Patent Application
20160016813
The present invention relates to an oxide layer, a method of producing the same, and a capacitor, a semiconductor device, and a microelectromechanical system including the same.
There has been conventionally developed an oxide layer including various functional compositions. A device including a ferroelectric thin film that possibly enables high speed operation is developed as an exemplary solid-state electronic device including the oxide layer. There has been also developed BiNbO4 as a dielectric material for a solid-state electronic device, for an oxide layer that does not contain Pb and can be baked at a relatively low temperature. There is a report on dielectric properties of such BiNbO4 formed in accordance with the solid phase epitaxy (Non-Patent Document 1).
There has been also developed a thin film capacitor exemplifying a solid-state electronic device and including a ferroelectric thin film that possibly enables high speed operation. Metal oxide as a dielectric material for a capacitor has been formed mainly in accordance with the sputtering technique (Patent Document 1).
An insulator made of BiNbO4 formed in accordance with the solid phase epitaxy has comparatively small relative permittivity. In order to widely adopt the insulator as a constituent element of a solid-state electronic device (e.g. a capacitor, a semiconductor device, or a microelectromechanical system), dielectric properties need to be further improved, inclusive of relative permittivity of an oxide layer or an oxide film (hereinafter, collectively called an “oxide layer” in this application).
The industry also strongly requires such oxide to be produced in accordance with an excellent production method from the industrial or mass productivity perspectives.
However, it is typically required to bring the inside of a film forming chamber into a high vacuum state in order to achieve fine properties (e.g. electrical properties or stability) of an oxide layer in the sputtering technique. The vacuum process or the photolithography technique other than the sputtering technique also typically requires relatively long time and/or expensive equipment. These processes lead to quite low utilization ratios of raw materials and production energy. When one of the above production methods is adopted, production of an oxide layer and a solid-state electronic device including the oxide layer requires many steps and long time, which is not preferred from the industrial or mass productivity perspectives. The conventional technique also causes the problem that increase in area is relatively difficult to achieve.
In view of the above, one of important technical objects for improvement in performance of an oxide layer and a solid-state electronic device including the oxide layer is to find oxide that has various properties, such as electrical properties, applicable to a solid-state electronic device and achieves various preferred properties through an excellent production method from the industrial or mass productivity perspectives.
The present invention solves the problems mentioned above, to significantly contribute to achievement of an oxide film having high dielectric properties (e.g. high relative permittivity) as well as simplification and energy saving in a process of producing such an oxide film.
The inventors of this application have gone through intensive researches on oxide of high performance, which can be included in a solid-state electronic device such as a capacitor or a thin film capacitor as well as can be formed even in accordance with an inexpensive and simple method. The inventors have found, through many trials and tests, that a specific oxide material replacing conventionally and widely adopted oxide includes a crystal phase having a novel crystal structure. The inventors have also reliably found that the crystal phase enables the specific oxide material to achieve relative permittivity much higher than the conventionally known level.
The inventors of this application have further found that a method of producing the oxide layer performed not necessarily in a high vacuum state achieves inexpensive and simple production steps. The inventors have also found that the oxide layer can be patterned in accordance with an inexpensive and simple method adopting the “imprinting” technique also called “nanoimprinting”. The inventors have thus found that it is possible to obtain oxide of high performance as well as form a layer of the oxide and produce a solid-state electronic device including such oxide layers in accordance with a process that achieves remarkable simplification or energy saving as well as facilitates increase in area in comparison to the conventional technique. The present invention has been devised in view of these points. In this application, “imprinting” is occasionally called “nanoimprinting”.
An oxide layer according to the present invention consists of bismuth (Bi) and niobium (Nb) (possibly including inevitable impurities). The oxide layer also includes a crystal phase of a pyrochlore crystal structure.
Because the oxide layer includes the crystal phase of the pyrochlore crystal structure, the oxide layer achieves higher relative permittivity than that of a conventional oxide layer. Particularly, the inventors of this application analyzed to clarify that, even if this oxide layer includes a crystal phase other than the crystal phase of the pyrochlore crystal structure and the entire oxide layer thus has not very high relative permittivity, the crystal phase of the pyrochlore crystal structure is significantly higher in relative permittivity than a conventional crystal phase. The oxide layer consisting of bismuth (Bi) and niobium (Nb) and having the crystal phase of the pyrochlore crystal structure thus improves electrical properties of various solid-state electronic devices. Any mechanism or any reason why a layer of oxide consisting of bismuth (Bi) and niobium (Nb) (hereinafter, also called “BNO oxide”) achieves the pyrochlore crystal structure has not yet been clarified at the present stage. It is, however, noted that this interesting extraordinary feature achieves the dielectric properties that have never been obtained before.
A method of producing an oxide layer according to the present invention includes the step of heating, in an atmosphere containing oxygen, a precursor layer obtained from a precursor solution as a start material including both a precursor containing bismuth (Bi) and a precursor containing niobium (Nb) as solutes, at a temperature of 520° C. or more and less than 600° C., to form the oxide layer including crystal phases of a pyrochlore crystal structure and consisting of bismuth (Bi) and niobium (Nb) (possibly including inevitable impurities).
The method of producing the oxide layer includes the step of forming an oxide layer that consists of bismuth (Bi) and niobium (Nb) and has the crystal phase of the pyrochlore crystal structure (possibly including inevitable impurities). The oxide layer produced in accordance with this production method thus has higher relative permittivity than that of a conventional oxide layer. Particularly, the inventors of this application analyzed to clarify that, even if this oxide layer includes a crystal phase other than the crystal phase of the pyrochlore crystal structure and the entire oxide layer thus has not very high relative permittivity, the crystal phase of the pyrochlore crystal structure is significantly higher in relative permittivity than a conventional crystal phase. The oxide layer consisting of bismuth (Bi) and niobium (Nb) and having the crystal phase of the pyrochlore crystal structure thus improves electrical properties of various solid-state electronic devices. Any mechanism or any reason why the BNO oxide layer achieves the pyrochlore crystal structure has not yet been clarified at the present stage. It is, however, noted that this interesting extraordinary feature achieves the dielectric properties that have never been obtained before.
According to the method of producing the oxide layer, the oxide layer can be formed through a relatively simple process not in accordance with the photolithography technique (but in accordance with the ink jet technique, the screen printing technique, the intaglio/relief printing technique, the nanoimprinting technique, or the like). There is thus no need to include a process requiring relatively long time and/or expensive equipment, such as the vacuum process. This method of producing the oxide layer is accordingly excellent from the industrial or mass productivity perspectives.
An oxide layer according to the present invention has relative permittivity higher than that of a conventional oxide layer and thus achieves improvement in electrical properties of various solid-state electronic devices.
A method of producing an oxide layer according to the present invention enables production of an oxide layer having higher relative permittivity than that of a conventional oxide layer. This method of producing the oxide layer is also excellent from the industrial or mass productivity perspectives.
a) and 26(b) are a cross-sectional TEM picture and an electron beam diffraction image each showing a crystal structure of an oxide layer serving as an insulating layer in the first embodiment of the present invention.
a) and 27(b) are a cross-sectional TEM picture and an electron beam diffraction image each showing a crystal structure of an oxide layer serving as an insulating layer in a comparative example 5 (the sputtering technique).
a) and 28(b) are a TOPO image (by a scanning probe microscope (in a supersensitive SNDM mode)) and a varied capacity image of each crystal phase in a plan view, of an oxide layer serving as an insulating layer in an example 6.
a) and 29(b) are a TOPO image (by a scanning probe microscope (in a supersensitive SNDM mode)) and a varied capacity image of each crystal phase in a plan view, of the oxide layer serving as an insulating layer in the comparative example 5 (the sputtering technique).
a) and 30(b) are relative permittivity images indicating distribution of calibrated relative permittivity from varied capacity images of each crystal phase in a plan view of the oxide layer serving as an insulating layer in the comparative example 5 (the sputtering technique) and the oxide layer serving as an insulating layer in the example 6.
A solid-state electronic device according to each of the embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In this disclosure, common parts are denoted by common reference signs in all the drawings unless otherwise specified. Furthermore, components according to these embodiments are not necessarily illustrated in accordance with relative scaling in the drawings. Moreover, some of the reference signs may not be indicated for the purpose of easier recognition of the respective drawings.
The substrate 10 can be made of any one of various insulating base materials including highly heat resistant glass, an SiO2/Si substrate, an alumina (Al2O3) substrate, an STO (SrTiO) substrate, an insulating substrate obtained by forming an STO (SrTiO) layer on a surface of an Si substrate with an SiO2 layer and a Ti layer being interposed therebetween, and a semiconductor substrate (e.g. an Si substrate, an SiC substrate, or a Ge substrate).
The lower electrode layer 20 and the upper electrode layer 40 are each made of any one of metallic materials including high melting metal such as platinum, gold, silver, copper, aluminum, molybdenum, palladium, ruthenium, iridium, or tungsten, alloy thereof, and the like.
In the present embodiment, the insulating layer made of a dielectric substance is formed by heating, in an atmosphere containing oxygen, a precursor layer obtained from a precursor solution as a start material including both a precursor containing bismuth (Bi) and a precursor containing niobium (Nb) as solutes (hereinafter, a production method including this step is also called the solution technique). There is thus formed the oxide layer 30 consisting of bismuth (Bi) and niobium (Nb) (possibly including inevitable impurities; this applies hereinafter). Furthermore, as to be described later, the present embodiment is characterized in that a heating temperature (a main baking temperature) for forming the oxide layer is set in the range from 520° C. or more to less than 600° C. (more preferably, 580° C. or less). The oxide layer consisting of bismuth (Bi) and niobium (Nb) is also called a BNO layer.
The present embodiment is not limited to this structure. Moreover, patterning of an extraction electrode layer from each electrode layer is not illustrated in order to simplify the drawings.
Described next is a method of producing the thin film capacitor 100. Temperatures indicated in this application are preset temperatures of a heater.
The oxide layer 30 is then formed on the lower electrode layer 20. The oxide layer 30 is formed through (a) the step of forming and preliminarily baking the precursor layer and then (b) the main baking step.
As shown in
The preliminary baking is then performed in the oxygen atmosphere or in the atmosphere (collectively called an “atmosphere containing oxygen”) for a predetermined time period at a temperature in the range from 80° C. or more to 250° C. or less. The preliminary baking sufficiently evaporates the solvent in the precursor layer 30a and causes a preferred gel state for exerting properties that enable future plastic deformation (possibly a state where organic chains remain before pyrolysis). The preliminary baking is performed preferably at a temperature of 80° C. or more and 250° C. or less in order to reliably cause the above phenomena. The formation of the precursor layer 30a in accordance with the spin coating technique and the preliminary baking are repeated for a plurality of times, so that the oxide layer 30 has desired thickness.
The precursor layer 30a is thereafter heated for a predetermined time period in the oxygen atmosphere (e.g. 100% by volume, although being not limited thereto) at a temperature in the range from 520° C. or more to less than 600° C. (more preferably, 580° C. or less) so as to be mainly baked. As shown in
The oxide layer 30 is preferably 30 nm or more in thickness. If the oxide layer 30 is less than 30 nm in thickness, the leakage current and dielectric loss increase due to decrease in thickness. It is impractical and thus not preferred for a solid-state electronic device to include such an oxide layer.
Table 1 indicates measurement results on the relationship among the atomic composition ratio between bismuth (Bi) and niobium (Nb) in the oxide layer 30, relative permittivity at 1 KHz, and a leakage current value upon applying 0.5 MV/cm.
The atomic composition ratio between bismuth (Bi) and niobium (Nb) was obtained by performing elementary analysis on bismuth (Bi) and niobium (Nb) in accordance with the Rutherford backscattering spectrometry (RBS). The methods of measuring the relative permittivity and the leakage current value are to be detailed later. Table 1 indicates the results of the relative permittivity upon applying the AC voltage of 1 KHz and the leakage current value upon applying the voltage of 0.5 MV/cm. According to Table 1, when the atomic composition ratio between bismuth (Bi) and niobium (Nb) in the oxide layer 30 is in the range from 0.8 or more to 3.3 or less relative to bismuth (Bi) assumed to be one, the relative permittivity and the leakage current value were found to be particularly preferably appropriate for various solid-state electronic devices (e.g. a capacitor, a semiconductor device, or a microelectromechanical system).
The upper electrode layer 40 is subsequently formed on the oxide layer 30.
According to the present embodiment, the oxide layer consisting of bismuth (Bi) and niobium (Nb) is formed by heating, in an atmosphere containing oxygen, the precursor layer obtained from the precursor solution as a start material including both the precursor containing bismuth (Bi) and the precursor containing niobium (Nb) as solutes. When the oxide layer is formed at a heating temperature of 520° C. or more and less than 600° C. (more preferably, 580° C. or less), the oxide layer achieves particularly preferred electrical properties. Furthermore, in the method of producing the oxide layer according to the present embodiment, the precursor solution for the oxide layer has only to be heated in an atmosphere containing oxygen without adopting the vacuum process. Accordingly, increase in area is facilitated and improvement from the industrial or mass productivity perspectives can be significantly achieved in comparison to the conventional sputtering technique.
A thin film capacitor exemplifying a solid-state electronic device according to the present embodiment includes a lower electrode layer and an upper electrode layer each of which is made of conductive oxide (possibly including inevitable impurities; this applies hereinafter) such as metal oxide.
As shown in
Examples of the lower electrode layer 220 and the upper electrode layer 240 can include an oxide layer consisting of lanthanum (La) and nickel (Ni), an oxide layer consisting of antimony (Sb) and tin (Sn), and an oxide layer consisting of indium (In) and tin (Sn) (possibly including inevitable impurities; this applies hereinafter).
Described next is a method of producing the thin film capacitor 200.
As shown in
When the lower electrode layer is a conducting oxide layer consisting of antimony (Sb) and tin (Sn), examples of a lower electrode layer precursor containing antimony (Sb) possibly include antimony acetate, antimony nitrate, antimony chloride, and any antimony alkoxide (e.g. antimony isopropoxide, antimony butoxide, antimony ethoxide, or antimony methoxyethoxide). Examples of a precursor containing tin (Sn) possibly include tin acetate, tin nitrate, tin chloride, and any tin alkoxide (e.g. antimony isopropoxide, antimony butoxide, antimony ethoxide, or antimony methoxyethoxide). When the lower electrode layer is made of conducting oxide consisting of indium (In) and tin (Sn), examples of a precursor containing indium (In) possibly include indium acetate, indium nitrate, indium chloride, and any indium alkoxide (e.g. indium isopropoxide, indium butoxide, indium ethoxide, or indium methoxyethoxide). Examples of a lower electrode layer precursor containing tin (Sn) are similar to those listed above.
The preliminary baking is then performed in an atmosphere containing oxygen for a predetermined time period at a temperature in the range from 80° C. or more to 250° C. or less, for the same reason on the oxide layer according to the first embodiment. The formation of the lower electrode layer precursor layer 220a in accordance with the spin coating technique and the preliminary baking are repeated for a plurality of times, so that the lower electrode layer 220 has desired thickness.
The lower electrode layer precursor layer 220a is then heated to 550° C. for about 20 minutes in the oxygen atmosphere so as to be mainly baked. As shown in
The oxide layer 30 is subsequently formed on the lower electrode layer 220. Similarly to the first embodiment, the oxide layer 30 according to the present embodiment is formed through (a) the step of forming and preliminarily baking the precursor layer and then (b) the main baking step.
As shown in
According to the present embodiment, the oxide layer consisting of bismuth (Bi) and niobium (Nb) is formed by heating, in an atmosphere containing oxygen, the precursor layer obtained from the precursor solution as a start material including both the precursor containing bismuth (Bi) and the precursor containing niobium (Nb) as solutes. When the oxide layer is formed at a heating temperature of 520° C. or more and less than 600° C. (more preferably, 580° C. or less), the oxide layer achieves particularly preferred electrical properties. Furthermore, in the method of producing the oxide layer according to the present embodiment, the precursor solution for the oxide layer has only to be heated in an atmosphere containing oxygen without adopting the vacuum process. This production method thus achieves improvement from the industrial or mass productivity perspectives. Furthermore, the lower electrode layer, the oxide layer serving as an insulating layer, and the upper electrode layer are each made of metal oxide and all the steps can be executed in an atmosphere containing oxygen without adopting the vacuum process. Accordingly, increase in area is facilitated and improvement from the industrial or mass productivity perspectives can be significantly achieved in comparison to the conventional sputtering technique.
Imprinting is performed in the step of forming every one of the layers in a thin film capacitor exemplifying a solid-state electronic device according to the present embodiment.
As shown in
A method of producing the thin film capacitor 300 will be described next.
The present embodiment exemplifies a case where the lower electrode layer 320 in the thin film capacitor 300 is a conducting oxide layer consisting of lanthanum (La) and nickel (Ni). The lower electrode layer 320 is formed through (a) the step of forming and preliminarily baking the precursor layer, (b) the imprinting step, and (c) the main baking step, in this order. Initially formed on the substrate 10 in accordance with the known spin coating technique is a lower electrode layer precursor layer 320a obtained from a lower electrode layer precursor solution as a start material including both a precursor containing lanthanum (La) and a precursor containing nickel (Ni) as solutes.
The lower electrode layer precursor layer 320a is then heated in an atmosphere containing oxygen for a predetermined time period at a temperature in the range from 80° C. or more to 250° C. or less so as to be preliminarily baked. The formation of the lower electrode layer precursor layer 320a in accordance with the spin coating technique and the preliminary baking are repeated for a plurality of times, so that the lower electrode layer 320 has desired thickness.
As shown in
The mold heating temperature is set in the range from 80° C. or more to 300° C. or less for the following reasons. If the heating temperature for the imprinting is less than 80° C., the temperature of the lower electrode layer precursor layer 320a is decreased so that plastic deformability of the lower electrode layer precursor layer 320a deteriorates. This leads to lower moldability during formation of an imprinted structure, or lower reliability or stability after the formation. In contrast, if the heating temperature for the imprinting exceeds 300° C., decomposition of organic chains (oxidative pyrolysis) exerting plastic deformability proceeds and the plastic deformability thus deteriorates. In view of the above, according to a more preferred aspect, the lower electrode layer precursor layer 320a is heated at a temperature in the range from 100° C. or more to 250° C. or less for the imprinting.
The imprinting can be performed with a pressure in the range from 1 MPa or more to 20 MPa or less so that the lower electrode layer precursor layer 320a is deformed so as to follow the shape of the surface of the mold. It is thus possible to highly accurately form a desired imprinted structure. The pressure to be applied for the imprinting is set in such a low range from 1 MPa or more to 20 MPa or less. In this case, the mold is unlikely to be damaged during the imprinting and increase in area can be also achieved advantageously.
The lower electrode layer precursor layer 320a is then entirely etched. As shown in
In this imprinting, preferably, a mold separation process is preliminarily performed on the surface of each of the precursor layers to be in contact with an imprinting surface and/or on the imprinting surface of the mold, and each of the precursor layers is then imprinted. Such a process is performed. Frictional force between each of the precursor layers and the mold can be thus decreased, so that the precursor layer can be imprinted with higher accuracy. Examples of a mold separation agent applicable in the mold separation process include surface active agents (e.g. a fluorochemical surface active agent, a silicon surface active agent, and a non-ionic surface active agent), and diamond-like carbon containing fluorine.
The lower electrode layer precursor layer 320a is subsequently mainly baked. As shown in
The oxide layer 330 serving as an insulating layer is subsequently formed on the lower electrode layer 320. The oxide layer 330 is formed through (a) the step of forming and preliminarily baking the precursor layer, (b) the imprinting step, and (c) the main baking step, in this order.
As shown in
As shown in
The precursor layer 330a is then entirely etched. As shown in
Similarly to the second embodiment, the precursor layer 330a is subsequently mainly baked. As shown in
The step of entirely etching the precursor layer 330a can be executed after the main baking. As described above, according to a more preferred aspect, the step of entirely etching the precursor layer is executed between the imprinting step and the main baking step. This is because the unnecessary region can be removed more easily in comparison to the case of etching each precursor layer after the main baking.
Similarly to the lower electrode layer 320, subsequently formed on the oxide layer 330 in accordance with the known spin coating technique is an upper electrode layer precursor layer 340a obtained from a precursor solution as a start material including both a precursor containing lanthanum (La) and a precursor containing nickel (Ni) as solutes. The upper electrode layer precursor layer 340a is then heated in an atmosphere containing oxygen at a temperature in the range from 80° C. or more to 250° C. or less so as to be preliminarily baked.
As shown in
As shown in
Also according to the present embodiment, the oxide layer consisting of bismuth (Bi) and niobium (Nb) is formed by heating, in an atmosphere containing oxygen, the precursor layer obtained from the precursor solution as a start material including both the precursor containing bismuth (Bi) and the precursor containing niobium (Nb) as solutes. When the oxide layer is formed at a heating temperature of 520° C. or more and less than 600° C. (more preferably, 580° C. or less), the oxide layer achieves particularly preferred electrical properties. Furthermore, in the method of producing the oxide layer according to the present embodiment, the precursor solution for the oxide layer has only to be heated in an atmosphere containing oxygen without adopting the vacuum process. Accordingly, increase in area is facilitated and improvement from the industrial or mass productivity perspectives can be significantly achieved in comparison to the conventional sputtering technique.
The thin film capacitor 300 according to the present embodiment is further provided, on the substrate 10, with the lower electrode layer 320, the oxide layer 330 serving as an insulating layer, and the upper electrode layer 340. The lower electrode layer 320, the oxide layer 330, and the upper electrode layer 340 are stacked on the substrate 10 in this order. Each of these layers is imprinted to have an imprinted structure. There is thus no need to include a process requiring relatively long time and/or expensive equipment, such as the vacuum process, a process in accordance with the photolithography technique, or the ultraviolet irradiation process. The electrode layers and the oxide layer can be thus patterned easily. The thin film capacitor 300 according to the present embodiment is accordingly quite excellent from the industrial or mass productivity perspectives.
Imprinting is performed in the step of forming every one of the layers in a thin film capacitor exemplifying a solid-state electronic device also according to the present embodiment.
Each of the precursor layers having been preliminarily baked is imprinted and then mainly baked. The configurations of the present embodiment similar to those of the first to third embodiments will not be described repeatedly. As shown in
Described next is a method of producing the thin film capacitor 400.
As shown in
The precursor layer 430a is then formed on the lower electrode layer precursor layer 420a having been preliminarily baked. Initially formed on the lower electrode layer precursor layer 420a is the precursor layer 430a obtained from a precursor solution as a start material including both a precursor containing bismuth (Bi) and a precursor containing niobium (Nb) as solutes. The precursor layer 430a is then heated in an atmosphere containing oxygen for a predetermined time period at a temperature in the range from 80° C. or more to 250° C. or less so as to be preliminarily baked.
Similarly to the lower electrode layer precursor layer 420a, subsequently formed on the preliminarily baked precursor layer 430a in accordance with the known spin coating technique is the upper electrode layer precursor layer 440a obtained from a precursor solution as a start material including both a precursor containing lanthanum (La) and a precursor containing nickel (Ni) as solutes. The upper electrode layer precursor layer 440a is then heated in an atmosphere containing oxygen at a temperature in the range from 80° C. or more to 250° C. or less so as to be preliminarily baked.
As shown in
The stacked body of the precursor layers (420a, 430a, and 440a) is then entirely etched. As shown in
The stacked body of the precursor layers (420a, 430a, and 440a) is subsequently mainly baked. As shown in
Also according to the present embodiment, the oxide layer consisting of bismuth (Bi) and niobium (Nb) is formed by heating, in an atmosphere containing oxygen, the precursor layer obtained from the precursor solution as a start material including both the precursor containing bismuth (Bi) and the precursor containing niobium (Nb) as solutes. When the oxide layer is formed at a heating temperature of 520° C. or more and less than 600° C. (more preferably, 580° C. or less), the oxide layer achieves particularly preferred electrical properties. Furthermore, in the method of producing the oxide layer according to the present embodiment, the precursor solution for the oxide layer has only to be heated in an atmosphere containing oxygen without adopting the vacuum process. Accordingly, increase in area is facilitated and improvement from the industrial or mass productivity perspectives can be significantly achieved in comparison to the conventional sputtering technique.
In the present embodiment, all the preliminarily baked precursor layers of the oxide layers are imprinted and then mainly baked. It is thus possible to shorten the steps of forming the imprinted structure.
Examples and comparative examples are provided to describe the present invention in more detail. The present invention is, however, not limited to these examples.
In each of the examples and comparative examples, measurement of physical properties of a solid-state electronic device and composition analysis of a BNO oxide layer were performed in the following manner.
The voltage of 0.25 MV/cm was applied between the lower electrode layer and the upper electrode layer to measure current. The measurement was performed using the analyzer 4156C manufactured by Agilent Technologies, Inc.
Dielectric loss in each of the examples and the comparative examples was measured in the following manner. The voltage of 0.1 V or the AC voltage of 1 KHz was applied between the lower electrode layer and the upper electrode layer at a room temperature to measure dielectric loss. The measurement was performed using the broadband permittivity measurement system 1260-SYS manufactured by TOYO Corporation.
Relative permittivity in each of the examples and the comparative examples was measured in the following manner. The voltage of 0.1 V or the AC voltage of 1 KHz was applied between the lower electrode layer and the upper electrode layer to measure relative permittivity. The measurement was performed using the broadband permittivity measurement system 1260-SYS manufactured by TOYO Corporation.
Elementary analysis was performed using Pelletron 3SDH manufactured by National Electrostatics Corporation in accordance with the Rutherford backscattering spectrometry (RBS), the Hydrogen Forward scattering Spectrometry (HFS), and the Nuclear Reaction Analysis (NRA), to obtain content percentages of carbon and hydrogen in the BNO oxide layer according to each of the examples and the comparative examples.
The BNO oxide layer according to each of the examples and the comparative examples was observed using a cross-sectional Transmission Electron Microscopy (TEM) picture and an electron beam diffraction image. A Miller index and an interatomic distance were obtained from the electron beam diffraction image of the BNO oxide layer according to each of the examples and the comparative examples, and fitting with a known crystal structure model was performed to analyze the structure. Adopted as the known crystal structure model was (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7, β-BiNbO4, or Bi3NbO7.
A thin film capacitor of the example 1 was produced in accordance with the production method of the present embodiment. A lower electrode layer is initially formed on a substrate and an oxide layer is formed subsequently. An upper electrode layer is then formed on the oxide layer. The substrate is made of highly heat resistant glass. The lower electrode layer made of platinum (Pt) was formed on the substrate in accordance with the known sputtering technique. The lower electrode layer was 200 nm thick in this case. Bismuth octylate was used as a precursor containing bismuth (Bi) and niobium octylate was used as a precursor containing niobium (Nb) for the oxide layer serving as an insulating layer. Preliminary baking was performed by heating to 250° C. for five minutes. Formation of a precursor layer in accordance with the spin coating technique and the preliminary baking were repeated for five times. The precursor layer was heated to 520° C. for about 20 minutes in the oxygen atmosphere so as to be mainly baked. The oxide layer 30 was about 170 nm thick. The thickness of each of the layers was obtained as a difference in height between each of the layers and the substrate in accordance with the tracer method. The atomic composition ratio between bismuth (Bi) assumed to be one and niobium (Nb) was 1:1 in the oxide layer. The upper electrode layer made of platinum (Pt) was formed on the oxide layer in accordance with the known sputtering technique. The upper electrode layer in this case was 100 μm×100 μm in size and 150 nm in thickness. Electrical properties exhibited the leakage current value of 3.0×10−4 A/cm2, the dielectric loss of 0.025, and the relative permittivity of 62. It was also found that the BNO oxide layer has a fine crystal phase of the pyrochlore crystal structure. More specifically, the pyrochlore crystal structure was found to be either the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 structure or substantially identical with or approximate to the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 structure.
A thin film capacitor according to the example 2 was produced under conditions similar to those of the example 1 except that the precursor layer was heated to 520° C. for one hour in the oxygen atmosphere so as to be mainly baked. Electrical properties exhibited the leakage current value of 3.0×10−8 A/cm2, the dielectric loss of 0.01, and the relative permittivity of 70. It was also found that the BNO oxide layer has a fine crystal phase of the pyrochlore crystal structure. More specifically, the pyrochlore crystal structure was found to be either the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 structure or substantially identical with or approximate to the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 structure. Furthermore, the carbon content percentage had a small value of 1.5 atm % or less, which is equal to or less than the detectable limit. The hydrogen content percentage was 1.6 atm %.
A thin film capacitor according to the example 3 was produced under conditions similar to those of the example 1 except that the precursor layer was heated to 530° C. for 20 minutes in the oxygen atmosphere so as to be mainly baked. Electrical properties exhibited the leakage current value of 3.0×10−6 A/cm2, the dielectric loss of 0.01, and the relative permittivity of 110. It was also found that the BNO oxide layer has a fine crystal phase of the pyrochlore crystal structure. More specifically, the pyrochlore crystal structure was found to be either the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 structure or substantially identical with or approximate to the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 structure.
A thin film capacitor according to the example 4 was produced under conditions similar to those of the example 1 except that the precursor layer was heated to 530° C. for two hours in the oxygen atmosphere so as to be mainly baked. Electrical properties exhibited the leakage current value of 8.8×10−8 A/cm2, the dielectric loss of 0.018, and the relative permittivity of 170. It was also found that the BNO oxide layer has a fine crystal phase of the pyrochlore crystal structure. More specifically, the pyrochlore crystal structure was found to be either the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 structure or substantially identical with or approximate to the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 structure. Furthermore, the carbon content percentage had a small value of 1.5 atm % or less, which is equal to or less than the detectable limit. The hydrogen content percentage was 1.4 atm %.
A thin film capacitor according to the example 5 was produced under conditions similar to those of the example 1 except that the precursor layer was heated to 550° C. for one minute in the oxygen atmosphere so as to be mainly baked. Electrical properties exhibited the leakage current value of 5.0×10−7 A/cm2, the dielectric loss of 0.01, and the relative permittivity of 100. It was also found that the BNO oxide layer has a fine crystal phase of the pyrochlore crystal structure. More specifically, the pyrochlore crystal structure was found to be either the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 structure or substantially identical with or approximate to the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 structure.
A thin film capacitor according to the example 6 was produced under conditions similar to those of the example 1 except that the precursor layer was heated to 550° C. for 20 minutes in the oxygen atmosphere so as to be mainly baked. Electrical properties exhibited the leakage current value of 1.0×10−6 A/cm2, the dielectric loss of 0.001, and the relative permittivity of 180. It was also found that the BNO oxide layer has a fine crystal phase of the pyrochlore crystal structure. More specifically, the pyrochlore crystal structure was found to be either the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 structure or substantially identical with or approximate to the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 structure. Furthermore, the carbon content percentage was 1.5 atm % or less and the hydrogen content percentage was 1.0 atm % or less, each of which had a small value equal to or less than the detectable limit.
A thin film capacitor according to the example 7 was produced under conditions similar to those of the example 1 except that the precursor layer was heated to 550° C. for 12 hours in the oxygen atmosphere so as to be mainly baked. Electrical properties exhibited the leakage current value of 2.0×10−5 A/cm2, the dielectric loss of 0.004, and the relative permittivity of 100. It was also found that the BNO oxide layer has a fine crystal phase of the pyrochlore crystal structure. More specifically, the pyrochlore crystal structure was found to be either the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 structure or substantially identical with or approximate to the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 structure.
A thin film capacitor according to the example 8 was produced under conditions similar to those of the example 1 except that the precursor layer was heated to 580° C. for 20 minutes in the oxygen atmosphere so as to be mainly baked. Electrical properties exhibited the leakage current value of 1.0×10−6 A/cm2, the dielectric loss of 0.001, and the relative permittivity of 100. It was also found that the BNO oxide layer has a fine crystal phase of the pyrochlore crystal structure. More specifically, the pyrochlore crystal structure was found to be either the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 structure or substantially identical with or approximate to the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 structure.
A thin film capacitor according to the comparative example 1 was produced under conditions similar to those of the example 1 except that the precursor layer was heated to 500° C. for 20 minutes in the oxygen atmosphere so as to be mainly baked. Electrical properties exhibited the leakage current value as large as 1.0×10−2 A/cm2, the dielectric loss of 0.001, and the relative permittivity of 100. It was also found that the BNO oxide layer has a fine crystal phase of the pyrochlore crystal structure.
A thin film capacitor according to the comparative example 2 was produced under conditions similar to those of the example 1 except that the precursor layer was heated to 500° C. for two hours in the oxygen atmosphere so as to be mainly baked. Electrical properties exhibited the leakage current value as large as 1.0×10−1 A/cm2, the dielectric loss of 0.007, and the relative permittivity of 180. It was also found that the BNO oxide layer has a fine crystal phase of the pyrochlore crystal structure. Furthermore, the carbon content percentage was 6.5 atm % and the hydrogen content percentage was 7.8 atm %, each of which had a large value.
A thin film capacitor according to the comparative example 3 was produced under conditions similar to those of the example 1 except that the precursor layer was heated to 600° C. for 20 minutes in the oxygen atmosphere so as to be mainly baked. Electrical properties exhibited the leakage current value of 7.0×10−6 A/cm2, the dielectric loss of 0.001, and the relative permittivity of 80. It was possible to obtain, regarding the composition of a crystal phase of the BNO oxide layer, a crystal phase of the β-BiNbO4 crystal structure.
A thin film capacitor according to the comparative example 4 was produced under conditions similar to those of the example 1 except that the precursor layer was heated to 650° C. for 20 minutes in the oxygen atmosphere so as to be mainly baked. Electrical properties exhibited the leakage current value of 5.0×10−3 A/cm2, the dielectric loss of 0.001, and the relative permittivity of 95. It was possible to obtain, regarding the composition of a crystal phase of the BNO oxide layer, a crystal phase of the β-BiNbO4 crystal structure.
In the comparative example 5, a BNO oxide layer serving as an insulating layer was formed on a lower electrode layer at a room temperature in accordance with the known sputtering technique, and was then heat treated at 550° C. for 20 minutes. A thin film capacitor was produced under conditions similar to those of the example 1, except for the above condition. Electrical properties exhibited the leakage current value of 1.0×10−7 A/cm2, the dielectric loss of 0.005, and the relative permittivity of 50. It was possible to obtain, regarding the composition of a crystal phase of the BNO oxide layer, a fine crystal phase of the Bi3NbO7 crystal structure. Furthermore, the carbon content percentage was 1.5 atm % or less and the hydrogen content percentage was 1.0 atm % or less, each of which had a small value equal to or less than the detectable limit.
Tables 2 and 3 indicate the configuration of the thin film capacitor, the conditions for forming the oxide layer, the obtained electrical properties, the content percentages of carbon and hydrogen in the BNO oxide layer, and the result of the crystal structure in each of the examples 1 to 8 and the comparative examples 1 to 5. The “composition of crystal phases” in Tables 2 and 3 includes a crystal phase and a fine crystal phase. BiNbO4 in Tables 2 and 3 indicates β-BiNbO4.
The signs “-” in these tables are indicative of not being obtained because there was no need to obtain with consideration of other disclosed data.
As indicated in Tables 2 and 3, in each of the examples, the relative permittivity at 1 KHz was 60 or more and the thin film capacitor exhibited sufficient properties as a capacitor. Table 2 indicates the relative permittivity value of the entire oxide layer in each of the examples. As to be described later, the inventors of this application have analyzed to clarify that, even if this oxide layer includes a crystal phase other than the crystal phase of the pyrochlore crystal structure and the entire oxide layer thus has not very high relative permittivity, the crystal phase of the pyrochlore crystal structure is significantly higher in relative permittivity than a conventional crystal phase. The entire oxide film in each of the comparative example 3 or 4 achieved relative permittivity equivalent to those of the examples. However, the oxide film in each of the comparative example 3 or 4 does not have any crystal phase of the pyrochlore crystal structure, and there was accordingly found no point of locally high relative permittivity. Furthermore, the high heating temperature in each of the comparative example 3 or 4 leads to increase in production cost and is thus not preferred. The BNO layer having the Bi3NbO7 crystal structure in the comparative example 5 exhibited the relative permittivity as low as 50 entirely as well as locally.
As indicated in Tables 2 and 3, in each of the examples, the leakage current value upon application of 0.25 MV/cm was 5.0×10−3 A/cm2 or less and the thin film capacitor exhibited sufficient properties as a capacitor. Leakage current in each of the examples was sufficiently lower than that in the comparative example 1 or 2. Leakage current in the comparative example 3 or 4 was found to be equivalent to those in the examples. However, the comparative example 3 or 4 has a high heating temperature and thus leads to increase in production cost.
It was found that a preferred value was obtained when the heating temperature for formation of the oxide layer was set to 520° C. or more and less than 600° C. (more preferably, 580° C. or less). Furthermore, the results obtained in each of the examples were equivalent to those of the BNO layer formed in accordance with the sputtering technique in the comparative example 5.
As indicated in Tables 2 and 3, in each of the examples, the dielectric loss at 1 KHz was 0.03 or less and the thin film capacitor exhibited sufficient properties as a capacitor. The oxide layer according to each of the examples is formed by baking a precursor solution including both a precursor containing bismuth (Bi) and a precursor containing niobium (Nb) as solutes. An oxide layer formed in accordance with the solution technique is thus a preferred insulating layer also in view of small dielectric loss. The oxide layer formed in accordance with the solution technique in each of the examples is regarded as having dielectric loss equivalent to that of the BNO layer formed in accordance with the sputtering technique in the comparative example 5.
Content percentages of carbon and hydrogen were obtained in the examples 2, 4, and 6 each having a main baking temperature in the range from 520° C. or more to less than 600° C. The BNO oxide layer was found to have a highly preferred carbon content percentage of 1.5 atm % or less in each of these examples. The carbon content percentage obtained in accordance with this measurement technique has a lower limit measurement value of about 1.5 atm %, so that the actual concentration is assumed to be equal to or less than the lower limit measurement value. It was also found that the carbon content percentage in each of these examples was at a level similar to that of the BNO oxide layer formed in accordance with the sputtering technique in the comparative example 5. When the main baking temperature is as low as 500° C. as in the comparative example 2, carbon in the solvent and the solute in the precursor solution is assumed to remain. The carbon content percentage had the value as large as 6.5 atm %. It is regarded that the leakage current thus had the value as large as 1.0×10−1 A/cm2.
In each of the examples 2, 4, and 6 having the main baking temperature in the range from 520° C. or more to less than 600° C., the BNO oxide layer had a preferred hydrogen content percentage of 1.6 atm % or less. The hydrogen content percentage obtained in accordance with this measurement technique has a lower limit measurement value of about 1.0 atm %, so that the actual concentration in the example 6 is assumed to be equal to or less than the lower limit measurement value. It was also found that the hydrogen content percentage in the example 6 was at a level similar to that of the BNO oxide layer formed in accordance with the sputtering technique in the comparative example 5. When the main baking temperature is as low as 500° C. as in the comparative example 2, hydrogen in the solvent and the solute in the precursor solution is assumed to remain. The hydrogen content percentage had the value as large as 7.8 atm %. Such a large hydrogen content percentage is also regarded as causing the leakage current to have the value as large as 1.0×10−1 A/cm2.
a) and 26(b) are a cross-sectional TEM picture and an electron beam diffraction image each showing the crystal structure of the BNO oxide layer according to the example 6.
From the cross-sectional TEM picture and the electron beam diffraction image shown in
The fine crystal phase of the pyrochlore crystal structure is found to have different appearance depending on the main baking temperature for the precursor layer of the oxide layer serving as an insulating layer. As in the comparative examples 3 and 4, it was found that a crystal phase only of the β-BiNbO4 crystal structure appears if the main baking temperature is 600° C. and 650° C.
In contrast, as in the examples 1 to 8, it was interestingly found that a fine crystal phase of the pyrochlore crystal structure appears if the main baking temperature is 520° C., 530° C., 550° C., and 580° C. More specifically, the pyrochlore crystal structure was found to be either the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 structure or substantially identical with or approximate to the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 structure.
The already known pyrochlore crystal structure is possibly obtained by including “zinc” as described above, but each of the examples had a result different from that according to the known aspect. It has not yet been clarified at the present stage why such a pyrochlore crystal structure appears in the composition not including zinc as in the examples. As to be described later, it was found that provision of a crystal phase of the pyrochlore crystal structure leads to preferred dielectric properties (high relative permittivity in particular) as an insulating layer of a thin film capacitor.
As in the examples 1 to 8, it was also found that an oxide layer serving as an insulating layer and having a crystal phase of the pyrochlore crystal structure exhibits preferred electrical properties as an insulating layer of a solid-state electronic device.
In contrast, neither a fine crystal phase of the pyrochlore crystal structure nor a crystal phase of the β-BiNbO4 crystal structure was found in the oxide layer formed in accordance with the sputtering technique in the comparative example 5. Instead, a fine crystal phase of the Bi3NbO7 crystal structure was found in the comparative example 5.
a) and 28(b) are a TOPO image (by a scanning probe microscope (in a supersensitive SNDM mode)) and a varied capacity image of each crystal phase in a plan view, of the BNO oxide layer in the representing example 6.
The TOPO images and the varied capacity images were obtained in the supersensitive SNDM mode by the scanning probe microscope (manufactured by SII Nanotechnology Inc.). The relative permittivity images indicating distribution of relative permittivity in
As indicated in
Found through further detailed analysis was that the BNO oxide layer in the example 6 includes a crystal phase of the pyrochlore crystal structure having relative permittivity much higher than that of any other crystal phase, a crystal phase of the β-BiNbO4 crystal structure indicated in a region Z (darker region) in
The inventors of this application have reached the conclusion, through analysis and study, that, in view of that the known crystal phase of the pyrochlore crystal structure possibly formed by inclusion of “zinc” has a comparatively high relative permittivity value, provision of the crystal phase of the pyrochlore crystal structure achieves exertion of high relative permittivity. Accordingly, even if the oxide layer includes a crystal phase other than the crystal phase of the pyrochlore crystal structure and the entire oxide layer has not very high relative permittivity, the oxide layer consisting of bismuth (Bi) and niobium (Nb) and having the crystal phase of the pyrochlore crystal structure thus improves electrical properties of various solid-state electronic devices. It is noted that this interesting extraordinary feature achieves the dielectric properties that have never been obtained. Similar phenomena are seen in the respective examples other than the example 6.
As described above, the fine crystal phases of the pyrochlore crystal structure are distributed in the oxide layer according to each of the embodiments. The oxide layer was thus found to have relative permittivity extraordinarily higher as a BNO oxide layer than that of a conventional oxide layer. The oxide layer according to each of the embodiments is produced in accordance with the solution technique, to achieve simplification in production process. Furthermore, when the oxide layer is formed at the heating temperature (main baking temperature) in the range from 520° C. or more to less than 600° C. (more preferably, 580° C. or less) in the production of the oxide layer in accordance with the solution technique, the BNO oxide layer thus obtained has preferred electrical properties of high relative permittivity as well as small dielectric loss. Moreover, the method of producing the oxide layer according to each of the above embodiments is simple and takes relatively short time with no need for complex and expensive equipment such as a vacuum system. These features remarkably contribute to provision of the oxide layer and various solid-state electronic devices including the oxide layer from the industrial or mass productivity perspectives.
The oxide layer according to each of the above embodiments is appropriate for various solid-state electronic devices configured to control large current with low drive voltage. The solid-state electronic device including the oxide layer according to each of the above embodiments is applicable to a large number of devices in addition to the thin film capacitor. The oxide layer according to each of the embodiments is applicable to a capacitor such as a stacked thin film capacitor or a variable capacity thin film capacitor, a metal oxide semiconductor junction field effect transistor (MOSFET), a semiconductor device such as a nonvolatile memory, a micro total analysis system (TAS), a device of a microelectromechanical system represented by a microelectromechanical system (MEMS) such as a micro chemical chip or a DNA chip, or a nanoelectromechanical system (NEMS).
As described above, the above embodiments have been disclosed not for limiting the present invention but for describing these embodiments. Furthermore, modification examples made within the scope of the present invention, inclusive of other combinations of the embodiments, will be also included in the scope of the patent claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-046550 | Mar 2013 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/050006 | 1/6/2014 | WO | 00 |
