This paper presents the interference effect of two intersecting waves on a surface acoustic wave(SAW) devices. The
SAW interference device consists of input-output interdigital transducers(IDTs) to transmit and receive a Rayleigh wave
and two interference IDTs to transmit shear-horizontal(SH) waves. The SH-waves intersects perpendicularly and
interferes with the Rayleigh wave at the delay line. We fabricated the SAW devices with center frequencies ranging from
40 MHz to 200 MHz on a 128° YX LiNbO3 wafer. The result of the characteristic test with a network analyzer shows
that the frequency response between the input-output IDTs is shifted by the interference. The center frequency decreases
as the magnitude of the interference wave increases, and the frequency shift is at its maximum when the frequency of the
interference wave coincides with the center frequency of the interference IDTs. The two interference waves applied
simultaneously make the interference effect about twice. Also, interference effect increases with the increase of the
center frequency of the interference IDT. This interference effect of two intersecting SAWs is useful to eliminate the
cross axis sensitivity in designing the SAW gyroscope based on the interference effect.
Various shapes of microlens arrays (MLAs) were developed by utilizing polymer coating on etched quartz substrates.
Spherical and non-spherical plano-concave curvatures were realized via isotropic wet etching of quartz in buffered oxide
etchant (BOE), based on diverse design parameters and calculated etching times. The fabricated curvatures showed a
high fill-factor and uniform elements in the array. By coating a higher refractive index polymer on the etched quartz, the
illuminated light was well focused at the focal plane forming a micronscale light spot array. The experimental focal
length was increased from 39.8 to 49.6 μm, as the shape of microlens was flattened. These results well correspond to
those obtained from an optical simulation.
A surface acoustic wave (SAW)-based gyroscope was developed on a piezoelectric substrate. The developed gyroscope
consists of two SAW oscillators, metallic dots, and absorber. Coupling of mode (COM) modeling was conducted to
determine the optimal device parameters prior to fabrication. Depending on the angular velocity, the difference of the
oscillation frequency was modulated. The obtained sensitivity was approximately 52.35 Hz/deg·s at an angular rate range
of 0~1000 deg/s.
A microlens array (MLA) was developed based on isotropic wet etching of quartz and coating of polymer on the etched
substrate for maskless lithography application. Through the optimized manufacturing procedures, uniform elements,
excellent light focusing ability, and dense fill factor were obtained. The fabricated MLA has the focal length ranging
from 32.2 to 45.4 μm depending on the etching time and the thickness of the coated polymer. The collimated light was
uniformly focused on the whole focal plane after passing through the fabricated array of microlenses and the size of the
each focused beam was ~1.5 μm. By using the compact imaging ability of the miniaturized lenses, the MLA was applied
to UV photolithography process. The illuminated UV passing the MLA focused on the photoresist, producing micron
scale pattern array. Various sizes and shapes of micropattern arrays were realized onto the PR via controlling the
experimental variables. Even at high temperature, the MLA performances were not changed indicating thermal stability
of the developed MLA.
A 440MHz wireless and passive surface acoustic wave (SAW) based chemical sensor was developed for
simultaneous measurement of CO<sub>2</sub> gas and relative humidity (RH) using a reflective delay line pattern as the
sensor element. The reflective delay line was structured by an inter-digital transducer (IDT) and several shorted
grating reflectors positioned both sites of the IDTs along the SAW propagation direction. A Teflon AF 2400 film
with large solubility, permeability, and selectivity towards to CO<sub>2</sub> and a hydrophilic SiO<sub>2</sub> layer for water vapor
sensing are used as the sensitive film and deposited onto the piezoelectric substrate. A simulation on the SAW
device was performed using the coupling of modes (COM). The measured reflection coefficient S<sub>11</sub> in time domain
of the fabricated SAW device shows sharp reflection peaks with high signal-to-noise (S/N) ratio, small signal
attenuation, and few spurious peaks. During the CO<sub>2</sub> and humidity testing, high sensitivity (~2<sup>o</sup> ppm<sup>-1</sup> for CO<sub>2</sub>
detection and 7.45<sup>o</sup>/%RH for humidity sensing), good linearity and repeatability were observed in the CO<sub>2</sub>
concentration of 50~400ppm and humidity of 20~80%RH. Temperature and humidity compensations were also
investigated during the sensitivity evaluation process.
This paper presents a sensitivity evaluation of a love wave sensor with multilayer structure consisting of polymethyl
methacrylate (PMMA)/SiO<sub>2</sub>/41<sup>o</sup> YX LiNbO<sub>3</sub>. A theoretical model is presented to describe wave propagation in love
wave devices with multilayered structure on large piezoelectric substrate. A complex dispersion equation expanded into
Taylor series was presented to describe the lossy mechanism of the PMMA layer. Using the gold film as the sensitive
interface, the mass loading sensitivity of the love wave sensor for biochemical application was evaluated theoretically,
and the effects from the SiO<sub>2</sub> and PMMA on the sensor sensitivity were investigated to allow the design of an optimized
structure. From the calculated results, the optimal thicknesses of SiO<sub>2</sub> and PMMA in the multilayered structure were
determined, and the sensitivity comparison between love waves in LiNbO<sub>3</sub>/SiO<sub>2</sub>/PMMA and LiNbO<sub>3</sub>/PMMA was
studied, which shows that there is larger mass loading sensitivity in love wave devices with multilayered structure.
This paper presents a configuration of a novel surface acoustic wave (SAW) micro-electro-mechanical-systems (MEMS)
interdigital transducer (IDT) gyroscope different from the current SAW MEMS-IDT gyroscope consists of a two-port
SAW resonator and a delay line as the sensor, this paper provides a new configuration of SAW gyroscope based on the
interference effect of two crossed SAWs, one is induced by the Coriolis force from the input rotation, and the other is
from the SAW device with same operation frequency. A differential structure of two delay line oscillator is used to
compensate the temperature effect. Based on the coupling of modes (COM) simulation, an 80MHz two ports SAW
resonator and dual-delay line were fabricated and characterized by the HP network analyzer. In the primary gyroscope
experimental results, a frequency change of 2500Hz was observed at rate of 500 deg/s from the SAW delay line by
interference effect between the secondary SAW induced by Coriolis force and the running SAW from the delay line.