JP5056086B2 - Thermal sensor - Google Patents

Description

  The present invention relates to a thermal sensor. Specifically, the present invention relates to a thermal sensor including a conductor junction heater (group) in which conductors such as metals and semiconductors having different resistivity are joined.

  FIG. 1 is a plan view showing a structure of a conventional uniaxial detection type thermal acceleration sensor 11 (thermal inclination sensor) for measuring an inclination angle. In this thermal acceleration sensor 11, an insulating film 14 is stretched on the surface of a Si substrate 12 having a cavity 13 formed on the upper surface, and a heater 15 is placed on the insulating film 14 so as to cross the cavity 13. Wiring is provided, and electrode pads 16 are provided at both ends of the heater 15. Further, temperature sensors 17 are symmetrically arranged on both sides of the heater 15. The temperature sensor 17 is a thermopile, for example, and has electrode pads 18 at both ends.

  2 and 3 are diagrams for explaining the principle of measuring the tilt angle by the thermal acceleration sensor 11. In the thermal acceleration sensor 11, a constant current is supplied from the electrode pad 16 to the heater 15, whereby the heater 15 generates a certain amount of heat, and the heat generated in the heater 15 spreads upward by natural convection. Therefore, a predetermined temperature distribution is generated around the heater 15.

  FIG. 2 shows a state where the thermal acceleration sensor 11 maintains a horizontal posture. In this state, the temperature distribution is equal on both sides of the plane K perpendicular to the insulating film 14 through the center of the heater, and the temperature sensor 17 is also arranged symmetrically with respect to the vertical plane K. Therefore, when the thermal acceleration sensor 11 is maintained in the horizontal posture, the detected temperatures of both the temperature sensors 17 are equal.

  On the other hand, when the thermal acceleration sensor 11 is tilted in the direction of the arrow in FIG. 1, the temperature distribution is not tilted as shown in FIG. The detected temperature of 17 is different. For example, when it is inclined as shown in FIG. 3, the temperature detected by the right temperature sensor 17 is higher than the temperature detected by the left temperature sensor 17. The inclination angle of the thermal acceleration sensor 11 can be calculated from the temperature difference between the temperatures detected by the two temperature sensors 17.

  Here, the output of the thermal acceleration sensor 11 is proportional to the strength of natural convection inside the sensor package, and the Grashof number Gr representing the strength of natural convection is proportional to the temperature difference ΔT between the heater temperature and the ambient temperature. . Therefore, in order to improve the output of the thermal acceleration sensor 11, the heat generation of the heater is increased in the region between the temperature sensors 17, and the heater heat generation is decreased in a region away from the temperature sensor 17, thereby increasing the heater temperature. It is desired to increase the temperature difference ΔT from the ambient temperature.

  As one method for that purpose, as shown in FIG. 4, the portion of the heater 15 where heat is to be generated is reduced in line width to the high resistance portion 15a, and the portion where heating is not desired is increased in width to reduce the resistance. It is conceivable that the temperature distribution due to heat generation is controlled by the line width ratio of the heater 15. For example, if the width of the high resistance portion 15a is 1/3 of the width of the low resistance portion 15b, the resistance value per unit length of the high resistance portion 15a is three times that of the low resistance portion 15b. Will also triple.

  However, in the method of changing the line width ratio, if the ratio of the heat generation amount of the high resistance portion 15a and the low resistance portion 15b is to be considerably increased, the line width of the high resistance portion 15a becomes very narrow, and the high resistance portion 15a Patterning becomes difficult and there is a risk of disconnection in the high resistance portion 15a. On the other hand, the line width of the low resistance portion 15b becomes very wide, and it is difficult to wire in the limited space of the small thermal acceleration sensor 11, which makes designing difficult.

  Further, as the biaxial detection type thermal acceleration sensor, there are those disclosed in Patent Document 1 and Patent Document 2. However, in the heater as disclosed herein, the heater is composed of the same material in any part, and heat is generated even in a portion other than the center where it is not desired to generate heat. Other axis sensitivity was likely to occur in the acceleration sensor.

JP 2005-326321 A JP 09-210684 A

  The present invention has been made in view of the technical problems as described above, and an object of the present invention is to provide a thermal sensor that is free from problems such as disconnection and difficulty in patterning and that has high sensitivity and accuracy. There is.

Thermal sensor according to the present invention, the thin portion is formed on the substrate, wherein the heating structure on the thin portion and the temperature sensing element is formed, heat of the electrically connected electrodes on the heating structure in formula sensor, the heating structure comprises a low resistance portion comprising a connecting conductors to the electrodes, and a high resistance portion consisting of the higher resistivity than the low resistance section conductor, the high and the low resistance portion A resistance part is connected in series, and both the heating structure and the temperature measuring element have a four-fold rotationally symmetric planar shape around an axis perpendicular to the thin part, and the heating resistance The junction part of the said low resistance part and said high resistance part in a body is arrange | positioned around the said axis | shaft 4 times rotationally symmetrically, It is characterized by the above-mentioned. Here, the conductor may be a metal or a semiconductor. For example, aluminum (Al) or the like can be used as the low resistivity conductor, and tungsten (W), polysilicon (PolySi), or the like can be used as the high resistivity conductor.

  In the thermal sensor of the present invention, since the low resistance portion and the high resistance portion having different resistivity are connected in series, a large amount of heat generation can be obtained in a portion with a high resistivity. The resistivity of the conductor can be changed depending on the choice of the conductor material, the type of impurity, the amount of impurities, etc., and the resistivity varies over a very wide range depending on the material. Even if the amount is increased, it is not necessary to reduce the line width of the conductor, and the degree of freedom in design is increased. Therefore, a heater having a large amount of heat generation can be easily manufactured, and the risk of disconnection is reduced.

In the thermal sensor according to the present invention, each of the heat generating structure and the temperature measuring element has a plane shape that is rotationally symmetrical four times around an axis perpendicular to the thin portion, and the bonding portion of the in the body and the low-resistance portion and the high resistance portion is disposed in rotational symmetry four times around the shaft, the other shaft it is possible to have sensitivity in two axial directions to the thermal sensor Sensitivity can be reduced. In addition, in the joint portion between the low resistance portion and the high resistance portion, heat is generated or absorbed due to the Peltier effect. However, in this embodiment, the joint portion between the low resistance portion and the high resistance portion is rotationally symmetric four times. Since it is arranged, the offset of the thermal sensor can be reduced by canceling the Peltier effect.

Certain embodiments of the thermal sensor according to the present invention, the low-resistance portion and said high-resistance portion of the bonded joined portion, and the joining portion and the joining portion of the heat absorbing side of the heat generating side is brought close to one another located It is characterized by that. In the joint portion between the low resistance portion and the high resistance portion, due to the Peltier effect, the temperature rises due to heat generation or the temperature falls due to heat absorption, but in this embodiment, the joint portion between the heat generation side and the heat absorption side Since the joining portions are arranged close to each other, the temperature change can be alleviated between the heating-side joining portion and the rapid heating-side joining portion, and unevenness in temperature distribution due to the Peltier effect can be reduced.

Another embodiment of the thermal sensor according to the present invention is characterized in that the exothermic side joining portion and the endothermic side joining portion, which are arranged close to each other, are covered together with a continuous metal film. According to this embodiment, since heat can be efficiently exchanged between the heat generating side bonded portion and the heat absorbing side bonded portion via the metal film, unevenness in temperature distribution due to the Peltier effect can be further reduced.

  In addition, the component demonstrated above of this invention can be combined arbitrarily as much as possible.

  Hereinafter, the thermal sensor of the present invention will be described in detail with reference to the drawings, with the thermal acceleration sensor as each example.

FIG. 5 is a plan view showing the structure of a uniaxial detection type thermal acceleration sensor 21 according to an embodiment of the present invention, and FIG. 6 is a cross-sectional view of the cross section along the conductor junction heater 26. The thermal acceleration sensor 21 is formed on the upper surface of a substrate 22 made of a semiconductor such as a Si substrate, and a cavity 23 is recessed in the upper surface of the substrate 22 by etching. An insulating film 24 (thin wall portion) made of SiO ₂ , SiN or the like is formed on the upper surface of the substrate 22 so as to cover the cavity 23. Accordingly, in the insulating film 24, the peripheral region in contact with the upper surface of the substrate 22 is a region where the specific heat is large and the temperature hardly changes, and the region extending in the air above the cavity 23 has a specific heat. The region is small and easily changes in temperature due to heat.

  A conductor bonding heater 26 is wired on the upper surface of the insulating film 24 so as to cross the center above the cavity 23, and metal electrode pads 25 are provided at both ends of the conductor bonding heater 26. As shown in FIG. 6, the conductor junction heater 26 includes two low-resistance wires 26a made of a low-resistivity metal such as Al, and a high-resistance wire 26b made of a high-resistance metal or semiconductor such as W or polysilicon. The low resistance wiring 26a and the high resistance wiring 26b have substantially the same line width and cross-sectional area. The low resistance wiring 26 a is formed in a region where the insulating film 24 is in contact with the upper surface of the substrate 22, and the high resistance wiring 26 b is formed in a region where the insulating film 24 is located above the cavity 23. .

  The low resistance wiring 26a and the high resistance wiring 26b are joined to each other in the lengthwise direction. At the junction between the low resistance wiring 26a and the high resistance wiring 26b, an insulating layer 29 is formed on the surface of one wiring 26a or 26b, and the low resistance wiring 26a and the high resistance wiring are passed through the contact hole 30 opened in the insulating layer 29. 26b is joined. Note that the low resistance wiring 26 a and the high resistance wiring 26 b may be directly joined without providing the insulating layer 29.

  On the upper surface of the insulating film 24, two temperature sensors 28 are arranged symmetrically with respect to the conductor bonding heater 26 on both sides of the conductor bonding heater 26, and electrode pads 27 are provided on both ends of the temperature sensor 28. Yes. The temperature sensor 28 is composed of a thermopile (thermocouple) in which Al and polysilicon wires are alternately connected. Both temperature sensors 28 are arranged on the insulating film 24 so as to straddle the region above the cavity 23 and the region outside the cavity 23. The cold junction 28a (constant temperature point) of the temperature sensor 28 is located at the end far from the conductor bonding heater 26, and is disposed on the insulating film 24 above the substrate 22 having a large specific heat. The temperature is difficult to change due to the heat of 26, and is kept at a constant reference temperature (room temperature). Further, the hot junction 28b (temperature measuring point) of the temperature sensor 28 is located at the end close to the conductor bonding heater 26, and is located on the insulating film 24 above the cavity 23 having a small specific heat. The temperature changes sensitively by the heat of the conductor junction heater 26. That is, the temperature sensor 28 with good sensitivity is formed.

  A current having a constant current value flows through the conductor bonding heater 26 by a power source (not shown) connected to the electrode pad 25, thereby generating heat. When the thermal acceleration sensor 21 is in a horizontal state, there is a temperature distribution (temperature gradient) between the temperature sensors 28 on both sides of the surface perpendicular to the thermal acceleration sensor 21 standing along the conductor junction heater 26. It is symmetrical. The temperature sensor 28 measures the temperature of a fixed point (the hot junction 28b) in the vicinity of the conductor junction heater 26 with the temperature of the cold junction 28a as a reference, and thereby the thermal acceleration sensor 21 or the thermal acceleration sensor 21 is attached. The tilt angle of the measured object is dynamically detected. The principle that the thermal acceleration sensor 21 detects the tilt angle has been described in the conventional example, and is omitted here.

  Moreover, in the conductor junction heater 26 of Example 1, the amount of heat generated per unit length is small in the low resistance wiring 26a located on the insulating film 24 in contact with the upper surface of the substrate 22, It is difficult to warm the substrate 22 by the heat of the conductor joining heater 26, and it is difficult to affect the temperature (reference temperature) of the cold junction 28 a of the temperature sensor 28. Further, the high resistance wiring 26b located between the hot contacts 28b of the temperature sensor 28 generates a large amount of heat per unit length, causing a steep temperature distribution around it. Therefore, in the conductor bonding heater 26 of the first embodiment, heat can be generated with a large heat generation amount in a necessary portion, and the heat generation amount can be suppressed in an unnecessary portion, thereby improving the heat generation efficiency and measuring the inclination angle. Sensitivity can be increased.

  Further, in this conductor-bonded heater 26, the heat generation amount is changed by connecting conductors having different resistivities. Therefore, some lines are changed as in the conventional example in which the heat generation amount is changed by changing the line width of the heater. The width does not become very narrow or wide, there is no fear that the conductor joining heater 26 is disconnected, and the pattern design of the conductor joining heater 26 can be easily performed.

  Next, a configuration of a two-axis detection type acceleration sensor using the conductor junction heater 26 similar to that of the first embodiment will be described.

(Comparative example)
Before describing the thermal acceleration sensor of the second embodiment, a comparative example will be described first. FIG. 7 is a plan view showing a thermal acceleration sensor of a comparative example. In the thermal acceleration sensor 31, four temperature sensors 28 and a conductor bonding heater 26 are provided on the upper surface of the insulating film 24. The high-resistance wiring 26 b of the conductor bonding heater 26 is formed in a square frame shape with a uniform thickness, and is disposed in the central portion above the cavity 23. The four temperature sensors 28 are arranged so as to straddle the region above the cavity 23 and the region outside the cavity 23 and to face each side of the high resistance wiring 26b. The two low-resistance wirings 26a are connected to the high-resistance wiring 26b in a straight line, and one end of the low-resistance wiring 26a is joined to two corners of the high-resistance wiring 26b. . The low resistance wiring 26 a is led in a diagonal direction, and electrode pads 25 a and 25 b are provided at the other end in a region outside the cavity 23.

  When the thermal acceleration sensor 31 is energized to the conductor junction heater 26, the same amount of current flows through the high resistance wiring 26 b divided into two paths at the junction with the low resistance wiring 26 a to generate heat. Therefore, an equal current flows through the opposing sides of the rectangular frame-shaped high-resistance wiring 26b. Therefore, by comparing the detected temperatures of the opposing temperature sensors 28, the two axes in the x and y directions shown in FIG. The tilt angle can be measured with. At this time, in the thermal acceleration sensor 31, as in the first embodiment, the high resistance wiring 26b of the conductor bonding heater 26 can generate heat with a large heat generation amount, and the low resistance wiring 26a can suppress the heat generation amount. The efficiency can be improved and the measurement sensitivity of the tilt angle can be increased.

  However, in the thermal acceleration sensor 31 of the comparative example, due to the Peltier effect described below, the amount of heat generated between opposite sides of the square frame-shaped high resistance wiring 26b is not equal, and the initial offset amount becomes large. I found out that

  Heat generation and heat absorption due to the Peltier effect will be described by taking as an example a case where the low resistance wiring is Al and the high resistance wiring is N-type polysilicon. As shown in FIG. 10 (a), when a current flows through the conductor bonding heater 26 from the V + side to the V− side, the moving direction of electrons is opposite to the current as shown in FIG. 10 (b). become. Since the energy level of electrons in the high resistance wiring 26b is higher than the energy level of electrons in the low resistance wiring 26a, the electrons moving from the low resistance wiring 26a to the high resistance wiring 26b absorb heat from the surroundings and are insufficient. Get kinetic energy. Then, the electrons passing through the high resistance wiring 26b and moving from the high resistance wiring 26b to the low resistance wiring 26a radiate excess kinetic energy to the surroundings. Therefore, when a current is passed through the conductor bonding heater 26, one (heat-absorbing bonding portion C) absorbs heat and the other (heat-generating bonding portion H) generates heat at the bonding portion between the low-resistance wiring 26a and the high-resistance wiring 26b. (Peltier effect). The amount of heat generation and the amount of heat absorption are both represented by the product of the intrinsic constant (Peltier coefficient) determined by the material of the low resistance wiring 26 a and the high resistance wiring 26 b and the current flowing through the conductor junction heater 26. If such heat generation or heat absorption exists, the temperature distribution around the heater becomes non-uniform, and the initial offset and other axis sensitivity of the thermal acceleration sensor may increase.

  In the thermal acceleration sensor 31 of the comparative example, when the electrode pad 25a is on the V + side and 25b is on the V− side, the upper left corner of the square frame-shaped high resistance wiring 26b is the heat generating joint portion H and the lower right corner is the endothermic joint portion C. The upper side and the left side of the opposing sides in FIG. 7 had higher temperatures than the lower side and the right side.

(Example 2)
FIG. 8 is a plan view showing a structure of a two-axis detection type thermal acceleration sensor 41 according to the second embodiment of the present invention. In the thermal acceleration sensor 41, a conductor bonding heater group including four conductor bonding heaters 26 is disposed on the upper surface of the insulating film 24.

  Each conductor bonding heater 26 is obtained by bonding a low resistance wiring 26a to both ends of a high resistance wiring 26b, and four conductor bonding heaters 26 are connected in series. Each low-resistance wiring 26a is formed of a material having a low resistivity such as Al, and each high-resistance wiring 26b is formed of a material having a high resistivity such as polysilicon or W. The low-resistance wiring 26a and the high-resistance wiring 26b has substantially the same line width and cross-sectional area.

  The high resistance wiring 26 b of each conductor junction heater 26 is arranged point-symmetrically (four-fold rotational symmetry) with the center of the region above the cavity 23 as the center. Each low-resistance wiring 26a connected to the high-resistance wiring 26b is wired diagonally toward the region outside the cavity 23, and these are also arranged substantially point-symmetrically (four-fold rotational symmetry). Moreover, the electrode pad 25 is provided in the low resistance wiring 26a of both ends.

  It can be said that the conductor junction heater group is one conductor junction heater 26 in which five low resistance wires 26a and four high resistance wires 26b are alternately connected.

  The four temperature sensors 28 are arranged on the upper surface of the insulating film 24 so as to straddle the region above the cavity 23 and the region outside the cavity 23 and to face the high resistance wiring 26b. The hot junction 28 b of the temperature sensor 28 faces the high resistance wiring 26 b above the cavity 23, and the cold junction 28 a is located above the upper surface of the substrate 22 outside the cavity 23.

  In the thermal acceleration sensor 41, when a current is passed through the conductor junction heater group, heat is generated mainly in the portion of the high resistance wiring 26b having a large resistance value. That is, a large calorific value can be obtained at the central portion of the region located above the cavity 23, and the calorific value at the peripheral portion can be reduced, so that the measurement accuracy of the inclination angle by the thermal acceleration sensor 41 is improved. be able to.

  Further, each high resistance wiring 26b is symmetric about the central axis, and is formed of the same material so as to have the same line width, the same cross-sectional area, and the same length. When the sensor 41 is in a horizontal state, heat can be generated with the same temperature distribution in the biaxial directions around the central axis, and the measurement accuracy of the thermal acceleration sensor 41 can be further improved. In addition, since a temperature distribution that is rotationally symmetrical four times around the central axis can be obtained, the sensitivity of the other axis of the thermal acceleration sensor 41 can be reduced, and the measurement accuracy of the thermal acceleration sensor 41 can be further improved.

  In contrast to the comparative example, in the thermal acceleration sensor 41 of the second embodiment, as shown in FIG. 9, the heat-generating bonding portion H and the heat-absorbing bonding portion C of the adjacent conductor bonding heaters 26 are arranged close to each other. Furthermore, as shown in FIG. 11, an insulating coating 43 is formed on the surfaces of the adjacent exothermic joining portion H and endothermic joining portion C, and then covered with a metal thermal coupling portion 42. Accordingly, the heat generated in the heat generating joint portion H is conducted through the heat coupling portion 42 and quickly moves to the heat absorbing joint portion C, and is absorbed by the heat absorbing joint portion C. By exchanging heat between the exothermic joining portion H and the endothermic joining portion C in this way, the temperature distribution in the exothermic joining portion H and the endothermic joining portion C can be leveled and the change in temperature distribution around the central axis can be reduced. Therefore, the heat generation and the heat absorption due to the Peltier effect can be made uniform to approximate an ideal temperature distribution, and the offset of the thermal acceleration sensor 41 in two directions can be made substantially zero.

  A prototype of the thermal acceleration sensor 31 of the comparative example and a prototype of the thermal acceleration sensor 41 of Example 2 were manufactured, and both were compared and evaluated. As a result, in the thermal acceleration sensor 31 of the comparative example, the initial offset amount was about 9 mV, whereas in the thermal acceleration sensor 41 of the second embodiment, the initial offset amount was only about 30 μV, and the initial offset amount was It became about 1/300. Further, in the thermal acceleration sensor 31 of the comparative example, the other axis sensitivity is about 9% FS, whereas in the thermal acceleration sensor 41 of the second embodiment, the other axis sensitivity is only about 3% FS, and the other axis The sensitivity was about 1/3. Therefore, according to the second embodiment, it is estimated that the accuracy of the thermal acceleration sensor can be further improved, and the temperature distribution around the central axis of the conductor bonding heater 26 is more accurately point-symmetric. The

  In the second embodiment, four conductor bonding heaters 26 are connected in series to form a conductor bonding heater group. However, as shown in FIG. 12, four conductor bonding heaters 26 are arranged in parallel to form a conductor bonding heater group. May be configured so that a current flows separately to each of the conductor junction heaters 26.

  The conductor junction heater (group) of the present invention can be used not only for the thermal acceleration sensor 3 for measuring the inclination angle as described above, but also for a flow sensor, a gas sensor, and other thermal sensors having a heater function.

FIG. 1 is a plan view showing the structure of a conventional uniaxial detection type thermal acceleration sensor (thermal inclination sensor). FIG. 2 is a diagram for explaining the principle of measuring the tilt angle using a thermal acceleration sensor, and represents a thermal acceleration sensor in a horizontal state. FIG. 3 is a diagram for explaining the principle of measuring the tilt angle by the thermal acceleration sensor, and represents the thermal acceleration sensor in a tilted state. It is a figure explaining the method for changing the magnitude | size of the emitted-heat amount in a heater. FIG. 5 is a plan view showing the structure of a uniaxial detection type thermal acceleration sensor according to an embodiment of the present invention. FIG. 6 is a cross-sectional view of the above thermal acceleration sensor. FIG. 7 is a plan view showing a structure of a biaxial detection type thermal acceleration sensor according to a comparative example. FIG. 8 is a plan view showing the structure of a two-axis detection type thermal acceleration sensor according to the second embodiment of the present invention. FIG. 9 is a plan view showing a heater portion of the thermal acceleration sensor. FIG. 10 (a) is a schematic diagram showing the direction of current and the heat generating and heat absorbing bonded portions in the conductor bonding heater, and FIG. 10 (b) shows the electron energy level and the electron moving direction along the conductor bonding heater. It is an energy level diagram. FIG. 11 is a cross-sectional view showing a heat-generating bonded portion and a heat-absorbing bonded portion of a conductor bonded heater covered with a thermal coupling portion. FIG. 12 is a plan view showing a conductor bonding heater group in which four conductor bonding heaters are arranged in parallel.

Explanation of symbols

21 Thermal Acceleration Sensor 22 Substrate 23 Cavity 24 Insulating Film 26 Conductor Bonding Heater 26a Low Resistance Wiring 26b High Resistance Wiring 28 Temperature Sensor 28a Cold Junction 28b Hot Junction 41 Thermal Acceleration Sensor 42 Thermal Coupling Unit 43 Insulating Coating C Endothermic Junction H Exothermic joint

Claims (3)

In the thermal sensor, a thin portion is formed on the substrate, a heating structure and a temperature measuring body are formed on the thin portion, and the electrode is electrically connected to the heating structure.
The heat generating structure includes a low resistance portion made of a conductor connected to the electrode, and a high resistance portion made of a conductor having a higher resistivity than the low resistance portion, and the low resistance portion and the high resistance portion are Connected in series,
Each of the heat generating structure and the temperature sensing element has a plane shape that is rotationally symmetrical four times around an axis perpendicular to the thin portion,
Thermal sensor you characterized in that the joining portion between the low-resistance portion and the high resistance portion of the heating resistor is arranged in rotational symmetry four times around the shaft. The low-resistance portion and said high-resistance portion of the bonded joined portion, characterized in that the junction portion and a joining portion of the heat absorbing side of the heat generating side arranged close to each other, according to claim 1 Thermal sensor. The thermal sensor according to claim 2 , wherein the heat-generating-side joining portion and the heat-absorbing-side joining portion arranged close to each other are covered with a continuous metal film.

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