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

We discuss the contribution of phonon interactions in determining the upper limit of f.Q product in micromechanical resonators. There is 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 [1]. In this paper, we discuss that for frequencies higher than ω τ = 1/τ, where τ is the phonon relaxation time, 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 micromechanical resonators. Moreover, we show that 〈100〉 is the preferred crystalline orientation for obtaining very high Q in bulk-acoustic-mode silicon resonators above ∼750 MHz, while 〈100〉 is the preferred direction for achieving high-Q at lower frequencies.

/pdf/effect-of-phonon-interactions-on-limiting-the-f-q-product-of-43v0vse8gl.pdf

Effect of phonon interactions on limiting the f.Q product of micromechanical resonators

This paper presents a passive temperature compensation technique that can provide full cancellation of the linear temperature coefficient of frequency (TCF1) in silicon resonators. A uniformly distributed matrix of silicon dioxide pillars is embedded inside the silicon substrate to form a homogenous composite silicon oxide platform (SilOx) with nearly perfect temperature-compensated stiffness moduli. This composite platform enables the implementation of temperature-stable microresonators operating in any desired in- and out-of-plane resonance modes. Full compensation of TCF1 is achieved for extensional and shear modes of SilOx resonators resulting in a quadratic temperature characteristic with an overall frequency drift as low as 83 ppm over the industrial temperature range ( -40°C to 80°C). Besides a 40 times reduction in temperature-induced frequency drift in this range, SilOx resonators exhibit improved temperature stability of Q compared with their single crystal silicon counterparts.

Temperature-Stable Silicon Oxide (SilOx) Micromechanical Resonators

In this paper, we present dual-mode (DM) AlN-on-silicon micromechanical resonators for self-temperature sensing. In-plane width-shear (WS) and width-extensional (WE) modes of [110]-oriented silicon resonators have been used as alternatives to first- and third-order modes to enhance DM temperature sensitivity by engineering device geometry, which reduces inherent beat frequency fb between the two modes. This configuration provides a 50× improvement in temperature coefficient of beat frequency (TCfb) compared with single-mode temperature measurement and eliminates the need for additional frequency multipliers to generate fb from its constituents. [100]-oriented WS/WE resonators provide 4× larger TCF difference between modes (ΔTCF) than first and third width-extensional resonators, which further contributes to TCfb enhancement. WS/WE mode resonators also demonstrate the capability of operating as a temperature-stable reference fb. The proposed modes for DM operation have high Q and low motional resistance, and are 180 ° out-of-phase when operated in two-port configuration, thus enabling mode-selective low-power oscillator interfacing for resonant temperature sensing.

Dual-Mode AlN-on-Silicon Micromechanical Resonators for Temperature Sensing

This paper reports on the design, implementation and characterization of a low phase-noise 27 MHz MEMS oscillator with sub-ppm temperature instability based on a high-Q composite bulk acoustic wave (BAW) resonator. An array of silicon dioxide (SiO 2 ) pillars has been uniformly embedded in the body of a piezoelectrically transduced silicon resonator to compensate its negative temperature coefficient of frequency (TCF). Using this technique, an overall frequency drift of 83 ppm is achieved for the resonator over the temperature range of −20°C to 100°C while resonator Q remains greater than 7,500 in atmospheric pressure. An electronically compensated oscillator using this resonator exhibits sub-ppm temperature instability with a consistent phase noise (PN) behavior over the entire temperature range and a value of −101dBc/Hz at 1 kHz offset-frequency. Long-term stability measurement has been carried out for both temperature-compensated resonator and oscillator in an environmental chamber to study their stability over time.

A 27 MHz temperature compensated MEMS oscillator with sub-ppm instability

This letter reports, for the first time, on a high-frequency resonant square micro-gyroscope using piezoelectric transduction. Degenerate pairs of orthogonal flexural resonance modes are used to provide energy exchange paths for the Coriolis-based resonant gyroscope in response to z-axis rotation. Aluminum nitride thin films have been used to provide highly efficient electromechanical transduction for drive and sense modes without requiring any dc polarization voltage for operation. A proof-of-concept design consisting of a 300 μm× 300 μm square gyro shows linear rate sensitivity of 20.38 μV/°/s when operating in its first flexural mode at ~ 11 MHz.

Roozbeh Tabrizian

Papers

Effect of phonon interactions on limiting the f.Q product of micromechanical resonators

Temperature-Stable Silicon Oxide (SilOx) Micromechanical Resonators

Dual-Mode AlN-on-Silicon Micromechanical Resonators for Temperature Sensing

A 27 MHz temperature compensated MEMS oscillator with sub-ppm instability

High-Frequency AlN-on-Silicon Resonant Square Gyroscopes