Voltage Controlled GaN-on-Si HFET Power Oscillator Using Thin-Film Ferroelectric Varactor Tuning

A 1.6 GHz power oscillator with a GaN-on-Si heterostructure field effect transistor (HFET) is reported. The voltage-controlled oscillator used a thin-film barium strontium titanate (BST) interdigital varactor as the tuning element. The surface-mount varactor was fabricated using sputtered BST film and copper metallization on alumina. An output power of 1.6 W (32 dBm) is obtained with a DC conversion efficiency of 25.5%. Flat tuning sensitivity of 500 kHz/V, 49 MHz linear frequency tuning, and power flatness of better than 0.5 dB are obtained with 0-100 V tuning voltage. The maximum oscillator phase noise is -81.4 dBc/Hz at 100 kHz offset..