阅读说明：本技术 具有集成阻尼结构的惯性传感器 (Inertial sensor with integrated damping structure ) 是由 汤俊 于 2020-09-11 设计创作，主要内容包括：一种惯性传感器包括与基板的表面间隔开的可移动质量块。所述可移动质量块适用于响应于在垂直于所述基板的所述表面的第一方向上施加在所述可移动质量块上的第一力而围绕位于所述可移动质量块的第一与第二端之间的旋转轴运动。所述惯性传感器另外包括阻尼系统,所述阻尼系统被配置成限制所述可移动质量块在垂直于所述第一方向的第二方向上的运动。所述阻尼系统包括联接到所述可移动质量块的第一阻尼结构；邻近所述第一阻尼结构的第二阻尼结构,所述第一和第二阻尼结构与所述基板的所述表面间隔开；以及在所述可移动质量块与所述第二阻尼结构之间互连的弹簧结构。(An inertial sensor includes a movable mass spaced apart from a surface of a substrate. The movable mass is adapted to move about an axis of rotation located between first and second ends of the movable mass in response to a first force exerted on the movable mass in a first direction perpendicular to the surface of the substrate. The inertial sensor additionally includes a damping system configured to limit motion of the movable mass in a second direction perpendicular to the first direction. The damping system comprises a first damping structure coupled to the movable mass; a second damping structure adjacent to the first damping structure, the first and second damping structures being spaced apart from the surface of the substrate; and a spring structure interconnected between the movable mass and the second damping structure.)

1. An inertial sensor, comprising:

a substrate;

a movable mass spaced from a surface of the substrate, the movable mass adapted to move about an axis of rotation located between first and second ends of the movable mass in response to a first force exerted on the movable mass in a first direction perpendicular to the surface of the substrate; and

a damping system configured to limit motion of the movable mass in a second direction perpendicular to the first direction, the damping system comprising:

a first damping structure coupled to the movable mass;

a second damping structure adjacent to the first damping structure, the first and second damping structures being spaced apart from the surface of the substrate; and

a spring structure interconnected between the movable mass and the second damping structure.

2. An inertial sensor according to claim 1, characterised in that the movable mass comprises a first portion between the rotational axis and the first end and a second portion between the rotational axis and the second end, wherein the mass of the second portion is greater than the mass of the first portion and the damping system is located in the second portion.

3. An inertial sensor according to claim 2, characterised in that the first and second damping structures of the damping system are configured to cause the second part of the movable mass to have a greater mass relative to the first part of the movable mass.

4. The inertial sensor of claim 1, further comprising at least one travel stop coupled to the surface of the substrate proximate the movable mass, and the damping system is configured to reduce a contact force between the movable mass and the at least one travel stop in response to restricting movement of the movable mass in the second direction.

5. An inertial sensor according to claim 1, wherein the first and second damping structures are spaced apart by a gas-containing gap having a predetermined width, the second damping structure is configured to be immovable relative to the first damping structure in response to a second force exerted on the movable mass in the second direction, the first damping structure is configured to move with the movable mass in response to the second force, and the width of the gap decreases as the first damping structure moves in the second direction, thereby causing the gas in the gap to be squeezed.

6. An inertial sensor according to claim 1, characterized in that it additionally comprises:

a plurality of first damping structures coupled to and extending from the second end of the movable mass, the first damping structure being one of the plurality of first damping structures;

a plurality of second damping structures interleaved with the plurality of first damping structures, the second damping structure being one of the plurality of second damping structures.

7. An inertial sensor according to claim 6, characterized in that:

a first spring end of the spring structure is coupled to the second end of the movable mass; and is

The inertial sensor additionally includes a beam member spaced from the surface of the substrate, the beam member displaced from the second end of the movable mass, wherein a second spring end of the spring structure is coupled to the beam member and the plurality of second damping structures are coupled to the beam member and extend from the beam member toward the second end of the movable mass.

8. An inertial sensor according to claim 7, wherein:

the axis of rotation is parallel to the surface of the substrate;

the beam member has a longitudinal dimension between first and second beam ends of the beam member parallel to the axis of rotation; and is

The inertial sensor additionally includes first and second damping stops coupled to the surface of the substrate and located proximate respective ones of the first and second beam ends.

9. An inertial sensor, comprising:

a substrate;

a movable proof mass spaced apart from a surface of the substrate, the movable proof mass adapted to move about a rotational axis between first and second ends of the movable proof mass in response to a first force exerted on the movable proof mass in a first direction perpendicular to the surface of the substrate, the movable proof mass comprising a first portion between the rotational axis and the first end and a second portion between the rotational axis and the second end, wherein a mass of the second portion is greater than a mass of the first portion; and

a damping system located at the second portion, the damping system configured to limit movement of the movable mass in a second direction perpendicular to the first direction, the damping system comprising:

a plurality of first damping structures coupled to the movable mass;

a plurality of second damping structures interleaved with the plurality of first damping structures, the first and second damping structures being spaced apart from the surface of the substrate; and

a spring structure interconnected between the movable mass and the second damping structure.

10. An inertial sensor, comprising:

a substrate;

a movable proof mass spaced apart from a surface of the substrate, the movable proof mass adapted to move about a rotational axis between first and second ends of the movable proof mass in response to a first force exerted on the movable proof mass in a first direction perpendicular to the surface of the substrate, the movable proof mass comprising a first portion between the rotational axis and the first end and a second portion between the rotational axis and the second end, wherein a mass of the second portion is greater than a mass of the first portion; and

a damping system located at the second portion, the damping system configured to limit movement of the movable mass in a second direction perpendicular to the first direction, the damping system comprising:

a first damping structure coupled to the movable mass;

a second damping structure adjacent to the first damping structure, the first and second damping structures being spaced apart from the surface of the substrate; and

a spring structure interconnected between the movable mass and the second damping structure, wherein the first and second damping structures are spaced apart by a gas-containing gap having a predetermined width, the second damping structure is configured to be immovable relative to the first damping structure in response to a second force exerted on the movable mass in the second direction, the first damping structure is configured to move with the movable mass in response to the second force, and the width of the gap decreases as the first damping structure moves in the second direction, thereby causing gas in the gap to be squeezed.

Technical Field

The present invention relates generally to micro-electromechanical system (MEMS) inertial sensors. More particularly, the present invention relates to inertial sensors with integrated damping structures.

Background

Microelectromechanical Systems (MEMS) sensors are widely used in applications such as automotive, inertial guidance systems, household appliances, protection systems for various devices, and many other industrial, scientific, and engineering systems. Such MEMS sensors are used to sense physical conditions such as acceleration, pressure, angular rotation, or temperature, and provide electrical signals representative of the sensed physical conditions.

Capacitive sensing MEMS inertial sensor designs are highly desirable for operation in both acceleration and angular rotation environments, as well as in miniaturized devices, due at least in part to the relatively low cost of the sensors. Capacitive accelerometers sense changes in capacitance with respect to acceleration to change the output of a powered circuit. One common form of accelerometer is a two-layer capacitive sensor having a "teeter-totter/se saw" configuration. This common sensor type uses a movable mass or plate that rotates over a substrate under Z-axis acceleration. The accelerometer structure can measure two different capacitances to determine a differential capacitance or a relative capacitance.

Disclosure of Invention

Aspects of the disclosure are defined in the appended claims.

In a first aspect, there is provided an inertial sensor comprising: a substrate; a movable mass spaced from a surface of the substrate, the movable mass adapted to move about an axis of rotation located between first and second ends of the movable mass in response to a first force exerted on the movable mass in a first direction perpendicular to the surface of the substrate; and a damping system configured to limit movement of the movable mass in a second direction perpendicular to the first direction. The damping system includes: a first damping structure coupled to the movable mass; a second damping structure adjacent to the first damping structure, the first and second damping structures being spaced apart from the surface of the substrate; and a spring structure interconnected between the movable mass and the second damping structure.

In a second aspect, there is provided an inertial sensor comprising: a substrate; a movable proof mass spaced apart from a surface of the substrate, the movable proof mass adapted to move about a rotational axis between first and second ends of the movable proof mass in response to a first force exerted on the movable proof mass in a first direction perpendicular to the surface of the substrate, the movable proof mass comprising a first portion between the rotational axis and the first end and a second portion between the rotational axis and the second end, wherein a mass of the second portion is greater than a mass of the first portion; and a damping system located at the second portion, the damping system configured to limit movement of the movable mass in a second direction perpendicular to the first direction. The damping system includes: a plurality of first damping structures coupled to the movable mass; a plurality of second damping structures interleaved with the plurality of first damping structures, the first and second damping structures being spaced apart from the surface of the substrate; and a spring structure interconnected between the movable mass and the second damping structure.

In a third aspect, there is provided an inertial sensor comprising: a substrate; a movable proof mass spaced apart from a surface of the substrate, the movable proof mass adapted to move about a rotational axis between first and second ends of the movable proof mass in response to a first force exerted on the movable proof mass in a first direction perpendicular to the surface of the substrate, the movable proof mass comprising a first portion between the rotational axis and the first end and a second portion between the rotational axis and the second end, wherein a mass of the second portion is greater than a mass of the first portion; and a damping system located at the second portion and configured to restrict movement of the movable mass in a second direction perpendicular to the first direction. The damping system includes: a first damping structure coupled to the movable mass; a second damping structure adjacent to the first damping structure, the first and second damping structures being spaced apart from the surface of the substrate; and a spring structure interconnected between the movable mass and the second damping structure, wherein the first and second damping structures are spaced apart by a gas-containing gap having a predetermined width, the second damping structure is configured to be immovable relative to the first damping structure in response to a second force exerted on the movable mass in the second direction, the first damping structure is configured to move with the movable mass in response to the second force, and the width of the gap decreases as the first damping structure moves in the second direction, thereby causing gas in the gap to be squeezed.

Drawings

The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which are not necessarily to scale and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.

FIG. 1 illustrates a plan view of a micro-electro-mechanical system (MEMS) inertial sensor, according to an embodiment;

FIG. 2 shows a side view of the inertial sensor of FIG. 1;

fig. 3 shows a plan view of the inertial sensor of fig. 1 when subjected to a force in a direction perpendicular to the sensing direction of the inertial sensor.

FIG. 4 illustrates a partial enlarged plan view of the inertial sensor of FIG. 1;

FIG. 5 shows a partially enlarged plan view corresponding to the view of FIG. 4 when subjected to a force in a direction perpendicular to the sensing direction;

FIG. 6 shows a plan view of an inertial sensor according to another embodiment; and is

FIG. 7 illustrates a plan view of an inertial sensor according to yet another embodiment.

Detailed Description

In general, embodiments disclosed herein require micro-electromechanical system (MEMS) inertial sensors with integrated damping structures to improve sensitivity and reliability with small form factors required for various functions. More specifically, the Z-axis teeter-totter inertial sensor includes a damping structure that is capable of effectively damping in-plane parasitic modes with little effect on the area of the movable mass. Although an inertial sensor in the form of an accelerometer is described herein, it is understood that the damping structure may be adapted for use with other inertial sensors to achieve improved sensitivity and/or reliability.

The present disclosure is provided to further explain in an enabling fashion at least one embodiment in accordance with the present invention. The disclosure is further offered to enhance an understanding and appreciation for the inventive principles and advantages thereof, rather than to limit in any manner the invention. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.

It is understood that the use of relational terms, if any, such as first and second, top and bottom, and the like are used solely to distinguish one from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. In addition, some of the figures may be illustrated using various shading and/or shading to distinguish different elements produced within various structural layers. These various elements within the structural layer may be created using current and upcoming microfabrication techniques such as deposition, patterning, etching, etc. Thus, while different shading and/or hatching is utilized in the illustration, different elements within a structural layer may be formed of the same material.

Referring to fig. 1-2, fig. 1 shows a plan view of a MEMS inertial sensor 20 according to an embodiment, and fig. 2 shows a side view of the inertial sensor 20. The inertial sensor 20 in the form of an accelerometer is configured as a "teeter-totter" type inertial sensor. Accordingly, the inertial sensor 20 is referred to herein as an accelerometer 20. By convention, accelerometer 20 is shown as having a generally planar structure in the X-Y plane, where X-axis 22 points to the left and right in FIG. 1, Y-axis 24 points up and down in FIG. 1, and Z-axis 26 points out of the page (perpendicular to X-axis 22 and Y-axis 24) in FIG. 1. Accordingly, a three-dimensional coordinate system is presented in the side view illustration of FIG. 2, with the X-axis 22 pointing left and right on the page, the Z-axis 26 pointing up and down on the page, and the Y-axis 24 pointing out of the page. In general, the accelerometer 20 is adapted to sense Z-axis acceleration, represented by arrow 28 in FIG. 2, while damping parasitic motion in the X-Y plane.

The accelerometer 20 includes a substrate 30 having a substantially planar surface 32. Electrode elements 34, 36 (see fig. 2) and suspension anchors 38 are formed on surface 32 of substrate 20. The movable mass 40 is spaced from the surface 32 of the substrate 30. More specifically, accelerometer 20 includes suspension springs 42, 44 interconnecting movable mass 40 with suspension anchors 38 such that movable mass 40 is suspended above substrate 30. Suspended anchor 38 is substantially centered within opening 46 along an axis of rotation 48 of movable mass 40, wherein axis of rotation 48 is located between a first end 50 and a second end 52 of movable mass 40.

For consistency throughout the description of the following figures, any structure, such as a suspension anchor 38, that is directly connected to the surface 32 of the substrate 30 or formed on the surface 32 of the substrate 30 is shown having an "X" passing therethrough. Elements suspended above the surface 32 of the substrate 30 are shown with narrow hatching lines down and to the right. The spring structure suspended above the surface 32 is generally indicated by a solid line.

Movable mass 40 includes a first portion 54 between rotational axis 48 and first end 50 and a second portion 56 between rotational axis 48 and second end 52. The movable mass 40 is adapted to rotate about an axis of rotation 48 in response to a first force (e.g., Z-axis acceleration 28) exerted on the movable mass 40 in a first direction perpendicular to the surface 32 of the substrate 30 (e.g., parallel to the Z-axis 26). When intended for use as a seesaw-type accelerometer, the second portion 56 of the movable mass 40 may be formed to have a relatively larger mass than the first portion 54 of the movable mass 40. Generally, a greater mass of the second portion 56 may be created by offsetting the axis of rotation 48 such that the second portion 56 is longer than the first portion 54. In other configurations, this mass difference may be achieved by adding mass to the second portion 56 relative to the first portion 54, by removing mass from the first portion 54 relative to the second portion 56, and so forth. However, in embodiments, the greater mass of the second portion 56 may be achieved at least in part by adding mass in the form of a damping system formed at the second end 52 of the movable mass 40 and suspended above the surface 32 of the base plate 30.

In a seesaw-type inertial sensor design, it is difficult to eliminate in-plane parasitic motion of the movable mass. The in-plane parasitic motion may be pivotal in a direction parallel to Y-axis 24 and/or in a direction parallel to X-axis 22 and/or in a plane about Z-axis 26. In-plane parasitic motions are typically under-damped due to the high Q factor and relatively heavy movable mass. The Q factor is a dimensionless parameter that describes the degree to which the oscillator may be underdamped. A higher Q factor indicates a lower rate of energy loss (i.e., oscillations die out more slowly) relative to the stored energy of the oscillator. Thus, under an in-plane high-g impact event, especially when the high-g impact is close to the formant of the movable mass, the movable mass may strike the travel stop or stop frame at high speed and large contact force. Such high g-impacts can damage the movable mass and/or the travel stop or stop frame. Disadvantageously, during assembly or in field applications, it may be difficult to avoid high g-impacts that cause damage.

Different approaches have been used to avoid this problem. For example, fixed damping fingers have been implemented to reduce or limit oscillations due to the effects of high-g shock events. Such damping fingers are coupled to a surface of the substrate and may be located within an opening extending through the movable mass. Damping occurs by the squeeze film effect, wherein gas present between the fixed damping fingers and the openings in the movable mass is squeezed as the movable mass translates in response to in-plane parasitic motion. In such a configuration, significant damping can be achieved by adding sufficient fixed damping fingers. However, the opening extending through the movable mass consumes area of the movable mass. In fact, the area consumption of the movable mass is greater in response to higher damping requirements. As the area of the movable mass is reduced, the actual mass or weight of the movable mass is correspondingly reduced. Therefore, the sensitivity of the inertial sensor may be reduced accordingly. Alternatively, a larger die size may be required to achieve the desired sensitivity, as opposed to the goal of minimizing die size.

Another approach is to tune the parasitic motion to frequencies to which the inertial sensor is less likely to be exposed. This approach requires a predefined "safe zone" as a design goal. However, this approach may not be feasible for many inertial sensors because the predefined "safe zone" is difficult to define. Furthermore, steering to spurious modes can be a challenge to maintain high sensitivity performance. The embodiments described herein require suspended movable damping fingers (instead of the fixed damping fingers discussed above) that greatly improve damping while having little effect on the area of the movable element.

Accordingly, accelerometer 20 additionally includes a damping system 58, which damping system 58 is configured to limit movement of movable mass 40 in a direction perpendicular to Z-axis 26. In the example of fig. 1-2, damping system 58 is configured to limit the movement of movable mass 40 in response to parasitic forces parallel to Y-axis 24. A damping system 58 is suspended above the surface 32 of the substrate and is located at the second portion 56 of the movable mass 40. In addition, the damping system 58 facilitates a greater mass of the second portion 56 relative to the first portion 54, as will be discussed in greater detail below. The accelerometer 20 additionally includes at least one travel stop 60 (six shown) coupled to the surface 32 of the base plate 30 or otherwise formed on the surface 32 of the base plate 30. As will be discussed further below, damping system 58 is configured to reduce a contact force between movable mass 40 and travel stop 60 in response to limiting movement of movable mass 40. Although travel stops 60 are shown as separate structures, in other embodiments, a single travel stop may be configured to surround the frame structure of movable mass 40 and damping system 58.

The damping system 58 includes a plurality of first damping structures 62, a plurality of second damping structures 64, and one or more spring structures 66 (two shown) interconnected between the movable mass 40 and the second damping structures 62. Each of the first and second damping structures 62, 64 is in a comb-like configuration such that the second damping structure 64 is generally interleaved with the first damping structure 62.

A first damping structure 62 is coupled to the second end 52 of the movable mass 40 and extends from the second end 52 of the movable mass 40. In addition, each spring structure 66 includes a first spring end 68 extending from second end 52 of movable mass 40. The beam member 70 is spaced from the surface 32 of the substrate 30 and is laterally displaced from the second end 52 of the movable mass 40. The second spring end 72 of the spring structure 66 is coupled to the beam member 70. In addition, a second damping structure 64 is coupled to beam member 70 and extends from beam member 70 towards the second end of movable mass 40. Thus, the spring structure 66 together with the beam element 70 suspends the second damping structure 64 from the movable mass 40 above the surface 32 of the substrate 30.

In general, a greater mass of second portion 56 of movable mass 40 relative to first portion 54 of movable mass 40 is important to produce a seesaw motion of movable mass 40 under Z-axis acceleration 28. The second portion 54 includes two arrays of damping structures. An array of damping structures, such as the first damping structure 62, is directly connected to the movable mass 40. While another array of damping structures, for example a second damping structure 64, is connected to the movable mass 40 via a spring structure 66. Thus, both the first and second damping structures 62, 64 cause the mass of the second portion 54 of the movable mass 40 to provide a greater moment under the Z-axis acceleration 28, and thus a greater sensitivity to the Z-axis acceleration 28.

The axis of rotation 48 is substantially parallel to the surface 32 of the substrate 30, and in this configuration, the axis of rotation 48 is parallel to the Y-axis 26. The beam member 70 has a longitudinal dimension 74 (e.g., length) between first and second beam ends 76, 78 of the beam member 70, wherein the longitudinal dimension 74 is parallel to the rotational axis 48. That is, the beam member 70 is aligned with the Y-axis 24. The accelerometer 20 additionally includes first and second damper stops 80, 82, the first and second damper stops 80, 82 being coupled to the surface 32 of the base plate and located near respective ones of the first and second beam ends 76, 78.

Referring now to fig. 3, fig. 3 shows a plan view of the inertial sensor 20 when subjected to a force in a direction perpendicular to the sensing direction of the inertial sensor 20. In this case, the force may be a high-g impact event represented by arrow 84 generally parallel to the Y-axis 24. This force is referred to herein as the Y-axis acceleration 84, labeled AY. Y-axis acceleration 84 is exerted on movable mass 40 in a direction parallel to Y-axis 24, thereby causing in-plane parasitic motion of movable mass 40.

In response to a high g Y axis acceleration 84 parallel to the Y-axis 24, the movable mass 40, along with the first and second damping structures 62, 64 of the damping system 58, can undergo in-plane torsional motion (i.e., pivotal motion about the Z-axis 26). For example, the positive Y-axis force 84 causes the Z-axis 26 to rotate such that the second portion 56 of the movable mass 40 having the greater mass translates in an opposite direction, such as the negative Y-direction. The movable mass 40 moves along with the first and second damping structures 62, 64 until one of the first and second beam ends 76, 78 contacts a corresponding one of the damping stops 80, 82. That is, there is no damping effect until either of the first and second beam ends 76, 78 contacts a corresponding one of the damping stops 80, 82. However, once one of the first and second beam ends 76, 78 contacts a corresponding one of the damping stops 80, 82, the second damping structure 64 becomes immovable relative to the first damping structure 62. That is, the spring structure 66 is suitably curved such that the first damping structure 62 may continue to move along with the movable mass 40. In this manner, the gap between the first and second damping structures 62, 64 is reduced. Such relative movement enables squeeze film damping effects to occur.

Referring to fig. 4 and 5 in conjunction with fig. 3, fig. 4 shows a partially enlarged plan view of the inertial sensor 20, and fig. 5 shows a partially enlarged plan view of the inertial sensor 20 when subjected to the Y-axis acceleration 84. The damping system 58 includes a plurality of interleaved first and second damping structures 62, 64, in each case creating a gas-containing gap 86. As best seen in fig. 4, the first and second damping structures 62, 64 are spaced apart by a gas-containing gap 86 having a defined width 88, thereby providing damping. In some embodiments, the gas may be air. However, other suitable gases may be implemented in other embodiments.

In the example presented in fig. 3 and 5, movable mass 40 moves along with first and second damping structures 62, 64 of damping system 58 until second beam end 78 of beam 70 contacts second damping stop 82. Thus, the second damping structure 64 becomes temporarily stationary while the first damping structure 62 continues to move due to the Y-axis acceleration 84. As best seen in FIG. 5, movement of the first damping structure 62 relative to the second damping structure 64 results in a decrease in the width 88 of the gap 86. The damping effect occurs when gas present in the gap 86 is compressed between the first and second damping structures 62, 64 in response to the width 88 of the gap 86 decreasing.

Damping may cause a reduction or limitation of parasitic in-plane motion of movable mass 40 due to parasitic Y-axis acceleration 84. That is, the damping effect may limit the movement of movable mass 40 along Y-axis 24. However, damping stops 80, 82 may not be sufficient to completely prevent in-plane parasitic motion of movable mass 40. As such, in some embodiments, the accelerometer 20 additionally includes a travel stop 60. Damping occurring after the second damping structure 64 becomes temporarily stationary may significantly reduce the contact force between the movable mass 40 and the travel stop 60 to correspondingly reduce the risk of breakage of the travel stop 60. Thereafter, after the Y-axis acceleration 84 is eliminated, the restoring force allows the movable mass 40 and the first and second damping structures 62, 64 to return to their nominal positions between the travel stop 60 and the damping stops 80, 82 (fig. 1).

The damping effect of the damping system 58 depends inter alia on the number and length of the first and second damping structures 62, 64 which are complementary to each other. As such, the design of the accelerometer 20 may be tuned to have more damping (e.g., by increasing the number of damping structures 62, 64 and/or by increasing the length of the damping structures 62, 64) or less mass, depending on the particular design requirements.

Accordingly, embodiments require a movable suspended damping structure that significantly improves damping of the Y-axis acceleration 84 while having little or no effect on the area of a single mass seesaw design, such as the movable mass 40. However, this damping method is not limited to damping in-plane parasitic motion in a direction parallel to the Y-axis 24. In addition, this damping method can be implemented to improve damping in both the X-direction and the Y-direction (fig. 6) or only in the X-direction (fig. 7).

Fig. 6 shows a plan view of an inertial sensor 90 according to another embodiment. Likewise, the inertial sensor 90 is configured as a "teeter-totter" type accelerometer. As such, the accelerometer 90 is adapted to sense Z-axis acceleration 28, which Z-axis acceleration 28 is represented by circled black dots to indicate its direction out of the page, while the accelerometer 90 dampens in-plane parasitic motion along both the X-axis 22 and the Y-axis 24. Accelerometer 90 is similar to accelerometer 20 (FIG. 1). Accordingly, common features will be referenced with the same numerals, and the description of such features will be shortened or omitted for the sake of brevity.

Accelerometer 90 includes a substrate 30 having a surface 32, electrode elements 34, 36 (not visible), and a suspended anchor 38 formed on surface 32 of substrate 20. The movable mass 40 is spaced from the surface 32 of the substrate 30 and suspended above the substrate 30 via suspension springs 42, 44. The movable mass 40 includes first and second portions 54, 56 and is adapted to rotate about the rotational axis 48 in response to the Z-axis acceleration 28.

According to the embodiment of fig. 6, accelerometer 90 additionally includes a damping system 92, which damping system 92 is configured to limit movement of movable mass 40 in a direction perpendicular to Z-axis 26. Specifically, damping system 92 is configured to limit the motion of movable mass 40 in response to parasitic forces parallel to Y-axis 24 (e.g., Y-axis acceleration 84) and in response to parasitic forces parallel to X-axis 22 (referred to herein as X-axis acceleration 94). The damping system 92 is located at the second portion 56 of the movable mass 40 and thus contributes to the second portion 56 having a greater mass relative to the first portion 54. In some embodiments, the accelerometer 90 additionally includes a travel stop 60 coupled to the surface 32 of the substrate 30 or otherwise formed on the surface 32 of the substrate 30.

Similar to damping system 58, damping system 92 further includes a plurality of first damping structures 96 coupled to second end 52 of movable mass 40 and extending from second end 52 of movable mass 40, and a plurality of second damping structures 98 coupled to beam members 100 and extending from beam members 100 toward second end 52 of movable mass 40. The beam member 100 is also parallel to the axis of rotation 48 and thus aligned with the Y-axis 24. The damping system 92 additionally includes one or more spring structures 102 (two shown), the spring structures 102 having a first spring end 104 coupled to the second end 52 of the movable mass and a second spring end 106 coupled to the beam member 100. Along with the first and second damping stops 80, 82, the accelerometer 90 additionally includes third and fourth damping stops 108, 110, the third and fourth damping stops 108, 110 being coupled to the surface 32 of the baseplate 30 and located near a middle region 112 of the beam member 100. In some embodiments, the beam member 100 additionally includes one or more protruding elements 114, 116 (two shown), the protruding elements 114, 116 extending from the intermediate region 112 of the beam member 100 and corresponding to the positions of the third and fourth damping stops 108, 110.

The spring structure 102 is suitably configured to flex in-plane in both the X-direction and the Y-direction to achieve a damping effect due to the X-axis acceleration 94 and/or the Y-axis acceleration 84. Damping in response to the Y-axis acceleration 84 has been previously described. Damping in response to the X-axis acceleration 94 occurs in a similar manner. For example, as the protruding elements 114, 116 of the beam member 100 contact the third and fourth damping stops 108, 110 in response to the X-axis acceleration 94, the second damping structure 98 stops moving while the first damping structure 96 continues to move with the movable mass 40. Thus, squeeze film damping becomes effective in the X direction in response to X-axis acceleration 94.

Fig. 7 shows a plan view of an inertial sensor 120 according to yet another embodiment. Likewise, the inertial sensor 120 is configured as a "teeter-totter" type accelerometer. As such, the accelerometer 120 is adapted to sense Z-axis acceleration 28, which Z-axis acceleration 28 is represented by circled black dots to indicate its direction out of the page, while the accelerometer 120 dampens in-plane parasitic motion along the X-axis 22. Accelerometer 120 is similar to accelerometer 20 (FIG. 1) and accelerometer 90 (FIG. 6). Accordingly, common features will be referenced with the same numerals, and the description of such features will be shortened or omitted for the sake of brevity.

Accelerometer 90 includes a substrate 30 having a surface 32, electrode elements 34, 36 (not visible), and a suspended anchor 38 formed on surface 32 of substrate 20. The movable mass 40 is spaced from the surface 32 of the substrate 30 and suspended above the substrate via suspension springs 42, 44. The movable mass 40 includes first and second portions 54, 56 and is adapted to rotate about the rotational axis 48 in response to the Z-axis acceleration 28.

According to the embodiment of fig. 7, accelerometer 120 additionally comprises a damping system 122, said damping system 122 being configured to limit the movement of movable mass 40 in a direction parallel to X-axis 22. In particular, damping system 122 is configured to limit the motion of movable mass 40 in response to parasitic forces parallel to X-axis 22 (e.g., X-axis acceleration 94). The damping system 122 is located at the second portion 56 of the movable mass 40 and thus contributes to the second portion 56 having a greater mass relative to the first portion 54. Although not shown, in some embodiments, the accelerometer 120 may additionally include travel stops coupled to or otherwise formed on the surface 32 of the substrate 30 proximate the first and second ends 50, 52 of the movable mass 40.

Damping system 122 includes a plurality of first damping structures 124 coupled to and extending from second end 52 of movable mass 40, and a plurality of second damping structures 126 coupled to and extending from one or more beam elements 128, wherein beam elements 128 are spaced apart from and parallel to surface 32 of substrate 30, and from one or more beam elements 128. The second damping structures 126 are interleaved with the first damping structures 124. Damping system 122 additionally includes one or more spring structures 130 interconnected between movable mass 40 and second damping structure 126. The illustrated configuration includes two beam members 128 and thus two corresponding spring structures 130. However, it should be understood that alternative embodiments may include a single beam member 128 or more than two beam members 128. According to the illustrated embodiment, each beam element 128 is oriented perpendicular to the axis of rotation 48. That is, each beam member 128 is aligned with the X-axis 22.

A first spring end 132 of spring structure 130 is coupled to movable mass 40 and a second spring end 134 of spring structure 130 is coupled to a first beam end 136 of beam member 128. Second damping structure 126 is coupled to beam member 128 and extends perpendicularly from beam member 128. More specifically, the first and second damping structures 124, 126 are oriented parallel to the rotational axis 48 such that the first and second damping structures 124, 126 are aligned with the Y-axis 24. The accelerometer 120 additionally includes a damping stop 138, 140, the damping stop 138, 140 being coupled to the surface 32 of the base plate 30 and located proximate a second beam end 142 of each beam element 128. In some embodiments, the beam element 128 may extend beyond the outer boundaries of the first and second damping structures 124, 126 toward the damping stops 138, 140.

The spring structure 124 is suitably configured to bend in-plane in the X-direction to achieve a damping effect due to the X-axis acceleration 94. Damping in response to the X-axis acceleration 94 occurs in a similar manner as described above. For example, as the second beam end 142 of the beam member 128 contacts the third and fourth damping stops 138, 140 in response to the X-axis acceleration 94, the second damping structure 126 stops moving while the first damping structure 124 continues to move with the movable mass 40. Thus, squeeze film damping becomes effective in the X direction in response to X-axis acceleration 94.

Embodiments disclosed herein require micro-electromechanical system (MEMS) inertial sensors with integrated damping structures to improve sensitivity and reliability with the small form factor required for various functions. More specifically, the Z-axis teeter-totter inertial sensor includes a damping structure that is capable of effectively damping in-plane parasitic modes with little effect on the area of the movable mass. Damping structures are disclosed that can attenuate in-plane parasitic motion along an X-axis, a Y-axis, or both the X-axis and the Y-axis.

This disclosure is intended to explain how to fashion and use various embodiments in accordance with the invention rather than to limit the true, intended, and fair scope and spirit thereof. The foregoing description is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications or variations are possible in light of the above teachings. The embodiment or embodiments were chosen and described to provide the best illustration of the principles of the invention and its practical application, and to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims, as may be amended during the pendency of this application for patent, and all equivalents thereof, when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.