Declan McDonagh

Development of a novel thick-film strain gauge sensor system

In this paper a novel strain gauge system on stainless steel and 96% alumina substrates is described incorporating a Wheatstone bridge network, thick-film piezoresistive strain gauges, instrumentation, and a novel thermal and resistor mismatch tolerance correction software. The resistors in the Wheatstone bridge are fabricated with a novel mixture of ruthenium, bismuth and indium oxides and three different thick-film layouts are used. Mechanical measurements are performed using the cantilever beam set-up. The linearity, hysteresis, repeatability, reproducibility, creep, stability and temperature effects are measured for the novel thick-film pastes. The linearity and temperature effect on the output of the different bridge layouts are also examined. The printing of resistors using thick-film technology can result in resistor tolerances of %. Also, thick-film piezoresistors are intrinsically cross sensitive to temperature. These two properties cause an offset voltage to appear at the output of the bridge under no-load/load conditions and a subsequent error in the calculated applied strain. In order to compensate for the offset error voltage, novel correction software has been developed and implemented using a microcontroller. The error in the predicted strain was measured before and after application of the correction software under different bridge layouts and temperature conditions. The error was reduced from a maximum of 45% to approximately 1%. The effectiveness of the correction software in reducing the error suggests that this technique can be used without the need for trimming or bridge balancing.

Negative resist image by dry etching as a surface imaging process using focused ion beams

Focused ion beam (FIB) lithography has significant advantages over the electron beam counterpart in terms of resist sensitivity, backscattering, and proximity effects. However, combining the FIB lithography with top surface imaging (TSI) will extend its advantages by allowing anisotropic processing of thicker resist layers. This article reports the development of novel single layer lithography process by combining focused Ga+ ion beam (Ga+ FIB) lithography, silylation, and oxygen dry etching. The negative resist image by dry etching is a TSI scheme for DNQ/novolak based resists and can result in either positive or negative resist images depending on the extent of the ion beam exposure dose. Results show that the Ga+ ion beam dose in the range of 1–50 μC/cm2 at 30 keV can successfully prevent silylation of the resist, thus resulting in the formation of a positive image after the dry etching. A negative image can be formed by using a second Ga+ ion beam exposure with a dose higher than 900 μC/cm2 at 30 keV ...

Focused ion beam lithography-overview and new approaches

Focused Ion Beam (FIB) lithography has significant advantages over the electron beam counterpart in terms of resist sensitivity, backscattering and proximity effects. Applying the Top Surface Imaging (TSI) principal to FIB lithography could further enhance its capability. In this paper we review different FIB lithography processes which utilise both wet and dry development. As of further development of this technology, we report a novel lithography process which combines focused Ga/sup +/ ion beam (Ga/sup +/ FIB) exposure, silylation and oxygen dry etching. The Negative Resist Image by Dry Etching (NERIME) is a TSI scheme for DNQ/novolak based resists and can result in either positive or negative resist images depending on the extent of the ion beam exposure dose. The NERIME process can resolve nanometer resist patterns as small as 30nm yet maintaining high aspect ratio of up to 15. The proposed lithography scheme could be utilised for advanced prototype ICs fabrication and critical CMOS lithography process steps.

Stable differential voltage to frequency converter with low supply voltage and frequency offset control

In this paper, the circuit for a new bipolar differential voltage-to-frequency converter is presented. The circuit operation and the calculation of the operating frequency are described. The circuit design is also realized using Zetex transistor array integrated circuits and a 3.3-V power supply. This circuit incorporates an adjustable operating frequency via an external capacitor. The operating frequency varied from 15 to 368 kHz by changing the external capacitor from 1 /spl mu/F to 22 pF. The circuit was tested with an applied differential voltage of /spl plusmn/15 mV. The deviation about the center frequency changed from /spl sim//spl plusmn/2.1 Hz to /spl sim//spl plusmn/38.22 kHz as the external capacitor was varied over the same range. The frequency offset control feature was implemented using a 4-bit current DAC (iDAC). As the iDAC input code was increased from 0 to 1111, the operating frequency varied quite linearly from /spl sim/156.5 to /spl sim/77.9 kHz. Thermal simulations with worst-case analysis were performed in PSPICE in order to estimate the thermal coefficient of frequency for the circuit. These simulations yielded a TC of /spl plusmn/192 ppm//spl deg/C for the operating frequency.

Modeling and simulation of a wireless sensor data acquisition system using PCM algorithms

This work presents a novel simulated model for a wireless data acquisition system. The system reads analogue information provided by two sensors and can be used for medical purposes. Real data has been obtained and a simulation of the two signals coming from both pH and pressure sensors embedded in the system has been employed. The created model contains four main units simulated using SIMULINK. At the first unit, the output signal is encoded to digital signal based on adapting one of the pulse coding modulation (PCM) algorithms. The second unit simulates the processor function that is responsible for framing, mixing and compressing the incoming bit streams from both sensors. The third unit, where the digital data is modulated and sent through different noisy channels, represents an efficient FSK transmitter/receiver model. At the receiver end, the signal is demodulated and processed inversely to extract the original analogue signal read by the two sensors. In this work, the performances of the systems using different PCM methods are studied comparatively in order to control the transmission and reduce the amount of data sent. This leads to a significant reduction in power consumption. In addition, efficiency of the RF channel in terms of bit error rate (BER) and through different noisy conditions is investigated.

Modelling and simulation of a wireless microsensor data acquisition system using PCM techniques

Abstract This paper presents a review of developed simulated models for a wireless data acquisition system. The system reads analogue information provided by two sensors used for medical purposes. The real data have been recorded by two, pH and pressure sensors used in diagnosing conditions of the esophagus that are employed to examine the system performance. The created model contains four main simulated units using SIMULINK. The first unit contains the output signal, which is encoded to digital signal based on adapting one of the pulse coding modulation (PCM) algorithms. The second unit simulates the processor function that is responsible for framing, mixing and compressing the incoming bit streams from both sensors. The third unit, where the digital data are modulated and sent through different noisy channels, represents an efficient FSK transmitter/receiver model. At the receiver end, the signal is demodulated and processed inversely to extract the original analogue signal read by the two sensors. In this work, the performance of the systems using different PCM methods will be studied comparatively in order to control the transmission and reduce the amount of data frames sent. This will lead to a significant reduction in power consumption. In addition, the performance of the RF unit through additive White Gaussian noise (AWGN) channel was examined by estimating the average bit error rate (BER) for different carrier frequencies. The effect of the multipath fading, inband/outband interference, and adjacent channel power ratio (ACPR) has also been investigated during system assessment.

Modelling and simulation of wireless sensor system for health monitoring using HDL and Simulinkw mixed environment

The aim of this study is to model and design an efficient wireless system that is easy to integrate with other technologies or infrastructures at a low cost. The system would read analogue information recorded by a biomedical sensor in a transmitting unit attached to the patient. The recorded data are converted digitally using analogue-to-digital converter and sent to frequency-shift keying (FSK) transmitter through field programmable gate arrays (FPGAs). Verilog-HDL has been used to implement the required functions of the FPGA, such as bus interfacing, data buffering, compression and data framing. On the other hand, Simulink® software has been used to model and simulate FSK transmitter/receiver architecture suitable for short-range communications. Basically, a two-tone FSK signal is generated and passed through a noisy channel, which is then downconverted to baseband and passed to the frequency-modulating detector to restore the original transmitted bit stream. These illustrate how easily the mixed signal modelling can be well mapped into hardware description language (HDL) and mathematical programming techniques. The developed simulation models are used to explore the design change options. The behavioural HDL design has been interfaced to the Simulink model using system generator in a co-simulation environment, and the overall performance has been verified.

Modeling remote system for sensor monitoring using Verilog HDL and SIMULINK/spl reg/ co-simulation

The aim of this study is to model and design an efficient wireless system that should be easy to integrate with other technologies or infrastructures at a low cost. The system is reading analog information recorded by a biomedical sensor in a transmitting unit attached to the patient. The recorded data is converted digitally using ADC and sent to FSK transmitter through FPGA. Verilog HDL has been used to implement the required functions of the FPGA. SIMULINK/spl reg/ software has been used to model and simulate frequency-shift keying (FSK) transmitter/receiver suitable for short-range communications. A two-tone FSK signal is generated, passed through a noisy channel, down converted to baseband and passed to FM detector to restore the original transmitted bit stream. The behavioral HDL design has been interfaced to the SIMULINK model and the overall performance has been verified.

DESIM: a simulator for the DESIRE process

DESIM is an exclusive simulator for the DESIRE process. It can model all the three unit processes i.e. surface imaging (projection/contact, conventional/phase-shifted mask), silylation (positive/negative tone, gas/liquid phase, pre-silylation baking), dry development (single and two step). This paper discusses some of the models and then evaluates the performance of the simulator by comparing the simulated results.

Simulation of resist exposure and development on topographic substrates

Abstract The application of software tools in the development of new processes and novel device structures has become a dominant feature in the microelectronics industry. The use of these tools enables technologists to advance optical lithography to submicron levels of IC fabrication, i.e. 64 Mbit DRAMs. In this work, 2D modelling and simulation of optical microlithography on topographic substrates is investigated. A new program called SLITS (simulation lithography on topographic.substrates) has been developed which calculates 2D latent and relief images. The latent image is calculated by solving the Helmholtz equation using finite element analysis. To generate the relief images, new boundary detection and air/resist movement algorithms, which are not features of any traditional lithographic simulator have been designed and implemented. Relief images produced by SLITS and an earlier program ANKAN for a resist on planar substrate are compared and analysed. We also have investigated notching effects in a ph...