In this work, we study the modes of vibration for two different families of aluminium nitride-actuated piezoelectric
microstructures: contour modes and flexure-actuated modes. For the contour modes, the structure vibrates at frequencies
determined by its edge dimensions whereas for the flexure-actuated modes a suspended structure is displaced by the
lateral bending of the flexures. We combine electrical and optical techniques to fully characterize the vibrating modes of
these types of in-plane MEMS structures. An electronic speckle pattern interferometry technique is used for a full 3D
detection of the movement of the structures. Quality factors as high as 5000 and motional resistance as low as 4 KOhm
were obtained for in-plane modes in air and a quality factor as high as 300 was obtained for an in-plane structure with
water on the top surface. This work shows the great flexibility in the selection of resonant modes in piezoelectric
resonators and actuators, implemented by a proper design of the electrode layout geometry.
In this paper we report on the high temperature compatibility of various adhesion layers for plat inum (Pt ) thin films. We
investigated different adhesion layers, such as titanium (Ti), tantalum (Ta), aluminium nitride (AlN), aluminium oxide
(Al2O3) and titanium oxide (TiO2). All films were deposited on SiO2/Si substrate by using the sputter technique. After
deposition the films were annealed in air at 800°C for different time lengths up to 16 h ours. After annealing, Al2O3 and
TiO2 showed a dense oxide layer between Pt and SiO2/Si and they seem to be suitable as adhesion layers for Pt at high
temperatures. AlN is not suitable as adhesion layer for Pt at high temperatures. Ti and Ta are also not suitable for high
temperatures, diffusing strongly into Pt layers and leading to the format ion of oxide precipitates (TiOx or TaOx) in the Pt
grain boundaries. In addition, the format ion of Pt-crystallites (hillocks) on the surface was common in all the films.
In this work, the fabrication process of piezoelectric AlN cantilevers is presented. The cantilevers were electrically
characterized in a vacuum chamber offering the possibility to close-loop control the back pressure from atmospheric
conditions down to 5x10-3 mbar. The quality factor (Q factor) is an important figure of merit to evaluate the performance
of micro-resonators. In particular, two different modes were detected and analyzed. The first bending mode detected at
19.5 kHz has a quality factor of 470 at atmospheric pressure which increases continuously to 985 at 1x10-1 mbar. The
corresponding resonant frequency shifted from 19.500 kHz at atmospheric pressure to 19.573 kHz at 5 mbar. Below this
pressure level, the resonance frequency stays unaffected within the measurement accuracy.
The second bending mode detected at 117.264 kHz exhibits a quality factor of about 570 at atmospheric pressure
increasing continuously to 1275 at 1x10-1 mbar. In agreement with the other resonant frequency under investigation the
corresponding resonant frequency decreased from 117.264 kHz at atmospheric pressure to 117.630 kHz at 5 mbar.
Flattop liquid crystal tunable optical interleavers have shown a great potential to perform in the DWDM systems. In this
paper, chromatic dispersion analyses are conducted for a flattop liquid crystal tunable optical interleaver based on
Combined Michelson and Gires-Tournois interferometers. In order to try to reduce the dispersion associated with the
interleaver's operation, tuning capability of the liquid crystal is used to tune the chromatic dispersion spectrum.
Simulation results show a 66.5% reduction in the chromatic dispersion for the simulated interleaver configuration when
compared to the air filled cavities in the interleaver. This reduction is achieved without any additional components or
design modifications but only with the tuning capability of the liquid crystal. Moreover, the chromatic dispersion
spectrum can be tuned. This provides more freedom for designers to try to minimize the chromatic dispersion effects on
the system performance.
Single fundamental mode, oxide-confined, polyimide planarized 980nm vertical cavity surface emitting lasers (VCSELs)
with a multi-oxide layer (MOL) structure to increase oxide aperture diameter and maintain single-mode operation are
fabricated and characterized. VCSELs with an 8μm active diameter and 16 mode suppression layers maintained single
transverse mode operation under continuous wave (CW) condition with a side-mode suppression ratio (SMSR) of more
than 32 dB at current densities up to 20 times threshold, which is five times higher than the previously reported value for
similar devices with only 3 mode suppression layers, and exhibited a maximum 3-dB modulation frequency bandwidth
of 13GHz. The threshold current and voltage were as low as 260μA and 1.45V, respectively, with a maximum optical
power and slope efficiency of 1mW and 0.31W/A, respectively.
Extrinsic electrical, thermal, and optical issues rather than intrinsic factors currently constrain the maximum bandwidth
of directly modulated vertical cavity surface emitting lasers (VCSELs). Intrinsic limits based on resonance frequency,
damping, and K-factor analysis are summarized. Previous reports are used to compare parasitic circuit values and
electrical 3dB bandwidths and thermal resistances. A correlation between multimode operation and junction heating
with bandwidth saturation is presented. The extrinsic factors motivate modified bottom-emitting structures with no
electrical pads, small mesas, copper plated heatsinks, and uniform current injection. Selected results on high speed
quantum well and quantum dot VCSELs at 850 nm, 980 nm, and 1070 nm are reviewed including small-signal 3dB
frequencies up to 21.5 GHz and bit rates up to 30 Gb/s.
Intrinsic and extrinsic limitations on conventional top-emitting high-speed VCSEL modulation bandwidth are discussed. A new VCSEL structure has been designed with reduced constraints on modulation bandwidth. The structure simultaneously addresses the primary extrinsic factors that limit the VCSEL modulation bandwidth. The new bottom-emitting, flip-chipped VCSEL structure improves heat-sinking, current injection uniformity, and reduces parasitic capacitance. We estimate the ultimate bandwidth of this new structure to be as high as 40Gb/s.
Oxide-confined, polyimide-planarized 850 nm vertical cavity surface emitting lasers (VCSELs) with excellent high-speed performance were fabricated and characterized. The reproducible, simple process provides good metal adhesion to photodefined polyimide offering low capacitance without implantation or semi-insulating substrates. Microwave measurements are used to extract parameters for a physically based equivalent circuit for the VCSEL.