Metal alloy electrodeposited microstructures

Abstract

NiW and NiFe microstructure alloys and other microstructure alloys are disclosed, along with a method of making those structures. The microstructures may have heights of 500 μm or greater, and the alloy composition may have a controllable gradient if it is desired to impart different properties to different parts of a structure. The microstructures are harder than conventional nickel microstructures, and have lower coefficients of thermal expansion. While both types of alloyed microdevices have improved hardness and reduced coefficients of thermal expansion, the NiW alloys may be primarily used where increased hardness is important, for example micro-gears and other microdevices with moving parts that would benefit from increased hardness at points of contact; while the NiFe alloys may be primarily used where a small coefficient of thermal expansion is desirable. The techniques are especially useful for plating NiW or NiFe into deep recesses of a microstructure.

We claim:  
     
         1 . A microstructure comprising a metal alloy, wherein: 
 (a) said alloy comprises between about 50% and about 99% by weight nickel;    (b) said alloy comprises between about 1% and about 40% by weight tungsten;    (c) said microstructure is between about 50 μm and about 2000 μm deep; and    (d) said microstructure has an aspect ratio greater than about 1.    
     
     
         2 . A microstructure as recited in  claim 1 , wherein said alloy comprises between about 1% and about 6% by weight tungsten.  
     
     
         3 . A microstructure as recited in  claim 1 , wherein the fraction of tungsten in said alloy varies as a function of position.  
     
     
         4 . A microstructure as recited in  claim 1 , wherein said microstructure is between about 50 μm and about 500 μm deep.  
     
     
         5 . A microstructure as recited in  claim 1 , wherein said microstructure has an aspect ratio greater than about 5.  
     
     
         6 . A microstructure comprising a metal alloy, wherein: 
 (a) said alloy comprises between about 58% and about 70% by weight iron;    (b) said alloy comprises between about 30% and about 42% by weight nickel;    (c) said microstructure is between about 50 μm and about 2000 μm deep; and    (d) said microstructure has an aspect ratio greater than about 1.    
     
     
         7 . A microstructure as recited in  claim 6 , wherein said microstructure is between about 50 μm and about 500 μm deep.  
     
     
         8 . A microstructure as recited in  claim 6 , wherein the fraction of iron in said alloy varies as a function of position.  
     
     
         9 . A microstructure as recited in  claim 6 , wherein said alloy comprises about 64% by weight iron, and about 36% by weight nickel.  
     
     
         10 . A microstructure as recited in  claim 6 , wherein: 
 (a) said alloy comprises between about 58% and about 65% by weight iron;    (b) said alloy comprises between about 32% by weight nickel; and    (c) said alloy comprises between about 3% and about 10% by weight cobalt.    
     
     
         11 . A microstructure as recited in  claim 6 , wherein said microstructure has an aspect ratio greater than about 5.  
     
     
         12 . A microstructure comprising a metal alloy, wherein: 
 (a) said alloy comprises tungsten and one or more metals selected from the group consisting of nickel, iron, and cobalt;    (c) said microstructure is between about 50 μm and about 2000 μm deep; and    (d) said microstructure has an aspect ratio greater than about 1.    
     
     
         13 . A microstructure as recited in  claim 12 , wherein the composition of said alloy varies as a function of position.  
     
     
         14 . A microstructure as recited in  claim 12 , wherein said microstructure is between about 50 μm and about 500 μm deep.  
     
     
         15 . A microstructure as recited in  claim 12 , wherein said microstructure has an aspect ratio greater than about 5.  
     
     
         16 . A process for making a metal alloy microstructure; wherein the alloy comprises two or more metals, at least one of which metals is selected from the group consisting of nickel, iron, tungsten, and cobalt; said process comprising the steps of: 
 (a) supplying into a mold an aqueous solution comprising salts of the metals, wherein the shape of the mold is complementary to the shape of the microstructure to be made, and wherein the mold includes one or more deep recesses having a depth of at least about 50 μm, and having an aspect ratio greater than about 1;    (b) depositing the metals from the aqueous solution into the mold by pulsed electroplating; wherein the electroplating pulses have an on time that is sufficiently short, and a duty cycle that is sufficiently low, that the products of the electroplating reactions and the products of any side reactions do not accumulate in concentrations that are sufficiently high to substantially interfere with the electroplating of the desired alloy into the deep recesses; and wherein the duty cycle is less than about 0.2; and wherein said depositing step is continued until a metal alloy microstructure has been formed having a height of at least about 50 μm, and having an aspect ratio greater than about 1.    
     
     
         17 . A process as recited in  claim 16 , wherein the duty cycle is less than about 0.125.  
     
     
         18 . A process as recited in  claim 16 , wherein the duty cycle is less than about 0.1.  
     
     
         19 . A process as recited in  claim 16 , wherein the on time is greater than about 0.1 second.  
     
     
         20 . A process as recited in  claim 16 , wherein the on time is greater than about 1 second.  
     
     
         21 . A process as recited in  claim 16 , wherein the on time is less than about 60 seconds.  
     
     
         22 . A process as recited in  claim 16 , wherein the mold includes one or more deep recesses having a depth between about 50 μm and about 500 μm deep.  
     
     
         23 . A process as recited in  claim 22 , wherein at least one of the deep recesses has an aspect ratio greater than about 5.  
     
     
         24 . A process as recited in  claim 16 , wherein the alloy comprises nickel and tungsten.  
     
     
         25 . A process as recited in  claim 16 , wherein the alloy comprises nickel and iron.  
     
     
         26 . A process as recited in  claim 16 , wherein the alloy comprises nickel, iron, and cobalt.  
     
     
         27 . A process as recited in  claim 16;  wherein one or more parameters selected from the group consisting of current density, on time, and duty cycle are varied as a function of time during the pulsed electroplating; and wherein the variation is sufficient to cause the composition of the alloy to vary as a function of depth.  
     
     
         28 . A microstructure produced by the process of  claim 16 .  
     
     
         29 . A microstructure produced by the process of  claim 17 .  
     
     
         30 . A microstructure produced by the process of  claim 18 .  
     
     
         31 . A microstructure produced by the process of  claim 19 .  
     
     
         32 . A microstructure produced by the process of  claim 20 .  
     
     
         33 . A microstructure produced by the process of  claim 21 .  
     
     
         34 . A microstructure produced by the process of  claim 22 .  
     
     
         35 . A microstructure produced by the process of  claim 23 .  
     
     
         36 . A microstructure produced by the process of  claim 24 .  
     
     
         37 . A microstructure produced by the process of  claim 25 .  
     
     
         38 . A microstructure produced by the process of  claim 26 .  
     
     
         39 . A microstructure produced by the process of  claim 27.