This paper reports a three degree-of-freedom (3DoF) microelectromechanical systems (MEMS) resonant sensing device consisting of three weakly coupled resonators with enhanced sensitivity to stiffness change. If one resonator of the system is perturbed by an external stimulus, mode localization occurs, which can be detected by a change of modal amplitude ratio. The perturbation can be, for example, a change in stiffness of one resonator. A detailed theoretical investigation revealed that a mode aliasing effect, along with the thermal noise floor of the sensor and the associated electrical system ultimately limit the dynamic range of the sensor. The nonlinearity of the 3DoF sensor was also analyzed theoretically. The 3DoF resonator device was fabricated using a silicon on insulator process. Measurement results from a prototype device agreed well with the predictions of the analytical model. A significant, namely 49 times, improvement in sensitivity to stiffness change was evident from the fabricated 3DoF resonator sensor compared with the existing state-of-the-art 2DoF resonator sensors, while the typical nonlinearity was smaller than ±2% for a wide span of stiffness change. In addition, measurements indicate that a dynamic range of at least 39.1 dB is achievable, which could be further extended by decreasing the noise of the device and the interface electronics.

This paper systematically investigates the characteristics of different output metrics for a weakly coupled three degree-of-freedom microelectromechanical systems resonant sensor. The key figures-of-merit examined are sensitivity and linear range. The four main output metrics investigated are mode frequency shift, amplitude difference, amplitude ratio, and eigenstate shift. It is shown from theoretical considerations, equivalent RLC circuit model simulations and electrical measurements, that there is a strong tradeoff between sensitivity and linear range. For instance, the amplitude difference has the best sensitivity but the worst linear range, whereas frequency shift has the widest linear range but the lowest sensitivity. We also show that using the vibrational amplitude ratio as an output metric provides the best balance between sensitivity and linear range. [2016-0077].

Grayscale lithography allows the creation of micrometer-scale features with spatially controlled height in a process that is fully compatible with standard lithography. Here, solid immersion lenses are demonstrated in silicon carbide using a fabrication protocol combining grayscale lithography and hard-mask techniques to allow nearly hemispherical lenses of 5μm radius to be etched into the substrate. Lens performance was benchmarked by studying the enhancement obtained in the optical collection efficiency for single quantum emitters hosted in silicon carbide. Enhancement by a factor of 4.4 ± 1.0 was measured for emitters not registered to the center of the lens, consistent with devices fabricated through other methods. The grayscale hard-mask technique is highly reproducible, scalable, and compatible with CMOS technology, and device aspect ratios can be tuned after resist patterning by controlling the chemistry of the subsequent dry etch. These results provide a reproducible, low-cost, high-throughput and industrially relevant alternative to focused ion beam milling for the creation of high-aspect-ratio, rounded microstructures for quantum technology, and microphotonic applications.

We report the realization of an acoustic capacitive microphone formed by graphene/poly(methyl methacrylate) (PMMA). It is the first time that the ultra-large graphene/PMMA membrane suspended fully over the cavity has been fabricated by releasing the silicon dioxide sacrificial layer underneath the membrane. The novelty in the fabrication method is that the silicon dioxide layer has been etched by hydrogen fluoride vapor from the back of the partly etched silicon substrate. Using the new process, the ultra-large graphene/PMMA membrane, with a diameter to thickness ratio of 7800, has been suspended over the cavity with a 2 μm air gap. The spacing of 2 μm is the minimum gap over the graphene-based acoustic capacitive microphones which have been reported so far. The static deformation of the suspended graphene/PMMA membrane after silicon dioxide has been etched is estimated to be 270 nm. The aspect ratio of the membrane’s diameter over its static deformation is around 13,000, which shows that the graphene/PMMA membrane with a diameter of a few millimeters can be transferred and suspended over the substrate with relatively small deformation by releasing the sacrificial silicon dioxide layer. The dynamic behavior of the device under electrostatic actuation has been characterized. The acoustic response of the graphene/PMMA capacitive microphone has been measured, and the sensitivity has been observed to be −47.5 dB V (4.22 mV/Pa) ± 10%. The strain in the graphene/PMMA membrane is estimated to be 0.034%.