Ultra-low dielectric constant porous silica thick films for high-speed IC packaging

Interconnect systems which are required in high-speed GaAs digital ICs use stripline techniques for signal traces which must be deposited over very low dielectric constant substrates. Materials with relative dielectric constant k less than 3 and having low-loss tangent up to microwave frequencies are required for ceramic materials. Such values are impossible to achieve in single-phase ceramic monoliths; composite approaches are necessary. A technique for preparing porous silica films 1-10-μm thick is presented. The dielectric constant of these films is in the range of 2.4 to 2.8 with a loss tangent less than 0.005 at 1 kHz