JP2742641B2 - Flow sensor - Google Patents
Flow sensorInfo
- Publication number
- JP2742641B2 JP2742641B2 JP4091600A JP9160092A JP2742641B2 JP 2742641 B2 JP2742641 B2 JP 2742641B2 JP 4091600 A JP4091600 A JP 4091600A JP 9160092 A JP9160092 A JP 9160092A JP 2742641 B2 JP2742641 B2 JP 2742641B2
- Authority
- JP
- Japan
- Prior art keywords
- thin film
- film heater
- flow
- temperature
- 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.)
- Expired - Fee Related
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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 a flow rate of a 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, an upstream side of the heater is cooled by a gas flow and a downstream side is heated by heat carried by the gas flow. Therefore, by measuring the temperature difference between the upstream side and the downstream side of the heater, the flow velocity of the gas can be detected. Based on such a principle, there has been proposed a flow sensor in which a temperature sensor is disposed on the upstream side and the downstream side of a micro heater (for example, see Japanese Patent Application Laid-Open No. 2-193017).
【０００３】[0003]
【従来の技術】従来のフローセンサはヒータが載ってい
る薄膜の上下両面が気体の流れにさらされるよう、薄膜
の上流側と下流側に大きな開口があいていた。この大き
な開口があるため、気体の流れが乱流になり、温度差と
気体流速の関係が簡単な公式から求めることができず、
面倒な校正が必要であった。2. Description of the Related Art A conventional flow sensor has large openings on the upstream and downstream sides of a thin film so that both upper and lower surfaces of a thin film on which a heater is mounted are exposed to a gas flow. Due to this large opening, the gas flow becomes turbulent, and the relationship between the temperature difference and the gas velocity cannot be determined from a simple formula.
Troublesome calibration was required.
【０００４】[0004]
【発明が解決しようとする課題】この発明は、薄膜ヒー
タを基板側と熱的および電気的に分離すると共に、気体
流に渦を生じさせないフローセンサを得ることを目的と
する。SUMMARY OF THE INVENTION It is an object of the present invention to provide a flow sensor that thermally and electrically separates a thin film heater from a substrate side and that does not generate a vortex in a gas flow.
【０００５】[0005]
【課題を解決するための手段】この発明のフローセンサ
は、気体の流れにさらされる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。SUMMARY OF THE INVENTION A flow sensor according to the present invention measures the temperatures of an upstream side and a downstream side of a thin film heater exposed to a flow of gas, respectively, with a temperature sensor, and detects the flow rate of the gas from the temperature difference. This is the same as before.
【０００６】 しかし、薄膜ヒータは基板に設けられた
空洞の上に形成し、該薄膜ヒータの上流側と下流側に、
該薄膜ヒータを基板側と切り離すスリットを設ける。該
スリットはすべて、気体の流れが層流を保つように細く
形成し、かつ、その長手方向が気体の流れ方向とほぼ直
角になるように配置する。 However, the thin film heater is formed on the cavity provided in the substrate, on the upstream side and the downstream side of the thin film heater,
A slit for separating the thin film heater from the substrate is provided. The slits are all narrow so that the gas flow remains laminar
And its longitudinal direction is almost perpendicular to the gas flow direction.
Arrange so that it becomes a corner.
【０００７】[0007]
【作用】ヒータを気体の流れに置いた場合、気体の流れ
が層流の場合、ヒータが気体によって奪われる熱量ΔＱ
は次の式で求めることができる。 ΔＱ＝ｋ(Re)1/2＝ｋ(VL/ν)1/2 ここで、Vは気体の流速、Reはレイノルズ数、νは気体
の粘性係数である。When the heater is placed in the gas flow, when the gas flow is laminar, the amount of heat ΔQ taken by the heater by the gas is used.
Can be obtained by the following equation. ΔQ = k (Re) 1/2 = k (VL / ν) 1/2 where V is the gas flow rate, Re is the Reynolds number, and ν is the viscosity coefficient of the gas.
【０００８】このフローセンサのスリットは気体流に渦
を生じさせない程度に細いので、気体流はスリットを越
える際に渦を生ずることがなく、層流状態を保つ。した
がって、温度差と気体流速の関係は、上式から簡単に導
くことができる。Since the slit of this flow sensor is small enough not to generate a vortex in the gas flow, the gas flow does not generate a vortex when passing through the slit and maintains a laminar flow state. Therefore, the relationship between the temperature difference and the gas flow rate can be easily derived from the above equation.
【０００９】また、スリットは、薄膜ヒータで生じたジ
ュール熱が基板側に逃げるのを阻止すると共に、薄膜ヒ
ータを流れる電流が基板側に漏れ出るのを阻止する。こ
れによってフローセンサの精度が上がる。The slit prevents the Joule heat generated in the thin film heater from escaping to the substrate side, and also prevents the current flowing through the thin film heater from leaking to the substrate side. This increases the accuracy of the flow sensor.
【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）。In FIG. 1, boron is applied to the surface of an n-type silicon substrate 1 at a high concentration using a spreading agent, for example, about 1%.
Add about × 10 20 cm -3 and thermally diffuse to form a high-concentration boron-added single-crystal silicon layer 2. This layer can be used as a heater because of its low electric resistance. This layer also
It becomes P ++ -Si (especially a high concentration of P-type silicon), and is metallic at a temperature of several hundred 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 square frame shape (this portion will be a groove 3 later).
【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。[0011] SiO 2 films 4 and 5 are formed on both surfaces of the substrate by thermal oxidation, and windows are formed in the SiO 2 film 5 on the back surface. When the substrate 1 is anisotropically etched in this manner, the n-type silicon substrate 1
A cavity 15 is formed, and the high-concentration boron-doped single-crystal silicon layer 2 is not affected by the anisotropic etchant and remains on the cavity 15 in a diaphragm shape. This is used as the thin film heater 6. The portion where boron has not been added is etched to form the groove 3 and separates the thin-film heater 6 and the surrounding high-concentration boron-doped 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 is formed on the thin film heater 6 through the small window opened in the SiO 2 film 4. The electrodes 7, 7 are applied to the thin-film heater 6 so that current flows along the flow of gas.
Are provided on the upstream and downstream sides.
【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。On the upstream and downstream sides 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 from the substrate 1. Slit 8
If is too thick, the gas flowing along the thin-film heater will have a vortex, and the amount of heat taken by the gas cannot be determined from a simple equation. Therefore, the width of the slit is made as small as about 20 μm.
【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. Various types of temperature sensors including a thermocouple can be used for each temperature sensor. In this embodiment, the temperature sensors are constituted by pn junction diodes. To make this, a window is opened in the SiO 2 film 4 on the thin film heater to expose the high-concentration boron-added single crystal silicon layer 2 which is the thin film heater 6, and an n-type silicon layer 10 is epitaxially grown on this portion. The high-concentration boron-doped single-crystal silicon layer 2, which is a thin-film heater, has p
Since 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, a pn junction diode is obtained. When 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 a temperature of 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 center monitors the temperature at the center of the thin film heater 6 with this, and controls the current flowing through the thin film heater so that the temperature becomes constant. In this manner, the temperatures on the upstream side and the downstream side of the thin film sensor 6 are measured by the temperature sensors 9a and 9c, and the gas flow velocity is obtained 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。Since the temperature coefficient of this thin-film heater is positive, the lower the temperature, the lower the electric resistance. At the same current, the power consumption is small and the heat generation is small. FIG.
In the above, since the upstream side of the thin film heater is cooled by the gas flow, the heat generation is small. Conversely, the downstream side is warmed up with respect to the same current as compared to the upstream side, so that 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 heating of the heater is also reduced and the temperature tends to be lower, and the downstream side is reversed, 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 thin-film heater has a negative temperature coefficient of resistance. An n-type silicon layer (having a thickness of about 3 μm) 22 is epitaxially formed on a p-type silicon substrate 21. Next, 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 a groove 23 later). SiO 2 films 24 on both sides of this substrate,
25 is formed by thermal oxidation, and a window is opened in the back surface 25.
Thus, when the n-type epitaxial layer 22 is subjected to electrolytic etching in a caustic soda aqueous solution at 60 ° C. and about 50%, the p-type silicon substrate 21 is anisotropically etched to form a cavity 35. The n-type silicon layer 22 remains in a diaphragm shape on the upper surface. 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 trench 2
3 and 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 in the thin film heater in a direction perpendicular to the flow of the fluid. The slit 28 is formed in the same manner as in 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 and 9c formed on the thin film heater 26 may be of any type, but here, a semiconductor thermistor is used. This is 0.2μ
The electrodes 31 and 32 are attached to a germanium layer 30 sputtered to a thickness of about m and heat-treated in N 2 at 400 ° C., which is suitable for use at a temperature of 100 ° C. or less.
【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 the current hardly flows on the upstream side. For this reason,
On the upstream side of the thin film heater, heat generation is suppressed. On the other hand, on the downstream side, it is heated by the movement of heat due to the flow of gas, so the resistance is reduced and the current flows more,
It generates extra heat.
【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 is further cooled at the temperature sensor 29a on the upstream side, and the temperature of the downstream sensor 29c is further reduced.
Is heated further, the temperature difference between the two temperature sensors increases, and the sensitivity increases. Temperature sensor 2 at the center
9b monitors the temperature at the center of the thin film heater as before.
【００２２】[0022]
【発明の効果】この発明は以上説明したように、薄膜ヒ
ータの上流側と下流側にスリットを設けたので、薄膜ヒ
ータで生じたジュール熱が基板側に逃げるのを阻止で
き、また、薄膜ヒータを流れる電流が基板側に漏れ出る
のを阻止できるので、フローセンサの精度が向上する。As described above, according to the present invention, the slits are provided on the upstream and downstream sides of the thin film heater, so that the Joule heat generated by the thin film heater can be prevented from escaping to the substrate side. Of the flow sensor can be prevented from leaking to the substrate side, thereby improving the accuracy of the flow sensor.
【００２３】 また、スリットはすべて、気体の流れが
層流を保つように細く形成し、かつ、その長手方向が気
体の流れ方向とほぼ直角になるように配置したので、気
体流はスリットを越える際、渦を生ずることがなく、層
流状態を保つ。したがって、薄膜ヒータの上下流の温度
差と気体流速の関係が簡単な公式から求めることができ
る。In addition, all the slits have a gas flow
It is formed thin to maintain laminar flow, and its longitudinal direction is
Since the gas flow is arranged so as to be substantially perpendicular to the flow direction of the body, the gas flow does not generate a vortex when passing through the slit, and maintains a laminar flow state. Therefore, the relationship between the temperature difference between the upstream and downstream of the thin film heater and the gas flow rate can be obtained from a simple formula.
【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, in which (a) is a plan view and (b) is a cross-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,
(A) is a plan view and (b) is a cross-sectional view.
１，２１ 基板 ６，２６ 薄膜ヒータ ８，２８ スリット ９，２９ 温度センサ １５，３５ 空洞 1,21 substrate 6,26 thin film heater 8,28 slit 9,29 temperature sensor 15,35 cavity
Claims (1)
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、基板に設けられた空洞の上に該薄膜
ヒータを形成し、該薄膜ヒータの上流側と下流側に、該
薄膜ヒータを基板側と切り離すスリットを設け、該スリ
ットはすべて、気体の流れが層流を保つように細く形成
し、かつ、その長手方向が気体の流れ方向とほぼ直角に
なるように配置したことを特徴とするフローセンサ。1. A flow sensor in which a temperature of an upstream side and a downstream side of a thin film heater exposed to a gas flow is measured by a temperature sensor, and a flow rate of the gas is detected from a difference between the temperatures. It was to form a thin film heater on the cavity, on the upstream side and the downstream side of the thin film heater, a slit to separate the thin film heater and the substrate side, and all the slits, so that the flow of gas to keep the laminar flow Thinly formed
And its longitudinal direction is almost perpendicular to the gas flow direction.
1. A flow sensor, wherein
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP4091600A JP2742641B2 (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 |
|---|---|---|---|
| JP4091600A JP2742641B2 (en) | 1992-03-17 | 1992-03-17 | Flow sensor |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH05264566A JPH05264566A (en) | 1993-10-12 |
| JP2742641B2 true JP2742641B2 (en) | 1998-04-22 |
Family
ID=14031055
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP4091600A Expired - Fee Related JP2742641B2 (en) | 1992-03-17 | 1992-03-17 | Flow sensor |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2742641B2 (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4074368B2 (en) * | 1998-02-27 | 2008-04-09 | 北陸電気工業株式会社 | Heat generation type thin film element sensor and manufacturing method thereof |
| JP3404300B2 (en) | 1998-10-28 | 2003-05-06 | 三菱電機株式会社 | Thermal flow sensor |
| JP3653498B2 (en) * | 2000-05-19 | 2005-05-25 | 三菱電機株式会社 | Thermosensitive flow rate detecting element and its holder |
| JP3678180B2 (en) | 2001-07-27 | 2005-08-03 | 株式会社デンソー | Flow sensor |
| KR100434540B1 (en) * | 2001-07-28 | 2004-06-05 | 삼성전자주식회사 | Structure having microchannel and sensor and heater contacting with fluid in microchannel and method for manufacturing the same |
| JP2003115683A (en) * | 2001-09-28 | 2003-04-18 | Ge Medical Systems Global Technology Co Llc | Filter clogging monitoring method and electronic appliance |
| JP4205116B2 (en) * | 2006-05-15 | 2009-01-07 | 三菱電機株式会社 | Flow detection element of thermal flow sensor |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2529895B2 (en) * | 1990-07-13 | 1996-09-04 | 山武ハネウエル株式会社 | Flow sensor |
-
1992
- 1992-03-17 JP JP4091600A patent/JP2742641B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH05264566A (en) | 1993-10-12 |
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