Preparation method of negative temperature coefficient flexible thermosensitive film for solvothermal low-temperature phase formation

Abstract

The invention provides a preparation method of a negative temperature coefficient flexible thermosensitive film for solvothermal low-temperature phase formation. According to the method, an insulating buffer layer, a negative temperature coefficient thermosensitive film and an electrode are grown on a substrate, and the negative temperature coefficient thermosensitive film is realized on the basis of a transition metal film in a solvothermal mode under the normal temperature condition. The negative temperature coefficient characteristic and the sensitivity of the thin film are regulated and controlled by regulating and controlling the type of the thin film, the growth preparation condition and the solvent and the temperature of solvothermal. The flexible thermosensitive film has the advantages of simple structure, light weight, excellent crystallinity and high temperature sensitivity. Through the combination of a coating process and a solvothermal annealing process, the low-temperature annealing phase formation of the ceramic film is realized, and the performance of the flexible thermosensitive film is qualitatively improved. The problems of high-temperature annealing and phase formation of the polymer-based ceramic film are effectively solved, the temperature measurement precision of the film is improved, and the method can be widely applied to accurate temperature measurement under various complex conditions.

Description

Technical Field

[0001] The present invention relates to the field of preparation of two-dimensional materials and flexible temperature sensing, and in particular to a method for preparing a solvent-thermal low-temperature phase-formed negative temperature coefficient (NTC) flexible thermosensitive film. Background Art

[0002] Faced with the growing number of special environments and special signals, flexible sensors have become an important pillar unit in the field of flexible electronics, and flexible temperature sensors are considered to be an indispensable link. As an important component of sensing materials, they have potential application value in wearable medical signal monitoring and other aspects. Existing flexible thermosensitive films are mostly conductive polymer (PEDOT: PSS)-based, carbon-based, and metal-based composite thermosensitive films prepared on polymer substrates. Although such materials have excellent ductility, their sensitivity still has a lot of room for improvement. In order to achieve real-time monitoring of body temperature and obtain accurate clinical-related information and health-related signals, researchers have continuously improved the temperature response sensitivity of corresponding thin film devices by optimizing the preparation process and designing composite materials. However, the problem of limited material selection of thermosensitive films due to the low temperature tolerance of the selected polymer substrate (no more than 350°C) reduces the way to improve the sensitivity of flexible devices. In order to further improve the sensitivity of flexible thermosensitive film devices, research on new flexible thermosensitive films has become a research hotspot.

[0003] In order to solve the above problems, the present invention proposes a method for preparing a solvent-thermal low-temperature phase-forming negative temperature coefficient flexible thermosensitive film. The method uses solvent vapor to make the ceramic crystallize and nucleate at low temperature and low pressure, so that the ceramic film and the polymer substrate are organically combined, which not only avoids the problem that the polymer substrate is difficult to tolerate under high temperature conditions, but also greatly improves the sensitivity and reliability of temperature measurement.

[0004] The object of the present invention is to provide a method for preparing a solvent-thermal low-temperature phased negative temperature coefficient flexible thermosensitive film, in which an insulating buffer layer, a negative temperature coefficient thermosensitive film and an electrode are grown on a substrate, and the negative temperature coefficient thermosensitive film is prepared based on a transition metal film by a solvent-thermal method under normal temperature conditions. By regulating the type of film, the growth preparation conditions, and the solvent and temperature of the solvent-thermal method, the negative temperature coefficient characteristics and sensitivity of the film are regulated. The flexible thermosensitive film has a simple structure, light weight, and excellent crystallinity and high temperature sensitivity. By combining the coating process and the solvent-thermal annealing process, the ceramic film is phased by low-temperature annealing, which promotes the qualitative improvement of the performance of the flexible thermosensitive film. The solvent-thermal low-temperature phase-forming method is applied to the phase-forming of traditional negative temperature coefficient thermosensitive films. On the one hand, it reduces the phase-forming temperature of transition metal oxide materials, makes the preparation process conditions easy to control, and has the advantages of repeated experiments and controllable performance; on the other hand, the obtained flexible thermosensitive film is light weight and high sensitivity. This method brings a new innovative perspective to the phase-forming of traditional negative temperature coefficient ceramics and provides ideas for the design of flexible thermosensitive films. The present invention effectively solves the high-temperature annealing and phase formation problems of polymer-based ceramic films, improves the temperature measurement accuracy of the films, and can be widely used to achieve accurate temperature measurement under various complex conditions.

[0005] The invention discloses a solvent-thermal low-temperature phase-formed negative temperature coefficient flexible thermosensitive film, which is carried out according to the following steps:

[0006] a. Substrate cleaning: ultrasonically clean the substrate with acetone, anhydrous ethanol, deionized water and anhydrous ethanol respectively, with the cleaning time being 10-30 minutes each. After cleaning, blow dry the substrate surface with high-purity dry nitrogen. The substrate is polyimide, polydimethylsiloxane, alloy or fluorphlogopite, and the substrate size is 1-6 inches.

[0007] b. Preparation of buffer layer: Al2O3, AlN, SiO2 or Si3N4 are selected as the insulating buffer layer material, and the substrate obtained in step a is grown with radio frequency magnetron sputtering. The radio frequency sputtering conditions are: the growth pressure is 10 -1 -10Pa, oxygen and argon contents are 0%-100% respectively, growth power is 10-80W, growth temperature is 50-500°C, and growth time is 60-600min, thus obtaining the substrate material of the insulating buffer layer;

[0008] c. Preparation of transition metal film: MnCoNi or LaMn is selected as the transition metal layer material, and the substrate material with the insulating buffer layer prepared in step b is placed in a magnetron sputtering device to grow the transition metal film. The sputtering conditions are: the growth pressure is 10 -1-10Pa, oxygen and argon contents are 0%-100% respectively, growth power is 10-80W, growth temperature is 50-500℃, growth time is 20-120min, and transition metal thin film material is obtained;

[0009] d. Preparation of negative temperature coefficient thermistor film: placing the transition metal film prepared in step c in a hydrothermal reactor for solvent thermal annealing, the annealing temperature is 80-200°C, the holding time is 30-360min, the solvent is ethanol, deionized water, sodium carbonate, any two of the mixed solution totaling 50ml, after annealing, a negative temperature coefficient thermistor film is obtained;

[0010] e. Electrode preparation: Cover the surface of the negative temperature coefficient thermistor film obtained in step d with an electrode mask, place it back in the tray of the DC sputtering equipment, and prepare Cr / Au or Ni / Au electrodes according to the conventional method. The growth power is 10-50W and the growth pressure is 10 -1 -10Pa, the growth time of the two materials is 3-15min respectively. After the growth is completed, a solvent-thermal low-temperature phase-formed flexible thermosensitive film with a negative temperature coefficient is obtained.

[0011] The method for preparing a solvent-thermal low-temperature phase-forming flexible thermosensitive film with negative temperature coefficient described in the present invention has the following characteristics compared with polymer-based flexible thermosensitive films:

[0012] The present invention uses a solvent thermal method to prepare a transition metal oxide functional film at low temperature and low pressure, which has higher sensitivity, stability and temperature measurement accuracy compared to polymer functional materials.

[0013] The present invention adopts a magnetron sputtering method to prepare the functional layer material, and can achieve performance optimization according to a simple change in process parameters, with better film uniformity and higher temperature measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is the resistance value of the flexible thermal film changing with temperature. DETAILED DESCRIPTION

[0015] The present invention and its effective technical effects are further described in detail below in conjunction with examples and drawings, but the embodiments of the invention are not limited thereto. Any modification or equivalent substitution of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0016] Example 1

[0017] a. Substrate cleaning: A 2-inch polyimide (PI) substrate was ultrasonically cleaned using acetone, anhydrous ethanol, deionized water, and anhydrous ethanol, respectively, for 10 minutes each. After cleaning, the substrate surface was blown dry with high-purity dry nitrogen;

[0018] b. Preparation of buffer layer: Al2O3 is selected as the insulating buffer layer material, and the polyimide (PI) substrate obtained in step a is subjected to DC magnetron sputtering for growing the insulating buffer layer, and the RF sputtering conditions are: growth pressure of 1Pa, argon content of 50%, growth power of 40W, growth temperature of 50°C, and growth time of 60min, to obtain an insulating buffer layer polyimide (PI) substrate;

[0019] c. Preparation of transition metal thin film: MnCoNi series materials are selected as transition metal layer materials, and the polyimide (PI) substrate with an insulating buffer layer prepared in step b is placed in a magnetron sputtering device to grow a transition metal thin film. The sputtering conditions are: growth pressure of 1 Pa, argon content of 50%, growth power of 40 W, growth temperature of 50 ° C, and growth time of 30 min, so as to obtain a transition metal thin film material;

[0020] d. Preparation of negative temperature coefficient thermistor film: placing the transition metal film prepared in step c in a hydrothermal reactor for solvent thermal annealing, the annealing temperature is 160° C., the holding time is 120 min, the solvent is a mixed solution of 25 ml of ethanol and 25 ml of deionized water, and a negative temperature coefficient thermistor film is obtained after annealing;

[0021] e. Electrode preparation: Cover the surface of the negative temperature coefficient thermistor film obtained in step d with the electrode mask respectively, and place it back in the tray of the DC sputtering equipment to prepare Cr / Au electrode by the conventional method. The growth power is 40W, the growth pressure is 1Pa, and the growth time of the two materials is 3 and 15min respectively. After the growth is completed, a solvent-thermal low-temperature phase-formed negative temperature coefficient flexible thermistor film is obtained.

[0022] Example 2

[0023] a. Substrate cleaning: Acetone, anhydrous ethanol, deionized water, and anhydrous ethanol were used to ultrasonically clean a 1-inch polydimethylsiloxane (PDMS) substrate, respectively, for 10 minutes each. After cleaning, the substrate surface was blown dry with high-purity dry nitrogen;

[0024] b. Preparation of buffer layer: AlN was selected as the insulating buffer layer material, and the polydimethylsiloxane (PDMS) substrate obtained in step a was used for growing the insulating buffer layer by radio frequency magnetron sputtering. The radio frequency sputtering conditions were: the growth pressure was 10 - 1Pa, oxygen and argon contents are 0% and 100% respectively, the growth power is 10 W, the growth temperature is 50° C., and the growth time is 600 min, thus obtaining an insulating buffer layer polydimethylsiloxane (PDMS) substrate;

[0025] c. Preparation of transition metal film: LaMn-based materials are selected as transition metal layer materials. The polydimethylsiloxane (PDMS) substrate with an insulating buffer layer prepared in step b is placed in a magnetron sputtering device to grow transition metal films. The sputtering conditions are: the growth pressure is 10 -1 Pa, oxygen and argon contents are 0% and 100% respectively, the growth power is 10W, the growth temperature is 50°C, and the growth time is 120min, thus obtaining a transition metal thin film material;

[0026] d. Preparation of negative temperature coefficient thermistor film: placing the transition metal film prepared in step c in a hydrothermal kettle for solvent thermal annealing, the annealing temperature is 80°C, the holding time is 360 min, the solvent is a mixed solution of 25 ml of ethanol and 25 ml of sodium carbonate, and a negative temperature coefficient thermistor film is obtained after annealing;

[0027] e. Electrode preparation: Cover the surface of the negative temperature coefficient thermistor film obtained in step d with the electrode mask plate respectively, and place it back in the tray of the DC sputtering equipment to prepare Ni / Au electrode according to the conventional method. The growth power is 50W, the growth pressure is 10Pa, and the growth time of the two materials is 3min respectively. After the growth is completed, a solvent-thermal low-temperature phase-formed negative temperature coefficient flexible thermistor film is obtained.

[0028] Example 3

[0029] a. Substrate cleaning: ultrasonically clean the 6-inch alloy substrate with acetone, anhydrous ethanol, deionized water and anhydrous ethanol respectively for 30 minutes each. After cleaning, blow dry the substrate surface with high-purity dry nitrogen;

[0030] b. Preparation of buffer layer: SiO2 is selected as the insulating buffer layer material, and the alloy substrate obtained in step a is subjected to RF magnetron sputtering for growing the insulating buffer layer. The RF sputtering conditions are: growth pressure is 10 Pa, oxygen and argon contents are 100% and 0% respectively, growth power is 80 W, growth temperature is 500° C., and growth time is 60 min, thus obtaining an insulating buffer layer alloy substrate;

[0031] c. Preparation of transition metal thin film: MnCoNi series materials are selected as transition metal layer materials, and the alloy substrate with insulating buffer layer prepared in step b is placed in a magnetron sputtering device to grow transition metal thin film. The sputtering conditions are: growth pressure is 10Pa, oxygen and argon contents are 100% and 0% respectively, growth power is 80W, growth temperature is 500°C, and growth time is 20min, so as to obtain transition metal thin film material;

[0032] d. Preparation of negative temperature coefficient thermistor film: placing the transition metal film prepared in step c in a hydrothermal reactor for solvent thermal annealing, the annealing temperature is 200° C., the holding time is 30 min, the solvent is a mixed solution of 10 ml of deionized water and 40 ml of sodium carbonate, and a negative temperature coefficient thermistor film is obtained after annealing;

[0033] e. Electrode preparation: Cover the surface of the negative temperature coefficient thermistor film obtained in step d with the electrode mask respectively, and place it back in the tray of the DC sputtering equipment to prepare Cr / Au electrode according to the conventional method. The growth power is 50 W, the growth pressure is 10 Pa, and the growth time of the two materials is 15 min and 3 min respectively. After the growth is completed, a solvent-thermal low-temperature phase-formed negative temperature coefficient flexible thermistor film is obtained.

[0034] Example 4

[0035] a. Substrate cleaning: ultrasonically clean a 3-inch fluorphlogopite substrate using acetone, anhydrous ethanol, deionized water, and anhydrous ethanol, respectively, for 30 minutes each. After cleaning, blow dry the surface of the fluorphlogopite substrate with high-purity dry nitrogen;

[0036] b. Preparation of buffer layer: Si3N4 was selected as the insulating buffer layer material, and the fluorophlogopite substrate obtained in step a was subjected to RF magnetron sputtering for growing the insulating buffer layer. The RF sputtering conditions were as follows: the growth pressure was 5 Pa, the oxygen and argon contents were 0% and 50% respectively, the growth power was 40 W, the growth temperature was 300° C., and the growth time was 300 min, thus obtaining the fluorophlogopite substrate with insulating buffer layer;

[0037] c. Preparation of transition metal thin film: LaMn-based materials are selected as transition metal layer materials, and the fluorphlogopite substrate with an insulating buffer layer prepared in step b is placed in a magnetron sputtering device to grow a transition metal thin film. The sputtering conditions are: growth pressure of 5 Pa, oxygen and argon contents of 0% and 50% respectively, growth power of 60 W, growth temperature of 300° C., and growth time of 40 min, to obtain a transition metal thin film material;

[0038] d. Preparation of negative temperature coefficient thermistor film: placing the transition metal film prepared in step c in a hydrothermal kettle for solvent thermal annealing, the annealing temperature is 140° C., the holding time is 140 min, the solvent is a mixed solution of 25 ml of ethanol and 25 ml of sodium carbonate, and a negative temperature coefficient thermistor film is obtained after annealing;

[0039] e. Electrode preparation: The surface of the negative temperature coefficient thermistor film obtained in step d was covered with an electrode mask, and then placed in the tray of the DC sputtering equipment to prepare Ni / Au electrodes in a conventional manner. The growth power was 50 W and the growth pressure was 10 - 1 Pa, the growth time of the two materials were 15min and 3min respectively. After the growth was completed, a solvent-thermal low-temperature phase-formed flexible thermosensitive film with a negative temperature coefficient was obtained.

[0040] Example 5

[0041] The solvent-thermal low-temperature phased negative temperature coefficient (NTC) flexible thermosensitive film prepared in Example 1 was tested and applied;

[0042] A constant temperature oil bath was used as the constant temperature device, and the temperature was tested by a computer-controlled thermometer. The temperature control range was 273.15-353.15K, the temperature increase was 5K each time, and the constant temperature time was 45 minutes per 5K. The resistance-temperature relationship test data obtained is shown in Table 1:

[0043] Table 1

[0044] Temperature / K Resistance / Ω Temperature / K Resistance / Ω 273.15 182.58144 313.15 104.08661 278.15 167.12298 318.15 99.22475 283.15 153.80669 323.15 94.916 288.15 142.30726 328.15 91.325 293.15 132.35636 333.15 88.284 298.15 123.7319 338.15 85.741 303.15 116.22608 343.15 83.655 308.15 109.71905 348.15 81.992

[0045] According to Table 1, the resistance-temperature performance relationship diagram is as follows Figure 1 As shown in Table 1 and Figure 1 It can be seen that the resistance-temperature performance curve of the prepared solvent-thermal low-temperature phase-forming negative temperature coefficient (NTC) flexible thermistor film shows a downward trend with increasing temperature, which is consistent with the negative temperature coefficient relationship.

Claims

1. A solvent-thermal low-temperature phase-forming negative temperature coefficient flexible thermosensitive film, characterized in that: Follow these steps: a. Substrate cleaning: ultrasonically clean the substrate with acetone, anhydrous ethanol, deionized water and anhydrous ethanol respectively, with the cleaning time being 10-30 minutes each. After cleaning, blow dry the substrate surface with high-purity dry nitrogen. The substrate is polyimide, polydimethylsiloxane, alloy or fluorphlogopite, and the substrate size is 1-6 inches. b. Preparation of buffer layer: Al2O3, AlN, SiO2 or Si3N4 are selected as the insulating buffer layer material, and the substrate obtained in step a is grown with radio frequency magnetron sputtering. The radio frequency sputtering conditions are: the growth pressure is 10 -1 -10Pa, oxygen and argon contents are 0%-100% respectively, growth power is 10-80W, growth temperature is 50-500℃, and growth time is 60-600min, thus obtaining the substrate material of the insulating buffer layer; c. Preparation of transition metal film: MnCoNi or LaMn is selected as the transition metal layer material, and the substrate material with the insulating buffer layer prepared in step b is placed in a magnetron sputtering device to grow the transition metal film. The sputtering conditions are: the growth pressure is 10 -1 -10Pa, oxygen and argon contents are 0%-100% respectively, growth power is 10-80W, growth temperature is 50-500℃, growth time is 20-120min, and transition metal thin film material is obtained; d. Preparation of negative temperature coefficient thermistor film: placing the transition metal film prepared in step c in a hydrothermal reactor for solvent thermal annealing, the annealing temperature is 80-200°C, the holding time is 30-360min, the solvent is ethanol, deionized water, sodium carbonate, any two of the mixed solution totaling 50ml, after annealing, a negative temperature coefficient thermistor film is obtained; e. Electrode preparation: Cover the surface of the negative temperature coefficient thermistor film obtained in step d with an electrode mask, place it back in the tray of the DC sputtering equipment, and prepare Cr / Au or Ni / Au electrodes according to the conventional method. The growth power is 10-50W and the growth pressure is 10 -1 -10Pa, the growth time of the two materials is 3-15min respectively. After the growth is completed, a solvent-thermal low-temperature phase-formed flexible thermosensitive film with a negative temperature coefficient is obtained.

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