JPH07159215A - Mass flowsensor - Google Patents

Abstract

PURPOSE:To prevent the reliability from lowering after long term use while making mass production possible by bonding a silicon substrate to a glass substrate on which a channel is formed and then forming a heater for detecting the flow rate of fluid thereon. CONSTITUTION:An elongated hole 22 is made, as a channel for fluid, through a glass substrate 21 by ultrasonic machining or laser machining. A silicon substrate 23 is bonded by anodic bonding, for example, to the upper face of the substrate 21 while covering the elongated hole 22 on one opening side thereof. An insulating layer of oxide film, for example, is formed on the upper face of the substrate 23 and heaters 25, 26 for detecting the flow rate of fluid are formed thereon of a metal having high temperature coefficient of resistance, e.g. platinum or nickel. The heaters 25, 26 are formed integrally and lead wires are extended from the intermediate and end parts thereof with bonding pads 30, 31, 32 being formed at the tips thereof. Since the mass flow sensors can be manufactured by batch process using semiconductor fabrication technology or micromachining technology, the mass flow sensors can be mass-produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass flow meter used in a mass flow meter for measuring a mass flow rate of a fluid or a mass flow controller for measuring a mass flow rate of a fluid and controlling the fluid flow rate.

[0002]

2. Description of the Related Art FIG. 6 shows a mass flow meter generally used in the past.
Is a main body block, and an inlet 2 through which a fluid such as gas flows is formed at one end side thereof, a fluid outlet 3 is formed at the other end side thereof, and the fluid inlet 2 and the fluid outlet 3 are connected to each other inside. A fluid flow path 4 is formed in the fluid flow path 4, and a bypass element 5 having a constant flow rate characteristic is provided in the fluid flow path 4 and configured as a bypass section 6.

Reference numeral 7 is a sensor fixing base provided on the upper part of the main body block 1. In this sensor fixed base 7,
A sleeve 10 having a hole 9 communicating with the flow path 4 in the main body block 1 via a communication passage 8 is detachably provided. 1
Reference numeral 1 is a seal member. A mass flow sensor 12 is connected to the sleeve 10 by a technique such as resistance welding,
A thin tube 13 as a measurement flow path that is vertically installed in the sensor fixing base 7 and the main body block 1 in a vertical and inverted U shape, and 2 wound around the outer periphery of a horizontal portion 13a at the center of the thin tube 13.
It consists of two heat-sensitive resistors 14 and 15. The heat sensitive resistors 14 and 15 are selected to have the same heat sensitive characteristics.

Reference numeral 16 is a hermetic terminal provided on the upper surface of the sensor fixing base 7 by resistance welding or the like. The heat-sensitive resistors 14 and 15 are connected to a bridge circuit (not shown) via the lead pins of the hermetic terminal 16. .
Reference numeral 17 denotes a sensor case for accommodating and covering the sensor unit 12, the hermetic terminal 16, and the like. In addition, the main body block 1, the sleeve 10, the thin tube 13, etc.,
It is made of metal with excellent corrosion resistance such as stainless steel, nickel, and Kovar.

In the above mass flow meter, when a fluid flows in the thin tube 13, the heat sensitive resistor 14 on the upstream side is deprived of heat by the fluid and cooled, and the heat sensitive resistor 15 on the downstream side is cooled by the fluid. It is heated by the heat carried from the upstream side. The change in the heat balance detects the mass flow rate of the fluid.

[0006]

In the conventional mass flow sensor 12, a thin tube 13 made of stainless steel having an inner diameter of 0.3 mm to 1 mm and having an insulation coating of polyimide resin or the like is used as a wire material of about several tens of μm. Since the heat-sensitive resistors 14 and 15 are manually wound with a space provided therebetween, the following problems occur.

In order to eliminate the influence of environmental temperature, it is necessary for the heat sensitive resistors 14 and 15 to have their resistance values equal to each other. Therefore, the winding is performed while measuring the resistance value, which takes a lot of trouble and is one of the major factors of the cost increase. Further, the heat sensitive resistors 14 and 15 are heated at a considerable temperature, but when used for a long period of time, there are cases where drift occurs due to loosening or the like.

The present invention has been made in consideration of the above matters, and an object of the present invention is to provide a mass flow sensor which does not deteriorate in reliability even after long-term use and can be mass-produced. There is.

[0009]

In order to achieve the above object, the mass flow rate sensor of the present invention comprises a glass substrate having a flow passage through which a fluid flows, and a silicon substrate bonded to the glass substrate so as to be in contact with the flow passage. A heater for fluid flow rate detection is formed on the surface of the silicon substrate that does not face the flow path side.

In this case, the silicon substrate may be used as a heater for detecting a fluid flow rate. Further, a plurality of flow paths may be formed.

[0011]

In the mass flow rate sensor, since the heater for detecting the fluid flow rate hardly changes with time, stable performance is maintained for a long period of time. Further, since the semiconductor manufacturing technology and the micromachining technology can be manufactured in a batch process, mass production is possible and cost reduction can be achieved.

Further, by forming a plurality of flow paths, the flow paths serve as a bypass, and the mass flow meter and the mass flow controller can be significantly downsized.

[0013]

1 and 2 show a mass flow sensor 20 according to the present invention. FIG. 1 is an overall perspective view of the mass flow sensor 20, FIG. 2 (A) is a plan view thereof, and FIG. ) Is a sectional view taken along the line AA of FIG.

The mass flow sensor 20 is constructed as follows. That is, 21 has a thickness of 0.3 mm to 1 m.
A glass substrate having a size of about m, and a long hole 22 of 0.3 mm to 1 mm square formed on the plane by ultrasonic processing or laser processing, for example.
Is installed throughout. This long hole 22 is, as will be described later,
It serves as a flow path for the fluid F.

Reference numeral 23 is a silicon substrate having a thickness of about 0.02 mm to 0.2 mm which is bonded to the upper surface of the glass substrate 21 by anodic bonding so as to cover one opening side of the elongated hole 22, for example. An insulating layer 24 made of an oxide film or the like is formed on the upper surface of the silicon substrate 23. Heaters 25, 26 for detecting the fluid flow rate are formed on the upper surface of the insulating layer 24 by a metal having a large temperature coefficient of resistance such as platinum or nickel. (Less than,
The upstream heater 25 and the downstream heater 26) are formed. These heaters 25 and 26 are formed integrally, but the lead portions 27 and 2 are formed from the middle and end portions thereof.
8 and 29 are extended, and bonding pads 30, 31, and 32 are formed at their tips.

The heaters 25 and 26 must be formed so that their resistance values and temperature coefficients of resistance are equal to each other, and a pattern of several hundred μm to several mm is formed in 0.1 μm.
It is formed by a photolithography technique with an accuracy of m to 0.5 μm.

Reference numeral 33 denotes a silicon substrate which is bonded to the lower surface of the glass substrate 21 so as to cover one opening side of the elongated hole 22 by, for example, anodic bonding, and is considerably thicker than the above-described upper surface silicon substrate 23. An inlet 34 and an outlet 35 for the fluid F are opened in the silicon substrate 33 on the lower surface side.

FIG. 3 shows an example of a procedure for manufacturing the mass flow sensor 20. First, 0.3mm-1mm
A glass substrate 21 of a certain size is prepared (see FIG. 3A).

An elongated hole 22 serving as a fluid channel is formed in a glass substrate 21 by ultrasonic processing or laser processing (FIG. 3).
(See (B)).

A slightly thick silicon substrate 23 is attached to the upper surface of the glass substrate 21 by anodic bonding (FIG. 3C).
reference).

Etching is performed using KOH (potassium hydroxide) until the silicon substrate 23 has a thickness of about 100 μm. Note that, instead of etching, mechanical polishing may be performed to obtain a predetermined thickness (FIG. 3).
(D)).

On the lower surface of the glass substrate 21, the silicon substrate 3
3 is bonded by anodic bonding. This silicon substrate 3
Holes 34 and 35 are formed in 3 by anisotropic etching, ultrasonic processing, laser processing or the like (see FIG. 3E).

By photolithography and etching,
The unnecessary silicon portion other than the portion covering the glass substrate 21 is removed. This is to minimize the heat capacity of the silicon substrate 23. A silicon oxide film or a silicon nitride film formed by CVD or sputtering is used as an etching mask (see FIG. 3F).

An insulating layer 24 is formed on the upper surface of the silicon substrate 23 on the upper surface side, and heaters 25, 2 are formed on the upper surface of the insulating layer 24 using a metal having a large temperature coefficient of resistance such as platinum or nickel.
6 is formed (see FIG. 3G).

Wirings 27 to 29 for taking out electrodes from the heaters 25 and 26 and bonding pads 30 to 32 are formed. For these, a thin film formed by vacuum deposition or sputtering may be used, or a thick film formed by screen printing may be used. In the case of a thin film bonding pad, wire bonding is performed from here using a gold wire or an aluminum wire. In the case of a thick film, the lead wire may be directly soldered to this.

Mass flow sensor 2 constructed as described above
As shown in FIG. 4, 0 indicates that the O-ring 3 is provided on the upper surface of the main body block 1 of the mass flow meter in a state where the inlet port 34 and the outlet port 35 communicate with the communication passages 8A and 8B of the main body block 1.
It is fixed through 6. In FIG. 4, reference numeral 37 denotes a cover body made of a heat insulating material for covering the mass flow rate sensor 20. The cover body 37 prevents adverse effects on the mass flow rate sensor 20 due to warmed atmospheric gas (atmosphere). is there.

The mass flow sensor 20 of the present invention can be driven by a constant current circuit or a constant temperature circuit, like the mass flow sensor used in a conventional mass flow meter or mass flow controller.

FIG. 5 shows a structure in which the mass flow sensor 20 is driven by a constant current circuit. The upstream heater 25 and the downstream heater 26 are two bridge resistors on a printed circuit board (not shown). A bridge circuit 40 is configured with 38 and 39. When the resistance values of the heaters 25 and 26 are set to several tens Ω to several hundreds Ω, the bridge resistance 3
The resistance value of 8, 39 is set to several kilo-ohms to several tens kilo-ohms. 41 is a constant current source, 42 is a first stage amplifier, and 43 is an output terminal.

When a constant current is supplied to the bridge circuit 40 by the constant current source 41, almost all the current flows through the upstream heater 25 and the downstream heater 26. Even if the fluid F flows through the flow path 22, the resistance values of the bridge resistors 38 and 39 do not change due to the flow rate of the fluid, but the flow of the fluid F through the flow path 22 causes the upstream heater 25 and the downstream heater 26 to be connected to each other. The balance of resistance values in Therefore, the bridge circuit 40 is out of balance, a voltage proportional to the fluid flow rate is generated in the first stage amplifier 42, and this appears at the output terminal 43. In an actual mass flow meter or mass flow controller, the voltage appearing at the output terminal 43 is used by performing zero adjustment or span adjustment.

In the mass flow rate sensor 20 described above, the heaters 25 and 26 for detecting the fluid flow rate are formed by patterning on the silicon substrate 23, instead of being composed of wire rods as in the conventional case. Moreover, the heater 2
Since the elements 5 and 26 are not arranged so as to come into contact with the flow path 22 through which the fluid flows, their good detection characteristics can be maintained even after long-term use. Therefore, the reliability of the mass flow meter and the mass flow controller is highly maintained over a long period of time. Further, the mass flow sensor 20 can be mass-produced by a batch process, and the cost can be reduced.

In the above embodiment, the silicon substrate 23 is anodically bonded to the glass substrate 21 and the heaters 25 and 26 are formed on the silicon substrate 23 with the insulating layer 24 interposed therebetween. Since the rate is small, the heat insulation of the heaters 25 and 26 is preferably performed. Since silicon has a high thermal conductivity, it is suitable for heating the entire sensor. In addition, the glass substrate 21 and the silicon substrates 23 and 33
By anodic bonding of and, both are chemically bonded. Therefore, compared to the method using adhesive,
It has a remarkably large coupling force and can be used with confidence in lines that require pressure resistance.

Further, the thickness of the silicon substrate 23 on the upper surface side can be easily controlled, and the thickness can be made smaller than that of the conventional thin tube 13 made of stainless steel. This is a great advantage in that the heat transfer efficiency with respect to the fluid flowing in the flow path 22 can be increased and the sensitivity is improved.
The thermal conductivity of silicon is 1.70 W / cm · d.
and the thermal conductivity of stainless steel (0.14 W /
(cm · deg) is more than 10 times larger, which also greatly contributes to improving the sensitivity.

The present invention is not limited to the above-mentioned embodiments, but can be carried out in various modified forms. For example, although not shown, the silicon substrate 21 on the upper surface side may be used as a heater as it is. Further, the silicon substrate 33 on the lower surface side may be omitted. Then, the mass flow sensor 20 may be directly bonded to the main body block 1. When used in a line where resins are disliked in terms of degassing characteristics, the mass flow rate sensor 20 may be die-bonded to the main body block 1 with gold-silicon.

In the above-described embodiment, the glass substrate 21 is provided with only one elongated hole 22. However, in addition to the elongated hole 22, elongated holes or grooves communicating with the elongated hole 22 are provided so that a plurality of flow holes are formed. The channels may be formed in the glass substrate 21. In this case, the plurality of flow paths serve as a bypass, and the mass flow meter and the mass flow controller can be significantly downsized.

[0035]

As described above, according to the present invention, since the heater for detecting the fluid flow rate hardly changes with time, stable performance is maintained for a long period of time. Further, since the semiconductor manufacturing technology and the micromachining technology can be manufactured in a batch process, mass production is possible and cost reduction can be achieved.

[Brief description of drawings]

FIG. 1 is a perspective view showing an entire mass flow rate sensor of the present invention.

FIG. 2A is a plan view of the mass flow sensor,
(B) is the sectional view on the AA line of (A).

FIG. 3 is a diagram showing an example of a manufacturing procedure of the mass flow sensor.

FIG. 4 is a diagram showing an example of a mass flow meter incorporating the mass flow sensor.

FIG. 5 is a diagram showing an example of a drive circuit of the mass flow sensor.

FIG. 6 is a diagram showing a mass flow meter incorporating a conventional mass flow sensor.

[Explanation of symbols]

21 ... Glass substrate, 22 ... Flow path, 23 ... Silicon substrate,
25, 26 ... Heater, F ... Fluid.

Claims (3)

[Claims] 1. A glass substrate having a flow path through which a fluid flows is bonded to a silicon substrate so as to be in contact with the flow path, and a heater for detecting a fluid flow rate is provided on a surface of the silicon substrate not facing the flow path side. A mass flow sensor characterized by being formed. 2. A mass flow rate characterized in that a silicon substrate is bonded to a glass substrate having a flow path through which a fluid flows so as to be in contact with the flow path, and the silicon substrate is used as a heater for fluid flow rate detection. Sensor. 3. The mass flow sensor according to claim 1, wherein a plurality of flow paths are formed.