JP5058879B2 - MEMS acceleration sensor - Google Patents

Description

  The present invention relates to a MEMS acceleration sensor that detects the acceleration of a measurement object based on the movement of a movable weight.

  An acceleration sensor that measures vibration acceleration of an object to be measured is used for measurement of shaking of a building, measurement of mechanical strength of an apparatus, and the like. In addition, there are various mechanical devices having a movable part that detect and control the acceleration of the movable part. An acceleration sensor is also used for such a mechanical device.

  The acceleration sensor is preferably downsized so that it can be easily attached to the measurement object. Therefore, a MEMS acceleration sensor configured as a so-called MEMS (Micro Electro Mechanical System) is widely used as the acceleration sensor. Some MEMS acceleration sensors include a weight formed of silicon or the like, and generate an electric signal according to the vibration of the weight.

JP 2006-242594 A

  Gas molecules surrounding it collide with the weight of the MEMS acceleration sensor. As a result, the weight vibrates and noise is output from the MEMS acceleration sensor even if the measurement object does not generate acceleration. It is known that this noise increases as the mass of the weight decreases. Therefore, if the weight of the weight is reduced by reducing the weight of the MEMS acceleration sensor in order to reduce the size of the MEMS acceleration sensor, such a noise level increases and the measurement resolution of the MEMS acceleration sensor decreases.

  The present invention has been made for such a problem. That is, an object is to provide a MEMS acceleration sensor that is small and has high measurement resolution.

The present invention provides a MEMS acceleration sensor that includes a movable weight that can be displaced according to a given acceleration, and that outputs a detection amount according to the movement of the movable weight. provided in the defect, e Bei and a dense member density is higher than the primary member, the base member is formed in a rotationally symmetrical shape, the MEMS acceleration sensor, the movable weight is of the primary member A support housing that supports the movable weight via a spring so as to be displaced in a rotationally symmetric axis direction, the spring including a plurality of leaf springs provided so that plate surfaces overlap in parallel; Supports the movable weight via the plurality of leaf springs so that the movable weight can be displaced in a direction perpendicular to the plate surfaces of the plurality of leaf springs, and the center of gravity of the movable weight is The density of the material forming the weight is uniform Characterized in that it coincides with the center of gravity when it is assumed that.

The present invention also provides a MEMS acceleration sensor that includes a movable weight that can be displaced according to a given acceleration, and that outputs a detection amount according to the movement of the movable weight. And a high density member having a higher density than the basic member, the basic member is formed in a plate shape having a rotationally symmetric plate surface, and the MEMS acceleration sensor is A support housing is provided for supporting the movable weight via a spring so that the movable weight is displaced in a rotationally symmetric axial direction perpendicular to the plate surface of the basic member, and the spring is provided so that the plate surfaces overlap in parallel. A plurality of leaf springs, and the support housing is configured to move the movable weight via the plurality of leaf springs so that the movable weight can be displaced in a direction perpendicular to the plate surfaces of the plurality of leaf springs. The MEMS acceleration sensor A plate surface of the basic member and the plate surface thereof are opposed to each other, and a housing plate is disposed with a space between the plate surface of the basic member, and the defect portion faces the housing plate The high-density member is filled in the defect portion so that an unfilled space is formed on a surface facing the housing plate .

In the MEMS acceleration sensor according to the present invention, the basic member includes silicon or glass, and the high-density member includes gold germanium, gold silicon, gold, platinum, iridium, nickel, copper, tungsten, Alternatively, it is preferable to include any of tantalum .

  According to the present invention, it is possible to provide a MEMS acceleration sensor that is small and has high measurement resolution.

  FIG. 1 is an exploded perspective view of a MEMS acceleration sensor 10 according to the first embodiment of the present invention. FIG. 2A is a view of the sensor main body 12 shown in FIG. 1 as viewed from above. FIG. 2B is a view when the MEMS acceleration sensor 10 is cut along the line AB in FIG. A cross-sectional view is shown.

  The MEMS acceleration sensor 10 converts a displacement amount of a measurement object into an electrical physical quantity. The MEMS acceleration sensor 10 is fixed to an acceleration measurement object. The movement of the measurement object is transmitted to the movable weight 20, and the movable weight 20 is displaced according to the movement of the measurement object. As a result, the electrostatic capacitance between the lower capacitive electrode 24 and the upper capacitive electrode 26 changes, so that the acceleration of the measurement object can be measured by measuring the electrostatic capacitance or the corresponding electrophysical quantity. .

  The MEMS acceleration sensor 10 includes a lower glass plate 14 and an upper glass plate 16 that form a part of the casing of the MEMS acceleration sensor 10, and a sensor main body 12 sandwiched between the lower glass plate 14 and the upper glass plate 16. Composed.

  The sensor body 12 includes a sensor housing frame 18 whose inner wall surface has a cylindrical shape. Silicon can be used as the material of the sensor housing frame 18. A disc-shaped movable weight 20 is provided in the frame of the sensor housing frame 18. Leaf springs 22 bridged between the inner wall surface of the sensor housing frame 18 are attached at equal angular intervals around the upper disk surface and the lower disk surface of the movable weight 20. Each leaf spring 22 is bridged between the movable weight 20 and the sensor housing frame 18 so as to obliquely cross the gap between the movable weight 20 and the sensor housing frame 18. The leaf springs 22 attached to the upper disk surface of the movable weight 20 and the leaf springs 22 attached to the lower disk surface of the movable weight 20 are arranged in parallel so that the plate surfaces face each other. A pair of leaf springs 22 arranged face to face form a parallel leaf spring. The sensor housing frame 18, the movable weight 20, and the leaf spring 22 can be integrally formed of silicon. A high density member 34 for improving the performance of the MEMS acceleration sensor 10 is added to the movable weight 20. The performance improvement of the high-density member 34 and the MEMS acceleration sensor 10 will be described later.

  According to such a configuration, the movable weight 20 can be supported in the frame of the sensor housing frame 18 so that the disk surface of the movable weight 20 and the frame opening surface of the sensor housing frame 18 are parallel to each other. . The movable weight 20 is supported at a stable position within the frame of the sensor housing frame 18 by the elastic force of the leaf spring 22 when the measurement object is stationary. When the measurement object moves, the elastic force returned to the stable position is received from the leaf spring 22 and is displaced in a direction perpendicular to the disk surface according to the movement of the measurement object.

  The leaf springs 22 are attached at equal angular intervals around the upper disk surface and the lower disk surface of the movable weight 20, so that the displacement of the movable weight 20 in the displacement direction can be reduced. Further, by providing the leaf spring 22 so as to obliquely cross the gap between the movable weight 20 and the sensor housing frame 18, the leaf spring 22 can be lengthened and the deflection of the leaf spring 22 can be increased. The measurement range can be increased. Furthermore, a pair of a leaf spring 22 attached to the upper disk surface of the movable weight 20 and a leaf spring 22 attached to the lower disk surface of the movable weight 20 forms a parallel leaf spring, whereby the movable weight 20 The displacement direction can be stabilized. That is, even when acceleration in a direction other than the direction perpendicular to the disk surface is given to the movable weight 20, it is possible to avoid the movable weight 20 being displaced in a direction other than the direction perpendicular to the disk surface.

  A lower glass plate 14 is attached to the bottom surface of the sensor main body 12 so as to close the lower opening surface of the sensor housing frame 18. An upper glass plate 16 is attached to the upper surface of the sensor main body 12 so as to close the upper opening surface of the sensor housing frame 18. When the sensor housing frame 18 is formed of silicon, an anodic bonding method can be used to attach the lower glass plate 14 and the upper glass plate 16. With such a configuration, the movable weight 20 is sealed by the lower glass plate 14, the upper glass plate 16, and the sensor housing frame 18.

  A lower capacitor electrode 24 facing the lower disk surface of the movable weight 20 is provided on the surface of the lower glass plate 14 facing the movable weight 20. Similarly, on the surface of the upper glass plate 16 facing the movable weight 20, an upper capacitive electrode 26 that faces the upper disk surface of the movable weight 20 is provided.

  Further, the lower terminal electrode 28 is provided on the surface opposite to the surface on which the lower capacitive electrode 24 of the lower glass plate 14 is provided, and the upper terminal electrode is provided on the surface opposite to the surface on which the upper capacitive electrode 26 of the upper glass plate 16 is provided. 30 are provided. The lower capacitor electrode 24 and the lower terminal electrode 28 are electrically connected by a through hole 32 provided in the lower glass plate 14. Similarly, the upper capacitor electrode 26 and the upper terminal electrode 30 are electrically connected by a through hole 32 provided in the upper glass plate 16. Instead of providing a through hole, the lower glass plate 14 and the upper glass plate 16 are each provided with a conductor pattern drawn from the lower capacitor electrode 24 and the upper capacitor electrode 26, and the terminals connected to the conductor pattern are MEMS. It may be configured to be provided on the outer surface of the acceleration sensor 10.

  The conductive thin films attached to the lower glass plate 14 and the upper glass plate 16, such as the lower capacitive electrode 24, the upper capacitive electrode 26, the lower terminal electrode 28, the upper terminal electrode 30, etc. can be formed by vapor deposition, sputtering, or the like. . As the material, titanium having high adhesion strength with glass, platinum which is difficult to oxidize, or the like can be used. For example, titanium can be adhered to the glass surface, and platinum can be adhered to the glass surface, whereby adhesion to the glass can be enhanced and oxidation resistance can be enhanced.

  The MEMS acceleration sensor 10 is fixed to the measurement object so that the acceleration measurement direction of the measurement object matches the displacement direction of the movable weight 20. As the measurement object moves, the movable weight 20 is displaced upward or downward in FIG. Thereby, the electrostatic capacitance between the upper capacitive electrode 26 and the lower capacitive electrode 24 changes, and the electrostatic capacitance between the upper terminal electrode 30 and the lower terminal electrode 28 changes. The measuring device connected to the upper terminal electrode 30 and the lower terminal electrode 28 measures a change in capacitance between the upper terminal electrode 30 and the lower terminal electrode 28, and the measurement object is measured according to the measurement result. Measure acceleration.

  In this embodiment, the shape of the movable weight is a disc shape. However, the movable weight is not necessarily a disc shape, and may be formed in a general polygonal plate shape. It is preferable that the polygon has a rotationally symmetric shape so that the movable weight is displaced in the rotationally symmetric axis direction. The shape of the inner wall surface of the sensor housing frame may be determined according to the shape of the movable weight. Furthermore, more generally, the movable weight may be configured as a rotationally symmetrical solid shape that is not a plate shape, and the movable weight may be displaced in the rotationally symmetric axis direction.

  In the present embodiment, a configuration in which the sensor main body 12 is sandwiched between the lower glass plate 14 and the upper glass plate 16 is employed. As a plate-like member that sandwiches the sensor main body 12, silicon or a metal plate may be used instead of the glass plate.

  Next, a detailed configuration of the movable weight 20 will be described. Gas exists in the internal space of a general MEMS acceleration sensor, and gas molecules collide with the movable weight. As a result, the movable weight vibrates, and noise is output from the MEMS acceleration sensor even when the measurement object is stationary. It is known that this noise increases as the mass of the movable weight decreases. Therefore, if the weight of the movable weight is reduced by reducing the volume of the movable weight in order to reduce the size of the MEMS acceleration sensor, such a noise level increases and the measurement resolution of the MEMS acceleration sensor decreases.

  Therefore, the movable weight 20 according to the present embodiment is configured to increase the mass while keeping the volume constant. The movable weight 20 is provided with a high-density member hole 36 penetrating the movable weight 20 from the upper disk surface to the lower disk surface at the center of the disk surface. The high-density member hole 36 has a cylindrical shape extending in the direction perpendicular to the disk surface.

  When the plate surface of the movable weight has a general rotationally symmetric shape other than a circle, the high-density member hole is preferably provided at a rotationally symmetric position on the plate surface of the movable weight. Moreover, it is preferable that the high-density member hole has a three-dimensional shape such that the center of gravity of the movable weight is located on the rotational symmetry axis of the movable weight.

  The high density member hole 36 is filled with a high density member 34 having a higher density than the basic member. Here, the basic member refers to a member that forms a portion of the movable weight 20 other than the high-density member hole 36. When silicon is used as the basic member, the high density member 34 can be made of gold germanium, gold silicon, gold, platinum, iridium, nickel, copper, tungsten, tantalum, or the like.

  Gold germanium (germanium content 12%, density 14.7 g / cc) and gold silicon (silicon content 1%, density 18.0 g / cc) have lower melting points than silicon. Therefore, these materials can be filled in the high-density member hole 36 by melting.

  Gold (density 19.3 g / cc), platinum (density 21.5 g / cc), iridium (density 22.7 g / cc), nickel (density 8.9 g / cc), copper (8.9 g / cc) It can be attached to silicon by electrolytic plating or electroless plating. Therefore, these materials can be filled in the high-density member hole 36 by electrolytic plating or electroless plating.

  Tungsten (density 19.3 g / cc) and tantalum (density 16.7 g / cc) can be attached to silicon by vapor deposition such as vapor deposition, sputtering, and CVD. Therefore, these materials can be filled into the high-density member hole 36 by vapor deposition.

  Note that a manufacturing process in which the high-density member hole 36 is filled with a metal that can be attached to silicon by discharge coating and has a higher density than silicon may be employed. Further, a manufacturing process may be employed in which a metal piece having a higher density than silicon is inserted into the high-density member hole 36 and the metal piece is fixed in the high-density member hole 36 by plating, molten metal filling, or the like.

  According to the MEMS acceleration sensor 10 according to the present embodiment, the mass of the movable weight can be increased as compared with the case where the movable weight is formed of silicon alone under the condition that the volume of the movable weight is constant. . Thereby, noise vibration of the movable weight due to collision of gas molecules can be reduced, and noise output from the MEMS acceleration sensor 10 can be reduced. Therefore, the measurement resolution of acceleration can be improved.

  In addition, a high-density member hole is arranged at a rotationally symmetric position on the plate surface of the movable weight, the movable weight is formed so that the center of gravity is located on the rotationally symmetric axis, and the movable weight is supported so as to be displaced in the rotationally symmetric axis direction. In this case, the displacement of the movable weight in the displacement direction can be reduced. Thereby, measurement accuracy can be improved. When the center of gravity of the movable weight provided with the high-density member is coincident with the three-dimensional center of the movable weight (the center of gravity when the density of the material forming the movable weight is assumed to be uniform) Rotational moment is not generated by the acceleration applied in the direction coinciding with the displacement direction of the movable weight. As a result, an excellent effect that more accurate acceleration can be detected is exhibited.

  FIGS. 3A and 3B show the configuration of the MEMS acceleration sensor 38 according to the application example of the first embodiment. 3A is a view of the sensor main body 40 as viewed from above, and FIG. 3B is a cross-sectional view of the MEMS acceleration sensor 38 cut along a straight line AB. The same components as those of the MEMS acceleration sensor 10 of FIGS. 1 and 2 are denoted by the same reference numerals, and description thereof is omitted.

  The MEMS acceleration sensor 38 is provided with a plurality of high-density member holes 36. Here, four high-density member holes 36 are provided at rotationally symmetric positions with a straight line passing through the center of the disk surface of the movable weight 42 as a rotationally symmetric axis. Each high-density member hole 36 has a cylindrical shape extending in a direction perpendicular to the disk surface of the movable weight 42. Each high-density member hole 36 penetrates the movable weight 42 from the upper disk surface of the movable weight 42 to the lower disk surface. Each high density member hole 36 is filled with a high density member 34.

  By providing a plurality of high-density member holes 36, it is possible to reduce noise vibration of the movable weight 42 due to collision of gas molecules, and to enhance the effect of reducing noise output from the MEMS acceleration sensor 38.

  Further, as the high-density member hole 36, a bag hole that does not pass through the movable weight 42 and has a dead end with a predetermined depth may be adopted. FIG. 3C shows the configuration of the MEMS acceleration sensor 44 that employs a bag hole. According to such a configuration, the process of filling the high density member 34 can be completed quickly. Here, the bag hole is adopted in the case where a plurality of high-density member holes 36 are provided, but the bag hole may be adopted in the configuration shown in FIGS. 1 and 2.

  4A and 4B show the configuration of the MEMS acceleration sensor 46 according to the second embodiment of the present invention. 4A shows a view of the sensor main body 48 viewed from above, and FIG. 4B shows a cross-sectional view of the MEMS acceleration sensor 46 cut along a straight line AB. The same components as those of the MEMS acceleration sensor 10 of FIGS. 1 and 2 are denoted by the same reference numerals, and description thereof is omitted.

  In the present embodiment, noise vibration of the movable weight due to collision of gas molecules is further reduced. In general, the noise vibration of the movable weight due to the collision of gas molecules around the movable weight becomes smaller as the gas pressure around the movable weight is smaller. Therefore, by reducing the pressure of the gas around the movable weight, the noise vibration of the movable weight can be reduced and the measurement resolution can be improved.

  In order to reduce the pressure of the gas around the movable weight, the compressibility of the gas volume with respect to the displacement of the movable weight may be reduced. For that purpose, the distance between the movable weight and the lower glass plate, and the distance between the movable weight and the upper glass plate are increased, and the volume of the gas sandwiched between the movable weight and the lower capacitive electrode, It is also conceivable to increase the volume of the gas sandwiched between the movable weight and the upper capacitive electrode. However, with such a configuration, the MEMS acceleration sensor becomes large.

  Therefore, in the MEMS acceleration sensor 46 according to the second embodiment, the vicinity of the center of the plate surface of the movable weight 50 is recessed, so that the rise in the gas pressure around the movable weight 50 is reduced. The basic member of the movable weight 50 of the MEMS acceleration sensor 46 shown in FIGS. 4 (a) and 4 (b) has the same shape as the basic member of the movable weight 20 of the MEMS acceleration sensor 10 shown in FIGS. 2 (a) and 2 (b). It shall have.

  The high-density member 34 does not fill the entire space inside the high-density member hole 36, but leaves an unfilled space on the surface facing the lower capacitive electrode 24 and the surface facing the upper capacitive electrode 26. Thereby, a dent can be provided on each plate surface of the movable weight 50.

  According to such a configuration, when the movable weight 50 approaches the lower capacitive electrode 24, the pressure of the gas sandwiched between the movable weight 50 and the lower glass plate 14 and the movable weight 50 becomes the upper capacitance. The rise in pressure of the gas sandwiched between the movable weight 50 and the upper glass plate 16 when approaching the electrode 26 can be mitigated. Thereby, noise vibration of the movable weight 50 due to collision of gas molecules can be reduced, and measurement resolution can be improved. By providing the recess of the movable weight 50 at the center of the plate surface, the effect of alleviating the increase in atmospheric pressure can be exerted evenly on the sealed space, so that the effect of reducing noise vibration can be enhanced.

  FIGS. 4C and 4D show a MEMS acceleration sensor 52 according to an application example of the second embodiment. FIG. 4C is a view of the sensor main body 54 viewed from above, and FIG. 4D is a cross-sectional view of the MEMS acceleration sensor 52 cut along a line AB. The same components as those in the MEMS acceleration sensor shown in FIGS. 1 to 3 are denoted by the same reference numerals, and the description thereof is omitted.

  In this application example, a plurality of high-density member holes 36 are provided and the vicinity of the center of the disk surface of the movable weight 56 is recessed. The entire space inside the high-density member hole 36 provided at the center of the disk surface of the movable weight 56 is not filled with the high-density member 34, and faces the lower capacitive electrode 24 and the upper capacitive electrode 26. Leave unfilled space on the surface. The high density member hole 36 provided surrounding the center of the disk surface of the movable weight 56 is a bag hole. According to such a configuration, the manufacturing process for filling the high-density member 34 can be completed quickly, and a MEMS acceleration sensor with high measurement resolution can be configured.

  5A and 5B show a configuration of a MEMS acceleration sensor 58 according to the third embodiment. FIG. 5A shows a view of the sensor body 60 from above, and FIG. 5B shows a cross-sectional view when the MEMS acceleration sensor 58 is cut along a line AB. The same components as those in the MEMS acceleration sensor shown in FIGS. 1 to 4 are denoted by the same reference numerals, and the description thereof is omitted.

  In the first and second embodiments described above, a configuration in which the high density member hole is filled with the high density member is employed. According to such a configuration, the manufacturing process can be completed quickly by melting the high-density member. However, when a high-density member is filled by plating, vapor deposition or the like, it often takes a longer time to complete the process than filling a molten metal. Therefore, in the movable weight 62 according to the third embodiment, the high-density member 34 is attached in a layered manner to the basic member formed in a plate shape.

  A high density member 34 is attached to each disk surface of the movable weight 62 by plating, vapor deposition or the like. When gold, platinum, iridium, nickel, copper or the like is used as the material of the high density member 34, electrolytic plating or electroless plating can be employed. When tungsten, tantalum, or the like is used as the material of the high density member 34, vapor deposition can be employed. According to such a configuration, the time required for manufacturing can be shortened as compared with a configuration in which the high-density member is filled in the high-density member hole by plating, vapor deposition or the like.

  FIGS. 6A and 6B show the configuration of the MEMS acceleration sensor 66 according to the fourth embodiment. 6A is a view of the sensor main body 68 as viewed from above, and FIG. 6B is a cross-sectional view when the MEMS acceleration sensor 66 is cut along a line AB. The same components as those of the MEMS acceleration sensor shown in FIGS. 1 to 5 are denoted by the same reference numerals, and the description thereof is omitted. In the present embodiment, the movable weight 70 includes two basic members 72, and the high-density member 34 is sandwiched between the two basic members 72. The boundary between the basic member 72 and the high density member 34 does not necessarily have to be continuous as a chemical substance. Therefore, the basic member 72 and the high-density member 34 may be joined so that the basic member 72 and the high-density member 34 are integrally displaced.

  7A and 7B show the configuration of the MEMS acceleration sensor 74 according to the fifth embodiment. FIG. 7A shows a view of the sensor body 76 from above, and FIG. 7B shows a cross-sectional view when the MEMS acceleration sensor 74 is cut along a line AB. The same components as those in the MEMS acceleration sensor shown in FIGS. 1 to 6 are denoted by the same reference numerals, and the description thereof is omitted.

  In the first to fourth embodiments described above, the acceleration of the measurement object is detected based on the change in capacitance between the upper capacitive electrode 26 and the lower capacitive electrode 24 in accordance with the displacement of the movable weight. . On the other hand, in the fifth embodiment, a piezoresistive element 78 is provided in the leaf spring 22 and the acceleration of the measurement object is detected based on a change in the resistance value of the piezoresistive element 78 according to the deformation of the leaf spring 22.

  The configuration of the movable weight 20 in FIG. 7 has the same configuration as that of the movable weight 20 in FIG. A piezoresistive element 78 is provided on the leaf spring 22 by attaching a piezoresistive material by plating, vapor deposition or the like. A conductor pattern (not shown) is drawn from the piezoresistive element 78 to the outer surface of the MEMS acceleration sensor 74. A detection terminal (not shown) that is electrically connected to the conductor pattern is provided on the outer surface of the MEMS acceleration sensor 74.

  The MEMS acceleration sensor 74 is fixed to the measurement object so that the acceleration measurement direction of the measurement object matches the displacement direction of the movable weight 20. As the measurement object moves, the movable weight 20 is displaced upward or downward in FIG. As a result, the leaf spring 22 is deformed, and the resistance value of the piezoresistive element 78 changes. The measuring device connected to the detection terminal measures the change in the resistance value of the piezoresistive element 78 and measures the acceleration of the measurement object according to the measurement result.

  As described above, even when the piezoresistive element is used, the noise vibration of the movable weight due to the collision of gas molecules is reduced and the noise output from the MEMS acceleration sensor is reduced as in the case of using the capacitive electrode. The effect to reduce can be acquired. Here, the case where a movable weight having the same configuration as that of the movable weight 20 in FIG. 2 is used as the fifth embodiment, but it has the same configuration as each movable weight shown in FIGS. A movable weight can also be used.

  8A and 8B show a configuration of a MEMS acceleration sensor 80 according to the sixth embodiment. FIG. 8A shows a view of the sensor body 82 from above, and FIG. 8B shows a cross-sectional view when the MEMS acceleration sensor 80 is cut along a line AB. The same components as those in the MEMS acceleration sensor shown in FIGS. 1 to 7 are denoted by the same reference numerals and description thereof is omitted.

  In the sixth embodiment, glass such as Pyrex (registered trademark) or Tempax (registered trademark) is used as a basic member in addition to silicon. The movable weight 84 includes two disk-shaped silicon plates 86 and a weight glass 88 sandwiched between the two disk-shaped silicon plates 86. The movable weight 84 extends in a direction perpendicular to the upper disk surface and the lower disk surface, and penetrates the movable weight 84 from the center of the upper disk surface to the center of the lower disk surface. Is provided. The high density member hole 36 is filled with the high density member 34. The weight glass 88 and the disk-shaped silicon 86 can be bonded by an anodic bonding method. Since glass is generally poor in elasticity, it is preferable to use other materials as the material of the leaf spring 22. Therefore, in this embodiment, the disc-shaped silicon 86 and the plate spring 22 are integrally formed by overlapping the disc-shaped silicon 86 and the weight glass 88, and the plate spring 22 is formed of silicon. Accordingly, even when glass is used as the material of the movable weight 84, the movable weight 84 can be supported at a stable position in the frame of the sensor housing frame 18, and according to the movement of the measurement object. The movable weight 84 can be elastically displaced.

  FIG. 9 shows the characteristics when the high-density member filling rate [%] is plotted on the horizontal axis and the mass ratio [%] relative to the mass of silicon alone is plotted on the vertical axis as a design reference material. Here, the high-density member filling rate indicates a volume ratio of a portion replaced with a high-density member in the total volume of silicon. The characteristics shown in this figure can be used as a design index for increasing the mass while keeping the volume of the movable weight constant. Pt indicates the characteristics of platinum, W indicates the characteristics of tungsten, AuGe indicates the characteristics of gold germanium, and Ni indicates the characteristics of nickel. From FIG. 9, when the basic member is formed of silicon and the high-density member is formed of platinum, tungsten, gold germanium, or nickel, the mass under the condition of constant volume increases as the high-density member filling rate increases. It can be seen that can be increased. In addition, FIG. 10 shows the characteristics when the horizontal axis represents the high density member filling rate [%] as a design reference material and the vertical axis represents the volume ratio [%] to the volume of silicon alone under a constant mass condition. . The characteristics shown in this figure can be used as a design index for reducing the volume while keeping the mass of the movable weight constant. From FIG. 10, when the basic member is formed of silicon and the high-density member is formed of platinum, tungsten, gold germanium, or nickel, the volume under the condition of constant mass increases as the high-density member filling rate increases. It can be seen that can be reduced.

It is a disassembled perspective view of the MEMS acceleration sensor which concerns on 1st Embodiment. It is a figure which shows the MEMS acceleration sensor which concerns on 1st Embodiment. It is a figure which shows the MEMS acceleration sensor which concerns on the application example of 1st Embodiment. It is a figure which shows the MEMS acceleration sensor which concerns on 2nd Embodiment. It is a figure which shows the MEMS acceleration sensor which concerns on 3rd Embodiment. It is a figure which shows the MEMS acceleration sensor which concerns on 4th Embodiment. It is a figure which shows the MEMS acceleration sensor which concerns on 5th Embodiment. It is a figure which shows the MEMS acceleration sensor which concerns on 6th Embodiment. It is a figure which shows the relationship between the mass ratio with respect to the mass of a silicon simple substance, and a high-density member filling rate under fixed volume conditions. It is a figure which shows the relationship between the volume ratio with respect to the volume of a silicon simple substance, and a high-density member filling rate on mass constant conditions.

Explanation of symbols

  10, 38, 44, 46, 52, 58, 66, 74, 80 MEMS acceleration sensor, 12, 40, 48, 54, 60, 68, 76, 82 Sensor body, 14 Lower glass plate, 16 Upper glass plate , 18 Sensor housing frame, 20, 42, 50, 56, 62, 70, 84 Movable weight, 22 leaf spring, 24 lower capacitive electrode, 26 upper capacitive electrode, 28 lower terminal electrode, 30 upper terminal electrode, 32 Through hole, 34 high density member, 36 high density member hole, 72 basic member, 78 piezoresistive element, 86 disk-shaped silicon plate, 88 weight glass.

Claims (3)

In a MEMS acceleration sensor that includes a movable weight that can be displaced according to a given acceleration, and that outputs a detection amount according to the movement of the movable weight.
The movable weight is
A basic member having a defect,
A high-density member provided in the defect portion and having a higher density than the basic member;
Bei to give a,
The basic member is formed in a rotationally symmetric shape,
The MEMS acceleration sensor is
A support housing that supports the movable weight via a spring so that the movable weight is displaced in the rotationally symmetric axis direction of the basic member;
The spring includes a plurality of leaf springs provided so that the leaf surfaces overlap in parallel,
The support housing is
Supporting the movable weight via the plurality of leaf springs so that the movable weight can be displaced in a direction perpendicular to the plate surfaces of the plurality of leaf springs,
The MEMS acceleration sensor according to claim 1, wherein the center of gravity of the movable weight coincides with the center of gravity when the density of the material forming the movable weight is assumed to be uniform . In a MEMS acceleration sensor that includes a movable weight that can be displaced according to a given acceleration, and that outputs a detection amount according to the movement of the movable weight.
The movable weight is
A basic member having a defect,
A high-density member provided in the defect portion and having a higher density than the basic member;
With
The basic member is formed in a plate shape having a rotationally symmetric plate surface,
The MEMS acceleration sensor is
A support housing that supports the movable weight via a spring so that the movable weight is displaced in a rotationally symmetric axis direction perpendicular to the plate surface of the basic member;
The spring includes a plurality of leaf springs provided so that the leaf surfaces overlap in parallel,
The support housing is
Supporting the movable weight via the plurality of leaf springs so that the movable weight can be displaced in a direction perpendicular to the plate surfaces of the plurality of leaf springs,
The MEMS acceleration sensor is
The plate surface of the basic member and the plate surface thereof are opposed to each other, and includes a casing plate disposed with a space between the plate surface of the basic member,
The missing part is
An opening on the surface facing the housing plate;
The high-density member is
The MEMS acceleration sensor, wherein the defect portion is filled so that an unfilled space is formed on a surface facing the casing plate . The MEMS acceleration sensor according to claim 1 or 2 ,
The basic member is
Formed with silicon or glass,
The high-density member is
A MEMS acceleration sensor comprising any one of gold germanium, gold silicon, gold, platinum, iridium, nickel, copper, tungsten, or tantalum.

Images