Design of a 3D integrated circuit for manipulating and sensing biological nanoparticles

We present the design of a mixed-technology microsystem for electronically manipulating and optically detecting nanometer scale particles in a fluid. This lab-on-a-chip is designed using 3D integrated circuit technology. By taking advantage of processing features inherent to 3D chip-stacking technology, we create very dense dielectrophoresis electrode arrays. During the 3D fabrication process, the top-most chip tier is assembled upside down and the substrate material is removed. This puts the polysilicon layer, which is used to create geometries with the process' minimum feature size, in close proximity to a fluid channel etched into the top of the stack. This technique allows us to create electrode arrays that have a gap spacing of 270 nm in a 0.18 ìm SOI technology. Using 3D CMOS technology also provides the additional benefit of being able to densely integrate analog and digital control circuitry for the electrodes by using the additional levels of the chip stack. For sensing particles that are manipulated by dielectrophoresis, we present a method by which randomly distributed nanometer scale particles can be arranged into periodic striped patterns, creating an effective diffraction grating. The efficiency of this grating can be used to perform a label-free optical analysis of the particles. The functionality of the 3D lab-on-a-chip is verified with simulations of Kaposi's sarcoma-associated herpes virus particles, which have a radius of approximately 125 nm, being manipulated by dielectrophoresis and detected optically