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EP-4156312-B1 - PIEZOELECTRIC SINGLE-CRYSTAL ELEMENT, MEMS DEVICE USING SAME, AND METHOD FOR MANUFACTURING SAME

EP4156312B1EP 4156312 B1EP4156312 B1EP 4156312B1EP-4156312-B1

Inventors

  • LEE, SANG GOO

Dates

Publication Date
20260506
Application Date
20210601

Claims (14)

  1. A piezoelectric single-crystal element (1), comprising: a wafer (10); a lower electrode (30) stacked on the wafer; a piezoelectric single-crystal thin film (20) stacked on the lower electrode (30); and an upper electrode (40) stacked on the piezoelectric single-crystal thin film (20), wherein the piezoelectric single-crystal thin film (20) is composed of lead magnesium niobate-lead titanate, PMN-PT, lead indium niobate-lead magnesium niobate-lead titanate, PIN-PMN-PT, or manganese-doped lead indium niobate-lead magnesium niobate-lead titanate, Mn:PIN-PMN-PT; and the piezoelectric single-crystal thin film (20) has a polarization direction set to a <001> axis, a <011> axis or a <111> axis, characterised in that: the upper electrode (40) includes an operation-part-side upper terminal portion (42), the lower electrode (30) includes an operation-part-side lower terminal portion (32), the piezoelectric single-crystal thin film (20) has an operation part formation hole (22) formed over the periphery of a central portion, a vibrable operation part (50) is defined as a central portion surrounded by the operation-part-side upper terminal portion (42), the operation-part-side lower terminal portion (32), and the operation part formation hole (22) of the piezoelectric single-crystal thin film (20), and a lower operation space (12) is formed below the operation part (50) on the wafer (10) to define the operation performance of the operation part (50).
  2. The element (1) of claim 1, wherein a via hole (24) is formed through the piezoelectric single-crystal thin film (20) in a vertical direction, and the lower electrode (30) includes a lower extension portion (34) extending in one direction from the operation-part-side lower terminal portion (32), a lower connection portion (36) connected to an end of the lower extension portion (34) and arranged below the via hole (24), a vertical extension portion (38) extending upward from the lower connection portion (36) and formed inside the via hole (24), and a lower electrode terminal portion (39) connected to an end of the vertical extension portion (38).
  3. The element (1) of claim 2, wherein the upper electrode (40) includes an upper extension portion (44) extending in the other direction from the operation-part-side upper terminal portion (42), and an upper electrode terminal portion (46) connected to an end of the upper extension portion (44), and the upper electrode terminal portion (46) and the lower electrode terminal portion (39) are positioned on the same level.
  4. The element (1) of any one of claims 1 to 3, wherein the operation-part-side upper terminal portion (42), the operation-part-side lower terminal portion (32) and the central portion of the piezoelectric single-crystal thin film (20), which constitute the operation part (50), and the lower operation space (12) are formed in a polygonal or circular shape.
  5. The element (1) of any one of claims 1 to 4, wherein the lower electrode (30), the piezoelectric single-crystal thin film (20) and the upper electrode (40) are formed so as to protrude further outward from one end of the wafer (10), so that protruding regions not supported by the wafer (10) are formed in the lower electrode (30), the piezoelectric single-crystal thin film (20) and the upper electrode (40), and the protruding regions are defined as the vibrable operation part (50).
  6. The element (1) of any one of claims 1 to 5, further comprising: an operation frequency adjustment part (48) stacked on the operation-part-side upper terminal portion (42) and configured to adjust an operation frequency to resonate with the frequency of a vibration signal applied from the outside.
  7. A MEMS device (2), comprising: the piezoelectric single-crystal element (1) of any one of claims 1 to 6, wherein the MEMS device (2) is configured to use an electric signal generated by the piezoelectric single-crystal element (1) as an input when an electromagnetic force or a physical vibration signal is applied from the outside.
  8. A MEMS device (2), comprising: the piezoelectric single-crystal element (1) of any one of claims 1 to 6, wherein the MEMS device (2) is configured so that a physical vibration signal is generated and outputted by the piezoelectric single-crystal element (1) when an electrical signal is applied from the outside.
  9. A MEMS device (2), comprising: the piezoelectric single-crystal element (1) of any one of claims 1 to 6, wherein the MEMS device (2) is configured to apply an electrical signal to generate and output a vibration signal of the piezoelectric single-crystal element (1) and to input a signal generated by the piezoelectric single-crystal element (1) from an external signal returned by reflection of the output signal.
  10. A MEMS device (2), comprising: the piezoelectric single-crystal element (1) of any one of claims 1 to 6, wherein the MEMS device (2) is configured to generate and apply an ultrasonic wave to the patient's skin, receive a signal reflected from the skin as an input again, and obtain a signal changed by heartbeat or muscle movement.
  11. A MEMS device (2), comprising: the piezoelectric single-crystal element (1) of any one of claims 1 to 6, wherein the MEMS device (2) is configured to generate an ultrasound wave, apply the ultrasound wave to the patient's skin, receive a signal reflected from the skin as an input again, and acquire an ultrasound image.
  12. A MEMS device (2), comprising: the piezoelectric single-crystal element (1) of any one of claims 1 to 6, wherein the piezoelectric single-crystal element (1) is configured to be used as one of a bulk acoustic wave, BAW, filter element for wireless mobile communication of 6 GHz band or less using a bulk acoustic wave, a film bulk acoustic resonator, FBAR, filter element, an electronic microphone element serving as an accelerometer that converts a mechanical vibration of 200 Hz or less into an electrical signal, a mechanical-to-electrical signal transducer, and a single-crystal gyroscope element in which single-crystal cantilevers are arranged in a crisscross pattern.
  13. A method for manufacturing a piezoelectric single-crystal element (1), comprising: a piezoelectric single-crystal thin film preparation step of preparing a piezoelectric single-crystal thin film (20); a lower electrode forming step of forming a lower electrode (30) vapor-deposited on a lower surface of the piezoelectric single-crystal thin film (20); a lower electrode patterning step of forming a predetermined pattern on the lower electrode (30); a wafer bonding step of bonding a wafer (10) to the lower surface of the piezoelectric single-crystal thin film (20) on which the lower electrode (30) is formed; a thin film trimming step of reducing the thickness of the piezoelectric single-crystal thin film (20); a piezoelectric single-crystal etching step of etching the piezoelectric single-crystal thin film (20) to form a via hole (24) and an operation part formation hole (22); an upper electrode vapor-deposition step of vapor-depositing and forming an upper electrode (40) on the piezoelectric single-crystal thin film (20); an upper electrode patterning step of forming a predetermined pattern on the upper electrode (40); and a wafer etching step of etching an upper surface of the wafer (10) to form a lower operation space (12) to provide an operation part (50), wherein the piezoelectric single-crystal thin film (20) is composed of lead magnesium niobate-lead titanate, PMN-PT, lead indium niobate-lead magnesium niobate-lead titanate, PIN-PMN-PT, or manganese-doped lead indium niobate-lead magnesium niobate-lead titanate, Mn:PIN-PMN-PT; and the piezoelectric single-crystal thin film (20) has a polarization direction set to a <001> axis, a <011> axis or a <111> axis.
  14. The method of claim 13, further comprising: a lead-metal compound single-crystal modifying step, wherein the lead-metal compound single-crystal modifying step includes an alternating current applying step of applying an alternating current to an electrode of the piezoelectric single-crystal element (1), and a direct current applying step of applying a direct current to the electrode of the piezoelectric single-crystal element (1) that has undergone the alternating current applying step.

Description

TECHNICAL FIELD The present invention relates to a piezoelectric single-crystal element, a MEMS device using same, and a method for manufacturing same. BACKGROUND Since the development of PZT (lead zirconate titanate) piezoelectric ceramic in the 1950s, the PZT piezoelectric ceramics has been widely used as a piezoelectric material. Over the past 70 years, improvements in the properties of the material itself have not been made any more. On the other hand, in the piezoelectric material application field, new materials have been required to improve the performance of sensors, transducers, and the like. In the 1980s, Professor Kuwata's group at Tokyo Institute of Technology in Japan and DARPA in the US have supported the development of new materials to improve a SONAR that detects submarines in the sea. A PZN-PT [Pb(Zn2/3Nb1/3)O3-PbTiO3] single crystal and a PMN-PT [Pb(Mg2/3Nb1/3)O3-PbTiO3] single crystal developed by Professor Tom Shrout's group were presented for the first time, thereby raising expectation for the advent of new piezoelectric materials. However, the main R&D was centered on PZN-PT, and the growth method thereof was also the Flux method, which had many problems in mass production of small single crystals. Since then, many research results have been published. Lee Sang-gu, et al succeeded in growing a 1-cm-order single crystal of PMN using the Bridgman method for the first time in 1997 [Appl. Phys. Letts. Vol. 74, no. 7, 1030 (1999)]. This made it possible to grow a lead-based (Pb-containing oxide) large piezoelectric single crystal. Thus, the direction of research was switched to PMN-PT worldwide. Research of PMN-PT began in earnest, and PMN-PT began to be commercialized. PMN-PT and PIN-PMN-PT piezoelectric single crystals, which show far superior piezoelectric properties as compared with existing PZT ceramics, have been called 'next-generation piezoelectric materials'. Currently, piezoelectric single-crystal materials with various compositions are being developed. In particular, a two-phase single-crystal (PMN-PT) material, which is a first generation single-crystal material, is widely used for ultrasonic transducers for medical devices, and a three-phase single-crystal (PIN-PMN-PT) material, which is a second generation single-crystal material, is widely used for military sonar sensors that require high output/environmental resistance. Recently, in order to increase the mechanical quality factor while maintaining the piezoelectric constant of the existing first and second generation piezoelectric single crystals, research is ongoing to develop a third generation piezoelectric single-crystal material (Mn:PIN-PMN-PT) added with a dopant such as Mn or the like, and to use the third generation piezoelectric single-crystal material as a transmission sensor for high-power military sonar systems or to apply the third generation piezoelectric single-crystal material to industrial ultrasonic motors (see Table 1). [Table 1] Comparison of piezoelectric properties of existing piezoelectric single crystals of different generationsMaterialsPolingRelative Dielectric Constant ε33(pC/N)Piezoelectric Constant d33(pC/N)Phase Transition Temperature Trt (degrees C)Coercive Field Ec (kV/cm)Mechanical Quality Factor QmPMN-PT (1st Generation)<001>≥50001500 to 2200≥85≥1.8≥80PIN-PMN-PT (2nd Generation)≥40001300 to 2200≥120≥4.5≥100Mn:PIN-PMN-PT (3rd Generation)≥29001080 to 1700≥120≥4.5≥700PMN-PT (1st Generation)<110>≥35001000 to 1500≥75≥1.8≥400PIN-PMN-PT (2nd Generation)≥3100900 to 1300≥110≥4.5≥500Mn:PIN-PMN-PT (3rd Generation)≥2600800 to 1100≥110≥8.0≥1030 Ref: J. Luo, W. Hackenberger, S. Zhang and T.R. Shrout, The Progress Update of Relaxor Piezoelectric Single Crystals, 2009 IEEE International Ultrasonics Symposium Proceedings. It has been reported that as shown in Table 1 above, the third generation piezoelectric single crystal is superior in coercive field and mechanical quality factor than the existing first and second generation piezoelectric single crystals. However, the third generation piezoelectric single crystal has a problem that the dielectric constant and the piezoelectric constant, which affect the sensitivity performance of a sensor, decrease. To solve this problem, domain engineering methods have been studied. Toshiba Corporation has announced that the piezoelectric constant and the dielectric constant were improved by applying an alternating current (AC) polling method to the first and second generation piezoelectric single-crystal transducers (US9966524B2). However, difficulties are involved in repolarization during the process, which makes it difficult to apply this technique widely in practice. In addition, there is no process for forming a MEMS device using a third generation piezoelectric single crystal. Research is required to commercialize a new concept MEMS device manufactured through such a process. In particular, in order to use a piezoelectric single-crystal material as a medical ultrason