Abstract:
The invention relates to a device and a method for the micromechanical positioning and handling of an object. The aim of the invention is to provide a device and an associated method for the micromechanical positioning and handling of objects by means of which the scanning speed can be increased and the positional accuracy be improved so that real time images or video rate images (ca. 25 images per second) having a lateral and vertical resolution in the nanometer range can be achieved. According to the invention, a monolithic component, preferably made of silicon, comprises a support element, an object carrier, a plurality of guide elements and elements for transmitting the movement, the preferably piezoresistive drive elements and the preferably piezoresistive position detectors being integrated into said monolithic component; Said micromechanical positioning device can be used, for example, in scanning probe microscopy and in nanopositioning and nanomanipulation technology.

Description:
This application is a 371 of PCT/EP2008/050963 filed Jan. 28, 2008, which in turn claims the priority of DE 10 2007 005 293.8 filed Jan. 29, 2007, the priority of both applications is hereby claimed and both applications are incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     The present invention pertains to a device and to a method for the micromechanical positioning and manipulation of an object with preferably piezoelectric actuators. 
     Micromechanical positioning devices are used in various areas. The most important areas of application are scanning probe microscopy and nanopositioning and nanomanipulation. Scanning probe microscopes are powerful tools used for the study of the surface properties of different types of materials, for example, also for the determination of molecular and atomic interactions on surfaces, and for the imaging of individual biological molecules. Nevertheless, commercial scanning probe microscopes are very large because of their positioning and position-control mechanisms, and this in turn limits the scanning speed and the scanning area as well as the areas of application of these types of microscopes. The drive mechanisms used in these microscopes, furthermore, do not allow higher dynamics. 
     A new positioning device is known from US 2006/0112760. This device has a higher scanning speed, but, because of its geometric dimensions and metallic design, it is usable to only a limited extent for real-time imaging (video rate imaging (at about 25 frames/s) with lateral and vertical resolutions in the nanometer range). 
     Electrostatically or thermally driven micromechanical positioning systems, furthermore, are known from U.S. Pat. No. 6,806,991 B1, by means of which, in spite of much smaller dimensions and masses, it is still impossible to realize higher scanning speeds. 
     In the case of scanning probe microscopy, the position controls are often realized by optical methods (e.g., interferometry). 
     SUMMARY OF THE INVENTION 
     The goal of the present invention is therefore to overcome the disadvantages known from the prior art and to provide a device and an associated method for the micromechanical positioning and manipulation of objects by means of which the scanning speed can be increased and the positioning accuracy can be improved, so that real-time images or video rate imaging (about 25 frames/s) with lateral and vertical resolution in the nanometer range can be realized. 
     According to the invention, this goal is achieved with the device for micromechanical positioning and manipulation of an object, comprising: at least one support element, an object carrier, guide elements, drive elements, elements for transmitting the movement from a drive element to the object carrier, and position detectors, where a contact point between the movement-transmitting elements and associated drive elements is formed as an arc, a ball, or a pointed tip, wherein the support element, the object carrier, the guide elements, and the movement-transmitting elements are a monolithic component. 
     Additional details and advantages of the invention can be derived from the following descriptive section, in which the invention is explained in greater detail with reference to the attached drawings, in which the same or similar parts are designated in all of the figures by the same reference numbers: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a first exemplary embodiment of an inventive device for the micromechanical positioning and manipulation of an object; 
         FIG. 1   a  shows an enlarged diagram of the guide elements of the device shown in  FIG. 1  with integrated position detectors; 
         FIG. 2  shows an enlarged diagram of the exemplary embodiment of  FIG. 1 ; 
         FIG. 3  shows an illustration of a displacement of the object carrier in the x direction by the push-pull principle; 
         FIG. 4  shows a second exemplary embodiment of the inventive device; 
         FIG. 5  shows a third exemplary embodiment of the inventive device; 
         FIG. 6  shows a fourth exemplary embodiment of the inventive device; 
         FIG. 7  shows a fifth exemplary embodiment of the inventive device; 
         FIG. 8  shows a sixth exemplary embodiment of the inventive device; 
         FIG. 9  shows a seventh exemplary embodiment of the inventive device; 
         FIG. 10  shows an eighth exemplary embodiment of the inventive device; 
         FIG. 11  shows a ninth exemplary embodiment of the inventive device; 
         FIG. 12  shows a tenth exemplary embodiment of the inventive device; and 
         FIG. 13  shows an eleventh exemplary embodiment of the inventive device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 and 1   a  show an exemplary embodiment of the inventive device and an enlarged part thereof. According to the invention, the support element  101 , the object carrier  116 , the guide elements  102 - 105 , and the elements  108 - 111  for transmitting the movement from the drive elements to the object carrier represent a monolithic component, preferably of silicon with a crystal orientation of &lt;111&gt; or &lt;100&gt;. On the basis of the semiconductor technologies known from the prior art, therefore, the inventive device can be miniaturized, and its weight can be reduced simultaneously. In addition, monocrystalline silicon, which is characterized by high rigidity and low mass density, has a high resonance frequency, as a result of which, a high limit frequency can be achieved with the inventive positioning device during the scanning or positioning process. 
     The object carrier  116  is connected by guide elements  102 - 105  to the one-piece support element  101 , wherein the guide elements can comprise a wide variety of different shapes (e.g., L-shaped). 
     The position detector or detectors  121 - 128 , which is/are preferably piezoresistive position sensors, is/are integrated into at least one guide element  102 - 105 . They serve as deflection sensors for the corresponding directions of movement. A field-effect transistor can also be used as a position detector. The channel serves here as a piezoresistive detection element. When silicon is used as a construction material for the inventive device, the necessary control electronics can be integrated into the support element, for example. 
     In an advantageous embodiment of the inventive device, position detectors are arranged on all of the guide elements. Simultaneous multiple evaluation of the position of the object carrier is thus possible. 
     To compensate for environmental influences such as temperature fluctuations, the position detectors (piezoresistive position sensors) are, in another preferred embodiment, connected to form a bridge circuit, wherein additional necessary elements of this bridge can be integrated into the nonmoving parts of the inventive device (e.g., the support element). 
     The drive elements  112 - 115  are integrated into the support element  101 . The movement generated by the drive elements is transmitted to the object carrier  116  in each case by way of point contacts or ball-shaped contact points  117 - 120  and by way of the movement-transmitting elements  108 - 111 . As a result of the point-like or ball-like contact points on the drive elements, it is possible to avoid any type of tipping forces. 
     According to the invention, piezoelectric actuators are preferably used as drive elements. Piezoelectric actuators are characterized by their rapid reaction to changes in voltage. Nevertheless, the object carrier  116 , because of its inertia, reacts much more slowly to a change in position determined by the piezoelectric actuators. To compensate for the reaction forces of the object carrier which occur at high accelerations, the drive elements (piezoelectric actuators) for one direction of movement operate according to the invention on the basis of the push-pull principle. The use of this principle also avoids any problems with overswing. 
     With a suitable arrangement of several drive elements, movements in the x-y plane as well as tipping, rotation, parallelism deviations, and elevations in the z direction can be detected and thus corrected, and they can also be produced intentionally. 
     Of course, it also lies within the scope of the invention to use other types of actuators such as piezoelectric bimorph actuators, electromagnetic or electrostatic actuators, or even bimetal actuators. 
       FIG. 2  shows an embodiment of the monolithic component described above comprising the object carrier  116 , the L-shaped guide elements  102 - 105 , and the elements  108 - 111  for transmitting the movement from the drive elements to the object carrier. In this embodiment, the drive and guide elements and the elements for transmitting the movement are positioned with mirror-image symmetry around the object carrier. 
       FIG. 3  shows the inventive method for movement of the object carrier  116  in the x direction by way of example. The symbol “V” stands for the voltage applied to the actuator, the voltage being proportional to the deflection. In a first step, the zero position is set up. For this purpose, the drive elements (piezoelectric actuators)  113 ,  115  are extended to one-half of their adjusting distances. This is necessary for the realization of the push-pull principle. The object carrier  116  does not change its position, because the action of the piezoelectric actuators  113 ,  115  via the elements  109 ,  111  for transmitting the movement compensate for each other. This position of the object carrier is detected as the zero position by the position detectors mounted on the guide elements  102 - 105 . 
     In the following step, the piezoelectric actuator  115  is extended and the piezoelectric actuator  113  located in the same direction of movement is retracted. As a result, the object carrier  116  is pushed in the x direction in correspondence with the extension of the piezoelectric actuator  115 , and the side pieces of the L-shaped guide elements  102 - 105  perpendicular to this direction of movement are bent. This brings about a change, proportional to the degree of extension, in the electrical resistance of the piezoresistive position sensors, which, according to the invention, are integrated into the guide elements  102 - 105 . When one position detector is used on each guide element, the displacement of the object carrier  116  can be determined from the difference of the change in resistance, and positional deviations, e.g., tipping, rotation, or parallelism deviations, can be recognized simultaneously and corrected if desired. 
       FIG. 4  shows a second embodiment of the inventive device. Here the drive and guide elements and the movement-transmitting elements are positioned in a rotationally symmetric manner around the object carrier. 
       FIG. 5  shows a third embodiment of the inventive device, in which the guide elements  102 - 105  are combined with the movement-transmitting elements  108 - 111 . Through this combination, the introduction of parasitic forces transverse to the direction of movement of the drive elements is avoided when the object carrier  116  moves in a direction orthogonal thereto. 
       FIG. 6  shows a fourth embodiment of the inventive device, in which bimorph actuators, e.g., bimorph piezoelectric actuators, are used as drive elements. As a result, the dimensions of the overall design can be considerably reduced. 
       FIG. 7  shows a fifth embodiment of the inventive device, in which only two drive elements are used, these being arranged asymmetrically. This embodiment does not work on the push-pull principle; instead, the restoring forces are generated by the guide elements  104 ,  103 . As a result, in comparison with the previously described embodiments, the number of required drive elements and associated control elements is reduced. 
       FIG. 8  shows an exemplary embodiment of the inventive positioning device in which the support element  101   a  is designed as a two-part unit, one part nested inside the other. The inner part of the support element, which carries the drive elements for one direction (e.g., the x direction) and the guide elements  102 - 105  and is moved by the drive elements in the direction perpendicular to that (y direction). The position detectors for the first direction of movement (x direction) are integrated into the guide elements  102 - 105 . The drive elements for the second direction of movement (y direction) are integrated into the outer part of the support element  101   a . The position detectors for the second direction of movement (y direction) are integrated into the guide elements  102   a - 105   a.    
       FIG. 9  shows an exemplary embodiment with 120° rotational symmetry. With this embodiment of the inventive device, it is possible to execute not only linear movements in the x and y directions but also partial rotational movements in a predetermined manner. 
       FIG. 10  shows an embodiment in which, in addition to the movements in the plane (x and y directions), tipping movements can also be executed in a targeted manner. For this purpose, the force is introduced by a first drive element  113  below the center of gravity of the object carrier  116  and by a second, opposite drive element above the center of gravity. When both drive elements are extended or both are retracted, the object carrier tips. When one of the drive elements is extended and the opposite drive element is retracted (push-pull principle), a movement in the plane of the object carrier  116  occurs. It is also possible to superimpose these two movements. 
       FIG. 11  shows another embodiment of the inventive device, which is suitable for generating movements in a plane, partial rotations, and tipping movements. The movements in a plane and the rotational movements are realized in a manner similar to that of the embodiment shown in  FIG. 9 . To generate tipping movements, the force is introduced on three different levels by the three drive elements. 
       FIG. 12  shows an embodiment of the invention for generating movements in a plane, partial rotations, and tipping movements. The movements in a plane are generated according to the principle of the embodiment shown in  FIG. 1 , wherein the actuators  112  and  112   a ,  113  and  113   a ,  114  and  114   a ,  115  and  115   a  operate on the in-phase principle. To generate a rotation, the actuators  112 ,  113 ,  114 ,  115  are extended, and the actuators  112   a ,  113   a ,  114   a  and  115   a  are retracted. Rotation in the opposite direction is generated in the inverse manner. To generate a tipping movement, the actuators  113  and  115   a , for example, are retracted, and the actuators  113   a  and  115  are extended. Other tipping movements are generated in a similar manner. 
       FIG. 13  shows by way of example an embodiment of the invention in which, in addition to the actuators  112 - 115  for generating the lateral, tipping, and partial rotational movements, one or more actuators  130  are installed underneath the object carrier  116  to generate elevations of the object carrier  116  along the z axis. The actuator or actuators  130  for generating elevations in the z direction can also be provided in any of the other embodiments of the invention according to  FIGS. 1-12 . 
     In a previously described preferred embodiment, position detectors are mounted on all of the guide elements to detect both movements in the x-y plane and rotations and tipping movements, so that, with the exemplary embodiments shown in  FIGS. 10-13 , these movements can be detected, monitored, and realized in a predetermined manner. 
     According to the invention, the entire device is produced as a single unit on a silicon wafer by means of traditional surface/volume micromechanical technology (surface micromachining or bulk micromachining). CMOS semiconductor fabrication technology, which has been continuously perfected over its many years of existence, makes it possible to fabricate the inventive micromechanical device for the positioning and manipulation of an object with minimal effort. 
     The inventive combination of the micromechanical design with suitable drive elements (piezoelectric actuators) and suitable position detectors (piezoresistive position sensors) makes it possible to integrate these elements into the monolithic component. This improves the accuracy with which the position of the object carrier can be determined, because the piezoresistive resistors can be positioned precisely where the actual movement of the object carrier can be detected most effectively. 
     The inventive positioning device achieves an increase in the scanning speed, and in association with that, it also opens up new areas of application (e.g., for real-time AFM or video rate imaging). It can be used under vacuum or in the atmosphere and is also suitable for use in liquids and in dusty environments. It is also resistant to many laboratory chemicals. 
     LIST OF REFERENCE NUMBERS 
     
         
           101  support element 
           101   a  two-piece support element 
           102 - 107  guide elements 
           102   a - 105   a  guide elements 
           108 - 111  elements for transmitting movement from the drive element to the object carrier 
           112 - 115  drive elements 
           112   a - 115   a  drive elements 
           116  object carrier 
           117 - 120  contact points 
           121 - 128  position detectors 
           129  fastening and mounting holes 
           130  drive element/actuator