Study on the voltage-controlled-oscillator circuit implemented with Al/HfO2/Si capacitors

Abstract

Voltage controlled oscillator (VCO) is the most ubiquitous element in all communication systems, wired or wireless. In a wireless system the quality of the communication link is determined in large part by the characteristics of the VCO. The capacitance of metal/insulator/semiconductor (MIS) shows larger variation from the accumulation region to the depletion region. The dielectric constant of hafnium dioxide is larger (around 25) than that Of SiO2 (similar to 3.9). Al/Hafnium oxide (HfO2)/Si show a field dependent permittivity and can be used as a dielectric in voltage tunable capacitors. In this work, we used two types of tunable capacitor in the VCO(LC tank and Colpitts circuit) integrated within PCB: one is Al/HfO2/Si (HfO) capacitor, the other one is Philips BB 135 p-n junction capacitor for a control. The maximum MIS capacitance ratio is 4.25. The Al/HfO2/Si capacitors are then implemented as the varactor in the VCO circuit.