Micromachined S-band patch antenna with reduced dielectric constant

A generic dielectric constant reduction method for silicon antenna substrates is presented in detail along with a process description to produce functional dielectric layers for planar antennas. Virtually any dielectric constant below 11.9 down to 3.8 aimed for in this paper can be produced. Very small honeycomb cells with wall thickness of 16 μm and inner wall length of 86.6 μm is etched down using deep reactive ion etch (DRIE) to 475 μm depth in each of two 525 μm 4-inch high ohmic wafers. These two wafers are bonded together with the etched side of both wafers facing each other. A volumetric averaging yields an average dielectric constant of 3.8 for the two bonded wafers. By adjusting the etch depth, different dielectric constants for bonded pairs of silicon wafers are attainable. A demonstration of the concept has been physically realized showing an increase in the resonance frequency of a simple coaxial-fed disk-patch antenna with a simulated resonance frequency of 2.5 GHz.