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

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 (~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 BB135 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.