JPH02284485A - Forming method of organic piezoelectric pyroelectric film - Google Patents

Abstract

PURPOSE:To improve orientation property and increase heat resistance by forming an organic piezoelectric pyroelectric film directly on a substrate in a vacuum. CONSTITUTION:In a processing chamber 1, a substrate 3 on which a deposition film of piezoelectric pyroelectric material is formed is retained on a holder 4; the thickness of a film formed on the substrate 3 is measured by a film thickness monitor 5. Facing the substrate 3, a vessel 6 is arranged which is used for evaporating diamine as pyroelectric raw material monomer (a) and di-isocyanate as raw material monomer (b); by an evaporation monitor 7 and a heater 8, the temperature of the vessel 6 is controlled to be a specified value to keep the evaporation of the monomer (a) and (b) always constant. The substrate 3 on which a polyurea film is formed is taken out and heated; electric field is applied to the polyurea film; heating is stopped; the film is gradually cooled and subjected to boring process.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is applicable to audio equipment such as microphones and diaphragms for speakers, measurement equipment such as various heat sensors, pressure sensors, infrared detectors, etc. The present invention relates to a method of forming an organic piezoelectric pyroelectric film using pyroelectricity.

(Prior Art) Conventionally, a poling-treated polyvinylidene fluoride film (hereinafter referred to as PVDF film) has been used as an organic piezoelectric pyroelectric film.

These organic piezoelectric pyroelectric films are formed by almost the same method, for example, in the case of forming a PVDF film, as follows.

First, for example, a polymer obtained by reacting vinylidene fluoride as a raw material monomer with distilled water and a peroxide catalyst such as Pennzoyl Peroxai F at a temperature of 60 to 80'C under a pressure of 90 to 950C and subjected to IH3. is formed into a sheet-like film using a film forming method. After stretching the formed film to increase its orientation (crystallinity of the film), the film was stretched at room temperature to 70°C in an electric field of 5°C.
A poling treatment (orienting dipoles in the direction of the electric field) is performed under conditions of 0 to 250 M V/m to form a piezoelectric pyroelectric PVDF film.

The reason for performing the poling process here is that the PVDF film contains a CF2 atomic group with a dipole moment in its molecular chain, so the poling process changes the dipole moment of the atomic group along the molecular chain. This is because the polymer chains are arranged in the same direction to cause residual polarization in the polymer film, which is an aggregate of polymer chains, and to impart piezoelectricity or pyroelectricity to the film.

In addition, PVDF film can only be formed into a film.
Since it is a mixture of zig-sag (β-type) molecules and helix (α-type) molecules, the polymer chain is stretched into a zigzag shape (β form) before the poling process is performed.

(Means to be Solved by the Invention) The method for forming an organic piezoelectric pyroelectric material such as the PVDF film requires a polymerization step of raw material monomers, a film forming step, and a stretching step before imparting piezoelectricity and pyroelectricity to the film. The workability is poor as it requires numerous steps such as process and poling process, and orientation cannot be obtained unless the film is stretched after film formation. Therefore, there are problems such as the inability to coat a substrate as a piezoelectric pyroelectric film.

In addition, since PVDF film has poor heat resistance,
When the film temperature reaches several tens of degrees, it gradually softens and the residual polarization decreases, and when the temperature is around 100 degrees Celsius, the elastic modulus of the film decreases, and as the dielectric constant increases, the piezoelectric constant and pyroelectric constant decrease. There are problems such as difficulty in using it for acoustic device sensors and the like.

In addition, aromatic films have heat resistance, but because they contain benzene rings in their constituent polymers, PV
In the normal poling process, which applies a high electric field directly to the film like F film, it is extremely difficult to reverse the dipoles in the molecular chains within the film, so sufficient remanent polarization cannot be obtained, and as a result, the piezoelectric constant is lower than that of PVDF. There is a problem in that the level is only about 1/200 of that of film.

An object of the present invention is to provide a method for forming an organic piezoelectric pyroelectric film that eliminates the above-mentioned problems.

(Means for solving the problem) The piezoelectric constant and pyroelectric constant of an organic piezoelectric pyroelectric film are determined by atomic groups having a large dipole moment, which play an important role.
The atomic group is F.

Not only CN and CΩ, but also 〉C-0 and NH groups have large dipole moments, and these 〉C=O and N
A polymer film containing H groups has excellent piezoelectric constant and pyroelectric constant.

Therefore, the present inventors focused on polymers containing 〉C=0 groups and NH groups, and as a result of intensive studies, they created a polyurea film with excellent orientation by vapor-depositing and polymerizing raw material monomers on a substrate in vacuum. We found that it is possible to form

The method for forming an organic piezoelectric pyroelectric film of the present invention was made based on the above-mentioned knowledge, and comprises evaporating raw material monomers consisting of diamine and diisocyanate in a vacuum, and then vapor-polymerizing them on a substrate. The method is characterized in that a polyurea film is formed on the substrate and a poling treatment is performed on the polyurea film.

The diamines used as one of the raw material monomers for polyurea include 44'-diaminodiphenyl ether, 4,4'
-diamino-3,3'dimethyldiphenylmethane, p,
Mention may be made of p'-diaminodiphenylmethane.

Examples of the diisocyanate used as the other raw material monomer include methylene diphenyl 4,4'-diisocyanate and 3,3'-dimethyldiphenyl 4,4'-diisocyanate.

Further, the degree of vacuum when evaporating both of the raw material monomers and polymerizing them on the substrate is 1×10 to I x ], 0
'Set to about Torr.

In addition, in the poling treatment performed on the polyurea film, the polyurea film is heated to a high temperature of about 180 to 200°C, close to the dissociation temperature, and an electric field of about 100 to 200 MV/m is applied to the polyurea film for a predetermined period of time. Cool slowly to room temperature.

The polymerization reaction of polyurea was carried out using 44'-diaminodiphenyl ether as the diamine and 4,
The following formula shows the case where methylene diphenyl 4'-diisocyanate is used.

〇20 This reaction is a reversible reaction, and at a temperature of 200°C (= 1), molecular motion becomes active. Therefore, after forming a polyurea film, poling at a temperature of 200°C will cause the molecules in the film to move. Because it is in a state of easy movement, it is extremely easy to orient.After orientation, by lowering the temperature, the molecules in the film are fixed in an oriented state, resulting in a polyurea film with a certain orientation. It will be done.

The polymer chain of polyurea contains HN-CO- for each monomer.
There are dipoles of NH with a dipole moment of about 5 Debye units, and under high electric fields these dipoles align in the direction of the electric field. In particular, at high temperatures where molecular motion can easily occur, the dipoles are oriented in a certain direction on the molecular chain.
Residual polarization occurs even after the formed film is cooled to room temperature. This residual polarization is stable and does not disappear even if the temperature is raised or lowered below the transition temperature of the polymer.

Furthermore, by reversing the direction of the electric field, the direction of the dipole can be changed to the opposite direction.

This is an advantage when forming a laminated film.

(Example) Examples of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an example of an apparatus for carrying out the method of the present invention, and in the figure, 1 indicates a processing chamber. A substrate 3 on which the inside of the processing chamber 1 is connected to an external vacuum pump or other evacuation system 2, and on which a vapor-deposited film of a piezoelectric pyroelectric material is to be formed inside the processing chamber 1.
is held on a holder 4 consisting of two rails, and the film thickness monitor 5 provided on the front surface of the substrate 3 measures the thickness of the substrate 3.
The thickness of the film formed on the surface was measured. Furthermore, glass evaporation containers 6, 6 are provided in the lower part of the processing chamber 1, facing the substrate 3, for evaporating diamine as the raw material monomer a of the pyroelectric body and diisocyanate as the raw material monomer b, respectively. Each of the evaporation containers 6 was able to be controlled at a predetermined temperature by a crystal vibration evaporation monitor 7 and a heater 8 provided in the vicinity thereof so as to keep the evaporation of the raw material monomers a and b constant. still,
In the figure, 9 indicates a shutter interposed between the substrate 3 and both evaporation containers 6, and 10 indicates a partition plate provided between both evaporation containers 6.

Next, specific examples of forming a polyurea film using the above-mentioned apparatus will be described together with comparative examples.

Example 1 First, raw material monomer a, that is, 4,4'-diaminodiphenyl ether as a diamine, was placed in one of the evaporation vessels 6, 6, and raw material monomer b, that is, 4,4'-diaminodiphenyl ether as a diisocyanate, was placed in the other.
, 4'-methylene diphenyl diisocyanate are respectively filled, and the total pressure in the processing chamber 1 is set to I.times.10@-5 Torr via the evacuation system 2 with the shutter 9 closed.

Next, while measuring the evaporation amount of each raw material monomer a and b from the evaporation container 6°6 with the evaporation monitor 7.
, 8 to a temperature of 135±2°C and methylene diphenyl 4,4′-diisocyanate to a temperature of 75±2°C, respectively.

Next, after the raw material monomers a and b reach a predetermined temperature and the required amount of evaporation is obtained, the shutter 9 is opened, and the substrate 3 (a slide glass) held in the holder 4 in the processing chamber 1 is After depositing the raw material monomers a and b to a thickness of 2000 mm on the substrate (on which aluminum is vapor-deposited) at a deposition rate of 2 mm/min, the shutter 9 is closed and a polymerization reaction of polyurea is caused on the substrate 3. A polyurea film was formed on the substrate 3.

Aluminum was further deposited on this polyurea film as an upper electrode.

The raw material monomers a and b were evaporated at a molar ratio of 1=1 by adjusting the evaporation amount so that a polyurea film was formed stoichiometrically. Furthermore, the pressure inside the processing chamber 1 during the evaporation of the raw material monomers a and b is 3 x 10-5To
It was set as rr.

The substrate 3 on which the polyurea film was formed in this manner was taken out and heated to a temperature of 200°C, and an electric field of 150 M V/m was applied between the upper electrode and the lower electrode, that is, to the polyurea film.
Heating was stopped while the voltage was being applied for 0 minutes, and the temperature of the polyurea film was gradually cooled from 200''C to room temperature to perform a poling treatment.

The polyurea film polled by the above method was heated to a temperature of 5
Fullllll pyroelectric current while heating from 0°C to 170°C
The pyroelectric constant (C/rrf' K ) was determined using the following formula.

Pyroelectric current (A) jiA electric rate- Temperature change rate (0C/min) The obtained pyroelectric constants at each temperature are shown in FIG. 2A.

Furthermore, when the piezoelectric constant was examined using a resonance method, it was found that d=5 pC/N.

Example 2 44'-diamino-3,3 as one raw material monomer a
'-dimethyldiphenylmethane was used, the heating temperature was ]]0±2°C, and methylene diphenyl 4,4'-diisocyanate was used as the other raw material monomer b,
A poling-treated polyurea film was formed on the substrate 3 in the same manner as in Example except that the heating temperature was 75±2°C.

Then, the pyroelectric constant was determined in the same manner as in Example 1, and the obtained pyroelectric constant at each temperature is shown in FIG. 2B.

In addition, when the piezoelectric constant was investigated using the same method as in Example], d
=12pc/N.

Example 3 4,4'-diaminodiphenyl ether was used as one raw material monomer a, and the heating temperature was 135±2°C, and 3,3' dimethyl 4,4'-diisocyanate was used as the other raw material monomer b. A poled polyurea film was formed on the substrate 3 in the same manner as in Example 1 except that diphenyl was used and the heating temperature was 100±2°C.

Then, the pyroelectric constant was determined in the same manner as in Example 1, and the obtained pyroelectric constant at each temperature is shown in FIG. 2C.

In addition, when the piezoelectric constant was investigated using the same method as in Example 1, c
l=4. There was p C/N.

Example 4 One of the raw material monomers a was p,p'-sia]2minodiphenylmethane, and the heating temperature was set to 105±.
2°C, and 4,4 as the other raw material monomer b.
A poled polyurea film was formed on a substrate 3'' in the same manner as in Example except that methylene diphenyl'-diisocyanate was used and the heating temperature was 75±2°C.

Then, the pyroelectric constant was determined in the same manner as in Example], and the obtained pyroelectric constant at each temperature is shown in the second figure.

In addition, when the piezoelectric constant was investigated using the same method as in Example 1, d
=4.5pc/N.

Comparative Example: After aluminum was vapor-deposited as electrodes on both sides of a PVDF film with a thickness of 25 μm, the film was heated to a temperature of room temperature to 70°C.
The poling process was performed at °C under the conditions of an electric field of 1.00 MV/m.

Then, the pyroelectric constant was determined in the same manner as in Example 1, and the obtained pyroelectric constant at each temperature is shown in FIG. 2E.

In addition, when the piezoelectric constant was investigated using the same method as in Example], d
=25pc/N.

Examples 1, 2.3.4 using diamine and diisocyanate as raw material monomers for the pyroelectric film as shown in FIG.
It was confirmed that the polyurea film had superior pyroelectricity at a high temperature of 100° C. to 200° C. compared to a comparative example using a PVDF film.

(Effects of the Invention) According to the present invention, an organic piezoelectric pyroelectric film can be directly formed (coated) on a substrate in a vacuum, so it is also possible to perform patterning on the substrate, for example. By combining it with an IC, it can also be used to form a sensor element, and the organic piezoelectric pyroelectric film can be formed without the need for stretching treatment as in conventional methods. The film is easy to produce and has the advantage of being able to form an organic piezoelectric pyroelectric film with excellent heat resistance.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an example of an apparatus for carrying out the method for forming an organic piezoelectric pyroelectric film of the present invention, and FIG. FIG. 3 is a characteristic diagram showing the relationship between rate and temperature change.

Claims (1)

[Claims] An organic piezoelectric focus, characterized in that raw material monomers consisting of diamine and diisocyanate are evaporated in vacuum, these are vapor-deposited and polymerized on a substrate to form a polyurea film on the substrate, and the polyurea film is subjected to a poling treatment. Method of forming an electric film.