Method for making a strain-relieved tunable dielectric thin film

Abstract

Tunable dielectric thin films are provided which possess low dielectric losses at microwave frequencies relative to conventional dielectric thin films. The thin films include a low dielectric loss substrate, a buffer layer, and a crystalline dielectric film. Barium strontium titanate may be used as the buffer layer and the crystalline dielectric film. The buffer layer provides strain relief during annealing operations.

What is claimed is:  
     
         1 . A method of making a tunable dielectric thin film, the method comprising the steps of: 
 depositing a buffer layer on a low dielectric loss substrate; and    depositing a layer of crystalline dielectric film on the buffer layer, wherein the buffer layer and the crystalline dielectric film comprise barium strontium titanate and wherein the barium strontium titanate eventually comprises a randomly oriented crystalline cubic phase in each of the buffer layer and the crystalline dielectric film.    
     
     
         2 . The method of  claim 1 , wherein in the depositing steps comprise at least one of RF sputtering, pulsed laser deposition, and metal-organic chemical vapor deposition.  
     
     
         3 . The method of  claim 1 , wherein the barium strontium titanate is of the formula Ba 1-x Sr x TiO 3 , where x is from about 0.0 to about 0.6.  
     
     
         4 . The method of  claim 1 , wherein the buffer layer is deposited at a first temperature, and the layer of crystalline dielectric film is deposited at a second temperature that is higher than the first temperature.  
     
     
         5 . The method of  claim 1 , wherein the randomly oriented crystalline cubic phase in the buffer layer is prepared by depositing at room temperature and then heating at a temperature higher than about 750° C. for more than about 20 minutes.  
     
     
         6 . The method of  claim 1 , further comprising the step of annealing the buffer layer after it was deposited on the low dielectric loss substrate.  
     
     
         7 . The method of  claim 1 , further comprising the step of annealing the crystalline dielectric film after it was deposited on the dielectric buffer layer.  
     
     
         8 . The method of  claim 7 , wherein the crystalline dielectric thin film is annealed at a temperature higher than a temperature at which the crystalline dielectric film is deposited.  
     
     
         9 . The method of  claim 7 , wherein the annealed crystalline dielectric film has an average grain size of from about 0.1 to about 0.5 micron.  
     
     
         10 . The method of  claim 7 , wherein the annealed crystalline dielectric film has a dielectric quality factor Q at 0 V CD  of greater than about 100 at a frequency of 2 GHz or 8 GHz.  
     
     
         11 . The method of  claim 7 , wherein the annealed crystalline dielectric film has a dielectric tuning of at least about 20 percent at 50V/micron at frequencies of 2 GHz and 8 GHz.  
     
     
         12 . The method of  claim 7 , wherein the annealed crystalline dielectric film has a dielectric quality factor Q that is substantially equal or increases with DC bias voltages.  
     
     
         13 . The method of  claim 7 , wherein the annealed crystalline dielectric film substantially maintains dielectric tuning at frequencies of 2 GHz and 8 GHz.  
     
     
         14 . The method of  claim 1 , wherein the tunable dielectric thin film is used within a tunable microwave device.  
     
     
         15 . A method of making a tunable dielectric thin film, the method comprising the steps of: 
 depositing a buffer layer on a low dielectric loss substrate;    annealing the buffer layer after it was deposited on the low dielectric loss substrate;    depositing a layer of crystalline dielectric film on the buffer layer; and    annealing the crystalline dielectric film after it was deposited on the dielectric buffer layer, wherein the buffer layer and the crystalline dielectric film comprise barium strontium titanate and wherein the barium strontium titanate comprises a randomly oriented crystalline cubic phase in each of the annealed buffer layer and the annealed crystalline dielectric film.    
     
     
         16 . The method of  claim 15 , wherein in the depositing steps comprise at least one of RF sputtering, pulsed laser deposition, and metal-organic chemical vapor deposition.  
     
     
         17 . The method of  claim 15 , wherein the barium strontium titanate is of the formula Ba 1-x Sr x TiO 3 , where x is from about 0.0 to about 0.6.  
     
     
         18 . The method of  claim 15 , wherein the buffer layer has a thickness of from about 0.0005 to about 0.2 micron.  
     
     
         19 . The method of  claim 15 , wherein the buffer layer has a thickness of from about 0.01 to about 0.1 micron.  
     
     
         20 . The method of  claim 15 , wherein the buffer layer is porous.  
     
     
         21 . The method of  claim 15 , wherein the crystalline dielectric film has a thickness of from about 0.1 to about 5 micron.  
     
     
         22 . The method of  claim 15 , wherein the crystalline dielectric film has a thickness of from about 0.3 to about 1 micron.  
     
     
         23 . The method of  claim 15 , wherein the barium strontium titanate of the buffer layer is deposited at a lower temperature than the barium strontium titanate of the crystalline dielectric film.  
     
     
         24 . The method of  claim 15 , wherein the crystalline dielectric film is strain relieved.  
     
     
         25 . The method of  claim 15 , wherein the crystalline dielectric film is substantially strain free.  
     
     
         26 . The method of  claim 15 , wherein the low dielectric loss substrate comprises at least one crystalline material selected from magnesium oxide, aluminum oxide and lanthanum aluminum oxide.  
     
     
         27 . The method of  claim 15 , wherein the low dielectric loss substrate has a thickness of from about 250 to about 500 micron.  
     
     
         28 . The method of  claim 15 , wherein the dielectric thin film has a dielectric quality factor Q at 0 V DC  of greater than about 100 at a frequency of 2 GHz or 8 GHz.  
     
     
         29 . The method of  claim 15 , wherein the dielectric thin film has a dielectric tuning of at least about 20 percent at 50 V/micron at a frequency of 2 GHz or 8 GHz.  
     
     
         30 . The method of  claim 15 , wherein the tunable dielectric thin film is used within a tunable microwave device.  
     
     
         31 . The method of  claim 15 , wherein the buffer layer is deposited on the low dielectric loss substrate in an oxygen background pressure of about 200 mTorr.  
     
     
         32 . The method of  claim 15 , wherein the crystalline dielectric film is deposited on the buffer layer and then annealed in flowing oxygen at about 1000° C. for about 6 hours.  
     
     
         33 . A method of making a tunable dielectric thin film, the method comprising the steps of: 
 depositing a buffer layer on a low dielectric loss substrate;    annealing the buffer layer after it was deposited on the low dielectric loss substrate;    depositing a layer of crystalline dielectric film on the buffer layer; and    annealing the crystalline dielectric film after it was deposited on the dielectric buffer layer, wherein the annealed buffer layer and the annealed crystalline dielectric film each have a randomly oriented crystalline cubic phase.    
     
     
         34 . The method of  claim 33 , wherein in the depositing steps comprise at least one of RF sputtering, pulsed laser deposition, and metal-organic chemical vapor deposition.  
     
     
         35 . The method of  claim 33 , wherein the buffer layer comprises at least one material selected from barium titanate, strontium titanate, barium calcium titanate, barium calcium zirconium titanate, lead titanate, lead zirconium titanate, lead lanthanum zirconium titanate, lead niobate, lead tantalate, potassium strontium niobate, sodium barium niobate/potassium phosphate, potassium niobate, lithium niobate, lithium tantalate, lanthanum tantalate, barium calcium zirconium titanate or sodium nitrate, Ba 1-x Sr x TiO 3  (0≦x≦1), Ba x Ca 1-x TiO 3  (0.2≦x≦0.8), Pb x Zr 1-x SrTiO 3  (0.05≦x≦0.4), KTa x Nb 1-x O 3  (0≦x≦1), Pb x Zr 1-x TiO 3  (0≦x≦1), and mixtures and composites thereof.  
     
     
         36 . The method of  claim 33 , wherein the crystalline dielectric film comprises at least one material selected from barium titanate, strontium titanate, barium calcium titanate, barium calcium zirconium titanate, lead titanate, lead zirconium titanate, lead lanthanum zirconium titanate, lead niobate, lead tantalate, potassium strontium niobate, sodium barium niobate/potassium phosphate, potassium niobate, lithium niobate, lithium tantalate, lanthanum tantalate, barium calcium zirconium titanate or sodium nitrate, Ba l-x Sr x TiO 3  (0≦x≦1), Ba x Ca 1-x TiO 3  (0.2≦x≦0.8), Pb x Zr 1-x SrTiO 3  (0.05≦x≦0.4), KTa x Nb 1-x O 3  (0≦x≦1), Pb x Zr 1-x TiO 3  (0≦x≦1), and mixtures and composites thereof.  
     
     
         37 . The method of  claim 33 , wherein the low dielectric loss substrate comprises at least one crystalline material selected from magnesium oxide, aluminum oxide and lanthanum aluminum oxide and/or with additional doping elements selected from manganese, iron, tungsten, alkali earth metal oxides, transition metal oxides, rare earth metal oxides, silicates, niobates, tantalates, aluminates, zirconates or titanates.  
     
     
         38 . The method of  claim 33 , wherein the crystalline dielectric thin film is annealed at a temperature higher than a temperature at which the crystalline dielectric film is deposited.  
     
     
         39 . The method of  claim 33 , wherein the annealed crystalline dielectric film has a dielectric quality factor Q at 0 V DC  of greater than about 100 at a frequency of 2 GHz or 8 GHz.  
     
     
         40 . The method of  claim 33 , wherein the annealed crystalline dielectric film has a dielectric tuning of at least about 20 percent at 50V/micron at frequencies of 2 GHz and 8 GHz.  
     
     
         41 . The method of  claim 33 , wherein the annealed crystalline dielectric film has a dielectric quality factor Q that is substantially equal or increases with DC bias voltages.  
     
     
         42 . The method of  claim 33 , wherein the annealed crystalline dielectric film substantially maintains dielectric tuning at frequencies of 2 GHz and 8 GHz.  
     
     
         43 . The method of  claim 33 , wherein the tunable dielectric thin film is used within a tunable microwave device.