JP3596266B2 - Nonlinear dielectric element - Google Patents

Description

【００２０】
表１から明らかなように、各種ガラスフリットを含む導電ペーストを塗布し、焼き付けることにより電極を形成した比較例１〜１４の非線形誘電体素子では、ガラスフリットの種類により異なるものの、ガラスフリットの含有割合が高くなる程パルス電圧が低くなり、ガラスフリット成分による特性の低下が見られた。
【００２１】
これに対して、実施例の非線形誘電体素子では、ガラスフリットを用いずに、スパッタリングにより電極３，４を形成しているため、パルス電圧が著しく高められている。
【００２２】
従って、上記実施例から明らかなように、スパッタリングにより形成された金属膜、すなわちガラスフリットを含まない薄膜形成法により形成された金属膜を用いることにより、誘電体２の非線形特性を十分に発揮させることができ、大きなパルス電圧を得ることができる非線形誘電体素子を提供し得ることがわかる。
【００２３】
なお、上述した実験例では、Ｃｕ−Ｎｉ合金膜とＡｇ膜との２層構造を有する電極３，４を形成したが、電極３，４は、単一層で構成されていてもよく、あるいは３層以上の薄膜形成法により形成された金属膜を積層した構造であってもよい。また、電極を構成する金属材料についても、Ｃｕ−Ｎｉ、Ａｇに限定されず、Ｃｕ、Ｎｉ、Ａｌ、Ｃｒ、Ｆｅ、Ｃｏ、Ｎｉ−Ｃｒ、Ｆｅ−Ｎｉなど種々の金属材料を用いることができる。もっとも、Ｌ形高圧ナトリウムランプの始動用に用いられる高圧パルス発生用コンデンサでは、前述した通り３００℃程度の高温にさらされるため、このような高温にさらされる用途に用いる場合には、電極３，４はＡｇやＮｉなどの耐熱性に優れた金属材料により形成することが好ましい。
【００２４】
また、電極３，４をＡｇで構成した場合には、電極間マイグレーションを防止するために、Ａｇよりなる金属膜よりも径の大きな他の金属膜上にＡｇ膜を積層した構造とすることが望ましい。
【００２５】
また、上述した実施例では、電極３，４を、スパッタリングにより形成したが、スパッタリングに代えて、蒸着やイオンプレーティングなどの他の乾式薄膜形成法により電極３，４を形成してもよい。すなわち、本発明は、上記のような乾式薄膜形成法により形成された金属膜により電極を構成することにより、ガラスフリットの使用に基づく非線形特性の低下を防止したことに特徴を有するものであり、従って、蒸着やイオンプレーティングなどの他の乾式薄膜形成法を用いて電極３，４を形成してもよい。
【００２６】
また、図１では、誘電体２の両面に電極３，４を形成したが、電極３，４を形成した後に、従来の非線形コンデンサ５１と同様に絶縁ガラス層等を形成したり、あるいはリード端子等を接合してもよく、その場合であっても、電極３，４が既に誘電体２に接合されているため、良好な非線形特性を発揮し得る非線形誘電体素子とすることができる。
【００２７】
【発明の効果】
請求項１に記載の発明に係る非線形誘電体素子では、非線形特性を示す誘電体セラミックスよりなる誘電体の第１，第２の面に形成される第１，第２の電極が、薄膜形成法により形成された金属膜により構成されているので、誘電体の非線形特性を十分に発揮させることができ、良好な非線形特性を発揮し得る非線形誘電体素子を提供することができる。すなわち、従来の導電ペーストを用いて電極を形成してなる非線形コンデンサでは、含有されているガラスフリットにより非線形特性が低下するのに対し、請求項１に記載の発明に係る非線形誘電体素子では、ガラスフリットを使用しないため、ガラスフリットに起因する非線形特性の低下を防止することができる。
【００２８】
加えて、従来の無電解メッキにより電極を形成した非線形コンデンサでは、メッキ液残渣により、誘電体セラミックスが劣化するおそれがあったのに対し、請求項１に記載の発明に係る非線形誘電体素子では、乾式薄膜形成法により電極が形成されているので、このような誘電体の劣化も生じ難い。従って、信頼性に優れた非線形誘電体素子を提供することができる。
【００２９】
本発明では、良好な非線形特性を利用して、例えばＨＩＤランプの始動に用いられるような高圧パルスを発生することが求められる用途に最適な高圧パルス発生用コンデンサを提供することができる。
【図面の簡単な説明】
【図１】本発明の一実施例に係る非線形誘電体素子を示す側面図。
【図２】実験例において非線形誘電体素子を評価するために構成した回路を説明するための回路図。
【図３】従来の非線形コンデンサを説明するための断面図。
【符号の説明】
１…非線形誘電体素子
２…誘電体
３，４…電極[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a nonlinear dielectric element suitably used for generating a high-voltage pulse, for example, when starting a high-intensity discharge lamp (HID lamp). More specifically, the nonlinear characteristic is improved by improving electrodes. A non-linear dielectric element.
[0002]
[Prior art]
Conventionally, the HID lamp has been used as a lamp for realizing high luminance. Some HID lamps of this type require a high-pressure pulse of about 1 to 4 kV at startup, such as a high-pressure sodium lamp or a metal halide lamp. Therefore, in this type of HID lamp, a capacitor having a non-linear characteristic is incorporated in order to generate a high-voltage pulse.
[0003]
For example, Japanese Patent Publication No. 5-87940 discloses a high-pressure discharge lamp having a built-in non-linear capacitor for generating the high-voltage pulse. FIG. 3 shows the structure of the nonlinear capacitor described in the prior art.
[0004]
The capacitor 51 has a structure in which electrodes 53 and 54 are formed on both surfaces of a ceramic plate 52 made of barium titanate-based ceramic. Lead terminals 56 and 57 are bonded to the centers of the electrodes 53 and 54 via bonding materials 55a and 55b. Except for the portions from which the lead terminals 56 and 57 are drawn out, the entirety is covered with a glass coating layer 58 formed by applying and baking a glass paste.
[0005]
The electrodes 53 and 54 are formed by applying and baking a conductive paste containing Ag powder and borosilicate glass or lead borosilicate glass.
However, the above-described conventional nonlinear capacitor 51 has a problem in that the nonlinear characteristics inherent to the ceramic plate 52 made of barium titanate-based ceramics cannot be sufficiently brought out. This is probably because the glass frit in the conductive paste used to form the electrodes 53 and 54 diffuses into the ceramic plate 52 when the electrodes are baked, thereby reducing the nonlinear characteristics of the ceramic plate 52.
[0006]
On the other hand, Japanese Patent Application Laid-Open No. 61-212009 discloses a high-voltage pulse generating capacitor in which electrodes are formed without using a glass frit. Here, electrodes are formed on both surfaces of the dielectric ceramic plate by electroless plating Ni. Therefore, it is considered that the non-linear characteristic is hardly reduced due to the diffusion of the glass frit.
[0007]
[Problems to be solved by the invention]
However, in the capacitor for generating a high-voltage pulse disclosed in Japanese Patent Application Laid-Open No. 61-212009, since electroless plating is used for forming the electrodes, residues of the plating solution penetrate into the ceramics, and the reliability is reduced. There was a risk of lowering.
[0008]
An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to sufficiently draw out the nonlinear characteristics of dielectric ceramics having nonlinear characteristics, exhibit good nonlinear characteristics, and have a highly reliable nonlinear dielectric. It is to provide an element.
[0009]
[Means for Solving the Problems]
The invention according to claim 1 is a non-linear dielectric element used as a high-voltage pulse generating capacitor incorporated in a high-intensity discharge lamp and exhibiting hysteresis in electric field-charge characteristics, and more preferably a dielectric ceramic exhibiting non-linear characteristics. And a first and second electrode respectively formed on first and second surfaces of the dielectric, wherein the first and second electrodes are formed of a metal formed by a thin film forming method. It is characterized by being constituted by a film.
[0010]
In the invention described in claim 2, the metal film is formed by sputtering, vapor deposition, or ion plating.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a side view showing one embodiment of the nonlinear dielectric element of the present invention. The nonlinear dielectric element 1 is used as a high-voltage pulse generating capacitor in an L-type high-pressure sodium lamp. In this application, the capacitor is exposed to a temperature on the order of 300 ° C. and a vacuum on the order of 1 × 10 ⁻⁵ torr.
[0012]
The nonlinear dielectric element 1 is configured using a plate-shaped dielectric 2 made of dielectric ceramics exhibiting nonlinear characteristics. In this specification, the non-linear characteristic refers to a characteristic that exhibits hysteresis in the electric field-charge characteristic. The dielectric 2 is made of an appropriate dielectric ceramic capable of exhibiting such non-linear characteristics. For example, a barium titanate-based ceramic material can be suitably used.
[0013]
A first electrode 3 is formed on an upper surface 2a as a first surface of the dielectric 2, and a second electrode 4 is formed on a lower surface 2b as a second surface.
The feature of the nonlinear dielectric element 1 of this embodiment is that the electrodes 3 and 4 are formed of a metal film formed by sputtering as a thin film forming method.
[0014]
The non-linear dielectric element 1 of this embodiment exhibits sufficient non-linear characteristics because the electrodes 3 and 4 are made of the above-mentioned metal film, that is, because they do not contain glass frit. Also, in the conventional method of forming an electrode by electroless plating, the reliability may be reduced due to a residue of a plating solution, whereas in the present embodiment, the electrode is formed by a dry thin film forming method. In addition, the deterioration of the dielectric 2 hardly occurs, so that the reliability is also improved. This will be described based on specific experimental examples.
[0015]
As a dielectric material exhibiting non-linear characteristics, a barium titanate-based ceramic powder was dry-pressed and fired to produce a disk-shaped dielectric 2 having a diameter of 18 mm and a thickness of 1 mm. Electrodes 3 and 4 having a diameter of 17 mm were formed on both surfaces of the dielectric 2 by sputtering. In forming the electrodes 3 and 4 by sputtering, first, a Cu—Ni alloy film was formed by sputtering, and then, an Ag film was formed on the Cu—Ni film by sputtering. That is, a metal film having a two-layer structure was formed by sputtering, electrodes 3 and 4 were formed, and the nonlinear dielectric element of the example was manufactured.
[0016]
Further, for comparison, various glass frits shown in Table 1 below were added to both surfaces of the same dielectric 2 used in the nonlinear dielectric element of the above example with respect to 100% by volume of Ag powder. As shown in FIG. 1, a conductive paste containing 3% by volume or 5% by volume was printed and baked at 850 ° C. to produce nonlinear dielectric elements of Comparative Examples 1 to 14.
[0017]
With respect to the nonlinear dielectric element obtained as described above, the generated pulse voltage was measured using the circuit shown in FIG. That is, in the circuit shown in FIG. 2, a 400 W high-pressure mercury lamp ballast 12 is connected in series with a power supply 11, and a nonlinear dielectric element 1 and a breakover voltage are provided downstream of the high-pressure mercury lamp ballast 12. A 150 V semiconductor switch 13 is connected. V indicates a voltmeter.
[0018]
Each of the nonlinear dielectric elements 1 of Examples and Comparative Examples 1 to 14 was connected as shown in FIG. 2 and the generated pulse voltage was measured. The results shown in Table 1 below were obtained.
[0019]
[Table 1]

[0020]
As is clear from Table 1, the non-linear dielectric elements of Comparative Examples 1 to 14 in which electrodes were formed by applying and baking conductive pastes containing various types of glass frit, although different depending on the type of glass frit, contained glass frit. The higher the ratio, the lower the pulse voltage, and a decrease in characteristics due to the glass frit component was observed.
[0021]
On the other hand, in the nonlinear dielectric element of the embodiment, since the electrodes 3 and 4 are formed by sputtering without using a glass frit, the pulse voltage is significantly increased.
[0022]
Therefore, as is apparent from the above-described embodiment, by using a metal film formed by sputtering, that is, a metal film formed by a thin film forming method that does not include a glass frit, the nonlinear characteristics of the dielectric 2 are sufficiently exhibited. It can be seen that a nonlinear dielectric element capable of obtaining a large pulse voltage can be provided.
[0023]
In the above-described experimental example, the electrodes 3 and 4 having the two-layer structure of the Cu—Ni alloy film and the Ag film were formed. However, the electrodes 3 and 4 may be formed of a single layer. It may have a structure in which metal films formed by a thin film forming method of more than two layers are stacked. Also, the metal material forming the electrode is not limited to Cu-Ni and Ag, and various metal materials such as Cu, Ni, Al, Cr, Fe, Co, Ni-Cr, and Fe-Ni can be used. . However, since the high-pressure pulse generating capacitor used for starting the L-type high-pressure sodium lamp is exposed to a high temperature of about 300 ° C. as described above, if it is used for an application exposed to such a high temperature, the electrode 3 4 is preferably formed of a metal material having excellent heat resistance, such as Ag or Ni.
[0024]
When the electrodes 3 and 4 are made of Ag, a structure in which an Ag film is laminated on another metal film having a diameter larger than that of the metal film made of Ag is used to prevent migration between the electrodes. desirable.
[0025]
Although the electrodes 3 and 4 are formed by sputtering in the above-described embodiment, the electrodes 3 and 4 may be formed by another dry thin film forming method such as vapor deposition or ion plating instead of sputtering. That is, the present invention is characterized in that by forming an electrode with a metal film formed by the dry thin film forming method as described above, a decrease in non-linear characteristics due to the use of glass frit is prevented, Therefore, the electrodes 3 and 4 may be formed using another dry thin film forming method such as vapor deposition or ion plating.
[0026]
1, the electrodes 3 and 4 are formed on both surfaces of the dielectric 2, but after the electrodes 3 and 4 are formed, an insulating glass layer or the like is formed in the same manner as the conventional nonlinear capacitor 51, or the lead terminals are formed. In such a case, since the electrodes 3 and 4 are already joined to the dielectric 2, a non-linear dielectric element capable of exhibiting good non-linear characteristics can be obtained.
[0027]
【The invention's effect】
In the nonlinear dielectric element according to the first aspect of the present invention, the first and second electrodes formed on the first and second surfaces of the dielectric made of dielectric ceramic exhibiting nonlinear characteristics are formed by a thin film forming method. Therefore, it is possible to sufficiently provide the nonlinear characteristics of the dielectric, and to provide a nonlinear dielectric element capable of exhibiting good nonlinear characteristics. That is, in the conventional nonlinear capacitor in which the electrodes are formed using the conductive paste, the nonlinear characteristic is reduced by the glass frit contained therein, whereas in the nonlinear dielectric element according to the invention of claim 1, Since no glass frit is used, it is possible to prevent a decrease in nonlinear characteristics caused by the glass frit.
[0028]
In addition, in a conventional non-linear capacitor in which electrodes are formed by electroless plating, there is a possibility that dielectric ceramics may be deteriorated due to plating solution residues, whereas in a non-linear dielectric element according to the invention according to claim 1, Since the electrodes are formed by the dry thin film forming method, such deterioration of the dielectric is unlikely to occur. Therefore, a highly reliable nonlinear dielectric element can be provided.
[0029]
According to the present invention, it is possible to provide a high-voltage pulse generating capacitor that is optimal for applications requiring generation of a high-voltage pulse, such as used for starting an HID lamp, by utilizing good nonlinear characteristics.
[Brief description of the drawings]
FIG. 1 is a side view showing a nonlinear dielectric element according to one embodiment of the present invention.
FIG. 2 is a circuit diagram for explaining a circuit configured to evaluate a nonlinear dielectric element in an experimental example.
FIG. 3 is a sectional view for explaining a conventional nonlinear capacitor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Nonlinear dielectric element 2 ... Dielectric 3, 4 ... Electrode

Claims (2)

A non-linear dielectric element that is used as a high-voltage pulse generating capacitor incorporated in a high-intensity discharge lamp and exhibits hysteresis in electric field-charge characteristics,
A dielectric made of dielectric ceramics exhibiting nonlinear characteristics;
First and second electrodes respectively formed on first and second surfaces of the dielectric,
A non-linear dielectric element, wherein the first and second electrodes are formed of a metal film formed by a thin film forming method. The nonlinear dielectric element according to claim 1, wherein the metal film is formed by sputtering, vapor deposition, or ion plating.

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