Method for making ferroelectric field effect transistors for nonvolatile memory applications having functional gradient material

Abstract

A nonvolatile nondestructible read-out ferroelectric FET memory comprising a semiconductor substrate, a ferroelectric functional gradient material (“FGM”) thin film, and a gate electrode. In one basic embodiment, the ferroelectric FGM thin film contains a ferroelectric compound and a dielectric compound. The dielectric compound has a lower dielectric constant than the ferroelectric compound. There is a concentration gradient of the ferroelectric compound in the thin film. In a second basic embodiment, the FGM thin film is a functional gradient ferroelectric (“FGF”), in which compositional gradients of ferroelectric compounds result in unconventional hysteresis behavior. The unconventional hysteresis behavior of FGF thin films is related to an enlarged memory window in ferroelectric FET memories. FGM thin films are preferably formed using a liquid source MOD methods, preferably a multisource CVD method.

We claim:  
     
         1 . A ferroelectric FET comprising: 
 a semiconductor substrate;    a ferroelectric FGM thin film; and    a gate electrode.    
     
     
         2 . A ferroelectric FET as in    claim 1   , wherein said ferroelectric FGM thin film is located above said semiconductor substrate, and said gate electrode is located above said ferroelectric FGM thin film.  
     
     
         3 . A ferroelectric FET as in    claim 1   , wherein said gate electrode is located on said ferroelectric FGM thin film.  
     
     
         4 . A ferroelectric FET as in    claim 1   , wherein said ferroelectric FGM thin film is located on said semiconductor substrate.  
     
     
         5 . A ferroelectric FET as in    claim 1   , further comprising a gate oxide layer located on said semiconductor substrate.  
     
     
         6 . A ferroelectric FET as in    claim 5   , wherein said ferroelectric FGM thin film is located on said gate oxide layer.  
     
     
         7 . A ferroelectric FET as in    claim 5   , further comprising an interface insulator layer located on said gate oxide layer.  
     
     
         8 . A ferroelectric FET as in    claim 1   , further comprising an interface insulator layer located between said ferroelectric FGM thin film and said semiconductor substrate.  
     
     
         9 . A ferroelectric FET as in    claim 8   , wherein said interface insulator layer is located on said semiconductor substrate.  
     
     
         10 . A ferroelectric FET as in    claim 9   , wherein said ferroelectric FGM thin film is located on said interface insulator layer.  
     
     
         11 . A ferroelectric FET as in    claim 1   , further comprising a floating electrode located between said semiconductor substrate and said ferroelectric FGM thin film.  
     
     
         12 . A ferroelectric FET as in    claim 11   , further comprising an adhesion layer located between said floating electrode and said semiconductor substrate.  
     
     
         13 . A ferroelectric FET as in    claim 12   , wherein said floating electrode is located on said adhesion layer, and said ferroelectric FGM thin film is located on said floating electrode.  
     
     
         14 . A ferroelectric FET as in    claim 1   , wherein said ferroelectric FGM thin film contains moieties of first metal atoms in relative molar proportions corresponding to a stoichiometric formula of a ferroelectric compound and moieties of second metal atoms in relative molar proportions corresponding to a stoichiometric formula of a dielectric compound, said dielectric compound having a dielectric constant less than said ferroelectric compound, and said ferroelectric FGM thin film having a functional gradient of said moieties of first metal atoms and second metal atoms.  
     
     
         15 . A ferroelectric FET as in    claim 14   , wherein said ferroelectric compound is a ferroelectric metal oxide.  
     
     
         16 . A ferroelectric FET as in    claim 15   , wherein said ferroelectric metal oxide is a ferroelectric layered superlaftice material.  
     
     
         17 . A ferroelectric FET as in    claim 16   , wherein said ferroelectric FGM thin film comprises at least two metals selected from the group consisting of strontium, calcium, barium, cadmium, lead, tantalum, hafnium, tungsten, niobium, zirconium, bismuth, scandium, yttrium, lanthanum, antimony, chromium, molybdenum, vanadium, ruthenium and thallium.  
     
     
         18 . A ferroelectric FET as in    claim 17   , wherein said first metal atoms include the metals strontium, bismuth, tantalum, and niobium.  
     
     
         19 . A ferroelectric FET as in    claim 18   , wherein said first metal atoms include the metals strontium, bismuth and tantalum in relative molar proportions corresponding to a stoichiometric formula SrBi 2+y (Ta 1-x Nb x ) 2 O 9 , wherein 0≦×≦1 and 0≦y≦0.20.  
     
     
         20 . A ferroelectric FET as in    claim 15   , wherein said ferroelectric metal oxide is an ABO3-type perovskite.  
     
     
         21 . A ferroelectric FET as in    claim 20   , wherein said first metal atoms include lead, zirconium and tantalum.  
     
     
         22 . A ferroelectric FET as in    claim 21   , wherein said first metal atoms include lead, zirconium and tantalum in relative molar proportions represented by a  30  generalized stoichiometric formula Pb 1+y (Zr 1-x Ti x )O 3 , wherein 0≦×≦1 and  0≦y≦0.1.    
     
     
         23 . A ferroelectric FET as in    claim 14   , wherein said dielectric compound comprises an oxide selected from the group consisting of ZrO 2 , CeO 2 , Y 2 O 3  and Ce 1-x Zr x O 2 , where 0≦×≦1.  
     
     
         24 . A ferroelectric FET as in    claim 1   , wherein said ferroelectric FGM thin film is a FGF thin film, said FGF thin film containing moieties of a plurality of types of metal atoms in relative molar proportions corresponding to stoichiometric formulas of ferroelectric compounds, said FGM thin film having a functional gradient of said moieties of metal atoms.  
     
     
         25 . A ferroelectric FET as in    claim 24   , wherein said ferroelectric compounds are ferroelectric metal oxides.  
     
     
         26 . A ferroelectric FET as in    claim 25   , wherein said ferroelectric metal oxides are ABO 3 -type perovskites.  
     
     
         27 . A ferroelectric FET as in    claim 26   , wherein said types of metal atoms are lead, zirconium and tantalum, and said stoichiometric formulas are represented by a generalized stoichiometric formula Pb(Zr 1-x Ti x )O 3 , wherein x varies in correspondence with said functional gradient and 0≦×≦1.  
     
     
         28 . A ferroelectric FET as in    claim 27   , wherein 0.25≦×≦0.45.  
     
     
         29 . A ferroelectric FET as in    claim 25   , wherein said ferroelectric metal oxides are layered superlattice materials.  
     
     
         30 . A ferroelectric FET as in    claim 29   , wherein said FGF thin film comprises at least two metals selected from the group consisting of strontium, calcium, barium, cadmium, lead, tantalum, hafnium, tungsten, niobium, zirconium, bismuth, scandium, yttrium, lanthanum, antimony, chromium, molybdenum, vanadium, ruthenium and thallium.  
     
     
         31 . A ferroelectric FET as in    claim 30   , wherein said types of metal atoms include strontium, bismuth, tantalum and niobium.  
     
     
         32 . A ferroelectric FET as in    claim 31   , wherein said stoichiometric formulas are represented by a generalized stoichiometric formula SrBi 2 (Ta 1-x Nb x ) 2 O 9 , wherein x varies in correspondence with said functional gradient and 0≦×≦1.  
     
     
         33 . A method of fabricating a ferroelectric FET comprising steps of: 
 preparing a substrate;    forming a ferroelectric FGM thin film; and    forming a gate electrode;    wherein said forming a ferroelectric FGM thin film includes:    providing a first precursor mixture and a second precursor mixture;    applying said first precursor mixture to said substrate;    applying said second precursor mixture to said substrate; and    treating said substrate to form said ferroelectric FGM thin film.    
     
     
         34 . A method of fabricating a ferroelectric FET as in    claim 33   , wherein said first precursor mixture comprises primary relative amounts of precursors for a ferroelectric compound and a dielectric compound, and said second precursor mixture comprises secondary relative amounts of precursors for said ferroelectric compound and said dielectric compound, said primary relative amounts being different from said secondary relative amounts.  
     
     
         35 . A method as in    claim 34   , wherein said ferroelectric compound is a ferroelectric metal oxide.  
     
     
         36 . A method as in    claim 35   , wherein said ferroelectric metal oxide is a layered superlattice material.  
     
     
         37 . A method as in    claim 36   , wherein said first precursor mixture and said second precursor mixture comprise at least two metals selected from the group consisting of strontium, calcium, barium, cadmium, lead, tantalum, hafnium, tungsten, niobium, zirconium, bismuth, scandium, yttrium, lanthanum, antimony, chromium, molybdenum, vanadium, ruthenium and thallium.  
     
     
         38 . A method as in    claim 37   , wherein said first precursor mixture and said second precursor mixture comprise precursor compounds selected from the group consisting of metal beta-diketonates, metal polyalkoxides, metal dipivaloylmethanates, and metal cyclopentadienyls.  
     
     
         39 . A method as in    claim 37   , wherein said first precursor mixture and said second precursor mixture comprise at least three metals selected from the group consisting of strontium, bismuth, tantalum and niobium.  
     
     
         40 . A method as in    claim 37   , wherein said first precursor mixture and said second precursor mixture comprise the metals strontium, bismuth, tantalum and niobium in relative molar proportions corresponding to a stoichiometric formula SrBi 2+y (Ta 1-x Nb x ) 2 O 9 , wherein 0≦×≦1 and  0≦y≦0.20.    
     
     
         41 . A method as in    claim 35   , wherein said ferroelectric metal oxide is an ABO 3 -type perovskite.  
     
     
         42 . A method as in    claim 41   , wherein said first precursor mixture and said second precursor mixture comprise lead, zirconium and titanium in relative molar proportions represented by a generalized stoichiometric formula Pb 1+y (Zr 1-x Ti x )O 3 , wherein 0≦×≦1 and  0≦y≦0.1.    
     
     
         43 . A method as in    claim 34   , wherein said dielectric compound is an oxide selected from the group consisting of ZrO 2 , CeO 2 , Y 2 O 3  and Ce 1-x Zr x O 2 , where 0≦×≦1.  
     
     
         44 . A method of fabricating a ferroelectric FET as in    claim 33   , wherein said first precursor mixture contains primary relative amounts of metal atoms for a first ferroelectric compound, and said second precursor mixture contains secondary relative amounts of metal atoms for a second ferroelectric compound, said primary relative amounts being different from said secondary relative amounts.  
     
     
         45 . A method of fabricating a ferroelectric FET as in    claim 44   , wherein said first ferroelectric compound and said second ferroelectric compound are ferroelectric metal oxides.  
     
     
         46 . A method of fabricating a ferroelectric FET as in    claim 45   , wherein said first precursor mixture and said second precursor mixture contain metal atoms for forming perovskite compounds represented by a generalized stoichiometric formula A(B 1-x C x )O 3 , where 0≦×≦1, in which the value of x varies in correspondence with a functional gradient.  
     
     
         47 . A method of fabricating a ferroelectric FET as in    claim 46   , wherein said first precursor mixture and said second precursor mixture contain lead, zirconium and titanium in relative amounts represented by a generalized stoichiometric formula Pb 1+y (Zr 1-x Ti x )O 3 , wherein 0≦×≦1 and  0≦y≦0.1 , and in which the value of x varies in correspondence with a functional gradient.  
     
     
         48 . A method of fabricating a ferroelectric FET as in    claim 47   , wherein 0.25≦×≦0.45.  
     
     
         49 . A method of fabricating a ferroelectric FET as in    claim 45   , wherein said first precursor mixture and said second precursor mixture contain metal atoms for forming layered superlattice material compounds.  
     
     
         50 . A method of fabricating a ferroelectric FET as in    claim 49   , wherein said first precursor mixture and said second precursor mixture contain strontium, bismuth, tantalum and niobium in relative proportions represented by a generalized stoichiometric formula SrBi 2 (Ta 1-x Nb x ) 2 O 9 , where 0≦×≦1, in which the value of x varies in correspondence to a functional gradient.  
     
     
         51 . A method of fabricating a ferroelectric FET as in    claim 33   , wherein a plurality of precursor mixtures are applied to said substrate, each of said precursor mixtures containing amounts of metal atoms in relative molar proportions for forming a metal oxide compound, said relative proportions of metal atoms not being identical in all of said precursor mixtures.  
     
     
         52 . A method of fabricating a ferroelectric FET as in    claim 51   , wherein said metal oxide compound is a ferroelectric layered superlattice material.  
     
     
         53 . A method of fabricating a ferroelectric FET as in    claim 51   , wherein said metal oxide compound is a ferroelectric perovskite compound.  
     
     
         54 . A method of fabricating a ferroelectric FET as in    claim 53   , wherein a plurality of precursor mixtures contain amounts of metal atoms as represented by a generalized stoichiometric formula Pb 1+y (Zr 1-x Ti x )O 3 , wherein 0≦×≦1 and  0≦y≦0.1.    
     
     
         55 . A method of fabricating a ferroelectric FET as in    claim 54   , wherein 0.25≦×≦0.45.  
     
     
         56 . A method of fabricating a ferroelectric FET as in    claim 33   , wherein said forming a ferroelectric FGM thin film uses a misted deposition process including: forming a first mist from said first precursor mixture; depositing said first mist on said substrate in a liquid coating; forming a second mist from said second precursor mixture; depositing said mist on said substrate in said liquid coating; and treating said liquid coating to form said ferroelectric FGM thin film.  
     
     
         57 . A method as in    claim 56   , wherein said step of treating said liquid coating is performed a first time after said step of depositing said first mist and a second time after said step of depositing said second mist.  
     
     
         58 . A method of fabricating a ferroelectric FET as in    claim 33   , wherein said forming a ferroelectric FGM thin film uses a chemical vapor deposition (“CVD”) process including: placing said substrate in a deposition reactor; forming a first vapor mixture from said first precursor mixture; flowing said first vapor mixture into said deposition reactor; depositing a solid film from said first vapor mixture on said substrate; forming a second vapormixture from said second precursormixture; flowing said second vapor mixture into said deposition reactor; and depositing a solid film from said second vapor mixture on said substrate.  
     
     
         59 . A method of fabricating a ferroelectric FET as in    claim 33   , further comprising a step of forming a gate electrode above said ferroelectric FGM thin film.  
     
     
         60 . A method of fabricating a ferroelectric FET as in    claim 33   , wherein said substrate comprises a gate oxide layer.  
     
     
         61 . A method of fabricating a ferroelectric FET as in    claim 60   , wherein said ferroelectric FGM thin film is formed on said gate oxide layer.  
     
     
         62 . A method of fabricating a ferroelectric FET as in    claim 60   , further comprising a step of forming an interface insulator layer on said gate oxide layer.  
     
     
         63 . A ferroelectric FET as in    claim 33   , further comprising a step of forming an interface insulator layer before said step of forming said ferroelectric FGM thin film.  
     
     
         64 . A method of fabricating a ferroelectric FET as in    claim 33   , further comprising a step of forming a floating electrode before forming said ferroelectric FGM thin film.  
     
     
         65 . A method of fabricating a ferroelectric FET as in    claim 64   , further comprising a step of forming an adhesion layer before said step of forming said floating electrode.  
     
     
         66 . A method as in    claim 33   , wherein said step of treating comprises a process selected from the group consisting of: exposing to vacuum, exposing to ultraviolet radiation, drying, heating, baking, rapid thermal processing, and annealing.  
     
     
         67 . A ferroelectric FET as in    claim 24   , wherein said FGF thin film has unconventional hysteresis behavior.  
     
     
         68 . A method as in    claim 44   , wherein said FGM thin film is a FGF thin film having unconventional hysteresis behavior.  
     
     
         69 . A ferroelectric FET comprising: 
 a semiconductor substrate;    a ferroelectric thin film; and    a gate electrode; wherein said ferroelectric thin film comprises ferroelectric material having unconventional hysteresis behavior.    
     
     
         70 . A ferroelectric FET as in    claim 69   , wherein said ferroelectric material comprises a ferroelectric metal oxide.  
     
     
         71 . A ferroelectric FET as in    claim 70   , wherein said ferroelectric metal oxide comprises an ABO 3 -type perovskite.  
     
     
         72 . A ferroelectric FET as in    claim 71   , wherein said ferroelectric metal oxide comprises a layered superlattice material.  
     
     
         73 . A ferroelectric FET as in    claim 72   , wherein said layered superlattice material comprises the metals strontium, bismuth, tantalum and niobium in relative molar proportions corresponding to a stoichiometric formula SrBi 2+y (Ta 1-x Nb x ) 2 O 9 , wherein 0≦×≦1 and  0≦y≦0.20 .