JPH05307045A - Flow speed sensor - Google Patents

Abstract

PURPOSE:To provide a small-sized flow speed sensor whose thermosensitive film exhibits stable characteristics on change with the passage of time and which can separately perform temp. sensing made by the film and control of its temp. CONSTITUTION:A heater 2 is formed from a diffusion layer consisting of p-type impurities such as boron and provided on one of the surfaces of a silicon base board 1. An insulative film 3 is formed on the oversurface of the heater 2, and a thermosensitive film 4 is formed on this insulative film 3. Because the films 4 and the heater 2 to heat it are formed separately, temp. sensing of the film 4 can be done separately from controlling the film temp. It is therefore possible to control the current to be fed to the heater 2 and heat the film 4 to a temp., which suits measurement of the flow speed, while the temp change is sensed by the film 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow velocity sensor for measuring the flow velocity of a fluid such as a liquid, and in particular, a thermistor is used as a temperature sensitive film, and the temperature change due to a change in electric resistance value of the thermistor in the fluid. The present invention relates to a flow velocity sensor that detects a temperature change and converts this temperature change into a flow velocity.

[0002]

2. Description of the Related Art Conventionally, a flow velocity sensor of this type has been used for measuring cardiac output by a right heart catheterization method for a cardiac function test, for example. For this flow velocity sensor,
In addition to a thermal sensor using a thermistor that is a resistor, a thermocouple sensor, a pn junction sensor, or the like is used.

Among these, in particular, in order to measure the flow velocity in a minute portion, the size of the sensor itself needs to be reduced, so that the thermal type which can have a simple structure is mainly used. Has been. In this thermal type flow velocity sensor, first, a large amount of current is passed through a temperature sensitive film (thermistor) which is a resistor to heat the temperature sensitive film to a high temperature. Next, the sensor itself is held in the fluid, the temperature change of the temperature sensitive film due to heat removal by the fluid is detected, and this temperature change is converted into the flow velocity of the fluid.

[0004]

However, in the conventional thermal type flow velocity sensor, when the temperature sensitive film is heated in advance and when the flow velocity is measured thereafter, the current is directly applied to the temperature sensitive film. It was not possible to detect the temperature in the membrane and control the temperature separately. That is, in order to set the temperature of the sensor to the best condition with respect to the temperature of the fluid and its surrounding environment, the value of the current flowing through the temperature sensitive film is changed,
It was necessary to control the amount of self-heating. Therefore, a large amount of current needs to flow through the temperature-sensitive film itself, and this current affects the electrical characteristics of the sensor. That is, there is a problem that a drift phenomenon such as a change in the resistance value in a certain direction is likely to occur.

The present invention has been made in view of the above problems, and an object thereof is to detect temperature in a temperature sensitive film and control the temperature separately, and to obtain stable characteristics of the temperature sensitive film over time. It is to provide a small flow rate sensor as shown.

[0006]

A flow velocity sensor according to the present invention includes a sensor substrate having two opposing surfaces, a temperature sensitive film provided on the sensor substrate for detecting a temperature change in a fluid to be detected, and the sensor. The heater is provided on the substrate separately from the temperature sensitive film and heats the temperature sensitive film to a predetermined temperature.

The heater and the temperature sensitive film may be provided in a laminated form on the same surface side of the sensor substrate via an insulating film, and the temperature sensitive film may be provided on one surface side of the sensor substrate. And the heater may be provided on the other surface side of the sensor substrate.

The heater may be an impurity diffusion layer formed in the sensor substrate or a polycrystalline silicon film formed on the sensor substrate. Further, the heater is made of titanium, tungsten, tantalum or the like and has a relatively large resistance value. You may form by a thin film.

As the sensor substrate, a semiconductor substrate made of silicon, germanium or the like is used, but it is preferable to use a silicon substrate which can be easily and inexpensively obtained. The temperature sensitive film is composed of germanium, silicon simple substance, manganese oxide, cobalt oxide, nickel oxide,
Alternatively, it is formed of a substance whose electric resistance value changes with temperature change, such as a complex of these. As the insulating film provided between the temperature sensitive film and the heater, a silicon oxynitride film (SiOxNy), a silicon oxide film (SiOx), a silicon nitride film (SiNy) or the like can be used.

In the flow velocity sensor of the present invention, since the temperature sensitive film and the heater for heating the temperature sensitive film are separately formed, the temperature detection by the temperature sensitive film and the temperature control of the temperature sensitive film are separately performed. Can be done at any time. Therefore, it is possible to freely set the temperature of the temperature sensitive film to a temperature suitable for flow velocity measurement by controlling the current flowing through the heater while detecting the temperature change due to the flow velocity in the temperature sensitive film. Further, it becomes unnecessary to apply a large amount of current to the temperature sensitive film. Therefore, the temperature-sensitive film can be made thin, and as a result, the time-dependent characteristics of the temperature-sensitive film are stabilized.

Further, the heater and the temperature sensitive film are laminated on one surface of the sensor substrate, so that the outer shape of the sensor itself can be made small, which reduces the heat capacity of the sensor and the response sensitivity. Get higher

[0012]

Embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 1 shows a plane structure of a flow velocity sensor according to an embodiment of the present invention, and FIG. 2 shows a sectional structure taken along line AA of FIG.

In the flow velocity sensor of this embodiment, the heater 2 is formed on one surface of the n-type silicon substrate 1. The heater 2 is formed of a diffusion layer of p-type impurities such as boron. An insulating film 3 is formed on the upper surface of the heater 2, and a temperature sensitive film 4 is formed on the insulating film 3. The temperature sensitive film 4 is made of, for example, amorphous germanium (a-Ge). Comb-shaped wiring layers 5a and 5b made of metal such as aluminum are connected to the temperature-sensitive film 4.

A contact pad 6 having a three-layer structure of an aluminum (Al) film 6a, a chromium (Cr) film 6b and a copper (Cu) film 6c is provided on the insulating film 3. The contact pad 6 and the wiring layers 5a and 5b are electrically connected. A lead wire 8 is connected to the copper film 6c of the contact pad 6 via a solder 7.
The lead wire 8 is connected to a detection circuit 16 (FIG. 3) described later. Furthermore, aluminum (Al) is formed on the insulating film 3.
Film 9a, chromium (Cr) film 9b, and copper (Cu) film 9c
A contact pad 9 having a three-layer structure is provided. The lead wire 12 is connected to the copper film 9c of the contact pad 9 via the solder 11. The lead wire 12 is connected to a heater control circuit 14 (FIG. 3) described later. A contact hole 10 is formed in the insulating film 3, and the contact pad 9 and the heater 2 are electrically connected via the contact hole 10.

FIG. 3 shows a schematic configuration of the entire measurement system using the flow velocity sensor 13 having such a configuration.

The temperature of the heater 2 is controlled by the heater control circuit 14. At the time of measurement, first, the flow velocity sensor 1
The ambient temperature is measured by the temperature sensitive film 4 while the sample 3 is held in the fluid to be detected 15. That is, the electric resistance value of the temperature sensitive film 4 changes according to the ambient temperature, and the detection circuit 16 detects the change of the current value or the voltage value due to the change of the electric resistance value. This detected temperature is sent to the heater control circuit 14,
The heater control circuit 14 controls the current flowing through the heater 2 based on the detected temperature, and heats the temperature sensitive film 4 to a temperature suitable for flow velocity measurement. After that, measurement is started, and the temperature-sensitive film 4 is deprived of heat in the fluid 15 to be detected, and its temperature changes. The electric resistance value of the temperature sensitive film 4 changes with the temperature change of the temperature sensitive film 4, and the detection circuit 16 detects the change of the current value or the voltage value due to the change of the electric resistance value. The detection result of the detection circuit 16 is sent to the flow velocity calculation circuit 17,
Here, the flow velocity is calculated. On the other hand, the detection result of the detection circuit 16 is fed back to the heater control circuit 14, and the heater control circuit 14 controls the temperature of the heater 2 based on the detection result.

In the present embodiment, the temperature sensitive film 4 which is a temperature sensor.
Since the heater 2 for heating the temperature sensitive film 4 is separately formed, the temperature of the temperature sensitive film 4 can be freely set. Therefore, it is possible to heat the temperature sensitive film 4 to a temperature suitable for flow velocity measurement by controlling the current flowing through the heater 2 by the heater control circuit 14 while detecting the temperature change due to the flow velocity in the temperature sensitive film 4.

Further, in the flow velocity sensor of this embodiment, since the heater 2 and the temperature sensitive film 4 are laminated on one surface of the silicon substrate 1, the outer shape of the sensor itself can be reduced. This reduces the heat capacity of the sensor and increases the response sensitivity. Further, as compared with the conventional sensor, when the temperature sensitive film 4 is heated to a temperature suitable for flow velocity measurement,
On the other hand, since it is not necessary to apply a large amount of current, the temperature sensitive film 4 can be thinned, and as a result, the time-dependent characteristics of the temperature sensitive film 4 are stabilized.

Next, a method of manufacturing the flow velocity sensor of this embodiment will be described with reference to FIGS.

First, as shown in FIG. 4A, for example, an n-type silicon substrate having a thickness of 300 μm (resistivity 4 to 8 Ω.
cm) 20 was prepared. Next, a silicon oxide film (SiO ₂ ) 21 was formed on both surfaces of this silicon substrate 20.
The silicon oxide film 21 is formed by pyrogenic oxidation, and the oxidation treatment at a temperature of 1100.degree.
A 6 μm thick silicon oxide film 21 was formed.

Then, the heater wiring is patterned with a resist, and a silicon oxide film (SiO 2) is formed by buffer hydrofluoric acid.
₂ ) 21 was etched to form an opening 22 for ion implantation as shown in FIG. The etching time was about 5 minutes at a temperature of 30 ° C.

Next, as shown in FIG.
2 through the p-type impurities on the surface of the silicon substrate 20.
For example, Boron B⁺23 ion implantations, then 110
Annealing treatment was performed at 0 ° C. for 40 minutes. This allows
As shown in FIG. 5A, a heater made of a p-type impurity diffusion layer is used.
24 is formed. Ion implantation uses acceleration voltage of 40 KeV
 , Dose 5 × 10¹⁵ions / cm²And Next, Siri
Plasma CVD (chemical vapor deposition) is performed on the surface of the substrate 20.
Insulation film such as silicon oxinit
A ride film (SiOxNy) 25 was formed. Silicon oxyna
The nitride film 25 is formed on the silicon substrate 21 by 500
Heated to ℃, pressure 0.45toor, high frequency output 400
W and silane (Si H 2_Four) To 10 SCC
M, nitrogen (N ₂) 207SCCM, nitrous oxide (N₂O)
28 SCCM, and the silicon film with a film thickness of 1 μm is taken in 10 minutes.
The xynitride film 25 was formed.

Next, sputtering is performed with germanium (Ge) as a target to form a film having a thickness of 1 μm on the silicon oxynitride film 25 on the surface of the silicon substrate 20.
Was formed into an amorphous germanium (a-Ge) film. In this sputtering, the substrate temperature is 300 ° C., the gas flow rate is argon (Ar) = 4 SCCM, and the film formation pressure is 3 × 1.
The test was performed for 10 minutes at 0 ^-3 Torr and a high frequency output of 120W. Then, reactive ion etching (RIE) is performed to pattern the amorphous germanium film,
The temperature sensitive film 26 as shown in FIG. In this reactive ion etching, for example, Freon (CF ₄ ) and oxygen (O ₂ ) are used as an etching gas, the flow rates thereof are CF ₄ = 38 SCCM, O ₂ = ₂ SCCM, the etching pressure is 0.2 Torr, and the high frequency output is applied. Was 150 W and the etching time was 7 minutes.

Subsequently, an insulating film, for example, a silicon oxynitride film 27 having a thickness of 0.2 μm was formed on the surface of the silicon substrate 20 as shown in FIG. The film forming conditions were the same as those shown in FIG. 5A except that the time was 2 minutes.

Next, as shown in FIG. 6A, the silicon oxynitride film 27 is comb-shaped etched with buffer hydrofluoric acid to form a large number of openings 28 and contact holes 35 for connecting heaters. Formed.

Subsequently, as shown in FIG. 3B, an aluminum (AL) film 29 and a chromium film (Cr) 3 are used as wiring materials.
0 and copper film (Cu) 31 are 1 μm and 0.05 μm, respectively.
m, 2 μm thick and deposited by vapor deposition, and then the aluminum film 29 is selectively etched to form a comb-shaped wiring layer 32.
a and 32b are formed, and the aluminum film 29, the chromium film 30 and the copper film 31 are selectively etched to form the contact pads 33 and 34. As a result, the contact pad 33 and the wiring layer 32b were connected, and the contact pad 34 and the heater 24 were electrically connected via the contact hole 35.

Next, as shown in FIG.
Under the same conditions as the step (C), a silicon oxynitride film 36 having a film thickness of 1 μm as shown in FIG. 6C was formed by the plasma CVD method.

Subsequently, the silicon oxynitride film 36 is selectively etched with buffer hydrofluoric acid,
As shown in FIG. 7A, contact holes 37 were formed on the contact pads 33 and 34, respectively.

Next, the back surface side of the silicon substrate 20 was etched together with the silicon oxide film 21 using an alkaline etching solution, for example, a hydrazine aqueous solution, to thin the silicon substrate 20 to about 150 μm. Through these steps, length 1mm, width 0.3mm, thickness 0.15mm
It was possible to fabricate a minute flow velocity sensor.

The present invention has been described above with reference to the examples.
The present invention is not limited to the above embodiments, but can be variously modified without departing from the scope of the invention. For example, in the above embodiment, the heater 24 and the temperature sensitive film 26 are formed by laminating on the same surface of the silicon substrate 20, but this is formed as shown in FIG.
May be formed on different surfaces, and with such a configuration, the same effect as that of the above embodiment can be obtained. The same components as those in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted.

[0032]

As described above, according to the flow velocity sensor of the present invention, the temperature sensitive film and the heater for heating the temperature sensitive film are separately formed, so that the temperature detection by the temperature sensitive film is performed. The temperature control of the temperature sensitive film can be performed separately. Therefore, it is possible to heat the temperature sensitive film to a temperature suitable for flow velocity measurement by controlling the current flowing through the heater while detecting the temperature change in the temperature sensitive film due to the flow velocity of the fluid to be detected. Further, since it is not necessary to apply a large amount of current to the temperature-sensitive film, the temperature-sensitive film can be thinned, and as a result, the time-dependent characteristics of the temperature-sensitive film are stabilized.

[Brief description of drawings]

FIG. 1 is a plan view of a flow velocity sensor according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG.

3 is a block diagram showing the overall configuration of a measurement system using the flow velocity sensor of FIG.

FIG. 4 is a cross-sectional view showing a manufacturing process of the flow velocity sensor of FIG.

FIG. 5 is a cross-sectional view showing a manufacturing process of the flow velocity sensor of FIG.

FIG. 6 is a cross-sectional view showing a manufacturing process of the flow velocity sensor of FIG.

FIG. 7 is a cross-sectional view showing a manufacturing process of the flow velocity sensor of FIG.

FIG. 8 is a sectional view showing a configuration of a flow velocity sensor according to another embodiment of the present invention.

[Explanation of symbols]

 1, 20 Silicon substrate 2, 24 Heater 426 Temperature sensitive film

Claims (1)

[Claims] 1. A sensor substrate having two facing surfaces, a temperature sensitive film provided on the sensor substrate for detecting a temperature change in a fluid to be detected, and a temperature sensitive film provided on the sensor substrate separately from the temperature sensitive film. And a heater for heating the temperature sensitive film to a predetermined temperature.