KR20100128820A - Thin film type piezoelectric element and manufacturing method thereof - Google Patents

Abstract

PURPOSE: A thin film piezoelectric element and a manufacturing method thereof are provided to form a piezoelectric layer having excellent piezoelectric property by excluding the variable which can occur during the process by implementing the following process after depositing all the piezoelectric film. CONSTITUTION: A top plate is arranged with a correction mass(60) and a piezoelectric drive(10). The piezoelectric drive comprises a piezoelectric-foil(15), a first electrode(14), and a second electrode(16). A center plate(20) is formed with a vacuum hollow(25) for driving the piezoelectric drive. The vacuum hollow is formed by etching the top of the middle plate in reversed triangle shape.

Description

Thin film type piezoelectric element and manufacturing method thereof

The present invention relates to a thin film type piezoelectric element and a method of manufacturing the same, and more particularly, to a piezoelectric driving type thin film type piezoelectric element manufactured using various process technologies of a microelectromechanical system (MEMS) and wafer-based packaging technology, and It relates to a manufacturing method.

Piezoelectricity is a property found in the late 19th century when mechanical stress is applied to a material to generate a charge or potential difference. This physical phenomenon is called a piezoelectric effect. Conversely, when a high frequency AC voltage is applied to the piezoelectric element, the piezoelectric element periodically expands and contracts to generate ultrasonic waves, which is called a reverse piezoelectric effect. Such a piezoelectric effect may be applied to the sensor, and the reverse piezoelectric effect may be applied to the driver.

Recently, piezoelectric materials have been widely used in MEMS sensors and actuators in the form of thin films, and are widely used in elastic transducers, pumps and valves for the transport and control of fluids and particles, accelerometers, micro speakers and microphones, physical sensors or chemical sensors. Is being studied.

Commercial MEMS devices are currently mainly based on electrostatic or piezoresistive sensing methods. While piezoelectric sensors and drivers require a rather complex material and manufacturing process, devices using piezoelectric drive methods are currently being steadily studied, which include fast response speed, low drive voltage and high linearity and sensing sensitivity, and low consumption of piezoelectric drive methods. This is due to several advantages such as power.

Integrating piezoelectric materials into MEMS technology is not easy because first, careful control of the microstructure of the piezoelectric film requires the establishment of careful conditions and process equipment. Second, most piezoelectric thin films are easy to react chemically or physically, so they must be handled carefully to avoid damage to the piezoelectric film in subsequent processes.

Conventional piezoelectric devices using MEMS technology have difficulty in optimizing large-scale processes because they cannot be used to correct subsequent characteristics once they are formed using thin films. In addition, piezoelectric devices using existing MEMS technology have difficulty in vacuum packaging process that can provide long-term reliability.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a thin film type piezoelectric element and a method of manufacturing the same, which are easily applied to a MEMS sensor or a driver element of a thin film piezoelectric material.

In addition, the present invention is a thin film type piezoelectric element having the ability to adjust while changing the value, if it does not fit after measuring the important sensing characteristics as a sensor element and the driving voltage characteristics as a driver element after manufacturing through a batch process and It aims at providing the manufacturing method.

In addition, the present invention provides a thin film type piezoelectric element and a method for manufacturing the same after forming both the piezoelectric film, which is a core process of the piezoelectric element, and an electrode film surrounding the same, in order to provide excellent piezoelectric properties and to ensure reproducibility of the process. It aims to provide.

In addition, an object of the present invention is to provide a thin film type piezoelectric element and a method of manufacturing the piezoelectric layer which can be prevented from being physically or chemically damaged during the subsequent micro-processing for the completion and operation of the MEMS device.

In addition, the present invention can be manufactured at a low cost by using an anisotropic wet etching process and wafer-based package technology to manufacture a compact microsensor or driver device using a highly reliable packaged piezoelectric MEMS technology with the smallest area size. An object of the present invention is to provide a thin film type piezoelectric element and a method of manufacturing the same.

A thin film type piezoelectric element according to the present invention for achieving the above object, the upper plate provided with a calibration mass and the piezoelectric drive unit; An intermediate plate bonded to the upper plate and having a vacuum cavity for driving the piezoelectric driver; And a lower plate bonded to the intermediate plate to seal the vacuum vacancy and provide mechanical stability.

Here, the vacuum cavity formed in the intermediate plate may be formed by etching from the upper surface in the shape of an inverted triangle.

Preferably, the piezoelectric drive unit, a piezoelectric film; A first electrode in contact with an upper surface of the piezoelectric film; A second electrode in contact with the bottom surface of the piezoelectric film; And a silicon oxide layer laminated on the first electrode.

In addition, it is preferable that a portion of the second electrode facing the vacuum cavity is etched.

In addition, the upper plate and the intermediate plate is preferably bonded by an adhesive layer containing epoxy.

In addition, the top plate and the intermediate plate is preferably bonded by applying a material and heat and pressure to be bonded through mutual diffusion.

In addition, the intermediate plate and the lower plate are preferably bonded by wafer unit through eutectic bonding.

In addition, the lower plate is preferably bonded to the intermediate plate by depositing a metal combination for performing eutectic bonding including Au-Sn to Au or Ag-Sn to Ag.

A thin film type piezoelectric element according to the present invention for achieving the above object, a piezoelectric film, a first electrode in contact with the upper surface of the piezoelectric film, a second electrode in contact with the lower surface of the piezoelectric film, and silicon laminated on the first electrode Piezoelectric drive unit provided with an oxide layer; An intermediate plate joined to the piezoelectric driver and having a vacuum cavity for driving the piezoelectric driver; And a thin plate type piezoelectric element including a lower plate bonded to the intermediate plate to seal the vacuum cavity and provide mechanical stability.

On the other hand, the thin film type piezoelectric element includes a piezoelectric drive unit including a piezoelectric film, a first electrode in contact with an upper surface of the piezoelectric film, a second electrode in contact with a lower surface of the piezoelectric film, and a silicon oxide layer laminated on the first electrode. Bonding an intermediate plate on which a vacuum triangle having an inverted triangle shape is formed; Opening a lower side of the vacuum cavity from a lower portion of the intermediate plate and etching a second electrode of the piezoelectric driver; And bonding a lower plate to a lower surface of the intermediate plate to seal the lower side of the vacuum cavity.

Here, the method of manufacturing the thin film type piezoelectric element may further include depositing a calibration mass on a top surface of the piezoelectric driver using a screen mask.

Preferably, the vacuum vacancy of the intermediate plate may be formed by depositing a dielectric on a silicon substrate, patterning a central portion by photolithography, and exposing the patterned portion to an anisotropic wet etching solution.

In addition, the piezoelectric drive unit and the intermediate plate may be bonded by an adhesive layer containing epoxy.

In addition, the piezoelectric driver and the intermediate plate may be joined by applying a material to be bonded through mutual diffusion and applying heat and pressure.

In addition, the intermediate plate and the lower plate may be bonded on a wafer basis through eutectic bonding.

In addition, the lower plate may be bonded to the intermediate plate by depositing a metal combination for performing eutectic bonding including Au—Sn to Au, or Ag—Sn to Ag.

According to the present invention, the thin film type piezoelectric element is manufactured by a wafer-bonded packaging process of the upper plate and the intermediate plate, and the intermediate plate and the lower plate. Because it can be used as a device, the device packaging cost after the manufacturing process can be reduced.

In addition, according to the present invention, after measuring the device in the last step, it is possible to adjust the driving voltage and the sensor sensitivity and the like to correct the difference in the characteristic value that may occur in the process variable.

In addition, according to the present invention, by depositing all the piezoelectric films, a subsequent process may be performed to stably obtain a piezoelectric film having excellent piezoelectric properties by excluding variables that may occur during the process.

In addition, according to the present invention, since the silicon oxide layer covers the entire surface, the piezoelectric layer is protected to reduce the deterioration of characteristics due to damage of the piezoelectric film in the subsequent process.

In addition, according to the present invention, although the bulk micromachining, which is a low-cost process, is applied, the area per individual device, which is similar to that of the surface micromachining, which is expensive, is greatly reduced, thereby having a large effect in miniaturizing the device.

Hereinafter, with reference to the accompanying drawings will be described a preferred embodiment of the present invention. However, the embodiments of the present invention described below are provided to enable those skilled in the art to more easily understand the present invention, and the scope of the present invention is not limited to the described embodiments.

1 is a view schematically showing a thin film type piezoelectric element according to the present invention. Referring to the drawings, the thin film type piezoelectric element according to the present invention is bonded to the upper plate and the upper plate provided with the calibration mass 60 and the piezoelectric drive unit 10, and the vacuum cavity 25 for driving the piezoelectric drive unit 10 is formed. It consists of an intermediate plate 20 and a lower plate 40 bonded to the intermediate plate 20 to seal the vacuum cavity 25 and provide mechanical stability. At this time, the upper plate and the intermediate plate 20 may be bonded by an adhesive layer 30 containing epoxy. Alternatively, the upper plate and the intermediate plate 20 may be joined by applying a material to be bonded through mutual diffusion and applying heat and pressure. In addition, the intermediate plate 20 and the lower plate 40 may be bonded on a wafer basis through eutectic bonding between metals or alloys. At this time, the lower plate 40 is preferably bonded to the intermediate plate by depositing a metal combination for performing eutectic bonding including Au-Sn to Au, or Ag-Sn to Ag.

Here, the piezoelectric driver 10 (also referred to as a piezoelectric capacitor) includes the piezoelectric film 15, the first electrode 14 in contact with the top surface of the piezoelectric film 15, and the second electrode in contact with the bottom surface of the piezoelectric film 15. 16 and a silicon oxide layer 13 laminated on the first electrode 14.

At this time, the piezoelectric drive unit 10 of the upper plate is preferably formed before all subsequent processes including the micromachining process. This is to stably obtain a piezoelectric layer having excellent characteristics.

The piezoelectric capacitor 10 formed on the upper plate is turned upside down, and the first electrode 14 deposited on the piezoelectric film 15, that is, the opposite side of the silicon substrate is brought into contact with the intermediate plate 20. This is to minimize the exposure and damage of the piezoelectric film 15 during the subsequent process to optimize the driving characteristics of the piezoelectric element.

The vacuum cavity 25 formed in the intermediate plate 20 is formed by etching from an upper surface of the intermediate plate 20 in the shape of an inverted triangle. The vacuum cavity 25 frees the drive of the piezoelectric drive unit 10 and is formed using a bulk microfabrication process utilizing an anisotropic wet etching process of silicon. In addition, the vacuum vacancy 25 occupies a small area, enabling the miniaturization of the thin film type piezoelectric element.

In this case, it is preferable that a portion of the second electrode 16 of the piezoelectric driver 10 that faces the vacuum cavity 25 is etched. In the d33 mode, the piezoelectric drive unit 10 is etched by etching the second electrode 16 through reactive ion etching with excellent linearity through the gap formed by the chemical mechanical polishing method from the substrate rear surface of the intermediate plate 20. To work.

In addition, by forming a hole through the uniform etching of the entire substrate from the rear surface by chemical mechanical polishing for the vacuum formation of the vacuum cavity 25 formed in the intermediate plate 20, by tilting the substrate vapor deposition (vacuum evaporation) by It is desirable to allow the hole to be easily clogged.

In addition, the metal layer formed on the back of the intermediate plate 20 and the metal layer 50 formed on the lower plate 40 by vacuum evaporation are made of a combination in which a eutectic bonding between the two metal layers can be formed, and the eutectic between these two layers Through the bonding, the intermediate plate 20 and the lower plate 40 are bonded on a wafer basis.

The calibration mass 60 of the upper plate is intended for subsequent adjustment by measuring a sensor sensing characteristic when the thin film type piezoelectric element is applied to the sensor and a driving voltage characteristic when applied to the driver. In order to improve the sensing sensitivity and reduce the driving voltage characteristic, the silicon oxide 13 protecting the piezoelectric driver 10 from above reduces the mass of the driver through etching, thereby reducing the sensitivity of the driver. In order to increase the driving voltage characteristic or to improve mechanical stability, it may be adjusted while depositing another dielectric layer on the upper silicon oxide 13.

FIG. 2 is a diagram sequentially illustrating a manufacturing process of the thin film type piezoelectric element of FIG. 1. First, referring to FIG. 2A, the top plate is formed by growing silicon oxides 12 and 13 on the silicon substrate 11 through an oxidation method, and then the first electrode 14, the piezoelectric film 15, and the polished silicon surface. The piezoelectric capacitor 10 is formed by sequentially depositing the second electrode 16. The piezoelectric capacitor 10 is used as a piezoelectric driver for a sensor or driving operation of the device in the future.

Referring to FIG. 2B, when the intermediate plate is deposited on the silicon substrate 20 through dielectric deposition, the center portion of the device is patterned by photolithography, and then exposed to an anisotropic wet etching solution (KOH, EDP, etc.). Grooves with a constant angle of 54.7 degrees are formed according to the surface and the etching speed of the surface. This groove becomes a vacuum cavity which is a space for moving the piezoelectric drive unit 10 of the upper plate in the future.

Referring to FIG. 2C, a cross-sectional view of an element after the process of joining the upper plate processed in FIG. 2A and the intermediate plate 20 processed in FIG. 2B is schematically illustrated, and the bonding of the two plates may include an adhesive layer 30 such as epoxy. For the high temperature process or for the future high temperature process, a material capable of obtaining a strong bonding force through mutual diffusion is applied to two surfaces, such as the second electrode 16 and the upper surface of the intermediate plate 20, of the piezoelectric capacitor 10, and heat and pressure are applied. It can also join by adding.

FIG. 2D is a schematic diagram of the piezoelectric capacitor 10 fabricated in FIG. 2A in the form of a piezoelectric drive element by photolithography or the like. After removing all of the silicon oxide 12, the silicon 11, and the like from the above in a dry or wet process, the silicon oxide 13, the first electrode 14, the piezoelectric film 15, the second electrode 16, etc. The pattern etching process is performed by the photolithography method using a mask using a photosensitive agent or a hard mask using a metal as a mask.

Figure 2e shows a process of opening the rear surface by performing a chemical mechanical polishing (CMP) process from the rear surface.

FIG. 2F illustrates a process of etching the second electrode 16 through the open rear surface as illustrated in FIG. 2E. Through this, the second electrode 16 may be separated, and a method of driving a device by applying a voltage between the two electrodes or measuring a voltage according to the displacement of the piezoelectric driver 10 between two electrodes of the same plane is a piezoelectric film. The d33 mode of (15) is used, and in general, the d33 mode provides excellent characteristics because the piezoelectric constant is 2 to 3 times higher than the d31 mode for measuring or applying a signal between the upper and lower electrodes 14 and 16. It becomes possible.

FIG. 2G illustrates a process of closing the hole opened in FIG. 2E in a vacuum while the metal is vacuum evaporated. If the substrate is inclined with respect to the direction in which the metal is evaporated in a vacuum, the second electrode 16 may not be attached to the metal, thereby increasing the process reproducibility and easily blocking the hole.

FIG. 2H illustrates a step of wafer-bonding the substrate (the substrate on which the upper plate and the intermediate plate are bonded) and the lower plate 40 prepared in FIG. 2G through eutectic bonding. The lower plate 40 is prepared by depositing a metal on a silicon substrate. The metal of the lower plate and the evaporated metal to be used for blocking holes in the intermediate plate should be made of a combination of metals which undergo eutectic bonding in the bonding of the intermediate plate 20 and the lower plate 40. Such metal combinations include Au-Sn to Au or Ag-Sn to Ag.

Figure 2i is the most suitable in terms of the stable process of the device is carried out by the vacuum evaporation method using a screen mask as the deposition process of the calibration mass for stable driving characteristics and high sensitivity when used as a sensor.

After applying the packaging process suitable for the purpose of use to the thin film type piezoelectric element completed through the process of Figure 2 after performing a capping process using benzocyclobutene (BCB), etc. and then cut it in the wafer state One well cut can be used as a packaged device.

Although the preferred embodiments of the present invention have been illustrated and described above, the present invention is not limited to the specific embodiments described above, and the present invention is not limited to the specific embodiments of the present invention without departing from the spirit of the present invention as claimed in the claims. Anyone skilled in the art can make various modifications, as well as such modifications are within the scope of the claims.

1 is a view schematically showing a thin film type piezoelectric element according to the present invention.

FIG. 2 is a diagram sequentially illustrating a manufacturing process of the thin film type piezoelectric element of FIG. 1.

Description of the Related Art

10: piezoelectric drive unit 13: silicon oxide

14: first electrode 15: piezoelectric film

16: second electrode 20: intermediate plate

25: vacuum vacancy 30: adhesive layer

40: lower plate 60: calibration mass

Claims (16)

A top plate provided with a calibration mass and a piezoelectric drive unit; An intermediate plate bonded to the upper plate and having a vacuum cavity for driving the piezoelectric driver; And And a lower plate bonded to the intermediate plate to seal the vacuum cavity and provide mechanical stability. The method of claim 1, The vacuum cavity formed in the intermediate plate is a thin film type piezoelectric element, characterized in that formed by etching from the upper surface in the shape of an inverted triangle. The method according to claim 1 or 2, The piezoelectric drive unit, Piezoelectric film; A first electrode in contact with an upper surface of the piezoelectric film; A second electrode in contact with the bottom surface of the piezoelectric film; And A thin film type piezoelectric element comprising a silicon oxide layer stacked on the first electrode. The method of claim 3, wherein The piezoelectric element of claim 2, wherein a portion of the second electrode facing the vacuum cavity is etched. The method according to claim 1 or 2, The upper plate and the intermediate plate is a thin film type piezoelectric element, characterized in that bonded by an adhesive layer containing an epoxy. The method according to claim 1 or 2, The top plate and the intermediate plate is a thin film type piezoelectric element, characterized in that the bonding by applying a material and heat and pressure bonded through mutual diffusion. The method according to claim 1 or 2, The intermediate plate and the lower plate is a thin film type piezoelectric element, characterized in that bonded by wafer unit through eutectic bonding. The method of claim 7, wherein A thin film type piezoelectric element, which is bonded to the intermediate plate by depositing a metal combination for eutectic bonding including Au—Sn to Au or Ag—Sn to Ag on the lower plate. A piezoelectric driver having a piezoelectric film, a first electrode in contact with an upper surface of the piezoelectric film, a second electrode in contact with a lower surface of the piezoelectric film, and a silicon oxide layer stacked on the first electrode; An intermediate plate joined to the piezoelectric driver and having a vacuum cavity for driving the piezoelectric driver; And And a lower plate bonded to the intermediate plate to seal the vacuum cavity and provide mechanical stability. An inverted triangular vacuum cavity is formed on a lower surface of the piezoelectric drive unit including a piezoelectric film, a first electrode in contact with an upper surface of the piezoelectric film, a second electrode in contact with a lower surface of the piezoelectric film, and a silicon oxide layer stacked on the first electrode. Bonding the formed intermediate plates; Opening a lower side of the vacuum cavity from a lower portion of the intermediate plate and etching a second electrode of the piezoelectric driver; And Bonding the lower plate to the lower surface of the intermediate plate to seal the lower side of the vacuum cavity. The method of claim 10, And depositing a calibration mass on the upper surface of the piezoelectric drive unit by using a screen mask. The method according to claim 10 or 11, wherein The vacuum cavity of the intermediate plate may be formed by depositing a dielectric on a silicon substrate, patterning a central portion by photolithography, and exposing the patterned portion to an anisotropic wet etching solution. . The method according to claim 10 or 11, wherein The piezoelectric drive unit and the intermediate plate are bonded to each other by a pressure-sensitive adhesive layer containing epoxy. The method according to claim 10 or 11, wherein The piezoelectric drive unit and the intermediate plate is a thin film type piezoelectric device manufacturing method characterized in that the bonding by applying a material and the heat and pressure are bonded to each other through diffusion. The method according to claim 10 or 11, wherein The intermediate plate and the lower plate is a wafer-type piezoelectric element manufacturing method characterized in that the bonding unit by wafer through eutectic bonding. The method of claim 15, A method of manufacturing a thin film piezoelectric element, wherein the lower plate is bonded to the intermediate plate by depositing a metal combination for performing eutectic bonding including Au-Sn to Au or Ag-Sn to Ag.

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