Development of passive devices on silicon substrate for microwave application

Abstract

In this these, passive devices such as transmission line and spiral inductor are developed on CMOS grade silicon substrate for microwave application. In chapter 2, Passive devices on membrane supported by porous silicon post were fabricated and measured. The porous silicon layer was obtained from <100> boron doped silicon substrate of 8 -12Ωcm resistivity by anodization process. The porous silicon layer is 40um thick, and it is the height from the etched silicon surface to the membrane. After the selectively poroused silicon layer is prepared, the dielectrics $(SiO_2/SiNx/SiO_2)$ for membrane is deposited with PECVD and RPCVD. The deposition of dielectric is followed by manufacturing of coplanar waveguide with conventional MMIC process, lithography, metal evaporation, lift off and gold plating or something, where NiCr/Au or Ti/Au were used in the metalization process. After that, the membrane dielectric is patterned and etched by RIE to fit to coplanar waveguide size for NaOH solution to permeate though the open area and etch porous silicon sacrificial layer rapidly. Finally, the porous silicon sacrificial layer is etched in 0.5% NaOH solution for 2 hours without any protecting mask for metals, the etching rate is higher than 2.5um/min. From this process, spiral inductor and coplanar waveguide were fabricated on membrane and the longest one is 5mm long. Maximum available gain of coplanar waveguide has been improved from -1.2dB/mm at 15GHz to higher than -0.3dB/mm up to 40GHz by adopting porous silicon post rather than silicon post and also improved from -0.59dB/mm at 40GHz to higher than -0.3dB/mm at the same frequency by etching the porous silicon layer under the signal line. The CPW separated by 100um from the silicon substrate has the maximum available gain of larger than -0.2dB/mm up to 40GHz. In this case, the simulation result shows that the dominant part of the signal loss is not the dielectric loss in the silicon substrate but the combination of the di...