Thin Film Conductors on Face-of-a-Cube

 

Thin film is a layer of conductive material either sputtered or evaporated onto a substrate in a vacuum to form conductors. Thin film conductors on face-of-a-cube is a method where vertical interconnections are performed on the cube face. There are two variants of this method as follows:

• Thin film `T-connects' and sputtered metal conductors: This method was jointly developed by Irvine Sensors and IBM. In this method, after the I/O signals are rerouted to one edge of the chip, a thin film metal layer is patterned on the surface of the stacked chips. Then, two processes, called lift-off photolithography and sputter-deposition, are performed on the face of the stack to form pads and bus lines, creating what is called `T-connections' [21] as shown in Figure .  

    
  Figure: A thin film metal ``T-connects'' for vertical interconnections.
  

• Direct laser write traces on epoxy cube face: An interconnect pattern on the faces of the cube is generated by laser trimming. This pattern is designed to intersect with the IC's wires cross section on the cube face [22, 23] as shown in Figure . This method is used by Thomson-CFS DOI for high density memories.  

    
  Figure: Direct laser writing process for vertical interconnections.