Sputtered transparent conductive aluminum doped zinc oxide films

Abstract

Disclosed are AZO films deposited on a transparent substrate by pulse DC using an oxide target with a composition in the range 0.5-2 wt % Al 2 O 3 , desirably at temperature above 325° C., resulting in films showing columnar grain structure with columns extending from the top to the bottom of the film, and small lateral grain size (less than 70 nm from substrate to top of film). The film has low resistivity at less than 10 Ohm/square at a thickness less than 400 nm, resistivity is desirably unchanged by annealing at temperatures of up to 450° C.

What is claimed is: 
     
         1 . A transparent substrate with an AZO film deposited thereon, comprising:
 a transparent substrate;   an aluminum-doped zinc oxide (AZO) film on and in contact with substrate, the film having a composition in the range 0.5-2 wt % Al 2 O 3  and a columnar grain structure having columns extending from the bottom to the top of the film, with in-plane grain size less than 70 nm.   
     
     
         2 . The substrate of  claim 1  wherein the AZO film has a sheet resistivity of less than 10 Ohm/square and a thickness less than 400 nm. 
     
     
         3 . The substrate of  claim 1  wherein the AZO film has and surface roughness R a  less than 10 nm and a film thickness greater than 500 nm. 
     
     
         4 . The substrate of  claim 3  wherein the AZO film has a sheet resistivity of less than 10 Ohm/square. 
     
     
         5 . The substrate according to any of  claims 1 - 4 , wherein the grain angle of the columnar grain of AZO film is less than 2°, wherein grain angle is defined as the angle between two side walls of the grain, the sidewalls extending in a direction generally perpendicular to the substrate. 
     
     
         6 . The substrate according to any of  claims 1 - 5  wherein the AZO film has an electron mobility of greater than (45 cm 2 )/(Vs) and a resistivity of less than 400×10 −6  Ohm·cm. 
     
     
         7 . The substrate according to any of  claims 1 - 6  wherein the AZO film resistivity is unchanged by annealing at temperatures of up to 450° C. 
     
     
         8 . The substrate of any of  claims 1 - 7  wherein the etch rate of said AZO film in acidic solutions is less than 50% of the rate observed for AZO films deposited below 300° C. and having grain structure of crown type and having a grain angle of greater than 5°, wherein grain angle is defined as the angle between two side walls of the grain. 
     
     
         9 . A The substrate of any of  claims 1 - 8  wherein the transparent substrate comprises a glass substrate. 
     
     
         10 . A method for depositing an AZO film is disclosed, including:
 providing an oxide target with a composition in the range of 0.5 to 2.0 wt % Al 2 O 3  in ZnO; and   depositing an AZO film by sputtering the oxide target.   
     
     
         11 . The method of  claim 10  wherein the step of depositing is performed at a temperature greater than 325° C. 
     
     
         12 . The method according to either of  claims 10  and  11 , wherein the step of depositing further comprises applying a pulsed DC voltage to the oxide target. 
     
     
         13 . The method according to any of  claims 10 - 12 , wherein applying a pulsed DC voltage to the target comprises applying a pulse having a duty cycle greater than 40%. 
     
     
         14 . The method according to any of  claims 10 - 13 , wherein the step of depositing further comprises forming a plasma having a power density of between 1 and 2 W/cm 2 . 
     
     
         15 . The method according to any of  claims 10 - 14  wherein the process pressure is less than 10 mtorr.