Measurements of ultra-stable langatate crystal oscillators

The use of the langatate (LGT, La₃Ga_5.5Ta_0.5O₁₄) crystal for the realization of ultra-stable oscillators is very recent. This material proved that it is capable of giving stability results as good as those achieved by quartz crystal. To the knowledge of the authors, until now there was no substitution material for the quartz crystal, for low noise applications. Indeed, investigations had proved that LGT is a good alternative. This paper describes quickly all the essential manufacturing steps related to the development of an oscillator using this pure synthetic crystal. It shows that the performances looked for, in terms of noise, are those obtained with the quartz crystal. Its content is as follows. It begins with the description of the resonator manufacturing, the resonator being the heart of the oscillator. Then, the development of the related electronics is discussed and noise measurements are given as a conclusion. Very first ageing measurements of a set of LGT crystal oscillators are also emphasized. Noise results are given in terms of standard Allan deviation as well as in power spectral density of phase fluctuations. These results are analyzed and finally compared to those of quartz crystal oscillators.