Experimental studies on flicker noise in quartz crystal resonators as a function of electrode volume, drive current, type of quartz, and fabrication process

We investigated the effect of electrode size, drive current, sweeping, type of polishing, and ultra-thin electrodes on the 1/f or flicker frequency and phase modulation (PM) noise of quartz crystal resonators. The 1/f noise of resonators with three different electrode diameters was measured and compared. The PM noise performances of all three resonator types, measured in a test oscillator, were similar with an average of -100 dBc/Hz, a variation of approximately ±10 dB, and a minimum value of L(10 Hz)=-110 dBc/Hz. (dBc/Hz refers to dB below the carrier in a 1 Hz bandwidth.) We also found that the 1/f noise in many of these resonators varied significantly (up to 10 dB) with drive current. We also had other groups of resonators made out of swept quartz bars, with a special polishing process and/or ultra-thin electrode edges. These groups yielded similar results: an average PM noise of -98 dBc/Hz, and a variation of ±10 dB. The amplitude-frequency effect of the resonators was also investigated. The frequency versus amplitude curve, measured using a network analyzer, showed discontinuities in some of the resonators with poor noise. There is some indication that these discontinuities or “jumps” may be due to stress relief in the crystal or noisy contacts