Glenn I. Matthews

Thin film piezoelectric response characterisation using atomic force microscopy with standard contact mode imaging

This article introduces a technique for observing and quantifying the piezoelectric response of thin films, using standard atomic force microscopes (AFMs). The technique has been developed and verified using strontium-doped lead zirconate titanate (PSZT) thin films, which are known for their high piezoelectric response. Quantification of the electro-mechanical voltage coefficient d(33) (pm/V) is made directly based on the applied peak-to-peak voltage and the corresponding peak-to-peak displacement in the obtained scan image. Under the proposed technique the AFM is configured in contact mode, where the silicon nitride tip is set to follow the film displacement at a single point. A known sinusoidal voltage is applied across the film and the displacement determined as a function of time, rather than the typical AFM measurement of displacement versus tip position. The resulting raster image contains several bands, which are directly related to the AFM scan frequency and the applied sinusoidal voltage and its frequency. Different combinations of the AFM scan frequency and the applied sinusoid frequency have been used to characterise the PSZT thin films, with estimated values of d(33) between 109 and 205 pm/V.

Determining the Optimum Exposure and Recovery Periods for Efficient Operation of a QCM Based Elemental Mercury Vapor Sensor

In recent years, mass based transducers such as quartz crystal microbalance (QCM) have gained huge interest as potential sensors for online detection of elemental mercury (Hg0) vapor from anthropogenic sources due to their high portability and robust nature enabling them to withstand harsh industrial environments. In this study, we determined the optimal Hg0 exposure and recovery times of a QCM based sensor for ensuring its efficient operation while monitoring low concentrations of Hg0 vapor (<400 ). The developed sensor was based on an AT-cut quartz substrate and utilized two gold (Au) films on either side of the substrate which functions as the electrodes and selective layer simultaneously. Given the temporal response mechanisms associated with mass based mercury sensors, the experiments involved the variation of Hg0 vapor exposure periods while keeping the recovery time constant following each exposure and vice versa. The results indicated that an optimum exposure and recovery periods of 30 and 90 minutes, respectively, can be utilized to acquire the highest response magnitudes and recovery rate towards a certain concentration of Hg0 vapor whilst keeping the time it takes to report an accurate reading by the sensor to a minimum level as required in real-world applications.

Null convention logic (NCL) based asynchronous design — fundamentals and recent advances

As clock skew and power consumption become major challenges in deep submicron design of synchronous circuits, asynchronous designs, especially Null Convention Logic (NCL) subset, is gaining more and more attention. The NCL methodology eliminates problems related to the clock tree and also, can significantly reduce power consumption, noise and electromagnetic interference (EMI). In this paper, we present a comprehensive introduction to the NCL design approach, from fundamentals to recent advances. In addition, automated design flows for NCL circuits are also discussed.

Development and experimental verification of a finite element method for accurate analysis of a surface acoustic wave device

Accurate analysis of surface acoustic wave (SAW) devices is highly important due to their use in ever-growing applications in electronics, telecommunication and chemical sensing. In this study, a novel approach for analyzing the SAW devices was developed based on a series of two-dimensional finite element method (FEM) simulations, which has been experimentally verified. It was found that the frequency response of the two SAW device structures, each having slightly different bandwidth and center lobe characteristics, can be successfully obtained utilizing the current density of the electrodes via FEM simulations. The two SAW structures were based on XY Lithium Niobate (LiNbO3) substrates and had two and four electrode finger pairs in both of their interdigital transducers, respectively. Later, SAW devices were fabricated in accordance with the simulated models and their measured frequency responses were found to correlate well with the obtained simulations results. The results indicated that better match between calculated and measured frequency response can be obtained when one of the input electrode finger pairs was set at zero volts and all the current density components were taken into account when calculating the frequency response of the simulated SAW device structures.

Analysis of additional surface mechanical features in micro-acoustic devices - A combined FEM-JTFA approach

In this paper, we propose a hybrid method for the analysis of mechanical features added to the surface of micro-acoustic devices. The proposed technique has been successfully applied to evaluate the influence of additional elastic protective barriers (EPBs) placed on the otherwise planar surface of an 128°YX-LiNbO3 Surface Acoustic Wave (SAW) device. The developed technique is based on the application of the Finite Element Method (FEM), followed by a problem-adapted Joint Time-Frequency Analysis (JTFA). The combined approach simultaneously considers the micro-acoustic device response in both time and frequency domains, thereby providing a comprehensive understanding of underlying physics. The technique is shown to be more sensitive to higher-order effects such as electromagnetic feedthrough than traditional methods. Furthermore, the proposed technique can be employed to assist in the design of SAW structures where protective barriers can be used to generate constructive interference, enhancing device response.

The study of ZnO/XY LiNbO/sub 3/ layered SAW devices for sensing applications

In this paper a study of layered surface acoustic wave (SAW) devices based on a ZnO/XY LiNbO/sub 3/ structure is presented. A 3-dimensional finite-element (3D-FE) approach has been applied to simulate device performance. Particle displacement profiles in depth and beam steering are presented. Furthermore, electrical interaction of the device to a modeled gas interaction is investigated. A comparison with experimental results is used to illustrate the accuracy of the model.

3K-5 Electrical Parameter Extraction of a Flexural Plate Wave Device Using the Finite Element Method

A study was conducted on the use of the Finite Element (FE) method to determine key electrical parameters of a Flexural Plate Wave (FPW) device. This paper illustrates that the FE method can be successfully applied to extract admittance and frequency response characteristics of complex acoustic wave devices. Second order effects such as electromagnetic feedthrough, triple transit and diffraction can be accounted for, which cannot be easily evaluated concurrently by other methods. Excellent agreement has been achieved between this novel approach and an alternative formulation based on a spectral Greens function

Finite Element Modeling of Misalignment in Interconnect Vias

Electrical resistance and hence heat generation in semiconductor chips are becoming more significant issues particularity as generations of silicon devices continue to have smaller features. The resistance of interconnect vias is a significant source of heat generation because of the increasing number of these on chips and increases in via resistance due to reduced size. Finite element modeling of voltage drops and current now through interconnect vias gives information to aid in designing geometry and materials used in forming vias. It can also be used for modeling the thermal distribution in a via and hence the contribution by vias to heating a chip. In this paper we examine the effect of misalignment of the via between the two metal layers M1 and M2 with regard to the interconnect via resistance. The effect of the interface specific contact resistance is examined in particular. Significant misalignment can be tolerated without increasing the via resistance. The heat generation due to electrical current flow in the via materials and interfaces is modelled using the same finite element mesh and software. The output of the electrical analysis is used as the heat generation input for the thermal analysis

Simultaneous multi-mode analysis of surface acoustic wave device temperature stability utilizing time-frequency methods

Perturbations in the boundary conditions of Surface Acoustic Wave (SAW) devices are typically quantified through the use of frequency-domain methods, where the device is incorporated as the feedback element in a closed-loop oscillator. While simple in implementation, this method is inherently limited to tracking a single acoustic mode, and discards potentially useful information from the time-domain. In this work an alternative approach utilizing time-frequency methods to extract meaningful information from SAW device transient responses are considered. The advantages of the proposed method are experimentally demonstrated by varying the operating temperature of an XY-cut LiNbO3 SAW device. The location in time and frequency of multiple acoustic modes was monitored simultaneously as temperature was varied between 30°C and 150°C. Data from the time-frequency domain demonstrates good agreement with conventional analysis techniques.

A closed-loop micro-stimulator controlled by muscle fatigue status and function impairment level for upper limb rehabilitation

Muscle contractions of upper limbs induced by functional electrical stimulation (FES) is a widely used rehabilitation method for stroke patients. However, FES tends to result in rapid muscle fatigue, which greatly limits activities such as FES-assisted rehabilitation exercises. In order to minimize the effect of muscle fatigue, an intelligent Muscle Fatigue Status (MFS) and an Function Impairment Level (FIL) controlled micro-stimulator are proposed. The stimulation parameters of the FES are updated according to the FIL of stroke patients initially. During the break of stimulation, mean frequency (MNF) and median frequency (MDF) are exacted from an electromyography (EMG) signal, which is directly detected from the stimulated muscle of stroke patients. The MFS that can be generated from MNF and MDF is used to control the operation mode of micro-stimulator. This implantable micro-stimulator will be designed and fabricated using system on chip technology.