JPH02261072A - Piezoelectric actuator - Google Patents

Abstract

PURPOSE:To keep a combined distortion quantity constant by using discs having circular center holes as a piezoelectric member. CONSTITUTION:A piezo-actuator is constituted of laminated piezoelectric discs 41-4n. The discs 41-4n have circular holes H in the central parts of them, they are put between plate-like electrodes 50-5n, and they are connected with band electrodes 61-62 in every other one. As a result, distortion quantity reaches the maximum at the intermediate section between an internal diameter and an external diameter, and the part stretches in the shape of a circle, so that a driven body can be positioned with high degree of accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a piezoelectric actuator that drives a driven body by an expansion and contraction operation that combines the strains of stacked piezoelectric parts.

[Conventional technology]

In recent years, a scanning tunneling microscope (STM) has attracted attention as a device that can observe the morphology of a solid surface in real space with atomic-scale resolution. This scanning tunneling microscope
When a metal needle is brought close to a solid surface until the distance is 1 nm or less and a voltage of several volts or less is applied between the needle and the solid surface, a tunnel current of several nA flows through the vacuum barrier between them. Depending on the polarity of the voltage, this tunneling current is proportional to the valence band of the sample or to the density of states of vacant levels in the conduction band of the sample. Therefore, the tunnel voltage is v1, the tunnel current is 1, and dI /dV is Vr
Measurement as a function of r rr provides information on the density of states of the band structure of the sample.

This device is equipped with a coarse movement mechanism that allows the sample to be moved over a wide range relative to the needle, and a fine movement mechanism that allows the needle to scan in three dimensions. Among these, coarse movement mechanisms include mechanisms that expand and contract piezoelectric plates such as PZT (lead zirconate titanate) and PLZT (lead lanthanate zirconate titanate) to allow two-dimensional walking, while fine movement mechanisms use piezoelectric plates. A mechanism called a "tri-bod" in which plates are arranged perpendicular to the X, Y, and Z directions is used.

By the way, since the strain of a single piezoelectric element, which has electrodes on both sides of a piezoelectric plate and applies a voltage to them, is slight, it is necessary to stack multiple piezoelectric elements in order to obtain the required amount of displacement. There is. In this specification, this laminate is referred to as a piezoelectric actuator.

FIGS. 3(a) and 3(b) are a plan view and a vertical cross-sectional view of a conventional piezoelectric actuator that can be used in both a coarse movement mechanism and a fine movement mechanism. Here, a large number of piezoelectric disks 11 to 1n are stacked such that they are sandwiched between plate-shaped electrodes 20 to 2n, and every other electrode 2
0. 22. . . is connected to the electrode 21 by the strip electrode 31.
23 . . . 2n are commonly connected by a strip electrode 32. When a power supply (not shown) is connected to these strip electrodes 31 and 32, equal voltages are applied between adjacent electrodes, and the piezoelectric disks 11 to 1n are respectively distorted, and these distortions are combined. Largely expands and contracts in the entire axial direction. This provides a drive mechanism with a large amount of displacement.

[Problem to be solved by the invention]

Generally, when electrodes are attached to both sides of a piezoelectric disk and a voltage is applied between these electrodes, the amount of strain at the center is greater than the amount of strain around the center, and the electrode attachment surface is deformed into a substantially spherical shape. Therefore, when a voltage is applied to the piezoelectric actuator shown in FIG. 3, each amount of strain is added in a state where the axes are in point contact, as shown in FIG. 4. At this time, the piezoelectric disk 11 is at point F with respect to the driven body. So, the piezoelectric disks 11 and 12 are at point F
1, piezoelectric disk 12.13 is at point F2, piezoelectric disk 1
3.14 is point F3...If they are in point contact, that is, if they are configured to make point contact on the same axis, a sufficiently large amount of displacement can be secured. Moreover, the positioning accuracy of the driven body 10 can also be improved.

However, the piezoelectric disk 11~Ins electrode 21~
It is difficult to make the shape and bonding state of each 2n uniform, and therefore it is almost impossible to make point contact on the same axis. For this reason, with conventional piezoelectric actuators, the amount of displacement resulting from the synthesis of strain is not constant, and when applied to a scanning tunneling microscope, the positioning accuracy with respect to the needle decreases, and the resolution decreases accordingly. There was a problem with this.

This invention was made in order to solve the above problems, and provides a piezoelectric actuator that can maintain a constant amount of displacement and thereby greatly improve the positioning accuracy of a driven object. With the goal.

[Means to solve the problem]

The present invention provides a piezoelectric actuator in which a plurality of piezoelectric members are laminated and a driven body is driven by an expansion/contraction operation that combines the strains of these piezoelectric members, in which the piezoelectric member is a disk having a circular center hole. It is characterized by the use of

[For production]

In this invention, since disks having a circular center hole are used as piezoelectric members to be laminated, the amount of strain is greatest at approximately the midpoint between the inner diameter and the outer diameter, and the portion with the largest amount of strain is Because they are connected in a circular manner, line contact along the circle can be made between the piezoelectric members and between the piezoelectric member and the driven body, and thereby the amount of combined strain can be kept constant. can.

〔Example〕

FIGS. 1(a) and 1(b) are a plan view and a longitudinal sectional view of an embodiment of the present invention. In the figure, a large number of piezoelectric discs 41 to 4n each having a circular hole H in the center are stacked such that they are sandwiched between plate-shaped electrodes 50 to 5n, and every other electrode 50, 52. ... are the strip electrodes 61, and the electrodes 51, 53, . . . 5n are the strip electrodes 6.
2 are commonly connected to each other. In this case, as the electrodes 50 to 5n, any of a conductive paste, a metal film formed by vapor deposition, or a metal plate punched and formed in advance may be used, but it is convenient to use a conductive paste as the strip electrodes 61 and 62. It is.

Note that the electrodes 50 to 5n are piezoelectric disks 41 having a center hole.
It is formed into a ring shape following the shape of ~4n. Therefore, when a voltage is applied to this, the portion along the dashed line A in FIG. 1(a) will be distorted the most.

FIG. 2 is a vertical cross-sectional view emphasizing the deformed state (the strip electrode is removed). That is, the piezoelectric disks 41 to 4n
has a central hole H, so A at approximately the midpoint between the inner diameter and the outer diameter. , A1...A4 points are the largest, and along the circle obtained by connecting these points, the distortion is
1 and the driven body 10 are in line contact.

In this way, if there is a line contact along a circle, the piezoelectric disk 4
Even if the shapes of electrodes 1 to 4n and electrodes 51 to 5n change slightly, or even if their bonding states change, the direction and magnitude of the strain can be aligned and the amount of combined strain can be kept constant. can.

Thus, this example can be applied to a scanning tunneling microscope (STM).
), the needle positioning accuracy can be greatly improved and at the same time, the resolution can be improved.

In this case, since a disk with a circular center hole H is used,
Ancillary benefits include reduced weight, capacitance and stress concentrations compared to conventional devices.

Although the above embodiments have been explained on the premise that the present invention is applied to a scanning tunneling microscope, the present invention is not limited thereto, and it goes without saying that it can also be applied to, for example, a laser beam moving device during IC manufacturing. stomach.

〔Effect of the invention〕

As is clear from the above explanation, according to this invention,
Since a disk with a circular center hole is used as the piezoelectric member, line contact can be made at the circular part approximately halfway between the inner and outer diameters, thereby keeping the amount of combined strain constant. It has the effect of being able to.

[Brief explanation of drawings]

FIGS. 1(a) and (b) are a plan view and a longitudinal sectional view of an embodiment of the present invention, and FIG. 2 is a longitudinal sectional view showing the deformed state of the piezoelectric disk in order to explain the operation of the embodiment. 3(a) and 3(b) are a plan view and a vertical sectional view of a conventional piezoelectric actuator, and FIG. 4 shows a deformed state of a piezoelectric disk in order to explain the operation of this piezoelectric actuator. FIG. 41-4n...piezoelectric disk, 50-5n...electrode,
61.62...Strip electrode, H...hole.

Claims (1)

[Claims] In a piezoelectric actuator in which a plurality of piezoelectric members are laminated and a driven body is driven by an expansion and contraction operation that combines the strains of these piezoelectric members, a disk having a circular center hole is used as the piezoelectric member. A piezoelectric actuator featuring: