CN105869807A - Preparation method of zinc oxide-bismuth oxide thin film varistor - Google Patents

Abstract

The invention relates to a preparation method of a zinc oxide-bismuth oxide film piezoresistor, belonging to the technical field of electronic information material preparation and application thereof. The present invention utilizes the radio frequency magnetron sputtering method, adopts non-stoichiometric sintered ZnO _n (n<1) as the matrix target material, and other metals or their oxides as the doping target material. Under the optimized sputtering process, the A low-resistivity zinc oxide film is deposited on a conductive substrate, and then embedded in bismuth oxide powder for hot dipping to obtain a zinc oxide-bismuth oxide film varistor. The film varistor has the characteristics of excellent non-linear performance, controllable varistor voltage, and small leakage current, and has broad application prospects in overvoltage protection of large-scale or ultra-large-scale integrated circuits. The film deposition and heat soaking conditions of the method are strictly controllable, the process has good repeatability, and a thin film device with uniform composition, structure and thickness can be obtained on a large-area substrate, which is suitable for large-scale production.

Description

A kind of preparation method of zinc oxide-bismuth oxide film varistor

technical field

The invention relates to a method for preparing a zinc oxide-bismuth oxide film piezoresistor, belonging to the technical field of electronic information material preparation and application thereof.

Background technique

A varistor (Varistor) is a semiconductor material device in which the current through it increases sharply with the increase of the applied voltage at a certain temperature and within a specific voltage range. It is widely used in valve components and various Overvoltage protection components for various electronic components, etc.

At present, commercial varistors are mainly electronic components based on ZnO-Bi ₂ O ₃ composite ceramic materials. And this ZnO varistor material is mixed and sintered with zinc oxide, bismuth oxide and various other metal oxide additives, such as nickel oxide, manganese oxide and rare earth metal oxides (F.Jiang, et al.Journal of Advanced Ceramics, 2013, 2:201-212.). The key structure of this varistor is that the semiconductive zinc oxide grains are covered by the high-resistance Bi ₂ O ₃ grain boundary layer, and the two are closely combined to form a double Schottky barrier between the grains, becoming A piezoresistor unit, and then multiple piezoresistor units are connected in series to form a piezoresistor. In other words, the pressure-sensitive characteristics of ZnO-Bi ₂ O ₃ ceramic varistors come from its grain boundary effect, and its typical structure is that zinc oxide grains are completely covered by bismuth oxide films to form effective grain boundaries; the higher the grain resistance The lower, the more complete the grain boundary structure or the higher the resistance, the better the nonlinearity of the varistor.

With the rapid development of electronic technology, the size of electronic devices is constantly shrinking, the requirements for the miniaturization of components are increasingly strong, and the operating voltage is continuously reduced. As a protective semiconductor component, varistors must also develop in the direction of low voltage. The main way to realize the low voltage and miniaturization of ZnO-Bi ₂ O ₃ ceramic varistors is to control the grain size of ZnO and reduce the thickness of varistors. Commonly used methods are solid phase sintering, tape casting and so on. However, the preparation of low-voltage ZnO-Bi ₂ O ₃ varistors by solid-state sintering is difficult to further miniaturize due to technical limitations; while the process of preparing low-voltage ZnO-Bi ₂ O ₃ varistors by tape-casting is complicated and the product consistency is poor . On the other hand, due to the development of surface engineering technology, thin film has become an effective way to miniaturize varistors, which has attracted widespread attention. For example, Suzuoki et al. deposited ZnO/Bi ₂ O ₃ double-layer films on glass substrates by radio frequency magnetron sputtering, with film thicknesses of 1 μm/0.3 μm. Linear coefficient (Y. Suzuoki, et al. Journal of Physics D, 1987, 20:511-517). In addition, various ZnO polycrystalline thin film varistors can also be prepared by using other thin film technologies, such as Sol-Gel spray pyrolysis method and pulsed laser deposition method. These studies show that thin film is an effective means to develop low-voltage varistors, and thin film is conducive to the miniaturization and integration of components.

Among many thin film deposition methods, magnetron sputtering method is a mature thin film preparation technology, which is widely used; compared with other methods, magnetron sputtering method has good adhesion, high density and low growth temperature. , fast deposition speed, large-area thin-film materials can be prepared in different growth atmospheres, etc., which are considered to be very suitable for large-scale industrial production. However, because the process of preparing composite zinc oxide-bismuth oxide composite thin films and multilayer zinc oxide/bismuth oxide thin film varistors by magnetron sputtering is relatively complicated or it is not easy to construct the typical structure of ZnO-Bi ₂ O ₃ varistors, The nonlinear coefficient of ZnO-Bi ₂ O ₃ thin film varistors that can be prepared at present is usually low.

Therefore, the present invention utilizes the radio frequency magnetron sputtering method, with non-stoichiometric sintered ZnO _n (n<1) as the matrix target, other metals or their oxides as the doping target, in optimized magnetron sputtering Under the process, a low-resistivity zinc oxide film is deposited on a conductive substrate, and then embedded in bismuth oxide powder for hot dipping, in order to construct a typical structure of a ZnO-Bi ₂ O ₃ varistor with complete grain boundaries , obtained a high-performance zinc oxide-bismuth oxide film varistor. The thin film varistor prepared by this method has the advantages of controllable material composition, simple structure, controllable varistor shape and film thickness, compact structure, excellent nonlinear performance, controllable varistor voltage, and low leakage current. Small and other characteristics, it has broad application prospects in the overvoltage protection of large-scale or ultra-large-scale integrated circuits. Moreover, zinc oxide-bismuth oxide film varistors are prepared by this method, the film deposition and hot-dipping conditions are strictly controllable, and the process repeatability is good. A thin film device with uniform composition, structure and thickness can be obtained on a large-area substrate. Large-scale production.

Contents of the invention

The object of the present invention is to propose a method for preparing a zinc oxide-bismuth oxide thin film varistor. In the thin film varistor prepared by this method, the zinc oxide grains in the varistor thin film are oxygen-deficient zinc oxide or doped zinc oxide, and the resistivity is low; and the zinc oxide grains are completely covered by the bismuth oxide thin layer, The grain boundary structure is complete and an effective grain boundary is formed, so the obtained zinc oxide-bismuth oxide varistor has excellent nonlinear performance. This kind of thin film varistor has the characteristics of controllable material composition, simple structure, controllable varistor shape and film thickness, compact structure, excellent nonlinear performance, controllable varistor voltage, and small leakage current. It has broad application prospects in the overvoltage protection of large-scale or ultra-large-scale integrated circuits. Moreover, zinc oxide-bismuth oxide film varistors are prepared by this method, the film deposition and hot-dipping conditions are strictly controllable, and the process repeatability is good. A thin film device with uniform composition, structure and thickness can be obtained on a large-area substrate. Large-scale production.

The preparation method of the zinc oxide-bismuth oxide thin film varistor proposed by the present invention is characterized in that the method utilizes the radio frequency magnetron sputtering method, and adopts non-stoichiometric sintered ZnO _n (n<1) as the matrix target , other metals or their oxides are used as doping targets. Under the optimized magnetron sputtering process, a low-resistivity zinc oxide film is deposited on a conductive substrate, and then embedded in bismuth oxide powder for hot dipping. A high-performance zinc oxide-bismuth oxide thin film varistor is obtained.

The preparation method of the zinc oxide-bismuth oxide film varistor proposed by the present invention comprises the following steps and contents:

(1) In the magnetron sputtering equipment, the non-stoichiometric sintered ZnO _n (n<1) is used as the matrix target, and other metals or their oxides are used as the doped target, and the target is fixed on the target position ; Fix the clean substrate on the sample stage; turn on the mechanical pump to draw to a low vacuum, and turn on the molecular pump when the vacuum degree of the system reaches 0.1Pa, until the vacuum degree of the system reaches above 2×10 ^-4 Pa.

(2) Introduce the working gas argon, first perform pre-sputtering to remove the pollutants on the target surface; when the glow stabilizes, start the sputtering deposition of the zinc oxide film.

(3) Take out the prepared thin film sample from the magnetron sputtering equipment, bury the prepared zinc oxide thin film in Bi ₂ O ₃ powder for hot dipping. After hot soaking, the samples were cooled to room temperature in the furnace.

(4) Electrodes are respectively applied on the upper and lower surfaces (film and substrate) of the sample containing zinc oxide-bismuth oxide composite film to obtain the piezoresistor.

In the above preparation method, the magnetron sputtering equipment in the step (1) is a radio frequency magnetron sputtering device.

In the above preparation method, n in the non-stoichiometric sintered ZnO _n in the step (1) is between 0.6-0.99.

In the above preparation method, the doping target in the step (1) is one or more of metals Fe, Co, Ni, Mn and oxides thereof.

In the above preparation method, the substrate in the step (1) is one of highly doped conductive silicon, copper and platinum.

In the above preparation method, the method for cleaning the substrate in the step (1) is as follows: first put the substrate into acetone and ethanol and use ultrasonic cleaning for 10 minutes respectively to remove oil stains and other pollutants on the surface of the substrate; then, Rinse with deionized water; finally, blow dry with dry _N2 gas and quickly put into a vacuum chamber.

In the above preparation method, the purity of the argon in the step (2) is above 99.99 vol.%.

In the above preparation method, the argon gas pre-sputtering time in the step (2) is 2-10 min.

In the above-mentioned preparation method, the zinc oxide film sputtering deposition condition in the described step ( ₂ ) is: take Ar as the sputtering gas, in Ar or Ar/O Mixed gas, at ambient temperature, sputtering ZnO _n Target and doped metal or oxide target, the sputtering power is 60-220W, the sputtering pressure is 0.4-4.0Pa, and the deposition time is 20-75min.

In the above preparation method, during the sputtering deposition of the film in the step (2), the purity of the oxygen used is above 99.99 vol.%, and the volume ratio of the two in the O ₂ /Ar mixed gas is 1-2.

In the above preparation method, the zinc oxide film obtained by sputtering deposition in the step (2) is an oxygen-deficient zinc oxide film when undoped, and is a doped zinc oxide film when doped.

In the above preparation method, the Bi ₂ O ₃ powder in the step (3) is commercially available analytically pure.

In the above preparation method, the hot soaking process conditions in the step (3) are as follows: in a muffle furnace, the temperature is 200-600° C., and the holding time is 20-120 minutes.

In the above preparation method, the electrode material in the step (4) is one of silver, aluminum, palladium, platinum and gold.

The zinc oxide-bismuth oxide film varistor prepared by this technology has controllable material composition, simple structure, controllable varistor shape and film thickness, compact structure, excellent nonlinear performance, and adjustable varistor voltage. Controlling, small leakage current and other characteristics, it has a broad application prospect in the overvoltage protection of large-scale or ultra-large-scale integrated circuits. And because the thickness of the film is controllable, this piezoresistor can be used in both high-voltage and low-voltage electrical appliances. In addition, zinc oxide-bismuth oxide thin film varistors are prepared by this method, the conditions of film deposition and hot dipping are strictly controllable, the process is repeatable, and thin film devices with uniform composition, structure and thickness can be obtained on large-area substrates. Suitable for large-scale production.

Description of drawings

Fig. 1 is the zinc oxide-bismuth oxide film varistor schematic diagram that the present invention proposes

Fig. 2 is the SEM photo of the composite film in the oxygen-deficient zinc oxide-bismuth oxide film varistor prepared in Example 1 of the present invention

Fig. 3 is the E-J curve of the oxygen-deficient zinc oxide-bismuth oxide film varistor made in Example 1 of the present invention

Fig. 4 is the SEM photo of the composite film in the doped zinc oxide-bismuth oxide film varistor prepared in Example 2 of the present invention

Fig. 5 is the E-J curve of the doped zinc oxide-bismuth oxide film varistor made in embodiment 2 of the present invention

detailed description

The technical solutions of the present invention will be further described below in conjunction with the embodiments.

The preparation method of the zinc oxide-bismuth oxide thin film varistor proposed by the present invention is characterized in that the method utilizes the radio frequency magnetron sputtering method, and adopts non-stoichiometric sintered ZnO _n (n<1) as the matrix target , other metals or their oxides are used as doping targets. Under the optimized magnetron sputtering process, a low-resistivity zinc oxide film is deposited on a conductive substrate, and then embedded in bismuth oxide powder for hot dipping. A high-performance zinc oxide-bismuth oxide thin film varistor is obtained.

The preparation method of the zinc oxide-bismuth oxide film varistor proposed by the present invention comprises the following steps and contents:

(1) In radio frequency magnetron sputtering equipment, non-stoichiometric sintered ZnO _n (n=0.6-0.99) is used as the matrix target material, one of metal Fe, Co, Ni, Mn and their oxides or A variety of doped targets, fix the target on the target position; fix the clean substrate on the sample stage; turn on the mechanical pump to low vacuum, and turn on the molecular pump when the vacuum of the system reaches 0.1Pa until the vacuum of the system The degree reaches above 2×10 ^-4 Pa.

(2) Pass in the working gas argon with a purity of more than 99.99vol.%, and first perform pre-sputtering for 2-10 minutes to remove the pollutants on the target surface; when the glow stabilizes, start the sputtering of the zinc oxide film shot deposition.

(3) Take out the prepared thin film sample from the magnetron sputtering equipment, in the muffle furnace, bury the prepared zinc _oxide thin film in the commercially available analytical pure _Bi2O3 powder for hot dipping, the hot dipping temperature is 200-600℃, holding time is 20-120min. After hot soaking, the samples were cooled to room temperature in the furnace.

(4) The substrate is one of highly doped conductive silicon wafers, copper sheets, and platinum sheets. The cleaning method is as follows: first put the substrate into acetone and ethanol and use ultrasonic cleaning for 10 minutes to remove the substrate. Oil stains and other pollutants on the surface of the chip; then, rinsed with deionized water; finally, dried with dry N ₂ gas and quickly placed in a vacuum chamber.

(5) the sputtering deposition condition of described zinc oxide thin film is: take Ar as sputtering gas, in Ar or Ar/O _In mixed gas, at ambient temperature, sputtering ZnO _n target and doped metal or oxide For the target, the sputtering power is 60-220W, the sputtering pressure is 0.4-4.0Pa, and the deposition time is 20-75min. And when the thin film is deposited by sputtering, the purity of the oxygen used is above 99.99vol.%, and the volume ratio of the two in the O ₂ /Ar mixed gas is 1-2; the obtained zinc oxide thin film is The oxygen-deficient zinc oxide film is a doped zinc oxide film when doped.

(6) The upper and lower surfaces (film and substrate) of the obtained sample containing zinc oxide-bismuth oxide composite film are respectively covered with electrodes to obtain the piezoresistor (see FIG. 1 ).

(7) The electrode material is one of silver, aluminum, palladium, platinum and gold.

The obtained varistor film was a blue-purple film in appearance.

Under a scanning electron microscope, it can be observed that the obtained zinc oxide-bismuth oxide composite thin film has a dense surface without pores, uniform crystal particles and high roundness. The current-voltage performance test shows that the film with this structure has good pressure-sensitive properties.

In a word, high-performance zinc oxide-bismuth oxide film varistors can be obtained with this technology.

Example 1: Fix the ZnO _0.78 target and the clean highly doped conductive silicon substrate at the corresponding positions of the radio frequency magnetron sputtering equipment, close the chamber, first turn on the mechanical pump to a low vacuum of 0.1Pa, and then turn on the molecular pump Evacuate to a high vacuum of 2×10 ^-4 Pa. Introduce high-purity argon gas, and pre-sputter for 10 minutes. Deposit at ambient temperature, then pass through a mixed gas with a ratio of Ar/O ₂ of 1:1, sputtering power of 220W, sputtering pressure of 1.0Pa, and deposition time of 20min. An oxygen-deficient zinc oxide film was obtained. Then, the prepared ZnO film was embedded in analytically pure Bi ₂ O ₃ powder for hot dipping at 400°C for 40 minutes, and then the sample was cooled to room temperature with the furnace. Coat the upper and lower surfaces of the sample with silver paste as electrodes, and solder the leads to obtain a varistor, and test its pressure-sensitive performance.

The obtained oxygen-deficient zinc oxide-bismuth oxide composite film has a dense surface without pores, uniform crystal particles and high roundness (see Figure 2), excellent nonlinear characteristics (see Figure 3), the nonlinear coefficient is 15.1, and the leakage current is the smallest It is 0.0223mA/cm ² , and the varistor voltage is 0.0176V/nm.

Example 2: Fix the ZnO _0.99 target, pure Fe target and clean highly doped conductive silicon substrate on the corresponding position of the magnetron sputtering equipment, close the chamber, first turn on the mechanical pump to a low vacuum of 0.1Pa, and then Turn on the molecular pump to pump to a high vacuum of 2×10 ^-4 Pa. Introduce high-purity argon gas, and pre-sputter for 2 minutes. Deposit at ambient temperature, only argon gas is passed through, ZnO _0.99 target and pure Fe target are turned on at the same time, the sputtering power is 60W, the sputtering pressure is 2.0Pa, and the deposition time is 60min. An iron-doped zinc oxide film was obtained. Then, the prepared ZnO thin film was embedded in analytically pure Bi ₂ O ₃ powder for hot dipping at a temperature of 500°C and a holding time of 60 min, and then the sample was cooled to room temperature with the furnace. Coat the upper and lower surfaces of the sample with silver paste as electrodes, and solder the leads to obtain a varistor, and test its pressure-sensitive performance.

The obtained oxygen-deficient zinc oxide-bismuth oxide composite film has a dense surface without pores (see Figure 4), excellent nonlinear characteristics (see Figure 5), a nonlinear coefficient of 11.8, a minimum leakage current of 0.0306mA/cm ² , and a pressure Sensitive voltage is 0.0137V/nm.

Claims (4)

1. the preparation method of a zinc oxide-bismuth oxide thin film piezoresitive device, it is characterised in that described method utilizes radio frequency Magnetically controlled sputter method, uses the sintering ZnO of non-stoichiometric_n(n < 1) is matrix target, other metals or its oxide For doping target, under the magnetron sputtering technique optimized, on conductive substrate, deposition obtains the zinc-oxide film of low-resistivity, Then imbedded and bismuth oxide powder carried out hot dipping, it is thus achieved that high performance zinc oxide-bismuth oxide thin film piezoresitive, including with Lower step:

(1) in rf magnetron sputtering equipment, with the sintering ZnO of non-stoichiometric_nFor matrix target, metal One or more in Fe, Co, Ni, Mn and oxide thereof are doping target, are fixed on target position by target；Will Cleaning substrate is fixed on sample stage；Opening mechanical pump and be evacuated to low vacuum, system vacuum reaches to open during 0.1Pa to divide Sub-pump, until the vacuum of system reaches 2 × 10^-4More than Pa；

(2) it is passed through argon working gas, first carries out pre-sputtering 2-10min, remove the pollution of target material surface with this Thing；After aura settles out, at ambient temperature, at argon gas or in argon gas and oxygen mix atmosphere, start oxygen Change the sputtering sedimentation of zinc film；

(3) from magnetron sputtering apparatus, prepared film sample is taken out, in Muffle furnace, the oxidation prepared Zinc film is embedded in the pure Bi of commercially available analysis₂O₃Powder carries out hot dipping；After hot dipping, sample is cooled to room temperature with stove；

(4) upper and lower surface (film and substrate) of the sample containing zinc oxide-bismuth oxide laminated film at gained is upper respectively By electrode, i.e. obtain described piezoresistor.

2. according to the preparation method described in claim 1, it is characterised in that the ZnO in described step (1)_nMatrix target N value in material is between 0.6-0.99；Described doping target is the one in metal Fe, Co, Ni, Mn and oxide thereof Or it is multiple；Described substrate is the one in highly doped conductive silicon chip, copper sheet, platinized platinum；Argon gas in described step (2) and Oxygen is high-purity gas, and purity is at more than 99.99vol.%；Bi in described step (3)₂O₃Powder is commercially available analysis Pure；Electrode material in described step (4) is the one in silver, aluminium, palladium, platinum, gold.

3. according to the preparation method described in claim 1, it is characterised in that in described step (2), zinc-oxide film spatters Penetrating sedimentary condition is: with Ar as sputter gas, at Ar or Ar/O₂In mixed gas, at ambient temperature, sputtering ZnO_n Target and doping metals or oxide target, sputtering power is 60-220W, and sputtering pressure is 0.4-4.0Pa, and sedimentation time is 20-75 min；And when thin film sputtering deposits, O₂In/Ar mixed gas, the volume ratio of the two is 1-2；The zinc-oxide film obtained It is oxygen-starved zinc-oxide film when undoped p, is doping zinc-oxide film when doping.

4. according to the preparation method described in claim 1, it is characterised in that zinc-oxide film in described step (3) Hot-dip process condition is: hot dipping temperature is 200-600 DEG C, and temperature retention time is 20-120min.