MEMS-based oscillators are an emerging class of highly miniaturized, batch manufacturable timing devices that can rival the electrical performance of well-established quartz-based oscillators. In this review, a description is given of the key properties of a MEMS resonator that determine the overall performance of a MEMS oscillator. Piezoelectric, capacitive and active resonator transduction methods are compared and their impact on oscillator noise and power dissipation is explained. An overview is given of the performance of MEMS resonators and MEMS-based oscillators that have been demonstrated to date. Mechanisms that affect the frequency stability of the resonator, such as temperature-induced frequency drift, are explained and an overview is given of methods that have been demonstrated to improve the frequency stability. The aforementioned performance indicators of MEMS-based oscillators are benchmarked against established quartz and CMOS technologies.

https://iopscience.iop.org/article/10.1088/0960-1317/22/1/013001/pdf

A review of MEMS oscillators for frequency reference and timing applications

WHEN metals are submitted to stress, the stress/swain relation is generally regarded as consisting of two parts, the elastic region and the region bfsplastiwin which a permanent set remains upon the remova of the stress. In the elastic region the absence of a permanent set does not necessarily imply that the relation between stress and strain is linear of even single-valued. Prof. Zener uses the term ‘anelasticity’ to describe the properties of solids, as a result of which stress and strain are not uniquely related. Examples are the elastic after-effect, the dependence of elastic constants on the method of measurement, and the dissipation of energy during vibration, which is often referred to as the damping capacity or internal friction of a solid. These effects have aroused much interest in recent years, largely owing to Prof. Zener's own work, and a good book on the subject is much to be desired. Elasticity and Anelasticity of Metals By Clarence Zener. Pp. x + 170. (Chicago: University of Chicago Press, London: Cambridge University Press, 1948.) 4 dollars.

Elasticity and Anelasticity of Metals

Background and History. Resonator and Filter Topologies. Baw Device Basics. Design and Fabrication of BAW Devices. FBAR Resonators and Filters. Comparison with SAW Devices. Films Deposition for BAW Devices. Characterization of BAW Devices. Monolithic Integration. System-in-Package (SiP) Integration. Index.

RF bulk acoustic wave filters for communications

This review surveys micromachined gyroscope structure and circuitry technology The principle of micromachined gyroscopes is first introduced Then, different kinds of MEMS gyroscope structures, materials and fabrication technologies are illustrated Micromachined gyroscopes are mainly categorized into micromachined vibrating gyroscopes (MVGs), piezoelectric vibrating gyroscopes (PVGs), surface acoustic wave (SAW) gyroscopes, bulk acoustic wave (BAW) gyroscopes, micromachined electrostatically suspended gyroscopes (MESGs), magnetically suspended gyroscopes (MSGs), micro fiber optic gyroscopes (MFOGs), micro fluid gyroscopes (MFGs), micro atom gyroscopes (MAGs), and special micromachined gyroscopes Next, the control electronics of micromachined gyroscopes are analyzed The control circuits are categorized into typical circuitry and special circuitry technologies The typical circuitry technologies include typical analog circuitry and digital circuitry, while the special circuitry consists of sigma delta, mode matching, temperature/quadrature compensation and novel special technologies Finally, the characteristics of various typical gyroscopes and their development tendency are discussed and investigated in detail

The Development of Micromachined Gyroscope Structure and Circuitry Technology

Gallium nitride (GaN) is a wide bandgap semiconductor material and is the most popular material after silicon in the semiconductor industry. The prime movers behind this trend are LEDs, microwave, and more recently, power electronics. New areas of research also include spintronics and nanoribbon transistors, which leverage some of the unique properties of GaN. GaN has electron mobility comparable with silicon, but with a bandgap that is three times larger, making it an excellent candidate for high-power applications and high-temperature operation. The ability to form thin-AlGaN/GaN heterostructures, which exhibit the 2-D electron gas phenomenon leads to high-electron mobility transistors, which exhibit high Johnson's figure of merit. Another interesting direction for GaN research, which is largely unexplored, is GaN-based micromechanical devices or GaN microelectromechanical systems (MEMS). To fully unlock the potential of GaN and realize new advanced all-GaN integrated circuits, it is essential to cointegrate passive devices (such as resonators and filters), sensors (such as temperature and gas sensors), and other more than Moore functional devices with GaN active electronics. Therefore, there is a growing interest in the use of GaN as a mechanical material. This paper reviews the electromechanical, thermal, acoustic, and piezoelectric properties of GaN, and describes the working principle of some of the reported high-performance GaN-based microelectromechanical components. It also provides an outlook for possible research directions in GaN MEMS.

Gallium Nitride as an Electromechanical Material

Nanomechanical resonators that can operate in the super high frequency (3–30 GHz) or the extremely high frequency (30–300 GHz) regime could be of use in the development of stable frequency references, wideband spectral processors and high-resolution resonant sensors. However, such operation requires the dimensions of the mechanical resonators to be reduced to tens of nanometres, and current devices typically rely on transducers, for which miniaturization and chip-scale integration are challenging. Here, we show that integrated nanoelectromechanical transducers can be created using 10-nm-thick ferroelectric hafnium zirconium oxide (Hf0.5Zr0.5O2) films. The transducers are integrated on silicon and aluminium nitride membranes, and can yield resonators with frequencies from 340 kHz to 13 GHz and frequency–quality-factor products of up to 3.97 × 1012. Using electrical and optical probes, we show that the electromechanical transduction behaviour of the Hf0.5Zr0.5O2 film is based on the electrostrictive effect, and highlight the role of nonlinear electromechanical scattering in the operation of the resonator. Nanomechanical resonators with frequencies from 340 kHz to 13 GHz can be created using an integrated 10-nm-thick transducer layer of hafnium zirconium oxide.

/pdf/an-ultrathin-integrated-nanoelectromechanical-transducer-1vf7cjwq6x.pdf

An ultrathin integrated nanoelectromechanical transducer based on hafnium zirconium oxide

This paper reports on the design, fabrication, and characterization of a small form factor, piezoelectrically transduced, tunable micromechanical resonator for real-time clock (RTC) applications (32.768 kHz). The device was designed to resonate in an out-of-plane flexural mode to simultaneously achieve low-frequency operation and reduced motional resistance in a small die area. Finite element simulations were extensively used to optimize the structure in terms of size, insertion loss, spurious-mode rejection, and frequency tuning. Microresonators with an overall die area of only 350 × 350 μm were implemented on a thin-film AlN on silicon-on-insulator (SOI) substrate with AlN thickness of 0.5 μm, device layer of 1.5 μm, and an electrostatic tuning gap size of 1 μm. A frequency tuning range of 3100 ppm was measured using dc voltages of less than 4 V. This range is sufficient to compensate for frequency variations of the microresonator across temperature from -20°C to 100°C. The device exhibits low motional impedance that is completely independent of the frequency tuning potential. Discrete electronics were used in conjunction with the resonator to implement an oscillator, verifying its functionality as a timing reference.

Electrostatically tunable piezoelectric-on- silicon micromechanical resonator for real-time clock

Recent years have witnessed breakthrough researches in micro- and nano-mechanical resonators with small dissipation.
Nano-precision micromachining has enabled the realization of integrated micromechanical resonators with record high Q
and high frequency, creating new research horizons. Not too long ago, there was a perception in the MEMS community
that the maximum f.Q product of a microresonator is limited to a frequency-independent constant determined by the
material properties of the resonator. In this paper, the contribution of phonon interactions in determining the upper limit
of f.Q product in micromechanical resonators will be discussed and shown that after certain frequency, the f.Q product is
no longer constant but a linear function of frequency. This makes it possible to reach very high Qs in GHz micro- and
nano-mechanical resonators and filters. Contributions of other dissipation mechanisms such as thermoelastic damping
and support loss in the quality factor of a microresonator will be discussed as well.

Energy dissipation in micromechanical resonators

This paper reports on a new temperature compensation technique for high-Q AlN-onSilicon bulk acoustic wave resonators. A uniform array of silicon dioxide (SiO2) pillars are formed in the silicon body of the resonator to generate a composite resonator with a near-zero temperature coefficient of frequency (TCF). At a resonance frequency of 24MHz, a total frequency drift of 90 ppm over the temperature range of −20 °C to 100 °C was measured while Q exceeded 10,000 at all temperatures. This compensation technique is applicable to bulk acoustic resonators with thick silicon substrate that demonstrate high Q as well as good power handling and linearity. Copyright Notice

/pdf/temperature-stable-high-q-aln-on-silicon-resonators-with-4bn0p0mnle.pdf

Temperature-Stable High-Q AlN-on-Silicon Resonators with Embedded Array of Oxide Pillars

This paper reports on the design, simulation and characterization of small form factor, tunable piezoelectric MEMS resonators for real time clock applications (32.768 kHz). The structures were fabricated on a thin-film AlN-on-SOI substrate to enable piezoelectric actuation of an out-of-plane flexural mode, as well as electrostatic frequency tuning by utilizing the handle layer as a DC voltage electrode. Resonators of only a few hundred of µm in size exhibit greater than 3100 ppm of tuning using voltages no larger than 4 V; this tuning sufficiently compensates for frequency variations across temperature from −25 to 100 °C. The devices exhibit low motional impedance that is completely independent of the tuning potential.

Roozbeh Tabrizian

Papers

An ultrathin integrated nanoelectromechanical transducer based on hafnium zirconium oxide

Electrostatically tunable piezoelectric-on- silicon micromechanical resonator for real-time clock

Energy dissipation in micromechanical resonators

Temperature-Stable High-Q AlN-on-Silicon Resonators with Embedded Array of Oxide Pillars

Tunable piezoelectric MEMS resonators for real-time clock