CN218676627U - Piezoresistor of aluminum electrode - Google Patents

Abstract

The utility model belongs to the technical field of electronic components, a piezo-resistor of aluminium electrode is disclosed, including ceramic layer, conducting layer and outside electric connection structure, the conducting layer sets up the both sides terminal surface at the ceramic layer respectively to outside electric connection structure and external circuit connection through the homonymy corresponds, the conducting layer includes at least one deck aluminium electrode layer, aluminium electrode layer thickness scope is 5-20um. The utility model discloses an adopt the electrode layer that the aluminium material made, compare other noble metals that adopt among the prior art, have lower material cost and manufacturing cost, owing to confirmed effectual thickness scope, just can realize that the noble metal material replacement originally is for aluminium electrode material, can guarantee its electric conductive property the same with current electrode material, especially to copper electrode material or silver electrode material.

Description

Piezoresistor of aluminum electrode

Technical Field

The utility model belongs to the technical field of the piezo-resistor, concretely relates to piezo-resistor of aluminium electrode.

Background

The piezoresistor is a voltage-limiting type protection device. By utilizing the nonlinear characteristic of the piezoresistor, when overvoltage appears between two poles of the piezoresistor, the piezoresistor can clamp the voltage to a relatively fixed voltage value, thereby realizing the protection of a post-stage circuit. The main parameters of the varistor are: voltage dependent voltage, current capacity, junction capacitance, response time, etc. The response time of the piezoresistor is ns grade, is faster than that of a gas discharge tube, and is slightly slower than that of a TVS tube, so that the response speed of the piezoresistor can meet the requirement of overvoltage protection of an electronic circuit under the common condition. The junction capacitance of the piezoresistor is generally in the order of magnitude range of hundreds to thousands of Pf, and is not suitable for being directly applied to the protection of a high-frequency signal line under many conditions.

When the voltage applied to the varistor is below its threshold value, the current flowing through it is extremely small, corresponding to a resistance of infinite value. That is, when the voltage across it is below its threshold, it behaves as an open-state switch. When the voltage across the varistor exceeds its threshold value, the current flowing through it increases sharply, corresponding to a resistor of infinite resistance. That is, when the voltage applied to it is above its threshold, it behaves as a closed-state switch.

The piezoresistor is manufactured by a typical semiconductor ceramic process. The core material is zinc oxide, and the microstructure of the zinc oxide comprises zinc oxide grains and a grain boundary layer around the grains. The zinc oxide crystal grain has low resistivity and the grain boundary layer has high resistivity, and a potential barrier corresponding to a Zener diode is formed between the crystal grain and the contact surface of the grain boundary layer to form a pressure-sensitive unit. The breakdown voltage of each cell is about 3.5V. A large number of such cells in a varistor are connected in series and in parallel to form the varistor substrate. The more cells are connected in series, the higher the breakdown voltage; the larger the cross-sectional area of the substrate, the more conductive paths that correspond to parallel connections, the greater the current (current capacity) that it allows to pass. When the piezoresistor works, each piezoresistor unit can bear surge energy, namely the whole resistor body can bear the energy, but the piezoresistor can not bear the electric power only by a junction area, such as a semiconductor voltage stabilizing diode (Zener diode), so that the piezoresistor can bear much larger passing current than the semiconductor voltage stabilizing diode. High performance varistor electrodes need to withstand higher density current surges, and electrode materials and processing techniques are key techniques for making varistors.

The zinc oxide core structure is provided with an electrode structure for conducting electricity, the existing electrode structure adopts metal materials with good conducting performance, such as silver and copper, but the cost of the materials is high, the cost of the metal materials is high in actual production, the cost needs to be reduced, and the cost is reduced as much as possible under the condition of keeping the performance unchanged.

SUMMERY OF THE UTILITY MODEL

In order to solve the problems existing in the prior art, the utility model provides an aluminum electrode's piezo-resistor and preparation method thereof, because it is not much as the electrode to adopt the aluminium material among the current piezo-resistor, and this kind of structure cost itself is far less than other noble metal electrodes, then the utility model discloses a sputtering technology sets up appropriate conducting layer and anti-oxidant inoxidizing coating thickness value and can guarantee that its performance can reach service condition and mass production.

The utility model discloses the technical scheme who adopts does:

in a first aspect, the utility model provides an aluminum electrode's piezo-resistor, including ceramic layer, conducting layer and outside electric connection structure, the conducting layer sets up the both sides terminal surface at the ceramic layer respectively to outside electric connection structure and external circuit connection through the homonymy corresponds, the conducting layer includes at least one deck aluminum electrode layer, aluminum electrode layer thickness scope is 5-20um.

In combination with the first aspect, the present invention provides the first embodiment of the first aspect, wherein the thickness of the aluminum electrode layer is in a range of 7-18um.

In combination with the first aspect, the present invention provides a second embodiment of the first aspect, wherein the surface of the aluminum electrode layer is coated with an anti-oxidation protective layer made of nickel-copper alloy or nickel, and the thickness of the protective layer is 0.1um-1.0um.

In combination with the first aspect, the present invention provides the third embodiment of the first aspect, wherein the conductive layer further comprises at least one bottom transition layer, and the thickness of the bottom transition layer is not more than 0.3um.

In combination with the first aspect, the present invention provides the fourth embodiment of the first aspect, wherein the external point connecting structure is an electrode pin, and one end of the electrode pin extends into the varistor and is attached to the aluminum electrode layer.

With reference to the first aspect, the present invention provides a fifth implementation manner of the first aspect, further comprising an insulating layer for covering the whole varistor.

Also discloses a preparation method of the piezoresistor of the aluminum electrode, which is used for preparing any piezoresistor and forming a conductive layer by a sputtering process.

Wherein, under the vacuum environment or inert gas environment, the thickness of the conducting layer of the piezoresistor is enabled to reach a corresponding value by carrying out the sputtering step for a plurality of times;

cooling to 80-90 deg.C between two adjacent sputtering steps.

The sputtering equipment adopted in the sputtering process is provided with a plurality of composite coating chambers, a cooling chamber is arranged between every two adjacent composite coating chambers, and the cooling chambers are in sealed connection with the composite coating chambers.

The sputtering equipment comprises a pre-pumping chamber, a pre-sputtering chamber, a first composite coating chamber, a first cooling chamber, a second composite coating chamber, a post-transition chamber and a second cooling chamber.

The utility model has the advantages that:

the utility model discloses an electrode layer that adopts the aluminium material to make compares other noble metals that adopt in prior art, has lower material cost and manufacturing cost, simultaneously owing to confirmed effectual thickness scope, just can realize that the noble metal material replacement originally is for aluminium electrode material, can guarantee its electric conductive property the same with current electrode material, especially to copper electrode material or silver electrode material.

Drawings

Fig. 1 is a front view of a varistor of the present invention;

fig. 2 is a schematic diagram of the inner plane of the varistor of the present invention after the outer insulating layer is cut;

fig. 3 is the inner shaft measuring and indicating diagram of the middle piezoresistor after sectioning the outer insulating layer.

In the figure: 1-insulating layer, 2-electrode pin, 3-ceramic layer, 4-aluminum electrode layer, 5-bottom transition layer and 6-protective layer.

Detailed Description

The present invention will be further explained with reference to the drawings and the embodiments.

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. The components of the embodiments of the present application, generally described and illustrated in the figures herein, can be arranged and designed in a wide variety of different configurations.

Thus, the following detailed description of the embodiments of the present application, presented in the accompanying drawings, is not intended to limit the scope of the claimed application, but is merely representative of selected embodiments of the application. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments in the present application without making any creative effort belong to the protection scope of the present application.

It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.

In the description of the present application, it should be noted that if the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. are used for indicating the orientation or positional relationship based on the orientation or positional relationship shown in the drawings or the orientation or positional relationship which is usually placed when the product of the application is used, the description is only for convenience and simplicity, and the indication or suggestion that the referred device or element must have a specific orientation, be constructed in a specific orientation and be operated, and thus, should not be construed as limiting the present application. Furthermore, the appearances of the terms "first," "second," and the like in the description herein are only used for distinguishing between similar elements and are not intended to be construed as indicating or implying relative importance.

Furthermore, the terms "horizontal", "vertical" and the like when used in the description of the present application do not require that the components be absolutely horizontal or overhanging, but may be slightly inclined. For example, "horizontal" merely means that the direction is more horizontal than "vertical" and does not mean that the structure must be perfectly horizontal, but may be slightly inclined.

Example 1:

the embodiment discloses a piezoresistor of an aluminum electrode, and the specific structure of the piezoresistor is shown in fig. 1-3.

The same as the prior art is that a layer of insulating layer 1 is arranged outside the piezoresistor, and the insulating layer 1 is coated on the surface of the inner core structure of the piezoresistor by adopting silica gel or epoxy materials, so that the protection effect is achieved. Similarly, other polymers or inorganic materials with the same performance may be used as an alternative, and the embodiment is not limited to the use of silicone rubber or epoxy material for the corresponding encapsulating layer.

Further, the core structure of the varistor in this embodiment includes a ceramic layer 3, and two sides of the ceramic layer 3 are respectively provided with an electrode layer, and the two electrode layers are respectively connected with an external electrical connection structure, which is a thin electrode pin 2 in this embodiment.

The electrode lead 2 includes a portion attached to the surface of the electrode layer and a portion extending out of the insulating layer 1 and connected to an external circuit.

In this embodiment, the electrode layer is designed to have a multi-layer structure, and includes at least two layers, i.e., an aluminum electrode layer 4 and a bottom transition layer 5.

Alternatively, the electrode layer is designed to be a single layer structure, i.e. the aluminum electrode layer 4.

Or, the electrode layer adopts a three-layer structure design, the main material is an aluminum electrode layer 4, the inner side of the aluminum electrode layer is in contact with the ceramic layer 3 and is a bottom transition layer 5, and the surface of the aluminum electrode layer 4 is coated with an anti-oxidation protective layer 6 adopting nickel-copper alloy or nickel, wherein the thickness of the protective layer 6 is 0.1-1.0 um.

In the embodiment, a double-layer structure design is adopted, but the thickness of the aluminum electrode layer 4 in the three schemes is limited within 5-20um and comprises two end values.

Compared with the prior art, the conductivity of the aluminum electrode is lower than that of the silver electrode and the copper electrode which are common in the prior art, and the optimal conductivity and impact resistance can be achieved by limiting the thickness and the manufacturing process of the aluminum electrode.

The thickness of the conducting layer can be increased through temperature control of a sputtering production line, the conducting capacity of the conducting layer is enhanced, the characteristic of low conductivity of the conducting layer is overcome, the same effect is achieved, meanwhile, the capacity of obtaining energy in the aluminum atom sputtering process is stronger than that of a silver-copper material, the deposition rate is higher, meanwhile, the temperature rise is lower, and the sputtering efficiency is higher than that of the silver-copper material.

In this embodiment, a vacuum sputtering coating process is adopted to manufacture the piezoresistor, wherein a vacuum sputtering coating device is adopted, the device comprises at least two complex degree coating chambers, and a first cooling chamber is arranged between two adjacent composite coating chambers and is used for reducing the temperature of the pressure-sensitive workpiece between the two adjacent composite coating chambers to be below a temperature threshold; the first cooling chamber is connected with the two adjacent composite coating chambers in a sealing mode. Wherein the temperature threshold value is 80-90 ℃.

Specifically, a channel is arranged between the composite coating chamber and the first cooling chamber, through which objects to be coated (in this embodiment, piezoresistors, and the piezoresistor semi-finished products which are produced in the equipment in a circulating manner are also called as piezoworkpieces) continuously pass. Wherein, first cooling chamber can adopt one of current multiple cooling technique, the utility model discloses according to the characteristic of sputtering process, with first cooling chamber preferred configuration: the pressure-sensitive workpiece is lowered below a temperature threshold using a molecular flow cooling technique (inert gas cooling technique, preferably nitrogen). And the first cooling chamber is connected with a vacuum generating device, after the temperature of the pressure-sensitive workpiece is reduced to be below a temperature threshold value, the environmental vacuum degree is reduced to be the same as or slightly lower than the vacuum degree of the composite coating chamber through the vacuum generating device, and after the vacuum degree meets the requirement, the pressure-sensitive workpiece is transferred from a corresponding channel of the first cooling chamber to the next composite coating chamber, so that continuous sputtering can be realized. Further, in this embodiment, the composite coating chamber sputters the conductive layer of the varistor with a sub-sputtering; and the temperature of all the composite coating chambers is lower than a safe temperature threshold value, wherein the safe temperature threshold value is as follows: 280-350 ℃. The composite coating chamber can adopt a single-sided sputtering chamber or a double-sided sputtering chamber: when single-side sputtering is adopted, the cold plate cooling is carried out on the other side. And a closed-loop magnetic field capable of increasing the deposition speed is arranged in the compound coating chamber, and an anode deflection electric field is additionally arranged so as to shorten the sputtering time and improve the processing efficiency.

Considering that the cost of the equipment is increased by adding the sputtering chamber, the composite coating chamber is preferably configured into two chambers, the vacuum sputtering coating equipment comprises a pre-pumping chamber, a pre-sputtering chamber, a first composite coating chamber, a first cooling chamber, a second composite coating chamber, a post-coating chamber and a second cooling chamber which are connected in sequence, wherein the second cooling chamber adopts molecular flow cooling.

The specific manufacturing method is as follows: the electrode layer of the piezoresistor is sealed and sputtered in a vacuum environment, namely the two-layer structure design mentioned in the above. The sputtering of the bottom transition layer 5 is performed in the sputtering transition chamber, and then the sputtering of the aluminum electrode layer 4 is performed in the first and second sputtering chambers, while cooling is performed in the cooling chamber. It should be noted that after the sputtering of the bottom transition layer 5, cooling is not required, and only the time is controlled to ensure the temperature of the first composite coating chamber.

Specifically, in a vacuum environment or an inert gas environment, the sputtering step is performed for several times, so that the thickness of the aluminum electrode layer 4 of the piezoresistor reaches 5-20um, the thickness of the bottom transition layer 5 is generally not more than 0.5um, and the piezoresistor can be formed only by single sputtering. Of course, the priming transition layer can be directly sputtered by aluminum material. Because the cooling treatment process is added in the adjacent sputtering process, the vacuum degree is reduced for the next sputtering step after the temperature of the workpiece to be sputtered is reduced to the temperature threshold value.

Specifically, in order to further verify the performance of the conductive layer of the varistor and the differences generated by adopting different manufacturing process conditions, the varistor is subjected to a test in the embodiment.

Table 1 shows that normally produced piezoresistor products (the performance of 14K621 product 8/20us can reach 7 KA/cm) are obtained by adopting a silver paste screen printing mode ² Example of the design reside in

Table 2, using copper as the conductive layer, 5 sets of different process samples were obtained:

table 3: the aluminum material can be directly used as a priming layer and a conductive layer, and 5 groups of samples of conductive layers with different thicknesses are obtained:

the zinc oxide varistor 14K621 ceramic tile was sampled for comparative experiments, and the diameter of the chip of the product was 13.5mm, and the diameter of the conductive layer of the sputtered ceramic tile was 11.2mm. The test products were encapsulated by soldering and then tested for initial electrical properties and withstand 8/20us currentAnd (5) impact capability detection. The current impact of 8/20us is firstly according to 7KA/cm ² Inspecting, and selecting a group of products with qualified impact to perform 8KA/cm ² And (5) impact current testing. The initial leakage current of the product is required to be not more than 20uA, the voltage-sensitive voltage change rate after current impact is not more than 10%, and the appearance is free from visible damage. The varistor products manufactured by the processes 1 to 11 in the tables 1 to 3 are subjected to test comparative test data, which are shown in the following tables 4 to 14:

table 4:

table 5:

the thickness of the printing silver layer reaches 13um and cannot meet 8KA/cm ² And (4) testing.

Table 6:

the sputtered copper layer reaches 5um and cannot meet the 8/20 wave impact current of 7KA/cm ² And (4) performance.

Table 7:

the copper layer reaches 6um and can meet the 8/20 wave impact current of 7KA/cm ² And (4) performance. Then the product of the process is taken again for 8KA/cm ² The results are shown in Table 8:

table 8:

the copper layer reaches 6um and cannot completely meet 8/20 wave impact current of 8KA/cm ² And (4) performance.

The product of the process 4 has over-high temperature in the process chamber, oxidized surface after the product comes out, poor welding and no performance impact test.

Table 9: copper material sample with 6um conducting layer meets 8/20 wave impact current 7KA/cm ² Performance, the conductive layer is a copper material sample of 7um and is directly subjected to 8KA/cm ² And (5) performance testing.

The copper layer reaches 7um and can meet 8/20 wave impact current of 8KA/cm ² And (4) performance.

The sputtering film layer of the product of the process 6 is thick, the process temperature is high, the surface of the product after coming out has partial oxidation phenomenon, and the performance meets 8KA/cm ² However, the sputtering time is long, which is not suitable for mass production.

Table 10:

the aluminum layer reaches 4.9um and cannot meet the 8/20 wave impact current of 7KA/cm ² And (4) performance.

Table 11:

the aluminum layer reaches 7.0um, and part of products can meet the 8/20 wave impact current of 7KA/cm ² Performance, most of which can not meet the requirement of 7KA/cm of 8/20 wave impact current ² And (4) performance.

Table 12:

the aluminum layer reaches 9.3um and meets the 8/20 wave impact current of 7KA/cm ² Performance, then the product of the process is taken again for 8KA/cm ² The results are shown in Table 13:

table 13:

the aluminum layer reaches 9.3um, and part of products can meet 8/20 wave impact current of 8KA/cm ² Performance, most of which can not meet 8/20 wave impact current 8KA/cm ² And (4) performance.

The product of the process 10 has over-high temperature in the process chamber, oxidized surface after the product comes out, overproof pressure-sensitive leakage current and unqualified product. No impact test was performed.

Table 14: the aluminum material sample with the conductive layer of 15.1um is directly subjected to 8KA/cm ² And (5) performance testing.

The aluminum layer reaches 15.0um and meets 8/20 wave impact current of 8KA/cm ² And (4) performance.

The experiment can show that the performances of the 13um silver printing layer, the 6um copper sputtering layer and the 9um aluminum sputtering layer under heavy current impact are consistent, and the 7KA/cm can be met ² The performance requirements of (1) are that the copper layer and the aluminum layer are both produced by adopting a sputtering process, because the electric conductivity of the aluminum and the copper materials is different, the electric conductivity of the aluminum material is about 65 percent of that of the copper material, and the same performance as the copper material can be achieved only by increasing the sputtering thickness of the aluminum material. In the aspect of production cost, taking 14K621 ceramic tiles as an example, the diameter of each chip is 13.5mm, the printing diameter is 11.2mm, the consumption of silver paste is 19 g/thousand, and the existing silver pasteThe unit price is 3500 yuan/kg, and the cost of printing silver paste of one thousand is about 66.5 yuan/thousand.

The diameter of the sputtering template is 11.2mm, the density of the copper material is 8.9g/cm ³ The sputtering thickness is 6um, the theoretical consumption of copper materials is 10.52 g/thousand, and in the actual sputtering process, the utilization rate of the target material can only reach about 70%, so the actual consumption of copper materials is 15.02 g/thousand, the current price of copper is 62000 yuan/ton, 62 yuan/kg, the cost of copper targets processed into copper targets is 124 yuan/kg according to one time of the material price, and the cost is 1.86 yuan/thousand.

The density of the aluminum material is 2.7g/cm ³ The sputtering thickness is 9um, the theoretical consumption of aluminum material is 4.79 g/thousand, the actual consumption is 6.84 g/thousand, the price of the aluminum is 18800 yuan/ton at present, the aluminum is processed into 37.6 yuan/kg of aluminum target, and the cost is 0.26 yuan/thousand.

According to the method, on the premise of achieving the same performance, the cost of printing a silver layer under thousands of silver layers is about 35.8 times of that of sputtering a copper layer, and is 255.8 times of that of sputtering an aluminum material, and the cost of sputtering a copper material is 7.1 times of that of sputtering the aluminum material. The sputtering aluminum material is used as the material of the zinc oxide piezoresistor electrode, so that the production cost can be greatly saved, the large-current tolerance capability can meet the requirement, and the batch production can be realized.

After the thickness of the aluminum electrode layer 4 exceeds 20um, the spraying cost is high, and the requirement of normally welding the piezoresistor is also exceeded, and the piezoresistor with the thickness of the electrode layer generally reaching 20um is used as a valve plate electrode material and is in a compression joint mode.

The embodiment also refers to the parameter settings of the process numbers 7-11, and the sputtered products cannot be welded without starting the sputtering of the nickel-copper protective layer 6. When the piezoresistor with pin plug uses aluminum material as the conducting layer, the electrode surface must be welded and oxidation-resistant protective layer. The protective layer structure is adopted only under the thickness of the aluminum electrode layer 4 of 7-20um, especially 7-16um, so that the conductive performance is better, the cost is lower, the lightning current impact resistance of the piezoresistor can be met, and the welding requirement can be met.

The present invention is not limited to the above-mentioned alternative embodiments, and other various products can be obtained by anyone in light of the present invention. The above detailed description should not be taken as limiting the scope of the invention, which is defined in the following claims, and which can be used to interpret the claims.

Claims (6)

1. The utility model provides an aluminum electrode's piezo-resistor, includes ceramic layer (3), conducting layer and outside electrical connection structure, and the conducting layer sets up respectively at the both sides terminal surface of ceramic layer (3) to outside electrical connection structure and external circuit connection through the homonymy corresponds, its characterized in that: the conducting layer comprises at least one layer of aluminum electrode layer (4), and the thickness range of the aluminum electrode layer (4) is 5-20um.

2. The aluminum electrode varistor as recited in claim 1, wherein: the thickness range of the aluminum electrode layer (4) is 7-18um.

3. The aluminum electrode varistor as recited in claim 1, wherein: the surface of the aluminum electrode layer (4) is coated with an oxidation-resistant protective layer (6) made of nickel-copper alloy or nickel, and the thickness of the protective layer (6) is 0.1-1.0 um.

4. The aluminum electrode varistor as recited in claim 1, wherein: the conducting layer still includes at least one deck bottom transition layer (5), and the thickness of bottom transition layer (5) is no more than 0.3um.

5. The aluminum electrode varistor as recited in claim 1, wherein: the external electric connection structure is an electrode pin (2), and one end of the electrode pin (2) extends into the piezoresistor and is welded with the aluminum electrode layer (4).

6. The aluminum electrode varistor as recited in claim 1, wherein: the varistor further comprises an insulating layer (1) for coating the whole varistor.

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