A 10-MHz FREE-FREE BEAM MICROMECHANICAL RESONATOR FABRICATION PROCESS USING SURFACE-MICROMACHINED TECHNOLOGY

The fabrication process for the designed MEMS resonator using surface-micromachined technology is presented in this paper. A 10-MHz Free-Free beam MEMS resonator is designed to vibrate in the second-mode shape, which is significant improvement compare to the fundamental mode. The design showed a Q value as high as 75,000, which is significant improvement compared to 8,400 VHF F-F beam MEMS resonator by K. Wang; and very low motional resistance (18kΩ). The surface-micromachined technology is used as the standard process for the design. The process is briefly described from the layout design to the experimental fabricated device.

PLL-based nanoresonator driving IC with automatic parasitic capacitance cancellation and automatic gain control

This paper presents a phase-locked loop (PLL) based resonator driving integrated circuit (IC) with automatic parasitic capacitance cancellation and automatic gain control. The PLL consisting of a phase frequency detector (PFD), a loop filter, and a voltage-controlled oscillator (VCO) makes the driving frequency to be locked at the resonant frequency. The resonator is modeled by Butterworth–Van Dyke equivalent circuit model with motional resistance of 72.8 kΩ, capacitance of 6.19 fF, inductance of 79.4 mH, and parasitic parallel capacitance of 2.59 pF. To mitigate the magnitude and phase distortion in the resonator frequency response, it is necessary to compensate for the parasitic capacitance. The proposed automatic parasitic capacitance cancellation loop is operated in the open-loop mode. In the automatic parasitic capacitance cancellation phase, the outputs of the transimpedance amplifier (TIA) at the lower and higher frequency than the resonant frequency (VH and VL), are compared, and the programmable compensation capacitor array matches the VH and VL using binary-searched algorithm to cancel the parallel parasitic capacitance. The automatic gain control (AGC) loop keeps the oscillation at the suitable amplitude, and the AGC output can be used as a measurement of the motional resistance. The AGC loop is also digitally controlled. The proposed resonator driving IC is designed in a 0.18-μm bipolar complementary metal oxide semiconductor double-diffused metal oxide semiconductor (BCDMOS) process with an active area of 3.2 mm2. The simulated phase noise is −61.1 dBc/Hz at 1 kHz and the quality factor ( Q-factor) is 59,590.

Multi-objective Design Optimization of Microdisk Resonator

Objective: This paper presents a multi-objective design optimization of MEMS disk resonator using two techniques. Methods: Determining the optimized dimensions of disk resonator for a particular resonance frequency so as to achieve higher quality factor and lower motional resistance is attempted. One technique used is constraint-based multi-objective optimization using the interior-point algorithm. The second technique is based on multi-objective genetic algorithm. Results: The algorithms are implemented using MATLAB. The two techniques of optimization are compared. Conclusion: The developed optimization methods can provide faster design optimization compared to full-wave simulators resulting in significant reduction of design time.

ANN Modeling of Motional Resistance for Micro Disk Resonator

This article describes how modeling is an integral part of design and development of any system that provides the theoretical characterization of the system and helps in understanding the relations between various parameters of the system, before the system is developed. The capability of an Artificial Neural Network (ANN) to model the complex relations between a set of inputs and outputs is exploited to model the motional resistance and resonance frequency for a contour mode disk resonator. The solution was to develop a multilayer feed forward neural network. The data set required to train the ANN is obtained by developing an electrical equivalent model and through the MEMS simulation software Coventorware. The network is trained using a Levenberg Marquardt algorithm. The number of hidden layers and the number of neurons in each hidden layer is optimized using a genetic algorithm. The ANN model developed an efficient model of the motional resistance and resonance frequency of the disk resonator. The ANN output is compared with the output of an electrical equivalent model and a reported fabricated structure.

Nanotribological Performance Factors for Aqueous Suspensions of Oxide Nanoparticles and Their Relation to Macroscale Lubricity

Quartz crystal microbalance (QCM) measurements of nanotribological properties of statistically diverse materials combinations of nanoparticles and substrate electrodes in aqueous suspensions are reported and compared to macroscale measurements of the same materials combinations for a subset of the nanoparticle combinations. Four ceramic nanoparticles, TiO2, SiO2, Al2O3, and maghemite (γ-Fe2O3) and ten substrate materials (Au, Al, Cr, Cu, Mo, Ni, Pt, SiO2, Al2O3, and SS304) were studied. The QCM technique was employed to measure frequency and motional resistance changes upon introduction of nanoparticles into the water surrounding its liquid-facing electrode. This series of experiments expanded prior studies that were often limited to a single nanoparticle - solid liquid combination. The variations in QCM response from one nanoparticle to another are observed to be far greater than the variation from one substrate to another, indicating that the nanoparticles play a larger role than the substrates in determining the frictional drag force levels. The results were categorized according to the direction of the frequency and motional resistance changes and candidate statistical performance factors for the datasets were generated. The performance factors were employed to identify associations between the QCM atomic scale results and the macroscale friction coefficient measurements. Macroscale measurements of friction coefficients for selected systems document that reductions (increases) in motional resistance to shear, as measured by the QCM, are linked to decreases (increases) in macroscale friction coefficients. The performance factors identified in the initial study therefore appear applicable to a broader set of statistically diverse samples. The results facilitate full statistical analyses of the data for identification of candidate materials properties or materials genomes that underlie the performance of nanoparticle systems as lubricants.

Self-Sustaining Square-Extensional Mode Resonator Oscillator for Mass Sensing in Liquid

We present a 5.41 MHz square-extensional (SE) mode resonator in closed-loop oscillation for resonant mass sensing in the liquid phase. The resonator has been fabricated in piezoelectric thin film aluminum nitride (AlN) on silicon (Si). The strain profile of the SE mode allows for higher electromechanical coupling efficiency using piezoelectric transduction to lower the motional resistance (Rm) given the expected low quality factors (Q) in liquid (136 compared to 942 in air). By locking the device into self-sustained oscillation, the minimum detectable frequency shift is reduced from 3680 ppm (open-loop in water) to 8.76 ppm (closed-loop in air).