Gino Putrino

Mercury-cadmium-telluride waveguides - A novel strategy for on-chip mid-infrared sensors

We report the first planar waveguides made from mercury-cadmium-telluride (MCT)-a material to date exclusively used for mid-infrared (MIR) detector elements-serving as on-chip MIR evanescent field transducers in combination with tunable quantum cascade lasers (tQCLs) emitting in the spectral regime of 5.78-6.35 μm. This novel MIR sensing approach utilizes structured MCT chips fabricated via molecular beam epitaxy (MBE) as waveguide enabling sensing via evanescent field absorption spectroscopy, as demonstrated by the detection of 1 nL of acetone. Complementary finite difference time domain (FDTD) simulations fit well with the experimentally obtained data and predict an improvement of the limit of detection by at least 2 orders of magnitude upon implementation of thinner MCT waveguides. With the first demonstration of chemical sensing using on-chip MCT waveguides, monolithically fabricated IR sensing systems directly interfacing the waveguide with the MCT detector element may be envisaged.

Model and Analysis of a High Sensitivity Resonant Optical Read-Out Approach Suitable for Cantilever Sensor Arrays

We investigate an optically resonant cavity which is created between a reflecting micro-cantilever and a diffraction grating etched into a silicon waveguide. Changes in cavity resonance, induced by small deflections of the micro-cantilever result in large changes in an optical signal transmitted through the waveguide. An analytical model can predict the cantilever position for maximum and minimum transmission and is confirmed by three-dimensional finite difference time domain (FDTD) simulations. This approach can be used to accurately determine the position of a micro-cantilever with a predicted optimal shot noise limited deflection noise density of 4.1 fm/ Hz.

Integrated Resonant Optical Readout Applicable to Large Arrays of MEMS Beams

A recent report by the authors presented theoretical studies of a new method of interrogation of the position of arrays of micro-electro-mechanical system (MEMS) cantilever and doubly clamped beams. This letter represents the first experimental evidence of the performance of such an interrogation technique, confirming the modelling and showing noise performance close to the theoretical predictions. Such a technique will be useful in applications such as MEMS-based chemical sensing. Our experimental results show the potential to realize a shot-noise limited component of minimum detectable deflection of 16

Ultrathin tunable terahertz absorber based on MEMS-driven metamaterial

{\rm fm}/\sqrt{\rm Hz}

Comparison of dynamic and static operation of a novel optical read-out technology for micromachined cantilever sensors

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Control of Sidewall Profile in Dry Plasma Etching of Polyimide

The realization of high-performance tunable absorbers for terahertz frequencies is crucial for advancing applications such as single-pixel imaging and spectroscopy. Based on the strong position sensitivity of metamaterials’ electromagnetic response, we combine meta-atoms that support strongly localized modes with suspended flat membranes that can be driven electrostatically. This design maximizes the tunability range for small mechanical displacements of the membranes. We employ a micro-electro-mechanical system technology and successfully fabricate the devices. Our prototype devices are among the best-performing tunable THz absorbers demonstrated to date, with an ultrathin device thickness (~1/50 of the working wavelength), absorption varying between 60% and 80% in the initial state when the membranes remain suspended, and fast switching speed (~27 μs). The absorption is tuned by an applied voltage, with the most marked results achieved when the structure reaches the snap-down state. In this case, the resonance shifts by >200% of the linewidth (14% of the initial resonance frequency), and the absolute absorption modulation measured at the initial resonance can reach 65%. The demonstrated approach can be further optimized and extended to benefit numerous applications in THz technology.

An optically resonant, grating-based technique for the sensitive detection of MEMS cantilever beam height

A novel, optical approach to the interrogation of MEMS cantilever sensors is discussed. We investigate the effects of placing a diffraction grating in a Si waveguide below a cantilever arm, to create a resonant cavity which will create interference on an optical signal through the waveguide. We look at FDTD simulations of the optical power transmitted through this device as the cantilevers height changes in relation to the diffraction grating. We discuss the use of this interrogation technique on micro-cantilever-based sensors operating in both the dynamic and static mode.

Multimodal atomic force microscopy with optimized higher eigenmode sensitivity using on-chip piezoelectric actuation and sensing

Spin-on polyimide is an organic thin film often used as a sacrificial layer for surface micromachining due to its high thermal stability, ease of removal, and compatibility with many materials and processes used in the realization of microelectromechanical systems (MEMS). The incorporation of sloped sidewalls in polyimide for fabricating pedestal structures is crucial in order to provide strong anchors in free-standing MEMS devices, especially in cases having a high aspect ratio and/or where structural materials have limited deposition conformality. This paper demonstrates a reliable reactive ion etching (RIE) methodology for tuning the polyimide sidewall angle, ranging from a vertical sidewall up to an angle of about 25° from the vertical. The key modifications to the process parameter space include changes to the process temperature and chamber pressure. This paper also presents a novel lift-off process, which is based on the use of an interfacial polymer layer to facilitate removal of an overlying silicon oxide hard mask. This procedure allows polyimide sacrificial layers employing a silicon oxide hard mask to be used on samples that have exposed silicon oxide layers elsewhere on the chip that are required to remain intact during hard mask removal. Therefore, this lift-off process is applicable in situations where the silicon oxide hard mask removal cannot be accomplished by wet etching in hydrofluoric acid solutions. [2016-0314]

Fast tunable terahertz absorber based on a MEMS-driven metamaterial

We present an experimental demonstration of an integrated technique designed to measure the height position of a micro-cantilever with extremely high precision. Our experimental results show that changing the beam height by 200 nm can result in an up to 40 dB change in optical power transmitted through an underlying optical waveguide.

An optical MEMS cross-bar switch

Atomic force microscope (AFM) cantilevers with integrated actuation and sensing provide several distinct advantages over conventional cantilever instrumentation. These include clean frequency responses, the possibility of down-scaling and parallelization to cantilever arrays as well as the absence of optical interference. While cantilever microfabrication technology has continuously advanced over the years, the overall design has remained largely unchanged; a passive rectangular shaped cantilever design has been adopted as the industry wide standard. In this article, we demonstrate multimode AFM imaging on higher eigenmodes as well as bimodal AFM imaging with cantilevers using fully integrated piezoelectric actuation and sensing. The cantilever design maximizes the higher eigenmode deflection sensitivity by optimizing the transducer layout according to the strain mode shape. Without the need for feedthrough cancellation, the read-out method achieves close to zero actuator/sensor feedthrough and the sensitivity is sufficient to resolve the cantilever Brownian motion.