Electrode comb, micromechanical component, and method for producing an electrode comb or a micromechanical component

An electrode comb for a micromechanical component includes at least one electrode finger for which a first electrode finger subunit with a first central longitudinal axis and a second electrode finger subunit with a second central longitudinal axis are defined. The second central longitudinal axis are defined is inclined in relation to the first central longitudinal axis about a bend angle not equal to 0° and not equal to 180°.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrode comb for a micromechanical component, and to a manufacturing method for an electrode comb.

2. Description of Related Art

A micromirror having an electrostatic drive is often used for deflecting optical beams, e.g., in barcode scanners and in projection systems, or for switching optical data links. For adjusting the micromirror, the micromirror may be induced to vibrate at its natural frequency. This is known as the resonant mode of the micromirror. An electrostatic drive having two electrode structures situated in a plane is used for the resonant mode in most cases.

The resonant mode of the micromirror allows great deflections of the micromirror for a comparatively low energy input, although only via a sinusoidal vibration at a frequency equal to the natural frequency of the micromirror. A reflected beam of the micromirror oscillating at its natural frequency scans the center of an image very rapidly and scans an edge of the image comparatively slowly, possibly resulting in problems in signal analysis. In addition, an adjustment of a micromirror in two spatial directions is difficult to accomplish via the resonant mode, in particular to allow projection in lines, and is associated with poor image resolution. An image constructed via the resonant mode often makes an out-of-focus impression on an observer based on the Lissajous figure in particular.

To circumvent these problems, a micromirror adjustable in at least one direction via a quasistatic mode is often used in line-by-line projection of video images. The electronic drive here often has two electrode combs situated one above the other and offset in parallel to one another, so-called OOP (out-of-plane) electrode combs. As an alternative to the OOP electrode combs, the electrostatic drive may also have electrode combs positioned at an inclination to one another, frequently referred to as AVC (angular vertical combs). When two AVC electrode combs are used, the stator electrode comb is rotated out of its mounting plane, so that even without a voltage applied between the electrode combs, the electrode fingers of the stator electrode comb protrude into the electrode interspaces of the actuator electrode comb. The placement of the two electrode combs at an inclination to one another is implemented, for example, via a mechanical influence, preferably at the time of packaging the two electrode combs, or by a shaping step.

BRIEF SUMMARY OF THE INVENTION

The present invention makes possible a micromechanical component, which combines the special advantages of two parallel offset electrode combs (OOP electrode combs) and two electrode combs positioned at an inclination to one another (AVC electrode combs).

In a refinement of the electrode comb, it has more than two subunits having different angles of inclination. In this case, at least one third electrode finger subunit of at least one electrode finger having a third central longitudinal axis is definable, the electrode finger subunit being inclined by a bend angle not equal to 0° C. and not equal to 180° C. with respect to the first central longitudinal axis and with respect to the second central longitudinal axis. This improves the advantages of the electrode comb in cooperation with another electrode comb in comparison with an OOP electrode comb or an AVC electrode comb. This advantage is also obtained when two electrode combs according to the present invention cooperate.

The micromechanical component according to the present invention may include in addition at least one third actuator electrode comb and at least one third stator electrode comb, a voltage optionally being applied between each additional actuator electrode comb and an associated additional stator electrode comb. The two electrode combs between which a voltage is optionally applied may be inclined to one another at least one third angle without an applied voltage, the third angle of inclination possibly not being equal to the first angle of inclination and not being equal to the second angle of inclination.

In an example embodiment, the micromechanical component includes an actuator which is adjustable by adjusting the first actuator electrode comb with respect to the first stator electrode comb and/or by adjusting the second actuator electrode comb with respect to the second stator electrode comb. It is thus possible to superimpose the individual torques of the first and second electrode comb pairs to obtain a total torque. This is advantageous for an adjustment angle, in which the two individual torques themselves are not constant over the adjustment angle but may be added up to form an almost constant total torque. It is likewise possible to trigger the two electrode comb pairs separately from one another. If the adjusting torque is adjusted by an adjustment angle in which the first or second electrode comb pair has a constant individual torque, then only this electrode comb pair is triggered in a targeted manner. The joint triggering and separate triggering of the two electrode comb pairs are easily executable over the entire range of possible adjustment angles.

The actuator is a micromirror plate or a micropincette, for example. The micromechanical component has many possible applications.

The actuator is preferably adjustable in a quasistatic operation. The deflection angle set for the actuator is in this case proportional to the square of the applied voltage within a limited adjustment angle range. Nonlinearities outside of this range may be compensated by combined triggering of the two comb electrode pairs.

In an example embodiment, the first actuator electrode comb is offset in parallel with the first stator electrode comb in its starting position. The first electrode comb pair is thus optimized for small angles of inclination. In this case, the first actuator electrode comb and the first stator electrode comb are preferably used for adjusting small deflection angles without having to use the electrode combs situated at an angle to one another. Thus, the electrode comb pair including the second stator electrode comb and the second actuator electrode comb is designed specifically for a high torque at large adjustment angles. The second actuator electrode comb and the second stator electrode comb are then used in particular to set large deflection angles without using the first actuator electrode comb and the first stator electrode comb.

The various actuator electrode combs and stator electrode combs are placed side-by-side along the axis of rotation of the actuator or nested radially about an axis of rotation of the actuator.

The advantages described in the preceding paragraphs are also ensured by using a corresponding manufacturing method. Due to the different placement of the various stator electrode combs and actuator electrode combs with respect to one another, the comb structures of the electrode combs may be manufactured from a thinner layer than is possible with an electrostatic drive of electrode combs offset only in parallel. This allows finer gaps and consequently allows a reduction in the number of electrodes.

A micromechanical component having at least two OOP electrode combs has the advantage that the first distance and the second distance may be selected in such a way that an advantageous torque curve is ensured for a larger range of an adjustment angle of an adjustable actuator. For example, an almost constant torque may be achieved over a wide adjustment angle range by targeted triggering of the first OOP electrode combs and/or the second OOP electrode combs.

The stator electrode combs and the actuator electrode combs may be manufactured from simple standard substrates using a standard method because of the thin useful layer. The use of expensive special wafers, e.g., SOI, may be dispensed with.

DETAILED DESCRIPTION OF THE INVENTION

The example embodiments of the micromechanical component and the electrode comb described in the following paragraphs may be used, for example, in a head-up display in the automotive field, in a miniprojector in the consumer field, in a surface scanner, or as a switch mirror in optical networks.

FIGS. 1A and 1Bshow two schematic diagrams to illustrate a functioning of two conventional OOP electrode combs.

The two electrode combs10and12shown here are embodied as actuator electrode comb10and as stator electrode comb12. Stator electrode comb12is fixedly mounted in a housing (not shown). In contrast, actuator electrode comb10is situated in the housing, so it is able to rotate about an axis of rotation14. Using a control device (not shown) and contact elements16, a voltage U may be applied between the two electrode combs10and12.

InFIG. 1A, no voltage U is applied between the two electrode combs10and12. Actuator electrode comb10is therefore in its starting position inFIG. 1A. In its starting position, actuator electrode comb10is situated parallel and offset to stator electrode comb12. The two electrode combs10and12may therefore be referred to as out-of-plane electrode combs (OOP electrode combs) or as an OOP drive comb pair. The angle of inclination of the two electrode combs10and12to one another is 0° or 180°.

A central longitudinal axis10aof actuator electrode comb10situated in its starting position runs offset in parallel to central longitudinal axis12aof stator electrode comb12. Top side10band bottom side10cof actuator electrode comb10are aligned parallel to top side12band bottom side12cof stator electrode comb12. In their starting positions, the electrode fingers of actuator electrode comb10are outside of the electrode finger interspaces of stator electrode comb12. Both electrode combs10and12are preferably a constant distance from one another over their entire extent.

InFIG. 1B, a voltage U not equal to zero is applied between the two electrode combs10and12. Because of applied voltage U, a torque M acts on actuator electrode comb10in the direction of stator electrode comb12. Actuator electrode comb10is rotated out of its starting position shown inFIG. 1Aby an adjustment angle α.

Top side10bof actuator electrode comb10is inclined with respect to its starting position (shown with dashed lines) by adjustment angle α inFIG. 1B. Longitudinal axes10aand12aof electrode combs10and12are inclined by adjustment angle α to one another. The electrode fingers of actuator electrode comb10protrude into the electrode finger interspaces of stator electrode comb12at the adjustment angle α shown here. The surfaces of the electrode fingers of actuator electrode comb10protruding into the electrode finger interspaces of stator electrode comb12are often referred to as overlap areas.

In the case of small adjustment angles α, the value of the overlap areas increases with an increase in adjustment angle α. The value of the overlap areas increases almost in proportion to adjustment angle α until reaching a limit angle α0. The torque acting on actuator electrode comb10is thus almost constant.

If adjustment angle α is equal to limit angle α0, then the electrode fingers of actuator electrode comb10are completely immersed at their outer ends in the electrode finger interspaces of stator electrode comb12. If adjustment angle α is greater than limit angle α0, then the outer ends of the electrode fingers of actuator electrode comb10protrude out of the electrode finger interspaces of stator electrode comb12. The increase in overlap areas therefore declines with an increase in adjustment angle α beyond limit angle α0. This is associated with a reduction in the torque acting on actuator electrode comb10.

FIG. 2shows a coordinate system to illustrate a relationship between an adjustment angle and a torque in the case of the OOP electrode combs according toFIGS. 1A and 1B. The abscissa of the coordinate system corresponds to a value range for adjustment angle α already described above. The ordinate of the coordinate system indicates a particular torque M acting on the actuator electrode comb.

At an adjustment angle α between 0° and limit angle α0, torque M constantly has a comparatively high value. The curve of torque M is thus stable within the value range of adjustment angle α between 0° and limit angle α0. However, torque M exerted on the actuator electrode comb declines significantly beyond limit angle α0.

Limit angle α0is defined by a length and a height of two electrodes10and12. If the two electrode combs10and12have a comparatively great height, then limit angle α0may be increased. However, electrode combs10and12having a great height are more difficult to manufacture than are electrode combs10and12having a smaller height, in particular by a manufacturing method using a trench process.

Designing electrode combs10and12with long electrode fingers increases torque M at an adjustment angle α between 0° and limit angle α0. However, electrode combs10and12having long electrode fingers have a comparatively small limit angle α0.

In summary, it may thus be concluded that OOP electrode combs10and12are suitable only for adjustment of an adjustment element by a comparatively small adjustment angle α. If adjustment angle α exceeds limit angle α0, then the movement of the actuator is definitely slowed or brought to a standstill.

FIGS. 3A and 3Bshow two schematic diagrams to illustrate a functioning of two conventional AVC electrode combs.

An actuator electrode comb20and a stator electrode comb22are shown. Although the electrode comb22is fixedly secured, actuator electrode20is able to rotate about an axis of rotation24in the direction of stator electrode comb22, with a voltage U applied via contact elements26between electrode combs20and22.

InFIG. 3A, no voltage is applied between the two electrode combs20and22. Actuator electrode comb20is thus in its starting position, in which it is aligned and inclined by an angle of inclination β with respect to stator electrode comb22. Central longitudinal axes20aand22aof the electrode fingers of the electrode combs20and22enclose angle of inclination β. Top side20band bottom side20cof actuator electrode comb20are also aligned and inclined by the angle of inclination β with respect to top side22band bottom side22cof stator electrode comb22. The two electrode combs20and22may therefore be referred to as AVC electrode combs20and22(angular vertical combs).

Even in the case of an applied voltage U equal to zero, the electrode fingers of actuator electrode comb20protrude into the electrode finger interspaces of stator electrode comb22at their internal ends. However, the increase in the overlap areas defined above is relatively low in the case of a change in the adjustment angle out of this position.

FIG. 3Bshows the electrode combs ofFIG. 3Aafter applying a voltage U not equal to zero between electrode combs20and22. Because of applied voltage U, actuator electrode comb20experiences a torque M in the direction of stator electrode comb22. Electrode comb20is thus adjusted by an adjustment angle γ with respect to its starting position shown inFIG. 3A. By rotation of actuator electrode comb20about axis of rotation24in the direction of torque M, the amount of the overlap areas is increased. However, the increase in overlap areas has comparatively small values up to a limit angle γ0.

FIG. 4shows a coordinate system to illustrate a relationship between an adjustment angle and a torque in the case of the AVC electrode combs ofFIGS. 3A and 3B. The abscissa of the coordinate system represents a value range of adjustment angle γ. The ordinate of the coordinate system represents a torque M acting on the actuator electrode comb.

In the case of an adjustment angle γ between 0° and limit angle γ0, torque M is comparatively small but increases with an increase in adjustment angle γ. This increase in torque M persists until reaching an overlap between the two electrode combs along the entire length of the electrode fingers. Beyond limit angle γ0, a constant torque M is maintained when adjustment angle γ increases. Torque M for an adjustment angle γ between limit angle γ0and a maximum possible adjustment angle γ has a comparatively large value. Below limit angle γ0there is an unstable range30in which torque M increases drastically with an increase in adjustment angle γ.

The disadvantages of two AVC electrode combs may be elucidated on the basis of the coordinate system ofFIG. 4. For an adjustment angle γ within unstable range30, a pull-in behavior of actuator electrode comb often occurs due to the high gradient in torque M. The position of the actuator electrode comb at an adjustment angle γ within unstable range30is thus unstable and is hardly triggerable quasistatically.

The width of unstable range30increases with an increase in the electrode fingers of the electrode combs. However, only comparatively long electrode fingers of the electrode combs ensure an adequate maximum torque M beyond limit angle γ0.

In comparison with the OOP electrode combs, AVC electrode combs have the advantage that torque M has a sufficiently high value at larger adjustment angles γ between limit angle γ0and a maximum possible adjustment angle γ. AVC electrode combs are thus suitable in particular for adjusting an actuator by a large adjustment angle γ.

FIGS. 5A and 5Bshow a schematic diagram of a first example embodiment of the micromechanical component.

The example embodiment shown here has an adjusting component50formed from a conductive material. Adjusting component50includes a mirror plate52, two web elements54protruding away from mirror plate52in opposite directions and eight electrode combs56and58protruding laterally away from web elements54. The electrode fingers of electrode combs56and58run parallel to one another in a direction perpendicular to the longitudinal directions of two web elements54. Each web element54has two electrode combs56and58on each side. Electrode combs56and58are made of the material of adjusting component50, so that they lie in a plane with mirror plate52and web elements54. Adjusting component50is etched out of a conductive layer, for example.

Mirror plate52is suspended via web elements54either directly or by cardan suspension. Four electrode combs56are situated on the sides of web elements54facing mirror plate52. Three electrode fingers of electrode combs56have a length L1. Four electrode combs58likewise equipped with three electrode fingers are mounted on the sides of web element54facing away from mirror plate52. Length L2of the electrode fingers of electrode combs58is much less than length L1of the electrode fingers of electrode combs56.

The present example embodiment is of course not limited to a certain number of electrode fingers for electrode combs56and58. Likewise instead of mirror plate52, another actuator, e.g., an active element of a micropincette, may be formed on adjusting component50.

One stator electrode comb60or62is allocated to each electrode comb56and58. Each of four stator electrode combs60is allocated to one electrode comb56. Correspondingly, one of four stator electrode combs62is mounted on each electrode comb58.

A voltage U may be applied between at least one of electrode combs56and58of adjusting component50and at least one of stator electrode combs60and/or62via contact elements (not shown) and a control device. The control device is designed in such a way that at least the triggering of each stator electrode comb60or62may take place separately from that of other stator electrode combs60and62.

InFIG. 5Ano voltage U is applied between one of electrode combs56and58of adjusting component50and one of stator electrode combs60or62. Adjusting component50is therefore in its starting position.

In the starting position of adjusting component50, each stator electrode comb60is attached to a particular electrode comb56in an inclined position. Angle of inclination β, which is definable via the central longitudinal axes of the electrode fingers (or the top sides) of electrode combs56and60is not equal to 0° or 180°. Both electrode combs56and60may thus be referred to as AVC electrode combs.

On the other hand, each stator electrode comb62is attached to its particular electrode comb58offset in parallel. The angle of inclination between two cooperating electrode combs58and62is thus 0° or 180°. The central longitudinal axes of the electrode fingers of electrode combs58and62run parallel to and at a distance from one another. The two electrode combs58and62situated side by side may therefore be referred to as OOP electrode combs.

FIG. 5Bshows the micromechanical component after a voltage U not equal to zero is applied between at least one of electrode combs56and58of adjusting component50and at least one stator electrode comb60and62. Because of applied voltage U, adjusting component50is rotated by an adjustment angle α about an axis along the central longitudinal axes of both web elements54. In this way the micromirrors52may be brought into a desired position.

The example embodiment described here may of course be modified by placing AVC electrodes58and62on the ends of web elements54facing away from mirror plate52, and OOP electrode combs56and60may be provided on the ends of web elements54next to mirror plate52. Likewise, instead of OOP electrode combs56and60, additional AVC electrode combs having different angles of inclination to one another may also be provided. In addition, the lengths of the electrode fingers and/or the positions of the axes of rotation on the actuator electrode combs56and68may also be varied.

An example embodiment of the micromechanical component explained with reference toFIGS. 5Aand B is of course also possible, having at least two OOP electrode combs, the central longitudinal axes of two electrode combs between which a voltage may be applied having at least two different spacings without an applied voltage.

FIG. 6shows a coordinate system for illustrating a relationship between an adjustment angle and a total torque in the example embodiment ofFIGS. 5A and 5B. The abscissa of the coordinate systems is a value range of adjustment angle α. The ordinate of the coordinate system corresponds to total torque M acting on the adjusting component.

Total torque M is obtained from additively superimposing the individual torques of the various electrode combs. Total torque M thus comprises the torques of the AVC electrode combs (dashed line) and of the OOP electrode combs (dotted lines) known fromFIGS. 2 and 4.

With an adjustment angle α within angle range70, total torque M may be kept constant through a combined triggering of the AVC electrode combs and the OOP electrode combs. It is thus possible to adjust the mirror plate reliably over quasistatic operation by joint triggering of the various electrode combs in angle range70, in which the individual torques of the OOP electrode combs and the AVC electrode combs are not constant.

At an adjustment angle α below angle range70, the torque of the AVC electrode combs increases with an increase in adjustment angle α. Total torque M may be generated from the individual torques of the OOP electrode combs at adjustment angle α below angle range70. However, at larger adjustment angles α above angle range70, the effect of the AVC electrode combs is constant, whereas the effect of the OOP electrode combs is negligible. Total torque M may be generated from the individual torques of the AVC electrode combs at an adjustment angle α above angle range70.

It is therefore advantageous to adjust the mirror plate by a small adjustment angle α below angle range70by triggering only the OOP electrode combs. Correspondingly, the mirror plate is adjusted by an adjustment angle α above angle range70by triggering only the AVC electrode combs. A constant total torque may thus be achieved over a larger adjustment angle range than by using only one type of electrode comb, i.e., exclusively OOP electrode combs or exclusively AVC electrode combs.

The example embodiment of the micromechanical component described above thus allows a reliable adjustment of a desired adjustment angle α via a joint triggering of the OOP electrode combs and the AVC electrode combs or via a specific triggering of the OOP electrode combs or the AVC electrode combs. In this way, an optimal curve of total torque M is thus achievable for small adjustment angles α as well as for large adjustment angles α.

FIGS. 7A and 7Bshow a schematic diagram of an example embodiment of an electrode comb.

An actuator electrode comb80having a top side80band a stator electrode comb82are shown. While stator electrode comb82is fixedly secured in a micromechanical component (not shown), actuator electrode comb80may be rotated about an axis of rotation84in the direction of stator electrode comb82by applying a voltage via contact elements86.

The electrode fingers of actuator electrode comb80point in one direction. Thus a central longitudinal axis80ais definable for the electrode fingers of actuator electrode comb80. However, the electrode fingers of stator electrode comb82have a bend. Two subunits88and90having different central longitudinal axes88aand90aare thus definable for each electrode finger of stator electrode comb82. Central longitudinal axes88aand90aare inclined toward one another by a bend angle δ.

The electrode comb pair formed by the two electrode combs80and82may be referred to as a combination of OOP electrode combs and AVC electrode combs. Operation of the two electrode combs80and82offers the advantages of the combination of OOP electrode combs and AVC electrode combs.

InFIG. 7A, no voltage U is applied between actuator electrode comb80and stator electrode comb82, and actuator electrode comb80is in its starting position.

FIG. 7Bshows the two electrode combs80and82after a voltage not equal to zero is applied. Actuator electrode comb80is adjusted out of its starting position by an adjustment angle α in the direction of stator electrode comb82by resulting torque M. Due to the shape of the electrode fingers of stator electrode comb82having a suitably selected bend angle δ, a great increase in the overlap areas and thus an advantageous torque M are achieved in the adjustment of the two electrode combs80and82relative to one another for a desired range of adjustment angle α. In the case of a suitably selected bend angle δ in particular, a constant torque M may be ensured for a middle angle range of adjustment angle α.

The shape of the stator electrode comb82described above may thus also be applied to actuator electrode comb80. Another advantage of a stator electrode comb82designed in this way and/or a corresponding actuator electrode comb80is thus that electrode combs80and82require much less space along an axis of rotation of an actuator. This in turn offsets the greater complexity in the manufacture of electrode combs80and82.