Sidewall slopes and roughness of SU-8 HARMST

In recent years we have investigated the feasibility of deep X-ray lithography in SU-8 as a means of fabricating very high aspect ratio and densely packed arrays of square channels. We have demonstrated how to overcome the problems in adhesion and stiction accompanying the fabrication of such high aspect ratio structures. We have also examined how to calculate the development time of these structures and how this can be used to optimize the dimensional fidelity of the resulting structures. More recently we have considered the effect of the non-uniform dose deposition and beam hardening as a function of depth in the resist on factors such as the surface roughness and the sidewall taper. In this paper we describe our experimental program, review these results and discuss their implications for the operation of our target device—the lobster-eye telescope.     

Effects of elevated temperature treatments in microstructurerelease procedures

Elevated temperature solvent rinses are shown to reduce stiction of micromechanical structures after release etch processing. Rinsing the structures in boiling methanol after rinsing in water significantly improves yields. Photographs taken during the drying process indicate two distinct modes of solvent vaporization, one of which leads to stiction. This process can be modeled and used to predict the critical length of cantilevered beams above which stiction occurs. A key element of this model is that the dynamics of the drying process are strongly influenced by the shape of the microstructure perimeter. The decrease in stiction cannot be explained solely by liquid bridging modeling in case of elevated rinse temperature. Stiction can be further decreased by drying at high temperature in a rapid thermal annealer; this suggests that instability of the trapped liquid under tension at elevated temperatures may be a dominant factor in reducing the stiction     

Recovery of stiction-failed MEMS structures using laser-induced stress waves

Stiction, or adhesion between suspended structures and the underlying surface, is a hurdle in batch fabricating long, freestanding MEMS structures. A novel technique is presented in this paper to release stiction. In this technique, a nanosecond rise time stress wave is launched on the backside of the Si substrate by impinging a 2.5 ns-duration Nd:YAG laser pulse onto a 3-mm-dia area. The compressive stress wave propagates through the Si substrate and arrives at the site of several stiction-failed cantilevers on the front Si surface. The compressive stress wave propagates through the cantilevered structures and is reflected into a tensile wave from their free surfaces. The returning tensile wave pries off the interface, releasing the cantilevers. The procedure is demonstrated on a MEMS chip with stiction-failed cantilevers with varying lengths from 100 /spl mu/m to 1000 /spl mu/m. The threshold laser energy to release stiction increased linearly with cantilever lengths. Beam recovery began at a laser fluence of 11 kJ/m/sup 2/ laser energy. 70% of the tested beams had been recovered after impingement with a fluence of 26 kJ/m/sup 2/. After the highest applied laser fluence of 40 kJ/m/sup 2/, 90% of the tested beams had been recovered. No damage to the structures or surrounding features was observed below 40 kJ/m/sup 2/. Because of rather low laser fluence, no thermal damage to the back surface of Si was noted. Since it literally takes few seconds to release stiction, the proposed technique can be implemented in MEMS foundry, and for repair of in-use stiction failed MEMS devices.     

Recommendations for the Use of an Atomic Force Microscope as an In-Fab Stiction Monitor

An atomic force microscope (AFM) can be used to monitor stiction (by measuring the work of adhesion) at different stages of manufacture, which then might be correlated to device performance. The four main challenges to using the AFM as an in-fab stiction monitor are calibration, effects from the angle of repose of the cantilever, surface roughness, and material properties. We measured the work of adhesion between different AFM tips and samples. There were 17 tips of four different types, with radii from 200 nm to 60, covering the range of typical microelectromechanical systems (MEMS) contacts. The samples were unpatterned amorphous silicon dioxide MEMS die with two types of surface conditions (untreated and treated with a few angstroms of vapor-deposited diphenylsiloxane). A simple correction for the surface roughness resulted in the expected linear dependence for work of adhesion on radius, but the magnitudes were higher than expected. Commercial and heat-treated AFM tips have minimal surface roughness and result in magnitudes that were more reliable. In this paper, we review the four main challenges and show their influence on the measured work of adhesion, from which we develop a set of recommendations for the use of an AFM as an in-fab stiction monitor.     

Optimisation of SU-8 processing parameters for deep X-ray lithography

The negative photoresist SU-8 has been recognised as an unique resist, equally useful for conventional UV lithography as well as deep X-ray lithography (DXRL) applications [2, 7, 12, 17, 18]. One of the major limitations in the use of SU-8 in lithographic processes is the occurrence of internal stress [15]. The processing parameters investigated for DXRL of SU-8 included resist thickness (450–850 m), soft bake time (7–11 h), exposure dose (30–70 J/cm³), post exposure bake time (20, 40, 60 min) and development time. The effect of these parameters on stress was evaluated using wafer curvature measurements. Taguchi optimisation techniques have been used to asses the contribution of these parameters on the stress of the developed structures. This study shows that softbake time contributes the most to stress in the SU-8 film at 50%, followed by the exposure dose and post exposure bake with 30% and 15% respectively. Stress varied somewhat linearly with thickness. At higher thickness, the deposition process needs to be changed for very high aspect ratio structures. The main objective of this work has been to optimise the processing conditions of thick SU-8 films for DXRL.This paper was first presented at the High Aspect Ratio Microstructurres (HARMST) conference in Montery California, June 2003.This work was supported by the Australian Synchrotron Research Program, which is funded by the Commonwealth of Australia under the Major National Research Facilities Program. Use of the Advanced Photon Source was supported by the U.S. Department of Energy, under Contract No. W-31-109-Eng-38. Support received from CRC for microTechnology (Australia) is also gratefully acknowledged. We also thank Dr. Brett Sexton and Fiona Smith from CSIRO (Australia), Dr. Francesco DeCarlo , Dr. Chian Liu, and Judy Yaeger from APS, and Dr. Jason Hayes and Dr. Matthew Solomon from Swinburne University for useful discussions and their help during some experimental work.     

Computing the minimum-support for mining frequent patterns

Frequent pattern mining is based on the assumption that users can specify the minimum-support for mining their databases. It has been recognized that setting the minimum-support is a difficult task to users. This can hinder the widespread applications of these algorithms. In this paper we propose a computational strategy for identifying frequent itemsets, consisting of polynomial approximation and fuzzy estimation. More specifically, our algorithms (polynomial approximation and fuzzy estimation) automatically generate actual minimum-supports (appropriate to a database to be mined) according to users’ mining requirements. We experimentally examine the algorithms using different datasets, and demonstrate that our fuzzy estimation algorithm fittingly approximates actual minimum-supports from the commonly-used requirements. This work is partially supported by Australian ARC grants for discovery projects (DP0449535, DP0559536 and DP0667060), a China NSF Major Research Program (60496327), a China NSF grant (60463003), an Overseas Outstanding Talent Research Program of the Chinese Academy of Sciences (06S3011S01), and an Overseas-Returning High-level Talent Research Program of China Human-Resource Ministry. A preliminary and shortened version of this paper has been published in the Proceedings of the 8th Pacific Rim International Conference on Artificial Intelligence (PRICAI ’04).     

Production issues for high aspect ratio Lobster-eye optics using LIGA

 A square packed array of square-channels with long channel axis aligned radially is a useful structure for condensing grazing incidence flux to a focus. These devices, known as Lobster-eye optics for their similarity to the eyes of the macruran crustaceans, show great promise as the focusing optic in the next generation of X-ray all-sky monitors. At X-ray wavelengths the optimal Lobster-eye structure requires an aspect ratio of channel length to width of greater than 30:1. Following recent success in fabricating a low aspect ratio Lobster-eye structure, we discuss some of the parameters for, and production issues involved in making, a useful Lobster-eye prototype using LIGA. We report on our initial attempts to produce high aspect ratio Lobster-eye optics using the LIGA process with a graphite substrate. Received: 10 August 2001/Accepted: 24 September 2001 AGP gratefully acknowledges receipt of an ARC post-doctoral fellowship. This work was supported by the Australian Synchrotron Research Program, which is funded by the Commonwealth of Australia under the Major National Research Facilities Program. Use of the Advanced Photon Source was supported by the U.S. Department of Energy, Basic Energy Sciences, Office of Energy Research, under Contract No. W-31-109-Eng-38. This paper was presented at the Fourth International Workshop on High Aspect Ratio Microstructure Technology HARMST 2001 in June 2001.     

A sticking model of suspended polysilicon microstructure includingresidual stress gradient and postrelease temperature

A sticking (stiction) model for a cantilevered beam is derived. This model includes the effect of the bending moment, which stems from stress gradient along the vertical direction of structural polysilicon, and the temperature during the release process. The bending moment due to the stress gradient will play an important role in evaluating antisticking efficiency since liquid tension and surface energy of microstructures tend to become smaller by newly developed antisticking techniques. The effects of stress gradient and temperature were analyzed and verified with surface-micromachined polysilicon cantilevers. By modifying the substrate polysilicon with grain-hole formation technique, the effects of residual stress gradient in polysilicon on stiction could be observed in the condition of low work of adhesion     

Automatic detection and quantification of stiction in control valves

Stiction is a common problem in spring-diaphragm type valves, which are widely used in the process industry. Although there have been many attempts to understand and detect stiction in control valves, none of the current methods can simultaneously detect and quantify stiction. Conventional invasive methods such as the valve travel test can easily detect stiction, but are expensive and tedious to apply to hundreds of valves to detect stiction. Thus there is a clear need in the process industry for a non-invasive method that can not only detect but also quantify stiction so that the valves that need repair or maintenance can be identified, isolated and repaired. This work describes a model free method that can detect and quantify stiction that may be present in control valves using routine operating data obtained from the process. No additional excitation or experimentation of the plant is required. Over a dozen industrial case studies have demonstrated the wide applicability and practicality of this method as an useful diagnostic aid in control loop performance monitoring.     

Identification of a process with control valve stiction using a fuzzy system: A data-driven approach

Many researchers focus on detecting and modelling the valve stiction because it has undesirable effects on the control loop performance, which consequently results in poor product quality and increased energy consumption. It is difficult to model a process with a sticky valve using the mathematical definition because of its nonlinear properties such as stiction, hysteresis, dead band and dead zone. This work aims to develop and determine the appropriate model of a process with stiction, which can be used in controller design to mitigate the undesirable effect of the stiction. To achieve this goal by mapping the process with valve stiction to a fuzzy system, a dynamic fuzzy model of the plant is derived through an iterative well-developed fuzzy clustering algorithm, which generates suitable antecedent parameters from a set of input–output measurements that are obtained from the control output (OP) and the process output (PV). To determine the consequent parameters, the least square (LS) estimation is applied. The results reveal that the obtained data-driven Takagi–Sugeno-type (TS) fuzzy rule-based model can effectively represent an appropriate model of the process with stiction for different amounts of stiction that are obtained from the simulation and different industrial loops.     

The construction of good extensible Korobov rules

In this paper, we introduce construction algorithms for Korobov rules for numerical integration which work well for a given set of dimensions simultaneously. The existence of such rules was recently shown by Niederreiter. Here we provide a feasible construction algorithm and an upper bound on the worst-case error in certain reproducing kernel Hilbert spaces for such quadrature rules. The proof is based on a sieve principle recently used by the authors to construct extensible lattice rules. We only treat classical lattice rules. The same ideas apply for polynomial lattice rules. The second author is supported by the Austrian Research Foundation (FWF), Project S9609 that is part of the Austrian National Research Network ``Analytic Combinatorics and Probabilistic Number Theory'. The support of the Australian Research Council under its Center of Excellence Program is greatfully acknowledged.     

Frequency analysis and experimental validation for stiction phenomenon in multi-loop processes

The existence of static friction, also known as stiction nonlinearity, in a control valve may lead the entire system to limit cycles. Despite numerous studies on modeling, detection and compensation of this phenomenon, lack of a reliable methodology to predict occurrence and properties of such oscillations, particularly in multi-loop settings, is quite sensible. This work focuses on frequency analysis of multi-loop processes oscillating due to stiction. Before using any of the existing stiction models for the analysis, a comparison between existing stiction models and actual lab data is carried out. Derivation of a mathematical representation of the condition, under which stiction-induced oscillations occur in a multi-loop system, is the main achievement of the proposed analysis. This condition enables users to predict and compare the severity of the oscillations, i.e. values of frequencies and magnitudes, in different situations. Results of the theoretical discussion are validated by both simulation and experimental studies.     

Perfect forward secure identity-based authenticated key agreement protocol in the escrow mode

The majority of existing escrowable identity-based key agreement protocols only provide partial forward secrecy. Such protocols are, arguably, not suitable for many real-word applications, as the latter tends to require a stronger sense of forward secrecy—perfect forward secrecy. In this paper, we propose an efficient perfect forward-secure identity-based key agreement protocol in the escrow mode. We prove the security of our protocol in the random oracle model, assuming the intractability of the Gap Biline...     

Frequency analysis and compensation of valve stiction in cascade control loops

Valve stiction is often a common problem in control loops and stiction induced oscillation is the main cause of poor performance in control systems. Cascade control is extensively applied in process industry as an effective strategy to restrain disturbances and compensate process nonlinearities. In recent years many studies have been performed on the detection and quantification of valve stiction in single feedback control loops. However, there is a lack in developing a mechanism which can analyze stiction induced oscillation in cascade control loops. This work focuses on the frequency analysis of stiction induced oscillations in cascade control loops and proposes a mechanism of oscillation compensation through outer and inner controller tuning. The effect of oscillation compensation by changing control strategies is also discussed. The theoretical analysis is evaluated through simulation examples and a pilot-scale flow-level cascade control experiment.     

A simple model-free butterfly shape-based detection (BSD) method integrated with deep learning CNN for valve stiction detection and quantification

Control valve stiction is a long-standing problem within process industries. In most methods for shape-based stiction detection, they rely heavily on the traditional controller output (OP) and process variable (PV) plot (i.e. PV-OP plot) that tends to produce an “elliptical” shape which is the widely acknowledged pattern indication for the presence of stiction. However, many of the methods suffered from unsatisfactory generalization capability when subjected to different loop dynamics. In this paper, a “butterfly” shape derived from the manipulation of the standard PV and OP data, which is more robust towards different loop dynamics, is developed for stiction detection. This simple model-free butterfly shape-based detection (BSD) method uses Stenman's one parameter stiction model, which results in a distinctive ‘butterfly’ pattern in the presence of stiction. The proposed BSD is tested on simulated data, as well as 26 benchmark industrial case studies and has shown a relatively higher generalization capability with relatively higher successful detection rate on stiction loops and on non-stiction loops. A simple quantification algorithm based on BSD-convolutional neural network (BSD-CNN) framework is then developed to quantify the stiction severity. Based on the 15 benchmark industrial loops with stiction, the proposed BSD-CNN quantification algorithm has shown reasonable accuracy when compared to other published quantification methods in literature.     

Semi-parametric optimization for missing data imputation

Missing data imputation is an important issue in machine learning and data mining. In this paper, we propose a new and efficient imputation method for a kind of missing data: semi-parametric data. Our imputation method aims at making an optimal evaluation about Root Mean Square Error (RMSE), distribution function and quantile after missing-data are imputed. We evaluate our approaches using both simulated data and real data experimentally, and demonstrate that our stochastic semi-parametric regression imputation is much better than existing deterministic semi-parametric regression imputation in efficiency and effectiveness. This work is partially supported by Australian large ARC grants (DP0449535, DP0559536 and DP0667060), a China NSF major research Program (60496327), China NSF grants (60463003, 10661003), an Overseas Outstanding Talent Research Program of Chinese Academy of Sciences (06S3011S01), a High-level Studying-Abroad Talent Program of the China Human-Resource Ministry and an Innovation Project of Guangxi Graduate Education (2006106020812M35).     

An autonomous valve stiction detection system based on data characterization

This paper proposes a valve stiction detection system which selects valve stiction detection algorithms based on characterizations of the data. For this purpose, novel data feature indexes are proposed, which quantify the presence of oscillations, mean-nonstationarity, noise and nonlinearities in a given data sequence. The selection is then performed according to the conditions on the index values in which each method can be applied successfully. Finally, the stiction detection decision is given by combining the detection decisions made by the selected methods. The paper ends demonstrating the effectiveness of the proposed valve stiction detection system with benchmark industrial data.     

A comparison of techniques for automatic detection of stiction: simulation and application to industrial data

This paper illustrates the effect of stiction in actuators on closed loop performance and the importance of techniques, to be incorporated in the monitoring system, for automatic detection of the onset of this phenomenon. Three different techniques are compared on the basis of simulation by means of stiction models and it is shown how loop variables are affected by stiction parameters and by process characteristics. A major finding is that every technique has an uncertainty region where no decision can be taken in the absence of further information about the process. The application on industrial data, recorded on loops affected by stiction during routine plant operation, allows to confirm this result and to assess relative efficiency of the techniques. A simple test to be performed directly on the plant is also proposed to solve the remaining uncertain cases.     

Adhesive surface design using topology optimization

Tailoring adhesive properties between surfaces is of great importance for micro-scale systems, ranging from managing stiction in MEMS devices to designing wall-scaling gecko-like robots. A methodology is introduced for designing adhesive interfaces between structures using topology optimization. Structures subjected to external loads that lead to delamination are studied for situations where displacements and deformations are small. Only the effects of adhesive forces acting normal to the surfaces are considered. An interface finite element is presented that couples a penalty contact formulation and a Lennard–Jones model of van der Waals adhesive forces. Two- and three dimensional design optimization problems are presented in which adhesive force distributions are designed such that load-displacement curves of delaminating structures match target responses. The design variables describe the adhesive energy per area of the interface between the surfaces, as well as the geometry of the delaminating structure. A built-in length scale in the formulation of the adhesion forces eliminates the need for filtering to achieve comparable optimal adhesive designs over a range of mesh densities. The resulting design problem is solved by gradient based optimization algorithms evaluating the design sensitivities by the adjoint method. Results show that the delamination response can be effectively manipulated by the method presented. Varying simultaneously both adhesive and geometric parameters yields a wider range of reachable target load-displacement curves than in the case varying adhesive energy alone.     

Experimental Measurements of the Strain Energy Release Rate for Stiction-Failed Microcantilevers Using a Single-Cantilever Beam Peel Test

In this paper, we present experimental measurements of the strain energy release rate for stiction-failed polysilicon microcantilevers using a newly developed single cantilever beam peel test. Our experiments show that dry-contacting microcantilevers adhere exclusively as tip-stuck, "arc-shaped" stiction failures, while adhesion under "wet" conditions generate exclusively "s-shaped" stiction failures. Microcantilevers were "peeled" from the substrate under displacement control using a piezoelectric actuator attached to one end of an array of microcantilever beams. The crack length was monitored using interferometric imaging, and related to the applied displacement using established equations from linear elastic fracture mechanics. The pull-off forces associated with "arc-shaped" stiction failures were an average value of 89.7 nN, for 1000 mum long beams, and an average value of 123 nN for 1500 mum long beams. Adhesion energies for s-shaped failures were measured as 13.7 mJ/m² for IPA released beams and 15.4 mJ/m² for deionized water released beams. These values are in good agreement with previous measurements. The proposed experimental method enables application of a simple fracture mechanics model using a standard specimen geometry. These experiments, using both wet and dry adhesion failure conditions, show that the quality of the adhesive failure depends upon the magnitude of the forces pulling the microcantilever into contact with the underlying substrate