Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02N—ELECTRIC MACHINES NOT OTHERWISE PROVIDED FOR
  • H02N2/00—Electric machines in general using piezoelectric effect, electrostriction or magnetostriction
  • H02N2/02—Electric machines in general using piezoelectric effect, electrostriction or magnetostriction producing linear motion, e.g. actuators; Linear positioners ; Linear motors
  • H02N2/028—Electric machines in general using piezoelectric effect, electrostriction or magnetostriction producing linear motion, e.g. actuators; Linear positioners ; Linear motors along multiple or arbitrary translation directions, e.g. XYZ stages
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/20—Piezoelectric or electrostrictive devices with electrical input and mechanical output, e.g. functioning as actuators or vibrators
  • H10N30/206—Piezoelectric or electrostrictive devices with electrical input and mechanical output, e.g. functioning as actuators or vibrators using only longitudinal or thickness displacement, e.g. d33 or d31 type devices

Definitions

• the invention relates to a piezoelectric fine positioning device for moving an object in three coordinate directions and a method for controlling the fine positioning device.
• Fine positioning in the sense of the invention means a positioning accuracy of better than 10 ⁇ 10m, ie a movement in the range of atomic dimensions.
• Devices of this type form, for example, the basis for the investigation of the surface topography using the tunnel effect.
• the fine positioning device moves a pointed scanning needle at a predetermined distance in a grid pattern over the surface to be examined, for example the tunnel flow being used to regulate the distance and the controlled variable being displayed as a function of the position signal of the scanning tip (raster tunnel microscopy) .
• the fine positioning device must meet two requirements in particular. It must be particularly stable mechanically in order to make the system insensitive to vibrations in the environment.
• the resonance frequency of the device should be as high as possible in order to be able to achieve the highest possible scanning speed for the scanning, which, in addition to greater spatial resolution, also permits better time resolution when observing dynamic processes.
• the invention was therefore based on the object of providing a fine positioning device which has low sensitivity to vibration, has a high resonance frequency, is largely insensitive to temperature and can also be used in the low-temperature range in particular, which has a flat design and is as simple as possible Construction enables.
• the prominent feature of the device according to the invention is the consequent minimization of parasitic, piezoelectrically inactive masses and at the same time extremely low overall mass of the actual drive body. It consists of a single, homogeneous piezoelectric component.
• the clamping device which rests relative to the drive body can be made of a material whose thermal expansion coefficient is matched to that of the drive body.
• Embodiments of the device according to the invention are shown schematically in the drawing. Their mode of operation is described below with reference to the figures. In detail show:
• FIG. 1 is a bottom view of the fine positioning device.
• FIG. 2 is a top view of the fine positioning device.
• FIG. 3 is a front view of the fine positioning device.
• FIG. 4 is a schematic illustration of the movements in a, b) tangential, c) axial and d ) radial direction
• FIG. 5 another possibility of the electrode arrangement
• FIG. 6 a block diagram of the control
• the fine positioning device shown in FIG. 1 contains a fork-shaped clamping device consisting of two legs 1, 2. The two legs 1, 2 are held together by a bearing screw 4 and can be adjusted against one another by a clamping screw 3 as pliers.
• the legs can be firmly connected in the area of the tensioning screw, with tensioning against the spring force of the legs then being possible in the area of screw 4.
• the jig can be made of brass.
• a ceramic or glass-ceramic material can also be selected if this is more expedient, for example because of the thermal properties.
• the actual drive body which consists of a round, approximately plane-parallel piezoelectric disk 5, is arranged within the legs 1, 2.
• the underside of the piezoelectric disk 5 shown in FIG. 1 is covered with three flat electrodes 6, 7, 8, to each of which an electrical control voltage can be applied via electrical connections 9, 10, 11.
• the dividing line 12 between the electrode fields has the shape of a Y.
• the areas of the electrodes 6, 7 are at least approximately the same size, while that of the electrode 8 is very small in comparison. Their maximum length and width should not be greater than the thickness of the disc 5.
• the piezoelectric disk 5 is held in the pressure points 13, 14 by the outer parts of the legs 1, 2 and lies in the inner region of the legs at two points 15, 16 lying close together, which can also be regarded as a single pressure point.
• the leg length with respect to the pressure points 13, 14 is selected such that the center of the disc 5 lies within the fork surface of the clamping device, which is closed off by the connecting line between the pressure points 13, 14, but in the vicinity of this connecting line. This measure ensures that the pane 5 cannot be pushed forward out of the clamping device on the one hand and on the other hand the largest possible area of the pane surface lies outside the pane surface enclosed by the pressure points 13, 14, 15, 16. It has proven expedient if the pressure points 13, 14 are selected such that at least 1/3 of the disk circumference spans the free part of the fork legs 1, 2.
• the orientation of the electrode surfaces is chosen such that the dividing line between the electrodes 6, 7 on the symmetry line of the clamping device and the surface lying in the wedge of the Y lie outside the disk surface enclosed by the pressure points 13, 14, 15, 16.
• the entire surface of the top of the piezoelectric disk 5 is covered with a further electrode 17, to which a specific electrical potential can likewise be applied via an electrical connection 18.
• this can e.g. also be the mass potential. All electrodes are applied to the piezoelectric disc 5 in such a way that they are sufficiently electrically insulated from one another and from the clamping device. Only in the case of an electrode provided as a ground electrode can it be expedient to electrically connect it directly to the clamping device if it consists of an electrically conductive material.
• a stylus 19th For use in a tunnel microscope, this can be a tungsten tip, for example.
• the scanning needle 19 can, for example, be attached to the electrode surface 17 with an electrically insulating adhesive, so that a current flow picked up by the scanning needle 19 can be derived for measurement purposes via an electrical connection 20.
• the fastening location of the scanning needle 19 lies in the electrical field area of the electrode 8.
• the tip of the scanning needle 19 extends slightly beyond the edge of the piezoelectric disk in the extension of the already mentioned line of symmetry of the clamping device.
• the front view in FIG. 3 shows how the piezoelectric disk 5 is held in the legs 1, 2 of the clamping device. As a supplement to FIGS.
• the clamping device is attached to a base plate 21 here.
• This can be a glass plate, for example.
• the fine positioning device itself thus becomes a positionable object that can be moved, for example, by the electrically controllable drive device described in the earlier application P 36 14996.9.
• FIG. 4 The greatly simplified representations shown in FIG. 4 and greatly exaggerated with regard to the volume shifts in the piezoelectric disk 5 are intended to explain the movements of the tip of the scanning needle 19 which are referred to as tangential, axial and radial. 4a, b, c are derived from the front view of FIG. 3, FIG. 4d corresponds to a side view of FIG. 2.
• a movement in the tangential direction is accordingly achieved if the difference in the potentials is changed with a constant sum of the potentials at the electrodes 6, 7.
• the thickness of the disk is small compared to the length or width of the disk, so that the main effect of the voltage change is to stretch or compress the piezo areas located under the electrodes in the direction of the disk plane. Since the effects in the area of the two electrodes are opposite to each other due to the special control voltages (constancy of the potential sum), the center line of the piezoelectric disk, which has the same direction as the dividing line between the electrodes 6, 7, is moved sideways. The scanning needle 19 fastened on this line therefore also moves in this direction, which is referred to as tangential.
• FIG. 4a illustrates the case where the potential at the electrode 6, a maximum dilatation and at the elec- 'trode 7 produces a maximal contraction. Since the outer boundary of the disc 5 cannot evade due to the clamping, the necessary volume compensation takes place in the area of the center line.
• the stylus follows the moving volume to the left. 4b shows the situation when the potential is reversed. The stylus is moved to the right. The maximum travel is determined by the difference in the control potential, the zero position by the sum of the potentials.
• the movement of the scanning needle in the axial direction which occurs at the same time as it moves out of the zero position from the two FIGS. 4a, b, can, as already explained above, be neglected in practice.
• the potential of the electrode 8 is responsible. Since the piezoelectric disk 5 is not fixed in this area, a change in voltage in this area essentially causes a change in thickness. The position of the needle tip changes by half the change in thickness, as illustrated in FIG. 4c. As already explained above, the thickness of the disk is greater than the length and width of the electrode 8 in this field region. The length change in the diameter of the disk associated with the change in thickness due to constant volume can therefore be neglected in practice.
• the movement of the scanning needle 19 in the radial direction is achieved by changing the sum of the potentials of the electrodes 6, 7 with a constant difference.
• the piezoelectric disk 5 is stretched or compressed overall in the direction of the disk surface.
• the change in length resulting from the constant volume in the radial direction can only have an effect in the direction of the open end of the legs 1, 2 due to the clamping of the disk 5.
• the superimposed movement in the axial direction that can be read from FIG. 4d is negligible in practice because of the relationship between the disk diameter and the disk thickness.
• the electrode arrangement shown in FIG. 5 differs from the aforementioned one in that the electrodes 6 ', 7' corresponding to the two electrodes 6, 7 'are now designed as semicircular surfaces.
• the electrode 8 'corresponding to the small electrode 8 is integrated in the electrode 17' corresponding to the electrode 17 and here carries the scanning needle 19.
• the movement tasks assigned to the individual potentials on these electrodes are the same as described above.
• the orientation of the piezoelectric disk in the clamping device is also analog.
• the simpler geometry of the electrode arrangement brings certain advantages in its manufacture and the mutual electrical insulation of the electrode surfaces.
• the device can be adapted to the respective measurement task with regard to resonance frequency and maximum deflection.
• FIG. 6 shows a block diagram for the generation of the required potentials at the electrodes 6, 7, 8, 17 of the fine positioning device according to FIGS. 1, 2, 3.
• the voltages U rac ⁇ , U ⁇ an »U ax s i nc * ⁇ en di spatial coordinates of the object to be positioned can be regulated proportionally and independently.
• An adder is connected upstream of the electrode 6 and a subtractor is connected upstream of the electrode 7.
• the basic potential U ra ( j required for the radial movement is supplied to both the adder and the non-inverting input of the subtractor as an input voltage.
• the voltage Ut an responsible for the tangential movement is supplied to the adder and the inverting input of the subtractor output voltages of the adder and the subtracter to a high voltage amplifier are respectively 60.70 supplied voltage as Steuer ⁇ whose outputs supplied to the respective electrodes to the desired potential.
• U rao is thus the sum of the potentials at the electrodes 6 and 7 constant, even if the difference of the potentials by changing U ⁇ to AEN changed.
• the time required for the axial movement voltage U ax is also passed through a high voltage amplifier 80 of the electrode 8, independently from the other voltages zu ⁇ .
• the electrode 17 is connected through a high voltage amplifier 170 on one knockout Constant potential, which can also be the ground potential, it being possible to dispense with the high-voltage amplifier.
• Utan is expediently periodically controlled linearly between its maximum values, U ax being increased linearly at the same time.
• the value U-tan determines the length of a scan line, while U a determines the spacing of the scan lines for a half period of the control of Utan.
• U ax can also be abruptly increased at the end of a scanning line by the value of a line spacing.
• U ra d determines the distance of the needle tip from the object to be examined. It can be regulated via U rac (in such a way that a constant measurement signal is obtained. However, it can also be kept constant during a measurement U rac
• the regulation of the voltages required for the desired movement of the scanning needle can advantageously be controlled in a manner known per se by a microprocessor.
• the superimposed movements described above as negligible in practice can also be compensated for by corresponding counter-voltages acting in this direction.
• the device according to the invention was tested with a piezoelectric disk approximately 10 mm in diameter and 2 mm thick, made of a material known under the name PXE 5 (from Valvo) and silver electrodes, the clamping device being made of brass.
• a tungsten tip was used as the object to be positioned, with which a gold layer was examined under normal conditions and an oil immersion between the tip and the gold layer. It was possible to clearly detect individual atoms in the gold layer, which corresponds to a lateral resolution of better than 3.10 " 10 m.

Landscapes

• Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
• General Electrical Machinery Utilizing Piezoelectricity, Electrostriction Or Magnetostriction (AREA)
• Control Of Position Or Direction (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

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• 1986
  • 1986-07-04 DE DE19863622557 patent/DE3622557A1/de active Granted
• 1987
  • 1987-07-02 EP EP87904233A patent/EP0273942A1/de not_active Withdrawn
  • 1987-07-02 US US07/183,187 patent/US4859896A/en not_active Expired - Fee Related
  • 1987-07-02 JP JP62503976A patent/JPH01500223A/ja active Pending
  • 1987-07-02 WO PCT/DE1987/000296 patent/WO1988000399A1/de not_active Application Discontinuation
• 1988
  • 1988-02-08 KR KR1019880700141A patent/KR880701975A/ko not_active Withdrawn

Non-Patent Citations (1)

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