Radio frequency reliability studies of CMOS RF integrated circuits for ultra-thin flexible packages

This Letter presents for the first time radio frequency (RF) reliability studies of fully integrated CMOS RF integrated circuits (RFICs) for next generation wireless communication applications involving conformal bodies where wireless communication RFICs will be embedded on ultra-thin flexible packages. As a test case, RF characteristics of a CMOS voltage-controlled oscillator (VCO) chip with multiple die-substrate thicknesses were measured and results are analysed. The CMOS VCO chip under study was designed and fabricated using 180 nm RF-CMOS process. Reliability of performances of the VCO chips are characterised and results are compared before and after die thinning from 250 to 50, 35, and 25 mu m, respectively. Critical RF performance parameters such as frequency of oscillation, output power, and phase noise are considered for analysis, respectively. All the dies are placed face-up for probing on the top of a metal chuck with ground connection inside the micro-chamber of a probe station. While the deviations of frequency and output power are within +/- 1% and +/- 1 dB, respectively, due to the die thinning affect, the phase noise deteriorations are observed significant. It confirms the well-known fact of phase noise sensitiveness to the substrate thickness due to the leakage and SOI CMOS is discussed widely to minimise these parasitic effects.