Multi-frequency pierce oscillators based on piezoelectric AlN contour-mode MEMS resonators

Abstract

This paper reports on the first demonstration of multi-frequency (176, 222, 307, and 482 MHz) oscillators based on piezoelectric AlN contour-mode MEMS resonators. All the oscillators show phase noise values between -88 and -68 dBc/Hz at 1 kHz offset and phase noise floors as low as -160 dBc/Hz at 1 MHz offset. The same Pierce circuit design is employed to sustain oscillations at the 4 different frequencies, while the oscillator core consumes at most 10 mW. The AlN resonators are currently wirebonded to the integrated circuit realized in the AMIS 0.5 μm 5 V CMOS process. This work constitutes a substantial step forward towards the demonstration of a single-chip multi-frequency reconfigurable timing solution that could be used in wireless communications and sensing applications. This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of the University of Pennsylvania's products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to pubs-permissions@ieee.org. By choosing to view this document, you agree to all provisions of the copyright laws protecting it.

A review of MEMS oscillators for frequency reference and timing applications

“…In contrast, flexural mode Si resonators show a relatively low Q-factor which might be caused by the fact that in a flexural mode resonator, the stress and strain are mostly located at the (lossy) resonator surface. AlN-based bulk mode piezoelectric resonators show a lower Q than bulk mode Si resonators [53,[72][73][74]76] and reported values are well below the theoretical f•Q limit especially for lower frequencies. The lower than expected Q-factor of AlNbased resonators can be explained by losses associated with the metal electrode that is deposited on the AlN needed for driving the resonator [161,162].…”

“…The loop gain is defined by the combined transfer of the resonator and the sustaining amplifier. It therefore depends on the amplifier topology being applied [51,53]. The amplifier topology that is most easy to analyze is the transimpedance amplifier (TIA) with buffered output, as is shown in figure 9(a).…”

“…Often the transducer element and resonator body are identical as is the case in FBAR and BAW resonators where a standing wave is excited inside the piezoelectric film. The piezoelectric material that is used in MEMS resonators is almost exclusively PVD AlN [53,[71][72][73][74][75][76], but sometimes other materials such as ZnO [77] are used as well. An important disadvantage of AlN-based resonators is that the Q-factors that can be obtained are relatively low.…”

Dual-beam actuation of piezoelectric AlN RF MEMS switches monolithically integrated with AlN contour-mode resonators

“…Furthermore, the switch effectively turns off the resonator by lowering its transmission response by at least 39.5 dB. For example, this switch could effectively turn on and off a bank of different frequency AlN resonators placed in the same used in a Pierce oscillator circuit as was like the one demonstrated in [34].…”

Alumimun nitride piezoelectric NEMS resonators and switches

“…This FOM can be seen as a more rigorous way of expressing the same considerations presented in section 1 in regards to energy efficiency and electromechanical coupling in guiding the choice of a transduction mechanism over another. It turns out that the FOM of a resonator ends up directly impacting key device performance in electronic systems such as insertion loss in a filter 41 and power consumption in an oscillator 42 . Another important parameter to take into account in the design of a mechanical resonator and that relates directly to the device geometry (i.e.…”