GB2615393A

GB2615393A - Composite film strain gauge based on magnetron sputtering and method for preparing the same

Info

Publication number: GB2615393A
Application number: GB2218066.5A
Authority: GB
Inventors: Yang Chengtao; Sun Shangyi; Xu Kangcai
Original assignee: Yangtze River Delta Research Institute of UESTC Huzhou
Current assignee: Yangtze River Delta Research Institute of UESTC Huzhou
Priority date: 2021-12-03
Filing date: 2022-12-01
Publication date: 2023-08-09
Also published as: GB202218066D0; CN114322740A

Abstract

A composite film strain gauge comprises a stainless steel substrate 1, an aluminium oxide insulating layer 2, a nickel chromium alloy film strain layer 3, aluminium oxide protective layer 5, and copper wire 6 cured on the surface of an electrode area of the strain layer through epoxy conductive adhesive 4. The strain layer may comprise four electrode areas and four strain gates, with the strain gates distributed in an array. A method for manufacturing the strain gauge includes preparing a strain layer die by spin-coating a photoresist on the substrate on which the aluminium oxide insulating layer is deposited, fitting using a photoresist mask that is positioned and then exposed in a UV lithography system, developing a hard film to obtain a die, and depositing the strain layer by magnetron sputtering. The protective layer and optionally the insulating layer are also deposited by magnetron sputtering.

Description

COMPOSITE FILM STRAIN GAUGE BASED ON MAGNETRON SPUTTERING AND METHOD FOR PREPARING THE SAME

TECHNICAL FIELD

100011 The present disclosure relates to the technical field of film sensor design and production, particularly to a composite film strain gauge based on magnetron sputtering and a method for preparing the same.

BACKGROUND

100021 A film refers to a material whose scale is far smaller than that of other two dimensions in a thickness direction, generally, a material having a thickness of 1 microns or less is called the film. Because the film material is extremely thin, there is an obvious size effect, that is to say, some itself properties of the film material vary with the thickness, so that the film material has unique properties. The film can be widely applied in many fields, including optics, electrics, magnetics, acoustics and mechanics, and there are multiple types of films. Besides, multifunctionalization and miniaturization are the trend of future technology development, and film devices are just suitable for this development direction. Furthermore, according to different application environments and needs, there are more and more film preparation methods, such as vacuum evaporation, ion plating, sputtering coating, molecular beam epitaxy and chemical vapor deposition. Therefore, more and more film-based devices are widely used in many scientific and life fields. A film strain gauge is a device for measuring stress and strain, which can transform a force signal into an electrical signal to be output after signal amplification and other processing after being connected with an external circuit.

100031 A stress measuring device mainly includes a metal wire type strain gauge, a foil strain gauge and a film strain gauge. For the metal wire type strain gauge, the strain gauge is usually bonded to the substrate by using insulating adhesive, in such the way, although they can be bonded on a curved surface, the adhesive is easily warped due to factors such as long-term working and temperature so as to cause inaccurate strain gauge measurement or even complete failure.

100041 At present, the structure of the commonly used film strain gauge is a composite film structure for the reason that the insulation layer is designed to prevent the formation of a short circuit between the strain layer and the metal substrate, and materials with high resistance and strong adhesion to the metal substrate in the working environment are generally selected. The strain layer can also be of a multi-layer composite structure to minimize the resistance temperature coefficient of the strain gauge so as to compensate for the resistance temperature coefficient. The protective layer is used to protect the strain layer from being oxidized or polluted by the external environment.

100051 At present, the strain layer film materials mainly include nickel chromium alloy, palladium chromium alloy and other alloys, as well as TaN (tantalum nitride) and other semiconductor materials. The research on film strain gauges is also relatively extensive in China, such as the master's thesis of University of Electronic Science and Technology of China, "Development of PdCr High Temperature Film Strain Gauge", which studies the preparation and performance of film strain gauges in high temperature environments. Although palladium chromium alloy films have better performance in high temperature environments, their resistance temperature coefficients are relatively large, and are not suitable for environments with sharp temperature changes The resistance temperature coefficients of the above semiconductor materials are large negative values.

100061 At present, the way of photoetching the patterned strain gate is to first deposit an alloy film on the substrate, then spin-coating a photoresist on the substrate, using the photoresist mask as the mask, developing the hard film to prepare the pattern after exposure by the UV lithography system, and then etching the nickel chromium film outside the strain gate pattern after ion beam etching, and then washing the photoresist This method increases the error caused by the etching process and other variable factors, and the precision of the graphic is low..

SUMMARY

[0007] The objective of the present disclosure is to provide a composite film strain gauge based on magnetron sputtering and a method for preparing the same in order to solve the existing problems. By using the composite film strain gauge and the method, the integration of a film strain gauge and a metal substrate is realized. The adhesion between the strain gauge and the substrate is improved, its reliability is enhanced, and the patterning process of the strain gate becomes simple and stable. The pattern precision is higher, and the strain gauge is easier to minimize. Any paired measurement gate and external circuit can also be used to form a Wheatstone bridge to measure the stress and strain, and more accurate results are obtained by comparing the property of any paired strain gate.

[0008] The technical solution of the present disclosure is as follows: [0009] Provided is a composite film strain gauge based on magnetron sputtering, comprising a stainless steel substrate, an aluminum oxide insulating layer, a nickel chromium alloy film strain layer, an epoxy conductive adhesive, an aluminum oxide protective layer and copper wires, wherein: [0010] the aluminum oxide insulating layer is deposited on the surface of the stainless steel substrate, the nickel chromium alloy film strain layer is deposited on the surface of the aluminum oxide insulating layer, the copper wire is cured on the surface of an electrode area of the nickel chromium alloy film strain layer through the epoxy conductive adhesive, and the aluminum oxide protective layer is deposited on the nickel chromium alloy film strain layer. [0011] Preferably, the nickel chromium alloy film strain layer is located between the aluminum oxide insulating layer and the aluminum oxide protective layer.

[0012] Preferably, the nickel chromium alloy film strain layer comprises four electrode areas and four strain gates, and the strain gates are distributed in an array and the same electrode area is conducted by adjacent two ends.

[0013] Provided is a method for preparing a composite film strain gauge based on magnetron sputtering, comprising the following steps: [0014] step 1: substrate washing: a stainless steel substrate is polished to reach a deposition requirement, and then the surface of the stainless steel substrate is washed for 5 min by using absolute ethanol and dei oni zed water; [0015] step 2: insulating layer preparation: an aluminum oxide insulating layer is deposited on the surface of the washed and dried stainless steel substrate; [0016] step 3: strain layer die preparation: a photoresist is spin-coated on the stainless steel substrate on which the aluminum oxide insulating layer is deposited, fitted by using a photoresist mask to be positioned and then exposed in a UV lithography system, and finally a hard film is developed to obtain a die whose shape is consistent to that of the nickel chromium alloy film strain layer; [0017] step 4: strain layer preparation: on the basis of step 3, the nickel chromium alloy film is deposited by using a magnetron sputtering method; [0018] step 5: photoresist washing: the stainless steel substrate on which the nickel chromium alloy film is deposited in step 4 is placed into the acetone solution to wash the excessive photoresist, so as to obtain the nickel chromium alloy film strain layer whose shape is consistent to that of the die; [0019] step 6: electrode preparation: on the basis of step 5, the copper wire and the electrode area of the nickel chromium alloy film strain layer are connected and cured by using the epoxy conductive adhesive to form the electrode; [0020] step 7: protective layer preparation: on the basis of step 6, the aluminum oxide protective layer is deposited on the nickel chromium alloy film strain layer by using the magnetron sputtering method.

[0021] Preferably, in step 2, the aluminum oxide insulating layer, which has a thickness of 12 gm, is deposited on the surface of the stainless steel substrate by using the magnetron sputtering method and setting a gas flow ratio of oxygen to argon as 1:20.

[0022] Preferably, in step 3, the photoresist mask has an exposed area whose shape is consistent to that of the nickel chromium alloy film strain layer, a non-exposed area at the periphery of the exposed area and a crossed location hole, and the photoresist is the positive photoresist AZ6216.

[0023] Preferably, in step 5, the nickel chromium alloy film strain layer has a thickness of 1000 nm.

[0024] Preferably, in step 6, the electrode area of the nickel chromium alloy film strain layer is bonded with the copper wire via the epoxy conductive adhesive, and then is heated and cured for two hours at 80°C.

[0025] Preferably, in step 7, the aluminum oxide protective layer, which has a thickness of I2 gm, is deposited on the nickel chromium alloy film strain layer by using the magnetron sputtering method and setting a gas flow ratio of oxygen to argon as 1:20.

[0026] The present disclosure has the beneficial effects: [0027] 1. In the present disclosure, UV lithography is used as the strain layer film patterning scheme, which can realize the strain gate pattern with smaller linear width and higher accuracy on the surface of the component, and is suitable for precise components with very high requirements on the pattern size and accuracy. Moreover, the photolithographic mask can be washed and reused for many times. The strain gauges prepared for many times have more consistency and are simple in steps, greatly simplified in production procedures, thereby reducing the influences of external factors to quickly obtain matured process conditions; [0028] 2. In the present disclosure, the strain layer is deposited by magnetron sputtering, and the film prepared by magnetron sputtering has better density compared with the film prepared by the evaporation method, and has better strain performance stability in medium and low temperature environments. Based on radio frequency magnetron sputtering, an aluminum target reacts with oxygen for sputtering, the deposited aluminum oxide film is good in density and insulativity, and the aluminum target is not prone to target poisoning.

[0029] 3. In the present disclosure, the pattern of the strain layer is composed of four groups of paired basic strain gate units which can be connected with an external circuit to form the Wheatstone bridge to measure strain, and can also realize independent measurement of the resistances of the four basic strain gate units. Besides, any two pairs can also used for measurement of four groups. The four groups of measured data are analyzed. If there is significant difference, the abnormal strain gate can be determined, and others can still work. If there is little difference for the four groups of data, an average value of the four groups of data can be taken as a final output.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 is a cross-sectional view according to the present disclosure; [0031] FIG. 2 is a top view of a photolithographic mask according to the present disclosure; [0032] FIG. 3 is a top view of a nickel chromium alloy film strain layer according to the

present disclosure;

[0033] In the figures, 1-stainless steel substrate; 2-aluminum oxide insulating layer; 3-nickel chromium alloy film strain layer; 4-epoxy conductive adhesive; 5-epoxy conductive adhesive; 6-copper wire; 7-electrode area; 8-strain gate; 9-photolithographic mask; 10-exposed area; 11non-exposed area; and 1 2-cro s sed positioning hole.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] Next, the technical solution of the embodiments of the present disclosure will be clearly and completely described in combination with drawings in the embodiments of the present disclosure, obviously, the described embodiments are only some embodiments of the present disclosure but not all the embodiments. Based on the embodiments in the present disclosure, other embodiments made by persons of ordinary skill in the art without creative efforts are all included within the protective scope of the present invention.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the technical field of the invention. The terms used in the specification of the invention herein are only for the purpose of describing specific embodiments, and are not intended to limit the present disclosure. The term "or/and" as used herein includes any and all combinations of one or more related listed items.

[0036] The present disclosure will be further described in combination with Figs.1-3.

[0037] A composite film strain gauge based on magnetron sputtering comprises a stainless steel substrate 1, an aluminum oxide insulating layer 2, a nickel chromium alloy film strain layer 3, an epoxy conductive adhesive 4, an aluminum oxide protective layer 5 and copper wires 6, wherein: the aluminum oxide insulating layer 2 is deposited on the surface of the stainless steel substrate 1, the nickel chromium alloy film strain layer 3 is deposited on the surface of the aluminum oxide insulating layer 2, the copper wire 6 is cured on the surface of an electrode area 7 of the nickel chromium alloy film strain layer 3 through the epoxy conductive adhesive 4, and the aluminum oxide protective layer 5 is deposited on the nickel chromium alloy film strain layer 3.

[0038] Specifically, the nickel chromium alloy film strain layer 3 is located between the aluminum oxide insulating layer 2 and the aluminum oxide protective layer 5.

[0039] Specifically, the nickel chromium alloy film strain layer 3 includes four electrode areas 7 and four strain gates 8, and the strain gates 8 are distributed in an array and the same electrode area 7 is conducted by adjacent two ends.

[0040] A method for preparing a composite film strain gauge based on magnetron sputtering comprises the following steps: [0041] step 1: substrate washing: a stainless steel substrate of (length x width x height) 15 x 15 x 2 mm was polished to reach a deposition requirement, then the surface of the stainless steel substrate 1 is washed for 5 mm by using absolute ethanol and deionized water in turn; [0042] step 2: insulating layer preparation: the washed and dried stainless steel substrate 1 was placed in a vacuum environment of 6.7-lot and then an aluminum oxide film was deposited on the surface of the stainless steel substrate 1 by introducing argon and oxygen as working gases and setting a ratio of oxygen to argon as 1:20 under the conditions of 100 W sputtering power and 1.2Pa pressure to form an aluminum oxide insulating layer 2; [0043] step 3: strain layer die preparation: the stainless steel substrate 1 on which the aluminum oxide insulating layer 2 was deposited was dried for 10 min in a heating platform at 100°C, then put in a spin-coating machine and the AZ6216 photoresist was dropped on the surface of the stainless steel substrate, the time was set as 30s, the stainless steel substrate 1 coated with the photoresist was taken out and heated for 2 min on the heating platform at 100°C again, the photoresist was fitted by using a photoresist mask 9, then the exposed area 10 (blank area in FIG.2) was exposed for 6s in UV lithography system, then the photoresist mask 9 was removed, the stainless steel substrate 1 coated with the photoresist was developed for 10 s in a developing solution and then blown to be dryness to obtain a die whose shape was consistent to that of the nickel chromium alloy film strain layer 3, the die was observed under a microscope, if the die was incomplete, the procedure in step 3 was repeated; [0044] step 4: strain layer preparation: the stainless steel substrate 1 in step 3 was put into a vacuum environment of 6/10, high-pure argon was introduced, and then the nickel chromium alloy film was deposited by magnetron sputtering under the conditions of 0.5 Pa working pressure and 50 W sputtering power; [0045] step 5: photoresist washing: the stainless steel substrate 1 on which the nickel chromium alloy film was deposited in step 4 was placed into an acetone solution to wash the excessive photoresist in the non-exposed area 11, so as to obtain the nickel chromium alloy film strain layer 3 whose shape was consistent to that of the die and which had a thickness of 1000 nm; [0046] step 6: electrode preparation: on the basis of step 5, the epoxy conductive adhesive was used to bond the copper wire with the electrode area 7 of the nickel chromium alloy film strain layer 3, and then heated for 2 h in an oven in an environment of 80°C to be cured to form the electrode; [0047] step 7: protective layer preparation: the stainless steel substrate 1 after step 6 was placed in a vacuum environment of 6.7x10', the aluminum oxide film with a thickness of 1-2 um was deposited on the nickel chromium alloy film strain layer 3 by introducing argon and oxygen as working gases and setting a ratio of oxygen to argon as 1:20 under the conditions of 100 W sputtering power and 1.2 Pa air pressure to form an aluminum oxide protective layer 5, so as to prepare the composite film strain gauge based on magnetron sputtering.

[0048] The above descriptions are only for understanding the method and core concept of the present disclosure. It should be noted that several improvements and modifications can be made by persons of ordinary skill in the art without departing from the principle of the present disclosure, and these improvements and modifications shall fall within the protective scope of the present disclosure.

Claims

CLAIMS1. A composite film strain gauge based on magnetron sputtering, the composite film strain gauge comprising a stainless steel substrate, an aluminum oxide insulating layer, a nickel chromium alloy film strain layer, an epoxy conductive adhesive, an aluminum oxide protective layer and copper wires, wherein: the aluminum oxide insulating layer is deposited on the surface of the stainless steel substrate, the nickel chromium alloy film strain layer is deposited on the surface of the aluminum oxide insulating layer, the copper wire is cured on the surface of an electrode area of the nickel chromium alloy film strain layer through the epoxy conductive adhesive, and the aluminum oxide protective layer is deposited on the nickel chromium alloy film strain layer.
2. The composite film strain gauge based on magnetron sputtering according to claim 1, wherein the nickel chromium alloy film strain layer is located between the aluminum oxide insulating layer and the aluminum oxide protective layer.
3. The composite film strain gauge based on magnetron sputtering according to claim 1, wherein the nickel chromium alloy film strain layer comprises four electrode areas and four strain gates, and the strain gates are distributed in an array and the same electrode area is conducted by adjacent two ends.
4. A method for preparing the composite film strain gauge based on magnetron sputtering according to any one of claims 1-3, comprising the following steps: step 1: substrate washing: after a stainless steel substrate is polished to reach a deposition requirement, the surface of the stainless steel substrate is washed for 5 min by using absolute ethanol and deionized water in turn; step 2: insulating layer preparation: an aluminum oxide insulating layer is deposited on the surface of the washed and dried stainless steel substrate; step 3: strain layer die preparation: a photoresist is spin-coated on the stainless steel substrate on which the aluminum oxide insulating layer is deposited, fitted by using a photoresist mask to be positioned and then exposed in a UV lithography system, and finally a hard film is developed to obtain a die whose shape is consistent to that of the nickel chromium alloy film strain layer; step 4: strain layer preparation: on the basis of step 3, the nickel chromium alloy film is deposited by using a magnetron sputtering method; step 5: photoresist washing: the stainless steel substrate on which the nickel chromium alloy film is deposited in step 4 is placed into the acetone solution to wash the excessive photoresist, so as to obtain the nickel chromium alloy film strain layer whose shape is consistent to that of the die; step 6: electrode preparation: on the basis of step 5, the copper wire and the electrode area of the nickel chromium alloy film strain layer are connected and cured by using the epoxy conductive adhesive to form the electrode; step 7: protective layer preparation: on the basis of step 6, the aluminum oxide protective layer is deposited on the nickel chromium alloy film strain layer by using the magnetron sputtering method.
5. The method for preparing the composite film strain gauge based on magnetron sputtering according to claim 4, wherein in step 2, the aluminum oxide insulating layer, which has a thickness of 1-2 pm, is deposited on the surface of the stainless steel substrate by using the magnetron sputtering method and setting a gas flow ratio of oxygen to argon as 1:20.
6. The method for preparing the composite film strain gauge based on magnetron sputtering according to claim 4, wherein in step 3, the photoresist mask has an exposed area whose shape is consistent to that of the nickel chromium alloy film strain layer, a non-exposed area at the periphery of the exposed area and a crossed location hole, and the photoresist is the positive ph otoresi st AZ6216.
7. The method for preparing the composite film strain gauge based on magnetron sputtering according to claim 4, wherein in step 5, the nickel chromium alloy film strain layer has a thickness of 1000 nm.
8. The method for preparing the composite film strain gauge based on magnetron sputtering according to claim 4, wherein in step 6, the electrode area of the nickel chromium alloy film strain layer is bonded with the copper wire via the epoxy conductive adhesive, and then is heated and cured for two hours at 80°C.
9. The method for preparing the composite film strain gauge based on magnetron sputtering according to claim 4, wherein in step 7, the aluminum oxide protective layer, which has a thickness of 1-2 urn, is deposited on the nickel chromium alloy film strain layer by using the magnetron sputtering method and setting a gas flow ratio of oxygen to argon as 1:20.