JPH05264565A - Flow sensor - Google Patents
Flow sensorInfo
- Publication number
- JPH05264565A JPH05264565A JP4091599A JP9159992A JPH05264565A JP H05264565 A JPH05264565 A JP H05264565A JP 4091599 A JP4091599 A JP 4091599A JP 9159992 A JP9159992 A JP 9159992A JP H05264565 A JPH05264565 A JP H05264565A
- Authority
- JP
- Japan
- Prior art keywords
- thin film
- temperature
- film heater
- flow
- gas
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Links
Landscapes
- Measuring Volume Flow (AREA)
Abstract
Description
【０００１】[0001]
【産業上の利用分野】この発明は、微細な気体の流速を
検出するためのフローセンサに関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow sensor for detecting the flow velocity of fine gas.
【０００２】[0002]
【従来の技術】気体の流れの中にヒータを置くと、ヒー
タの上流側は気体流で冷やされ、下流側は気体流で運ば
れる熱で暖められる。そこで、ヒータの上流側と下流側
の温度差を測れば、気体の流速を検出することができ
る。このような原理に基づき、マイクロヒータの上流側
と下流側に温度センサを配置したフローセンサが提案さ
れている（例えば、特開平２−１９３０１９号公報参
照）。2. Description of the Related Art When a heater is placed in a gas flow, the upstream side of the heater is cooled by the gas flow and the downstream side is warmed by the heat carried by the gas flow. Therefore, the gas flow velocity can be detected by measuring the temperature difference between the upstream side and the downstream side of the heater. Based on such a principle, a flow sensor has been proposed in which temperature sensors are arranged on the upstream side and the downstream side of the microheater (for example, see Japanese Patent Laid-Open No. 2-193019).
【０００３】[0003]
【発明が解決しようとする課題】この発明は、ヒータの
上流と下流とで大きな温度差を得ることによって、フロ
ーセンサの感度を向上することを目的とする。SUMMARY OF THE INVENTION An object of the present invention is to improve the sensitivity of a flow sensor by obtaining a large temperature difference between the upstream side and the downstream side of a heater.
【０００４】[0004]
【課題を解決するための手段】この発明のフローセンサ
は、気体の流れに薄膜ヒータをさらし、該薄膜ヒータの
上流側と下流側の温度をそれぞれ温度センサで測定し、
それらの温度差から気体の流速を検出するようにした点
は従来通りである。しかし、ヒータの抵抗温度係数が正
か負によって、薄膜ヒータに流れる電流の方向が異な
る。A flow sensor of the present invention exposes a thin film heater to a gas flow, and measures the temperature of each of the upstream side and the downstream side of the thin film heater with a temperature sensor,
The point where the flow velocity of gas is detected from the temperature difference is the same as in the past. However, the direction of the current flowing through the thin film heater differs depending on whether the temperature coefficient of resistance of the heater is positive or negative.
【０００５】該薄膜ヒータが正の電気抵抗温度係数を有
する場合は、該薄膜ヒータは、気体の流れに沿った方向
に電流が流れるように配置する。該薄膜ヒータが負の温
度係数を有している場合は、薄膜ヒータは、気体の流れ
に直角な方向に電流が流れるように配置する。When the thin film heater has a positive temperature coefficient of electric resistance, the thin film heater is arranged so that an electric current flows in the direction along the gas flow. When the thin film heater has a negative temperature coefficient, the thin film heater is arranged so that current flows in a direction perpendicular to the gas flow.
【０００６】[0006]
【作用】薄膜ヒータの電気抵抗の温度係数が正（すなわ
ち、温度が高くなるにしたがって電気抵抗が大きくな
る）場合を考えてみる。この場合、この発明では、薄膜
ヒータは、気体の流れに沿って電流が流れるように配置
される。Operation: Consider a case where the temperature coefficient of the electric resistance of the thin film heater is positive (that is, the electric resistance increases as the temperature increases). In this case, in the present invention, the thin film heater is arranged so that an electric current flows along the gas flow.
【０００７】薄膜ヒータの上流側は気体の流れで冷やさ
れるので温度が下がり、逆に、下流側は、上流側から運
ばれた熱で温度が上がる。このため、気体流に沿った電
流の通り道は、上流側で分布抵抗が小さくなり、下流側
で分布抵抗が大きくなる。この結果、上流側は発熱量が
減って一層温度が下がり、下流側は発熱量が増して、一
層温度が上がる。こうして、上流側と下流側に大きな温
度差が生ずる。このことは、フローセンサの感度が上が
り、小さな流速をも検出できることを意味する。Since the upstream side of the thin film heater is cooled by the flow of gas, the temperature of the thin film heater is lowered, and conversely, the temperature of the downstream side is increased by the heat carried from the upstream side. Therefore, in the passage of the current along the gas flow, the distributed resistance becomes small on the upstream side and becomes large on the downstream side. As a result, the amount of heat generation decreases on the upstream side and the temperature further decreases, and the amount of heat generation increases on the downstream side and the temperature further increases. Thus, a large temperature difference occurs between the upstream side and the downstream side. This means that the sensitivity of the flow sensor is increased and even a small flow velocity can be detected.
【０００８】次に、薄膜ヒータの電気抵抗の温度係数が
負の場合であるが、この場合、この発明では、薄膜ヒー
タは、気体の流れに直角な方向に電流が流れるように配
置されている。Next, the temperature coefficient of the electric resistance of the thin film heater is negative. In this case, in the present invention, the thin film heater is arranged so that an electric current flows in a direction perpendicular to the flow of gas. ..
【０００９】この場合も、薄膜ヒータの上流側は、気体
の流れで冷やされるので温度が下がってヒータの分布抵
抗が大きくなり、逆に、下流側は、上流側から運ばれた
熱で温度が上がるので分布抵抗は小さくなる。このた
め、ヒータの電流は、上流側を流れにくく、下流側を流
れやすくなる。この結果、上流側は発熱量が減って一層
温度が下がり、下流側は発熱量が増して、一層温度が上
がる。こうして、上流側と下流側に大きな温度差が生ず
る。Also in this case, since the upstream side of the thin film heater is cooled by the flow of gas, the temperature is lowered and the distributed resistance of the heater is increased, and conversely, the downstream side is heated by the heat carried from the upstream side. As it rises, the distributed resistance becomes smaller. Therefore, the current of the heater is hard to flow on the upstream side and easily flows on the downstream side. As a result, the amount of heat generation decreases on the upstream side and the temperature further decreases, and the amount of heat generation increases on the downstream side and the temperature further increases. Thus, a large temperature difference occurs between the upstream side and the downstream side.
【００１０】[0010]
【実施例】図１において、ｎ形シリコン基板１の表面に
塗布拡散剤を用いてホウ素を高濃度に、たとえば、約１
×１０20cm-3程度添加、熱拡散し、高濃度ホウ素添加単
結晶シリコン層２を形成する。この層は、電気抵抗が小
さいので、ヒータとして利用できる。また、この層は、
P++-Si（特に高濃度のＰ形シリコンの意味）となり、数
百℃以下の温度では金属的で、正の抵抗温度係数をも
つ。なお、ホウ素はｎ形シリコン基板の全面に添加する
のではなく、ホウ素を添加しない部分を四角形の枠状に
残す（この部分は後で溝３になる）。DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, the surface of an n-type silicon substrate 1 is coated with a diffusing agent so as to have a high concentration of boron, for example, about 1.
About 10 20 cm -3 is added and thermal diffusion is performed to form a high-concentration boron-added single crystal silicon layer 2. Since this layer has a low electric resistance, it can be used as a heater. Also, this layer is
It becomes P ++ -Si (especially meaning high-concentration P-type silicon), is metallic at a temperature of several hundreds of degrees Celsius or less, and has a positive temperature coefficient of resistance. Note that boron is not added to the entire surface of the n-type silicon substrate, but a portion to which boron is not added is left in a rectangular frame shape (this portion will later become the groove 3).
【００１１】この基板の両面にSiO2膜４、５を熱酸化の
手法で形成し、裏面のSiO2膜５に窓をあける。こうして
基板１を異方性エッチングすると、ｎ形シリコン基板１
に空洞１５ができ、高濃度ホウ素添加単結晶シリコン層
２は異方性エッチャントに侵されず、空洞１５の上にダ
イヤフラム状に残る。これを薄膜ヒータ６として利用す
る。ホウ素を添加しなかった部分はエッチされて溝３に
なり、薄膜ヒータ６と周囲の高濃度ホウ素添加単結晶シ
リコン層２を分離する。SiO 2 films 4 and 5 are formed on both surfaces of this substrate by a thermal oxidation method, and windows are opened in the SiO 2 film 5 on the back surface. By anisotropically etching the substrate 1, the n-type silicon substrate 1 is obtained.
A cavity 15 is formed in the cavity 15, the high-concentration boron-doped single crystal silicon layer 2 is not attacked by the anisotropic etchant, and remains on the cavity 15 like a diaphragm. This is used as the thin film heater 6. The portion to which boron is not added is etched to form a groove 3, which separates the thin film heater 6 and the surrounding high-concentration boron-added single crystal silicon layer 2.
【００１２】次いで、SiO2膜４にあけた小窓から薄膜ヒ
ータ６に一対の電極７、７を形成する。薄膜ヒータ６に
は気体の流れに沿って電流が流れるように、電極７，７
は上流側と下流側に設ける。Next, a pair of electrodes 7, 7 is formed on the thin film heater 6 through a small window formed in the SiO 2 film 4. The thin film heater 6 has electrodes 7, 7 so that an electric current flows along with the flow of gas.
Are provided on the upstream side and the downstream side.
【００１３】薄膜ヒータ６の上流側と下流側において、
溝３の上のSiO2膜４にスリット８を形成し、薄膜ヒータ
６と基板１を熱的および電気的に分離する。スリット８
は太すぎると、薄膜ヒータに沿って流れる気体に渦がで
き、気体によって奪われる熱量を簡単な式から求めるこ
とができなくなる。そこで、スリットの幅は２０μmほ
どの小さなものにしている。なお、スリット８はこの発
明に不可欠のものではなく、設けなくてもよい。On the upstream side and the downstream side of the thin film heater 6,
A slit 8 is formed in the SiO 2 film 4 on the groove 3 to thermally and electrically separate the thin film heater 6 and the substrate 1. Slit 8
If is too thick, vortices are created in the gas flowing along the thin film heater, and the amount of heat taken by the gas cannot be obtained from a simple equation. Therefore, the width of the slit is made as small as about 20 μm. The slit 8 is not essential to the present invention and may be omitted.
【００１４】薄膜ヒータ上には、気体の流れに沿って、
上流側、中央部、下流側にそれぞれ温度センサ９ａ，
ｂ，ｃを設ける。各温度センサは熱伝対をはじめ様々な
タイプのものが使えるが、この実施例ではｐｎ接合ダイ
オードで構成されている。これをつくるには、薄膜ヒー
タ上のSiO2膜４に窓をあけて薄膜ヒータ６である高濃度
ホウ素添加単結晶シリコン層２を露出させ、この部分に
ｎ形シリコン層１０をエピタキシャル成長させる。薄膜
ヒータである高濃度ホウ素添加単結晶シリコン層２はｐ
形であるので、ｎ形シリコン層１０と高濃度ホウ素添加
単結晶シリコン層２のそれぞれに電極１１，１２を付け
ればｐｎ接合ダイオードとなる。ｐｎ接合ダイオード
は、１５０℃以上であると、逆方向飽和電流の温度依存
性から温度を知ることができ、感度も非常に高い。ま
た、１００℃以下で使用するときは、順方向電流の立上
がり電圧の変化から、その接合部の温度を知ることがで
きる。On the thin film heater, along the flow of gas,
Temperature sensors 9a, 9a,
b and c are provided. Although various types of temperature sensors such as thermocouples can be used, each temperature sensor is composed of a pn junction diode in this embodiment. To make this, a window is opened in the SiO 2 film 4 on the thin film heater to expose the high-concentration boron-doped single crystal silicon layer 2 which is the thin film heater 6, and the n-type silicon layer 10 is epitaxially grown in this portion. The high-concentration boron-doped single crystal silicon layer 2 which is a thin film heater is p
Since it is of a pn junction type, the electrodes 11 and 12 are attached to the n-type silicon layer 10 and the high-concentration boron-doped single crystal silicon layer 2, respectively. If the temperature of the pn junction diode is 150 ° C. or higher, the temperature can be known from the temperature dependence of the reverse saturation current, and the sensitivity is very high. When used at 100 ° C. or lower, the temperature of the junction can be known from the change in the rising voltage of the forward current.
【００１５】中央部の温度センサ９ｂは、これで薄膜ヒ
ータ６の中央部の温度をモニタし、該温度が一定になる
ように該薄膜ヒータに流れる電流を制御する。こうして
おいて、温度センサ９ａ，９ｃで薄膜センサ６の上流側
と下流側の温度を計測し、その温度差から気体の流速を
求める。The temperature sensor 9b at the central portion monitors the temperature of the central portion of the thin film heater 6 by this, and controls the current flowing through the thin film heater so that the temperature becomes constant. In this way, the temperature sensors 9a and 9c measure the temperatures on the upstream side and the downstream side of the thin film sensor 6, and the gas flow velocity is determined from the temperature difference.
【００１６】ところで、この薄膜ヒータの温度係数は正
であるので、温度が低いほど電気抵抗が小さく、同一の
電流のときは、消費電力が小さく、発熱が少ない。図１
において、薄膜ヒータの上流側は気体の流れで冷やされ
るので発熱が少ない。逆に、下流側は、同一電流に対し
て、上流側に比べて暖まるので、ヒータの電気抵抗が大
きくなり、一層発熱することになる。したがって、上流
側は気体流によって冷やされると、ヒータ加熱も小さく
なり、さらに低い温度になる傾向になり、下流側は、そ
の逆になり、上流側と下流側に大きな温度差が発生す
る。したがって、気体の流れを高感度に検知することが
できる。By the way, since the temperature coefficient of this thin film heater is positive, the lower the temperature, the smaller the electric resistance, and the smaller the power consumption and the heat generation at the same current. Figure 1
In the above, since the upstream side of the thin film heater is cooled by the gas flow, heat generation is small. On the contrary, since the downstream side is warmer than the upstream side with respect to the same current, the electric resistance of the heater is increased and the heat is further generated. Therefore, when the upstream side is cooled by the gas flow, the heater heating also becomes smaller and the temperature tends to be lower, and the downstream side becomes the opposite, and a large temperature difference occurs between the upstream side and the downstream side. Therefore, the gas flow can be detected with high sensitivity.
【００１７】図２は、薄膜ヒータの抵抗温度係数が負の
場合の実施例である。ｐ形シリコン基板２１の上にｎ形
シリコン層（厚みは３μm程度）２２をエピタキシャル
形成する。次いで、ｎ形シリコン層２２にホウ素を熱拡
散して矩形枠状のｐ形シリコン領域（この部分は後で溝
２３になる）をつくる。この基板の両面にSiO2膜２４，
２５を熱酸化の手法で形成し、裏面２５に窓をあける。
こうして、６０℃、５０％程度の苛性ソーダ水溶液中
で、ｎ形エピタキシャル層２２を正になるようにして電
解エッチングすると、ｐ形シリコン基板２１が異方性エ
ッチされて空洞３５ができ、その空洞の上にｎ形シリコ
ン層２２がダイヤフラム状に残る。このダイヤフラム部
分を薄膜ヒータ２６として利用する。この薄膜ヒータの
温度係数は負となる。FIG. 2 shows an embodiment in which the temperature coefficient of resistance of the thin film heater is negative. An n-type silicon layer (thickness is about 3 μm) 22 is epitaxially formed on the p-type silicon substrate 21. Then, boron is thermally diffused into the n-type silicon layer 22 to form a rectangular frame-shaped p-type silicon region (this portion will be the groove 23 later). SiO 2 film 24 on both sides of this substrate,
25 is formed by a thermal oxidation method, and a window is opened on the back surface 25.
Thus, when the n-type epitaxial layer 22 is electrolytically etched in a caustic soda aqueous solution at 60 ° C. and about 50% so as to be positive, the p-type silicon substrate 21 is anisotropically etched to form a cavity 35. The n-type silicon layer 22 remains on the upper surface in a diaphragm shape. This diaphragm portion is used as the thin film heater 26. The temperature coefficient of this thin film heater is negative.
【００１８】なお、ホウ素拡散領域はエッチされて溝２
３になり、薄膜ヒータと周囲のｎ形エピタキシャル層２
２を分離する。薄膜ヒータには流体の流れに直角な方向
に電流が流れるように、電極２７は流れを挟んで対向位
置に設ける。スリット２８は図１と同様に形成する。The boron diffusion region is etched to form the groove 2.
3, the thin film heater and the surrounding n-type epitaxial layer 2
Separate 2 The electrodes 27 are provided at opposite positions across the flow so that a current flows through the thin film heater in a direction perpendicular to the flow of the fluid. The slit 28 is formed similarly to FIG.
【００１９】薄膜ヒータ２６の上に形成される温度セン
サ９ａ，ｂ，ｃはどんな種類のものでもよいが、ここで
は半導体サーミスタが使われている。これは、０．２μ
m程度の厚みにスパッタリングし、４００℃、N2 中で熱
処理したゲルマニーム層３０に電極３１，３２を取り付
けたもので、１００℃以下の温度で使用するのに適す
る。The temperature sensors 9a, 9b, 9c formed on the thin film heater 26 may be of any type, but a semiconductor thermistor is used here. This is 0.2μ
The germanium layer 30 which is sputtered to a thickness of about m and heat-treated at 400 ° C. in N 2 is attached with the electrodes 31 and 32, and is suitable for use at a temperature of 100 ° C. or lower.
【００２０】この薄膜ヒータ２６の温度係数は負である
ので、温度が下がると電気抵抗が大きくなる。そして、
薄膜ヒータを流れる電流の方向が気体の流れに直角であ
るので、流れの上流側は冷えて、ヒータの分布抵抗が大
きくなり、電流は上流側を流れにくくなる。このため、
薄膜ヒータの上流側では、発熱が押えられる。一方、下
流側では、気体の流れによる熱の移動で暖められるの
で、抵抗が小さくなり、電流が余計流れるようになり、
その分、余分に発熱する。Since the temperature coefficient of the thin film heater 26 is negative, the electric resistance increases as the temperature decreases. And
Since the direction of the current flowing through the thin film heater is perpendicular to the gas flow, the upstream side of the flow cools, the distributed resistance of the heater increases, and it becomes difficult for the current to flow through the upstream side. For this reason,
Heat generation is suppressed on the upstream side of the thin film heater. On the other hand, on the downstream side, it is warmed by the heat transfer due to the flow of gas, so the resistance becomes smaller and the extra current flows,
That much extra heat is generated.
【００２１】このように、上流側の温度センサ２９ａの
ところでは一層冷えるようになり、下流側センサ２９ｃ
のところでは一層熱せられ、２つの温度センサの温度差
が大きくなり、感度が増大する。中央部の温度センサ２
９ｂは前と同じように、薄膜ヒータの中央部の温度をモ
ニタする。As described above, the temperature sensor 29a on the upstream side is cooled further, and the sensor 29c on the downstream side is cooled.
However, the temperature is further heated, the temperature difference between the two temperature sensors becomes large, and the sensitivity increases. Central temperature sensor 2
9b monitors the temperature at the center of the thin film heater as before.
【００２２】[0022]
【発明の効果】以上説明したように、この発明は、薄膜
ヒータの抵抗温度係数が正のときは、気体の流れに沿っ
て電流が流れるように薄膜ヒータを配置し、抵抗温度係
数が負のときは、気体流に直角に電流が流れるように配
置したものであり、いずれの場合も、薄膜ヒータの下流
側の発熱量が上流側より大きくなり、薄膜ヒータの上流
と下流とで大きな温度差が得られ、高い感度が得られ
る。As described above, according to the present invention, when the resistance temperature coefficient of the thin film heater is positive, the thin film heater is arranged so that the current flows along the gas flow, and the resistance temperature coefficient is negative. In this case, the amount of heat generated on the downstream side of the thin film heater is larger than that on the upstream side, and a large temperature difference occurs between the upstream side and the downstream side of the thin film heater. Is obtained and high sensitivity is obtained.
【００２３】なお、上流側と下流側温度センサの間に第
３の温度センサを置き、これで薄膜センサの中央部の温
度をモニタし、該中央部温度がほぼ一定になるように該
薄膜ヒータに流れる電流を制御するようにすれば、放熱
条件が変化しないので、校正が容易になる。A third temperature sensor is provided between the upstream side and downstream side temperature sensors to monitor the temperature of the central portion of the thin film sensor so that the central portion temperature becomes almost constant. If the current flowing through the device is controlled, the heat radiation condition does not change, so that the calibration becomes easy.
【図１】フローセンサの第１の実施例であり、（ａ）は
平面図、（ｂ）は断面図である。FIG. 1 is a first embodiment of a flow sensor, (a) is a plan view and (b) is a sectional view.
【図２】フローセンサの第２の実施例であり、同じく、
（ａ）は平面図、（ｂ）は断面図である。FIG. 2 is a second embodiment of the flow sensor, similarly,
(A) is a plan view and (b) is a sectional view.
６，２６ 薄膜ヒータ ９ 温度センサ 6,26 Thin film heater 9 Temperature sensor
Claims (3)
流側と下流側の温度をそれぞれ温度センサで測定し、そ
れらの温度差から気体の流速を検出するようにしたフロ
ーセンサにおいて、該薄膜ヒータが正の抵抗温度係数を
有しており、該薄膜ヒータが気体の流れに沿った方向に
電流が流れるように配置されていることを特徴とするフ
ローセンサ。1. A flow sensor in which the temperature of each of an upstream side and a downstream side of a thin film heater exposed to a flow of gas is measured by a temperature sensor, and a gas flow velocity is detected from a temperature difference between them. Has a positive temperature coefficient of resistance, and the thin film heater is arranged so that an electric current flows in a direction along the flow of gas.
流側と下流側の温度をそれぞれ温度センサで測定し、そ
れらの温度差から気体の流速を検出するようにしたフロ
ーセンサにおいて、該薄膜ヒータが負の抵抗温度係数を
有しており、該薄膜ヒータが気体の流れに直角の方向に
電流が流れるように配置されていることを特徴とするフ
ローセンサ。2. A flow sensor in which the temperature of each of the upstream side and the downstream side of a thin film heater exposed to the flow of gas is measured by a temperature sensor, and the flow velocity of the gas is detected from the temperature difference between them. Has a negative temperature coefficient of resistance, and the thin film heater is arranged so that an electric current flows in a direction perpendicular to the gas flow.
つの温度センサを置き、これで薄膜センサの中央部の温
度を測定し、該中央部温度がほぼ一定になるように該薄
膜ヒータに流れる電流を制御するようにした請求項１ま
たは２に記載のフローセンサ。3. A thin film heater is provided between the upstream temperature sensor and the downstream temperature sensor to measure the temperature of the central portion of the thin film sensor, so that the central portion temperature is substantially constant. The flow sensor according to claim 1 or 2, wherein a current flowing through the flow sensor is controlled.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP4091599A JP2584702B2 (en) | 1992-03-17 | 1992-03-17 | Flow sensor |
| US08/033,783 US5406841A (en) | 1992-03-17 | 1993-03-17 | Flow sensor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP4091599A JP2584702B2 (en) | 1992-03-17 | 1992-03-17 | Flow sensor |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH05264565A true JPH05264565A (en) | 1993-10-12 |
| JP2584702B2 JP2584702B2 (en) | 1997-02-26 |
Family
ID=14031026
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP4091599A Expired - Fee Related JP2584702B2 (en) | 1992-03-17 | 1992-03-17 | Flow sensor |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2584702B2 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR3065281B1 (en) * | 2017-04-18 | 2019-06-14 | Centre National De La Recherche Scientifique | DEVICE FOR MEASURING SPEED OR GAS FLOW |
-
1992
- 1992-03-17 JP JP4091599A patent/JP2584702B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JP2584702B2 (en) | 1997-02-26 |
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