Source: http://www.google.com/patents/US7371473?dq=6373188
Timestamp: 2014-04-16 16:21:49
Document Index: 790261493

Matched Legal Cases: ['Application No. 10', 'Application No. 2002', 'Application No. 2003', 'Application No. 2003', 'Application No. 2003', 'Application No. 2003']

Patent US7371473 - Ferroelectric film, ferroelectric capacitor, ferroelectric memory ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsA ferroelectric film is formed by an oxide that is described by a general formula AB1-xNbxO3. An A element includes at least Pb, and a B element includes at least one of Zr, Ti, V, W, Hf and Ta. The ferroelectric film includes Nb within the range of: 0.05 ≦x<1. The ferroelectric film can be used for...http://www.google.com/patents/US7371473?utm_source=gb-gplus-sharePatent US7371473 - Ferroelectric film, ferroelectric capacitor, ferroelectric memory, piezoelectric element, semiconductor element, method of manufacturing ferroelectric film, and method of manufacturing ferroelectric capacitorAdvanced Patent SearchPublication numberUS7371473 B2Publication typeGrantApplication numberUS 11/286,286Publication dateMay 13, 2008Filing dateNov 25, 2005Priority dateOct 24, 2002Fee statusPaidAlso published asEP1555678A1, EP1555678A4, EP1555678B1, US7255941, US20040214352, US20060083933, US20060088731, WO2004038733A1Publication number11286286, 286286, US 7371473 B2, US 7371473B2, US-B2-7371473, US7371473 B2, US7371473B2InventorsTakeshi Kijima, Yasuaki Hamada, Eiji Natori, Koji OhashiOriginal AssigneeSeiko Epson CorporationExport CitationBiBTeX, EndNote, RefManPatent Citations (54), Non-Patent Citations (5), Referenced by (2), Classifications (78), Legal Events (1) External Links: USPTO, USPTO Assignment, EspacenetFerroelectric film, ferroelectric capacitor, ferroelectric memory, piezoelectric element, semiconductor element, method of manufacturing ferroelectric film, and method of manufacturing ferroelectric capacitorUS 7371473 B2Abstract A ferroelectric film is formed by an oxide that is described by a general formula AB1-xNbxO3. An A element includes at least Pb, and a B element includes at least one of Zr, Ti, V, W, Hf and Ta. The ferroelectric film includes Nb within the range of: 0.05 ≦x<1. The ferroelectric film can be used for any of ferroelectric memories of 1T1C, 2T2C and simple matrix types.
1. A ferroelectric film that is described by AB1-xNbxO3,
wherein a B element includes at least Zr and Ti, and
wherein X is within the range of: 0.1<X≦0.4.
2. A ferroelectric film that is described by AB1-xNbxO3,
wherein a B element includes at least Zr and Ti,
wherein X is within the range of: 0.05≦X≦0.4, and
further comprising Si.
3. The ferroelectric film as defined by claim 2, wherein Si is within the range of: 0.5 to 5 mol %.
4. The ferroelectric film as defined by claim 2, further comprising Ge.
5. The ferroelectric film as defined by claim 2, having a crystal structure of at least one of tetragonal and rhombohedral systems.
6. The ferroelectric film as defined by claim 2,
wherein an amount of Pb vacancy is less than 20 mol % of a stoichiometric composition of the AB1-xNbxO3.
7. The ferroelectric film as defined by claim 6, wherein the amount of Pb vacancy is half of X.
a transistor formed on the substrate,
a ferroelectric capacitor formed above the substrate, and
wherein the ferroelectric capacitor comprises a ferroelectric film as defined by claim 2.
a piezoelectric element formed above the substrate, and
wherein the piezoelectric element comprises a ferroelectric film as defined by claim 2. Description
CROSS-REFERENCE TO RELATED APPLICATION This application is a divisional of Application No. 10/690,021, now U.S. Pat. No. 7,255,941 filed Mar. 8, 2002, which application is incorporated herein by reference in its entirety.
The disclosures of Japanese Patent Application No. 2002-309487, filed on Oct. 24, 2002, Japanese Patent Application No. 2003-76129, filed on Mar. 19, 2003, Japanese Patent Application No. 2003-85791, filed on Mar. 26, 2003, Japanese Patent Application No. 2003-294072 filed on Aug. 18, 2003, and Japanese Patent Application No. 2003-302900 filed on Aug. 27, 2003 are hereby incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION The present invention relates to a ferroelectric film, a ferroelectric capacitor, a ferroelectric memory, a piezoelectric element, a semiconductor element, a method of manufacturing a ferroelectric film, and a method of manufacturing a ferroelectric capacitor.
First of all, a PZT tetragonal thin film tends to have a high leakage current density after crystallization, which increases as the ratio of Ti contained therein increases. In addition, static imprint testing in which data is written once in either the positive or negative direction and the memory device is heated and held at 100� C. has shown that most of the written data disappears after 24 hours. These problems are intrinsic to the ionic crystals of PZT and to the Pb and Ti that are constituent elements of PZT, and create the greatest technical problem relating to PZT tetragonal thin film in which large proportions of the constituent elements are Pb and Ti. This technical problems is great because PZT Perovskite is ionic crystals, and is intrinsic to PZT.
A list of the main energies involved in the bonds between the constituent elements of PZT is shown in FIG. 44. It is known that PZT includes many oxygen vacancies after crystallization. In other words, it can be expected from FIG. 44 that Pb�O bonds have the smallest bond energy among the constituent elements of PZT and will simply break during baking or polarization inversions. In other words, if Pb escapes, O will also escape for reasons of charge neutrality.
During sustained heating such as imprint testing, the constituent elements of PZT vibrate and collide repeatedly, and the Ti that is the lightest constituent element of PZT can easily be knocked out by these vibrational collisions during high-temperature retention. Therefore, if Ti escapes, O will also escape for reasons of charge neutrality. Since the maximum valence of +2 for Pb and +4 for Ti contribute towards bonding, there is no way to maintain charge neutrality other than allowing O to escape. In other words, two negative O ions escape readily for every positive ion of Pb or Ti, so that Schottky defects easily form.
BRIEF SUMMARY OF THE INVENTION The present invention may provide a 1T1C, 2T2C, or simple matrix type of ferroelectric memory including a ferroelectric capacitor having a hysteresis characteristic that can be used in any of a 1T1C, 2T2C, or simple matrix type of ferroelectric memory. The present invention may also provide a ferroelectric film that is suitable for the above-described ferroelectric memory, together with a method of manufacturing the same. The present invention may further provide a piezoelectric element and semiconductor element in which the above-described ferroelectric film is used. The present invention may still further provide a ferroelectric capacitor, a method of manufacture thereof, and a ferroelectric memory in which the ferroelectric capacitor is used, wherein satisfactory characteristics are maintained by a simple process that does not necessitate a barrier film.
A ferroelectric film according to one aspect of the present invention is described by a general formula AB1-xNbxO3, an A element includes at least Pb, a B element includes at least one of Zr, Ti, V, W, Hf and Ta, and Nb is included within the range of: 0.05≦�<1.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic section through a ferroelectric capacitor;
FIG. 2 is a flowchart of the formation of a PZTN film by a spin-coating method
FIG. 3 is a hysteresis curve of polarization (P) versus voltage (V) of the ferroelectric capacitor;
FIGS. 4A to 4C show the surface morphologies of PZTN films in accordance with a first embodiment;
FIGS. 5A to 5C show the crystallinities of PZTN films in accordance with the first embodiment;
FIGS. 6A to 6C show the relationship between film thickness and surface morphology of PZTN films in accordance with the first embodiment;
FIGS. 7A to 7C show the relationship between film thickness and crystallinity of PZTN films in accordance with the first embodiment;
FIGS. 8A to 8C show the hysteresis characteristics for film thicknesses of PZTN films in accordance with the first embodiment;
FIGS. 9A to 9C show the hysteresis characteristics for film thicknesses of PZTN films in accordance with the first embodiment;
FIGS. 10A and 10B show the leakage current characteristics of PZTN films in accordance with the first embodiment;
FIG. 11A shows the fatigue characteristic of a PZTN film in accordance with the first embodiment, and FIG. 11B shows the static imprint characteristic of a PZTN film in accordance with the first embodiment;
FIG. 12 shows the configuration of a ferroelectric capacitor in accordance with the first embodiment in which a SiO2 protective film is formed by ozone TEOS;
FIG. 13 shows the hysteresis characteristic of the ferroelectric capacitor in accordance with the first embodiment in which a SiO2 protective film is formed by ozone TEOS;
FIGS. 14 shows the leakage current characteristics of a conventional PZTN film;
FIG. 15 shows the fatigue characteristic of a ferroelectric capacitor using a conventional PZTN film;
FIG. 16 shows the static imprint characteristic of a ferroelectric capacitor in accordance with the first embodiment, which uses a conventional PZT film;
FIGS. 17A and 17B show the hysteresis characteristics of PZTN films in accordance with a second embodiment.
FIGS. 18A and 18B show the hysteresis characteristics of PZTN films in accordance with a second embodiment.
FIGS. 19A and 19B show the hysteresis characteristics of PZTN films in accordance with a second embodiment.
FIG. 20 shows X-ray diffraction patterns of PZTN films in accordance with the second embodiment;
FIG. 21 shows the relationship between Pb insufficiency and Nb compositional ratio in a PZTN crystal in accordance with the second embodiment;
FIG. 22 is illustrative of the WO3 crystal structure that is a Perovskite crystal;
FIGS. 23A to 23C are schematic sections illustrating the process of manufacturing a PZTN film in accordance with a third embodiment;
FIGS. 24A and 24B are illustrative of changes in lattice constant in a PZTN film in accordance with the third embodiment;
FIG. 25 is illustrative of changes in lattice mismatch ratio between PZTN films and Pt metal films in accordance with the third embodiment;
FIG. 26 is a flowchart of the formation of a conventional PZT film by a spin-coating method, as a reference example;
FIGS. 27A to 27E show the surface morphologies of PZTN films, as a reference example;
FIGS. 28A to 28E show the crystallinities of PZTN films, as a reference example;
FIGS. 29A and 29B show the hysteresis loops of tetragonal PZT films, as reference examples;
FIG. 30 shows the hysteresis loop of a conventional tetragonal PZT film, as a reference example;
FIGS. 31A and 31B show the results of degassing analysis on tetragonal PZT films as reference examples;
FIGS. 32A to 32C show a process of manufacturing a ferroelectric capacitor;
FIGS. 33A and 33B show the hysteresis characteristics of ferroelectric capacitors;
FIG. 34 shows the electrical characteristics of ferroelectric capacitors
FIG. 35A is a schematic plan view of a simple matrix type of ferroelectric memory device and FIG. 35B is a schematic section through the simple matrix type of ferroelectric memory device;
FIG. 36 is a section through an example of a ferroelectric memory device in which a memory cell array and a peripheral circuit are integrated together on the same substrate;
FIG. 37A is a schematic section through a 1T1C type of ferroelectric memory and FIG. 37B is an equivalent circuit schematically showing the 1T1C type of ferroelectric memory;
FIGS. 38A to 38C show the process of manufacturing ferroelectric memory;
FIG. 39 is an exploded perspective view of a recording head;
FIG. 40A is a plan view of the recording head and FIG. 40B is a section through the recording head;
FIG. 41 is a schematic section through the layer structure of a piezoelectric element;
FIG. 42 is a schematic view of an example of an inkjet-type recording device;
FIG. 43A shows the hysteresis characteristic of a ferroelectric film in which Ta has been added to PZT and FIG. 43B shows the hysteresis characteristic of a ferroelectric film in which W has been added to PZT;
FIG. 44 lists characteristics relating to bonds of constituent elements of PZT-family ferroelectric materials;
FIGS. 45A to 45C are illustrative of Schottky defects in the Brownmillerite crystal structure; and
FIG. 46 is illustrative of ferroelectric spatial charge polarization.
DETAILED DESCRIPTION OF THE EMBODIMENT 1) A ferroelectric film according to an embodiment of the present invention is described by a general formula AB1-xNbxO3, an A element includes at least Pb, a B element includes at least one of Zr, Ti, V, W, Hf and Ta, and Nb is included within the range of: 0.05≦�<1.
2) A ferroelectric film according to an embodiment of the present invention is described by a general formula (Pb1-yAy)(B1-xNbx)O3, and an A element includes at least one of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, Yb and Lu, a B element includes at least one of Zr, Ti, V, W, Hf and Ta, and Nb is included within the range of: 0.05≦�<1 (more desirably 0.1≦x≦0.3).
3) With a PZT-family ferroelectric film according to an embodiment of the present invention, a Ti composition is greater than a Zr composition, and at least 2.5 mol % and not more than 40 mol % (more desirably at least 10 mol % and not more than 30 mol %) of the Ti composition is substituted by Nb. This PZT-family ferroelectric film may have a crystal structure of at least one of tetragonal and rhombohedral systems. This PZT-family ferroelectric film may include Si, or Si and Ge of at least 0.5 mol % (more desirably at least 0.5 mol % and less than 5 mol %).
This PZT-family ferroelectric film may be formed by using a sol-gel solution.
4) A PZT-family ferroelectric according to an embodiment of the present invention is described by a general formula ABO3, Pb is included as a constituent element in an A site and at least Zr and Ti are included as constituent elements in a B site. Amount of Pb vacancy in the A site is equal to or less than 20 mol % of the stoichiometric composition of the ABO3. This PZT-family ferroelectric film may include Nb in the B site with a compositional ratio equivalent to twice the Pb vacancy in the A site. With this PZT-family ferroelectric film, a Ti composition may be higher than a Zr composition in the B site, and also the ferroelectric may have a crystal structure of rhombohedral system. This PZT-family ferroelectric film may be formed by using a sol-gel solution.
5) With a method of manufacturing the above ferroelectric film according to an embodiment of the present invention, a mixture of at least a sol-gel solution for PbZrO3, a sol-gel solution for PbTiO3, and a sol-gel solution for PbNbO3 is used as the sol-gel solution for forming the ferroelectric film.
6) With a method of manufacturing the above ferroelectric film according to an embodiment of the present invention, when the stoichiometric composition of Pb that is a constituent element of the A site is assumed to be 1, the ferroelectric film is formed by using a sol-gel solution in which Pb is included within the range of 0.9 to 1.2.
7) With this method of manufacturing the ferroelectric film, the PZT-family ferroelectric film may be formed on a metal film formed of a platinum-group metal.
8) With this method of manufacturing the ferroelectric film, the platinum-group metal may be at least one of Pt and Ir.
9) The ferroelectric memory in accordance with an embodiment of the present invention includes a first electrode leading up from the source or drain electrode of a CMOS transistor that has been formed on an Si wafer previously, a ferroelectric film formed on the first electrode, and a second electrode formed on the ferroelectric film. A capacitor formed of the first electrode, the ferroelectric film and the second electrode is a ferroelectric memory that performs a selection operation by the CMOS transistor that was formed on an Si wafer in advance. The ferroelectric film is formed from tetragonal PZT having a Ti ratio of at least 50%, at least 5 mol % but not more than 40 mol % of the Ti composition is substituted by Nb, and Si and Ge of at least 1 mol % is included therein.
10) The ferroelectric memory in accordance with an embodiment of the present invention is a ferroelectric memory including a previously formed first electrode, a second electrode arranged in a direction intersecting the first electrode, and a ferroelectric film disposed in at least an intersecting region between the first electrode and the second electrode. Capacitors form of the first electrode, the ferroelectric film, and the second electrode are disposed in a matrix. The ferroelectric film is formed from tetragonal PZT having a Ti ratio of at least 50%, at least 5 mol % but not more than 40 mol % of the Ti composition is substituted by Nb, and Si and Ge of at least 1 mol % is included therein.
11) A method of manufacturing a ferroelectric memory in accordance with an embodiment of the present invention includes crystallizing a sol-gel solution for forming PbZrO3 that is a first raw material solution, a sol-gel solution for forming PbTiO3 that is a second raw material solution, a sol-gel solution for forming PbNbO3 that is a third raw material solution, and sol-gel solution for forming PbSiO3 that is a fourth raw material solution, after the first to fourth solutions have been coated. The first, second, and third raw material solutions are liquids of raw materials for forming the ferroelectric layer and the fourth raw material solution is a liquid of a raw material for forming an ordinary paraelectric layer having a catalytic effect that is essential for forming the ferroelectric layer from the first, second, and third raw material solutions.
12) A method of manufacturing a ferroelectric capacitor according to an embodiment of the present invention includes:
13) With this method of manufacturing a ferroelectric capacitor, preliminary thermal processing may be performed on the ferroelectric film in an oxidizing atmosphere during the formation of the ferroelectric film, to put the PZTN complex oxide into an amorphous state until thermal processing for crystallizing the PZTN complex oxide is performed.
14) With this method of manufacturing a ferroelectric capacitor, the protective film may be a silicon dioxide film and is formed by using trimethylsilane.
15) With this method of manufacturing a ferroelectric capacitor, the thermal processing for crystallizing the PZTN complex oxide may be performed in a non-oxidizing atmosphere.
16) A ferroelectric capacitor according to an embodiment of the present invention is manufactured by using the above manufacture method of the ferroelectric capacitor.
17) The above ferroelectric film and ferroelectric capacitor can be applied to a ferroelectric memory, piezoelectric element, and semiconductor element using the same. Preferred embodiments of the present invention are described below in detail with reference to the accompanying figures.
Up to now, the Nb doping into PZT has been mainly performed into Zr-rich trigonal crystal regions and is extremely small, on the order of 0.2 to 0.025 mol % (refer to J. Am. Ceram. Soc, 84 (2001) 902 and Phys. Rev. Let, 83 (1999) 1347). The reason why it has not been possible to dope large quantities of Nb in this manner is considered to be because the addition of 10 mol % of Nb, for example, would require an increase in crystallization temperature to at least 800� C.
When the ferroelectric film 101 is formed from PbZr0.2Ti0.8Nb0.2O3 (PZTN) by using the above first, second, and third raw material solutions, by way of example, the ratios of (the first raw material solution):(the second raw material solution):(the third raw material solution) could be 2:6:2. However, any attempt to use these mixed solutions for crystallization as they are would necessitate a high crystallization temperature for the manufacture of the PZTN ferroelectric film 101. In other words, since the mixing in of Nb will cause the crystallization temperature to rise abruptly, making crystallization impossible within the temperature range that enables the creation of the component at not more than 700� C., a substitution for Ti by Nb has not been used more than 5 mol % in the conventional art and it has been used only as an additive. In addition, there have been absolutely no examples of PZT tetragonal crystals in which there is more Ti than Zr. This is discussed in the previously cited J. Am. Ceram. Soc, 84 (2001) 902 and Phys. Rev. Let, 83 (1999) 1347.
In other words, the use of the above-described mixture of the first, second, third, and fourth solutions makes it possible to move the crystallization temperature of the PZTN to a practicable temperature range of not more than 700� C.
First of all, the film for the lower electrode is formed to cover a precious metal for the electrode, such as Pt, on a Si substrate (step ST10). A mixed liquid is then painted thereon by a method such as spin-coating (step ST11). More specifically, the mixed solution is dropped onto the Pt-covered substrate. After spinning at approximately 500 rpm with the objective of spreading the dropped solution over the entire surface of the substrate, the angular velocity is dropped to not more than 50 rpm for about 10 seconds. The dry thermal processing is done at 150� C. to 180� C. (step ST13). The dry thermal processing is done by using a hot-plate or the like in the atmosphere. Similarly, the absorbent thermal processing is done in the atmosphere on the hot-plate, which is held at 300� C. to 350� C. (step ST13). The baking for crystallization is done by using rapid thermal annealing (RTA) or the like in an oxygen atmosphere (step ST14).
A hysteresis curve of electric polarization (P) versus voltage (V) of the ferroelectric capacitor 100 is shown schematically in FIG. 3. First of all, when a voltage +Vs is applied, the polarization magnitude is P(+Vs), then when the voltage becomes 0 the polarization magnitude becomes Pr. When the voltage changes to − 1/3 Vs, the polarization magnitude is P(−⅓Vs). When the voltage then becomes −Vs, the polarization magnitude becomes (−Vs), and when the voltage is again 0, the polarization magnitude becomes −Pr. When the voltage becomes + 1/3 Vs, the polarization magnitude becomes P(+ 1/3 Vs), and when the voltage is again +Vs, the polarization magnitude returns to P(+Vs).
The ferroelectric capacitor 100 also has the features described below, with respect to the hysteresis characteristic. If a voltage Vs is applied and the polarization magnitude has gone to P(+Vs) then the applied voltage goes to 0, the hysteresis loop follows the path indicated by the arrow A in FIG. 3 and the polarization magnitude holds the stable value PO(0). If a voltage −Vs is applied and the polarization magnitude has gone to P(−Vs) then the applied voltage goes to 0, the hysteresis loop follows the path indicated by the arrow B in FIG. 3 and the polarization magnitude holds the stable value PO(1). Thorough utilization of this difference between the polarization magnitude PO(0) and the polarization magnitude PO(1) makes it possible to operate a simple matrix type of ferroelectric memory device by the drive method disclosed in Japanese Patent Laid-Open No. 9-116107.
The ferroelectric capacitor 100 of this embodiment enables a reduction in the crystallization temperature, an improvement in the squareness of hysteresis loop, and an improvement in Pr. The improvement in squareness of hysteresis loop achieved by the ferroelectric capacitor 100 has the obvious effect of stabilizing major disturbances in the driving of the simple matrix type of ferroelectric memory device. In a simple matrix type of ferroelectric memory device, a voltage of � 1/3 Vs is applied even to cells that are not being written to or read, so it is necessary to have a stable disturbance characteristic to ensure that the polarization does not change with these voltage changes. The present inventors have confirmed for a general PZT that a deterioration of approximately 80% of the polarization magnitude is seen when a 1/3 Vs pulse is applied 108 times in the direction opposite to the polarization from a stable polarization state, but the deterioration in the ferroelectric capacitor 100 of this embodiment is not more than 10%. The use of the ferroelectric capacitor 100 of this embodiment in a ferroelectric memory device therefore makes it possible to realize a simple matrix type of memory.
FIRST EMBODIMENT This embodiment compares the PZTN of the present invention and the PZT of the conventional art. The entire film formation flow shown in FIG. 2 was used.
The surface morphologies of the films in this case are shown in FIGS. 4A to 4C. When the crystallinity of these films were measured by an X-ray diffraction method, the results were as shown in FIGS. 5A to 5C. With the 0% (none) case shown in FIG. 5A, only ordinary paraelectric pyrochlore is obtained, even when the crystallization temperature rises to 800� C. With the 0.5% case shown in FIG. 5B, PZT and the pyrochlore are mixed. With the 1% case shown in FIG. 5C, a single orientated film of PZT (111) is obtained. The crystallinity thereof is also good, of a quality that can not be achieved up to now.
The leakage characteristics were also extremely good at 5�10−8 to 7�10−9 A/cm2 when 2 V (saturation) was applied thereto, regardless of the film composition and film thickness, as shown in FIGS. 10A and 10B.
Tests were also performed on an SiO2 film 605 formed by ozone TEOS on a ferroelectric capacitor 600 in which a lower electrode 602, a PZTN ferroelectric film 603 of this embodiment, and an upper electrode 604 are formed on a substrate 601, as shown in FIG. 12. It is known in the art that, if an SiO2 film is formed by ozone TEOS on PZT, the hydrogen emitted by the TEOS passes through the upper Pt and reduces, and the PZT crystal is so destroyed that the hysteresis phenomenon does not occur.
Evaluation with a conventional PZT ferroelectric film was done for comparison, the conventional PZT samples had Pb:Zr:Ti ratios of 1:0.2:0.8, 1:0.3:0.7, and 1:0.6:0.4. The leakage characteristics thereof are such that the leakage characteristics deteriorate with increasing T1 content, as shown in FIG. 14, so that it is clear that when Ti is 80% and 2 V was applied, the characteristic was 10−5 A/cm2, making it unsuitable for memory applications. Similarly, the fatigue characteristic deteriorated with increasing Ti content, as shown in FIG. 15. After imprinting, it was clear that most of the data could not be read, as shown in FIG. 16.
SECOND EMBODIMENT This embodiment is a comparison of the ferroelectric characteristics obtained when the amount of Nb added to the PZTN ferroelectric film was varied to 0, 5, 10, 20, 30, 40 mol %. 5 mol % of PbSiO3 was added to all the testpieces. In addition, methyl succinate was added to the sol-gel solutions for forming the ferroelectric films, includes of raw materials for film formation, to adjust the pH to 6. The entire film formation flow shown in FIG. 2 was used therefor.
FIG. 17A shows that when the quantity of added Nb is 0, leaky hysteresis is obtained, whereas FIG. 17B shows that when the quantity of added Nb is 5 mol %, a good hysteresis characteristic with a high level of insulation is obtained.
FIG. 18A shows that substantially no change is seen in the ferroelectric characteristic until the quantity of added Nb reaches 10 mol %. Even when the quantity of added Nb is 0, it is leaky by no change is seen in the ferroelectric characteristic. FIG. 18B shown that when the quantity of added Nb is 20 mol %, a hysteresis characteristic with an extremely good squareness is obtained.
THIRD EMBODIMENT This embodiment investigates the validity of using a PZTN film from the viewpoint of lattice regularity, when the PZTN film has been formed on a metal film formed of a platinum-group metal such as Pt or Ir as an electrode material for a ferroelectric capacitor that forms a memory cell portion of ferroelectric memory or a piezoelectric actuator that configures an ink ejection nozzle portion of an inkjet printer, by way of example. Platinum-group metals act as underlayer films that determine the crystal orientation of ferroelectric films, and are also useful as electrode materials. However, since the lattice regularities of the two materials are not sufficient, a problem arises concerning the fatigue characteristics of ferroelectric films when applied to elements.
First of all, a given substrate 11 was prepared, as shown in FIG. 23A. A TiOx layer formed on an SOI substrate was used as the substrate 11. Note that a preferred material could be selected from known materials as this substrate 11.
It has therefore been confirmed that use of the method of the present invention reduces lattice mismatches between the metal film that is the electrode material and the ferroelectric film, such that the lattice mismatch ratio is improved to the order of 2% at a quantity of added Nb of 30 mol %, by way of example. This is considered to be because strong bonds having both ionic bonding between Nb atoms that have substituted for Ti atoms at the B sites in the PZTN crystal structure and O atoms and covalence, these bonds act in directions that compress the crystal lattice, causing changes in the direction in which the lattice constant decreases.
REFERENCE EXAMPLE For this example, PbZr0.4Ti0.6O3 ferroelectric films were manufactured.
As shown in FIG. 31A, it was confirmed that the conventional ferroelectric film manufactured by PZT sol-gel solutions always degases with respect to H and C, as the temperature rises from room temperature to 1000� C.
1) First of all, as shown in FIG. 32A, a lower electrode 102, the ferroelectric film 101, and an upper electrode 103 are formed in sequence as a stack on a given substrate 110.
The ferroelectric film 101 includes Pb, Zr, Ti, and Nb as constituent elements, and thus is called a PZTN complex oxide. The ferroelectric film 101 can be formed by using a spin-coating method or the like to paint sol-gel solutions including Pb, Zr, Ti, and Nb onto the lower electrode 102. Mixtures of a first sol-gel solution in which a condensation polymer for forming PbZrO3 Perovskite crystals by Pb and Zr is dissolved in a non-aqueous state in a solvent such as n-butanol; a second solution in which a condensation polymer for forming PbTiO3 Perovskite crystals by Pb and Ti, from among constituent metal elements for the PZTN ferroelectric phase, is dissolved in a non-aqueous state in a solvent such as n-butanol; and a third sol-gel solution in which a condensation polymer for forming PbTiO3 Perovskite crystals by Pb and Ti, from among constituent metal elements for the PZTN ferroelectric phase, is dissolved in a non-aqueous state in a solvent such as n-butanol could be used as these sol-gel solutions. In addition, during the formation of the ferroelectric film 101, a sol-gel solution including a silicate or germanate for reducing the crystallization temperature of the PZTN complex oxide could be added. More specifically, at least 1 mol % but less than 5 mol % of a fourth sol-gel solution in which a condensation polymer for forming PbSiO3 crystals is dissolved in a non-aqueous state in a solvent such as n-butanol could be further added to the above-described mixture of sol-gel solutions. The mixing in of this fourth sol-gel solution makes it possible for the crystallization to occur within a temperature range that enables the creation of elements at a crystallization temperature for the PZTN complex oxide of 700� C., although the inclusion of Nb as a constituent element would normally increase the crystallization temperature.
It is preferable that the painted film for the ferroelectric film 101 is subjected to preliminary thermal processing at a temperature (such as not more than 400� C. ) that does not cause crystallization of the PZTN complex oxide in an oxidizing atmosphere, to put the PZTN complex oxide into an amorphous state. This enables the advance of the previously described process while preventing the diffusion of constituent elements in a state in which the ferroelectric film 101 is in an amorphous state, with no grain boundaries. The performing of this preliminary thermal processing in an oxidizing atmosphere has the effect of introducing into the ferroelectric film 101 the oxygen component that is necessary for the crystallization of the PZTN complex oxide after the formation of a protective film, which will be described layer.
2) Next, as shown in FIG. 32B, the lower electrode 102, the ferroelectric film 101, and the upper electrode 103 are etched to a desired shape, and a protective film 104 of silicon dioxide (SiO2) is formed to cover them. The protective film 164 in this case can be formed by a CVD method, using trimethylsilane (TMS). With trimethylsilane (TMS), there is a smaller quantity of hydrogen generated during the CVD process, in comparison with the tetraethyl orthosilicate (TEOS) that is generally used for forming a silicon dioxide film. If trimethylsilane (TMS) is used for that reason, it is possible to reduce processing damage to the ferroelectric film 101 due to the reductive reaction. Since the process of using trimethylsilane (TMS) to form the protective film 104 can be done at a lower temperature (from room temperature to 350� C.) than the process using TEOS (a film-formation temperature of at least 400� C.), it is possible to maintain the amorphous state achieved by the process of (1), preventing crystallization of the PZTN complex oxide by the heat generated by this process of forming the protective film 104.
3) Next, as shown in FIG. 32C, thermal processing is performed to crystallize the PZTN complex oxide that configures the ferroelectric film 101, making it possible to obtain a ferroelectric capacitor having a PZTN ferroelectric crystal film 101 a. This thermal processing could be done, not in an oxygen atmosphere, but in an atmosphere of a non-oxidizing gas such as Ar or N2 or in air, to enable the crystallization of the PZTN complex oxide.
FIGS. 33A and 33B show results obtained by measuring the hysteresis characteristics of capacitors in which the manufacture method of this embodiment was employed to form a SiO2 protective film by using TMS over a ferroelectric capacitor formed of a Pt lower electrode, a PZTN ferroelectric film, and a Pt upper electrode, when the PZTN ferroelectric film was subjected to thermal processing in an oxygen atmosphere or air after this SiO2 protective film was formed. FIG. 33A shows the results of thermal processing in an oxygen atmosphere and FIG. 33B shows the results of thermal processing in air. FIGS. 33A and 33B show that hysteresis characteristics with good squareness were obtained, regardless of whether the thermal processing was done in an oxygen atmosphere or air, even though a hydrogen-resisting barrier film was not formed. This is because preliminary thermal processing was performed in an oxidizing atmosphere during the formation of the ferroelectric film 101 so that the oxygen necessary for the crystallization had previously entered the film. In other words, the manufacture method of this embodiment makes it possible to crystallize the ferroelectric film without being dependent on the atmosphere for thermal processing. In addition, when the thermal processing for crystallization is performed in a non-oxidizing gas atmosphere, it is possible to prevent oxidation damage due to high-temperature thermal processing on peripheral components (for example, metal wiring) other than the capacitor, when applied to a method of manufacturing a ferroelectric memory that will be described later. Note that since the thermal processing for crystallizing the PZTN complex oxide in this process is not very dependent on the type of gas in the atmosphere, contact holes for forming metal wiring for connecting the upper electrode 103 to the exterior can be formed after the protective film 104 is formed.
FIG. 34 shows the results of measurements obtained by measuring the hysteresis characteristic for examples in which the manufacture method of this embodiment was employed to form a SiO2 protective film by using TMS over a ferroelectric capacitor formed of a Pt lower electrode, a PZTN ferroelectric film, and a Pt upper electrode, and the PZTN ferroelectric film was crystallized after the formation of this SiO2 protective film, where the formation temperature of the SiO2 protective film was room temperature, 125� C., and 200� C.; and the hysteresis characteristic of a reference example in which the PZTN ferroelectric film was crystallized without the SiO2 protective film being formed, and calculating the corresponding change in residual polarization magnitude 2 Pr. From FIG. 34 it can be seen that there was no change in residual polarization magnitude 2 Pr, whether the SiO2 protective film was formed at room temperature, 125� C., or 200� C., which confirms that the formation of the SiO2 protective film does not result in an inferior product. In other words, by performing the thermal processing for crystallizing the PZTN complex oxide even after damage is done by hydrogen during the processing of the ferroelectric film 101 in the formation of the protective film 104, the manufacture method of this embodiment ensures that the PZTN complex oxide is crystallized while any such damage is repaired. This makes it possible to omit the process of forming a barrier film for protecting against reductive reactions of the ferroelectric film 101, which is necessary in the conventional art, enabling an increase in productivity and a reduction in production costs.
In the ferroelectric memory device 300 in which memory cells configured of this simple matrix are arrayed, the operations of writing to and reading from the ferroelectric capacitors formed at the intersections between the word lines 301 to 303 and the bit lines 304 to 306 are done by peripheral drive circuits and a read amplifier circuit (called �peripheral circuit� although not shown in the figures). This peripheral circuit could be formed of MOS transistors on another substrate than the memory cell array, or the peripheral circuit could be integrated on the same substrate as the memory cell array.
FIG. 36 is a section through an example of the ferroelectric memory device 300 in which the memory cell array is integrated on the same substrate as the peripheral circuit.
The description now turns to a case in which the manufacture method described in �2. Method of Manufacturing Ferroelectric Capacitor� is applied to a method of manufacturing ferroelectric memory.
FIGS. 38A to 38C are schematic sections showing an example of the process of manufacturing the ferroelectric memory in accordance with this embodiment.
A partial perspective view of parts of an inkjet-type recording head in accordance with an embodiment of the present invention is shown in FIG. 39, a plan view and a section taken along the line A-A′ of FIG. 39 are shown in FIGS. 40A and FIG. 40B, and a schematic view of the layer structure of a piezoelectric element 700 is shown in FIG. 41. As shown in these figures, a flow path shaping substrate 10 is formed of a (110)-orientation silicon monocrystalline substrate in accordance with this embodiment, and an elastic film 50 of thickness 1 to 2 μm is formed of silicon dioxide by previous thermal oxidation on one surface thereof. A plurality of stress generating chambers 12 are arrayed in the widthwise direction of the flow path shaping substrate 10. A connective portion 13 is formed in the longitudinal direction of a region on the outer side of the stress generating chambers 12 of the flow path shaping substrate 10 and the connective portion 13 and the stress generating chambers 12 communicate through an ink supply path 14 provided for each stress generating chamber 12. Note that the connective portion 13 forms part of a reservoir 800 that forms a common ink chamber for the stress generating chambers 12 communicating with a reservoir portion of a sealing substrate 30 that will be described later. Each ink supply path 14 is formed to width that is narrower than the stress generating chamber 12, to keep the resistance of ink flowing into the stress generating chamber 12 from the ink supply path 14 constant.
On the opposite side from the aperture surface of the flow path shaping substrate 10, the elastic film 50 of a thickness of approximately 1.0 μm, by way of example, is formed as mentioned previously, and a dielectric film 55 of a thickness of approximately 0.4 μm, by way of example, is formed on that elastic film 50. In addition, a lower electrode film 60 of a thickness such as approximately 0.2 μm, a piezoelectric layer 70 of a thickness such as approximately 1.0 μm, and an upper electrode film 80 of a thickness such as approximately 0.05 μm are formed in a stack on the dielectric film 55 by processing that will be described later, to form the piezoelectric element 700. In this case, the piezoelectric element 700 is the portion including the lower electrode film 60, the piezoelectric layer 70, and the upper electrode film 80. In general, one electrode of the piezoelectric element 700 is a common electrode and the other electrode and the piezoelectric layer 70 are patterned to form each stress generating chamber 12. A portion formed of the thus-patterned electrode and the piezoelectric layer 70 that generates piezoelectric strain by the application of a voltage to the two electrodes is called an active piezoelectric portion. With this embodiment, the lower electrode film 60 is the common electrode of the piezoelectric element 700 and the upper electrode film 80 is the other electrode of the piezoelectric element 700, but there is no obstacle to reversing these roles to suit the circumstances of the drive circuit or wiring. In either case, an active piezoelectric portion is formed for each stress generating chamber. In this case, the combination of the piezoelectric element 700 and the vibrating plate in which displacements are generated by the driving of that piezoelectric element 700 is called a piezoelectric actuator. Note that the piezoelectric layer 70 is provided independently for each stress generating chamber 12 and is configured of a plurality of layers of ferroelectric film 71 (71 a to 71 f).
1) Since covalence is increased in the piezoelectric layer, the piezoelectric constant is increased.
2) It is easy to apply an electrical field that suppresses the generation of faults in the interface between the piezoelectric layer and the electrode, for suppressing any insufficiency of PbO in the piezoelectric layer, enabling an increase in the efficiency thereof as a piezoelectric element.
3) Since leakage currents in the piezoelectric layer are suppressed, it is possible to make a thin film of the piezoelectric layer.
4) Since a reduction in fatigue deterioration of the piezoelectric layer is enabled, time-related changes in the displacement magnitude of the piezoelectric layer can be suppressed, enabling an increase in reliability.
Patent CitationsCited PatentFiling datePublication dateApplicantTitleUS4051465Dec 16, 1974Sep 27, 1977The United States Of America As Represented By The Secretary Of The ArmyFerroelectric ceramic devicesUS5164882Dec 17, 1991Nov 17, 1992Kabushiki Kaisha ToshibaCeramic capacitorUS5279996Jul 21, 1992Jan 18, 1994Murata Manufacturing Co., Ltd.Piezoelectric ceramic compositionUS5471363Sep 19, 1994Nov 28, 1995Olympus Optical Co., Ltd.Ferroelectric capacitive elementUS5625529Mar 28, 1995Apr 29, 1997Samsung Electronics Co., Ltd.PZT thin films for ferroelectric capacitor and method for preparing the sameUS5858451Jul 29, 1997Jan 12, 1999Sandia CorporationProcess for production of solution-derived (Pb,La)(Nb,Sn,Zr,Ti)O.sub.3 thin films and powdersUS6465260Jun 28, 2000Oct 15, 2002Hyundai Electronics Industries Co., Ltd.Semiconductor device having a ferroelectric capacitor and method for the manufacture thereofUS6548342Mar 24, 1997Apr 15, 2003Hitachi, Ltd.Method of producing oxide dielectric element, and memory and semiconductor device using the elementUS6559003Jan 3, 2001May 6, 2003Infineon Technologies AgMethod of producing a ferroelectric semiconductor memoryUS6624462Aug 17, 2000Sep 23, 2003Matsushita Electric Industrial Co., Ltd.Dielectric film and method of fabricating the sameUS6777248Nov 10, 1997Aug 17, 2004Hitachi, Ltd.Dielectric element and manufacturing method thereforUS7008669Jun 12, 2002Mar 7, 2006Seiko Epson CorporationCeramic and method of manufacturing the same, dielectric capacitor, semiconductor device, and elementUS20040136891Sep 3, 2001Jul 15, 2004Takeshi KijimaOxide material, method for preparing oxide thin film and element using said materialUS20040229384Mar 24, 2004Nov 18, 2004Seiko Epson CorporationFerroelectric capacitor, method of manufacturing the same, ferroelectric memory, and piezoelectric deviceUS20050271823 *May 16, 2005Dec 8, 2005Seiko Epson CorporationPrecursor composition, method for manufacturing precursor composition, method for manufacturing ferroelectric film, piezoelectric element, semiconductor device, piezoelectric actuator, ink jet recording head, and ink jet printerUS20060088731 *Nov 25, 2005Apr 27, 2006Seiko Epson CorporationFerroelectric film, ferroelectric capacitor, ferroelectric memory, piezoelectric element, semiconductor element, method of manufacturing ferroelectric film, and method of manufacturing ferroelectric capacitorUS20060138382 *Dec 20, 2005Jun 29, 2006Seiko Epson CorporationPrecursor composition, method of manufacturing precursor composition, inkjet coating ink, method of manufacturing ferroelectric film, piezoelectric device, semiconductor device, piezoelectric actuator, inkjet recording head, and inkjet printerUS20070119343 *Nov 28, 2006May 31, 2007Seiko Epson CorporationComplex metal oxide raw material compositionUS20070278545 *May 24, 2007Dec 6, 2007Seiko Epson CorporationFerroelectric capacitor, method of manufacturing ferroelectric capacitor, and ferroelectric memoryUS20070296008 *Jun 6, 2007Dec 27, 2007Seiko Epson CorporationSemiconductor deviceCN1301992AJul 12, 2000Jul 4, 2001国际商业机器公司Leveling methodCN1303128AJan 3, 2001Jul 11, 2001因芬尼昂技术股份公司Manufacturing method of ferroelectric semi conductor storageEP0238241A2Mar 9, 1987Sep 23, 1987Matsushita Electric Industrial Co., Ltd.Multi-layer ceramic capacitorEP1031545A2Feb 21, 2000Aug 30, 2000Infrared Integrated Systems Ltd.Ferroelectric ceramicsEP1071121A1Jul 1, 2000Jan 24, 2001Infineon Technologies AGProcess for the formation of a collar oxide in a trench in a semiconductor substrateEP1078998A2Aug 17, 2000Feb 28, 2001Matsushita Electric Industrial Co., Ltd.Dielectric film with a perovskite structure and method of fabricating the sameJP2000114484A Title not availableJP2000236075A Title not availableJP2000299512A Title not availableJP2000319065A Title not availableJP2001019432A Title not availableJP2001036030A Title not availableJP2001080995A Title not availableJP2003204088A Title not availableJP2005100660A * Title not availableJP2005101512A * Title not availableJP2006182642A * Title not availableJP2006188427A * Title not availableJPH0437076A Title not availableJPH01148750A Title not availableJPH01225304A Title not availableJPH06150716A Title not availableJPH08335676A Title not availableJPH09116107A Title not availableJPH11209173A Title not availableJPS62241826A Title not availableKR20010004363A Title not availableKR20010031913A Title not availableWO1998008255A1Mar 24, 1997Feb 26, 1998Higashiyama KazutoshiMethod for manufacturing oxide dielectric device, and memory and semiconductor device usign the deviceWO2000017936A1Sep 24, 1999Mar 30, 2000Telcordia Tech IncFerroelectric thin films of reduced tetragonalityWO2002032809A1Sep 3, 2001Apr 25, 2002Sharp KkOxide material, method for preparing oxide thin film and element using said materialWO2002102712A1Jun 13, 2002Dec 27, 2002Seiko Epson CorpCeramic and method for preparation thereof, and dielectric capacitor, semiconductor and elementWO2003017479A2Aug 14, 2002Feb 27, 2003Koninkl Philips Electronics NvElectronic device and method of testing and of manufacturingWO2004038733A1 *Oct 23, 2003May 6, 2004Seiko Epson CorpFerroelectric film, ferroelectric capacitor, ferroelectric memory, piezoelectric device, semiconductor device, method for manufacturing ferroelectric film, and method for manufacturing ferroelectric capacitor* Cited by examinerNon-Patent CitationsReference1Bellaiche et al., "Intrinsic Piezoelectric Response in Perovskite Alloys: PMN-PT versus PZT," Physical Review Letters, vol. 83, No. 7, pp. 1347-1350, Aug. 16, 1999.2I. Pintilic, "Enhancement of the Photoconductive Properties of PbS Films Deposited on Ferroelectric Substrates", Materials Science and Engineering B44, pp. 292-296, (1997).3Kijima et al., "New Development of Ferro-electric Material for FeRAM," Abstracts of the 49<SUP>th </SUP>Meeting of the Japan Society of Applied Physics and Related Societies, 2002.4Miyazawa et al., "Electronic States of Perovskite-Type Oxides and Ferroelectricity," Jpn. J. Appl. Phys., vol. 39, pp. 5679-5682, 2000.5Ryu et al., "Effect of Heating Rate on the Sintering Behavior and the Piezoelectric Properties of Lead Zirconate Titanate Ceramics," J. Am Ceram. Soc., 84, pp. 902-904, 2001.Referenced byCiting PatentFiling datePublication dateApplicantTitleUS8012449Jun 26, 2007Sep 6, 2011Seiko Epson CorporationMethod of manufacturing complex metal oxide powder and amorphous complex metal oxideUS8389300Apr 2, 2010Mar 5, 2013Centre National De La Recherche ScientifiqueControlling ferroelectricity in dielectric films by process induced uniaxial strainClassifications U.S. Classification428/702, 257/E21.271, 257/E27.104, 428/701, 257/295, 252/62.90R, 252/62.9PZ, 257/E21.272, 257/E21.664, 428/697, 257/E21.009International ClassificationH01G4/33, H01L21/314, H01L27/115, H01L21/316, H01B1/08, H01L41/22, H01L21/77, H01G4/12, B32B9/00, H01L21/84, H01L21/02, C01G35/00, H01L41/18, H01L41/09, H01L41/08, B41J2/16, B05C5/00, B41J2/055, H01B3/12, H01L41/24, B41J2/045, H01L41/187, C04B35/49, H01L27/10, H01L21/8246, C01G33/00, C01G25/02, H02N2/00, H01L27/105Cooperative ClassificationH01L21/316, H01L41/0805, H01L41/1876, C01P2006/40, H01L41/318, H01L28/55, H01L27/11507, C01P2002/72, C01P2006/80, C01G35/006, H01L21/31691, C01G33/006, H01G4/33, C01P2004/80, H01B1/08, H01L28/57, H01G4/1254, H01L27/11502, H01L21/02197, C01P2004/04, H01L21/02282, C01P2002/77European ClassificationH01L28/55, H01L28/57, H01L21/02K2E3L, H01L21/02K2C1M5, H01L41/187P2, H01L41/08C, H01L41/318, H01B1/08, C01G35/00D, H01G4/12B6, H01L21/316, H01L21/316D, C01G33/00D, H01G4/33, H01L27/115C, H01L27/115C4Legal EventsDateCodeEventDescriptionSep 19, 2011FPAYFee paymentYear of fee payment: 4RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services©2012 Google