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 S 0 for AlN plates with h/λ < 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 S 0 -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 SiO 2 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.

1.05-GHz CMOS oscillator based on lateral- field-excited piezoelectric AlN contour- mode MEMS resonators

“…at this relatively large aln thickness, the dispersion of the phase velocity deteriorates to a certain extent. despite that, the frequency sensitivity to process variations (aln thickness and electrode thickness) for lFE aln contour-mode MEMs resonators is generally lower than (or at least comparable to) aln FBar resonators [7].…”

“…In this way, simultaneous high Q (up to 2,200) and k t 2 (up to 1.2%) have been achieved for lFE aln resonators from 843 MHz to 1.64 GHz, as listed in Table I. The reason for this choice of film thickness mainly comes from the lamb wave theory, where the maximum electromechanical coupling happens at 0.45λ for S 0 lamb waves in aln excited by IdT [7]- [10]. at this relatively large aln thickness, the dispersion of the phase velocity deteriorates to a certain extent.…”

“…For oscillator applications, another important figure of merit (FoM) related to the resonator design is the k t 2 •Q product. Therefore, in addition to the quality factor optimization, the electromechanical coupling coefficient k t 2 has been maximized in this work by making the film thickness T equal to about 0.45 times the desired wavelength of operation, λ, as illustrated in Fig. 2 [7]. In this way, simultaneous high Q (up to 2,200) and k t 2 (up to 1.2%) have been achieved for lFE aln resonators from 843 MHz to 1.64 GHz, as listed in Table I.…”

“…1). By depositing a piezoelectric aln layer directly on silicon wafers and making the film thickness, T, equal to approximately 0.45 times (which can be explained by lamb wave theory [7]- [10] as it will be discussed in more details in the next section) the desired wavelength of operation, λ, both the material quality (therefore resonator Q) and k t 2 have been optimized without being negatively affected by the quality of bottom metal films. In this way, simultaneous high Q (up to 2,200) and k t 2 (up to 1.2%) have been achieved from 843 MHz to 1.64 GHz for lFE aln resonators without a floating bottom electrode [5].…”

Wireless actuation of bulk acoustic modes in micromechanical resonators

“…The LWRs typically have high quality factors (Q), robust thermal compensation, low noise floor and high frequency of operation. [6][7][8][9][10][11] These thin plate guided waves are a type of ultrasonic waves that remain guided between the upper and lower surfaces of a piezoelectric plate, and thus are able to travel longer distances with little attenuation. These waves propagate in piezoelectric plates that are thinner in comparison to the wavelength of the wave being transduced by the Inter-Digitated Transducers (IDTs) patterned on top of the piezoelectric resonator.…”