Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-12-01
2002-02-26
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06351057
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microactuator and a method for fabricating the same, and more particularly to a microactuator having a piezoelectric element formed on a substrate to have a desired thickness and patterned using an etching process. The present invention also relates to a method for fabricating such a microactuator.
2. Description of the Prior Art
Typically, a microactuator includes a lower structure including a substrate and a chamber, a piezoelectric element attached to the upper surface of the substrate and adapted to generate a mechanical deformation thereof upon receiving a voltage, and an electrode (electrodes) adapted to transmit the voltage to the piezoelectric element.
In such an actuator having the above mentioned configuration, the piezoelectric element has a property exhibiting a poling phenomenon when an electrical field is applied thereto. In other words, the piezoelectric element exhibits an orientation when an electrical field is applied thereto. When a voltage is repeatedly applied across the piezoelectric element between upper and lower electrodes respectively formed at the upper and lower surfaces of the piezoelectric element, repeated mechanical deformation and recovery of the piezoelectric element occur, thereby causing the piezoelectric element to vibrate.
Since the actuator drives by virtue of an electrical field applied thereto, it is necessary to continuously apply a drive voltage to the actuator for such a driving of the actuator.
A variety of conventional methods are known in association with the manufacture of microactuators.
One method is a method in which a lower electrode is formed on a thin substrate patterned to have an accurate size. The resulting structure is then baked at a temperature of 1,200° C. Thereafter, a paste for formation of a piezoelectric element is formed over an exposed surface of the lower electrode, and then baked at a temperature of 1,000° C. or more, thereby forming a piezoelectric element. Subsequently, an upper electrode is formed on the piezoelectric element and then baked at a temperature of about 800° C. Thus, a microactuator is fabricated.
Another method is a method in which a piezoelectric sheet including a plurality of piezoelectric elements is prepared and then bonded to a metal substrate using a third material. In this case, the resulting piezoelectric plate is subjected to a machining process to simultaneously obtain a plurality of actuators each corresponding to one of the piezoelectric elements. Alternatively, a piezoelectric element machined to have a size corresponding to one actuator is bonded to a metal substrate, thereby obtaining an actuator.
Microactuators fabricated in the above mentioned methods have a cross-sectional structure having vertically extending lateral end surfaces. For this reason, the upper electrode for each actuator can be formed only on the upper surface of the piezoelectric element.
Meanwhile, for an application of a drive voltage or other signals to the actuator, input lines should be connected between the upper electrode and a circuit for supplying the drive voltage and other signals.
In order to connect such input lines to the upper electrode for an application of the drive voltage and other signals, a variety of connection methods have been used. For example, a wire bonding method has been used. Also, a method has been used in which input lines are directly connected to the upper electrode.
In accordance with the method in which input lines are connected to the upper electrode of the actuator using a wire bonding process, pads are formed at both the upper electrode and an insulating layer on a substrate, respectively. Wires are then bonded to the pads, respectively. For this reason, the process used is complex, resulting in a degradation in productivity. Moreover, wires, which are exposed, interfere with a process for coupling a printer head provided with the actuator with a cartridge. In severe cases, a part of such wires may be cut. Accordingly, there are problems of a degradation in reliability in terms of quality and a degradation in durability.
The method for directly connecting input lines to the upper electrode of the actuator is advantageous in that the connecting process is simple because it is unnecessary to form an insulating layer and pads for the connection of the input lines to the upper electrode. In this case, however, pressure and heat generated during the connection of the input lines to the upper electrode are directly applied to the piezoelectric element of the actuator, thereby causing the piezoelectric element to be changed in physical properties. As a result, the resulting product may be damaged.
The direct connection of the input lines to the upper electrode of the actuator may also have an adverse influence on a desired deformation of the actuator occurring in response to an application of a drive voltage to the upper electrode.
The above mentioned conventional methods exhibit a further degradation in productivity and quality in the case using an increased number of actuator cells.
In order to solve the above mentioned problems, the applicant has proposed a microactuator fabrication method which involves the steps of attaching a piezoelectric element having a desired thickness to the upper surface of a substrate, and patterning the piezoelectric element using an etching process, thereby forming a microactuator having a desired piezoelectric element pattern.
FIG. 1
schematically illustrates a method for forming a piezoelectric element using an etching process.
In accordance with the illustrated method, a metal substrate
10
is first prepared. A piezoelectric element
14
is then formed over the prepared substrate
10
. The piezoelectric element
14
is then patterned using an etching process. Thereafter, an upper electrode
16
is formed on the patterned piezoelectric element
14
.
FIG. 2
schematically illustrates a method for forming a piezoelectric element using an etching process.
In accordance with this method, a metal substrate
20
is first prepared. A lower electrode
22
is then formed over the prepared substrate
20
. Thereafter, a piezoelectric element
24
is formed over the lower electrode
22
. The piezoelectric element
24
is then patterned using an etching process. An upper electrode
26
is subsequently formed on the patterned piezoelectric element
24
.
Where a microactuator is fabricated in accordance with the above mentioned method of
FIG. 1
or
2
using an etching process, its piezoelectric element has a cross-sectional structure having, at its lateral ends, an inclined shape instead of a vertical shape. Accordingly, it is possible for the upper electrode to be formed not only on the upper surface of the piezoelectric element, but also on a lateral end surface of the piezoelectric element. In other words, the upper electrode formed on the upper surface of the piezoelectric element can extend to the substrate on which the piezoelectric element is formed.
Where the upper electrode exists not only the upper surface of the piezoelectric element, but also on a lateral end surface of the piezoelectric element, it is possible to connect input lines to the portion of the upper electrode disposed at the lateral end surface of the piezoelectric element. This allows for an easy connection of input lines to the actuator.
However, where the piezoelectric element is etched using a general etching pattern, it may have a non-uniform inclination along its etched lateral end surface. In particular, the piezoelectric element has a sharp inclination at a portion of its lateral end surface near the upper end thereof, so that it has a shape edge.
It is difficult to form an upper electrode on the sharp upper portion of the lateral end surface of the piezoelectric element. For this reason, it is easy for the short circuit to be partially cut at the lateral end surface of the piezoelectric element, as shown in FIG.
3
. Thus, it is difficult for the upper electrode to extend completely
Medley Peter
Ramirez Nestor
Samsung Electro-Mechanics Co., LTD
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