Frequency flicker of 2.3 GHz AlN-sapphire high-overtone bulk acoustic resonators

We report the detailed characterization of 2.3 GHz AlN-Sapphire high-overtone bulk acoustic resonators (HBARs), with a typical loaded Q-factor of 25-30 x 10(3), 15-20 dB insertion loss, and resonances separated by about 10 MHz. The temperature coefficient of frequency of HBARs is measured to be about -25 ppm/K. We observe at high-input microwave power a significant distortion of the HBAR resonance lineshape, attributed to non-linear effects. The power-induced fractional frequency variation of the HBAR resonance is measured to be about -5 x 10(-10)/mu W. The residual phase noise of a HBAR is measured in the range of -110 to -130 dBrad(2)/Hz at 1Hz Fourier frequency, yielding resonator fractional frequency fluctuations at the level of -205 to -225 dB/Hz at 1Hz and an ultimate HBAR-limited oscillator Allan deviation about 7 x 10(-12) at 1 s integration time. The 1/f noise of the HBAR resonator is found to increase with the input microwave power. A HBAR resonator is used for the development of a low phase noise 2.3 GHz oscillator. An absolute phase noise of -60, -120, and -145 dBrad(2)/Hz for offset frequencies of 10 Hz, 1 kHz, and 10 kHz, respectively, in excellent agreement with the Leeson effect, is measured. Published by AIP Publishing.