Suppression of the unwanted response of an SC-cut crystal unit

Research on the radius of curvature of plano-convex crystal wafers and the beveling operation for the purpose of suppressing the unwanted response of the 3rd overtone 5-MHz SC-cut crystal units to be used in an OCXO (oven-controlled crystal oscillator) is discussed. An SC-cut crystal unit whose unwanted responses are suppressed has superior frequency temperature characteristics, free from activity dips. Measurement of the equivalent circuit parameter revealed that the Q value is 2.14×10⁶, the capacitance ratio is 1.78×10⁴, the equivalent resistance is 80 Ω and the motional inductance is 5.5 H. The OCXO using an SC-cut crystal unit whose unwanted responses are suppressed, has a phase noise of -105 dBc/Hz in terms of 1-Hz offset frequency from the carrier. Thermal hysteresis and the orientation effect of frequency are on the order of 10^-10, while the aging rate is 2×10^-9