WO2009132719A2

WO2009132719A2 - Micromechanical component, method for operating a micromechanical component and method for producing a micromechanical component

Info

Publication number: WO2009132719A2
Application number: PCT/EP2008/066535
Authority: WO
Inventors: Joerg Muchow; Joachim Fritz
Original assignee: Robert Bosch Gmbh
Priority date: 2008-04-30
Filing date: 2008-12-01
Publication date: 2009-11-05
Also published as: WO2009132719A3; DE102008001465A1

Abstract

The invention relates to a micromechanical component comprising an adjusting element (10) which can be adjusted in relation to a fixture and which is connected to said fixture by at least one spring element (16), a first end of said spring element (16) being fastened to a first anchoring section which is a subsection of the fixture, and a second end of the spring element (16) being fastened to a second anchoring section (20) which is a subsection of the adjusting element (10). The micromechanical component further comprises at least one piezoresistive element (22) which is arranged on a surface and/or inside a volume of the first anchoring section and/or the second anchoring section (20) in such a manner that a deformation of the spring element (16) causes a change in the resistance of the piezoresistive element (22). The invention additionally relates to a method for operating a micromechanical component. The invention further relates to a method for producing a micromechanical component.

Description

description

title

Micromechanical component, method for operating a micromechanical component and production method for a micromechanical component

The invention relates to a micromechanical component. In addition, the invention relates to a method for operating a micromechanical component. Furthermore, the invention relates to a production method for a corresponding micromechanical component.

State of the art

For a reliable control of a micromechanical component with an adjustable adjusting element, for example a micromirror, determining a current position of the actuating element is often advantageous. Conventionally, a light beam is often directed onto a reflective surface of the actuating element. Depending on the current position of the actuating element, the light beam is deflected from the reflecting surface to another detectable point of impact of a detection system, for example a CCD camera. However, carrying out this optical method requires a suitable light source for emitting the light beam and the detection system and is therefore relatively expensive and space-consuming. In addition, the execution of the opti- see method is relatively cumbersome.

Another possibility for determining the current position of the control element is to measure a capacitance between an electrode attached to the control element and a, preferably fixedly arranged in the micromechanical component counter electrode. During a movement of the actuating element, the capacitance changes, if, due to the movement, the average distance between the two electrodes increases or decreases and / or the position of the two electrodes relative to one another is changed. The control element itself can be used as an electrode in an advantageous embodiment. Such capacitive methods are used in inertial sensors, for example for position detection. However, the capacitive method requires expensive electronics which are designed to eliminate interference signals. Performing the capacitive method for determining the current position of the actuating element is relatively expensive due to the suppression. As an alternative or as a supplement to the two methods described in the upper paragraphs, a piezoresistive sensor element can also be used in order to determine the current position of the actuating element within the micromechanical component. Conventionally, the piezoresistive sensor element, for example a Wheatstone bridge or an X-Ducer, is mounted on a surface or within a volume of a spring element which connects the adjustable adjusting element with an immovable holder of the micromechanical component. By the piezoresistive sensor element, a current with a certain current can then be passed. Upon bending of the spring element, the resistance of the piezoresistive sensor element changes. This change in resistance can be determined and then evaluated with respect to a probable current position of the control element.

Preferably, a spring element which connects an actuating element with a stationary holder of a micromechanical component should be designed such that it has a comparatively low bending stiffness. However, attaching a Wheatstone bridge on the surface or within the volume of the spring element, as well as arranging line elements to direct the current through the Wheatstone bridge, significantly increases the flexural rigidity of the spring element.

It is therefore desirable to dispose of a cost-effective, easily executable and / or bending stiffness of a spring element hardly influencing possibility for detecting a Versteilens an actuating element of a micromechanical component.

Disclosure of the invention

The invention provides a micromechanical component with the features of claim 1, a method for operating a micromechanical component having the features of claim 12 and a manufacturing method for a micromechanical component having the features of claim 13.

The present invention is based on the finding that in a bending of a spring element, which connects an adjustable actuator with a stationary support of a micromechanical component, a mechanical stress within an anchoring region of the actuating element and / or the holder, to which one end of the spring element is attached, is generated. This is also referred to as shear stresses which occur within at least one anchoring region of the spring element. The anchoring area is thus a mainland to which one end of the spring element is attached. The anchoring area preferably has a bending stiffness which is significantly above the mean bending stiffness of the spring element. Perpendicular to the longitudinal direction of the spring element, the anchoring area is characterized by an extension. net, which lies significantly above the extent of the spring element perpendicular to the longitudinal direction of the spring element.

The anchoring area, to which one end of the spring element is attached, can also be designated as a contact area of the spring element within the holder and / or within the setting element. An anchorage region is also referred to as an attack region in which a bending of the spring generates a mechanical stress without significantly changing the shape of the attack region. The anchoring area is a region of the holder and / or of the adjusting element with an extension which is preferably less than 500 μm. In particular, the extent of the anchoring region can be less than or equal to 100 μm. The extent of the anchoring region can be, for example, 30 μm.

A problem with the design of the electrostatically adjustable actuator is that the forces for adjusting the actuator should be relatively low. To achieve this, spring elements must have a relatively low bending stiffness. In order for this to be ensured, the expansions of the spring elements perpendicular to the longitudinal directions of the spring elements are frequently less than 50 μm, for example less than 10 μm.

In a preferred embodiment, if a change in the resistance of the piezoresistive element is detected, the sensor and evaluation device is designed to determine that the spring element is deformed and to output a corresponding signal. Thus, a deformation of the spring element can be reliably detected in a simple manner.

Preferably, the actuating element is rotatable from a starting position into at least one end position, wherein the sensor and evaluation device is additionally designed to determine an adjustment angle between the starting position and the at least one end position on the basis of the tapped voltage. This ensures a reliable control of the micromechanical component for adjusting the actuating element in a desired position.

The adjusting element can be arranged gimbally by means of two spring elements on the holder. This allows rotation of the actuating element about an axis parallel to the longitudinal axis of the two spring elements. The adjustment angle can assume a comparatively large value.

In a preferred embodiment, the at least one spring element comprises a double-stranded spring. Double-stranded springs have a comparatively high rigidity against lateral bending. In contrast, the torsional rigidity of the double-stranded springs is relatively low. This ensures that the double-stranded spring is bendable, as it is advantageous for the desired adjustment of the actuating element.

In this case, the at least one double-stranded spring can be V-shaped. V-shaped springs cause shear stress in a torsion in their anchoring area that extends at least 20 μm into the mainland. For example, the shear stresses on the 100 microns in the mainland.

In a preferred refinement of the micromechanical component, the piezoresistive element X-Ducer comprises an element via which an electrical voltage is detected when mechanical shear stresses occur. Preferably, the first anchoring region and / or the second anchoring region comprises an outer region with a doping of a first doping type, wherein in the outer region an inner region is arranged which has a doping of a second doping type different from the first doping type.

In an alternative piezoresistive element in the form of a Wheatstone bridge, which is arranged on a surface of an anchoring region or within a volume of the anchoring region, a mechanical stress causes a change in resistance. By tapping the voltage, it is thus possible to detect the change in resistance of the piezoresistive sensor element.

While a Wheatstone bridge requires a minimum width of 50 μm and a minimum length of 150 μm, the X-Ducer piezoresistive sensor element in the upper paragraph is also capable of being extended on a surface and / or within a volume of an anchoring area of about 20 microns x 20 microns to be arranged.

In a preferred embodiment, the first anchoring region and / or the second anchoring region has an outer region with a doping of a first doping type, wherein in the outer region an inner region is arranged which has a doping of a second doping type different from the first doping type , The outer region preferably covers an area smaller than 100 μm x 100 μm. In particular, the outer area covers an area of about 20 microns x 20 microns. The embodiment described here is therefore also suitable for micromechanical components, in which the anchoring regions, within which mechanical stresses occur when bending a spring element, are too small to implement a Wheatstone bridge. Since the piezoresistive sensor element described here requires a comparatively small application volume, it is suitable to operate within a small anchorage. tion area to detect the occurring during bending of the at least one spring element mechanical stress.

The advantages described in the upper paragraphs are also ensured in such a method for operating a micromechanical component and in a corresponding manufacturing method for a micromechanical component.

Brief description of the drawings

Further features and advantages of the invention will be explained below with reference to the figures. Show it:

1 and 2 is a plan view and a side view of an upper side of an actuating element for

Depicting an embodiment of the micromechanical component; and

3 shows an enlarged detail of FIG. 1.

Embodiment of the invention

1 and 2 show a plan view and a side view on an upper side of an actuating element for illustrating an embodiment of the micromechanical component.

The actuator 10 includes a mirror plate 12 and two arranged on opposite sides of the mirror plate 12 web elements 14 which project in the y direction of the mirror plate 12. At each of the mirror plate 12 opposite end of a bar member 14, a spring element 16 is attached. For example, the spring element 16 is a double-stranded spring, in particular a V-shaped spring.

By means of the two spring elements 16, the adjusting element 10 is fastened to a holder (not shown) of the micromechanical component. Preferably, the actuator 10 is integrally formed. The two spring elements 16 may also be formed integrally with the adjusting element 10. For example, the actuator 10 and the two spring members 16 are made of a semiconductor plate or a plate of a conductive material. This can be done for example by etching the semiconductor plate or the plate of conductive material. Furthermore, the spring elements 16 may be integrally formed with at least a part of the holder. The micromechanical component has a drive (not shown), such as an electrostatic drive or a magnetic drive. The drive is designed to adjust the adjusting element 10 relative to the holder, wherein the adjustment causes a bending of at least one of the two spring elements 16, for example a torsion and / or a twisting of the two spring elements 16. For example, the web elements 14 may be formed as drive combs, wherein electrodes are arranged on the web elements 14.

Fig. 1 shows the actuator 10 in a starting position in which the mirror plate 12 is parallel to the xy plane. In contrast, the mirror plate 12 in FIG. 2 is adjusted by the drive by an adjustment angle α from the xy plane.

In order to allow a good adjustment of the mirror plate 12 within a wide range of values of the adjustment angle α, the two spring elements 16 are designed such that they have a high flexural rigidity in the y-direction, but a comparatively low torsional rigidity. For this purpose, the two subunits of the V-shaped spring elements 16 are preferably shaped so that a maximum width dl of the spring elements 16 is significantly less than a maximum width d2 of the web elements 14. For example, the spring elements 16 have a maximum width dl of about 5 microns. The torsional stiffness of the spring elements 16 is thus significantly below the torsional rigidity of the web elements 14. Preferably, the ratio between the torsional stiffness of the spring elements 16 and the torsional stiffness of the web elements 14 is selected so that the web elements 14 are hardly bent during an adjustment of the mirror plate 12.

FIG. 3 shows an enlarged detail of FIG. 1.

The region of the illustrated bar member 14, to which the spring element 16 is attached, may be referred to as the anchoring area 20 of the spring element 16 on the bar element 14, since a bending of the spring element 16, in particular a torsion of a V-shaped spring, causes a mechanical stress inside the bar Anchoring area 20 causes. In this case, a maximum width dl of the spring elements 16 of about 5 μm is also sufficient in order to generate detectable mechanical stresses within the anchoring region 20.

The anchoring region 20 can also be referred to as a contact region or as an engagement region of the spring element 16 on the web element 14. Preferably, the anchoring portion 20 has an extension which is less than 500 microns. The extent of the anchoring region 20 is, for example, less than 100 μm, in particular less than 50 μm. Preferably, the anchoring region 20 is monocrystalline, so that an X-Ducer 22 can be implemented on a surface of the anchoring region 20 and / or within a volume of the anchoring region 20 as a piezoresistive element. The X-Ducer 22, which can also be designated as an x-Ducer, has an inner region (core) 24 made of a material of a first doping type, for example of a p-doped material. The outer region 26 surrounding the inner region 24 comprises a material of a second, different doping type. If the inner region 24 is p-doped, the outer region 26 is n-doped. The doping of the regions 24 and 26 is easily carried out. The X-Ducer 22 can thus be produced by means of an easily executable process.

On the X-Ducer 22 (not shown) contacts and leads are attached, with which a current flow with a desired current I through the areas 24 and 26 can be conducted and an e- lectric voltage U can be tapped. The areas 24 and 26 and the contacts together occupy an area of approximately 20 μm x 20 μm.

Upon bending of the spring elements 16 for adjusting the mirror plate 12 relative to the fixed

Holding the micromechanical component 10, a mechanical stress occurs within the anchoring region 20, which can be detected by a change in resistance at the X-Ducer 22. Thus, a sensor and evaluation device (not shown) can detect a bending of the spring element 16 by evaluating the electrical voltage U picked up at the X-Ducer 22. Preferably, the sensor and evaluation device is designed to determine a current position of the mirror plate 12 based on the tapped electrical voltage U. Thus, the embodiment shown offers a cost effective way to determine the current position of the mirror plate 12 within the micromechanical component by means of a comparatively low cost.

The X-Ducer 22 described here thus has the advantage that it can be easily implemented in the volume of the attack area 20. The comparatively small dimensions of the engagement region 20 do not represent an obstacle to the attachment of the X-Ducer 22. When attaching the X-Ducer 22 as a piezoresistive element on the surface and / or within the volume of the engagement region 20, there is no need for any conductor tracks over the spring elements 16 are performed. For example, the contact elements and the supply lines extend only via the adjusting element 10.

This prevents that the metallic conductor tracks, which are conventionally guided over the spring element 16 in the case of a piezoresistive element arranged on a surface of a spring element 16 or in a volume of the spring element 16, cause an attenuation of the spring element 16. This eliminates the disadvantages of occurring due to the damping hysteresis and / or nonlinearity, which often occur in a piezoresistive element disposed on the surface of the spring element 16 or in a volume of the spring element 16.

In the upper paragraphs, the present invention will be described with reference to a designed as a mirror plate 12 th actuator 10. Of course, the present invention is also applicable to micromechanical components with other adjustable control elements. Likewise, instead of the X-Ducers 22, another piezoresistive element in the form of a Wheatstone bridge can be used.

Claims

claims

1. Micromechanical component with:

a relative to a holder adjustable actuator (10) which is connected by means of at least one spring element (16) with the holder, wherein a first end of the spring element (16) is attached to a first anchoring portion, which is a portion of the holder, and a second End of the spring element (16) is fastened to a second anchoring area (20), which is a partial area of the adjusting element (10);

at least one piezoresistive element (22) which is arranged on a surface and / or within a volume of the first anchoring region and / or the second anchoring region (20) such that upon deformation of the spring element (16) a resistance of the piezoresistive element (22 ) is changeable.

2. Micromechanical component according to claim 1, characterized by a piezoresistive element (22) coupled to the sensor and evaluation device for detecting a change in the resistance of the piezoresistive element (22).

3. micromechanical component according to claim 2, wherein the sensor and evaluation device is adapted to, if a change in the resistance of the piezoresistive element (22) is detected to determine that the spring element (16) is deformed and output a corresponding signal.

4. The micromechanical component according to claim 3, wherein the adjusting element (10) is rotatable from an initial position into at least one end position, and wherein the sensor and evaluation device is additionally designed to use the tapped voltage (U) to obtain an adjustment angle (α). between the starting position and the at least one end position to determine.

5. Micromechanical component according to one of the preceding claims, wherein the adjusting element (10) is gimbal-mounted by means of two spring elements (16) on the holder.

6. micromechanical component according to one of the preceding claims, wherein the at least one spring element (16) comprises a double-stranded spring.

7. The micromechanical component according to claim 6, wherein the at least one double-stranded spring is V-shaped.

8. micromechanical component according to one of the preceding claims, wherein the piezoresistive element (22) comprises an X-Ducer.

9. The micromechanical component according to claim 8, wherein the first anchoring area and / or the second anchoring area (20) comprises an outer area (26) with a doping of a first doping type, and wherein in the outer area (26) an inner area (24 ) having a doping of a second doping type different from the first doping type.

10. The micromechanical component according to claim 9, wherein the outer region (26) covers an area which is smaller than 100 μm x 100 μm.

11. A micromechanical device according to claim 10, wherein the outer region (26) covers an area of about 20μm x 20μm.

12. A method for operating a micromechanical component having a holder and an adjusting element (10) which is adjustable relative to the holder and which is connected to the holder by means of at least one spring element (16), wherein a first end of the spring element (16) is connected to a first anchoring region, which is a partial region of the holder, is fastened and a second end of the spring element (16) is fastened to a second anchoring region (20), which is a partial region of the adjusting element (10), and wherein at least one piezoresistive element (22) so on a surface and / or within a volume of the first anchoring region and / or the second anchoring region (20) is arranged such that upon deformation of the spring element (16) a resistance of the piezoresistive element (22) is variable, with the step:

Detecting a change in the resistance of the piezoresistive element (22); and

Operating the micromechanical device taking into account a detected change in resistance.

13. A manufacturing method for a micromechanical component with a holder and a relative to the holder adjustable adjusting element (10) which is connected by means of at least one spring element (16) with the holder, wherein a first end of the spring element (16) on a first Anchoring area, which is a portion of the holder, is fixed and a second end of the spring element (16) on a second anchoring portion (20), which is a portion of the adjusting element (10) is attached, comprising the steps:

Forming at least one piezoresistive element (22) on a surface and / or within a volume of the first anchoring area and / or the second anchoring area (20) such that upon deformation of the spring element (16), a resistance of the piezoresistive element (22) is variable ,