Fabrication of microlens arrays with long focus for improving responsivity of PtSi IR detector array device

Abstract

For the first time, diffractive rectangle-based multilevel steps Si microlens arrays are fabricated by a new method, named part etching. The new method proposed can increase focal length of diffractive microlenses arrays. The 256x256 element microlens arrays are designed for a center wavelength of 4micrometers , with 40micrometers (Horizontal) x 30micrometers (Vertical) quadrate pixel dimension and a speed (F number) of F/2.53 (in air). The focal length of the microlens array is 400micrometers in Si material, much longer than focal length of the microlens arrays of the same size fabricated by conventional binary optics method. The method also includes photolithography and ion beam milling process. The 256x256 element microlens arrays and the same 256x256 element PtSi IR Focal Plan Arrays (FPAs) are monolithic integrated on the same wafer. The IR response characteristics of the integration device are improved greatly.