Silicon Microneedle Structure and Production Method

Abstract

A microneedle structure has one or more microneedles ( 104 ) projecting from the major surface ( 102 ) of a substrate ( 100 ). The microneedle has a penetrating tip ( 106 ) formed at an intersection between upright surfaces ( 108 ) and an inclined surface ( 110 ) corresponding to a (1 1 1) crystallographic plane. The microneedle has an expanding portion bounded by a continuation of the upright surfaces ( 108 ) and inclined surface ( 110 ), and a constant cross-section portion bounded by a continuation of the upright surfaces and a slicing plane ( 112 ) extending from an edge ( 114 ) of inclined surface ( 110 ) towards, and perpendicular to, major surface ( 102 ) of the substrate. A width W of inclined surface ( 110 ) increases monotonically from penetrating tip ( 106 ) to edge ( 114 ).

What is claimed is: 
     
         1 . A microneedle structure formed from a single crystal of silicon, the microneedle structure comprising:
 (a) a substrate having a major surface;   (b) at least one microneedle integrally formed with said substrate so as to project from said major surface, said at least one microneedle comprising: 
 (i) a penetrating tip formed at an intersection between at least one upright surface perpendicular to said major surface of said substrate and an inclined planar surface corresponding to a (1 1 1) crystallographic plane, 
 (ii) an expanding cross-section portion bounded by a continuation of said at least one upright surface and said inclined surface, and 
 (iii) a constant cross-section portion bounded by a continuation of said at least one upright surface and a slicing plane extending from an edge of said inclined surface towards, and perpendicular to, said major surface of said substrate, 
 
wherein a width of said inclined surface increases monotonically from said penetrating tip to said edge, and wherein said slicing plane extends to, and meets, a cut edge of said substrate. 
     
     
         2 . The microneedle structure of  claim 1 , wherein said constant cross-section portion extends for at least a fifth of a height of said penetrating tip from said major surface of said substrate. 
     
     
         3 . The microneedle structure of  claim 1 , wherein a ratio of a height of said penetrating tip from said major surface of said substrate to a maximum dimension of said microneedle adjacent to said major surface is at least 1.6. 
     
     
         4 . The microneedle structure of  claim 1 , wherein a ratio of a height of said penetrating tip from said major surface of said substrate to a maximum dimension of said microneedle adjacent to said major surface is at least 1.7. 
     
     
         5 . The microneedle structure of  claim 1 , wherein a height of said penetrating tip from said major surface of said substrate is at least 750 microns, and wherein a maximum dimension of said microneedle parallel, and adjacent, to said major surface is no more than 500 microns. 
     
     
         6 . The microneedle structure of  claim 1 , wherein a height of said penetrating tip from said major surface of said substrate is at least 800 microns, and wherein a maximum dimension of said microneedle parallel, and adjacent, to said major surface is no more than 450 microns. 
     
     
         7 . The microneedle structure of  claim 1 , wherein a cross-section taken through said constant cross-section portion of said microneedle parallel to said major surface of said substrate has a length dimension perpendicular to said slicing plane and a width parallel to said slicing plane, said length being at least 50% greater than said width. 
     
     
         8 . The microneedle structure of  claim 1 , wherein said at least one upright surface adjacent to said penetrating tip comprises a first planar surface and a second planar surface smoothly linked by an arcuate surface, said first and second planar surfaces being symmetrically deployed on opposite sides of a center plane passing through said microneedle and forming between them an angle of between 45 degrees and 75 degrees. 
     
     
         9 . The microneedle structure of  claim 8 , wherein said arcuate surface has a radius of curvature between 10 microns and 40 microns. 
     
     
         10 . The microneedle structure of  claim 8 , wherein said at least one upright surface further comprises a third planar surface and a fourth planar surface arranged symmetrically on opposite sides of said center plane, said third and fourth planar surfaces forming between them of between 5 degrees and 25 degrees. 
     
     
         11 . The microneedle structure of  claim 1 , further comprising a bore extending from said inclined surface through said expanding portion, through said constant cross-section portion and through said substrate to a rear surface of said substrate. 
     
     
         12 . The microneedle structure of  claim 1 , wherein said slicing plane is also an edge of said substrate. 
     
     
         13 . The microneedle structure of  claim 1 , wherein said at least one microneedle is implemented as a plurality of microneedles integrally formed with said substrate, said plurality of microneedles having co-planar slicing planes.