Cazimir G. Bostan

Surface acoustic wave humidity sensor

Embodiments of the present disclosure include devices and methods for humidity and temperature sensing. For example, in one embodiment, a sensing device can include a first surface acoustic wave (SAW) component, wherein the first SAW component is a temperature component, a second SAW component, wherein the second SAW component is a humidity component, a third SAW component, wherein the third SAW component is a reference component, and a piezoelectric layer, wherein the first SAW component, the second SAW component, and the third SAW component are on a surface of the piezoelectric layer.

Surface Acoustic Wave devices and their sensing capabilities

Since mid 60s, Surface Acoustic Wave (SAW) devices have been using extensively in electronics for telecommunication. However, their potential use in the sensors field is only a matter of recent interest. This paper presents an overview of the sensing mechanisms that allow detection of temperature, strain (for pressure & torque), mass, conductivity (e.g. gas detection) and viscosity by means of SAW based devices. Design and technological challenges are presented, as well as solutions to overcome them in order to obtain reliable devices. The possibility of using such devices as passive wireless sensors is also discussed.

Selection of gas sensing materials using the Hard Soft Acid Base theory; application to Surface Acoustic Wave CO 2 detection

The Hard Soft Acid Base (HSAB) theory is introduced as a new tool to select or design sensitive materials for carbon dioxide detection with SAW-BAW (Surface Acoustic Waves - Bulk Acoustic Waves) devices. According to HSAB, CO2 is hard acid, thus small organic or inorganic molecules, or polymers which can act as hard bases could be suitable candidates as sensing layers for carbon dioxide detection. As a consequence of this theory, we propose the following polymers as potential candidates for CO2 sensing: simple polyallylamine, N-substituted polyallylamine, polydiallylamine and polyvinylamine, and mixtures of these polymers. The SAW device coated with one of the selected polymers, polyallyamine, shows good sensitivity for CO2 concentration (in the range 500–5000 ppm), long term stability and repeatability.

Fabrication of photonic crystal slabs and defects using laser interference lithography and focused ion beam-assisted deposition

A method is described for fabricating photonic crystal slabs, using a combination of laser interference lithography for generating a regular periodic structure (the crystal lattice), and focused ion beam-assisted deposition for defining defects in this lattice, which may act as waveguides or resonators. As an example, results will be shown of a photonic crystal slab with a line defect in silicon nitride.

Damping effects in MEMS resonators

Damping effects are very important in MEMS-based sensors and actuators. In this paper we use analytical models and finite element (FE) computations to quantify the energy losses due to viscous fluid damping, acoustic radiation and thermo-elastic damping. To treat the case where squeeze/slide film models can not be applied, we have implemented in a commercial FE package a new incompressible flow solver based on a gauge formulation. We are thus able to solve for full flows around complex 3D geometries in the frequency domain and predict viscous damping of resonant MEMS structures. The full methodology is exemplified on the response of a MEMS silicon resonator, including acoustic driving and piezoelectric sensing.

Amino groups-based polymers for CO 2 detection; A comparison between two sensing mechanism models

Two CO2 sensing mechanisms, based on the Hard Soft Acids Bases (HSAB) and Bronsted-Lowry theories, are discussed and compared. They are evaluated by selecting amino groups-based coating layers, which are deposited on Surface Acoustic Wave (SAW) devices for CO2 detection. Experimentally measured CO2 sensitivities of different coating layers, such as polyallylamine (PAA), polyethyleneimine (PEI), nanocomposite matrix based on PAA-aminocarbon nanotubes and PEI-aminocarbon nanotubes, emeraldine, 4-sulfocalix[4]arene-doped polyaniline, matrix based emeraldine and carbonic anhydrase (PACA) are compared and evaluated according to their corresponding sensing mechanism.

A novel concept for low drift chemical sensing at micro and nano-scale

It is the purpose of this paper to present a novel generic concept for low drift chemical sensing which is applicable at micro and nanometer scale, based on a new, all-differential approach. At micrometer level, our principle is explained by means of surface acoustic wave (SAW) chemical sensing, while at nano level, we are using the resonant sensing principle to develop our genuine differential concept. Unlike the traditional differential approaches based on functionalized sensing layer in the sensing loop, and on a uncoated surface in the reference loop, our all differential concept provides a better response subtraction between the two paths, as the sensing loop consists of a functionalized sensing layer, as before, but, the reference loop consists of a functionalized non-sensing layer, with the same ageing and humidity behavior as the sensing layer. Twinned electronic reading is used for both loops, and thus all the common mode signals are subtracted in the differential reading, assuring the minimum base line drift of the sensor. Preliminary results of all differential sensor response to humidity and temperature variations are shown for the SAW sensors, with the sensor signal kept independent of their changes.

Modeling and process design for laser interference lithography used in fabricating two-dimensional periodic structures

Laser interference lithography (LIL) is a technique that can be successfully used for realization of 2D periodic structures, with excellent uniformity over large areas. However, detailed modeling is needed in order to extract the optimum design parameters. In this paper, we refer to a design procedure for LIL applied to fabricating photoresist templates for photonic crystal semiconductor slabs with periodic lattices of holes.

SOI membrane-based pressure sensor in stress sensitive differential amplifier configuration

This paper introduces a pressure sensing structure configured as a stress sensitive differential amplifier (SSDA), built on a Silicon-on-Insulator (SOI) membrane. Theoretical calculation show the significant increase in sensitivity which is expected from the pressure sensors in SSDA configuration compared to the traditional Wheatstone bridge circuit. Preliminary experimental measurements, performed on individual transistors placed on the membrane, exhibit state-the-art sensitivity values (1.45mV/mbar).

Design of waveguides, bends and splitters in photonic crystal slabs with hexagonal holes in a triangular lattice

Waveguides in photonic crystal slabs (PCS) can be obtained by omitting a row of holes (Wl-waveguides). In general the propagation properties in such waveguides suffer from the unavoidable periodic sidewall corrugation caused by the remaining parts of the crystal. The corrugation acts as a Bragg reflector, causing the occurrence of so-called mini stopbands in the transmission of the waveguide. The effect is quite strong in PCS with circular holes, but it can be significantly reduced if correctly oriented hexagonal holes are used. This so-called hexagon-type PCS allows the design of waveguides, bends and splitters having a relatively high group velocity and a wide transmission window in the PCS stopband for modes having their magnetic field oriented mainly perpendicular to the slab.