JP3324855B2 - Mass flow sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass flow sensor used for 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 prior art.
Is a main body block having an inlet 2 formed at one end thereof for flowing a fluid such as a gas, and a fluid outlet 3 formed at the other end, and connecting the fluid inlet 2 and the fluid outlet 3 therein. The fluid flow path 4 is formed. The fluid flow path 4 is provided with a bypass element 5 having a constant flow rate characteristic.

[0005] Reference numeral 7 denotes a sensor fixing base provided on the upper part of the main body block 1. This sensor fixing base 7 includes:
A sleeve 10 having a hole 9 communicating with the flow path 4 in the main body block 1 through the communication passage 8 is provided detachably. 1
1 is a sealing member. Reference numeral 12 denotes a mass flow sensor, which is connected to the sleeve 10 by a method such as resistance welding.
A thin tube 13 as a measurement flow path which is provided upright in the inverted U-shape in the sensor fixing base 7 and the main body block 1, and is wound around the outer periphery of a central horizontal portion 13 a of the thin tube 13.
And one thermal resistor 14 and 15. The heat-sensitive resistors 14 and 15 are selected to have the same heat-sensitive characteristics.

Reference numeral 16 denotes 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 lead pins of the hermetic terminal 16. .
Reference numeral 17 denotes a sensor case for accommodating and covering the sensor section 12, the hermetic terminal 16, and the like. In addition, the main body block 1, the sleeve 10, the thin tube 13, etc.
Made of metal with excellent corrosion resistance such as stainless steel, nickel and Kovar.

In the mass flow meter, when a fluid flows through the thin tube 13, the upstream thermal resistor 14 is deprived of heat by the fluid and cooled, and the downstream thermal resistor 15 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]

The conventional mass flow sensor 12 is composed of a stainless steel thin tube 13 having an inner diameter of about 0.3 mm to 1 mm. Since the heat-sensitive resistors 14 and 15 are formed by being wound manually at intervals, there are the following problems.

The heat-sensitive resistors 14 and 15 need to have the same resistance value in order to eliminate the influence of the environmental temperature. For this reason, winding is performed while measuring the resistance value, which takes a great deal of time and is one of the major factors of cost increase. The thermal resistors 14 and 15 are heated at a considerable temperature. However, if the thermal resistors 14 and 15 are used for a long time, the thermal resistors 14 and 15 may be loosened or drift.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned problems, and has as its object to provide a mass flow sensor which does not decrease in reliability even when used for a long time and which can be mass-produced. I have.

[0009]

In order to achieve the above object, a mass flow sensor according to the present invention is characterized in that a silicon substrate is bonded to a glass substrate having a flow path through which a fluid flows, so as to contact the flow path, A heater for detecting a fluid flow rate is formed on a 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 sensor, since the heater for detecting the fluid flow rate hardly changes with time, stable performance is maintained for a long period of time. In addition, since the semiconductor device can be manufactured by a batch process using a semiconductor manufacturing technology or a micromachining technology, mass production becomes possible and cost can be reduced.

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 reduced in size.

[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. 2A is a plan view thereof, and FIG. 3) is a sectional view taken along line AA of FIG.

The mass flow sensor 20 is configured as follows. That is, 21 has a thickness of 0.3 mm to 1 m
A glass substrate having a length of about 0.3 mm to 1 mm is formed on the plane by ultrasonic processing or laser processing.
Is pierced. This long hole 22 is, as described later,
This serves as a flow path for the fluid F.

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

The heaters 25 and 26 need to be formed so that their resistance value and resistance temperature coefficient are equal to each other.
It is formed by a photolithography technique capable of obtaining 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 by, for example, anodic bonding so as to cover one opening side of the elongated hole 22, and is considerably thicker than the above-described silicon substrate 23 on the upper surface side. The silicon substrate 33 on the lower surface is provided with an inlet 34 and an outlet 35 for the fluid F.

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

A long hole 22 serving as a fluid flow path is formed in a glass substrate 21 by ultrasonic processing or laser processing.
(B)).

A slightly thick silicon substrate 23 is bonded 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. Instead of etching, mechanical polishing may be performed so as to have a predetermined thickness (FIG. 3).
(D)).

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

By photolithography and etching,
Unnecessary silicon portions other than the portion covering the glass substrate 21 are removed. This is to make the heat capacity of the silicon substrate 23 as small as possible. 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 and 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 (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. These may be thin films formed by vacuum deposition or sputtering, or thick films formed by screen printing or the like. In the case of a bonding pad using a thin film, wire bonding is performed from here using a gold wire or an aluminum wire. In the case of a thick film, a lead wire may be directly soldered thereto.

The mass flow sensor 2 configured as described above
0 denotes an O-ring 3 in a state where the inlet 34 and the outlet 35 communicate with the communication paths 8A and 8B of the main body block 1 on the upper surface of the main body block 1 of the mass flow meter as shown in FIG.
6 is fixed. In FIG. 4, reference numeral 37 denotes a cover made of a heat insulating material for covering the mass flow sensor 20, and the cover 37 prevents a heated atmosphere gas (atmosphere) from adversely affecting the mass flow sensor 20. is there.

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

FIG. 5 shows a configuration in the case where the mass flow sensor 20 is driven by a constant current circuit. The upstream heater 25 and the downstream heater 26 include two bridge resistors on a printed circuit board (not shown). Together with 38 and 39, a bridge circuit 40 is formed. When the resistance values of the heaters 25 and 26 are set to several tens Ω to several hundred Ω, the bridge resistance 3
The resistance values of 8, 39 are set to several kilo-ohms to several tens of 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, the current almost flows to 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 according to the flow rate of the fluid. However, the flow of the fluid F through the flow path 22 causes the upstream heater 25 and the downstream heater 26 The balance of the resistance value at the time is broken. Therefore, the balance of the bridge circuit 40 is shifted, and 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 above-described mass flow sensor 20, the heaters 25 and 26 for detecting the fluid flow rate are not formed of wires as in the prior art, but are patterned on a silicon substrate 23. Moreover, the heater 2
Since the elements 5 and 26 are not arranged so as to be in contact with the flow path 22 through which the fluid flows, the good detection characteristics can be maintained even after long-term use. Therefore, the reliability of the mass flow meter or the mass flow controller is maintained at a high level for a long period of time. Further, the mass flow sensor 20 can be mass-produced by a batch process, and 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 suitably performed. Since silicon has a high thermal conductivity, it is suitable for heating the entire sensor. Further, the glass substrate 21 and the silicon substrates 23, 33
Are chemically bonded by anodic bonding. Therefore, compared to the method using an adhesive,
It can be used with confidence in lines where the bonding force is extremely large and pressure resistance is required.

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

The present invention is not limited to the above embodiment, but can be implemented in various modifications. 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 the resin is used in a line where resin is disliked in terms of degassing characteristics, the mass flow sensor 20 may be die-bonded to the main body block 1 with gold-silicon.

In the above-described embodiment, only one long hole 22 is provided in the glass substrate 21. However, in addition to the long hole 22, a long hole or a groove communicating with the long hole 22 is provided to provide a plurality of flow holes. The path 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 reduced in size.

[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 time. In addition, since the semiconductor device can be manufactured by a batch process using a semiconductor manufacturing technology or a micromachining technology, mass production becomes possible and cost can be reduced.

[Brief description of the drawings]

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

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

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01F 1/68 G05D 7/06

Claims (3)

(57) [Claims] 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 formed. 2. A mass flow rate, wherein 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 detecting a fluid flow rate. Sensor. 3. The mass flow sensor according to claim 1, wherein a plurality of flow paths are formed.