SOI technology for radio-frequency integrated-circuit applications

This paper presents a silicon-on-insulator (SOI) integration technology, including structures and processes of OFF-gate power nMOSFETs, conventional lightly doped drain (LDD) nMOSFETs, and spiral inductors for radio frequency integrated circuit (RFIC) applications. In order to improve the performance of these integrated devices, body contact under the source (to suppress floating-body effects) and salicide (to reduce series resistance) techniques were developed for transistors; additionally, locally thickened oxide (to suppress substrate coupling) and ultra-thick aluminum up to 6 μm (to reduce spiral resistance) were also implemented for spiral inductors on high-resistivity SOI substrate. All these approaches are fully compatible with the conventional CMOS processes, demonstrating devices with excellent performance in this paper: 0.25-μm gate-length offset-gate power nMOSFET with breakdown voltage (BV_DS) ∼ 22.0 V, cutoff frequency (f_T)∼15.2 GHz, and maximal oscillation frequency (f_max)∼8.7 GHz; 0.25-μm gate-length LDD nMOSFET with saturation current (I_DS)∼390 μA/μm, saturation transconductance (g_m)∼197 μS/μm, cutoff frequency ∼ 25.6 GHz, and maximal oscillation frequency ∼ 31.4 GHz; 2/5/9/10-nH inductors with maximal quality factors (Q_max) 16.3/13.1/8.95/8.59 and self-resonance frequencies (f_sr) 17.2/17.7/6.5/5.8 GHz, respectively. These devices are potentially feasible for RFIC applications.