Substrate-decoupled, bulk-acoustic wave gyroscopes: Design and evaluation of next-generation environmentally robust devices.

This paper reports on a new type of high-frequency mode-matched gyroscope with significantly reduced dependencies on environmental stimuli such as temperature, vibration, and shock. A novel stress-isolation system is used to effectively decouple an axis-symmetric bulk-acoustic wave (BAW) vibratory gyro from its substrate, minimizing the effect that external sources of error have on the offset and scale factor of the device. Substrate-decoupled (SD) BAW gyros with a resonance frequency of 4.3 MHz and Q values near 60 000 were implemented using the high aspect ratio poly and single-crystal silicon (HARPSS) process to achieve ultra-narrow capacitive gaps. Wafer-level packaged sensors were interfaced with a customized application-specific integrated circuit (ASIC) to achieve low variations in the offset across temperature (±26° s-1 from -40 to 85 °C), supreme random-vibration immunity (0.012° s-1 gRMS -1) and excellent shock rejection. With a scale factor of 800 µV (°s-1)-1, the SD-BAW gyro system attains a large full-scale range (±1250° s-1) with a non-linearity of less than 0.07%. A measured angle-random walk (ARW) of 0.39°/√h and a bias instability of 10.5°h-1 are dominated by the thermal and flicker noise of the integrated circuit (IC), respectively. Additional measurements using external electronics show bias-instability values as low as 3.5°h-1, which are limited by feed-through signals coupled from the drive loop to the sense channel, which can be further reduced through proper re-routing of the gyroscope pin-out configuration.

Electrochemical threshold conditions during electro-optical switching of ionic electrophoretic optical devices.

Electro-optical modulation by electrophoresis of dye ions is a promising technique for applications such as electronic paper displays and nonmechanical beam steering devices. To achieve a sufficient response rate in these devices, the transition time between two different optical states can be decreased by increasing the magnitude of the voltage applied across the electrodes, but this also leads to irreversible and undesirable electrochemical reactions. An electron tunneling model has been developed to describe the electrochemical reaction and to better understand the conditions determining its onset. The model gives rise to three predictions that were subsequently confirmed experimentally: the magnitude of the applied surface charge density should determine the rate of electrochemical activity, the bulk concentration of ions in the solution should shift the threshold voltage at which electrochemical reactions occur, and the reaction rate should be substantially enhanced around nanometer-sized bumps on the electrode surface. Applying this new understanding, the transition time of a device incorporating porous zinc antimonate (ZnSb2O6) electrodes and a solution of Methylene Blue dye in methanol was reduced by a factor of approximately 20.

Photoluminescence emission profiles of Y(2)O(3) : Eu films composed of high-low density stacks produced by glancing angle deposition.

Periodic high-/low-index film stacks composed of Y(2)O(3) : Eu were grown by glancing angle deposition on silicon and fused silica substrates. Postdeposition annealing at temperatures from 600 to 1000 degrees C for 1 h in air was performed to activate photoluminescence. Absolute photoluminescence spectra were obtained as a function of observation angle. The angular emission distribution was non-Lambertian, with peak emission at angles of 50 to 60 degrees with respect to substrate normal. Spectroscopic transmittance and ellipsometry measurements were performed to characterize the films. Using this description, we were able to reproduce the angular photoluminescence patterns of the films.