JP2010232460A - Voltage nonlinear resistor element and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a voltage nonlinear resistor element with excellent thermal stability whose threshold voltage in voltage-current characteristics is hard to vary by heat, and a method of manufacturing the same. <P>SOLUTION: The voltage nonlinear resistor element 100 includes: opposite conductor layers 2, 6a and 6b; and a multilayer structure 20 provided among the conductor layers and comprising a first NiO layer 3, a group-III-element-containing ZnO layer 4 containing ZnO and a group III element, and a second NiO layer 5, which are laminated in the order named. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a voltage non-linear resistance element and a manufacturing method thereof, and more particularly to a voltage non-linear element used for an overvoltage (surge) protection device in an electronic circuit and a switching element of a driving circuit and a manufacturing method thereof.

  Voltage non-linear resistance elements such as Zener diodes and bulk ceramic varistors are used in overvoltage (surge) protection devices in electronic circuits.

  In recent years, with the miniaturization and high density of electronic components and electronic devices, ultra-small protective elements such as thin film varistors have been actively studied. For example, in Patent Documents 1 and 2 below, there is a voltage nonlinear resistance element using a pn junction in which a NiO thin film that is a p-type semiconductor and a ZnO thin film that is an n-type semiconductor are stacked on a substrate such as a glass substrate. It is disclosed. Further, this document describes that when a pnp structure composed of NiO layer / ZnO layer / NiO layer and an npn structure composed of ZnO layer / NiO layer / ZnO layer are provided, symmetric voltage nonlinearity is exhibited in both directions. Has been.

JP-A-3-268401 JP-A-3-268402

  Generally, a voltage nonlinear resistance element used for ESD (electrostatic discharge) countermeasures is required to flow a large current instantaneously. In this case, although it is a short time, it is said that the temperature of the element rises and reaches several hundred degrees Celsius or more.

  When the present inventors examined the voltage-current characteristic (IV characteristic) of the voltage nonlinear resistance element of the said patent document, when the element receives the temperature of 250 degreeC or more, Vth of IV characteristic ( It was found that the so-called rising voltage (threshold voltage) gradually increases, and the rising voltage rapidly increases above 300 ° C. Moreover, although the initial rising voltage was 10 V or less, it was also found that when a heat treatment at 300 ° C. for 1 hour was applied, the rising voltage increased to 50 V or more.

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a voltage non-linear resistance element excellent in thermal stability in which a rising voltage in voltage-current characteristics is less likely to fluctuate due to heat, and a method for manufacturing the same. And

  The present inventors infer the factors of the thermal instability of the IV characteristics in the conventional NiO layer / ZnO layer / NiO layer laminated structure as follows. The origin of the carrier of the p-type NiO thin film to which no Group I element such as Li is added is excess oxygen existing between the crystal lattices of NiO, while no Group III element such as Al or B is added. In an n-type ZnO thin film, oxygen vacancies in ZnO crystals are considered to be the main carrier origin. The pn junction due to the stacked structure of NiO layer / ZnO layer is considered to be due to the fact that the oxygen-excess semiconductor and the oxygen-deficient semiconductor are in direct contact and a pn junction is formed in the vicinity of the interface. When this junction is heated, it is considered that excess oxygen in NiO diffuses into ZnO and a phenomenon occurs that compensates for oxygen vacancies in the ZnO crystal. When the excess oxygen concentration in NiO decreases, the carrier concentration in p-type NiO decreases, while when the oxygen deficiency concentration in ZnO decreases, the carrier concentration in n-type ZnO decreases. As a result of such oxygen movement due to heating, the carrier concentration of the NiO layer functioning as the p-type layer and the ZnO layer functioning as the n-type layer is decreased, the diffusion potential of the pn junction is decreased, and the breakdown of the pn junction is reduced. It is presumed that the voltage required to occur increases and Vth (threshold voltage) of the IV characteristic is increased.

  As a result of intensive studies based on the above inferences, the present inventors have determined that a specific thin film stack is formed from the viewpoint of suppressing oxygen transfer between the NiO layer / ZnO layer during heating and sufficiently increasing the diffusion potential at the pn junction. By producing a structure and subjecting it to a predetermined heat treatment, the rising voltage of the IV characteristic can be made a suitable range as a varistor, and the rising voltage fluctuates with respect to the subsequent heating. The inventors have found that it is sufficiently small and have completed the present invention.

  A first voltage non-linear resistance element of the present invention includes an opposing conductor layer and a first NiO layer, a Group III element-containing ZnO layer containing ZnO and a Group III element, disposed between these conductor layers, And a laminated structure in which the second NiO layer is laminated in this order.

  The first voltage non-linear resistance element of the present invention can exhibit a symmetric voltage non-linearity in both directions, and the rising voltage in the voltage-current characteristics can be increased by heat by performing a predetermined heat treatment. It can be excellent in thermal stability which does not easily fluctuate. The present inventors consider the reason why such an effect is obtained as follows.

  The group III element-containing ZnO layer can have a sufficient carrier concentration by including the group III element, and thus can function as an n-type layer without increasing the oxygen deficiency concentration. By laminating the group III element-containing ZnO layer capable of reducing the oxygen deficiency concentration and the NiO layer, excess oxygen is difficult to move from the NiO layer, and even in the NiO layer even after the device is heated to a high temperature. It is conceivable that fluctuations in carrier concentration can be reduced. Also for the group III element-containing ZnO layer, the carrier concentration is not easily influenced by the oxygen deficiency concentration, and the fluctuation of the oxygen deficiency concentration due to the movement of oxygen is suppressed. It is conceivable to have By applying a predetermined heat treatment to such a laminated structure, while suppressing the above-described characteristic deterioration due to the movement of oxygen, a group III element is replaced with a Zn site to obtain a stable state in which the carrier concentration is sufficiently increased, As a result of the formation of a pnp structure in which the carrier concentration does not easily fluctuate even by subsequent heating, the present inventors speculate that the effect of the present invention was achieved.

  In addition, the first voltage nonlinear resistance element of the present invention has an advantage that it can be manufactured under conditions where a glass substrate or the like can be used. That is, the laminated structure can be formed by a sputtering method or the like, and the predetermined heat treatment can be performed at a temperature of 300 ° C. or higher and 500 ° C. or lower. An inexpensive glass substrate can be used without being limited to single crystals such as sapphire and quartz.

  The second voltage non-linear resistance element of the present invention is a III layer including a first NiO layer, a first ZnO layer, ZnO and a group III element disposed between opposing conductor layers and the conductor layers. A group element-containing ZnO layer, a second ZnO layer, and a second NiO layer are stacked in this order.

  The second voltage non-linear resistance element of the present invention can be excellent in thermal stability in which the rising voltage in the voltage-current characteristics is less likely to fluctuate due to heat by being subjected to predetermined heat treatment. In addition, the leakage current can be smaller.

  The present inventors consider that the reason why the leakage current is small is that the first and second ZnO layers can suppress the group III element contained in the group III element-containing ZnO layer from diffusing into the NiO layer. ing.

  In the first and second voltage nonlinear resistance elements of the present invention, the group III element is preferably Al.

  The present invention also includes an opposing conductor layer, a first NiO layer, a group III element-containing ZnO layer containing ZnO and a group III element, and a second NiO layer in this order. A method of manufacturing a voltage non-linear resistance element having a laminated structure in which a first NiO layer is formed on one conductor layer so that the NiO layer contains excess oxygen. And forming a Group III element-containing ZnO layer on the first NiO layer, and forming a second NiO layer on the Group III element-containing ZnO layer so that the NiO layer contains excess oxygen. And providing a first voltage non-linear resistance element manufacturing method comprising: a step of forming a laminated structure; and a heating step of heating the laminated structure at 300 ° C. to 500 ° C.

  The present invention also provides an opposing conductor layer, a first NiO layer, a first ZnO layer, a Group III element-containing ZnO layer containing ZnO and a Group III element, and a second NiO layer disposed between these conductor layers. A method for manufacturing a voltage non-linear resistance element having a laminated structure in which a ZnO layer and a second NiO layer are laminated in this order, wherein the NiO layer contains excessive oxygen on one conductor layer The step of forming the first NiO layer, the step of forming the first ZnO layer on the first NiO layer, and the step of forming the group III element-containing ZnO layer on the first ZnO layer And forming a second ZnO layer on the group III element-containing ZnO layer, and forming a second NiO layer on the second ZnO layer so that the NiO layer contains excess oxygen. A step of forming a laminated structure and a laminated structure of 300 ° C. or more and 500 ° C. or less A heating step of heating, to provide a manufacturing method of the second voltage nonlinear resistor element comprising a.

  In the present invention, “the NiO layer contains oxygen excessively” means that the ratio of Ni to oxygen is stoichiometric, not 1: 1, but oxygen is contained in excess of 1. .

  In the first and second voltage nonlinear resistance element manufacturing methods of the present invention, the group III element is preferably Al.

  Moreover, it is preferable that the said heating process is a process of heating a laminated structure at 350 to 450 degreeC.

  The present invention also provides a voltage non-linear resistance element obtained by the method for producing the first or second voltage non-linear resistance element of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the voltage non-linear resistance element excellent in the thermal stability which the rise voltage in a voltage-current characteristic cannot change easily with heat, and its manufacturing method can be provided.

It is a schematic cross section which shows one Embodiment of the voltage nonlinear resistance element of this invention. It is a schematic cross section which shows other embodiment of the voltage nonlinear resistance element of this invention. It is a schematic cross section which shows other embodiment of the voltage nonlinear resistance element of this invention. It is a figure which shows the VI characteristic of the voltage nonlinear resistance element which concerns on Example 1. FIG. It is a figure which shows the VI characteristic of the voltage nonlinear resistance element which concerns on Example 2. FIG. It is a figure which shows the VI characteristic of the voltage nonlinear resistance element which concerns on Example 3. FIG. It is a figure which shows the VI characteristic of the voltage nonlinear resistance element which concerns on Example 4. FIG. It is a figure which shows the VI characteristic of the voltage nonlinear resistance element which concerns on the comparative example 1. FIG.

  FIG. 1 is a schematic cross-sectional view showing a preferred embodiment of the voltage nonlinear resistance element of the present invention. A voltage non-linear resistance element 100 shown in FIG. 1 includes a substrate 1, a conductor layer 2 provided on the substrate 1, a conductor layer 2, and a first NiO layer 3, ZnO, and III. A group structure element-containing ZnO layer 4 containing a group element and a second NiO layer 5 are laminated in this order, and conductor layers 6 a and 6 b provided on the second NiO layer 5. Have. Although the voltage non-linear resistance element 100 has two conductor layers 6a and 6b opposite to the conductor layer 2, there may be three or more conductor layers.

  FIG. 2 is a schematic cross-sectional view showing another embodiment of the voltage nonlinear resistance element of the present invention. A voltage non-linear resistance element 110 shown in FIG. 2 includes a substrate 1, a conductor layer 7 provided on the substrate 1, a conductor layer 7, and a first NiO layer 3, ZnO, and III. A group structure element-containing ZnO layer 4 containing a group element and a second NiO layer 5 are laminated in this order, and a conductor layer 8 provided on the second NiO layer 5 ing.

Examples of the substrate 1 include a glass substrate, a silicon substrate having a surface formed with a thermal oxide film, and a ceramic substrate subjected to surface smoothing. From the viewpoint of obtaining the element at a lower cost, the substrate 1 is preferably a glass substrate made of alkali-free glass or low alkali glass, or a substrate made of soda lime glass having SiO ₂ formed on the surface. When the voltage nonlinear resistance element of the present invention is formed on a circuit board, the board 1 is a circuit board in which wiring and functional parts are formed on a glass / ceramic composite material having a heat resistance of 300 ° C. or higher. It can be.

  In the voltage non-linear resistance element 100, for example, when the conductor layer 6a is a signal line side electrode for connecting to an external signal line, and the conductor layer 6b is a ground electrode for connecting to an external ground line, the conductor layer When a predetermined voltage is applied between 6a and 6b, a current can flow in the stacking direction of the stacked structure 20. The voltage non-linear resistance element 100 at this time functions as a double series varistor element in which two laminated structures 20 are connected in series via a conductor layer 2 that functions as a series connection line. The layer 6a, the laminated structure 20, the conductor layer 2, the laminated structure 20, and the conductor layer 6b are in this order or vice versa.

  In the above case, examples of the conductor layer 2 include an electrode made of Mo, Ni, Ti, Ta, W, or the like. The thickness of the conductor layer 2 can be 300 to 700 nm. Examples of the conductor layers 6a and 6b include electrodes made of Mo, Ni, Ti, Ta, W, and the like. The thickness of the conductor layers 6a and 6b can be 200 to 500 nm.

  In the voltage non-linear resistance element 110, for example, when the conductor layer 7 is a ground electrode that connects to an external ground line, and the conductor layer 8 is a signal line side electrode that connects to an external signal line, the conductor layer When a predetermined voltage is applied between 7 and 8, a current can flow in the stacking direction of the stacked structure 20.

  In the above case, examples of the conductor layer 7 include electrodes made of Mo, Ni, Ti, Ta, W, and the like. The thickness of the conductor layer 7 can be 300 to 700 nm. Examples of the conductor layer 8 include an electrode made of Mo, Ni, Ti, Ta, W, or the like. The thickness of the conductor layer 8 can be 200 to 500 nm.

Examples of the first NiO layer 3 and the second NiO layer 5 include those formed so as to contain oxygen excessively by using a sputtering method using a NiO sintered body as a target. It is preferable that the first NiO layer 3 and the second NiO layer 5 do not contain impurities other than oxygen. The first NiO layer 3 and the second NiO layer 5 preferably have an acceptor concentration of 2 × 10 ¹⁶ / cm ³ or more and 5 × 10 ¹⁶ / cm ³ or more and 5 × 10 ¹⁸ / cm ³ or less. It is more preferable that

  Further, the first NiO layer 3 and the second NiO layer 5 have a specific resistance of a single film measured by a four-probe method from the viewpoint of carrier concentration and mobility suitable for obtaining a good pn junction, It is preferably in the range of about 0.1 Ωcm to 10 Ωcm.

  200-700 nm is preferable and, as for the thickness of the 1st NiO layer 3 and the 2nd NiO layer 5, 300-500 nm is more preferable. When the thickness is less than 200 nm, the voltage at which the current rises tends to increase, and when it exceeds 700 nm, the leakage current tends to increase.

Examples of the group III element-containing ZnO layer 4 include a layer formed by sputtering using a ZnO sintered body added with a compound containing a group III element as a target. Examples of the group III element include Al, B, Ga, and In, but Al is preferable in that a target having a stable composition is easily obtained and the controllability of the carrier concentration is excellent. In this case, it is preferable to use a ZnO sintered body to which Al ₂ O ₃ is added at a concentration of preferably 0.05 to 3.0 mol%, more preferably 0.1 to 2.0 mol% as the target.

The group III element-containing ZnO layer 4 preferably has a donor concentration of 2 × 10 ¹⁶ / cm ³ or more and 1 × 10 ¹⁹ / cm ³ or less from the viewpoint of carrier concentration suitable for obtaining a good pn junction, More preferably, it is 5 × 10 ¹⁶ / cm ³ or more and 5 × 10 ¹⁸ / cm ³ or less.

Further, the group III element-containing ZnO layer 4 preferably has an oxygen deficiency concentration of 1 × 10 ¹⁷ / cm ³ or less, preferably 1 × 10 ¹⁶ / cm ³ or less, from the viewpoint of thermal stability of current-voltage characteristics. More preferably. The “oxygen vacancy concentration” means the concentration of oxygen vacancies in the ZnO film, and can be estimated from the carrier concentration obtained by hole measurement for a ZnO layer to which no impurity is added.

Further, as the group III element-containing ZnO layer 4, the carrier concentration at the center is 2 × 10 ¹⁶ / cm ³ or more and 1 × 10 ¹⁹ / cm ³ or less, and the first NiO layer 3 and the second NiO layer 5 A group III element-containing ZnO layer having a carrier concentration on the contact side of less than 2 × 10 ¹⁶ / cm ³ , more preferably 1 × 10 ¹⁶ / cm ³ or less can be provided. By providing such a layer, leakage current can be reduced. The reason why the leakage current is small is that the side of the group III element-containing ZnO layer in contact with the first NiO layer 3 and the second NiO layer 5 is the group III element contained in the group III element-containing ZnO layer on the NiO layer side. The present inventors think that it functions as a diffusion barrier when it diffuses into the surface.

  The thickness of the group III element-containing ZnO layer 4 is preferably 300 to 1500 nm, and more preferably 500 to 800 nm. When the thickness is less than 300 nm, the leakage current tends to increase. When the thickness exceeds 1500 nm, the substrate warps due to the influence of stress, or the film tends to crack after the heat treatment.

  The voltage nonlinear resistance elements 100 and 110 can have two or more stacked structures 20. When a plurality of stacked structures 20 are stacked in the stacking direction on the substrate 1, it is preferable to provide an electrode layer such as Mo between the stacked structures 20. In the case of the voltage nonlinear resistance element 100, a pair of conductor layers (electrodes) are opposed to the conductor layer 2 on the second NiO layer 5 of each stacked structure 20 as shown in 6a and 6b of FIG. A structure in which the two are aligned is preferable.

  In the voltage non-linear resistance element 100, a balance between the rising voltage of the varistor characteristic and the capacitance can be achieved by changing the number of elements connected in series. The rising voltage increases in proportion to the number of elements connected in series, while the capacitance is inversely proportional to the number of connected elements. In addition, even when an element breaks down, by connecting a plurality of elements in series, the probability of breaking down in the short-circuit mode is greatly reduced. Thereby, the voltage nonlinear resistance element 100 can be excellent in durability.

  FIG. 3 is a schematic cross-sectional view showing another embodiment of the voltage nonlinear resistance element of the present invention. A voltage nonlinear resistance element 120 shown in FIG. 3 includes a substrate 1, a conductor layer 2 provided on the substrate 1, a conductor layer 2, a first NiO layer 3, a first conductor layer 2 ZnO layer 10, group III element-containing ZnO layer 4 containing ZnO and group III elements, second ZnO layer 12, and second NiO layer 5 are stacked in this order, and a second NiO layer 5 and conductor layers 6a and 6b provided on the substrate. The voltage non-linear resistance element 120 has two conductor layers 6a and 6b facing the conductor layer 2, but there may be three or more conductor layers.

  The voltage nonlinear resistance element 120 includes the first ZnO layer 10 and the second ZnO layer 4 between the first NiO layer 3 and the second NiO layer and the group III element-containing ZnO layer 4 in the voltage nonlinear resistance element 100, respectively. The structure is the same as that of the voltage nonlinear resistance element 100 except that two ZnO layers 12 are stacked.

  Examples of the first ZnO layer 10 and the second ZnO layer 12 include those formed by sputtering using a ZnO sintered body to which no impurity is added. The voltage nonlinear resistance element 120 including the first ZnO layer 10 and the second ZnO layer 12 can reduce the leakage current as compared with the voltage nonlinear resistance element 100.

The first ZnO layer 10 and the second ZnO layer 12 have an oxygen deficiency concentration of 2 × 10 ¹⁶ / cm so that oxygen atoms excessively contained in the NiO layer can be prevented from diffusing into the ZnO layer at a high temperature. preferably ³ or less, more preferably 1 × ¹⁰ 16 / cm ³ or less.

  100-500 nm is preferable and, as for the thickness of the 1st ZnO layer 10 and the 2nd ZnO layer 12, 200-400 nm is more preferable. When the thickness is less than 100 nm, the leakage current tends to increase, and when it exceeds 500 nm, the rising voltage tends to increase.

  The laminated structure 20 of the voltage non-linear resistance elements 100 and 110 and the laminated structure 22 of the voltage non-linear resistance element 120 are preferably subjected to predetermined heat treatment. This heat treatment can be performed, for example, by heating the voltage nonlinear resistance element at 300 to 500 ° C., preferably 350 to 450 ° C. The atmosphere during heating is preferably in an inert gas such as nitrogen or argon or in vacuum (reduced pressure) for the purpose of preventing oxidation of the conductive layer material. The heating time can be 30 minutes to 1 hour.

  In the voltage non-linear resistance element according to the present invention, the initial rising voltage in the voltage-current characteristic can be 8V to 32V or more. The initial rising voltage can be set in a desired range depending on the number of elements connected in series. In the case of ESD countermeasures for high-speed, large-capacity signal transmission lines, it is preferable to connect 2 to 4 elements in series, set the rising voltage to 16 V to 32 V, and the capacitance to 0.5 pF or less.

  Next, a method for manufacturing a voltage nonlinear resistance element according to the present invention will be described.

  A first method for manufacturing a voltage nonlinear resistance element according to the present invention includes a conductive layer facing each other and a group III element disposed between these conductive layers and including the first NiO layer, ZnO, and a group III element. A voltage non-linear resistance element manufacturing method having a laminated structure in which a ZnO layer containing and a second NiO layer are laminated in this order, wherein the NiO layer has excessive oxygen on one conductor layer. A step of forming a first NiO layer to contain, a step of forming a Group III element-containing ZnO layer on the first NiO layer, and a NiO layer containing excess oxygen on the Group III element-containing ZnO layer. A step of forming a second NiO layer so as to be contained in the laminated structure to form a laminated structure, and a heating step of heating the laminated structure at 300 ° C. to 500 ° C. According to this manufacturing method, the voltage non-linear resistance elements 100 and 110 described above can be obtained.

  The conductor layer on which the first NiO layer is formed is formed by depositing a material such as Mo, Ni, Ti, Ta, W on the substrate by a method such as sputtering, MOCVD, or EB evaporation. Created. The conductor layer can be formed by patterning by a method such as photolithography, reactive ion etching (RIE), or mechanical scribing as necessary. Further, a conductor layer patterned in advance by masking during film formation may be formed. From the viewpoint of the resistance value of the conductor layer when the two elements are connected in series and the residual stress in the film, the thickness of the conductor layer is preferably in the range of 300 to 700 nm.

  Examples of the method for forming the first NiO layer include a sputtering method using a NiO sintered body as a target. At this time, by forming the film in an environment where oxygen is present, the formed NiO layer can be oxygen-excess.

The first NiO layer is preferably formed so that the acceptor concentration is 2 × 10 ¹⁶ / cm ³ or more. The adjustment of the acceptor concentration of the first NiO layer can be performed by the following procedure, for example. The correlation between the film formation conditions and the acceptor concentration is obtained in advance for a sample in which a NiO layer is formed on a glass substrate. Then, the first NiO layer is formed on the conductor layer under the film forming conditions based on this correlation. The acceptor concentration of the NiO layer in the above sample is a hole capable of measuring the Hall voltage of a high-resistance semiconductor with respect to a measurement sample in which a NiO layer is formed on a glass substrate with a thickness of 500 nm and a Mo electrode is formed thereon with a measurement electrode of 200 nm. It can be obtained by measuring the Hall coefficient using a measuring device and calculating the carrier concentration from the Hall coefficient of the NiO layer. In this case, the acceptor originates from excess oxygen, and the acceptor concentration and the excess oxygen concentration are considered to be equivalent.

The first NiO layer is formed so that the acceptor concentration is 5 × 10 ¹⁶ / cm ³ or more and 5 × 10 ¹⁸ / cm ³ or less in terms of carrier concentration suitable for obtaining a good pn junction. Is preferred.

Examples of the method for forming the group III element-containing ZnO layer include a sputtering method using a ZnO sintered body to which a compound containing a group III element is added as a target. Examples of the group III element include Al, B, Ga, and In, but Al is preferable in that a target having a stable composition is easily obtained and the controllability of the carrier concentration is excellent. In this case, it is preferable to use a ZnO sintered body to which Al ₂ O ₃ is added at a concentration of preferably 0.05 to 3.0 mol%, more preferably 0.5 to 2.0 mol%, as the target.

The group III element-containing ZnO layer is formed so that the donor concentration is 2 × 10 ¹⁶ / cm ³ or more and 1 × 10 ¹⁹ / cm ³ or less from the viewpoint of carrier concentration suitable for obtaining a good pn junction. It is preferable to form a film so as to be 5 × 10 ¹⁶ / cm ³ or more and 5 × 10 ¹⁸ / cm ³ or less.

  Adjustment of the donor concentration of the group III element-containing ZnO layer can be performed, for example, by the following procedure. For a sample in which a group III element-containing ZnO layer is formed on a glass substrate, the correlation between the film formation conditions and the donor concentration is obtained in advance. Then, a group III element-containing ZnO layer is formed on the first NiO layer under the film forming conditions based on this correlation. The donor concentration of the group III element-containing ZnO layer of the sample is obtained by a method similar to the method for calculating the NiO carrier concentration.

  In the present embodiment, the donor concentration of the group III element-containing ZnO layer can be adjusted by appropriately changing the amount of the compound containing the group III element described above and the oxygen deficiency concentration of the group III element-containing ZnO layer.

The group III element-containing ZnO layer is preferably formed such that the oxygen deficiency concentration is 2 × 10 ¹⁶ / cm ³ or less, and more preferably 1 × 10 ¹⁶ / cm ³ or less. . As a method of reducing the oxygen deficiency concentration of the group III element-containing ZnO layer, for example, a method of forming a film in an environment where oxygen exists in a sputtering method using a ZnO sintered body to which a compound containing a group III element is added as a target Is mentioned. The oxygen deficiency concentration can be estimated from the carrier concentration obtained by the hole measurement of ZnO to which no impurity is added.

  The second NiO layer can be formed on the group III element-containing ZnO layer in the same manner as the method for forming the first NiO layer.

  By forming the second NiO layer, a stacked structure is formed in which the first NiO layer, the group III element-containing ZnO layer containing ZnO and a group III element, and the second NiO layer are stacked in this order. The thickness of each layer is preferably within the range described in the description of the voltage nonlinear resistance elements 100 and 110.

  In this embodiment, a conductor layer is formed on the second NiO layer before the step of heating the laminated structure at 300 ° C. or more and 500 ° C. or less. The conductor layer is formed, for example, by depositing a material such as Mo, Ni, Ti, Ta, or W on the second NiO layer by a method such as a sputtering method or an EB vapor deposition method, and then, if necessary, a photolithography method. It can be formed by patterning by a method such as reactive ion etching (RIE) or mechanical scribing. Further, a conductor layer patterned in advance by masking during film formation may be formed. From the viewpoint of workability, the thickness of the conductor layer is preferably in the range of 200 to 500 nm.

  As a method of heating the laminated structure at 300 ° C. or more and 500 ° C. or less, for example, the voltage nonlinear resistance element formed up to the conductor layer is heated at 300 to 500 ° C. in an atmosphere heat treatment furnace. The atmosphere at this time can be in an inert gas such as nitrogen or argon, or in a vacuum (reduced pressure).

  The heating temperature is preferably set to 350 to 450 ° C. in terms of improving the crystallinity of each layer and diffusing the group III element in the group III element-containing ZnO layer. When the heating temperature is less than 350 ° C., the improvement in crystallinity is insufficient, or the activation rate of the donor in the group III element-containing ZnO layer tends not to be sufficiently high. Group III elements in the group element-containing ZnO layer tend to diffuse to the NiO layer.

  The heating time can be 30 minutes to 1 hour.

  In addition, a second method for manufacturing a voltage nonlinear resistance element according to the present invention includes a conductive layer facing each other and a conductive layer between these layers, a first NiO layer, a first ZnO layer, ZnO, and A Group III element-containing ZnO layer containing a Group III element, a second ZnO layer, and a laminated structure in which a second NiO layer is laminated in this order, and a method for manufacturing a voltage nonlinear resistance element, Forming a first NiO layer on the conductor layer so that the NiO layer contains oxygen excessively; forming a first ZnO layer on the first NiO layer; A step of forming a Group III element-containing ZnO layer on the ZnO layer, a step of forming a second ZnO layer on the Group III element-containing ZnO layer, and a NiO layer containing oxygen on the second ZnO layer. A second NiO layer is formed so as to contain excessively to form a laminated structure And a step, a heating step of heating the laminated structure at 300 ° C. or higher 500 ° C. or less, the. According to this manufacturing method, the voltage nonlinear resistance element 120 described above can be obtained.

  The second method for manufacturing a voltage non-linear resistance element according to the present invention includes the step of forming the first ZnO layer and the step of forming the second ZnO layer. It can be performed in the same manner as the first manufacturing method of the linear resistance element.

Examples of the method of forming the first ZnO layer include a sputtering method that targets a ZnO sintered body to which no impurity is added. Further, the first ZnO layer has an oxygen deficiency concentration of 2 from the viewpoint of suppressing oxygen atoms contained in excess in the first NiO layer from diffusing into oxygen deficient portions in the first ZnO layer. it is preferred to deposited to × a ¹⁰ 16 / cm ³ or less, and more preferably deposited to a 1 × ¹⁰ 16 / cm ³ or less. As a method for reducing the oxygen deficiency concentration of the ZnO layer, for example, there is a method of forming a film in an environment where oxygen exists in a sputtering method using a ZnO sintered body as a target.

  The second ZnO layer can also be formed in the same manner as the method for forming the first ZnO layer.

  The voltage non-linear resistance element obtained by the above-described method for manufacturing a voltage non-linear resistance element according to the present invention exhibits symmetric voltage non-linearity in both directions and has a rising voltage in the voltage-current characteristic. Is excellent in thermal stability, which does not easily change due to heat. Since the voltage non-linear resistance element according to the present invention can achieve both a capacitance of 0.5 pF or less and a varistor voltage of 20 V or less, it is suitable for ESD protection for high-speed and large-capacity signal transmission ICs. It can be used suitably.

<Production of voltage nonlinear resistance element>
Example 1
On a glass substrate (low alkali glass, 3 inch diameter wafer), Mo was deposited to a thickness of 500 nm by a sputtering method using Mo (4 inch diameter, 5 mm thickness) as a target to form a first electrode.

Next, on the first electrode, a NiO sintered body (diameter 4 inches, thickness 5 mm) is used as a target, and sputtering is performed under the following conditions, whereby an oxygen-excess first NiO layer (acceptor concentration: 5 × 10 6). ¹⁶ / cm ³ or more) with a thickness of 400 nm.
Substrate temperature: 180 ° C., Ar flow rate: 40 sccm, O ₂ flow rate: 60 sccm, pressure: 2 Pa, RF power: 400 W, deposition time: 40 minutes.

Next, a ZnO sintered body (diameter 4 inches, thickness 5 mm) added with 0.5 mol% of Al ₂ O ₃ is used as a target on the first NiO layer, and sputtering is performed under the following conditions to thereby obtain ZnO: Al. A layer (Al content: about 0.5 atomic%) was formed with a thickness of 500 nm. The oxygen deficiency concentration determined from the Hall coefficient was 1 × 10 ¹⁶ / cm ³ or less, and the donor concentration was 2.5 × 10 ¹⁷ / cm ³ .
Substrate temperature: 180 ° C., Ar flow rate: 40 sccm, O ₂ flow rate: 10 sccm, pressure: 0.5 Pa, RF power: 400 W, film formation time: 30 minutes.

Next, on the ZnO: Al layer, a NiO sintered body (diameter 4 inches, thickness 5 mm) is used as a target, and sputtering is performed under the following conditions, whereby an oxygen-excess second NiO layer (acceptor concentration: 5 × 10 6). ¹⁶ / cm ³ or more) with a thickness of 400 nm.
Substrate temperature: 180 ° C., Ar flow rate: 40 sccm, O ₂ flow rate: 60 sccm, pressure: 2 Pa, RF power: 400 W, deposition time: 40 minutes.

  Next, Mo was deposited to a thickness of 200 nm on the second NiO layer by sputtering using Mo (diameter 4 inches, thickness 5 mm) as a target to form a second electrode.

  Thus, an element having a NiO / ZnO: Al / NiO structure was produced. Next, this element was heated in nitrogen at 350 ° C. for 30 minutes using an atmospheric heat treatment furnace to obtain a voltage nonlinear resistance element.

(Example 2)
In the formation of the ZnO: Al layer, a ZnO: Al layer (Al content: about 0.05 atomic%) with a ZnO sintered body (diameter 4 inches, thickness 5 mm) added with 0.05 mol% of Al ₂ O ₃ as a target A voltage non-linear resistance element was obtained in the same manner as in Example 1 except that was formed. The donor concentration obtained from the Hall coefficient of the ZnO: Al layer was 5 × 10 ¹⁶ / cm ³ .

Example 3
The first NiO layer was formed in the same manner as in Example 1. Next, on the first NiO layer, a ZnO sintered body (4 inches in diameter, 5 mm in thickness) to which no impurities are added is used as a target, and sputtering is performed under the following conditions, whereby the first ZnO layer (Hall coefficient) is obtained. The oxygen deficiency concentration determined from the above was 1 × 10 ¹⁶ / cm ³ or less) with a thickness of 250 nm.
Substrate temperature: 180 ° C., Ar flow rate: 40 sccm, O ₂ flow rate: 10 sccm, pressure: 0.5 Pa, RF power: 400 W, film formation time: 15 minutes.

Next, a ZnO sintered body (diameter 4 inches, thickness 5 mm) to which 0.5 mol% of Al ₂ O ₃ is added is used as a target on the first ZnO layer, and sputtering is performed under the following conditions to thereby obtain ZnO: Al A layer (Al content: about 0.5 atomic%) was formed with a thickness of 250 nm. The oxygen deficiency concentration determined from the Hall coefficient was 1 × 10 ¹⁶ / cm ³ or less, and the donor concentration was 2.5 × 10 ¹⁷ / cm ³ .
Substrate temperature: 180 ° C., Ar flow rate: 40 sccm, O ₂ flow rate: 10 sccm, pressure: 0.5 Pa, RF power: 400 W, film formation time: 15 minutes.

  Next, a second ZnO layer having a thickness of 250 nm was formed on the ZnO: Al layer under the same conditions as the first ZnO layer.

Next, an oxygen-excess second NiO layer (acceptor concentration: 5 ×) is formed on the second ZnO layer by sputtering with a NiO sintered body (diameter 4 inches, thickness 5 mm) as a target under the following conditions. 10 ¹⁶ / cm ³ or more) with a thickness of 400 nm.
Substrate temperature: 180 ° C., Ar flow rate: 40 sccm, O ₂ flow rate: 60 sccm, pressure: 2 Pa, RF power: 400 W, deposition time: 40 minutes.

  Next, Mo was deposited to a thickness of 200 nm on the second NiO layer by sputtering using Mo (diameter 4 inches, thickness 5 mm) as a target to form a second electrode.

  Thus, an element having a NiO / ZnO / ZnO: Al / ZnO / NiO structure was produced. Next, this element was heated in nitrogen at 350 ° C. for 30 minutes using an atmospheric heat treatment furnace to obtain a voltage nonlinear resistance element.

Example 4
In the formation of a ZnO: Al layer, a ZnO: Al layer (Al content: about 2.9 atomic%) is formed using a ZnO sintered body (diameter 4 inches, thickness 5 mm) to which 3 mol% of Al ₂ O ₃ is added as a target. A voltage nonlinear resistance element was obtained in the same manner as in Example 3 except that. The donor concentration determined from the Hall coefficient of the ZnO: Al layer was 1 × 10 ¹⁹ / cm ³ .

(Comparative Example 1)
The first NiO layer was formed in the same manner as in Example 1. Next, on the first NiO layer, a ZnO sintered body to which no impurity is added (diameter 4 inches, thickness 5 mm) is used as a target, and sputtering is performed under the following conditions so that the ZnO layer has a thickness of 500 nm. Formed. Note that oxygen was not flown during the formation of the ZnO layer, and the obtained ZnO layer had a slight oxygen deficiency, so that it became an n-type semiconductor, and the donor concentration was about 1 × 10 ¹⁷ / cm ³ . In this case, it is considered that the origin of the donor is oxygen deficiency and the oxygen deficiency concentration is about 1 × 10 ¹⁷ / cm ³ .
Substrate temperature: 180 ° C., Ar flow rate: 50 sccm, pressure: 0.5 Pa, RF power: 400 W, film formation time: 25 minutes.

Next, on the ZnO layer, a NiO sintered body (diameter 4 inches, thickness 5 mm) is used as a target, and sputtering is performed under the following conditions, whereby an oxygen-excess second NiO layer (acceptor concentration: 5 × 10 ¹⁶ / cm ³ or more) with a thickness of 400 nm.
Substrate temperature: 180 ° C., Ar flow rate: 40 sccm, O ₂ flow rate: 60 sccm, pressure: 2 Pa, RF power: 400 W, deposition time: 40 minutes.

  Thus, an element having an element having a NiO / ZnO / NiO structure was produced. Next, this element was heated in nitrogen at 350 ° C. for 30 minutes using an atmospheric heat treatment furnace to obtain a voltage nonlinear resistance element.

<Evaluation of voltage nonlinear resistance element>
For the voltage nonlinear resistance elements obtained in Examples 1 to 4 and Comparative Example 1, the voltage-current characteristics (VI characteristics) and the threshold voltage (Vth) of the current were examined.

  FIG. 4 is a diagram illustrating VI characteristics when a voltage is applied between the first electrode and the second electrode of the voltage nonlinear resistance element according to the first embodiment. For reference, FIG. 4 also shows the VI characteristics of the element before heat treatment. In FIG. 4, a solid line shows the thing before heat processing, and a broken line shows the thing after heat processing. As shown in FIG. 4, the voltage non-linear resistance element of Example 1 exhibits a good voltage non-linearity with a Vth of about 8 V by heat treatment. In addition, the voltage non-linear resistance element of Example 1 sufficiently maintained the initial Vth even by the subsequent heating (450 ° C., 30 minutes).

  FIG. 5 is a diagram illustrating a VI characteristic when a voltage is applied between the first electrode and the second electrode of the voltage nonlinear resistance element according to the second embodiment. For reference, FIG. 5 also shows the VI characteristics of the element before heat treatment. In FIG. 5, a solid line shows the thing before heat processing, and a broken line shows the thing after heat processing. The voltage non-linear resistance element of Example 2 shows a good voltage non-linearity with a Vth of about 8 V by heat treatment, and can sufficiently maintain the initial Vth by subsequent heating (450 ° C., 30 minutes). confirmed.

  FIG. 6 is a diagram illustrating VI characteristics when a voltage is applied between the first electrode and the second electrode of the voltage nonlinear resistance element according to Example 3. For reference, FIG. 6 also shows the VI characteristics of the element before the heat treatment. In FIG. 6, a solid line shows the thing before heat processing, and a broken line shows the thing after heat processing. As shown in FIG. 6, the voltage non-linear resistance element of Example 3 exhibits a good voltage non-linearity with a Vth of about 7 V by heat treatment. Further, the voltage nonlinear resistance element of Example 3 sufficiently maintained the initial Vth even by the subsequent heating (450 ° C., 30 minutes). Furthermore, it was confirmed that the voltage nonlinear resistance element of Example 3 had a leakage current of 1 μA or less per 6 V, and had equivalent performance even when compared with a commercially available Zener diode. .

  FIG. 7 is a diagram illustrating VI characteristics when a voltage is applied between the first electrode and the second electrode of the voltage nonlinear resistance element of Example 4. For reference, FIG. 7 also shows the VI characteristics of the element before the heat treatment. In FIG. 7, a solid line shows the thing before heat processing, and a broken line shows the thing after heat processing. The voltage non-linear resistance element of Example 4 shows a good voltage non-linearity with a Vth of about 7 V by heat treatment, and the initial Vth can be sufficiently maintained by subsequent heating (450 ° C., 30 minutes). confirmed.

  FIG. 8 is a diagram illustrating VI characteristics when a voltage is applied between the first electrode and the second electrode of the voltage nonlinear resistance element of Comparative Example 1. For reference, FIG. 8 also shows the VI characteristics of the element before the heat treatment. In FIG. 8, a solid line shows the thing before heat processing, and a broken line shows the thing after heat processing. As shown in FIG. 8, in the voltage non-linear resistance element of Comparative Example 1, the voltage Vth of 8 to 9 V before the heat treatment is increased to about Vth 45 V by the heat treatment. Further, with subsequent heating (450 ° C., 30 minutes), Vth further increased, and the leakage current increased rapidly, which was thermally unstable.

DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2 ... Conductor layer, 3 ... 1st NiO layer, 4 ... III group element containing ZnO layer, 5 ... 2nd NiO layer, 6a, 6b ... Conductor layer, 10 ... 1st ZnO layer , 12 ... second ZnO layer, 20, 22 ... laminated structure, 100, 110, 120 ... voltage non-linear resistance element.

Claims (7)

Opposing conductor layers;
A stacked structure in which a first NiO layer, a Group III element-containing ZnO layer containing ZnO and a Group III element, and a second NiO layer are stacked in this order, disposed between the conductor layers;
A voltage non-linear resistance element. Opposing conductor layers;
A first NiO layer, a first ZnO layer, a group III element-containing ZnO layer containing ZnO and a group III element, a second ZnO layer, and a second NiO layer are stacked in this order, disposed between the conductor layers. A laminated structure consisting of
A voltage non-linear resistance element.   The voltage nonlinear resistance element according to claim 1, wherein the group III element is Al. A laminated structure in which an opposing conductor layer, a first NiO layer, a group III element-containing ZnO layer containing ZnO and a group III element, and a second NiO layer are laminated in this order, disposed between the conductor layers. And a method of manufacturing a voltage nonlinear resistance element having:
Forming the first NiO layer on one of the conductor layers so that the NiO layer contains excess oxygen;
Forming the group III element-containing ZnO layer on the first NiO layer;
Forming the second NiO layer on the Group III element-containing ZnO layer so that the NiO layer contains excess oxygen to form the stacked structure;
A heating step of heating the laminated structure at 300 ° C. or more and 500 ° C. or less;
A method for manufacturing a voltage non-linear resistance element. An opposing conductor layer, a first NiO layer, a first ZnO layer, a Group III element-containing ZnO layer containing ZnO and a Group III element, a second ZnO layer, and a second ZnO layer disposed between the conductor layers A laminated structure in which NiO layers are laminated in this order, and a manufacturing method of a voltage nonlinear resistance element,
Forming the first NiO layer on one of the conductor layers so that the NiO layer contains excess oxygen;
Forming the first ZnO layer on the first NiO layer;
Forming the group III element-containing ZnO layer on the first ZnO layer;
Forming the second ZnO layer on the group III element-containing ZnO layer;
Forming the stacked structure by forming the second NiO layer on the second ZnO layer so that the NiO layer contains excessive oxygen; and
A heating step of heating the laminated structure at 300 ° C. or higher and 500 ° C. or lower;
A method for manufacturing a voltage non-linear resistance element.   The method for manufacturing a voltage nonlinear resistance element according to claim 4, wherein the group III element is Al. The voltage nonlinear resistance element obtained by the manufacturing method of the voltage nonlinear resistance element as described in any one of Claims 4-6.

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