The present disclosure relates to an angular velocity sensor element used for an angular velocity sensor, which is used in various kinds of electronic device.
A conventional angular velocity sensor element will hereinafter be described with reference to the drawings.
Each of fixed part 11, fixed part 13, detecting body 12, detecting body 14 and detecting body 15 is made of silicon (hereinafter referred to as Si). One end of detecting body 12 is connected to fixed part 11, and the other end of detecting body 12 is connected to fixed part 13. A detecting electrode (not shown) is provided on an upper surface of detecting body 12.
One end of detecting body 14 is connected to approximately a center of detecting body 12. Detecting body 14 is extending in a direction (the lateral direction in
One end of detecting body 15 is connected to approximately a center of detecting body 12. Detecting body 15 is extending in a direction (the lateral direction in
Driving body 16 is extending as a whole from the other end of detecting body 14 in an oblique direction of +45 degrees, which is a direction between the extending direction of detecting body 12 and the extending direction of detecting body 14. A driving electrode (not shown) is provided on an upper surface of driving body 16.
Driving body 17 is extending as a whole from the other end of detecting body 14 in an oblique direction of −45 degrees, which is a direction between the extending direction of detecting body 12 and the extending direction of detecting body 14. A driving electrode (not shown) is provided on an upper surface of driving body 17.
Driving body 18 is extending as a whole from the other end of detecting body 15 in an oblique direction of −45 degrees, which is a direction between the extending direction of detecting body 12 and the extending direction of detecting body 15. A driving electrode (not shown) is provided on an upper surface of driving body 18.
Driving body 19 is extending as a whole from the other end of detecting body 15 in an oblique direction of +45 degrees, which is a direction between the extending direction of detecting body 12 and the extending direction of detecting body 15. A driving electrode (not shown) is provided on an upper surface of driving body 19.
Next, operations of the conventional angular velocity sensor element configured as above will be described.
Here, such a case will be considered that an angular velocity around the Y-axis direction is generated on the angular velocity sensor element.
Application of an AC voltage to the driving electrode (not shown) provided on the upper surface of each of driving body 16, driving body 17, driving body 18 and driving body 19 causes a driving oscillation of each of driving body 16, driving body 17, driving body 18 and driving body 19 at velocity V in the X-axis direction. In this condition, each of driving body 16, driving body 17, driving body 18 and driving body 19 oscillates around the Y-axis due to the Coriolis force.
These oscillations cause detecting body 14 and detecting body 15 to twist, so that detecting body 12 bends on the side of fixed part 11 and on the side of fixed part 13 in opposite directions to each other.
As a result, an electric charge corresponding to the angular velocity is generated at the detecting electrode (not shown) provided on the upper surface of detecting body 12. The electric charge is amplified through a circuit pattern (not shown) to be detected as the angular velocity around the Y-axis.
A known prior art reference related to the present application is, for example, PTL 1.
PTL 1: International Patent Publication No. 2007/086337
An angular velocity sensor element of the present disclosure has a configuration as described below.
An angular velocity sensor element of the present disclosure includes: a fixed part; a first detecting body connected to the fixed part and extending in a first direction, the first detecting body being provided with a first detecting electrode; a second detecting body connected at one end to the first detecting body and extending in a second direction approximately perpendicular to the first direction, the second detecting body being provided with a second detecting electrode; and a driving body connected to the other end of the second detecting body and disposed on a plane on which the first detecting body and the second detecting body are disposed, the driving body being provided with a driving electrode. The driving body has a folded shape with two or more bent portions such that a direction from a connecting portion of the second detecting body and the driving body to an end of the driving body is between the first direction and the second direction in a top view.
Before describing the present exemplary embodiment, a problem of the conventional angular velocity sensor element the inventor(s) found will be described.
First, referring to the conventional angular velocity sensor element shown in
In Formula 1, λ denotes a constant, l denotes a length of a driving oscillation body [m], E denotes a longitudinal elastic modulus [Pa], I denotes a moment of inertia of the driving oscillation body [m4], p denotes a density of the driving oscillation body [Kg/m3], A denotes a sectional area of the driving oscillation body [m2], and S denotes an area in an extending direction of a driving body [m2].
When specific values are assigned to the variables in Formula 1 as λ=1.87, 1=1.05×10−3 [m], E=1.66×1011 [Pa], I=1.55×10−22 [m4], p=2.33 [Kg/m3], A=5.16×10−11, and f=7.35×105 [Hz], an area S in the extending direction of each of driving bodies 16, 17, 18, 19 becomes as S=5.56×10−7 [m2].
The angular velocity sensor element shown in
Next, an angular velocity sensor element in accordance with an exemplary embodiment of the present disclosure will be described with reference to the drawings.
Each of
Description will be made with reference to
Detecting body 57 is made of Si. One end of detecting body 57 is connected to fixed part 51. Detecting electrode 58 and detecting electrode 59 are provided on an upper surface of detecting body 57.
Formed below detecting electrode 58 are, for example, a common ground (GND) electrode (not shown) made of an alloy thin film composed of Pt and Ti, and a piezoelectric layer (not shown) made of a PZT (lead zirconate titanate) thin film provided on an upper surface of the common GND electrode (not shown). That is, detecting electrode 58 is provided on the upper surface of detecting body 57 through the common GND electrode and the piezoelectric layer.
Fixed part 60 is made of Si. Fixed part 60 is connected to the other end of detecting body 57. Detecting electrode land 61, detecting electrode land 62 and monitoring electrode land 63 are provided on an upper surface of fixed part 60.
Detecting electrode 58 formed on detecting body 57 is electrically connected to detecting electrode land 54 formed on fixed part 51. Detecting electrode 59 formed on detecting body 57 is electrically connected to detecting electrode land 61 formed on fixed part 60.
Detecting body 64 is made of Si. One end of detecting body 64 is connected to approximately a center of detecting body 57. Detecting body 64 is extending from approximately the center of detecting body 57 in a direction (the rightward direction in
Detecting body 66 is made of Si. One end of detecting body 66 is connected to approximately the center of detecting body 57. Detecting body 66 is extending from approximately the center of detecting body 57 in a direction (the leftward direction in
Detecting electrode 67 formed on detecting body 66 is electrically connected to detecting electrode land 62 formed on fixed part 60.
Driving body 68 is made of Si. Supposing that a direction in which driving body 68 is extending as a whole is defined as a direction from a center of the other end of detecting body 64 to a center of one end of driving body 68, the direction in which driving body 68 is extending as a whole becomes “DIRECTION A” indicated by an arrow in
Driving body 68 is configured to have a folded shape by a combination of driving part 69 extending in the same direction as the extending direction of detecting body 57 and driving part 70 extending in the same direction as the extending direction of detecting body 64. Although plural driving parts 69 and plural driving parts 70 are formed, only a part of the driving parts is indicated by reference marks in
By a combination of driving part 69 extending in the X-axis direction and driving part 70 extending in the Y-axis direction, driving body 68 includes plural bent portions 100 (shown in
A pair of driving electrodes 71 is provided on an upper surface of driving body 68.
Here, details of driving electrodes 71 will be described with reference to
As described above, an angular velocity sensor element in accordance with the present exemplary embodiment includes: fixed part 51; detecting body 57 connected to fixed part 51, provided with detecting electrode 58, and extending in the X-axis direction; detecting body 64 connected at one end to detecting body 57, extending in the Y-axis direction approximately perpendicular to the X-axis direction, and provided with detecting electrode 65; and driving body 68 connected to the other end of detecting body 64, disposed on a plane on which detecting body 57 and detecting body 64 are disposed, and provided with driving electrode 71. In addition, driving body 68 has a folded shape with two or more bent portions 100. Further, a direction from a connecting portion of detecting body 64 and driving body 68 to an end of driving body 68 is between the X-axis direction and the Y-axis direction in a top view (DIRECTION A).
According to this configuration, driving body 68 is extending in a direction which is different from the extending direction of detecting body 57 (the X-axis direction) and the extending direction of detecting body 64 (the Y-axis direction). Accordingly, it is possible to detect angular velocities in biaxial directions by an oscillation of driving body 68. In addition, since driving body 68 in accordance with the present exemplary embodiment has a folded shape, the driving frequency of the driving body may be low, and it is possible to provide a small-size angular velocity sensor element.
In the angular velocity sensor element in accordance with the present exemplary embodiment, driving body 68 may preferably have driving part 69 extending in the X-axis direction, which is the extending direction of detecting body 57, and driving part 70 extending in the Y-axis direction, which is the extending direction of detecting body 64. Driving electrode 71 is provided on each of driving part 69 and driving part 70.
According to this configuration, it is possible by driving part 69 to drive the angular velocity sensor element to oscillate in a direction (the Y-axis direction) perpendicular to the extending direction of driving part 69 (the X-axis direction). Also, it is possible by driving part 70 to drive the angular velocity sensor element to oscillate in a direction (the X-axis direction) perpendicular to the extending direction of driving part 70 (the Y-axis direction). This makes it possible to improve the output sensitivity of angular velocity detection signals in biaxial directions.
Preferably, the angular velocity sensor element in accordance with the present exemplary embodiment may further include weight part 74. Weight part 74 is connected to an end of driving body 68.
According to this configuration, increase in the mass of the angular velocity sensor element due to weight part 74 increases the Coriolis force generated by the angular velocity. Accordingly, it is possible to improve the sensitivity of angular velocity detection signals in biaxial directions.
Next, a result of an oscillation analysis of driving body 68 and weight part 74 will be described.
A result of an oscillation analysis of driving body 68 and weight part 74 by Finite Element Analysis (FEA) will be described.
First, a driving frequency will be calculated in the case of the conventional angular velocity sensor element described with reference to
On the other hand, to achieve the required driving frequency in the case of the angular velocity sensor element in accordance with one exemplary embodiment of the present disclosure, as shown in
In other words, in the angular velocity sensor element in accordance with the present exemplary embodiment, driving body 68 is extending in the direction which is different from both the extending direction of detecting body 57 and the extending direction of detecting body 64. Accordingly, it is possible by the oscillation of driving body 68 to perform detection by the angular velocity sensor in bidirectional directions. Also, since driving body 68 has a folded shape, it is possible to lower the driving frequency of driving body 68 and to make the angular velocity sensor element small-sized.
Hereinabove, driving body 68 at the upper right in
Hereinafter, configurations of driving body 75, driving body 80 and driving body 85 will be sequentially described. However, since each of them is the same in configuration as driving body 68, the description on them will be partly omitted.
Driving body 75 is made of Si, and is extending as a whole from the other end of detecting body 64 in a direction between the extending direction of detecting body 57 and the extending direction of detecting body 64. In other words, driving body 75 is extending in the direction of −α degrees.
Driving part 76 of driving body 75 is extending in the same direction as the extending direction of detecting body 57. Further, driving part 77 is extending in the same direction as the extending direction of detecting body 64. Driving body 75 is configured in a folded shape formed by combining plural driving parts 69 extending in the X-axis direction and second driving parts 77 extending in the Y-axis direction.
Although plural driving parts 76 and plural driving parts 77 are formed, only a part of them is indicated by reference marks in
A pair of driving electrodes 78 is provided on an upper surface of driving body 75. Driving electrodes 78 are formed to be the same in configuration as driving electrodes 71 which have been described with reference to
Driving body 80 is made of Si, and is extending as a whole from the other end of detecting body 66 in a direction between the extending direction of detecting body 57 and the extending direction of detecting body 66. In other words, driving body 80 is extending in the direction of −α degrees.
Driving part 81 of driving body 80 is extending in the same direction as the extending direction of detecting body 57. Further, driving part 82 is extending in the same direction as the extending direction of detecting body 66. Driving body 80 is configured in a folded shape formed by combining plural driving parts 81 extending in the X-axis direction and plural driving parts 82 extending in the Y-axis direction.
Although plural driving parts 81 and plural driving parts 82 are formed, only a part of them is indicated by reference marks in
A pair of driving electrodes 83 is provided on an upper surface of driving body 80. Driving electrodes 83 are formed to be the same in configuration as driving electrodes 71 which have been described with reference to
Driving body 85 is made of Si, and is extending as a whole from the other end of detecting body 66 in a direction between the extending direction of detecting body 57 and the extending direction of detecting body 66. In other words, driving body 85 is extending in the direction of +α degrees.
Driving part 86 of driving body 85 is extending in the same direction as the extending direction of detecting body 57. Further, driving part 87 is extending in the same direction as the extending direction of detecting body 66. Driving body 85 is configured in a folded shape formed by combining plural driving parts 86 extending in the X-axis direction and plural driving parts 87 extending in the Y-axis direction.
Although plural driving parts 86 and plural driving parts 87 are formed, only a part of them is indicated by reference marks in
A pair of driving electrodes 88 is provided on an upper surface of driving body 85. Driving electrodes 88 are formed to be the same in configuration as driving electrodes 71 which have been described with reference to
As described above, driving bodies 68, 75, 80, 85 are the same in configuration. Since the angular velocity sensor element in accordance with the present exemplary embodiment has four driving bodies 68, 75, 80, 85, it is possible to largely reduce the volume of the entire angular velocity sensor element compared to the conventional angular velocity sensor element.
Monitoring electrode 91 is provided at each of a portion between driving electrode 71 and driving electrode 78 and a portion between driving electrode 83 and driving electrode 88. Formed below monitoring electrode 91 are, for example, a common GND electrode (not shown) made of an alloy thin film composed of Pt and Ti, and a piezoelectric layer (not shown) made of a PZT thin film provided on an upper surface of the common GND electrode (not shown). That is, monitoring electrode 91 is provided on an upper surface of driving body 68 or driving body 75 through the common GND electrode and the piezoelectric layer.
Next, a method of assembling the angular velocity sensor element in accordance with the present exemplary embodiment will be described with reference to
First, as shown in
Next, the upper surface of wafer 92 is coated with resist film 93 made, for example, of aluminum, titanium, silicon oxide or silicon nitride by spin coating.
Then, as shown in
Next, wafer 92 is set in a dry etching machine (not shown). Then wafer 92 made of Si is etched at the parts other than the parts on which resist film 93 has been formed by introducing a fluorinated gas such, for example, as SF6 or CF6 to form grooves 94 as shown in
Next, as shown in
Next, the back surface of wafer 92 is ground by rotating back grinding wheel 96 as shown in
Next, film 95 is irradiated by an ultraviolet (UV) ray to reduce the adhesive strength of film 95, and to cause film 95 to be peeled off from the lower surface of resist film 93. Finally, resist film 93 is removed, and individual angular velocity sensor elements are taken out from wafer 92.
Next, operations of the angular velocity sensor element in accordance with the present exemplary embodiment will be described with reference to
First, an alternating current (AC) voltage is applied to driving electrode land 52 (not shown in
On the other hand, a compressive stress is generated in a case where the direction of the polarized crystallographic axis of driving electrode 88 is opposite to the direction in which electric charges are flown in driving electrode 88.
Accordingly, each of driving body 68, driving body 75, driving body 80 and driving body 85 causes a driving oscillation at velocity V in each of the X-axis direction and the Y-axis direction depending on the phase of the AC voltage. This driving oscillation propagates to each of weight part 74, weight part 79, weight part 84 and weight part 89, so that each of driving body 68, driving body 75, driving body 80 and driving body 85 causes the driving oscillation at velocity V in each of the X-axis direction and the Y-axis direction as shown in
Next, description will be made on a case in which an angular velocity around the X-axis is generated on the angular velocity sensor element with reference to
As shown in
Aa a result, an electric charge corresponding to the angular velocity is generated at detecting electrode 65 provided on detecting body 64, and is output to detecting electrode land 55 provided on fixed part 51 through a circuit pattern (not shown).
Also, an electric charge corresponding to the angular velocity is generated at detecting electrode 67 provided on detecting body 66, and is output to detecting electrode land 62 provided on fixed part 60 through a circuit pattern (not shown).
The electric charges output to detecting electrode land 55 and detecting electrode land 62 are converted to voltages, and these electric charges are amplified. Then, a difference between the amplified electric charges is taken to detect the angular velocity around the X-axis.
Next, description will be made on a case in which an angular velocity around the Y-axis is generated on the angular velocity sensor element with reference to
As shown in
Aa a result, an electric charge corresponding to the angular velocity is generated at detecting electrode 58 provided on detecting body 57, and is output to detecting electrode land 54 provided on fixed part 51 through a circuit pattern (not shown).
Also, an electric charge corresponding to the angular velocity is generated at detecting electrode 59 provided on detecting body 57, and is output to detecting electrode land 61 provided on fixed part 60 through a circuit pattern (not shown).
The electric charges output to detecting electrode land 54 and detecting electrode land 61 are converted to voltages, and these electric charges are amplified. Then, a difference between the amplified electric charges is taken to detect the angular velocity around the Y-axis.
Particularly, the angular velocity sensor element in accordance with the present exemplary embodiment is configured such that driving body 68 is configured by driving part 69 approximately parallel to detecting body 57 and driving part 70 approximately parallel to detecting body 64, and that driving electrodes 71 are provided on both of driving part 69 and driving part 70. According to this configuration, driving electrodes 71 provided on both of driving part 69 and driving part 70 allow driving part 69 to cause a driving oscillation in a direction perpendicular to the extending direction of driving part 69, and allow driving part 70 to cause a driving oscillation in a direction perpendicular to the extending direction of driving part 70. Accordingly, it is possible to improve the sensitivity of the angular velocity detection signals in biaxial directions.
Although weights 74, 79, 84, 89 are formed in the angular velocity sensor element in accordance with the present exemplary embodiment, the weights may not necessarily be formed.
Although driving body 68, for example, is configured by combining driving part 69 extending in the X-axis direction and driving part 70 extending in the Y-axis direction, driving body 68 may be configured by combining driving parts that are extending in oblique directions. Each of the driving parts configuring driving body 68 may not necessarily be extending only in the X-axis direction or the Y-axis direction. Driving body 68 may as a whole be extending in a direction between the X-axis direction and the Y-axis direction. Much the same is true on other driving bodies 75, 80, 85.
Although driving body 68 in accordance with the present exemplary embodiment has four bent portions 100, driving body 68 may not necessarily have four bent portions 100. Driving body 68 may have at least two bent portions 100 to form a folded shape. Much the same is true on other driving bodies 75, 80, 85.
According to the present disclosure, it is possible to provide an angular velocity sensor element that is driven at a low driving frequency of the driving body and small in size. Particularly, the present disclosure is useful as an angular velocity sensor element used for angular velocity sensors which are employed in various kinds of electronic device.
Number | Date | Country | Kind |
---|---|---|---|
2014-176829 | Sep 2014 | JP | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/JP2015/004247 | 8/25/2015 | WO | 00 |