Intrinsic temperature compensation of aluminum nitride Lamb wave resonators for multiple-frequency references

Abstract

In this paper we present the temperature compensation of aluminum nitride (AlN) Lamb wave resonators for a future application to XOs and TCXOs for a frequency ranging from 100 MHz to 1000 MHz. The temperature coefficient of frequency (TCF) for the lowest symmetric Lamb wave mode S0 for AlN plates with h/lambda<0.3 is found to be around -30 ppm/K. A zero TCF resonator is obtained by adding a compensating silicon dioxide layer. The low dispersion of the phase velocity for the S0-mode propagating in thin AlN plates reduces not only the fabrication tolerances towards thickness variations of the AlN layer, but also enables resonators operating over a wide frequency range, i.e. from 100 MHz to 1000 MHz, based on two absolute film thicknesses for AlN and SiO2 achieving near zero TCF over the entire frequency range. The acoustic properties and different layer configurations of zero TCF Lamb wave devices are discussed in detail.