Effects of Material and Dimension on TCF,Frequency,and Q of Radial Contour Mode AlN-on-Si MEMS Resonators

This paper investigates the effects of material and dimension parameters on the frequency splitting,frequency drift,and quality factor(Q)of aluminium nitride(AlN)-on-n-doped/pure silicon(Si)microelectromechanical systems(MEMS)disk resonators through analysis and simulation.These parameters include the crystallographic orientation,dopant,substrate thickness,and temperature.The resonators operate in the elliptical,higher order,and flexural modes.The simulation results show that i)the turnover points of the resonators exist at 55°C,-50°C,40°C,and-10°C for n-doped silicon with the doping concentration of 2×1019 cm-3 and the Si thickness of 3.5μm,and these points are shifted with the substrate thickness and mode variations;ii)compared with pure Si,the modal-frequency splitting for n-doped Si is higher and increases from 5%to 10%for all studied modes;iii)Q of the resonators depends on the temperature and dopant.Therefore,the turnover,modal-frequency splitting,and Q of the resonators depend on the thickness and material of the substrate and the temperature.This work offers an analysis and design platform for high-performance MEMS gyroscopes as well as oscillators in terms of the temperature compensation by n-doped Si.

Design and characterization of a 3D encapsulation with silicon vias for radio frequency micro-electromechanical system resonator

In this paper, we present a three-dimensional（3D） vacuum packaging technique at a wafer level for a radio frequency micro-electromechanical system（RF MEMS） resonator, in which low-loss silicon vias is used to transmit RF signals.Au–Sn solder bonding is adopted to provide a vacuum encapsulation as well as electrical conductions. A RF model of the encapsulation cap is established to evaluate the parasitic effect of the packaging, which provides an effective design solution of 3D RF MEMS encapsulation. With the proposed packaging structure, the signal-to-background ratio（SBR） of 24 dB is achieved, as well as the quality factor（Q-factor） of the resonator increases from 8000 to 10400 after packaging.The packaged resonator has a linear frequency–temperature（ f –T） characteristic in a temperature range between 0℃ and 100℃. And the package shows favorable long-term stability of the Q-factor over 200 days, which indicates that the package has excellent hermeticity. Furthermore, the average shear strength is measured to be 43.58 MPa among 10 samples.

VIBRATION MEASUREMENT OF DOUBLE-ENDED TUNING FORKS RESONATOR

To enhance the coherence and reliability of the double-ended tuning fork （DETF） resonator, a measurement system of resonator vibration is presented to check its dynamic characteristics. Laser Doppler techniques are utilized and the relation between DETF vibration velocity and output current of photodetector is obtained. Resonator vibration equation is also analyzed and its driving power only depends on the direct current bias voltage and the amplitude of alternative voltage. Furthermore, a special resonator driving control circuit based on measurement is designed. The amplitude and frequency of circuit is controlled by a computer so that highly stable and strong driving signal can be output. Experiments on driving and measuring double-ended tuning fork have been done, The frequency of driving signal is 8 kHz and the peak-to-peak value of driving voltage is 140 V. Experimental results indicate resonator can be drived stably by driving control circuit and dynamic characteristics of DETF may be measured in real time.

A review: aluminum nitride MEMS contour-mode resonator

Over the past several decades, the technology of micro-electromechanical system（MEMS） has advanced. A clear need of miniaturization and integration of electronics components has had new solutions for the next generation of wireless communications. The aluminum nitride（AlN） MEMS contour-mode resonator（CMR）has emerged and become promising and competitive due to the advantages of the small size, high quality factor and frequency, low resistance, compatibility with integrated circuit（IC） technology, and the ability of integrating multi-frequency devices on a single chip. In this article, a comprehensive review of AlN MEMS CMR technology will be presented, including its basic working principle, main structures, fabrication processes, and methods of performance optimization. Among these, the deposition and etching process of the AlN film will be specially emphasized and recent advances in various performance optimization methods of the CMR will be given through specific examples which are mainly focused on temperature compensation and reducing anchor losses. This review will conclude with an assessment of the challenges and future trends of the CMR.

Analysis of reliability factors of MEMS disk resonator under the strong inertial impact

Increasing the bias voltage is a method of reducing the motional resistance of the capacitive disk res- onator to match the impedance of the RF circuit. But there are few reports on the study of reliable working range of bias voltage under the shock and vibration environment. Therefore, the reliability of disk resonator under the step and pulse acceleration impact respectively is systematically analyzed in this paper. By the expression of the biggest inertial acceleration the disk can bear under the reliable condition, the maximal reliable range curves of the disk resonator under the dynamic impact environment are obtained. According to the actual sizes of disk in the literature, it can be seen that when a step shock of 13000g is supplied, the reliability range is reduced to 75% compared with the original state. For the pulse shock, the reliability range is related to the pulse amplitude and time width. Research of this paper can provide the basis for the selection of bias voltage of disk resonator under the inertial shock.

On-chip mechanical computing:status,challenges,and opportunities

With increasing challenges towards continued scaling and improve-ment in performance faced by electronic computing,mechanical com-puting has started to attract growing interests.Taking advantage of the mechanical degree of freedom in solid state devices,micro/nano-electromechanical systems(MEMS/NEMS)could provide alternative solutions for future computing and memory systems with ultralow power consumption,compatibility with harsh environments,and high reconfigurability.In this review,MEMS/NEMS-enabled memories and logic processors were surveyed,and the prospects and challenges for future on-chip mechanical computing were also analyzed.

Resonant pitch and roll silicon gyroscopes with sub-micron-gap slanted electrodes:Breaking the barrier toward high-performance monolithic inertial measurement units

This paper presents the design,fabrication,and characterization of a novel high quality factor(Q)resonant pitch/roll gyroscope implemented in a 40μm(100)silicon-on-insulator(SOI)substrate without using the deep reactive-ion etching(DRIE)process.The featured silicon gyroscope has a mode-matched operating frequency of 200 kHz and is the first out-of-plane pitch/roll gyroscope with electrostatic quadrature tuning capability to fully compensate for fabrication non-idealities and variation in SOI thickness.The quadrature tuning is enabled by slanted electrodes with sub-micron capacitive gaps along the(111)plane created by an anisotropic wet etching.The quadrature cancellation enables a 20-fold improvement in the scale factor for a typical fabricated device.Noise measurement of quadrature-cancelled mode-matched devices shows an angle random walk(ARW)of 0.63°√h^(−1) and a bias instability of 37.7°h^(−1),partially limited by the noise of the interface electronics.The elimination of silicon DRIE in the anisotropically wet-etched gyroscope improves the gyroscope robustness against the process variation and reduces the fabrication costs.The use of a slanted electrode for quadrature tuning demonstrates an effective path to reach high-performance in future pitch and roll gyroscope designs for the implementation of single-chip high-precision inertial measurement units(IMUs).