JP2016058523A - Ferroelectric capacitor and electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ferroelectric capacitor capable of storing the charges generated from natural energy, and an electronic device using the same.SOLUTION: A ferroelectric capacitor 100 comprises: a ferroelectric single crystal 120 which includes a charge storage region 110 and in which a polarization direction is controlled, the charge storage region 110 being at least a partial region of the surface of the ferroelectric single crystal 120; a metal layer 130 located around the charge storage region 110; and a dielectric layer 160 located at least between the ferroelectric single crystal 120 and the metal layer 130. The band gap of the dielectric layer 160 is larger than the band gap of the ferroelectric single crystal 120. The charges based on the ferroelectric single crystal 120 are confined and stored on the charge storage region 110.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ferroelectric capacitor and an electronic device, and more particularly to a ferroelectric capacitor that accumulates electric charges generated by natural energy and an electronic device using the same.

  In recent years, energy harvesting using natural energy has attracted attention. As such an energy harvesting technology, a capacitor using lead zirconate titanate (PZT) is known (see, for example, Non-Patent Documents 1 and 2). According to Non-Patent Documents 1 and 2, it is disclosed that a capacitor made of a PZT bulk material can accumulate charges generated by using the pyroelectric effect. However, since the material contains lead, there is a concern about the influence on the natural environment, and development of a lead-free material is desired.

Koji Iwaiwa et al., “Energy Harvest from Pb (Zr, Ti) O3 Ceramics and Other Materials”, 16p-B3-14, 59th Joint Lecture on Applied Physics, March 2012 Koji Iwaiwa, “Pyroelectric Energy Harvesting and Electrocaloric Effect of Ferroelectric Materials”, 17p-F5-5, 59th Joint Conference on Applied Physics, March 2012

  As described above, an object of the present invention is to provide a ferroelectric capacitor that accumulates charges generated by natural energy, and an electronic device using the same.

The ferroelectric capacitor according to the present invention is a ferroelectric single crystal having a charge storage region in which the direction of polarization is controlled, wherein the charge storage region is at least a part of the surface of the ferroelectric single crystal. A ferroelectric single crystal, a metal layer positioned around the charge storage region, and at least a dielectric layer positioned between the ferroelectric single crystal and the metal layer, The band gap of the layer is larger than the band gap of the ferroelectric single crystal, and charges based on the ferroelectric single crystal are confined and accumulated on the charge storage region, thereby solving the above-mentioned problem.
The ferroelectric single crystal may be a lithium niobate single crystal or a lithium tantalate single crystal.
The metal layer may be a metal selected from the group consisting of Al, Cr, and Au.
The dielectric layer and the metal layer may be positioned so as to surround the charge storage region.
The dielectric layer may be located on the charge storage region in addition to between the ferroelectric single crystal and the metal layer.
The dielectric layer may be a dielectric material selected from the group consisting of SiO ₂ , Al ₂ O ₃ and HfO ₂ .
The dielectric layer may have a thickness of 5 nm to 1 μm.
The dielectric layer may have a relative dielectric constant of 3 or more and a thickness in the range of 5 nm to 1 μm.
The dielectric layer may have a relative dielectric constant of 3.5 or more and a thickness in the range of 5 nm to 200 μm.
The charge is induced by the spontaneous polarization of the ferroelectric single crystal, the charge induced by the piezoelectric effect of the ferroelectric single crystal, or the pyroelectric effect of the ferroelectric single crystal. It may be a charge.
The diameter of the charge storage region may be in the range of 1.5 μm to 55 μm.
The direction of polarization of the ferroelectric single crystal is controlled so as to have a single polarization structure, and the polarity inside the surface of the ferroelectric single crystal corresponding to the charge storage region is + polarity or -polarity. Any of these may be sufficient.
The direction of polarization of the ferroelectric single crystal is controlled so as to have a polarization reversal structure, and the polarity inside the surface of the ferroelectric single crystal corresponding to the charge storage region is + polarity or −polarity. Either may be sufficient.
In an electronic device comprising a ferroelectric capacitor and a semiconductor element according to the present invention, the ferroelectric capacitor is the ferroelectric capacitor described above, and the semiconductor element is interposed between the charge storage region and the metal layer. It is connected and operates by the charge accumulated on the charge accumulation region, or the change of the charge amount of the charge accumulated on the charge accumulation region is detected, thereby solving the above problem.

  In the ferroelectric capacitor according to the present invention, since the dielectric layer having a band gap larger than the band gap of the ferroelectric single crystal is located between the ferroelectric single crystal and the metal layer, the Fermi level is ferroelectric. It is controlled to be located within the band of the body single crystal, and a sufficient barrier is formed. As a result, charges can be confined and accumulated on the charge accumulation region. Further, the trapped / accumulated charge is a charge generated by natural energy based on the spontaneous polarization, pyroelectric effect or piezoelectric effect of the ferroelectric single crystal. Thereby, the ferroelectric capacitor of the present invention can function as a power source using natural energy. In addition, since the size of the ferroelectric capacitor of the present invention is not limited, it becomes an ultra-compact power source of nanoscale to microscale size, and enables further miniaturization of electronic devices.

The schematic diagram which shows the structure of the ferroelectric capacitor of this invention Schematic diagram showing a band structure of a ferroelectric single crystal, a dielectric layer, and a metal layer in the ferroelectric capacitor of the present invention. Schematic diagram showing a cross-sectional view of another ferroelectric capacitor of the present invention The figure which shows the various patterns of the charge storage area | region and metal layer in the ferroelectric capacitor of this invention The figure which shows a mode that the ferroelectric capacitor of this invention accumulate | stores a surface charge by the piezoelectric effect The figure which shows a mode that the ferroelectric capacitor of this invention accumulate | stores a surface charge by the pyroelectric effect Schematic diagram showing an electronic device using the ferroelectric capacitor of the present invention The figure which shows the process which manufactures the ferroelectric capacitor of the comparative example 1 The figure which shows the process which manufactures the ferroelectric capacitor of Example 3. The figure which shows the shape image and electric potential image of the ferroelectric capacitor of the comparative example 1 The figure which shows the shape image and electric potential image of the ferroelectric capacitor of the comparative example 2 The figure which shows the shape image and electric potential image of the ferroelectric capacitor of Example 3. The figure which shows the shape image and electric potential image of the ferroelectric capacitor of Example 4. The figure which shows the shape image and electric potential image of the ferroelectric capacitor of Example 5. The figure which shows the shape image and potential image of the ferroelectric capacitor of the comparative example 6 The figure which shows the shape image and electric potential image of the ferroelectric capacitor of Example 7. The figure which shows the shape image and potential image of the ferroelectric capacitor of Example 8 The figure which shows the shape image and electric potential image of the ferroelectric capacitor of the reference example 9

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same number is attached | subjected to the same element and the description is abbreviate | omitted.

  FIG. 1 is a schematic diagram showing the structure of a ferroelectric capacitor of the present invention.

  FIG. 1A is a top view of the ferroelectric capacitor of the present invention, and FIGS. 1B and 1C are cross-sectional views of the ferroelectric capacitor of the present invention.

  The ferroelectric capacitor 100 of the present invention includes a ferroelectric single crystal 120 having a charge storage region 110 with a controlled polarization direction, a metal layer 130 positioned around the charge storage region 110, and at least a dielectric single crystal. 120 and a dielectric layer 160 located between the metal layer 130. The charge storage region 110 is a partial region of the surface 140 of the ferroelectric single crystal 120. In the ferroelectric capacitor 100 of the present invention, the band gap of the dielectric layer 160 is larger than that of the ferroelectric single crystal 120.

  With such a configuration, the ferroelectric capacitor 100 of the present invention has a charge 150 (that is, the ferroelectric single crystal 120) collected from the outside of the ferroelectric capacitor 100 so as to shield polarization charges derived from the ferroelectric single crystal 120. Can be confined and accumulated on the charge accumulation region 110. Hereinafter, for the sake of easy understanding, the charge 150 accumulated on the charge accumulation region 110 is referred to as a surface charge 150.

  The ferroelectric single crystal 120 is not particularly limited in material, but is preferably composed of an environmentally friendly material, and is preferably a uniaxial ferroelectric single crystal in which the polarization direction can be easily controlled. More specifically, the ferroelectric single crystal 120 is preferably a lithium niobate single crystal or a lithium tantalate single crystal. These materials have uniaxial polarization along the Z direction of the crystal, and a technique for controlling the direction of the polarization has been established. Further, these materials have an excellent piezoelectric effect, pyroelectric effect, electro-optic effect, and nonlinear optical effect, so that the surface charge 150 can be more efficiently accumulated on the charge accumulation region 110. Among these, the ferroelectric single crystal 120 is preferably a lithium niobate single crystal. The lithium niobate single crystal is excellent in workability and can provide a high-quality ferroelectric capacitor.

  In this specification, the term “lithium niobate single crystal (LN single crystal)” means an LN single crystal having a congruent composition (CLN), an LN single crystal having a stoichiometric composition (SLN), and a dopant to these. The added LN single crystal is intended. Similarly, in this specification, the term “lithium tantalate single crystal (LT single crystal)” means an LT single crystal having a congruent composition (CLT), an LT single crystal having a stoichiometric composition (SLT), and a dopant LT single crystals with added are intended. The dopant is, for example, Mg, Ca, Sr, Ba, Mn, Fe, Tb, etc., and is appropriately selected for improving the characteristics. For example, Mg, Ca, Sr, Ba, etc. improve the light damage resistance of LN or LT. Mn, Fe, Tb, etc. increase the photorefractive effect of LN or LT.

  The thickness of the ferroelectric single crystal 120 is not particularly limited, but is preferably 1 μm or more and 10 mm or less. Within this range, handling is simple and polarization charges are likely to be generated by the piezoelectric effect or pyroelectric effect described later, so that more surface charges can be accumulated.

  FIG. 1B shows a cross-sectional view of the dotted line portion of the ferroelectric capacitor 100 of FIG. The arrow in FIG. 1 (B) shows the direction of polarization. In FIG. 1B, the ferroelectric single crystal 120 has a single polarization structure.

  Specifically, in FIG. 1B, the polarization directions are all substantially perpendicular to the surface of the charge storage region 110, and the polarization direction is from the bottom to the top of the ferroelectric single crystal 120. An example in which the polarity inside the surface of the ferroelectric single crystal 120 corresponding to the charge storage region 110 is + polarity is shown. In this case, as the surface charge 150, a negative charge sufficient to shield + polarity is accumulated. Although not shown, a positive charge may be accumulated as the surface charge 150 by using the negative polarity surface which is the back surface of FIG. Note that “substantially vertical” means that all the polarization directions do not have to be completely vertical, but may be as long as they can be used as a so-called Z-cut substrate.

  FIG. 1C is a cross-sectional view of a ferroelectric capacitor different from that in FIG. Again, the arrow in FIG. 1 (C) indicates the direction of polarization. In FIG. 1C, the ferroelectric single crystal 120 has a domain-inverted structure.

  Specifically, in FIG. 1C, the directions of polarization are all substantially perpendicular to the surface of the charge storage region 110, and the polarization direction of the charge storage region 110 and the polarization of the other regions In the example, the polarity inside the surface of the ferroelectric single crystal 120 corresponding to the charge storage region 110 is negative. In this case, as the surface charge 150, a positive charge sufficient to shield -polarity is accumulated. Although not shown, a negative polarity surface as the surface charge 150 may be accumulated by using the surface of the charge accumulation region 110 having a positive polarity which is the back surface of FIG.

  As shown in FIGS. 1B and 1C, in the ferroelectric capacitor 100 of the present invention, at least the direction of polarization of the charge storage region 110 is substantially perpendicular to the surface of the charge storage region 110. It is preferable to be controlled so as to be in a different direction. As a result, electric charges (also referred to as polarization charges) inside the surface of the ferroelectric single crystal 120 corresponding to the charge storage region 110 more efficiently due to the spontaneous polarization of the ferroelectric single crystal, the piezoelectric effect, and the pyroelectric effect. Will occur. As a result, the ferroelectric capacitor 100 of the present invention can effectively accumulate the surface charge 150 that only shields these polarization charges.

  FIG. 2 is a schematic diagram showing a band structure of a ferroelectric single crystal, a dielectric layer, and a metal layer in the ferroelectric capacitor of the present invention.

  2A is a schematic diagram showing a band structure of a ferroelectric single crystal and a metal layer, and FIG. 2B shows a band structure of the ferroelectric single crystal, the dielectric layer, and the metal layer. It is a schematic diagram shown.

  FIG. 2A shows an example in which the ferroelectric single crystal is an LN single crystal. According to FIG. 2A, when Cr is selected as the metal layer, a p-type Schottky junction is formed when the LN single crystal is brought into contact with Cr. As a result, since no hole carrier path is formed between the LN single crystal and Cr, the surface charge 150 (FIG. 1) is not neutralized and confined on the charge storage region 110 (FIG. 1).

  However, when Al is selected as the metal layer, a p-type ohmic junction is formed when the LN single crystal is brought into contact with Al. As a result, a hole carrier path is formed between the LN single crystal and Al, so that the surface charge 150 is neutralized and disappears from the charge storage region 110.

  As described above, when the ferroelectric single crystal and the metal layer are brought into direct contact, the junction state changes depending on the type of the ferroelectric single crystal and the metal layer. A combination with the dielectric single crystal needs to be selected as appropriate, which complicates the design of the ferroelectric capacitor.

  On the other hand, as shown in FIG. 2B, a dielectric layer 160 having a band gap larger than the band gap of the ferroelectric single crystal 120 is located between the ferroelectric single crystal 120 and the metal layer 130. Thus, the Fermi level (Ef) can be controlled so as to be located in the band of the ferroelectric single crystal 120. As a result, a sufficient barrier is formed between the ferroelectric single crystal 120 and the metal layer 130, so that no carrier path is formed, and the surface charge 150 is confined and accumulated on the charge accumulation region 110. be able to.

The material of the dielectric layer 160 is not particularly limited because the band alignment shown in FIG. 2B is formed if the band gap is larger than that of the ferroelectric single crystal 120. What is necessary is just to be comprised from the body material. In this specification, the dielectric is a material having dielectric properties having a specific resistance value of at least 10 ⁻³ (Ωcm) or less and having a dielectric constant of at least 3 or more. Intended. Tables 1 and 2 summarize the band gaps and relative dielectric constants of various ferroelectrics and various dielectrics.

A person skilled in the art can appropriately design the materials of the ferroelectric single crystal 120 and the dielectric layer 160 with reference to, for example, Tables 1 and 2, and the dielectric layer 160 is preferably made of SiO 2. ₂ and a dielectric material selected from the group consisting of Al ₂ O ₃ and HfO ₂ . These materials are known to be dielectric materials, so-called wide band gap materials, and even when combined with any ferroelectric single crystal 120, the band alignment shown in FIG. 2B is formed. The design of the ferroelectric capacitor is easy. Further, with these dielectric materials, a film forming technique has been established, and a dielectric layer 160 with a high quality and a controlled thickness can be formed.

  The thickness of the dielectric layer 160 is not particularly limited, but is preferably 5 nm or more and 1 μm or less. If the thickness is controlled as described above, a desirable band alignment can be formed among the ferroelectric single crystal 120, the dielectric layer 160, and the metal layer 130, so that a confinement effect with a high surface charge can be expected.

  The material of the metal layer 130 is not particularly limited, but a metal selected from the group consisting of Al, Cr, and Au is preferable. These materials are easily available, and the technique for forming the metal layer 130 has been established, so that the high-quality metal layer 130 can be formed.

  The thickness of the metal layer 130 is not particularly limited, but is preferably 10 nm or more and 1 μm or less. If the thickness is controlled as described above, a desirable band alignment can be formed among the ferroelectric single crystal 120, the dielectric layer 160, and the metal layer 130, so that the surface charge confinement effect can be improved.

  FIG. 3 is a schematic diagram showing a cross-sectional view of another ferroelectric capacitor of the present invention.

  The ferroelectric capacitor 100 shown in FIG. 3A is different from the ferroelectric capacitor 100 except that the dielectric layer 160 is located between the ferroelectric single crystal 120 and the metal layer 130 and also on the charge storage region 110. This is the same as that of FIG. By adopting such a configuration, it is not necessary to remove the dielectric layer located on the charge storage region 110 by etching or the like after forming the dielectric layer in the manufacturing process to be described later. It is advantageous. In FIG. 3A, the dielectric layer 160 is located between the ferroelectric single crystal 120 and the metal layer 130 and on the charge storage region 110, but is located on the entire surface of the ferroelectric single crystal 120. You may do it.

  FIG. 3B is a schematic diagram showing a state of a junction between the ferroelectric single crystal 120 and the dielectric layer 160 in the charge storage region 110 of the ferroelectric capacitor 100 of FIG. 3B, when the dielectric layer 160 is positioned on the ferroelectric single crystal 120, it can be understood that the ferroelectric single crystal 120 and the capacitor of the dielectric layer 160 are directly connected.

For example, the relative dielectric constant of the ferroelectric single crystal 120 is ε _F , the thickness is d _F , and the electric capacity is _CF, and the relative dielectric constant of the dielectric layer 160 is ε _D , the thickness is d _D , and the electric capacity is When C _D , the area of the charge storage region 110 is S, and the vacuum dielectric constant is ε ₀ , the following relationship is established.
C _F = ε ₀ ε _F × (S / d _F )
C _D = ε ₀ ε _D × (S / d _D )
From these, the combined capacitance C is obtained as follows.
C = C _F × C _D / (C _F + C _D )
= Ε ₀ ε _F ε _DS / (ε _F d _F + ε _D d _D ) (1)

In the equation (1), when the relative permittivity ε _F and thickness d _{F of} the ferroelectric single crystal 120 and the area S of the charge storage region 110 are constant, the dielectric layer 160 has a relative permittivity ε _D It can be seen that the composite capacitance C increases as the thickness d _D is made of a large dielectric material. The larger the synthetic capacitance C, the larger the surface charge 150 can be accumulated.

  From this point of view, when the dielectric layer 160 is located not only between the ferroelectric single crystal 120 and the metal layer 130 but also on the charge storage region 110 as shown in FIG. The dielectric layer 160 preferably has a high dielectric constant and a small thickness. For example, if the dielectric layer 160 has a relative dielectric constant of 3 or more and a thickness in the range of 5 nm to 1 μm, the surface charge 150 can be accumulated. Further, as shown in the example, when the ferroelectric single crystal 120 is a material having a dielectric constant similar to the dielectric constant (85) of the LN single crystal, the dielectric layer 160 has a ratio of 3.5 or more. If it has a dielectric constant and a thickness in the range of 5 nm or more and 200 nm or less, surface charges can be effectively accumulated.

  Hereinafter, for the sake of simplicity, description will be made assuming that the dielectric layer 160 is located only between the ferroelectric single crystal 120 and the metal layer 130.

  FIG. 4 is a diagram showing various patterns of the charge storage region and the metal layer in the ferroelectric capacitor of the present invention.

  In FIG. 4, it should be noted that a dielectric layer 160 (not shown) having the same shape as the metal layer 130 is located between the ferroelectric single crystal 120 and the metal layer 130. Although FIG. 1 shows an example in which the charge storage region 110 is circular and the metal layer 130 and the dielectric layer 160 are positioned so as to surround the charge storage region 110, the metal layer 130 and the dielectric layer 160 are However, the present invention is not limited to this as long as it is located around the accumulation region 110. For example, as shown in FIG. 4A, the charge storage region 110 may be circular, and the metal layer 130 and the dielectric layer 160 located around the charge storage region 110 may be partially missing. However, it is preferable that the metal layer 130 and the dielectric layer 160 completely surround the charge storage region 110 because the surface charge confinement effect is improved.

  In addition, as illustrated in FIG. 4B, the charge accumulation region 110 may be rectangular. Further, as shown in FIG. 4C, a plurality of charge storage regions 110 may be formed in a dot shape, or as shown in FIG. 4D, a plurality of charge storage regions 110 may be formed in a line shape. . Of course, the pattern of the charge storage region and the metal layer and dielectric layer may be a combination thereof. A single domain structure or a domain-inverted structure may be combined with various patterns of the charge storage region, the metal layer, and the dielectric layer.

  The diameter D of the charge storage region 110 is preferably in the range of 1.5 μm to 55 μm. If the diameter D is less than 1.5 μm, the charge accumulation region 110 is too small, and thus sufficient surface charge may not be accumulated. When the diameter D exceeds 55 μm, the charge density becomes small and may become inefficient. When the charge accumulation region 110 is rectangular, the length in the longitudinal direction may be regarded as the diameter D.

  FIG. 5 is a diagram showing how the ferroelectric capacitor of the present invention accumulates surface charges due to the piezoelectric effect.

  FIG. 5A shows an initial state of the ferroelectric single crystal 120, and the polarization direction of the ferroelectric single crystal 120 is a direction substantially perpendicular to the surface of the charge storage region 110. Of the ferroelectric single crystal 120 is controlled so as to be from the bottom to the top, and the polarity inside the surface of the ferroelectric single crystal 120 corresponding to the charge storage region 110 is + polarity. Show. In FIG. 5A, the ferroelectric capacitor 100 of the present invention can accumulate the surface charge 150 that shields the polarization charge caused by the spontaneous polarization of the ferroelectric single crystal 120.

  FIG. 5B shows a case where the ferroelectric single crystal 120 is compressed. As described above, the ferroelectric capacitor 100 of the present invention has a surface charge based on the piezoelectric effect in addition to the surface charge based on the spontaneous polarization (that is, the charge induced by the piezoelectric effect of the ferroelectric single crystal 120). Can be accumulated.

  Specifically, as shown in FIG. 5B, when a pressure 410 is applied to the ferroelectric single crystal 120 (that is, the ferroelectric single crystal 120 is compressed or pulled), the ferroelectric single crystal 120 is In the crystal 120, the charge is biased in a specific direction, and more positive charges are induced on the upper surface side of the ferroelectric single crystal 120 and more negative charges are induced on the lower surface side as compared with FIG. The As a result, the ferroelectric capacitor 100 of the present invention can accumulate more surface charge 420 on the charge accumulation region 110 that shields these induced positive charges. That is, the ferroelectric capacitor 100 of the present invention can increase the surface charge accumulated on the charge accumulation region 110 by the piezoelectric effect.

  FIG. 6 is a diagram showing how the ferroelectric capacitor of the present invention accumulates surface charges due to the pyroelectric effect.

  FIG. 6A shows an initial state of the ferroelectric single crystal 120, and the polarization direction of the ferroelectric single crystal 120 is a direction substantially perpendicular to the surface of the charge storage region 110. Of the ferroelectric single crystal 120 is controlled so as to be from the bottom to the top, and the polarity inside the surface of the ferroelectric single crystal 120 corresponding to the charge storage region 110 is + polarity. Show. In FIG. 6A, the ferroelectric capacitor 100 of the present invention can accumulate a surface charge 150 that shields a polarization charge due to spontaneous polarization of the ferroelectric single crystal 120.

  FIG. 6B shows the case where the ferroelectric single crystal 120 is heated. As described above, the ferroelectric capacitor 100 of the present invention is induced by the surface charge based on the pyroelectric effect in addition to the surface charge based on the spontaneous polarization (that is, induced by the pyroelectric effect of the ferroelectric single crystal 120). Charge) can be accumulated.

  Specifically, as shown in FIG. 6B, when the ferroelectric single crystal 120 is irradiated with light 510 such as infrared rays or heated by a heating device 520 such as a hot plate, the ferroelectric single crystal 120 is heated. Internally, the charge is biased in a specific direction, and more positive charges are induced on the upper surface side of the ferroelectric single crystal 120 and more negative charges are induced on the lower surface side as compared with FIG. As a result, the ferroelectric capacitor 100 of the present invention can accumulate more surface charges 530 on the charge accumulation region 110 that shield these induced positive charges. That is, the ferroelectric capacitor 100 of the present invention can increase the surface charge accumulated on the charge accumulation region 110 by the pyroelectric effect.

  4 to 6 exemplify the case where the dielectric layer 160 is located between the ferroelectric single crystal 120 and the metal layer 130, the dielectric layer 160 may be the same as the ferroelectric single crystal 120. Even if it is located between the metal layer 130 and the charge storage region 110, the same effect can be obtained.

  Next, an example of a method for manufacturing a ferroelectric capacitor of the present invention will be described.

  First, a ferroelectric single crystal whose polarization direction is controlled is prepared. The selection of the material of the ferroelectric single crystal is as described with reference to FIG. The ferroelectric single crystal in which the direction of polarization is controlled may be a single crystal substrate that has been poled to have a single polarization structure, or a single crystal that has been domain-engineered to have a polarization inversion structure. It may be a substrate. Such a single crystal substrate is manufactured by, for example, manufacturing a ferroelectric single crystal made of an oxide typified by lithium niobate, lithium tantalate or the like having a single polarization structure with reference to Registration No. 3551242. Alternatively, referring to JP-A-05-289137, a domain-inverted structure having a periodic structure may be formed. Gruberman et al., Appl. Phys. Lett. 69, 3191 (1996), Kitamura et al., Thin Film and Surface Physics Subcommittee of the Japan Society of Applied Physics, NEWS LETTER [120] (2004), 12-18, scanning force microscope (SFM) or atomic force microscope ( AFM may be used to form a domain-inverted structure having a nanoscale.

  A dielectric layer is applied to the surface of the ferroelectric single crystal by physical vapor deposition or chemical vapor deposition. Next, the metal layer is patterned around the charge storage region of the ferroelectric single crystal provided with the dielectric layer by lithography. The selection of the material for the metal layer is as described with reference to FIG.

  An example of the patterning of the metal layer is as follows. A resist sensitive to an electron beam is applied to the entire surface including the charge storage region of the ferroelectric single crystal. Next, the resist is irradiated with an electron beam (EB) to draw a desired pattern, and then immersed in a developer to remove the exposed resist. Thereby, only the part which wants to attach a metal layer is exposed. Next, a metal layer is applied by physical vapor deposition or chemical vapor deposition. Finally, unnecessary resist is removed by a lift-off process. This is a case where a positive type resist is used. However, when a negative type resist is used, the procedure is the same except that a non-photosensitive portion is removed. In this way, the ferroelectric capacitor of the present invention is manufactured.

  The patterning of the metal layer is not limited to electron beam lithography, and photolithography may be used, or an etching process may be employed instead of the lift-off process. Lithography using an electron beam is preferable for manufacturing a nanoscale ferroelectric capacitor because it allows fine processing. In order to obtain a ferroelectric capacitor having a charge storage region of a desired size and shape, a lithography technique known in the existing semiconductor technology or the like can be appropriately employed for the patterning of the metal.

  The dielectric layer located on the charge storage region is removed by an existing etching technique such as dry etching using reactive ion etching (RIE), wet etching using hydrofluoric acid, or plasma etching using plasma. May be.

  The ferroelectric capacitor of the present invention thus obtained can accumulate surface charges based on a ferroelectric single crystal as described above. Utilizing such surface charges, the ferroelectric capacitor of the present invention is connected to various elements such as sensors and charge transfer switches and functions as a power source for operating them, or under certain conditions (for example, Since the charge amount of the accumulated surface charge changes under pressure or heating), it itself functions as a sensor.

  FIG. 7 is a schematic view showing an electronic device using the ferroelectric capacitor of the present invention.

  An electronic device 600 of the present invention includes the ferroelectric capacitor 100 of the present invention and an element 610. The ferroelectric capacitor 100 is as described with reference to FIG. The element 610 is connected between the charge storage region 110 and the metal layer 130 of the ferroelectric capacitor 100 and operates by the surface charge stored on the charge storage region 110 or on the charge storage region 110. A change in the amount of surface charge accumulated in the surface is detected.

  For example, when the element 610 is a diode or the like, the electronic device 600 of the present invention functions as a diode sensor or the like that does not require an external power source because the device 610 operates easily by the surface charge accumulated on the charge accumulation region 110.

  For example, when the element 610 is a sensor whose resistance value changes with respect to an adsorbent such as dust, the electronic device 600 of the present invention functions as a dust sensor that does not require an external power source. The electronic device 600 of the present invention uses the surface charge accumulated on the charge accumulation region 110 of the ferroelectric capacitor 100 to measure the resistance value between the elements 610 or the current value flowing through the element 610. If there is a change in the value, the presence of adsorbate can be detected.

  For example, when the element 610 is a voltmeter or an ammeter, the electronic device 600 of the present invention functions as a switch that does not require an external power supply. In the electronic device 600 of the present invention, the element 610 detects a change in the charge amount of the surface charge accumulated on the charge accumulation region 110 due to heat (light) or pressure. It can function as a switch that turns on (or off) and turns off (or on) if the charge amount is less than a certain amount.

  7 exemplifies the case where the dielectric layer 160 is positioned between the ferroelectric single crystal 120 and the metal layer 130, the dielectric layer 160 includes the ferroelectric single crystal 120 and the metal layer 130. The same effect can be obtained even if it is positioned between and on the charge storage region 110.

  The present invention will now be described in detail using specific examples, but it should be noted that the present invention is not limited to these examples.

[Comparative Example 1]
In Comparative Example 1, the ferroelectric single crystal 120 is a stoichiometric composition lithium niobate (SLN) single crystal (thickness 0.5 mm) having a single polarization structure, and the charge accumulation region 110 has a + polar plane (ie, The ferroelectric single crystal 120 corresponding to the charge storage region 110 is a circular region (diameter 2 μm) having a positive polarity inside the surface, the metal layer 130 is an Al layer, and the dielectric layer 160 is A ferroelectric capacitor without it was manufactured.

  8 is a diagram showing a process for manufacturing the ferroelectric capacitor of Comparative Example 1. FIG.

  FIG. 8 is a cross-sectional view showing a process of manufacturing a ferroelectric capacitor, and a top view of the manufactured ferroelectric capacitor. A resist (NEB-22, manufactured by SUMITOMOCHEMICAL Co., LTD) 710 sensitive to an electron beam was applied to the positive polarity surface (upper surface in FIG. 7) of the SLN single crystal 120. An e-spacer (not shown) was applied to the resist 710 to prevent charging. The resist 710 was exposed to a donut shape by electron beam lithography, the e-spacer was removed by washing with water, and the resist 710 was immersed in a developer (TMAH 2.38%) to remove the resist in the exposed region 720. Then, it rinsed with the pure water. Next, an Al layer 730 was deposited on the SLN single crystal 120 from which the resist was partially removed by an electron beam deposition method. The thickness of the Al layer was 150 nm. Next, the resist 710 and the Al layer 730 other than the region 720 were removed by a lift-off process using N-methylpyrrolidone (NMP). As a result, the ferroelectric capacitor of Comparative Example 1 including the SLN single crystal 120 having a circular charge storage region 110 (diameter: 2 μm) and the Al layer 130 positioned so as to surround the charge storage region 110. Was manufactured.

  The shape image of the surface of the ferroelectric capacitor of Comparative Example 1 was observed with an atomic force microscope (AFM, manufactured by SII, NanoNavi II & E-sweep). The observation was performed in a tapping mode using an Si cantilever under an argon atmosphere. The results are shown in FIG.

  The temperature dependence of the potential image in the charge storage region of the ferroelectric capacitor of Comparative Example 1 was observed with a Kelvin force microscope (KFM, manufactured by SII, NanoNavi II & E-sweep) equipped with a heater. Observation was performed at room temperature (25 ° C.), 40 ° C., 55 ° C., 70 ° C. and 90 ° C. under an argon atmosphere (1 atm) using an Rh-coated cantilever in an applied voltage of 5 V and cyclic scan mode. It was. The results are shown in FIGS.

[Comparative Example 2]
In Comparative Example 2, the ferroelectric single crystal 120 is a stoichiometric lithium niobate (SLN) single crystal (thickness 0.5 mm) having a single polarization structure, and the charge accumulation region 110 is a -polar plane (ie, The ferroelectric single crystal 120 corresponding to the charge storage region 110 is a circular region (diameter 2 μm) having a negative polarity inside the surface, the metal layer 130 is an Al layer, and the dielectric layer 160 is A ferroelectric capacitor without it was manufactured. The charge storage region 110 was manufactured in the same procedure as in Comparative Example 1 except that the polar surface of the charge storage region 110 was reversed.

  The shape image and potential image of the ferroelectric capacitor of Comparative Example 2 were observed in the same manner as in Comparative Example 1. The results are shown in FIG.

[Example 3]
In Example 3, the ferroelectric single crystal 120 is a monolithic lithium niobate (SLN) single crystal (thickness 0.5 mm) having a single polarization structure, and the charge storage region 110 has a circular shape having a + polar plane. A ferroelectric capacitor having a region of 2 μm in diameter, the dielectric layer 160 being a SiO ₂ layer, and the metal layer 130 being an Al layer was manufactured. In the ferroelectric capacitor according to the third embodiment, as described with reference to FIG. 3, the dielectric layer 160 is provided between the ferroelectric single crystal 120 and the metal layer 130 on the charge storage region 110. Also located.

  FIG. 9 is a diagram illustrating a process for manufacturing the ferroelectric capacitor of Example 3. FIG.

FIG. 9 is a sectional view showing a process of manufacturing a ferroelectric capacitor, and a top view of the manufactured ferroelectric capacitor. A SiO ₂ layer (thickness: 200 nm) was formed as the dielectric layer 160 on the entire + polar plane (upper surface in FIG. 7) of the SLN single crystal 120 by chemical vapor deposition (CVD). The subsequent procedure is the same as that in FIG. In Example 3, the SiO ₂ layer, which is the dielectric layer 160 on the charge storage region 110, is not removed. Needless to say, the SiO ₂ layer can be easily removed by various existing etching techniques. Those skilled in the art will understand that a ferroelectric capacitor having a dielectric layer 160 only between the single crystal 120 and the metal layer 130 can also be manufactured.

  The shape image and potential image of the ferroelectric capacitor of Example 3 obtained in this way were observed in the same manner as in Comparative Example 1. The results are shown in FIG.

[Example 4]
In Example 4, the ferroelectric single crystal 120 is a monolithic lithium niobate (SLN) single crystal (thickness 0.5 mm) having a single polarization structure, and the charge storage region 110 has a circular shape having a -polar plane. A ferroelectric capacitor having a region of 2 μm in diameter, the dielectric layer 160 being a SiO ₂ layer, and the metal layer 130 being an Al layer was manufactured. The same procedure as in Example 3 was performed except that the polarity of the charge storage region 110 was different.

  The shape image and potential image of the ferroelectric capacitor of Example 4 were observed in the same manner as in Comparative Example 1. The results are shown in FIG.

[Example 5]
In Example 5, the ferroelectric single crystal 120 is a monolithic composition lithium niobate (SLN) single crystal (thickness 0.5 mm) having a single polarization structure, and the charge storage region 110 is a rectangle having a + polar plane. A ferroelectric capacitor having a region of 50 μm in the longitudinal direction, the dielectric layer 160 being a SiO ₂ layer, and the metal layer 130 being an Al layer was manufactured. In Example 5, it manufactured by the procedure similar to Example 3 except the pattern which irradiates an electron beam differing.

  The shape image and potential image of the ferroelectric capacitor of Example 5 were observed in the same manner as in Comparative Example 1. The results are shown in FIG.

[Comparative Example 6]
In Comparative Example 6, the ferroelectric single crystal 120 is a stoichiometric composition lithium niobate (SLN) single crystal (thickness 0.5 mm) having a single polarization structure, and the charge storage region 110 is a circular shape having a + polar plane. A ferroelectric capacitor having a diameter of 2 μm, the metal layer 130 being a Cr layer, and not having the dielectric layer 160 was manufactured. The same procedure as in Comparative Example 1 was conducted except that the metal layer was different.

  The shape image and potential image of the ferroelectric capacitor of Comparative Example 6 were observed in the same manner as in Comparative Example 1. The results are shown in FIG.

[Example 7]
In Example 7, the ferroelectric single crystal 120 is a monolithic composition lithium niobate (SLN) single crystal (thickness 0.5 mm) having a single polarization structure, and the charge storage region 110 has a circular shape having a + polar plane. A ferroelectric capacitor having a region of (diameter 2 μm), a dielectric layer 160 being a SiO ₂ layer, and a metal layer 130 being a Cr layer was manufactured. Manufactured in the same procedure as in Example 3 except that the metal layer was different.

  The shape image and potential image of the ferroelectric capacitor of Example 7 were observed in the same manner as in Comparative Example 1. The results are shown in FIG.

[Example 8]
In Example 8, the ferroelectric single crystal 120 is a monolithic lithium niobate (SLN) single crystal (thickness 0.5 mm) having a single polarization structure, and the charge storage region 110 is a circular shape having a + polar plane. The ferroelectric capacitor was manufactured by combining a region (diameter 2 μm) and a rectangle (length in the longitudinal direction 3 μm), the dielectric layer 160 being a SiO ₂ layer, and the metal layer 130 being a Cr layer. Further, the metal layer 130 was deposited so as to partially open without surrounding the charge storage region 110. Manufactured in the same procedure as in Example 3 except that the pattern for irradiating the electron beam and the metal layer were different.

  The shape image and potential image of the ferroelectric capacitor of Example 8 were observed in the same manner as in Comparative Example 1. The results are shown in FIG.

[Reference Example 9]
In Reference Example 9, the ferroelectric single crystal 120 is a stoichiometric lithium niobate (SLN) single crystal (thickness 0.5 mm) having a single polarization structure, and the charge storage region 110 is a circle having a -polar plane. A ferroelectric capacitor having a diameter of 2 μm and a metal layer 130 of an Au layer was manufactured. Manufactured in the same procedure as in Comparative Example 1 except that the type of the metal layer is different and the polar surface of the charge storage region 110 is reversed.

  The shape image and potential image of the ferroelectric capacitor of Reference Example 9 were observed in the same manner as in Comparative Example 1. The results are shown in FIG.

Table 3 shows a list of experimental conditions of the above Examples, Comparative Examples, and Reference Examples for simplicity.

FIG. 10 is a diagram showing a shape image and a potential image of the ferroelectric capacitor of Comparative Example 1.
FIG. 11 is a diagram showing a shape image and a potential image of the ferroelectric capacitor of Comparative Example 2.

  In the shape image, the brightly shown region and the darkly shown region indicate that there is a difference in height of the object, and the height of the brightly shown region is higher than the height of the darkly shown region. According to FIGS. 10A and 11A, the ferroelectric capacitors of Comparative Example 1 and Comparative Example 2 have circular (diameter 2 ± 0.5 μm) charge storage regions around the ferroelectric capacitor. It was confirmed that a difference in height was caused by the presence of the metal layer.

  In the potential image, it is shown that there is a difference in potential between the region shown bright and the region shown dark, and the potential of the region shown bright is different from the potential of the region shown dark. According to FIGS. 10B to 10F and FIGS. 11B to 11F, the ferroelectric capacitors of Comparative Example 1 and Comparative Example 2 are both charged even when the SLN single crystal is heated. It was found that there was no potential increase in the region and no surface charge was accumulated.

FIG. 12 is a diagram showing a shape image and a potential image of the ferroelectric capacitor of Example 3.
FIG. 13 is a diagram showing a shape image and a potential image of the ferroelectric capacitor of Example 4.

  According to FIGS. 12A and 13A, it was confirmed that the ferroelectric capacitors of Example 3 and Example 4 had a circular (diameter 2 ± 0.5 μm) charge storage region.

  According to FIGS. 12B and 13B, the potential of the charge storage region and the potential of the metal layer of the ferroelectric capacitors of Examples 3 and 4 were almost equal. From this, the ferroelectric capacitors of Example 3 and Example 4 show an increase in potential in the charge storage region at room temperature, and surface charges induced by spontaneous polarization on the charge storage region including the dielectric layer. Was found to accumulate.

  Further, according to FIGS. 12 (C) to (F) and FIGS. 13 (C) to (F), the ferroelectric capacitors of Example 3 and Example 4 accumulate charge even when the SLN single crystal is heated. An increase in potential within the region was shown. More specifically, the ferroelectric capacitor of Example 3 having a charge storage region having a positive polarity surface shows an increase in potential to 90 ° C. as the temperature of the SLN single crystal increases, whereas it has a negative polarity surface. In the ferroelectric capacitor of Example 4 having the charge storage region, as the temperature of the SLN single crystal increased, the potential increased most around 55 ° C., and then the potential decreased. From this, it was found that the ferroelectric capacitors of Examples 3 and 4 accumulate the surface charge induced by the pyroelectric effect.

  According to the above Comparative Examples 1-2 and Examples 3-4, the ferroelectric capacitor of the present invention accumulates charges by positioning the dielectric layer at least between the ferroelectric single crystal and the metal layer. It has been found that charge can be confined and accumulated on the region. It was also confirmed that the accumulated charge was a surface charge generated by natural energy based on spontaneous polarization, pyroelectric effect, etc. of the ferroelectric single crystal.

  FIG. 14 is a diagram showing a shape image and a potential image of the ferroelectric capacitor of Example 5.

  According to FIG. 14A, it was confirmed that the ferroelectric capacitor of Example 5 had a rectangular (longitudinal length 50 ± 5 μm) charge storage region.

  According to FIGS. 14B and 14C, the ferroelectric capacitor of Example 5 shows an increase in potential in the vicinity of the metal layer in the charge accumulation region at room temperature, and accumulates surface charges due to spontaneous polarization. I found out that From this, it is suggested that the diameter (or length in the longitudinal direction) of the charge accumulation region capable of efficiently accumulating surface charges is 55 μm or less.

FIG. 15 is a diagram showing a shape image and a potential image of the ferroelectric capacitor of Comparative Example 6.
FIG. 16 is a diagram showing a shape image and a potential image of the ferroelectric capacitor of Example 7.

  According to FIGS. 15A and 16A, it was confirmed that the ferroelectric capacitors of Comparative Example 6 and Example 7 had a circular (2 ± 0.5 μm diameter) charge storage region.

  According to FIGS. 15B and 16B, the ferroelectric capacitors of Comparative Example 6 and Example 7 both show an increase in potential in the charge storage region at room temperature, which is caused by spontaneous polarization. It was found to accumulate surface charge. In the ferroelectric capacitors of Comparative Example 6 and Example 7, the potential of the charge storage region and the potential of the metal layer were almost equal. From this, the ferroelectric capacitors of Comparative Example 6 and Example 7 show an increase in potential in the charge storage region at room temperature, and when the metal layer is Cr, regardless of the presence or absence of the dielectric layer It was found that the surface charge induced by spontaneous polarization is accumulated on the charge accumulation region.

  Further, according to FIGS. 15 (C) to 15 (F) and FIGS. 16 (C) to (F), the ferroelectric capacitors of Comparative Example 6 and Example 7 accumulate the charge by heating the SLN single crystal. An increase in potential within the region was shown. More specifically, the ferroelectric capacitor of Example 7 having a dielectric layer showed an increase in potential to a higher temperature than the ferroelectric capacitor of Comparative Example 6 having no dielectric layer.

  According to Comparative Example 6 and Example 7 described above, the charge storage capability of the ferroelectric capacitor can be improved by positioning the dielectric layer at least between the ferroelectric single crystal and the metal layer. I understood.

  FIG. 17 is a diagram showing a shape image and a potential image of the ferroelectric capacitor of Example 8.

  According to FIG. 17A, the ferroelectric capacitor of Example 8 has a charge storage region in which a circle (diameter 2 ± 0.5 μm) and a rectangle (longitudinal length 3 ± 0.5 μm) are combined. Confirmed to have. In this case, the diameter of the charge storage region can be estimated to be 5 μm.

  According to FIG. 17B, it was found that the ferroelectric capacitor of Example 8 showed an increase in potential in the charge accumulation region at room temperature and accumulated surface charges due to spontaneous polarization. In the ferroelectric capacitor of Example 8, it was confirmed that the metal layer did not completely surround the charge storage region and was partially open, but the surface charge accumulation was not affected.

  According to Example 8 described above, in the ferroelectric capacitor of the present invention, it is not necessary to completely surround the charge accumulation region, and it is sufficient that the metal layer is located at least around the charge accumulation region. It was done. Moreover, in the ferroelectric capacitor of the present invention, it has been shown that the shape of the charge storage region is not limited to a circle but may be an arbitrary shape.

  FIG. 18 is a diagram showing a shape image and a potential image of the ferroelectric capacitor of Reference Example 9.

  According to FIG. 18A, it was confirmed that the ferroelectric capacitor of Reference Example 9 had a circular (diameter: 2 ± 0.5 μm) charge storage region. According to FIG. 18B, it was found that the ferroelectric capacitor of Reference Example 9 showed an increase in potential in the charge accumulation region at room temperature and accumulated surface charge induced by spontaneous polarization.

  As described with reference to FIG. 15 and FIG. 16, the ferroelectric capacitor of the present invention has a ferroelectric single crystal at least between the metal layer and the ferroelectric single crystal regardless of the type of metal. Since the surface charge is efficiently accumulated by positioning the dielectric layer having a large band gap, the dielectric layer is similarly formed between Au and the ferroelectric single crystal even when the metal layer is Au. By positioning, more efficient surface charge accumulation can be expected.

  Since the ferroelectric capacitor of the present invention can accumulate charges (surface charges) sufficient to shield polarization charges derived from a ferroelectric single crystal, it can function as a power source using natural energy. In addition, the ferroelectric capacitor of the present invention changes the charge amount of the surface charge that is accumulated by being induced by the pyroelectric effect or the piezoelectric effect. Therefore, the ferroelectric capacitor can also function as a switch using such a change in charge amount. . Furthermore, an electronic device can be constructed by connecting the ferroelectric capacitor of the present invention as a power source to a sensor, a charge transfer switch, or the like. In addition, since the ferroelectric capacitor of the present invention can be nanoscaled by a selected manufacturing technique such as electron beam lithography, a nanoscale power supply or electronic device can be provided.

DESCRIPTION OF SYMBOLS 100 Ferroelectric capacitor 110 Charge storage area 120 Ferroelectric single crystal 130 Metal layer 140 Surface of ferroelectric single crystal 150, 420, 530 Surface charge 160 Dielectric layer 410 Pressure 510 Light 520 Heating device 600 Electronic device 610 Element 710 Resist 720 region 730 Al layer

Claims (14)

A ferroelectric single crystal having a charge accumulation region in which the direction of polarization is controlled, wherein the charge accumulation region is at least a partial region of the surface of the ferroelectric single crystal; ,
A metal layer located around the charge storage region;
A dielectric layer positioned at least between the ferroelectric single crystal and the metal layer,
The band gap of the dielectric layer is larger than the band gap of the ferroelectric single crystal,
A ferroelectric capacitor in which charges based on the ferroelectric single crystal are confined and stored on the charge storage region.   The ferroelectric capacitor according to claim 1, wherein the ferroelectric single crystal is a lithium niobate single crystal or a lithium tantalate single crystal.   The ferroelectric capacitor according to claim 3, wherein the metal layer is a metal selected from the group consisting of Al, Cr, and Au.   The ferroelectric capacitor according to claim 1, wherein the dielectric layer and the metal layer are positioned so as to surround the charge storage region.   2. The ferroelectric capacitor according to claim 1, wherein the dielectric layer is located on the charge storage region in addition to between the ferroelectric single crystal and the metal layer. The ferroelectric capacitor according to claim 1, wherein the dielectric layer is a dielectric material selected from the group consisting of SiO ₂ , Al ₂ O _3, and HfO ₂ .   The ferroelectric capacitor according to claim 1, wherein a thickness of the dielectric layer is not less than 5 nm and not more than 1 μm.   The ferroelectric capacitor according to claim 5, wherein the dielectric layer has a relative dielectric constant of 3 or more and a thickness in a range of 5 nm to 1 μm.   The ferroelectric capacitor according to claim 8, wherein the dielectric layer has a relative dielectric constant of 3.5 or more and a thickness in a range of 5 nm to 200 μm.   The charge is induced by the spontaneous polarization of the ferroelectric single crystal, the charge induced by the piezoelectric effect of the ferroelectric single crystal, or the pyroelectric effect of the ferroelectric single crystal. The ferroelectric capacitor according to claim 1, wherein the ferroelectric capacitor is a charge.   2. The ferroelectric capacitor according to claim 1, wherein a diameter of the charge storage region is in a range of 1.5 μm to 55 μm. The ferroelectric single crystal is controlled in the direction of polarization so as to have a single polarization structure,
2. The ferroelectric capacitor according to claim 1, wherein a polarity inside the surface of the ferroelectric single crystal corresponding to the charge storage region is either a positive polarity or a negative polarity. In the ferroelectric single crystal, the direction of polarization is controlled so as to have a polarization inversion structure,
2. The ferroelectric capacitor according to claim 1, wherein a polarity inside the surface of the ferroelectric single crystal corresponding to the charge storage region is either a positive polarity or a negative polarity. An electronic device comprising a ferroelectric capacitor and a semiconductor element,
The ferroelectric capacitor is a ferroelectric capacitor according to any one of claims 1 to 13,
The semiconductor element is connected between the charge storage region and the metal layer, and operates by the charge stored on the charge storage region or the charge stored on the charge storage region. An electronic device that detects changes in charge.