Semiconductor ceramic, monolithic semiconductor ceramic capacitor, method for manufacturing semiconductor ceramic, and method for manufacturing monolithic semiconductor ceramic capacitor

• US 7,872,854 B2
• Filed: 03/03/2008
• Issued: 01/18/2011
• Est. Priority Date: 05/31/2006
• Status: Active Grant

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Kawamoto, Mitsutoshi
• Primary Examiner(s): Ha; Nguyen T
• Application Number:
  US12/041,407
• Publication Number:
  US 20080186655A1
• Time in Patent Office: 1,051 Days
• Field of Search: 361/321.1, 361/321.2, 361/321.4, 361/301.4, 361/306.1, 361/306.3, 361311-313, 361/321.5
• US Class Current: 361/321.1
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C01G 23/006 Alkaline earth titanates
• CPC Class Codes: C01G 45/006 Compounds containing, besides manganese, two or more other elements, with the exception of oxygen or hydrogen manganates, manganites or permanganates C01G45/12
• CPC Class Codes: C01P 2002/50 Solid solutions
• CPC Class Codes: C01P 2002/52 containing elements as dopants
• CPC Class Codes: C01P 2004/62 Submicrometer sized, i.e. from 0.1-1 micrometer
• CPC Class Codes: C01P 2006/12 Surface area
• CPC Class Codes: C01P 2006/40 Electric properties
• CPC Class Codes: C04B 2235/3201 Alkali metal oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3203 Lithium oxide or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3224 Rare earth oxide or oxide forming salts thereof, e.g. scandium oxide
• CPC Class Codes: C04B 2235/3225 Yttrium oxide or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3227 Lanthanum oxide or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3229 Cerium oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3236 Alkaline earth titanates
• CPC Class Codes: C04B 2235/3241 Chromium oxides, chromates, or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3251 Niobium oxides, niobates, tantalum oxides, tantalates, or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3258 Tungsten oxides, tungstates, or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3262 Manganese oxides, manganates, rhenium oxides or oxide-forming salts thereof, e.g. MnO
• CPC Class Codes: C04B 2235/3267 MnO2
• CPC Class Codes: C04B 2235/3275 : Cobalt oxides, cobaltates or cobaltites or oxide forming salts thereof, e.g. bismuth cobaltate, zinc cobaltite
• CPC Class Codes: C04B 2235/3279 : Nickel oxides, nickalates, or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3281 : Copper oxides, cuprates or oxide-forming salts thereof, e.g. CuO or Cu2O
• CPC Class Codes: C04B 2235/3409 : Boron oxide, borates, boric acids, or oxide forming salts thereof, e.g. borax
• CPC Class Codes: C04B 2235/36 : Glass starting materials for making ceramics, e.g. silica glass
• CPC Class Codes: C04B 2235/5409 : expressed by specific surface values
• CPC Class Codes: C04B 2235/5454 : nanometer sized, i.e. below 100 nm
• CPC Class Codes: C04B 2235/6025 : Tape casting, e.g. with a doctor blade
• CPC Class Codes: C04B 2235/6582 : Hydrogen containing atmosphere
• CPC Class Codes: C04B 2235/6584 : at an oxygen percentage below that of air
• CPC Class Codes: C04B 2235/6588 : Water vapor containing atmospheres
• CPC Class Codes: C04B 2235/663 : Oxidative annealing
• CPC Class Codes: C04B 2235/785 : Submicron sized grains, i.e. from 0,1 to 1 micron
• CPC Class Codes: C04B 2235/79 : Non-stoichiometric products, e.g. perovskites (ABO3) with an A/B-ratio other than 1
• CPC Class Codes: C04B 2235/85 : Intergranular or grain boundary phases
• CPC Class Codes: C04B 35/47 : based on strontium titanates
• CPC Class Codes: C04B 35/6262 : of calcined, sintered clinker or ceramics
• CPC Class Codes: C04B 35/62685 : characterised by the order of addition of constituents or additives
• CPC Class Codes: C04B 35/62805 : Oxide ceramics
• CPC Class Codes: C04B 35/62807 : Silica or silicates
• CPC Class Codes: H01G 4/1227 : based on alkaline earth titanates
• CPC Class Codes: H01G 4/30 : Stacked capacitors H01G4/33 takes precedence
• CPC Class Codes: Y10T 29/435 : Solid dielectric type

Abstract

A semiconductor ceramic comprising a donor element within the range of 0.8 to 2.0 mol relative to 100 mol of Ti element contained as a solid solution with crystal grains, a first acceptor element in an amount less than the amount of the donor element is contained as a solid solution with the crystal grains, a second acceptor element within the range of 0.3 to 1.0 mol relative to 100 mol of a Ti element is present in crystal grain boundaries, and the average grain size of the crystal grains is 1.0 μm or less. A monolithic semiconductor ceramic capacitor is obtained by using this semiconductor ceramic. To form the semiconductor ceramic, in a first firing treatment to conduct reduction firing, a cooling treatment is conducted while the oxygen partial pressure at the time of starting the cooling is set at 1.0×10⁴ times or more the oxygen partial pressure in the firing process. In this manner, a SrTiO₃ based grain boundary insulation type semiconductor ceramic having a large apparent relative dielectric constant ∈r_APP of 5,000 or more and a large resistivity log ρ (ρ: Ω·cm) of 10 or more even when crystal grains are made fine to have an average grain size of 1.0 μm or less, a monolithic semiconductor ceramic capacitor including the semiconductor ceramic, and methods for manufacturing them are realized.

Claims

1. A SrTiO₃ based grain boundary insulation type semiconductor ceramic comprising:

a solid solution with crystal grains, the solid solution containing;

a donor element within the range of 0.8 to 2.0 mol relative to 100 mol of the Ti element;

a first acceptor element in an amount less than the amount of the donor element; and

a second acceptor element within the range of 0.3 to 1.0 mol relative to 100 mol of the Ti element in crystal grain boundaries,

wherein an average grain size of the crystal grains is 1.0 μ

m or less.

2. The semiconductor ceramic according to claim 1, wherein the donor element comprises at least one element selected from the group consisting of La, Sm, Dy, Ho, Y, Nd, Ce, Nb, Ta, and W.

3. The semiconductor ceramic according to claim 1, wherein the first acceptor element comprises at least one element selected from the group consisting of Mn, Co, Ni, and Cr.

4. The semiconductor ceramic according to claim 1, wherein the second acceptor element comprises at least one element selected from the group consisting of Mn, Co, Ni, and Cr.

5. The semiconductor ceramic according to claim 1, wherein the first acceptor element and the second acceptor element are the same element.

6. The semiconductor ceramic according to claim 5, wherein the first acceptor element and the second acceptor element comprise at least one element selected from the group consisting of Mn, Co, Ni, and Cr.

7. The semiconductor ceramic according to claim 1, wherein the first acceptor element and the second acceptor element are different types of elements.

8. The semiconductor ceramic according to claim 1, wherein the semiconductor ceramic further comprises a low-melting-point oxide within the range of 0.1 mol or less relative to 100 mol of the Ti element.

9. The semiconductor ceramic according to claim 8, wherein the low-melting-point oxide is in the crystal grain boundaries.

10. The semiconductor ceramic according to claim 8, wherein the low-melting-point oxide is SiO₂.

11. A monolithic semiconductor ceramic capacitor comprising:

a component element assembly formed from the semiconductor ceramic according to claim 1;

internal electrodes disposed in the component element assembly; and

external electrodes electrically connectable to the internal electrodes disposed on a surface of the component element assembly.

12. A method for manufacturing a SrTiO₃ based grain boundary insulation type semiconductor ceramic, the method comprising:

weighing, mixing, and pulverizing a predetermined amount of ceramic raw material containing a donor compound and a first acceptor compound and conducting a calcination treatment so as to prepare a calcined powder;

mixing a predetermined amount of a second acceptor compound with the calcined powder and conducting a heat treatment so as to prepare a heat-treated powder; and

subjecting the heat-treated powder to a primary firing treatment in a reducing atmosphere and conducting a secondary firing treatment in one of a weak reducing atmosphere, an air atmosphere, and an oxidizing atmosphere,

wherein the donor compound is weighed to be within the range of 0.8 to 2.0 mol relative to 100 mol of Ti element, the predetermined amount of the first acceptor compound is weighed to be within the range of 0.3 to 1.0 mol relative to 100 mol of the Ti element.

13. A method for manufacturing a SrTiO₃ based grain boundary insulation type semiconductor ceramic monolithic capacitor, the method comprising:

weighing, mixing, and pulverizing a predetermined amount of ceramic raw material containing a donor compound and a first acceptor compound and conducting a calcination treatment so as to prepare a calcined powder;

mixing a predetermined amount of a second acceptor compound with the calcined powder and conducting a heat treatment so as to prepare a heat-treated powder;

subjecting the heat-treated powder to molding to prepare ceramic green sheets;

laminating internal electrode layers and the ceramic green sheets alternately so as to form a ceramic laminate; and

subjecting the ceramic laminate to a primary firing treatment in a reducing atmosphere and conducting a secondary firing treatment in one of a weak reducing atmosphere, an air atmosphere, and an oxidizing atmosphere,

wherein the first firing treatment is carried out on the basis of a firing profile including a temperature raising process, a firing process, and a cooling process, and

wherein the oxygen partial pressure at a time of starting the cooling process is set at 1.0×

10⁴ times or more the oxygen partial pressure in the firing process.

14. The method for manufacturing a monolithic capacitor according to claim 13, wherein steam is supplied at the time of starting the cooling process.

15. The method for manufacturing a monolithic capacitor according to claim 14, wherein a supply rate of H₂ gas is decreased at the time of starting the cooling process.