JP2020012159A - Pzt element, and pzt element production method - Google Patents

Abstract

To provide a PZT element that does not have high breakdown voltage but has high durability.SOLUTION: A PZT element 5 is obtained by sputtering a ground layer 23 composed of an LaNiOthin film grown in a range of 485°C or more and 585°C or less with a sputtering target composed of PZT having Ni added thereto, and forming a PZT layer 24 containing Ni of 0.1 at% or more and 5 at% or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to the reliability of a PZT element, and more particularly, to a PZT element with improved durability.

Piezoelectricity refers to a property in which a polarization or an electric field is generated inside a crystal when a stress is applied from the outside, and a distortion or a stress is generated in the crystal when an electric field is applied. This dielectric material having piezoelectricity is called a piezoelectric material. Lead titanate (PbTiO ₃ ), lead zirconate (PbZrO ₃ ), lead zirconate titanate (Pb (Zr · Ti) O ₃ ), metaniobium Lead acid (PbNb ₂ O ₆ ), bismuth titanate (Bi ₄ Ti ₃ O ₁₂ ) and the like can be mentioned.

  Among them, lead zirconate titanate is commonly called PZT and is a ferroelectric having a crystal structure called a perovskite type. PZT not only has good piezoelectric properties but also has very stable temperature characteristics, so it is used as a main material in piezoelectric materials for components such as ignition elements, ultrasonic elements, actuators, sensors, and ceramic filters. .

  PZT elements are used for piezoelectric actuators that require precise position control, such as the stage for ultra-fine movement of semiconductor exposure equipment and the precision positioning probe, because of their features such as high displacement accuracy, large generating force, and fast response speed. , Long life is required.

  The reliability of PZT is described in the following document.

“AC and DC Electrical Stress Reliability of Piezoelectric Lead Zirconate Titanate (PZT) Thin Films”, The International Journal of Microcircuits and Electronic Packaging, Volume 23, Number I, First Quarter 2000 (ISSN 1063-1674)

  Conventionally, the breakdown voltage of a PZT element was determined, and a PZT element having a large breakdown voltage was determined to have a long life. However, when an acceleration test in which a voltage was applied to the PZT layer at a high temperature was performed, the breakdown voltage was large. It was found that there was no correlation between the value and the value of MTTF (Mean Time to Failure).

  In particular, even in a PZT element having a large breakdown voltage, when the MTTF measured at a high temperature is converted to a low temperature of 100 ° C., the MTTF becomes a value of about 100 hours, and a failure may occur in a short time.

The present invention has been made in order to solve the above-mentioned problems of the related art, and has a substrate, a first electrode layer disposed on the substrate, and an underlayer disposed on the first electrode layer. And a second electrode layer disposed on the PZT layer, the PZT layer containing an additive metal disposed on the underlayer in a range of 0.1 at% to 5 at%. Ni is used as the additive metal, and the PZT layer is a PZT element that is a PZT crystal grown on the surface of the first electrode layer by sputtering a PZT target.
The present invention is the PZT element, wherein the underlayer is made of LaNiO ₃ .
According to the present invention, the PZT crystal is a PZT element in which the underlayer is grown at a temperature in a temperature range of 485 ° C. or more and 585 ° C. or less.
The present invention provides a first electrode layer, a base layer disposed on the first electrode layer, a PZT layer disposed on the base layer, and a PZT layer disposed on the PZT layer. A PZT element manufacturing method for manufacturing a PZT element having an electrically connected second electrode layer, the PZT target containing Ni as an additive metal in a range of 0.1 at% or more and 5 at% or less. Forming a PZT layer by growing PZT crystals on the surface of the underlayer, and forming a second electrode layer on the PZT layer by forming a second electrode layer on the PZT layer And a method for manufacturing a PZT element having:
The present invention is the method for manufacturing a PZT element, wherein in the PZT layer forming step, the underlayer is heated to a temperature in a temperature range of 485 ° C or more and 585 ° C or less.

By adding Ni, a crystal defect is reduced and a PZT element having a long MTTF can be obtained.
When a PZT layer is formed on a LaNiO ₃ underlayer by a sputtering method, a PZT crystal can be grown at a temperature lower than 600 ° C., so that a PZT layer with further reduced crystal defects can be obtained.

(a) to (c): diagrams for explaining a manufacturing process of a PZT element An example of a sputtering apparatus for forming a PZT layer Graph for explaining that there is no correlation between breakdown voltage and MTTF Graph for obtaining MTTF at actual use temperature from the result of accelerated test

<PZT element manufacturing process>
Reference numeral 21 in FIG. 1A denotes a ceramic substrate such as silicon for forming a PZT layer. A first electrode layer 22 is formed on the surface of the substrate 21, and a first electrode layer 22 is formed on the surface of the first electrode layer 22. An underlayer 23 is formed.

The first electrode layer 22 is a metal thin film of platinum or the like, and the underlayer 23 has electrical conductivity and is a crystal having a lattice constant close to that of PZT. Here, a LaNiO ₃ thin film is used for the underlayer 23. ing.

  The substrate 21 is carried into the vacuum chamber 11 of the sputtering apparatus 10 of FIG. The underlayer 23 is exposed on the surface of the substrate 21 on the table 32, and a sputtering target 37 attached to a backing plate 36 is disposed at a location facing the underlayer 23.

  The sputtering target 37 is composed of PZT and an additional metal added to PZT in a range of 0.1 at% or more and 5.0 at% or less. In the present invention, Ni is used as the additional metal.

  The inside of the vacuum chamber 11 is evacuated by a vacuum exhaust device 35, and a sputtering gas is introduced into the vacuum chamber 11 by a gas introducing device 33.

  The substrate 21 is heated to a temperature in a temperature range of 485 ° C. or more and 585 ° C. or less, and while maintaining the temperature, a voltage is applied to the backing plate 36 by the sputtering power supply 34 to generate a plasma of a sputtering gas, thereby setting the sputtering target 37. Sputter.

  By the sputtering, atoms constituting PZT from the sputtering target 37 and the added metal added to the PZT are sputtered out of the sputtering target 37 as sputtered particles, arrive at the substrate 21 and adhere to the underlayer 23, as shown in FIG. As shown in (b), a PZT layer 24 composed of a PZT thin film containing an additional metal is grown.

  Here, the substrate 21 was heated during sputtering, and the PZT layer was grown while maintaining a temperature of 485 ° C. on the substrate 21.

  If the temperature of the substrate 21 during sputtering is 465 ° C. or higher even if the temperature is lower than 485 ° C., a highly durable PZT layer can be formed, but the piezoelectric characteristics of the PZT layer deteriorate. Therefore, the substrate temperature during sputtering is desirably 485 ° C. or higher.

  On the other hand, if the substrate temperature is 700 ° C. or lower, the PZT layer can be formed by a sputtering method. However, if the temperature is higher than 585 ° C., the durability is deteriorated.

  In a film forming method other than the sputtering method, a PZT layer having good piezoelectric characteristics is not grown at a substrate temperature of 600 ° C. or lower.

  The composition of the PZT layer 24 formed by the sputtering method is the same as that of the sputtering target 37, and the PZT layer 24 of the present invention contains Ni as an additive metal in a range of 0.1 at% or more and 5.0 at% or less. I have.

  After the PZT layer 24 is formed to a predetermined thickness, the substrate 21 is moved to another sputtering apparatus, and a second electrode layer 25 is formed on the surface of the PZT layer 24 as shown in FIG. Element 5 is obtained.

  When a voltage is applied between the first and second electrode layers 22 and 25, the PZT element 5 expands and contracts by a length corresponding to the polarity and magnitude of the voltage, and moves the target object precisely by a desired distance. be able to.

<Weibull distribution>
In the Weibull distribution, when a shape parameter (shape parameter) m and a scale parameter (scale parameter) β are used, the distribution function F (t) is expressed by the following equation (1) of the function of the failure time t.

  Equation (1) can be rewritten into the following equation (2).

  The value on the left side of the equation (2) is a logarithmic value of the cumulative failure rate obtained from the number of failures and the failure time t. From the linearity of the value of lnt on the right side, the value of the shape parameter m and the scale parameter β Is obtained.

  The MTTF (mean time to failure) can be obtained from the following equation (3) using the shape parameter m, the scale parameter β, and the gamma function Γ (·).

<Measurement of MTTF>
Samples of the PZT element prepared under various conditions, such as a condition of adding Ni and a condition of not adding Ni, are placed in a predetermined high-temperature atmosphere, and the same measurement is performed between the first and second electrode layers 22 and 25 as in actual use. An acceleration test was performed in which a voltage was applied and a failure time t until a current equal to or more than the upper limit flowed was measured.

  Here, the thickness of the PZT layer of each PZT element is 2 μm, and the measurement voltage is 40 V, so that the PZT layer is placed in an electric field of 0.2 MV / cm.

Apart from the accelerated test, after applying a low voltage between the first and second electrode layers of another PZT element prepared under the same conditions, the applied voltage is increased and the current (1 μA / cm ² ) A destruction test was performed in which the voltage at the time of the flow was measured as a breakdown voltage BV.

  From the acceleration test and the breakdown test, the failure time t and the breakdown voltage BV of the PZT element formed under the same conditions are determined. From the failure time t and the number of failures, the MTTF can be obtained from the above equations (1) to (3).

  The horizontal axis of the graph of FIG. 3 is the electric field value (MV / cm) obtained by converting the breakdown voltage BV into the magnitude of the electric field (= breakdown voltage / 2 μm), and the vertical axis is the value of MTTF.

  Symbols A, B, and a to d in the graph of FIG. 3 indicate plots specified by measurement results including combinations of the values of the breakdown voltage BV and the value of the MTTF of the PZT element under specific conditions.

  Plot A is a measurement result of the PZT element 5 when the PZT layer 24 contains 0.5 at% of Ni, and plot B is a PZT element when the PZT layer 24 contains 0.5 at% of Ni and La. 9 shows the measurement result of the element 5. Plots A and B are measurement results of the PZT element of the present invention.

  On the other hand, plot a is a measurement result of the PZT element when Ca was contained, and plot b was when the PZT layer was formed by performing sputtering at a temperature similar to that of the present invention without containing an additive. It is a measurement result of a PZT element. Plot c shows the measurement result of the PZT element when the sputtering was performed at a high temperature of 600 ° C. or higher without containing any additive. Plot d is a measurement result of a PZT element in which a PZT layer was formed using a target having a small Pb content.

  A PZT element having a large breakdown voltage BV was expected to have a large value of MTTF. However, from the plot of FIG. 3, there is no correlation between the magnitude of the breakdown voltage BV and the value of the MTTF. I understand.

  On the other hand, plots A and B showing the measurement results of the present invention show that the crystallinity is high due to low-temperature film formation and Ni fills crystal defects, so that even if the breakdown voltage BV is small, the value of MTTF is large. You can see that it has become.

  The acceleration test of the PZT element 5 of the present invention and the PZT element without adding Ni was performed at a plurality of temperatures, the failure time t was measured, and the MTTF was determined.

  The horizontal axis of the graph in FIG. 4 is the temperature of the acceleration test, and the vertical axis is the value of the MTTF obtained.

The measurement result 15 of the PZT element 5 of the present invention and the measurement result 16 of the PZT element to which Ni is not added are arranged on the straight lines L ₁ and L ₂ in the measured temperature range, respectively. _1, when extending the L _2, the value of MTTF at 100 ° C. is an actual working temperature, PZT element 5 in 1,000,000 hours of the invention, it reads to be about 100 hours for PZT element without the addition of Ni. It can be seen that the life of the PZT element 5 of the present invention is long.

  The temperature of the substrate during sputtering when forming a PZT element to which Ni is not added is 485 ° C. which is the same as in the present invention.

5 PZT element 21 Substrate 22 First electrode layer 23 Underlayer (LaNiO ₃ layer)
24 PZT layer 25 Second electrode layer

Claims (5)

Board and
A first electrode layer disposed on the substrate,
An underlayer disposed on the first electrode layer,
A PZT layer containing the additive metal disposed on the underlayer in a range of 0.1 at% or more and 5 at% or less;
A second electrode layer disposed on the PZT layer,
Ni is used for the additive metal,
The PZT element, wherein the PZT layer is a PZT crystal grown on a surface of the first electrode layer by sputtering a PZT target. The underlayer PZT element according to claim 1, wherein comprised of LaNiO _3.   3. The PZT device according to claim 2, wherein the PZT crystal has the underlayer grown at a temperature in a temperature range of 485 ° C. or more and 585 ° C. or less. A first electrode layer,
An underlayer disposed on the first electrode layer,
A PZT layer disposed on the underlayer;
A second electrode layer disposed on the PZT layer and electrically connected to the PZT layer, a method for manufacturing a PZT element, comprising:
Forming a PZT layer by sputtering a PZT target containing Ni as an additive metal in a range of 0.1 at% or more and 5 at% or less, growing a PZT crystal on the surface of the underlayer, and forming the PZT layer; ,
A second electrode layer forming step of forming the second electrode layer on the PZT layer.   The PZT element manufacturing method according to claim 4, wherein in the PZT layer forming step, the underlayer is heated to a temperature in a temperature range of 485 ° C. or more and 585 ° C. or less.

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