JP2000065850A - Thermal type acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal type acceleration sensor having an output terminal capable of monitoring the state of the sensor always other than a normal acceleration output, and capable of informing a system of unexpected sensitivity reduction caused by the change of fluid. SOLUTION: This acceleration sensor is so composed that a heater 22 used as a heat generating source is installed on the central beam among heat- separated three beams 21 and that a first thermocouple 23 is installed on the left beam and the central beam in the state where a cold junction 24 and a hot junction 25 are arranged near the center parts of the left and central beams respectively, and that, in the same way, a second thermocouple 26 is installed on the right beam and the central beam in the state where a cold junction 27 and a hot junction 28 are arranged near the center parts of the right and central beams respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a heat generating means in a closed container and a temperature measuring means for measuring the temperature of a fluid filled in the container, and obtains a detection output corresponding to an applied acceleration. The present invention relates to a high-accuracy and high-accuracy acceleration sensor capable of generating an output signal for judging an abnormality when a change in pressure / gas composition in a closed container causes a change in sensitivity in a thermal acceleration sensor.

[0002]

2. Description of the Related Art As a conventional thermal acceleration sensor, for example, "CONVEC" described in US Pat.
TIVE ACCELEROMETER AND IN
CLINOMETER ",
This is shown in FIG. Although not shown in the drawing, the closed container is filled with a fluid such as a liquid or a gas. Three wires 01, 02, and 03 are stretched near the center. When an electric current is applied to the center wire 01 to generate heat, the temperature of the surrounding fluid rises. When the temperature of the fluid rises, the density decreases, so the fluid moves in the direction opposite to the direction in which acceleration is applied, and when it reaches the wall of the closed vessel, heat is deprived there and this time, the density increases and it is opposite to the previous The fluid moves in the direction. Due to the convection in the closed container, a temperature distribution is generated in the closed container. Since the temperature distribution changes depending on the magnitude and direction of the applied acceleration, the change in the temperature distribution is caused by the other two wires 02 and 03. The acceleration can be detected by capturing the change in the electrical resistance of the object. FIG. 8 shows an example of a circuit for detecting acceleration in a conventional thermal acceleration sensor. FIG.
Are connected in series, and acceleration is detected based on a difference ΔVout between the divided potential and a divided potential of another reference resistor.
Such a sensor using convection due to heat has a feature that it has a strong structure and a high reliability since it has no movable part unlike a general acceleration sensor. Further, since convection is used, the response speed is relatively slow, and unnecessary high-frequency acceleration components are removed without an external electric filter. Therefore, the present invention is suitable as a sensor for measuring the inclination of an automobile.

[0003]

However, the above-described conventional example has the following problems. In the sensor using the temperature distribution due to the convection as described above, it is preferable to use a fluid having a low thermal conductivity as much as possible in order to increase the sensitivity.
In terms of gas, for example, the thermal conductivity of Xe is about 1/5 that of Air.
Therefore, a considerable increase in sensitivity can be expected. The sensitivity also depends on the pressure of the fluid, and the higher the pressure, the higher the sensitivity.
Therefore, in order to obtain high sensitivity, it is necessary to confine a fluid having a low thermal conductivity and a high pressure in an airtight container. In order to confine a fluid in a closed container, welding or bonding of the container is generally used, but especially when a special gas different from air is used at high pressure for high sensitivity, high reliability is required. Sealing is required. However, if the airtightness cannot be maintained for some reason, such as manufacturing variations and system changes, the pressure will drop, and if the special gas inside the sealed container is replaced with outside air even when the pressure is almost the same as the outside, the sensitivity will not be maintained. Will decrease. In the conventional example, as shown in FIG. 8, since the temperature difference between two points is simply measured and the acceleration output is obtained, the sensitivity is simply reduced even when the unexpected airtightness is reduced as described above. It was impossible to detect the abnormality of the sensor itself.

The present invention has been made to solve the above-mentioned problems, and has an output terminal capable of constantly monitoring the state of a sensor in addition to a normal acceleration output. It is an object of the present invention to provide a thermal acceleration sensor capable of notifying a system of a drop in sensitivity.

[0005]

According to a first aspect of the present invention, there is provided a thermal acceleration sensor, comprising: a sealed container; a heat generating means provided in the container; A first temperature measuring means for measuring the temperature, a second temperature measuring means for measuring the temperature at a position at a certain distance from the heat generating means, and a position at a certain distance from the heat generating means, different from the position And third temperature measuring means for measuring the temperature of
In a thermal acceleration sensor for detecting acceleration from a temperature difference between the two portions caused by application of acceleration, a first temperature is calculated by calculating a temperature difference between the first temperature measuring means and the second temperature measuring means. Outputs the difference signal, calculates the temperature difference between the first temperature measuring means and the third temperature measuring means, outputs the second temperature difference signal, and outputs the first temperature difference signal and the second temperature difference signal. The acceleration is detected from the difference between the first temperature difference signal and the second temperature difference signal, and the abnormality of the sensor is detected from the sum of the first temperature difference signal and the second temperature difference signal. In the thermal acceleration sensor according to claim 2 of the present invention, in the invention according to claim 1, instead of detecting the acceleration from the difference between the first temperature difference signal and the second temperature difference signal,
Fourth temperature measuring means for directly measuring the temperature difference between the two parts is provided, and the acceleration is detected from the output of the fourth temperature measuring means. According to a third aspect of the present invention, in the thermal acceleration sensor according to the first or second aspect, any one or all of the first to fourth temperature measuring means is a single thermocouple. Alternatively, the thermopile is a thermopile in which a plurality of thermocouples are connected in series, and a configuration utilizing a temperature difference between a hot junction and a cold junction of the thermocouple or the thermopile.

[0006]

FIG. 1 shows a first embodiment of the present invention. In the conventional example, a structure in which a heating wire or a temperature measuring wire is stretched on a lead of a can package is used. However, in the present embodiment, a method using a semiconductor manufacturing process that is easy to manufacture and can be expected to be manufactured at low cost by mass production will be described. Of course, the structure of the present embodiment can be realized without using a semiconductor manufacturing process.

In this embodiment, three elongated beams 21 made of a material having a low thermal conductivity such as an oxide film are formed on a semiconductor substrate 20. The part other than this beam is the semiconductor substrate 20
Is a space removed by etching, so that fluid such as gas can move freely. However, the entire sensor is connected and fixed at the outermost rim. A heater 2 as a heat source is provided on a central beam among the three beams 21 thermally separated.
2 are provided. A first thermocouple 23 is provided on the left beam and the center beam, and a cold junction 24 and a hot junction 25 are provided near the center of the left and center beams, respectively. The second thermocouple 2 on the beam at the center and the beam at the center
6 is provided in a state where the cold junction 27 and the hot junction 28 are arranged near the center of the right and center beams, respectively. Although a thermocouple is used in the present embodiment, a so-called thermopile in which a plurality of thermocouples are connected in series may be used.

Next, signal processing of the thermal acceleration sensor according to this embodiment will be described with reference to FIG. In the figure, TCL and TCR correspond to the first thermocouple 23 and the second thermocouple 26 shown in FIG. 1, and the electromotive force from these thermocouples is amplified by the amplifiers 30 and 31. Here, the output of the first thermocouple 23 is the temperature difference ΔT1 between the heater 22 and the left temperature measuring unit, and the output of the second thermocouple 26 is the temperature difference ΔT2 between the heater 22 and the right temperature measuring unit. Is shown.
In the subsequent processing circuit, the sum of each output ($ Tout1
= △ T2 + △ T1 = 2 (Th- (TL + TR) / 2)
And the difference between the respective outputs (△ Tout2 = △ T2- △ T
1 = TL-TR). This sum △ Tout1 is E
The RROR signal and the difference ΔTout2 are treated as an acceleration output signal. Here, Th is the temperature of the heater, TL
Is the temperature at the left temperature measuring section, and TR is the temperature at the right temperature measuring section.

Next, the operation of the first embodiment will be described. FIG.
When the acceleration is applied only in the Z-axis direction (corresponding to sensor inclination = 0) and when the acceleration is applied only in the X-axis direction (corresponding to sensor inclination = 90 degrees), the gas The figure shows a total of four types of temperature distribution on the X-axis in the case of cannon (hereinafter, Xe) with air (hereinafter, Air). Note that the XY plane corresponds to the surface of the semiconductor substrate 20, the X axis is a direction perpendicular to the heater 22, the Y axis is a direction parallel to the heater 22, and the Z axis is an XY plane, that is, an axis perpendicular to the semiconductor substrate 20. Show. Since a certain current is applied to the heater 22 to generate heat, the temperature has risen to the temperature indicated by Th in FIG.

First, the case where the gas is Air will be described. Curves 40 and 41 in FIG. 3 correspond to this. When Z = 1G, the temperature distribution on the X axis is ideally bilaterally symmetrical as shown by a curve 41, and the left temperature measurement position L on the beam at a certain distance from the center heater 22 and the right temperature measurement position L The temperature at the temperature position R becomes equal. Next, when the acceleration changes from the Z-axis to the X-axis, the convection distribution of the gas changes, and the temperature distribution becomes asymmetric as shown in FIG. 3 and a temperature difference ΔT _Air occurs. Note that ΔT _Air is a small value as compared with the temperature difference with the heater 22, although it depends on the design. In order to improve the linearity of acceleration output, ΔT _Air is usually set to X = 1G and X =
TL, TR
The difference between the average temperature and the heater temperature keeps a substantially constant value regardless of the acceleration. In FIG. 3, Th− (TL + TR) / 2
This is a value indicated by (＠Air).

Next, the temperature distribution when the gas is Xe will be described. In this case, the temperature distribution is represented by curves 43 and 44. In the case of Z = 1G, the temperature distribution is symmetrical about the heater position as indicated by the curve 44 as in the case of Air, and the temperature difference ΔT _Xe is zero. In the case of X = 1G, it becomes like a curve 43, and a temperature difference ΔT _Xe also occurs. Here, since Xe has a thermal conductivity as small as about 1/5 of Air, the temperature distribution is also A
Unlike the case of ir, even if the same acceleration is applied, △ T _Xe > △ T _Air , so that in the case of Xe, a temperature difference larger than that of Air is generated, and the sensitivity is increased. Also, similarly to the above, usually, ΔT _Xe is designed to have the same value at X = 1G and X = −1G, so that the difference between the average temperature of TL and TR and the heater temperature is almost independent of acceleration. Keep a constant value. In FIG. 3, it is a value represented by Th− (TL + TR) / 2 (＠Xe). Here, when Air is compared with Xe, Xe has a lower thermal conductivity than Air, and therefore Th- (T
L + TR) / 2 (＠Air) <Th− (TL + TR) /
2 (＠Xe) always holds regardless of acceleration.

In the acceleration detection method shown in FIG. 2, a normal acceleration output can be obtained by performing an operation represented by ΔTout2. On the other hand, at the same time, the operation indicated by $ Tout1 is performed and the result is output as an ERROR signal.
As described above, the value of Th− (TL + TR) / 2 depends on the type, pressure, and the like of the gas in the hermetic container without depending on the acceleration. It is possible to detect the composition of the gas in the container and a decrease in sensitivity due to a change in pressure.

Further, since this output can be always output during the operation of detecting the acceleration, for example, another type of acceleration having a movable mass and being detected by displacement / strain of a beam caused by the acceleration acting on the movable mass. Unlike a sensor self-diagnosis device, there is no disadvantage that acceleration cannot be detected during self-diagnosis.

FIG. 4 shows an example of a method of manufacturing the thermal acceleration sensor according to the first embodiment. (A) An insulating film having a low thermal resistance, for example, an oxide film 51 is formed on the surface of the semiconductor substrate 20, and the heater 2
A first thermocouple 23 and a second thermocouple 26 are formed at predetermined positions by patterning a metal thin film or a poly-Si or the like. The thermocouple may be, for example, a combination of AL / poly Si or N-type poly-Si / P-type poly-Si. (B) Then, unnecessary portions of the insulating film are partially etched away. (C) Finally, dry etching, wet etching, and the like are combined to remove a predetermined portion of the semiconductor substrate 20 by etching so as not to hinder convection, thereby forming a heat isolation structure, a heater 22, and a temperature measuring means. .

FIG. 5 illustrates a second embodiment. The basic structure is the same as that of the first embodiment, but a third thermocouple 60 is newly formed in order to directly detect the temperature difference between the left and right temperature measuring units, not to calculate. The third thermocouple 60 has a hot junction 61 on the left and a cold junction 62 on the right, and the temperature difference between the two contacts is directly output as an electromotive force of the third thermocouple 60.

FIG. 6 shows an acceleration detection method for performing acceleration and abnormality detection output when the present embodiment is used.
The schematic operation is the same as that of the first embodiment, and therefore will not be described.
In the first embodiment, the temperature difference between the left and right temperature measuring units is calculated by calculation, whereas in the present embodiment, the electromotive force of the third thermocouple 60 becomes the acceleration output signal as it is, Acceleration detection accuracy is improved as compared with 1. Of course, similarly to the first embodiment, the first thermocouple 23 and the second thermocouple 2
6 may be used as the acceleration output, but if a slight temperature difference occurs between the contacts in the center beam, an output error occurs. Particularly, a small temperature difference must be detected depending on the design. For example, when it is desired to reduce the size of the sensor. The temperature distribution due to the convection largely depends on the size of the closed vessel. Generally, when the size is reduced, the difference in the temperature distribution disappears, and the temperature difference between the two temperature measuring units has to be reduced. In this case, relatively, the heater 2
2, the temperature difference between the left and right temperature measuring units and the temperature difference between the left and right temperature measuring units become large. Left and right same first thermocouple 23, second thermocouple
In the thermocouple 26, the temperature difference between the two contacts disposed close to the central heater 22 is ideally zero, but it may actually be slightly different due to manufacturing variations.
This appears as an output error. Even in such a case, in the present embodiment, the third thermocouple 60 is disposed, and the temperature difference between the left and right temperature measuring units is directly detected by the third thermocouple 60 to obtain the acceleration output. can get.

The following is a description of a simple equation. Left temperature measuring part temperature: To-ΔT, Right temperature measuring part temperature: To + ΔT (To> ΔT) Temperature of left and right temperature measuring parts when acceleration Z = 1G Temperature measuring part near center left heater: Th Assuming that the temperature measuring part near the center right heater is Th + △ Th (Th> △ Th), the temperature difference ΔT1 of the left first thermocouple 23 is ΔT1 = Th− (To−ΔT) Equation 1 Right second thermoelectric The temperature difference ΔT2 of the pair 26 is ΔT2 = Th + ΔTh− (To + ΔT) Expression 2. Therefore, their sum and difference are respectively: Sum: Expression 1 + Expression 22 2Th−2To + ΔTh Expression 3 : Equation 1-Equation 2-{Th + 2} T ... Equation 4 Here, if △ Th ~ △ T <To, Th,
Equation 3 becomes 2 (Th−To) Equation 5. Therefore, an error in the heater temperature measurement unit does not significantly affect the ERROR output. On the other hand, as can be seen from Expression 4, a large error occurs in the acceleration output.

[0018]

As described above, in the thermal acceleration sensor according to the present invention, not only the temperature difference between two points apart from the heater is output as an acceleration output, but also the temperature difference between the heater temperature and each of the two points at the same time. Since the average temperature difference is always output, for example, due to an unexpected failure of the hermetically sealed container, the gas composition in the hermetic seal changes, the pressure changes, and even if the sensitivity is reduced. , And ERROR output, the system can detect sensor abnormalities, so that a highly reliable system can be constructed.

[Brief description of the drawings]

FIG. 1A is a perspective view showing a thermal acceleration sensor according to Embodiment 1 of the present invention, and FIG. 1B is a plan view.

FIG. 2 is a diagram showing an acceleration detection method of the thermal acceleration sensor according to the first embodiment.

FIG. 3 is a diagram showing a difference in temperature distribution between Air and Xe.

FIG. 4 is a diagram illustrating a method of manufacturing the thermal acceleration sensor according to the first embodiment.

FIG. 5 is a diagram showing a second embodiment of the present invention.

FIG. 6 is a diagram showing an acceleration detection method according to a second embodiment.

7A is a plan view showing a conventional thermal acceleration sensor, FIG. 7B is a side view, and FIG. 7C is a front view.

FIG. 8 is a diagram illustrating an acceleration detection method of a conventional thermal acceleration sensor.

[Explanation of symbols]

 Reference Signs List 20 semiconductor substrate 21 beam 22 heater 23 first thermocouple 24 cold junction 25 hot junction 26 second thermocouple 27 cold junction 28 hot junction 30 amplifier 31 amplifier 40 curve 41 curve 43 curve 44 curve 51 oxide film 60 third thermocouple 61 Hot junction 62 Cold junction

Claims (3)

[Claims] 1. A closed container, a heat generating means provided in the container, a first temperature measuring means for measuring a temperature of the heat generating means, and a temperature at a position separated by a certain distance from the heat generating means. A second temperature measuring means for measuring, and a third temperature measuring means for measuring a temperature at a position different from the position, separated from the heat generating means by a certain distance, and In a thermal acceleration sensor that detects acceleration from a temperature difference between both parts, while calculating a temperature difference between the first temperature measuring means and the second temperature measuring means and outputting a first temperature difference signal, Calculate the temperature difference between the first temperature measurement means and the third temperature measurement means, output the second temperature difference signal, and detect the acceleration from the difference between the first temperature difference signal and the second temperature difference signal Then, the abnormality of the sensor is detected from the sum of the first temperature difference signal and the second temperature difference signal. A thermal acceleration sensor, characterized in that: 2. The method according to claim 1, wherein the acceleration is detected by a fourth temperature measuring means for directly measuring the temperature difference between the two parts, instead of detecting the difference from the first temperature difference signal and the second temperature difference signal. Provided,
2. The thermal acceleration sensor according to claim 1, wherein an acceleration is detected from an output of the fourth temperature measuring means. 3. A thermocouple in which one or all of the first to fourth temperature measuring means is a single thermocouple or a plurality of thermocouples connected in series, and a hot junction of the thermocouple or the thermopile. 3. The method as claimed in claim 1, wherein the temperature difference between the cold junction and the cold junction is utilized.
4. A thermal acceleration sensor according to claim 1.