EP0357113A2 - Production process of a non-linear voltage-dependent resistor - Google Patents

Abstract

A method for manufacturing a voltage-dependent, non-linear resistor having a ceramic sinter body on the basis of the oxides of titanium, bismuth and zinc oxide containing at least one transition metal as resistor material, the sinter body being manufactured by shaping the powdery resistor material and subsequently sintering in air at a temperature in the range of 1,200 to 1,350 DEG C and subsequently being fitted with electrodes, grains being added to the powdery resistor material from resistor material of a medium grain size in the range of 4 to 12 mu m prefired at a temperature in the range of 1,200 to 1,400 DEG C and in a quantity of 1 to 50% by weight. <IMAGE>

Description

The invention relates to a method for producing a non-linear voltage-dependent resistor with a ceramic sintered body based on the oxides of titanium, bismuth and at least one transition metal containing zinc oxide as the resistance material, wherein the sintered body by deforming the powdery resistance material and then sintering in air at a temperature in Range from 1200 to 1350 ^o C and then provided with electrodes.

)^α
worin bedeuten:
I = Strom durch den Varistor
V = Spannungsabfall am Varistor
C = geometrieabhängige Konstante;
sie gibt das Verhältnis

an. In praktischen Fällen kann dieses Verhältnis einen Wert zwischen 15 und einigen 1000 annehmen.
α = Stromindex, Nichtlinearitätskoeffizient oder Regelfaktor; er ist materialabhängig und ist ein Maß für die Steilheit der Strom-Spannungs-Kennlinie; typische Werte liegen im Bereich von 20 bis 80.Nonlinear voltage-dependent resistors (also referred to as varistors in the following) are resistors whose electrical resistance decreases very strongly with increasing voltage at a constant temperature above a response voltage U _A. This behavior can be approximately described by the following formula:
I = ( $\frac{\text{v}}{\text{c}}$

) ^α
in which mean:
I = current through the varistor
V = voltage drop at the varistor
C = geometry-dependent constant;
it gives the relationship

at. In practical cases, this ratio can range from 15 to several 1000.
α = current index, non-linearity coefficient or control factor; it depends on the material and is a measure of the steepness of the current-voltage characteristic; typical values are in the range from 20 to 80.

Varistors are used in many ways to protect electrical systems, devices and expensive components against voltages and voltage peaks. The response voltage U _A of varistors is in the order of 3 V to 3000 V; it is usually defined as the voltage at which a current density of 1 mA / cm² is reached in the varistor. To protect sensitive electronic components, such as integrated circuits, diodes or transistors, low-voltage varistors are increasingly required, whose response voltage U _{A is} below approximately 30 V and which have the highest possible values for the non-linearity coefficient α. The larger the value for the non-linearity coefficient α, the better the effect as a surge limiter and the lower the power consumption of the varistor.

Zinc oxide-based varistors have sintered bodies which are produced from materials in which components are provided which act as donor doping and thus make the zinc oxide grains semiconducting, and which also contain components such as titanium dioxide and bismuth oxide. Titanium dioxide additives promote grain growth and thus reduce the response voltage U _A.

As a result of the doping, the interior of the polycrystalline ZnO grains becomes low-resistance and high-resistance barriers form at the grain boundaries due to the addition of bismuth oxide. The contact resistance between two grains is relatively high at voltages <3.2 V, but decreases at voltages> 3.2 V with increasing voltage by several orders of magnitude.

The response voltage U _A of varistors is essentially determined by the number of grain boundaries that the current I must pass between the electrodes. Low-voltage varistors must therefore either consist of very thin layers with only a few grain boundaries per layer or of materials with very coarse grains. While thin varistor layers made of ceramic based on zinc oxide have so far hardly been used for technical reasons due to a lack of mechanical stability, varistors with coarse-grained sintered bodies based on zinc oxide are the usual way of producing low-voltage varistors.

Sintered bodies made of doped zinc oxide with a relatively coarse grain structure with grain sizes> 100 µm are obtained, for example, when material of the ZnO-Bi₂O₃ system is mixed with about 0.3 to about 1 mol% TiO₂. The TiO₂ addition promotes the reactivity between the liquid Bi₂O₃ and the solid ZnO phase and accelerates the grain growth of the ZnO. The disadvantage, however, is that relatively long, rod-shaped ZnO crystallites often form here, which make it very difficult to check the microstructure of the ceramic structure. The always very wide and almost always inhomogeneous grain distributions in a TiO₂-mixed resistance material from the ZnO-Bi₂O₃ system make the manufacture of varistors with reproducible values for the response voltage U _A <20 V and reproducible values for the non-linearity coefficient α> 20 almost impossible.

Another disadvantage of low-voltage varistors with inhomogeneous microstructures is the low electrical pulse load capacity.

Mechanical damage and electrical degradation of the varistor can be observed after exposure to an electrical impulse with an energy density of <100 Joule / cm³ and a duration of a few µs. The electrical degradation manifests itself in a lowering of the response voltage U _A , in an increase in the leakage current at voltages below U _A and in an asymmetry of the current-voltage characteristic curve which is noticeable when the polarity of the varistor is reversed.

From J. Appl. Phys. 54 (1983), page 1095 ff, a process for the production of varistors based on zinc oxide is known, wherein the ceramic sintered body is given a structure that is as coarse as possible in that the green ceramic raw materials to promote the growth of individual grains seed seeds in the form of undoped Zinc oxide grains with an average grain size in the range from 63 to 105 μm are added. The sintered bodies obtained after sintering have relatively coarse-grained structures, which could make them suitable for the production of low-voltage varistors; However, varistors manufactured from the sintered bodies have non-linearity coefficients α with unusually low values.

In the sintered bodies produced by the known method, the grain density in the structure of the sintered body (number of large grains / volume) is directly proportional to the number of seed nuclei added to the unsintered ceramic mass.

The invention has for its object to provide varistors and in particular low-voltage varistors, which have a sintered body with an improved structural homogeneity and thus an improved mechanical and electrical stability.

This object is achieved according to the invention in that the powdery resistance material comprises grains of resistance material prebaked at a temperature in the range from 1200 to 1400 ^° C. (hereinafter also referred to as “prebaked grains”) with an average grain size in the range from 4 to 12 μm and in one Amount of 1 to 50% by weight can be added.

The invention is based on the following finding: The causes of the electrical degradation and the mechanical destruction of varistors based on zinc oxide with pulse loading are not yet sufficiently known. However, it can be assumed that an inhomogeneity of the microstructure leads to an uneven distribution of the energy in the varistor under pulse load. With an uneven distribution of the grain sizes and the grain boundary phases, there is then a partial electrical overload and degradation of individual grains in the varistor.

According to advantageous developments of the method according to the invention, grains are added to the resistance material in an amount of 3 to 15% by weight and preferably an average grain size of 6 and / or 4.3 μm. If grains of pre-fired resistance material with an average grain size of ≦ 6 µm are added to the unfired resistance mass, a sintered body with a relatively fine-grained structure and a grain size distribution within relatively narrow limits is obtained. The grain size distribution is homogeneous over the entire sintered body and compensates for fluctuations in the density of the unfired green body.

According to a further advantageous embodiment of the method according to the invention, zinc oxide with an addition of the oxides of titanium, antimony, bismuth, manganese, cobalt and nickel is used as the powdery resistance material.

Zinc oxide with an average grain size in the range from 0.7 to 1 μm is preferably used. The selection of the grain size range from 0.7 to 1 μm is advantageous because the resistance material thereby becomes more reactive during sintering, which promotes natural nucleation and supports the growth-regulating influence exerted by the prebaked grains.

For example, a conventional starting mass for varistors, based on zinc oxide with an average grain size in the range of 0.7 to 1 µm with the addition of about 1 to 5 wt.% Bi₂O₃, about 0.5 wt.% Sb₂O₃, about 0.5 wt % Mn₂O₃, about 0.5% by weight of CoO and about 0.5% by weight of TiO₂ according to the present process with different amounts of prebaked grains of the same composition with an average grain size in the range of 4 to 12 µm, so it can be with small amounts of 1 to 3% by weight of the additive, a drastic decrease in the "giant grains" otherwise present in such masses after sintering can be found in the microstructure. Surprisingly, it has been shown that the average grain size in sintered bodies from starting materials produced in this way by the present process does not differ significantly from that of sintered bodies which were sintered under the same conditions, but without the addition of prebaked grains from the resistance material with a defined grain size . However, the structure of sintered bodies produced by the present method is much more homogeneous than that of sintered bodies produced by the known method. This means that the grain growth of the individual grains proceeds more evenly during the sintering process if the present method is used.

With the addition of grains with an average grain size of 12 µm in an amount of up to 3% by weight, the average grain size remains constant, with additions of> 3 to 7% by weight, the average grain size within the structure of the sintered body increases by a factor ≈ 2 observed. With additions in the range> 7 to ≈ 20% by weight, the average grain size in the structure of the sintered body decreases again continuously. The structure or the microstructure of such sintered bodies are relatively homogeneous.

In contrast to the structure of according to the from J. Appl. Phys. Sintered bodies produced by known methods, the grain density (number of large grains / volume) in sintered bodies produced by the present method does not increase proportionally, but rather to the third power of the added number of grains of a defined narrow grain size range.
The added grains of a defined narrow grain size range influencing the microstructure of the sintered bodies produced according to the present method therefore do not represent seed germs for increasing the growth of individual grains, but rather represent additives with a growth-regulating influence.

Surprisingly, a considerable improvement in the electrical properties was observed in the ceramic sintered bodies produced by the present method and the varistors produced from them, in particular with regard to the reproducibility of the values for the electrical parameters response voltage U _A and non-linearity coefficient α. In addition, the varistors produced by the present method showed a significant increase in the pulse capacity.

The individual improvements were as follows: When adding 3 to 15% by weight of the additives mentioned from pre-fired grains with an average grain size of 12 μm, the values for the nonlinearity coefficient α increased by about 20%. The result was adjustable values for the response voltage U _A , irrespective of the sintering temperature and the sintering time, with the addition of grains of a defined average grain size range from 4.3 to 12 µm in an amount of 7 to 50% by weight in the range from 30 V to 200 V with a thickness of the sintered body of 1 mm. The values for the response voltage U _{A were} halved when prebaked grains with a grain size of 12 μm were added in an amount of 7% by weight.

A particular advantage in the case of varistors produced by the present method is a minimization of the standard deviations of the values for the nonlinearity coefficient α and the response voltage U _A by a factor of 5 to 10 compared to the values in the case of varistors produced by known methods. Another particular advantage of the varistors produced by the present method is the increase in their electrical and mechanical stability when subjected to electrical impulses.

• Fig. 1 Verteilungskurven der Standardabweichungen der Werte für U_A für Varistoren mit Sinterkörpern, die mit und ohne Zusatz von vorgebrannten Körnern eines definierten engen Korngrößenbe­reiches gesintert wurden,
• Fig. 2 Verteilungskurven der Standardabweichungen der Werte für α für Varistoren mit Sinterkörpern, die mit und ohne Zusatz von vorgebrannten Körnern eines definierten engen Korngrößenbe­reiches gesintert wurden.

Exemplary embodiments of the invention are described with reference to the drawing and their mode of operation is explained. Show it:

• 1 distribution curves of the standard deviations of the values for U _A for varistors with sintered bodies, which were sintered with and without the addition of pre-fired grains of a defined narrow grain size range,
• Fig. 2 distribution curves of the standard deviations of the values for α for varistors with sintered bodies, which were sintered with and without the addition of pre-fired grains of a defined narrow grain size range.

The production of a starting mass for a ceramic sintered body for a varistor based on zinc oxide is described as an exemplary embodiment.
The starting mass was mixed by mixing 950 g ZnO, 15 g Bi₂O₃, 10 g Co₃O₄, 15 g NiCO₃.2 Ni (OH) ₂.4 H₂O, 5 g TiO₂, 8 g Mn₃O₄, 1 g Sb₂O₃ and 5 g H₃BO₃ in a ball mill produced.

To produce prebaked grains, the same oxide mixture as for the starting mass is granulated with an aqueous dilute solution of polyvinyl alcohol and then prebaked as granules in an open Al₂O₃ crucible over a period of 2 h at a temperature of 1350 ^o C. The pre-fired mass is ground in a ball mill over a period of 12 h to an average grain size of <100 μm.
Grain fractions from the prebaked, ground oxide mixture, which are to be used as an additive to green starting materials, are produced in a sedimentation column. A 0.1% aqueous solution of Na₄P₂O₇.10 H₂O is used as the medium for sedimentation.

The following grain fractions were produced: I: 12 µm; (10%> 16.5 µm, 10% <8.5 µm) II: 6 µm; (10%> 8.9 µm, 10% <5.8 µm) III: 4.3 µm; (10%> 5.5 µm, 10% <3.7 µm).

The grain fractions I, II and III were then wet-mixed with the starting mass prepared as described above in the ratios: Mix 1) 1: 100 Mix 2) 3: 100 Mix 3) 7: 100 Mix 4) 15: 100 Mix 5) 100: 100.

Mixtures of the three grain fractions were prepared, which are designated as I₁ to I₅, II₁ to II₅ and III₁ to III₅.

The powder mixtures were mechanically pressed at a pressure of 1700 bar to cylindrical bodies with a diameter of 15 mm and a thickness of 1.8 mm. The green density was about 55% of the theoretical density. The compacts were then sintered in air at sintering temperatures T _S in the range from 1200 ^o C to 1350 ^o C and a duration of the maximum temperature t in the range from 30 to 480 min. Is advantageously a heating rate during sintering of 40 ^o C / min; it has been shown that the rate of heating during sintering is directly proportional to the number of nuclei formed here. The density of the sintered bodies was 90 to 97% of the theoretical density. After sintering, the sintered bodies had a diameter in the range from 13 to 13.5 mm and a thickness of 1.2 mm.

Metal layer electrodes were applied as electrodes, preferably in the form of Cr-Ni / Au layers, which were reinforced by tin or conductive silver layers for some measurements.

The measurement of the electrical characteristic data nonlinearity coefficient α and response voltage U _A took place in the range from 10⁻⁵ to 10⁻² A. The response voltage U _A was defined as the voltage (V / mm) standardized to 1 mm sintered body thickness, at which a current density in the varistor of 1 mA / cm² occurs.

The mechanical and electrical stability of the sintered body produced by the present method and the varistors made from them were tested by short-pulse loads.

Table 1 shows values for the non-linearity coefficient α and the response voltage U _A for samples of the compositions I₁ to I₅, II₂, II₃ and III₂, which were sintered at sintering temperatures T _S of 1200, 1275 and 1350 ^o C, the maximum sintering temperature in each case was held over a duration t of 30, 60, 120, 240 and 480 min.

Table 2 shows the statistical scatter of the values for the nonlinearity coefficient α and the response voltage U _A of varistors, the sintered bodies of the compositions I₃ and II₃ have compared to a varistor with a sintered body without the addition of pre-fired grains (sample "0").
The sintered bodies were each sintered at a sintering temperature T _S = 1200 ^° C., the maximum temperature in each case being maintained for a period t of 155 minutes or 312 minutes before the cooling process was initiated. From Table 2 it can be seen that the varistors produced by the present method have a significantly smaller statistical spread of their mean values for the response voltage U _A and the non-linearity coefficient α than varistors which were produced without the addition of prebaked grains to the starting mass for the sintered body (sample "0").

• Test 1: 10 Impulse einer Stromstärke von 800 A und einer Spannung von 200 V (1,3 Joule) mit jeweils einem zeitlichen Abstand von 30 s; I_max wurde in 8 µs, I_max/₂wurde nach 20 µs erreicht.
• Test 2: 10 Impulse einer Stromstärke von 2500 A und einer Spannung von 600 V (12 Joule) mit jeweils einem zeitlichen Abstand von 30 s; I_max wurde nach 8 µs erreicht,I_max/₂ wurde nach 20 µs erreicht.

The mechanical and electrical stability of varistors produced by the method according to the invention in comparison to varistors with sintered bodies without the addition of prebaked grains to the starting mass was tested by short-pulse loads with the following parameters:

• Test 1: 10 pulses with a current of 800 A and a voltage of 200 V (1.3 joules), each with a time interval of 30 s; I _max was reached in 8 µs, I _max / ₂ was reached after 20 µs.
• Test 2: 10 pulses with a current of 2500 A and a voltage of 600 V (12 joules), each with a time interval of 30 s; I _max was reached after 8 µs, I _max / ₂ was reached after 20 µs.

The pulse load capacity with regard to the mechanical stability of varistors with sintered bodies, which were produced according to the present method, was tested with short pulse loads according to test 2. The experiments showed that all the varistors, whose sintered bodies had received an addition of prebaked grains with an average grain size in the range from 6 to 12 μm in an amount of 6.5% by weight, remained mechanically stable after 10 pulses, whereas varistors did Sintered bodies without the addition of pre-fired grains were destroyed after only a few pulses in such a way that either punctiform melting zones were formed on the sintered body or that the sintered bodies shattered as a result of thermal stresses.

The pulse resilience with regard to the electrical stability (electrical degradation) of varistors, the sintered bodies of which were produced with or without the addition of prebaked grains in accordance with the present method, was examined with short-pulse loads in accordance with Test 1. Measurement results are shown in Table 3.

The tests showed that varistors with sintered bodies without the addition of prebaked grains, which had been sintered at a sintering temperature T _S = 1200 ^° C. and a duration of the maximum temperature t = 312 min, had a medium decrease in the values at a measuring current density of 1 mA / cm² for the response voltage U _A measured in the pulse direction by up to 55% and measured against the pulse direction by up to 82%.

Varistors with sintered bodies with the addition of prebaked grains with an average grain size of 12 µm in an amount of 6.5% by weight showed, under appropriate test conditions, an average reduction in the values for the response voltage U _A measured in the pulse direction by only up to 20% and counter Pulse direction measured by only up to 40%.

• 1. Zusatz von vorgebrannten Körnern einer mittleren Korngröße von 6,0 µm in einer Menge von 6,5 Gew.%, Sintertemperatur T_S 1200 ^oC, Sinterdauer bei Maximaltemperatur t = 155 min;
  U _A = 50,43 V/mm (Kurve 1);
• 2. Zusatz von vorgebrannten Körnern einer mittleren Korngröße von 12 µm in einer Menge von 6,5 Gew.%, Sintertemperatur T_S = 1200 ^oC, Sinterdauer bei Maximaltemperatur t = 312 min;
  U _A = 35,57 V/mm (Kurve 2);
• 3. Kein Zusatz von vorgebrannten Körnern, Sintertemperatur T_S = 1200 ^oC, Sinterdauer bei Maximaltemperatur t = 155 min;
  U _A = 55,76 V/mm (Kurve 3);
• 4. Kein Zusatz von vorgebrannten Körnern, Sintertemperatur T_S = 1200 ^oC, Sinterdauer bei Maximaltemperatur t = 312 min;
  U _A = 36,21 V/mm (Kurve 4).

1 shows distribution curves of the standard deviation (RH = relative frequency) of the values for the response voltage U _A of different mean values for the response voltage ( U _A ) for varistors with sintered bodies, which were manufactured as follows:

• 1. addition of pre-fired grains with an average grain size of 6.0 μm in an amount of 6.5% by weight, sintering temperature T _S 1200 ^o C, sintering time at maximum temperature t = 155 min;
  U _A = 50.43 V / mm (curve 1);
• 2. Addition of prebaked grains of a mean grain size of 12 .mu.m in an amount of 6.5% by weight, sintering temperature T _S = 1200 ^° C, sintering time at the maximum temperature t = 312 min.
  U _A = 35.57 V / mm (curve 2);
• 3. No addition of pre-fired grains, sintering temperature T _S = 1200 ^o C, sintering time at maximum temperature t = 155 min;
  U _A = 55.76 V / mm (curve 3);
• 4. No addition of pre-fired grains, sintering temperature T _S = 1200 ^o C, sintering time at maximum temperature t = 312 min;
  U _A = 36.21 V / mm (curve 4).

• 1. Zusatz von vorgebrannten Körnern einer mittleren Korngröße von 6 µm in einer Menge von 6,5 Gew.%, Sintertemperatur T_S = 1200 ^oC, Sinterdauer bei Maximaltemperatur t = 155 min; α = 23,13 (Kurve 1);
• 2. Zusatz von vorgebrannten Körnern einer mittleren Korn­größe von 12 µm in einer Menge von 6,5 Gew.%, Sinter­temperatur T_S = 1200 ^oC, Sinterdauer bei Maximal­temperatur t = 312 min; α = 22,27 (Kurve 2);
• 3. Kein Zusatz von vorgebrannten Körnern, Sintertemperatur T_S = 1200 ^oC, Sinterdauer bei Maximaltemperatur t = 155 min; α = 18,60 (Kurve 3);
• 4. Kein Zusatz von vorgebrannten Körnern, Sintertemperatur T_S = 1200 ^oC, Sinterdauer bei Maximaltemperatur t = 312 min; α = 18,13 (Kurve 4).

Tabelle 1 Probe 0 Probe I₁ Probe I₂ Probe I₃ Probe I₄ Probe I₅ Probe II₂ Probe II₃ Probe III₂ Ts = 1200 °C t = 30 min U_A * * * 69 * * 126,1 * 130 α * * * 24,3 * * 18 * * t = 60 min U_A 90,5 83 85 55 65 112,2 80,4 73,3 85,2 α 22,5 23,7 25,4 25 24 12 22,4 22,8 24,6 t = 120 min U_A 58 54 57 40 51 100 66,2 55 63 α 21 22 24 23 21 8 22,5 24,1 26 t = 240 min U_A * * * * * * 45,6 44,7 48,6 α * * * * * * 23,2 23,8 26,2 t = 480 min U_A * * * * * * 37,9 37,1 36,3 α * * * * * * 23,6 25 24,8 Ts = 1275 °C t = 30 min U_A 80,5 72 76 52 54 111 * * * α 25 24 28 27 18 10 * * * t = 60 min U_A 59 54 55 42 49 90 * * * α 23 28 28 23 25 14 * * * t = 120 min U_A 42 42 43 36 38 66 * * * α 23 26 26 24 24 13 * * * Ts = 1350 °C t = 30 min U_A 61 56 58 44 48 76 * * * α 27 27 27 27 23 13 * * * t = 60 min U_A 45 44 44 37 39 56 * * * α 26 25 25 25 21 12 * * * t = 120 min U_A 38 37 36 32 33 42 * * * α 27 26 25 24 21 10 * * * T_S = Sintertemperature, t= Sinterdauer bei Maximaltemperatur * = nicht bestimmt Tabelle 2 U_A T_S = 1200 °C, t = 155 min T_S = 1200 °C, t = 312 min Probe O Probe II₃ Probe O Probe I₃ arithmetrischer Mittelwert U _A (V/mm) 55,8 50,4 36,2 35,6 Standardabweichung Δ U_A 3,7 0,98 4,13 1,01 normiert auf U _A (ΔU_A/U _A) 100% 6,6% 1,9% 11,4% 2,9% α arithmetrischer Mittelwert α 18,6 23,13 18,1 22,3 Standardabweichung Δ α 2,3 0,6 1,97 0,74 normiert auf α (Δα/α) 100% 12,5 2,5 11% 3,3% Tabelle 3 Probe Erniedrigung der Werte für U_A nach Impulsbelastungstest 1 Meßstromdichte 0,01 mA/cm² Meßstromdichte 1 mA/cm² in Pulsrichtung gemessen gegen Pulsrichtung gemessen in Pulsrichtung gemessen gegen Pulsrichtung gemessen 0 - 72% - 77% - 55% - 82% I₃ - 45% - 65% - 20% - 40% T_S = 1200 °C, t = 312 min 2 shows distribution curves of the standard deviation (RH = relative frequency) of the values for the non-linearity coefficient α from different mean values for the non-linearity coefficient ( α ) for varistors with sintered bodies, which were manufactured as follows:

• 1. Addition of prebaked grains of an average grain size of 6 microns in an amount of 6.5% by weight, sintering temperature T _S = 1200 ^° C, sintering time at the maximum temperature t = 155 min. α = 23.13 (curve 1);
• 2. Addition of prebaked grains of a mean grain size of 12 .mu.m in an amount of 6.5% by weight, sintering temperature T _S = 1200 ^° C, sintering time at the maximum temperature t = 312 min. α = 22.27 (curve 2);
• 3. No addition of pre-fired grains, sintering temperature T _S = 1200 ^o C, sintering time at maximum temperature t = 155 min; α = 18.60 (curve 3);
• 4. No addition of pre-fired grains, sintering temperature T _S = 1200 ^o C, sintering time at maximum temperature t = 312 min; α = 18.13 (curve 4).

Table 1 Sample 0 Sample I₁ Sample I₂ Sample I₃ Sample I₄ Sample I₅ Sample II₂ Sample II₃ Sample III₂ Ts = 1200 ° C t = 30 min U _A * * * 69 * * 126.1 * 130 α * * * 24.3 * * 18th * * t = 60 min U _A 90.5 83 85 55 65 112.2 80.4 73.3 85.2 α 22.5 23.7 25.4 25th 24th 12 22.4 22.8 24.6 t = 120 min U _A 58 54 57 40 51 100 66.2 55 63 α 21st 22 24th 23 21st 8th 22.5 24.1 26 t = 240 min U _A * * * * * * 45.6 44.7 48.6 α * * * * * * 23.2 23.8 26.2 t = 480 min U _A * * * * * * 37.9 37.1 36.3 α * * * * * * 23.6 25th 24.8 Ts = 1275 ° C t = 30 min U _A 80.5 72 76 52 54 111 * * * α 25th 24th 28 27th 18th 10th * * * t = 60 min U _A 59 54 55 42 49 90 * * * α 23 28 28 23 25th 14 * * * t = 120 min U _A 42 42 43 36 38 66 * * * α 23 26 26 24th 24th 13 * * * Ts = 1350 ° C t = 30 min U _A 61 56 58 44 48 76 * * * α 27th 27th 27th 27th 23 13 * * * t = 60 min U _A 45 44 44 37 39 56 * * * α 26 25th 25th 25th 21st 12 * * * t = 120 min U _A 38 37 36 32 33 42 * * * α 27th 26 25th 24th 21st 10th * * * T _S = sintering temperature, t = sintering time at maximum temperature * = not determined U _A T _S = 1200 ° C, t = 155 min T _S = 1200 ° C, t = 312 min Sample O Sample II₃ Sample O Sample I₃ arithmetic mean U _A (V / mm) 55.8 50.4 36.2 35.6 Standard deviation Δ U _A 3.7 0.98 4.13 1.01 normalized to U _A (ΔU _A / U _A ) 100% 6.6% 1.9% 11.4% 2.9% α arithmetic mean α 18.6 23.13 18.1 22.3 Standard deviation Δ α 2.3 0.6 1.97 0.74 normalized to α (Δα / α ) 100% 12.5 2.5 11% 3.3% sample Lowering of the values for U _A after pulse exercise test 1 Measuring current density 0.01 mA / cm² Measuring current density 1 mA / cm² measured in the pulse direction measured against pulse direction measured in the pulse direction measured against pulse direction 0 - 72% - 77% - 55% - 82% I₃ - 45% - 65% - 20% - 40% T _S = 1200 ° C, t = 312 min

Claims (6)

1. A method for producing a nonlinear voltage-dependent resistor with a ceramic sintered body based on the oxides of titanium, bismuth and at least one transition metal containing zinc oxide as the resistance material, the sintered body by deforming the powdery resistance material and then sintering in air at a temperature in the range of 1200 to 1350 ^o C is produced and then provided with electrodes,
characterized,
that grains of resistance material prebaked at a temperature in the range from 1200 to 1400 ^° C. with an average grain size in the range from 4 to 12 μm and in an amount of 1 to 50% by weight are added to the powdery resistance material. 2. The method according to claim 1,
characterized,
that grains are added to the resistance material in an amount of 3 to 15% by weight. 3. The method according to claims 1 and 2,
characterized,
that grains with an average grain size of 6 microns are added to the resistance material. 4. The method according to claims 1 and 2,
characterized,
that grains with an average grain size of 4.3 microns are added to the resistance material. 5. The method according to at least one of claims 1 to 4,
characterized,
that zinc oxide with an addition of the oxides of titanium, antimony, bismuth, manganese, cobalt and nickel is used as the powdery resistance material. 6. The method according to claim 5,
characterized,
that zinc oxide with an average grain size in the range of 0.7 to 1 µm is used.

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