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We present an experimental study of conservative nonlinearities in bulk acoustic mode (bulk-mode) silicon MEMS resonators with degenerate doping. Three types of bulk acoustic mode resonators oriented in $\langle 110\rangle $ and \langle 100\rangle $ silicon crystalline directions are used to analyze both linear and nonlinear elastic behavior of silicon with p- ( N \cong 4.19e+18$ to 1.63e+20 ) and n-type ( N \cong 1.58e+18$ to 5.91e+19$ cm ) doping. For accurate characterization of the amplitude-dependent nonlinear stiffness constant, we employ two methods: amplitude-frequency response and ringdown measurement. Experimental results show that the nonlinear behavior of these resonators is dominated by material-dependent mechanical nonlinearities and strongly depends on the doping type and crystal orientation. These results are useful for understanding the material-induced nonlinear properties of doped silicon and design of MEMS resonators with desired dynamic behavior, and may provide a new avenue for tailoring resonator response characteristics. [2015-0301] [ABSTRACT FROM AUTHOR]

Bias voltages are typically required for the operation of many capacitive microelectromechanical systems (MEMS) devices. A stored charge can be used in place of a bias voltage supply, granting benefits in terms of power consumption and circuit area. However, charges stored on a device typically tend to leak out over time to the environment, and in this paper, the charge storage capability of resonators fabricated in the epi-seal encapsulation platform is evaluated. Charges were introduced on the resonators using a mechanical switch located within the epi-seal cavity, and no leakage was observed over a year at room temperature. At higher temperatures, the leakage follows an Arrhenius relationship with an activation energy of 1.87 eV, with the leakage pathway believed to be through the buried silicon dioxide support. A 3-dB drop in the resonant peak requires a leakage time of approximately two days at 350 °C, indicating extreme charge trapping capabilities at lower temperatures are possible within the epi-seal platform. [2015-0091] [ABSTRACT FROM PUBLISHER]

In this paper, we present the fabrication and test results of an oxide-coated polysilicon disk resonator gyroscope in a wafer-scale encapsulation process. We demonstrate the effects of an oxide coating on the device structure and the key performance parameters of resonant-based sensors, such as the temperature coefficient of frequency and quality factor ( $Q$ ). Results from the as-fabricated device show that a thin oxide coating reduces the surface roughness of a fully encapsulated device by $10\times $ , compared with a polysilicon device without the oxide coating. This increases the uniformity across the wafer, providing higher process yield. The open-loop rate measurement mode reveals an angle random walk of 0.18°/ $\surd $ hr and a bias instability of 1.43°/hr. [2015-0124] [ABSTRACT FROM AUTHOR]

Resonators fabricated in heavily doped silicon have been noted to have a reduced frequency-temperature dependence compared with lightly doped silicon. The resonant frequency of silicon microelectromechanical systems (MEMS) resonators is largely governed by the material’s elastic properties, which are known to depend on doping. In this paper, a suite of different types and orientations of resonators were used to extract the first- and second-order temperature dependences of the elastic constants of p-doped silicon up to 1.7e20 \mathrmcm^\mathrm \mathbf -3 , and n-doped up to 6.6e19 \mathrmcm^\mathrm \mathbf -3 . It is shown that these temperature-dependent elastic constants may be used in finite element analysis to predict the frequency-temperature dependence of similarly doped silicon resonators. [2013-0331] [ABSTRACT FROM AUTHOR]

In this paper, we present four design methods to overcome (100) silicon crystalline anisotropy and achieve mode-matching in wineglass-mode disk resonator gyroscope (DRG). These methods were validated through experimental characterization of more than 145 different devices that arose from simulations. With the proposed methods, the frequency split of the 250-kHz DRG wineglass modes in (100) silicon was reduced from >10 kHz to as low as 96 Hz (<0.04% of 250-kHz resonant frequency) without any electrostatic tuning. Perfect mode-matching is then achieved using electrostatic tuning. Mode-matching was maintained within ±10 Hz over a temperature range from −20 °C to 80 °C. The temperature dependence of quality factor is also discussed in this paper. These results allow for the development of high-performance miniature DRGs tuned for degenerate wineglass mode operation from high-quality crystalline silicon material. [2013-0303] [ABSTRACT FROM AUTHOR]

The fatigue lifetime of single crystal silicon (SCS) was characterized in an environment free of oxygen, humidity, and organics. Long-term ( > 10^10 Hz) fatigue experiments performed with smooth-walled SCS devices showed no signs of fatigue damage up to 7.5 GPa. In contrast, experiments using SCS devices with a silicon dioxide (SiO2) coating and rough sidewalls due to scalloping from deep reactive ion etching exhibited fatigue drift at 2.7 GPa and suffered from short-term (< 10^10 Hz) fatigue failure at stress levels >3 GPa. In these SCS-SiO2 experiments, the initiation of fracture occurs in the SiO2 layer. It is concluded that fatigue in this case is likely attributed to a subcritical cracking mechanism; not reaction-layer nor dislocation related. A cross-comparison with other works from literature is developed to show that packaging a pristine device in an inert environment is necessary in order to operate devices at high-stress levels. [2013-0267] [ABSTRACT FROM AUTHOR]

The frequency stability of single-crystal silicon microelectromechanical systems resonators encapsulated with epitaxial polysilicon (epi-seal) is investigated. As silicon resonators have significant temperature dependence, the inherent frequency stability of the resonators is masked by temperature-induced noise. Using two resonators side-by-side and assuming identical temperatures and fluctuations, temperature effects are eliminated, resulting in the two resonators tracking each other within \pm10~ppb, or 3\,\times 10^-4^\circC, over a month. Power and thermal cycling the resonators produced no observable effects on the resonant frequency. This result indicates that silicon resonators make excellent on-chip thermometers, or high stability timing references if temperature is compensated well. [ABSTRACT FROM PUBLISHER]