Experimental study of SAW quartz resonators at very low temperature

Previous works in the frequency range of 5 to 23 MHz have shown that the limitation of the Q-factor in high performance quartz bulk wave resonators at room temperature is mainly due to the intrinsic acoustic losses. However by cooling down the device to liquid helium (4.2 K) the contribution of acoustic losses vanishes, thus enabling an increase of the Q-factor, by one order of magnitude and the evaluation of other sources of losses. In the present paper, a similar approach has been followed for high frequency Rayleigh wave resonators at 416 MHz. It is shown that for surface waves propagating in a state of the art quartz SAW resonator, the main source of losses is also due to intrinsic acoustic losses. By cooling down the device below 30 K, the dependence of the Q-factor versus temperature follows a behavior in T⁴, characteristic of internal acoustic losses, and then reaches a plateau region at about 4-10 K. High Q factors in the range of 1.5×10⁵ have been obtained at 4.2 K for 416 MHz devices, yielding a Q.f product in the range of 7×10¹⁴ to be compared to the best results obtained with cooled bulk wave devices : 2.4×10¹⁴