JP4492416B2 - Physical quantity sensor - Google Patents

Description

  The present invention relates to a physical quantity sensor that detects a physical quantity to be detected as a change in resistance value due to strain of a gauge resistance.

  Conventionally, as this kind of physical quantity sensor, a semiconductor pressure sensor, a semiconductor acceleration sensor, and the like using a piezoresistor whose resistance value changes when an external force is applied to a semiconductor crystal as a gauge resistance have been provided.

  On the other hand, in recent years, physical quantity sensors using carbon nanotubes that have attracted attention in the field of nanotechnology as gauge resistance have been proposed (see, for example, Patent Documents 1 and 2).

  Here, the pressure sensor using carbon nanotubes as the gauge resistance has, for example, the configuration shown in FIG.

  The pressure sensor having the configuration shown in FIG. 9 is formed by processing a silicon substrate by a micromachining technique and has a sensor structure 1 having an insulating film 2 made of a silicon oxide film on one surface side, and insulation of the sensor structure 1. Two gauge resistors R1 and R3 and two reference resistors R2 and R4, each of which is arranged on the film 2 and made of one carbon nanotube, and a glass base 9 fixed to the other surface of the sensor structure 1 And.

  The sensor structure 1 includes a rectangular frame-shaped frame portion 1a and a thin diaphragm portion 1b continuously and integrally connected to the frame portion 1a inside the frame portion 1a. That is, the sensor structure 1 is formed with a diaphragm portion 1b that is positioned inside the frame portion 1a and supported by the frame portion 1a over the entire circumference. When pressure is applied from the thickness direction of the diaphragm portion 1b, the diaphragm 1b is formed. The part is bent and deformed. Here, the gauge resistors R1 and R3 are disposed so as to straddle the diaphragm portion 1b and the frame portion 1a, and the reference resistors R2 and R4 are disposed on the frame portion 1a. The sensor structure 1 is formed by providing a recess 1c on the other surface of the silicon substrate by anisotropic etching using an alkaline solution. On the other hand, the base 9 is provided with an introduction hole 9a for introducing a fluid into the recess 1c of the sensor structure 1 in the thickness direction.

  Further, the two gauge resistors R1 and R3 and the two reference resistors R2 and R4 described above are illustrated by a plurality of metal wirings 4 formed on the insulating film 2 on the one surface side of the sensor structure 1. 10 are connected to form a bridge circuit shown in FIG.

  Therefore, if a suitable power supply E for detection is connected between one terminal at the diagonal position of the bridge circuit, the voltage between the other terminals Vo1 and Vo2 at the other diagonal position is detected, and an appropriate correction is applied, the diaphragm portion A voltage proportional to the pressure acting on 1b can be obtained. In the pressure sensor described above, a part of each of the four metal wirings 4 constitutes a pad as a terminal.

  By the way, a catalytic metal material (for example, iron, nickel, cobalt) for growing carbon nanotubes is formed between the resistors R1 to R4 and the metal wirings 4 electrically connected to the resistors R1 to R4. And the like, and a voltage is applied between the pair of electrodes 5 and 5 and a source gas containing carbon is supplied to the one surface side of the sensor structure 1 to form a pair. Carbon nanotubes are grown between 5 and 5. Therefore, each carbon nanotube constituting each of the resistors R1 to R4 is interposed between the pair of electrodes 5 and 5.

  Next, an example of an acceleration sensor using carbon nanotubes as a gauge resistance will be described with reference to FIG.

  The acceleration sensor having the configuration shown in FIG. 11 is formed by micromachining a silicon substrate and has a sensor structure 11 having an insulating film 12 made of a silicon oxide film on one surface side, and an insulating film 12 of the sensor structure 11. Two gauge resistors R11, R12 and two reference resistors R13, R14 each formed of one carbon nanotube, and a glass cover 19 fixed to the other surface of the sensor structure 11, A glass cover (not shown) fixed to one surface side of the sensor structure 11 is provided.

  The sensor structure 11 includes a frame portion 11a having a rectangular frame shape, and one side around a weight portion 11b arranged away from the frame portion 11a inside the frame portion 11a is thinner than the frame portion 11a. It has a structure that is continuously and integrally connected to the frame portion 11a via two flexure portions 11c. That is, in the sensor structure 11, a weight portion 11b that is located inside the frame portion 11a and is sensitive to acceleration is supported by the frame portion 11a via two bending portions 11c, and the weight portion 11b is bent around the weight portion 11b. A slit 11d is formed between the frame portion 11a except for the portion 11c. Moreover, the bending part 11c is spaced apart in the direction along one side of the weight part 11b, and is formed in two places.

  The weight portion 11b is formed, for example, by anisotropically etching a portion corresponding to the slit 11d in the silicon substrate from the other surface side using an alkaline solution, and then setting the portion corresponding to the slit 11d to one surface of the silicon substrate. It is formed by etching from the side. Further, a recess 19b for securing a swinging space of the weight portion 11b is formed on the surface of the cover 19 on the other surface side of the sensor structure 11 facing the sensor structure 11. Similarly, a recess for securing a swinging space of the weight portion 11b is also formed on the surface of the cover on the one surface side of the sensor structure 11 that faces the sensor structure 11.

  The two gauge resistors R11 and R12 and the two reference resistors R13 and R14 described above form a bridge circuit by the metal wiring 14 formed on the insulating film 12 on the one surface side of the sensor structure 11. They are connected so as to be configured (note that an interlayer insulating film (not shown) is interposed between the metal wirings 14 and 14 that overlap in the thickness direction of the sensor structure 11).

  In the acceleration sensor described above, when an external force (acceleration) including a component in the thickness direction of the sensor structure 11 acts on the weight part 11b, the weight part 11b acts on the frame part 11a due to the inertia of the weight part 11b. 11 is relatively displaced in the thickness direction, and as a result, the bent portion 11c is bent, the gauge resistors R11 and R12 are deformed, and the resistance values of the gauge resistors R11 and R12 are changed. In contrast, the resistance values of the reference resistors R13 and R14 arranged so as to overlap the frame portion 11a do not change even when the weight portion 11b is displaced.

  Therefore, by detecting a change in the resistance values of the gauge resistors R11 and R12, it is possible to detect the acceleration acting on the sensor structure 11. In other words, if an appropriate power source for detection is connected between one terminal at the diagonal position of the bridge circuit, a voltage between the other terminal at the diagonal position is detected, and appropriate correction is applied, the weight 11b is acted on. A voltage proportional to the acceleration to be obtained can be obtained.

The gauge resistors R11 and R12 are arranged with the extending direction of the bent portion 11c as the longitudinal direction, and are deformed in the same manner as the bent portion 11c. Here, a catalytic metal material (for example, iron, nickel, etc.) for growing carbon nanotubes is formed between the resistors R11 to R14 and the metal wires 14 electrically connected to the resistors R11 to R14. An electrode 15 made of cobalt or the like is interposed, a voltage is applied between the pair of electrodes 15 and 15, and a source gas containing carbon is supplied to the one surface side of the sensor structure 11 to form a pair. Carbon nanotubes are grown between the electrodes 15 and 15. Therefore, each carbon nanotube constituting each of the resistors R11 to R14 is interposed between the pair of electrodes 15 and 15.
JP 2004-53424 A JP 2004-163373 A

  By the way, in the physical quantity sensor using the carbon nanotube as the gauge resistance as described above, high sensitivity is expected by improving the gauge ratio of the gauge resistance.

  However, regarding the relationship between the bending angle β and the gauge factor when the inventors of the present application bent a carbon nanotube CNT having a length L of 5 μm at a bending angle β as indicated by a solid line, as indicated by a one-dot chain line in FIG. As a result of the examination, as shown in FIG. 13, when the bending angle β is in the range of 172 ° to 179 °, the gauge factor is about 120. The finding that the gauge factor was approximately 120 was obtained.

  The present invention has been made in view of the above reasons, and an object of the present invention is to provide a physical quantity sensor capable of increasing the sensitivity as compared with the prior art.

  The invention of claim 1 is a physical quantity sensor for detecting a physical quantity to be detected as a change in resistance value due to strain of the gauge resistance, and the gauge resistance is a pair of supports protruding from one surface side of the sensor structure. It consists of carbon nanotubes installed between the base parts, and presses the intermediate part of the carbon nanotubes constituting the gauge resistance on the one surface side of the sensor structure in a state where no force is applied to the sensor structure. A bias portion that bends the middle portion of the nanotube is provided.

  According to the present invention, since the bias portion for bending the intermediate portion of the carbon nanotube constituting the gauge resistance is provided in a state where no force is applied to the sensor structure, no force is applied to the sensor structure. Compared with the conventional physical quantity sensor in which the carbon nanotubes constituting the gauge resistance are not bent in the state, it is possible to increase the gauge factor of the carbon nanotubes constituting the gauge resistance, and to achieve higher sensitivity than before. It becomes possible. In addition, since the carbon nanotubes constituting the gauge resistance are installed between the support bases, the intermediate part of the carbon nanotubes can be easily bent by the bias part, and the gauge factor of the carbon nanotubes can be increased.

  According to a second aspect of the present invention, in the first aspect of the invention, the carbon nanotubes constituting the gauge resistance are grown between the catalyst metal portions stacked on each of the paired support base portions, It is characterized by being formed of silicon.

  According to this invention, since the melting point of the support base becomes higher than the process temperature in the process of forming the carbon nanotube constituting the gauge resistance, it is possible to prevent the support base from being thermally deteriorated in the carbon nanotube formation process. it can.

  According to a third aspect of the present invention, in the first aspect of the present invention, the support base portion has conductivity and serves also as an electrode of a gauge resistance.

  According to the present invention, the manufacturing process can be simplified and the cost can be reduced as compared with the case where a gauge resistor electrode is provided separately from the support base.

  According to a fourth aspect of the present invention, in the third aspect of the invention, the carbon nanotubes constituting the gauge resistance are grown between the catalyst metal portions stacked on each of the paired support base portions, It is characterized by comprising a polycrystalline silicon layer.

  According to the present invention, since the melting point of the support base becomes higher than the process temperature in the process of forming the carbon nanotubes constituting the gauge resistance, the support base is thermally deteriorated in the process of forming the carbon nanotubes constituting the gauge resistance. Can be prevented.

  According to a fifth aspect of the present invention, in the third aspect of the present invention, the support base is made of a metal layer.

  According to this invention, the resistance of the gauge resistor electrode can be reduced as compared with the invention of claim 4.

  The invention of claim 6 is the invention of claim 3, wherein the carbon nanotubes constituting the gauge resistance are grown between the catalyst metal parts laminated on each of the pair of support base parts, And a silicon layer and a refractory metal layer laminated on the silicon layer.

  According to the present invention, since the melting point of the support base becomes higher than the process temperature in the process of forming the carbon nanotubes constituting the gauge resistance, the support base is thermally deteriorated in the process of forming the carbon nanotubes constituting the gauge resistance. In addition, the resistance of the electrode of the gauge resistance can be reduced as compared with the invention of claim 4.

  The invention according to claim 7 is the invention according to claim 1, wherein the carbon nanotubes constituting the gauge resistance are grown between the catalyst metal parts stacked on each of the pair of support base parts, It is formed of silicon dioxide or silicon nitride.

  According to the present invention, it is possible to prevent the catalytic metal portion from silicidizing and increasing the resistance when forming the carbon nanotube constituting the gauge resistance. In addition, the manufacturing process can be simplified compared to the case of forming a barrier layer that is interposed between the support base and the catalyst metal part to prevent silicidation of the catalyst metal part separately from the process of forming the support base part. I can plan.

  According to an eighth aspect of the present invention, there is provided the cover according to any one of the first to seventh aspects of the present invention, further comprising a cover fixed to the one surface side of the sensor structure, and the bias portion from a surface of the cover facing the sensor structure. It is characterized by being projected.

  According to the present invention, by fixing the cover to the one surface side of the sensor structure, the intermediate portion of the carbon nanotube constituting the gauge resistance can be bent by the bias portion.

  According to the first aspect of the present invention, the carbon nanotube gauge constituting the gauge resistance is compared with the conventional physical quantity sensor in which the carbon nanotube constituting the gauge resistance is not bent in a state where no force is applied to the sensor structure. It is possible to increase the rate, and there is an effect that it is possible to achieve higher sensitivity than in the past.

  In this embodiment, a pressure sensor exemplified as an example of a physical quantity sensor that detects a physical quantity to be detected as a change in resistance value due to strain of a gauge resistance will be described with reference to FIGS.

  The pressure sensor of the present embodiment is a sensor having an insulating film 2 made of a silicon oxide film on one surface side, which is formed by processing a silicon substrate (hereinafter referred to as a first silicon substrate), which is a semiconductor substrate, by micromachining technology. Structure 1, two gauge resistors R 1 and R 3 and two reference resistors R 2 and R 4 that are arranged on the one surface side of sensor structure 1 and are each made of carbon nanotube CNT, and sensor structure 1 Includes a cover 7 formed by processing another silicon substrate (hereinafter referred to as a second silicon substrate) by a micromachining technique and fixed to the one surface side of the sensor structure 1. Note that the number of carbon nanotubes CNT constituting each of the resistors R1 to R4 is not particularly limited, and may be one or plural. The cover 7 is not limited to the second silicon substrate, and may be formed of a glass substrate.

  The sensor structure 1 includes a rectangular frame-shaped frame portion 1a and a thin diaphragm portion 1b continuously and integrally connected to the frame portion 1a inside the frame portion 1a. That is, the sensor structure 1 is formed with a diaphragm portion 1b that is positioned inside the frame portion 1a and supported by the frame portion 1a over the entire circumference. When pressure is applied from the thickness direction of the diaphragm portion 1b, the diaphragm 1b is formed. The portion 1b is bent and deformed. Here, the gauge resistances R1 and R3 have a longitudinal direction in the direction corresponding to the boundary between the diaphragm portion 1b and the frame portion 1a at a portion corresponding to the peripheral portion of the diaphragm portion 1b on the one surface side of the sensor structure 1. The reference resistors R2 and R4 have a longitudinal direction in a direction corresponding to the boundary between the diaphragm portion 1b and the frame portion 1a at a portion corresponding to the frame portion 1a on the one surface side of the sensor structure 1. It is arranged. That is, the gauge resistors R1 and R3 have four sides constituting the outer periphery of the diaphragm portion 1b (boundary between the diaphragm portion 1b and the frame portion 1a) so that the amount of change in the resistance value accompanying the bending deformation of the diaphragm portion 1b is increased. The reference resistors R2 and R4 are disposed in a portion corresponding to the frame portion 1a so that the resistance value does not change even when the diaphragm portion 1b is bent and deformed. .

  Here, the sensor structure 1 is formed by, for example, performing the anisotropic etching using an alkaline solution such as KOH (potassium hydroxide) or TMAH (tetramethylammonium hydroxide) on the back surface of the first silicon substrate (for sensor). It is formed by providing a recess 1c on the other surface of the structure 1 and providing an insulating film 2 on the surface of the first silicon substrate.

  A so-called SOI substrate in which an insulating layer made of a buried oxide film (silicon oxide film) is formed in the middle in the thickness direction instead of the first silicon substrate as a semiconductor substrate serving as the basis of the sensor structure 1. If a substrate in which the insulating layer is interposed between a silicon layer on the front surface side and a silicon substrate on the back surface side is employed, the diaphragm portion 1b can be obtained by using the insulating layer as an etching stopper layer during etching from the back surface side. The thickness dimension can be managed with high accuracy, the yield can be improved, and the cost can be reduced as a result.

  The two gauge resistors R1 and R3 and the two reference resistors R2 and R4 are a plurality of (for example, four) formed on the insulating film 2 on the one surface side of the sensor structure 1. The above-described bridge circuit shown in FIG. 10 is connected by metal wiring (not shown) or the like.

  Therefore, if a suitable power supply E for detection is connected between one terminal at the diagonal position of the bridge circuit, the voltage between the other terminals Vo1 and Vo2 at the other diagonal position is detected, and an appropriate correction is applied, the diaphragm portion A voltage proportional to the pressure acting on 1b can be obtained. In the pressure sensor of this embodiment, a part of each of the four metal wirings constitutes a pad as a terminal.

  By the way, each of the resistors R1 to R4 is composed of carbon nanotubes that are installed between the pair of support bases 3 and 3 that protrude from the one surface side of the sensor structure 1. In other words, the sensor structure 1 is provided with four supporting base portions 3 and 3 in pairs. Each support base 3 is laminated with a catalyst metal portion 6 (see FIG. 1D) made of a catalyst metal material (for example, Fe, Ni, Co, etc.) for growing carbon nanotubes.

The planar shape of each support base 3 is an elongated rectangular shape whose longitudinal direction is the direction intersecting the parallel arrangement direction of the pair of support bases 3, 3, and is between the pair of support bases 3, 3. The distance is substantially constant, and the planar shape of the catalyst metal parts 6 and 6 is the same as that of the support base parts 3 and 3. Accordingly, an appropriate voltage is applied between the pair of catalytic metal parts 6 and 6, and the source gas containing carbon on the one surface side of the sensor structure 1 (for example, C ₂ H ₂ gas containing hydrocarbon, C ₂ H ₄ gas, CH ₄ gas, etc.) can be supplied to grow carbon nanotubes between the pair of catalyst metal parts 6 and 6 by the CVD method, and the catalyst metal on the pair of support base parts 3 and 3 The carbon nanotubes CNT installed between the parts 6 and 6 grow linearly.

  Here, each support base 3 is made of a conductive material and also serves as an electrode for each of the resistors R1 to R4. Therefore, compared to the case where the electrodes for each of the resistors R1 to R4 are provided separately from the support base 3. Thus, the manufacturing process can be simplified and the cost can be reduced. Further, a metal wiring (not shown) electrically connected to each electrode formed by each support base 3 is formed on the insulating film 2 of the sensor structure 1 before the formation of the resistors R1 to R4. In this case, when applying a voltage between the pair of catalytic metal parts 6 and 6 in the carbon nanotube CNT forming step, the supporting base parts 3 and 3 that also serve as electrodes in the paired catalytic metal parts 6 and 6, respectively. What is necessary is just to apply a voltage between the metal wiring electrically connected through this. However, the metal wiring forming step is not necessarily performed before the carbon nanotube CNT forming step, and may be performed after the carbon nanotube CNT forming step.

  Each of the support bases 3 described above includes a silicon layer imparted with conductivity (for example, a low-resistance single crystal silicon layer imparted with conductivity by doping impurities, a low-resistance imparted conductivity by doping impurities). A resistive polycrystalline silicon layer, etc.) 3a and a refractory metal layer 3b made of a refractory metal (for example, W, Ti, Mo, Pt, Cr, etc.). Since the melting point of each of the silicon layer 3a and the refractory metal layer 3b is higher than the process temperature (for example, about 500 to 1000 ° C.) in the formation process of a certain carbon nanotube CNT, each support base in the formation process of the carbon nanotube CNT The thermal deterioration of the part 3 can be prevented. Further, since the refractory metal layer 3b is interposed between the silicon layer 3a to which conductivity is imparted and the catalytic metal part 6, the catalytic metal part 6 is silicided in the process of forming the carbon nanotube CNT, and the contact resistance is reduced. It is possible to prevent the increase. Each support base 3 is not limited to the laminated structure of the silicon layer 3a and the refractory metal layer 3b provided with conductivity as described above, but a single layer of a low-resistance polycrystalline silicon layer provided with conductivity. You may comprise by the single layer structure of the metal layer which consists of a structure, a high melting point metal, etc. Here, also when each support base part 3 is constituted by a single-layer structure of a polycrystalline silicon layer imparted with conductivity, the melting point of each support base part 3 becomes higher than the process temperature in the carbon nanotube CNT forming step. Therefore, the thermal deterioration of each support base part 3 can be prevented. Further, even when each support base 3 is formed of a metal layer made of a refractory metal, the melting point of each support base 3 becomes higher than the process temperature in the carbon nanotube CNT forming step. In addition, the resistance of the electrode can be reduced as compared with the case where it is composed of a polycrystalline silicon layer.

  Moreover, as each support stand 3, for example, as shown in FIG. 4C, a laminated structure of a silicon layer 3c and a silicon oxide film 3d on the silicon layer 3c may be adopted. Even when the structure is adopted, since the melting point of the support base 3 becomes higher than the process temperature in the carbon nanotube CNT formation process, it is possible to prevent the support base 3 from being thermally deteriorated in the carbon nanotube CNT formation process. it can.

  Here, if only the thermal degradation of the support base 3 is prevented, the support base 3 may be formed of silicon (that is, it may be formed only of the silicon layer 3c), but the silicon layer 3c and the catalytic metal part By interposing the silicon oxide film 3 d between the first and second electrodes 6, silicidation of the catalyst metal portion 6 on the support base 3 can be prevented.

  When each support base 3 is constituted by the silicon layer 3c and the silicon oxide film 3d on the silicon layer 3c, the thickness direction as shown in FIG. 4A, an SOI substrate 100 having an insulating film 2 made of a silicon oxide film is prepared, and a silicon layer on one surface side of the SOI substrate 100 is used as shown in FIG. 4B by using a photolithography technique and a dry etching technique. After patterning 100c, a plurality of silicon layers 3c constituting a part of each support base 3 are formed, and then a silicon oxide film is formed on the surface side of each silicon layer 3c as shown in FIG. 3d may be formed.

  In addition, each support base portion 3 is, for example, as shown in FIG. 5C, a part of one surface side of the silicon substrate that is the basis of the sensor structure 1 is selectively selected by a LOCOS (Local Oxidation Of Silicon) method. Of the silicon oxide film 2c formed by oxidation, a portion protruding from the insulating film 2 is formed (that is, each support base 3 is formed of silicon dioxide), and each support base 3 is provided with a catalyst metal portion. 6 may be laminated. To obtain the structure shown in FIG. 5C, a silicon nitride film 8 is formed on the insulating film 2 on the first silicon substrate of the sensor structure 1 by a CVD method or the like, and a photolithography technique and dry etching are performed. The structure shown in FIG. 5A is obtained by removing the portion of the silicon nitride film 8 that overlaps the region where the support base 3 is to be formed by using the technique, and then the first silicon substrate is formed by the LOCOS method. The silicon oxide film 2c is formed by selective oxidation to obtain the structure shown in FIG. 5 (b). Thereafter, the silicon nitride film 8 is removed, and then the silicon oxide film 2c is partially removed. The structure shown in FIG. 5C may be obtained by forming the catalyst metal portion 6 on the support base portion 3 to be formed. As described above, if the support base 3 is formed of silicon dioxide, the catalyst metal part 5 is silicided by being interposed between the support base 3 and the catalyst metal part 6 separately from the process of forming the support base 3. The manufacturing process can be simplified as compared with the case where a barrier layer for preventing the above is formed. The support base 3 may be formed of silicon nitride instead of silicon dioxide. When the support base 3 is formed of silicon nitride, the support base 3 is formed separately from the step of forming the support base 3. The manufacturing process can be simplified as compared with the case where the above-described barrier layer is formed between 3 and the catalytic metal portion 6.

  Next, the cover 7 fixed to the one surface side of the sensor structure 1 will be described.

  The above-described cover 7 has a rectangular plate shape, and a recess 7a for securing a displacement space of the diaphragm portion 1b of the sensor structure 1 is formed on a surface facing the sensor structure 1. The circumference is fixed to the sensor structure 1 over the entire circumference. Here, the cover 7 and the sensor structure 1 are fixed by anodic bonding. Note that the cover 7 is set to have a shorter dimension in the left-right direction in FIG. 1A than the sensor structure 1 so that the pads on the one surface side of the sensor structure 1 can be exposed. It is.

  Here, on the inner bottom surface of the recess 7a in the cover 7, each of the carbon nanotubes CNT constituting the gauge resistors R1 and R3 in a state where no force (pressure in this embodiment) is applied to the sensor structure 1. Two protruding bias portions 7b are provided so as to press the intermediate portion and bend the intermediate portion of each carbon nanotube CNT. That is, in the present embodiment, the intermediate portions of the carbon nanotubes CNT constituting the gauge resistors R1 and R3 are pressed and bent by the bias portion 7b in a state where the force is not applied to the sensor structure 1. In addition, the relative positional relationship between the position of each carbon nanotube CNT constituting the gauge resistors R1 and R3 and the bias portion 7b is set. More specifically, the gauge resistance is obtained in a state where the tip surface of the bias portion 7b and the joint surface of the cover 7 to the sensor structure 1 are aligned on the same plane and the force is not applied to the sensor structure 1. The protruding height from the insulating film 2 of the pair of support bases 3 and 3 is set so that the middle part of each carbon nanotube CNT constituting R1 and R3 is pressed and bent by the bias part 7b. is there. The bias portion 7b has a rectangular shape with a cross section orthogonal to the thickness direction of the cover 7, and has a cross-sectional area that gradually decreases as the distance from the inner bottom surface of the recess 7a increases. As shown in (d), a gap is formed between the tip of the bias portion 7b and the pair of support base portions 3 and 3.

  Therefore, in the present embodiment, since the sensor structure 1 is provided with bias portions 7b and 7b that bend the intermediate portions of the carbon nanotubes CNT constituting the gauge resistors R1 and R3 in a state where no force is applied to the sensor structure 1, Compared with the conventional pressure sensor in which the carbon nanotubes CNT constituting the gauge resistors R1 and R3 are not bent in a state where no force is applied to the sensor structure 1, the carbon nanotubes CNT constituting the gauge resistors R1 and R3 It is possible to increase the gauge factor, and it is possible to achieve higher sensitivity than in the past. Further, since the carbon nanotubes CNT constituting the gauge resistors R1 and R3 are installed between the pair of support bases 3 and 3, the intermediate part of the carbon nanotubes CNT can be easily bent by the bias part 7b, The gauge factor of the nanotube CNT can be increased.

  By the way, without providing the support bases 3 and 3 projecting from the insulating film 2 in the sensor structure 1, a concave groove 2 b is provided in the insulating film 2 as shown in FIG. It is conceivable that the front end surface of the bias portion 7b is brought into contact with the intermediate portion of the carbon nanotube CNT in a state where no pressure is applied to the diaphragm portion 1b. In the configuration of FIG. When pressure is applied to the diaphragm portion 1b of the structural body 1 from below in FIG. 7 (a), the diaphragm portion 1b is curved and deformed as shown by a two-dot chain line in FIG. 7 (b), while the carbon nanotube CNT The intermediate portion of the first electrode is bent into a V-shape that protrudes in the opposite direction to the displacement direction of the diaphragm portion 1b by the bias portion 7b, and enters the inside of the groove 2b. However, since the cover 7 integrally provided with the bias portion 7b as described above is fixed to the frame 1a of the sensor structure 1 by anodic bonding or the like, a wafer and a cover on which a large number of sensor structures 1 are formed. Direction in which the relative positions of the carbon nanotubes CNT and the bias portion 7b in the thickness direction of the sensor structure 1 are separated from each other due to warpage of wafers on which a large number of wafers 7 are formed, variations in the thickness of the insulating film 2, and the like. In such a case, it is considered that even if a pressure is applied to the sensor structure 1, the intermediate portion of the carbon nanotube CNT is not pressed by the bias portion 7b.

  On the other hand, in the pressure sensor of the present embodiment, a pair of support bases 3 and 3 are provided on the one surface side of the sensor structure 1 so that no pressure is applied to the sensor structure 1. Since the projecting heights of the paired support bases 3 and 3 are set so that the intermediate part of the carbon nanotube CNT is pressed and bent by the bias part 7b, pressure acts on the sensor structure 1. The intermediate portions of the carbon nanotubes CNT constituting the gauge resistances R1 and R3 can be reliably bent even when the pressure is not applied, and the gauge factor of the gauge resistances R1 and R3 when the pressure is applied is increased. Compared to the sensor, it is possible to increase the gauge factor of the carbon nanotubes CNT constituting the gauge resistors R1 and R3, and it is possible to achieve higher sensitivity than in the past. The carbon nanotubes CNT constituting the reference resistors R2 and R4 do not need to be installed between the pair of support bases 3 and 3, and the catalyst metal parts 6 and 6 are formed on the insulating film 2 as a pair. Then, it may be allowed to grow between the pair of catalytic metal parts 6 and 6.

  In the present embodiment, the bias portion 7b presses the intermediate portion of the carbon nanotubes CNT constituting the gauge resistors R1 and R3 in a state where no pressure is applied to the sensor structure 1, and the intermediate portion is shown in FIG. As shown in FIG. 6, if the protruding heights of the support bases 3 and 3 are set so that the bending angle β of the carbon nanotube CNT is 172 ° as shown in FIG. Even when the pressure is applied to the body 1, even if the pressure is small, the bending angle of the carbon nanotubes CNT constituting the gauge resistances R1 and R3 is smaller than 172 ° and the gauge rate is increased, so that higher sensitivity is achieved. Can do. Here, the position pressed by the bias portion 7b in the carbon nanotube CNT may be any position as long as it is an intermediate portion in the longitudinal direction of the carbon nanotube CNT. In order to increase the strain rate of the carbon nanotubes CNT constituting the gauge resistors R1 and R3 and increase the gauge factor, it is desirable to press the substantially central position in the longitudinal direction. Further, the number of bias portions 7b that press and bend the intermediate portion of each carbon nanotube CNT constituting the gauge resistors R1 and R3 is not limited to one, but may be plural (carbon nanotubes constituting the gauge resistors R1 and R3). When a plurality of bias portions 7b are provided for each of the CNTs, a plurality of bias portions 7b may be provided in parallel in the direction in which the pair of support base portions 3 and 3 are provided in parallel.

  By the way, in this embodiment, the sensor structure 1 constitutes a pressure sensor structure, and the gauge resistors R1 and R3 are arranged on the periphery of the diaphragm portion 1b of the sensor structure 1. When the gauge resistances R1 and R3 are disposed in the central portion where the displacement amount of the diaphragm portion 1b due to pressure is large, the gauge resistors R1 and R3 are disposed around the peripheral portion where the displacement amount of the diaphragm portion 1b due to pressure is small If the sensitivity is the same, the thickness of the diaphragm portion 1b can be increased, and the mechanical strength of the sensor structure 1 can be increased.

  In the above-described embodiment, the pressure sensor is illustrated as an example of the physical quantity sensor. However, the technical idea of the present invention is not limited to the pressure sensor, and for example, other physical quantity sensors using a gauge resistance (for example, an acceleration sensor, As an example, when applied to an acceleration sensor, for example, carbon nanotubes CNT constituting gauge resistors R11 and R12 in the same acceleration sensor as the conventional example shown in FIG. As shown in FIG. 8, a pair of support bases 3 and 3 projecting on the one surface side of the sensor structure 11 is installed (only the gauge resistance R12 appears in FIG. 8), and the sensor What is necessary is just to provide the above-mentioned bias part 7b which protrudes from the inner bottom face of the recess 7a in the cover 7 which adheres to the said one surface side of the structure 11. FIG.

Embodiments are shown, (a) is a schematic plan view, (b) is an AA ′ sectional view of (a), (c) is a BB ′ sectional view of (a), and (d) is (b). It is an enlarged view of the principal part C of FIG. The structure for sensors in the same as above is shown, in which (a) is a schematic plan view, (b) is a sectional view taken along line A-A 'in (a), and (c) is a sectional view taken along line B-B' in (a). The cover in the same as above is shown, (a) is a schematic plan view, (b) is a sectional view taken along line AA 'in (a), (c) is a sectional view taken along line BB' in (a), and (d) is a bottom view. It is. It is principal process sectional drawing for demonstrating the manufacturing method of the other structural example same as the above. It is principal process sectional drawing for demonstrating the manufacturing method of the other structural example same as the above. It is principal part explanatory drawing same as the above. It is operation | movement explanatory drawing of a comparative example same as the above. Other embodiment is shown, (a) is a schematic sectional drawing, (b) is an enlarged view of the principal part C of (a). A prior art example is shown, (a) is a schematic plan view, (b) is a schematic cross-sectional view, and (c) is an enlarged view of the main part of (b). It is operation | movement explanatory drawing same as the above. Another prior art example is shown, (a) is a schematic plan view, (b) is a schematic cross-sectional view, and (c) is an enlarged view of a main part of (b). It is explanatory drawing of the bending angle of a carbon nanotube. FIG. 4 is a relationship diagram between a bending angle of a carbon nanotube and a gauge factor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sensor structure 1a Frame part 1b Diaphragm part 1c Recess 2 Insulating film 3 Support base part 3a Silicon layer 3b Refractory metal layer 6 Catalyst metal part 7 Cover 7a Recess 7b Bias part CNT Carbon nanotube R1, R3 Gauge resistance R2 , R4 Reference resistance

Claims (8)

  A physical quantity sensor for detecting a physical quantity to be detected as a change in resistance value due to strain of a gauge resistance, wherein the gauge resistance is installed between a pair of support bases protruding on one surface side of the sensor structure. It consists of carbon nanotubes, and presses the middle part of the carbon nanotube that constitutes the gauge resistance on the one surface side of the sensor structure without any force acting on the sensor structure to bend the middle part of the carbon nanotube A physical quantity sensor comprising a bias unit to be operated.   The carbon nanotube constituting the gauge resistance is grown between the catalyst metal parts stacked on each of the pair of support bases, and the support bases are formed of silicon. The physical quantity sensor according to 1.   The physical quantity sensor according to claim 1, wherein the support base part has conductivity and serves also as an electrode of a gauge resistance.   The carbon nanotube constituting the gauge resistance is grown between the catalytic metal parts stacked on each of the pair of support base parts, and the support base part is made of a polycrystalline silicon layer. 3. The physical quantity sensor according to 3.   The physical quantity sensor according to claim 3, wherein the support base is made of a metal layer.   The carbon nanotubes constituting the gauge resistance are grown between the catalyst metal parts stacked on each of the paired support base parts, and the support base part is a silicon layer and a refractory metal stacked on the silicon layer. The physical quantity sensor according to claim 3, comprising a layer.   The carbon nanotubes constituting the gauge resistance are grown between the catalyst metal parts stacked on each of the paired support base parts, and the support base parts are formed of silicon dioxide or silicon nitride. The physical quantity sensor according to claim 1.   8. The sensor structure according to claim 1, further comprising a cover fixed to the one surface side of the sensor structure, wherein the bias portion protrudes from a surface of the cover facing the sensor structure. The physical quantity sensor according to any one of the above.

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