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A micro Coriolis flow sensor accurately measures small mass flows without being affected by properties of the fluid. This paper presents a micro Coriolis mass flow sensor driven by PZT thin film piezoelectric actuators, which allows a combination of large actuation force, low power dissipation and virtually no self-heating. The sensor was fabricated using surface channel technology, resulting in a tube diameter of 40 $\mu \text{m}$ and a thin silicon-rich silicon nitride tube wall of 1.2 $\mu \text{m}$ thick, with a few additional steps to form the integrated piezoelectric actuators. The integrated actuators can actuate the sensor into both swing mode and twist mode. Both actuation modes were evaluated for different fluids and the results are presented in this paper. In the case of swing mode actuation, an optical readout was used to detect the resulting Coriolis movement, resulting in a relatively low sensitivity. In the case of twist mode actuation, a capacitive readout was used and, in comparison to previously published devices, a high mass flow sensitivity was achieved thanks to an optimized readout design. The measurement results show the read-out noise has a standard deviation of 0.15% of the full scale of 1.8 gh−1 when actuated in the twist mode. [2020-0392] [ABSTRACT FROM AUTHOR]

Silicon microfabrication technology was employed in the generation of a cavity in the form of a truncated inverted pyramid with very smooth sidewalls and a silicon dioxide UV transparent optical window at the bottom. This can be used as a micro-cuvette for testing of fluids. 100nl fluid volumes can be tested using this platform by ultraviolet absorbance spectroscopy employing a deuterium lamp and an UV spectrometer. Mixtures of commercially sourced diesel with ethanol, and diesel with kerosene were tested in this work. Two zones of interest were identified in the absorption spectrum of diesel. For a 0 to 10% diesel in ethanol mixture, a clear shift of the UV absorption edge from 297nm to 336nm was observed. For the diesel in kerosene mixture a linear shift of the absorption edge from 335nm to 365nm was observed for the entire composition range. Our results indicate that a single wavelength source and detector at 345nm is sufficient to determine the diesel in kerosene composition using this micro-cuvette, which would be very useful in detection of adulteration in fuels. [2020-0344] [ABSTRACT FROM AUTHOR]

This paper reports on the investigation of anomalous low quality factors (${Q}\text{s}$) in AlN thin film-based length extensional (LE)-mode resonators using finite element method (FEM), analytical modeling, and experimental techniques. Different heterostructures of LE resonators having Al/AlN/Si, Al/AlN, AlN/Si, and Si are designed and fabricated using standard MEMS processes. Experimental ${Q}\text{s}$ along with resonances are obtained using electrical and optical readout and are compared with the modeled and analytically obtained ${Q}\text{s}$. The results show that the thermoelastic damping (TED) in metal electrode, anchor loss, and charge redistribution loss are not the dominant loss mechanisms. With the help of Mason’s network modeling, we investigated the dielectric loss, which is also observed to be negligible for these resonators. An internal mechanical loss, originating from the columnar growth of AlN and observed using Mason’s model, is proved to be the dominant loss mechanism. This observation is confirmed and reinforced by the COMOSL’s FEM analysis of TED in AlN, having columnar growth effect and by experimental results. [2018-0258] [ABSTRACT FROM AUTHOR]

The optical knife-edge displacement measurement technique can be used to quantify in-plane vibrations of microstructures at radio frequencies. This paper presents an analytical model and experimental results for this technique that demonstrate precise displacement measurements for electrostatic microelectromechanical resonators at frequencies ranging from 13 MHz to 895 MHz. It is also shown that high-resolution spatial mapping of displacement mode shapes for fundamental and higher order vibration modes can be achieved. The optical knife-edge measurements have a resolution as low as 455 fm/ $\surd$ Hz at 13.6 MHz, and under 1 pm/ $\surd$ Hz up to 1.4 GHz. This paper expands the capabilities of the knife-edge technique by working with all types of in-plane microelectromechanical resonators, improving the resolution by at least a factor of 2, and increasing the frequency range by a factor of 60. [2018-0094] [ABSTRACT FROM AUTHOR]

This paper presents the curvature characterization results of released back-end-of-line 5~\mu \textm -wide cantilevers for two different 0.18- \mu \textm 1P6M complementary metal–oxide semiconductor microelectromechanical systems processes. Results from different runs and lots from each foundry are presented. The methodology and accuracy of the characterization approach, based on optical measurements of test cantilever curvature, are also discussed. Special emphasis is given to the curvature average and variability as a function of the number of stacked layers. Analythical equations for modeling the bending behavior of stacked cantilevers as a function of the tungsten (W) vias that join the metal layers are presented. In addition, the effect of various post-processing conditions and design techniques on the curvature of both single and stacked cantilevers is analyzed. In particular, surpassing certain time-dependent temperature stress conditions after release lead to curvature shifts larger than one order of magnitude. Also, the W via design was found to strongly affect the curvature of the test cantilevers. [2016-0293] [ABSTRACT FROM PUBLISHER]

This paper presents the characterization results of the release step with vapor hydrofluoric acid on a Complementary Metal Oxide Semiconductor-Microelectromechanical Systems (CMOS-MEMS) process obtained with a new methodology for controlling the release etch process of CMOS-MEMS devices. The effect of release hole size on etch rate and uniformity was investigated. No appreciable effects were observed for release hole sizes between 0.48 and 1 \mu \textm^2 . With-in-wafer uniformity better than 3% and wafer-to-wafer variability better than 2.5% were found, while achieving constant etch rates of $\sim 0.25~\mu $ mmin ^{-1} and maintaining the required selectivity. The new characterization methodology is based on monitoring capacitance values of a set of test structures distributed across the analyzed wafers rather than monitoring oxide undercuts. A new parameter defined as etch ratio greatly improved the accuracy of this methodology by removing undesirable contributions to the capacitance coming from sources not related to the release process itself. Results showed that this methodology provides a characterization accuracy one order of magnitude better than what was achieved with a method based on optical measurements of oxide lateral undercuts. [2015-0290] [ABSTRACT FROM PUBLISHER]

Glaucoma is a group of degenerative ocular diseases that affects millions of people worldwide. While the causes of glaucoma are still unidentified, there are recent studies that establish a link between glaucoma and the age-related loss in accommodation (presbyopia) resulting from the increasing inelasticity of the membrane attaching the ciliary muscle to the back of the eye. Consequently, to understand this relationship better, it becomes imperative that we be able to measure the strain at the choroid and correlate it with the intraocular pressure within the eye. Here, we report the development of an implantable, flexible, and biocompatible optical strain sensor based on a near-wavelength high contrast grating array. The change in the grating period corresponding to the choroidal strain results in a change in the observed color, allowing us to observe and measure small deformations. [2018-0034] [ABSTRACT FROM AUTHOR]

With the development of silicon micromachining technologies, non-contact measurement techniques for in-depth non-destructive inspection of layered and microstructured samples are becoming increasingly relevant. In this paper, we apply optical low-coherence reflectometry (OLCR) to detect the optical path between the interfaces of several silicon devices with characteristic distance in the range 3–17 \mu \textm . The implemented configuration is based on a fiberoptic Michelson interferometer that exploits infrared broadband radiation in the wavelength range of 1.2–1.7 \mu \textm , with coherence length shorter than 2 \mu \textm , for performing spot tomographic measurements. OLCR enabled out-of-plane measurements on a MEMS linear accelerometer and in-plane measurements on vertical periodic silicon/air microstructures. The optical distance between hidden interfaces was found well in agreement with the design parameters. [2015-0108] [ABSTRACT FROM AUTHOR]

We present the design, fabrication, and optical and mechanical characterization of silicon-/silicon-oxide-based optical filters and distributed Bragg reflectors in sizes ranging from 500 ~\mu m \times 500 ~\mu m to 5~mm \times 5~mm . They are designed to be used in conjunction with either single-element photodetectors or large-area focal plane arrays to realize tunable multispectral sensors or adaptive focal plane arrays in the shortwave infrared wavelength range. Surface optical profile measurements indicate a flatness of the order of 30 nm in the fabricated structures across several millimeters. Single-point spectral measurements on devices show an excellent agreement with simulated optical models, and demonstrate Si-SiOx-Si fixed optical filters with a 94% transmission at 1940 nm with a full-width at half-maximum of 250 nm. Distributed Bragg reflectors demonstrate 90% reflectance across the 1560–2050-nm wavelength range, making them suitable as broadband reflectors. The optical spatial uniformity across a 3-mm $\times 3$ -mm device shows only a 3% variation across the entire optically active area. Finally, the mechanical resonance characteristic of a 1-mm $\times 1$ -mm fabricated device shows the lowest resonant frequency of the suspended structure to be 39 kHz, indicating excellent immunity to extraneous low-frequency vibrations. [2014-0278] [ABSTRACT FROM AUTHOR]

A 1.2-mm-diameter gold–silicon bimorph varifocal micromirror (VFM) has been designed and investigated for imaging applications. Several prototypes have been fabricated in a 10-\mu \m-thick single-crystal silicon-on-insulator material. Controlled variation of the radius of curvature using electrothermal and optothermal actuation has been demonstrated. A finite-element-based simulation of the device behavior has been undertaken. Experimental characterization has shown that the device focusing power varied from an initial 87 dioptre to 69 dioptre by applying dc electrical power of 33 mW and produced a focusing power value of 59 dioptre when optothermally actuated with a normally incident laser beam of 488-nm wavelength and 43 mW. When electrothermally driven, the mechanical rise and fall times of the device were measured as 130 and 120 ms, respectively. Experimental and theoretical analyses using Zernike coefficients show that, throughout the actuation range, the aberration of the VFM is mainly a small defocus term, with negligible higher order aberrations. A compact active imaging system incorporating the VFM has been also demonstrated. This system was capable of focusing several objects located along the optical axis with a maximum tracking range of 134 mm. \hfill[2012-0175] [ABSTRACT FROM PUBLISHER]

A simple optical method is proposed for performing in-plane experimental modal analysis of micromachined structures with a conventional charge-coupled device (CCD) camera. The motion of a micromechanical device actuated by high-frequency sinusoidal forces (kilohertz range) is recorded at the fixed sampling rate of a camera (typically, 28 frames/s) which is configured with a short shutter aperture time (1/5000 s). Provided a CCD sensor with sufficient sensitivity, much information is contained in the video on the dynamics of the vibrating system despite the limited frame rate. Taking advantage of the theory of undersampling, we show that the dynamics of the systems with several-kilohertz bandwidth can be retrieved very easily. For demonstration purposes, we first study a push–pull electrostatic comb-drive actuator, which is a well-known damped harmonic oscillator system. Then, we show that our measurement method also provides useful information on the behavior of nonlinear systems. In particular, we can characterize the systems' superharmonic and subharmonic resonances in a straightforward way. \hfill[2011-0281] [ABSTRACT FROM AUTHOR]

We present a 3-D surface profiling method for microlenses that utilizes a Shack–Hartmann wavefront sensor. This method applies to both solid microlenses and liquid–liquid interfaces in liquid microlenses. The wavefront at the aperture stop of a microlens is measured by a Shack–Hartmann wavefront sensor and is then used to calculate the 3-D surface profile of the microlens. Three types of microlenses—a photoresist microlens, a hydrogel-driven tunable liquid lens, and an electrowetting-driven tunable liquid lens—were fabricated and measured. The variable-focus liquid lenses were tested within a wide focal length range. The obtained surface profiles were fitted to spherical and conical surface models to study their geometrical properties. The photoresist microlens was found to be approximately spherical. For the hydrogel-driven microlens, the profile was smooth and nearly spherical at the center but became steep and linear at the aperture edges. The electrowetting-driven liquid lens was also fitted better with the conical model, and its conic constant was determined. The obtained surface profiles were used to estimate the optical properties of microlenses in an optical analysis software package. The comparison between the simulation and experiment results indicated that the accuracy of the estimation is rough and the error could be due to the wavefront measurement and surface fitting approximation.\hfill[2011-0321.R1] [ABSTRACT FROM PUBLISHER]

This paper reports on the fabrication of polymer-based metallic wire-grid polarizers using a direct metal contact printing method. The proposed method can directly transfer a metal pattern from a silicon mold to a soft plastic substrate simply by roller pressing and infrared (IR) heating. With properly chosen loading contact pressure and heating temperature, metallic linear grating structures with a linewidth of 60 nm, a period of 170 nm, and an area size of 2.5 \times 2.5\ \cm^2 are successfully formed on the surface of a polyethylene terephtalate (PET) substrate. The optical performance of the fabricated flexible polarizers is experimentally measured and numerically analyzed in the near-IR spectrum with wavelength from 800 to 1500 nm. Inspired by the numerical simulation results, the optical characteristics of the flexibe polarizers are further enhanced by reactive ion etching on the PET substrate. Good agreements between experiments and theoretical simulation are obtained. Future developments and potential applications of this metal contact transfer lithography method will be addressed.\hfill[2011-0041] [ABSTRACT FROM PUBLISHER]

We present a set of displacement-based high-resolution (50 pN) micromechanical force sensors with a large force measurement range (1 \mu\N). Typically, force sensors that have high resolution have a limited force measurement range and vice versa. The force sensors presented here overcome this limitation and, in addition, have a highly linear force–displacement response. The sensors (\approx 3\ \mm \times 4\ \mm \times 150\ \mu\m) are composed of a series of flexible beams attached to a rigid probe that deform when subjected to an external force. The force is obtained by optically measuring the displacement of the probe with respect to a fixed reference beam. The force sensors are fabricated using a simple two-mask process that allows for their stiffness to be varied over a wide range. Furthermore, we have developed a novel scheme to avoid capillary forces during the immersion and removal of these sensors from aqueous environments, which makes them highly suited for biological studies. We illustrate the capability and versatility of these sensors by measuring the in vivo force-deformation response of axons in Drosophila melanogaster (fruit fly).\hfill[2009-0327] [ABSTRACT FROM PUBLISHER]

This letter presents the design, fabrication, and optical characterization of silicon-air-silicon-based surface micro-machined distributed Bragg reflectors (DBRs) for the visible to near infrared wavelength range (540–960 nm). The DBR (mirror) consisted of two quarter wave thick silicon films separated by a quarter-wave air gap. A mirror array was successfully fabricated, consisting of mirrors ranging in diameter between 270 and 420 \mu \textm . Calibrated optical measurements indicate that a peak reflectivity close to 92% has been achieved for visible wavelengths, despite the fact that silicon has strong absorbtion in the visible wavelength range. The mirrors are shown to be broadband reflectors, having 85% or more reflectivity over a 160-nm wavelength range. A spatially resolved optical transmission mapping and optical transmission profile of the mirrors demonstrates high uniformity across the fabricated array of DBRs. [2015-0140] [ABSTRACT FROM PUBLISHER]

This letter presents an initial version of an optical method for measuring and controlling strain over very short gauge lengths. Reflective indentations which are 200 \mu\m apart are put in a steel microspecimen which is 3 mm long. When illuminated with a laser, interference fringes are produced; their motion is monitored with photomultiplier tubes. A computer system converts fringe motion to strain and controls the test. The specimen preparation and measurement system is described, and the control of peak cyclic strain at 1140\pm10\ \mu\strain is demonstrated. \hfill[2010-0216] [ABSTRACT FROM AUTHOR]