Enhancement of Photoemission on P-type GaAs using Surface Acoustic Waves

We demonstrate that photoemission properties of GaAs photocathodes (PCs) can be altered by surface acoustic waves (SAWs) generated on the PC surface due to dynamical piezoelectric fields of SAWs. Simulations with COMSOL indicate that electron effective lifetime in p-doped GaAs may increase by a factor of 10x to 20x. It implies a significant, by a factor of 2x to 3x, increase of quantum efficiency (QE) for GaAs PCs. Essential steps in device fabrication are demonstrated, including deposition of an additional layer of ZnO for piezoelectric effect enhancement, measurements of I-V characteristic of the SAW device, and ability to survive high-temperature annealing.Comment: 5 pages, 4 figure

Computational Methodology for Absolute Calibration Curves for Microfluidic Optical Analyses

Optical fluorescence and absorption are two of the primary techniques used for analytical microfluidics. We provide a thorough yet tractable method for computing the performance of diverse optical micro-analytical systems. Sample sizes range from nano- to many micro-liters and concentrations from nano- to milli-molar. Equations are provided to trace quantitatively the flow of the fundamental entities, namely photons and electrons, and the conversion of energy from the source, through optical components, samples and spectral-selective components, to the detectors and beyond. The equations permit facile computations of calibration curves that relate the concentrations or numbers of molecules measured to the absolute signals from the system. This methodology provides the basis for both detailed understanding and improved design of microfluidic optical analytical systems. It saves prototype turn-around time, and is much simpler and faster to use than ray tracing programs. Over two thousand spreadsheet computations were performed during this study. We found that some design variations produce higher signal levels and, for constant noise levels, lower minimum detection limits. Improvements of more than a factor of 1,000 were realized

CMOS design and implementation of sigma-delta analog-to-digital data converter suitable for MEMS devices

MicroElectroMechanical systems (MEMS) are rapidly gaining popularity over a wide range of applications today. An example of full integration in MEMS is the smart sensor where both the sensors and the electrical signal processing circuitry are placed on the same chip. The idea is to place the sensor as close as possible to the signal-processing interface to avoid signal degradation. In this paper we present the design and implementation of an interface circuit for CMOS sensor systems. A first-order sigma-delta ( Sigma; Delta;) analog-to-digital converter was designed and simulated using Cadence and SpectreS. An experimental prototype of the 10-bit Sigma; Delta; modulator was then fabricated using 1.6 um CMOS technology through MOSIS

Modeling and fabrication of CMOS surface acoustic wave resonators

A fully integrated two-port surface acoustic wave (SAW) resonator, fabricated using a standard 0.6- m complementary metal–oxide semiconductor (CMOS) process is described in this paper. Only three micromachining processes, namely, reactive ion etching, zinc–oxide deposition, and wet etching, implemented subsequent to the standard process, are required to realize these resonators. Three design examples of these resonators are given to demonstrate the characteristics of these resonators at different operating frequencies. Experimental measurements of the S21 transmission characteristics were conducted on the fabricated resonators and they were found to have parallel resonant frequencies of 1.02 GHz, 941 MHz, and 605 MHz and quality (Q) factors of 44, 86, and 285, respectively. Based on these measurements and the fabrication layers of the device, an equivalent-circuit model tailored specifically for standard CMOS two-port resonators was developed. Finite-element modeling of the SAW resonators was performed to verify the measured series resonant frequency. Comparison between the developed model and measurement characteristics was also presented. Improvement in factor was observed when reflector height was increased

RF oscillator implementation using integrated CMOS surface acoustic wave resonators

This work is a proof of concept that a monolithic CMOS surface acoustic wave (SAW) resonator can function as an RF oscillator. The design of the oscillator includes the measurement characteristics of the CMOS SAW resonator, its matching networks, and RF amplifier is described. The integrated SAW resonator, with its operating frequency controlled by the spacing of its transducers was fabricated using a combination of CMOS plus post- CMOS processes. Based on the operation and performance of the SAW resonators, an equivalent circuit model of the CMOS SAW resonator was developed. A series resonant oscillator design was simulated using Microwave OfficeTM. The designed matching network improves both the insertion losses and the phase slope of the resonator, while the RF amplifier provides sufficient gain to ensure oscillation. Measurements conducted on the RF-CMOS SAW oscillator demonstrated oscillation at 600 MH

Design and implementation of a 1GHz CMOS resonator utilizing surface acoustic wave

The design and fabrication of an integrated 1GHz surface acoustic wave (SAW) resonator is described in this paper. The SAW resonator was fabricated using a combination of CMOS plus surface micromachining techniques. Utilizing the minimum feature size of the available 0.6 micron AMI CMOS process, the periodic distance of the interdigitated fingers of the SAW resonator was designed to create an ultra high frequency resonator of 1.15 GHz. Measurements and characterization of the fabricated resonator were performed and used as a basis to develop a two-port equivalent circuit model. To complement the resonator, a Pierce oscillator circuit was designed in CMOS to create a frequency synthesizer capable of generating frequencies up to 1.15GHz without the complexity of a phase-locked-loop (PLL) circui

Micro-hotplate based temperature stabilization system for CMOS SAW resonators

Due to the sensitivity of the piezoelectric layer in surface acoustic wave (SAW) resonators to temperature, a method of achieving device stability as a function of temperature is required. This work presents two methods of temperature control for CMOS SAW resonators using embedded polysilicon heaters. The first approach employs the oven control temperature stabilization scheme. Using this approach, the device’s temperature is elevated using on-chip heaters to Tmax = 42°C to maintain constant device temperature. Both DC and RF measurements of the heater together with the resonator were conducted. Experimental results have indicated that the TCF of the CMOS SAW resonator of -97.2 ppm/°C has been reduced to -23.19 ppm/°C when heated to 42°C. The second scheme uses a feedback control circuit to switch the onchip heaters on and off depending on the ambient temperature. This method provided reduction of the TCF from -165.38 ppm/°C, to -93.33 ppm/°C. Comparison of both methods was also provided