram of an example of a vapor deposition device used for manufacturing a moisture-sensitive element of the present invention, and FIG. 3 is a schematic structure of an example of a vacuum heating device. FIGS. 4 and 5 are diagrams showing changes over time in the humidity sensitivity of the humidity sensor of the present invention and the conventional humidity sensor, respectively. FIGS. 6 and 7 are each a diagram showing the humidity sensor of the present invention. 8 and 9 show the humidity-sensitive characteristics of the humidity-sensitive element according to the prior art before and after being left in a high-temperature and high-humidity environment, respectively.
FIG. 10 and FIG. 11 are diagrams showing time-dependent changes in temperature characteristics of the humidity-sensitive element according to the present invention and the humidity-sensitive element according to the conventional example at 40 ° C., respectively. DESCRIPTION OF SYMBOLS 1 ... Insulating substrate, 2 ... Lower electrode 3 ... Moisture sensitive dielectric thin film, 4 ... Upper electrode 19,31 ... Bell jar, 21,33 ... Moisture sensitive element material 23,34 ... Support base , 25… Nichrome wire 27… Heating filament 32… Tungsten filament 35… Thermocouple

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-188835 (JP, A) JP-A-57-141546 (JP, A) JP-A-1-121745 (JP, A)

Claims (1)

(57) [Claims] 1. An insulating substrate, a lower electrode formed on the substrate, a polymer moisture-sensitive derivative thin film formed on the lower electrode, and a moisture-permeable metal film formed on the thin film In the moisture-sensitive element obtained by sequentially laminating the upper electrode made of the above, the moisture-sensitive derivative thin film was heat-treated at 250 to 500 ° C. in a vacuum of 1 × 10 ⁻⁶ Torr or less after being formed by the plasma polymerization method. A moisture-sensitive element, characterized in that: