Smart chemical sensing microsystem : towards a nose-on-a-chip

The electronic nose is a rudimentary replica of the human olfactory system. However there has been considerable commercial interest in the use of electronic nose systems in application areas such as environmental, medical, security and food industry. In many ways the existing electronic nose systems are considerable inferior when compared to their biological counterparts, lacking in terms of discrimination capability, processing time and environmental adaptation. Here, the aim is to extract biological principles from the mammalian olfactory systems to create a new architecture in order to aid the implementation of a nose-on-a-chip system. The primary feature identified in this study was the nasal chromatography phenomena which may provide significant improvement by producing discriminatory spatio-temporal signals for electronic nose systems. In this project, two different but complimentary groups of systems have been designed and fabricated to investigate the feasibility of generating spatio-temporal signals. The first group of systems include the fast-nose (channel 10 cm x 500 μm2), proto-nose I (channel 1.2 m x 500 μm2) and II (channel 2.4 m x 500 μm2) systems that were build using discrete components. The fast-nose system was used to characterise the discrete sensors prior to use. The proto-nose systems, in many ways, resembles gas chromatography systems. Each proto-nose system consists of two microchannels (with and without coating) and 40 polymer-composite sensors of 10 different materials placed along it. The second group of systems include the hybrid-nose and the aVLSI-nose microsensor arrays assembled with microchannel packages of various lengths (5 cm, 32 cm, 7lcm, 240 cm) to form nose-on-a-chip systems. The hybrid-nose sensor array consists of 80 microsensors built on a 10 mm x 10 mm silicon substrate while the aVLSI-nose sensor array consists of 70 microsensors built on a 10 mm x 5 mm silicon substrate using standard CMOS process with smart integrated circuitries. The microchannel packages were fabricated using the Perfactory microstereolithography system. The most advanced microchannel package contains a 2.4 m x 500 J.lm2 microchannel with an external size of only 36 mm x 27 mm x 7 mm. The nose-on-a-chip system achieved miniaturisation and eliminates the need for any external processing circuitries while achieving the same capability of producing spatio-temporal signals. Using a custom-designed vapour test station and data acquisition electronics, these systems were evaluated with simple analytes and complex odours. The experimental results were in-line with the simulation results. On the coated proto-nose II system, a 25 s temporal delay was observed on the toluene vapour pulse compared to ethanol vapour pulse; this is significant compared to the uncoated system where no delay difference was obtained. Further testing with 8 analyte mixtures substantiated that spatio-temporal signals can be extracted from both the coated proto-nose and nose-on-a-chip (hybrid-nose sensor array with 2.4 m long microchannel) systems. This clearly demonstrates that these systems were capable of imitating certain characteristics of the biological olfactory system. Using only the temporal data, classification was performed with principal components analysis. The results reinforced that these additional temporal signals were useful to improve discrimination analysis which is not possible with any existing sensor-based electronic nose system. In addition, fast responding polymer-composite sensors were achieved exhibiting response times of less than 100 ms. Other biological characteristics relating to stereolfaction (two nostrils sniffing at different rates), sniffing rate (flow velocity) and duration (pulse width) were also investigated. The results converge with the biological observations that stereolfaction and sniffing at higher rate and duration improve discrimination. Last but not least, the characterisation of the smart circuitries on the aVLSI-nose show that it is possible to achieve better performance through the use of smart processing circuitries incorporating a novel DC-offset cancellation technique to amplify small sensor response with large baseline voltage. The results and theories presented in this study should provide useful contribution for designing a higher-performance electronic nose incorporating biological principles

Packaging Technologies for Millimeter Scale Microsystems in Harsh Environment Applications

Microsystems capable of sensing temperature, pressure and other parameters are needed for many applications, for example, gathering information in downhole environments for oil and gas exploration. Certain target locations limit the size of the microsystems to millimeter or even sub-millimeter scale. In addition, the high temperature, high pressure, and corrosive ambient environments are challenging for microsystems. Target environments include 125°C temperature, 50 MPa pressure, and salinity standards consistent with American Petroleum Institute (API) brine (8% NaCl + 2% CaCl2). Other chemicals including hydrocarbons and cement slurry are also found in these environments. The system package plays a critical role as it protects the system components against environment, while also providing the physical coupling to the environment, e.g., for communication modules and pressure sensors. The package must be made of mechanically and chemically robust materials. High temperature assembly steps must be avoided in the packaging process (such as bonding above 200°C), because these steps are generally incompatible with embedded batteries and polymer-based sensors. The development of system package and relevant technologies is the focus of this dissertation. This dissertation first describes the design and fabrication of sapphire-on-steel packages in two sizes (0.8 mm and 8 mm), which are capable of isolating high pressure while allowing optical communication. These packages have been operated with embedded electronics at 125ºC and ≈70 MPa in API brine, hydrocarbons, and cement slurry. Additionally, polymer-in-tube packages are reported, which allow the embedded pressure sensors to couple with the environment. These packages have been successfully operated with embedded electronics and sensors at 125ºC and 50 MPa in API brine. A third approach of encapsulation that is reported involves polymer film encapsulation, which has the potential to significantly improve the chemical resistance of microsystems. Finally a batch-mode packaging process is presented based on micro-crimping, enabling room temperature assembly for sub-millimeter scale packages made by metal alloys. This packaging process has been demonstrated by a 5×5 array of 0.5 mm packages. These packages have survived at least 200 MPa pressure and at least 72 h in API brine.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/135761/1/yushuma_1.pd

A Study on Low-Cost, Effective, and Reliable Liquid Crystal Polymer-Based Cochlear Implant System

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 2. 김성준.The pace of technological change in implantable devices such as cochlear implants, artificial retinas, and deep brain stimulators has been relatively slow compared to that in other areas, such as memory and mobile phones. Most implantable devices, including cochlear implants, still use bulky titanium electronic packages with complex fabrication processes and wire-based electrodes which are manually fabricated by skilled workers. As a result, the cost of these devices is very high and the widespread use of these devices is limited in low- and middle income countries. Innovative approaches are essential to make implantable devices as affordable as possible while not sacrificing their performance metrics. In this study, we adopt high-performance liquid crystal polymer (LCP) as a backbone for a novel polymer-based cochlear implant. As a material for cochlear implants, LCP enables new capabilities such as miniaturization, a simpler manufacturing process, better long-term reliability, and MRI compatibility, all of which are distinct from the properties of conventional cochlear implants. Moreover, LCP also enables an extremely low-cost device based on mass production with low materials and labor costs. In this study, we report a fabrication method for the creation of a LCP-based cochlear implant system. Specifically, LCP-based electronics and packaging techniques are addressed in detail. Previous studies of LCP-based packaging use a thermally deformed package cover to secure the electronics cavity and additional laser-cut LCP bonding layers with lower melting temperatures. This method, however, requires additional metal jigs to deform the package cover, and it requires a cavity-filling material such as PDMS. We applied a recessed cavity for the electronics with the stacking of laser-cut LCP multilayers. All packaging layers are composed of the same LCP films, which have a low melting temperature. Thus, the stacked multilayer structure itself acts as a bonding layer. This packaging technology enables the device packaging with a thin credit-card shape for miniaturized, simply fabricated and less invasive devices. Implantable electronics components were also fabricated using copper-clad LCP films with PCB technology. A patterned planar coil was integrated into an LCP electronics board to replace the thick platinum coil of the conventional implant, which is located outside of the metal package. Thus, we can reduce the device dimensions and realize a more efficient receiving coil with greater uniformity. Our group has developed an atraumatic 16-channel LCP-based cochlear electrode array using MEMS technology. This electrode array was used to develop the first functional prototype of an all-LCP-based cochlear implant system. We also evaluated the effectiveness of the developed LCP-based cochlear implant. The device was implanted into an animal model and the electrically evoked auditory brainstem response was successfully measured. We also verified the MRI compatibility of the LCP-based device compared to a metal-based implant, showing that the developed device has greatly superior MRI compatibility compared to a conventional metal-based device in a 3.0-T and an ultra-high 7.0-T MRI machine. In order to enhance the long-term reliability of the LCP-based device, we developed novel leak-barrier structures which have a nanoporous surface and microscale barriers with an anti-trapezoidal cross-sectional shape. This structure increases the water leakage path length and improves the mechanical interlocking force between the polymer and the metal layer. The reliability of the leak-barrier structure was determined by accelerated lifetime soak tests (110, 95, 75 °C). Preliminary results show that both the nanoporous surface and microscale barriers make significant contributions to improving the lifetime of the polymer-based electrode array. Lastly, we conducted a manufacturing cost analysis of the developed LCP-based cochlear implant system for a better understanding of the detailed cost structure and to determine if the cost could be reduced further. Our group also has experience in the development of cochlear implant systems, including titanium packages and wire-based electrode arrays similar to those in conventional devices, and the system developed by our group had been approved by the Korean FDA. The manufacturing costs of devices developed in the past were also analyzed for a comparison with the cost of an LCP-based device. The analysis revealed that the developed LCP-based cochlear implant has a significantly lower cost with regard to the materials. Also, the manufacturing cost per unit is approximately 10 % of the cost of a titanium-based cochlear implant. Also, the LCP-based device is a batch-processable product that therefore requires less labor. Thus, the manufacturing cost is greatly reduced in proportion to the overall production. This reduction in the manufacturing cost enables disruptive opportunities with regard to the use of cochlear implants in developing countries.Abstract Contents List of Figures List of Tables Chapter 1 Introduction 1.1 Overview of Cochlear Implants 1.2 Review of Cochlear Implant Research 1.3 Challenges for Future Cochlear Implant Systems 1.4 Proposed Cochlear Implant System 1.5 Objectives of the Dissertation Chapter 2 Materials and Methods 2.1 System Description 2.1.1 External Speech Processor 2.1.1.1 Hardware Design and Implementation based on Traditional Approach 2.1.1.2 Speech Processing Strategy for Cochlear Stimulation 2.1.1.3 Novel Speech Processor using Smartphone 2.2 Liquid Crystal Polymer (LCP)-Based Implantable Cochlear Implant System 2.2.1 Implantable Electronic Module for the LCP-based Cochlear Implant 2.2.1.1 Electronics Design 2.2.1.2 Electronics Fabrication and Assembly 2.2.2 Electronics Packaging for the LCP-based Cochlear Implant 2.2.3 LCP-based Thin-Film Cochlear Electrode Array 2.3 System Evaluation 2.3.1 Bench-Top Tests of the Fabricated LCP-based Cochlear Implant System 2.3.2 Preliminary In Vivo Animal Study 2.3.2.1 Animal Preparation 2.3.2.2 Experimental Setup and Protocol 2.3.3 In Vivo Animal Study 2.3.3.1 Animal Preparation 2.3.3.2 Improved Experimental Setup and Protocol 2.3.4 Magnetic Resonance Imaging Compatibility Tests 2.4 Leak-Free LCP-based Neural Electrode using Multiple Barrier Structures 2.4.1 Test Devices and Sample Categorization 2.4.2 Fabrication Methods 2.4.3 Electrochemical Characterization of the Electrode 2.4.4 Long-Term Reliability Test of the Leak-Free LCP-Based Neural Electrode 2.5 Manufacturing Cost Analysis 2.5.1 Overview of the Cost Structure 2.5.2 Comparative Analysis of the Manufacturing Cost of the LCP- and Titanium-Based Cochlear Implants Chapter 3 Results 3.1 Fabricated System 3.1.1 External Speech Processor 3.1.2 LCP-based Cochlear Implant 3.1.2.1 Packaging Process 3.1.2.2 Fabricated LCP-based Cochlear Implant 3.1.2.3 Bench-Top Test of the LCP-based Cochlear Implant 3.2 In Vivo Animal Study 3.3 Magnetic Resonance Imaging Compatibility 3.4 Leak-Free LCP-based Neural Electrode using Multiple Barrier Structures 3.4.1 Fabricated Electrode 3.4.2 Characterization of the Electrode 3.4.3 Long-Term Reliability 3.5 Comparative Analysis of the Manufacturing Cost of the LCP- and Titanium-based Cochlear Implants Chapter 4 Discussion 4.1 LCP-based Electronics Packaging 4.2 Comparison of LCP-Based Cochlear Implant to Conventional Metal-Based Cochlear Implant 4.3 Effectiveness of the LCP-Based Cochlear Implant 4.4 Reliability of the Titanium- and LCP-Based Neural Prostheses 4.5 MRI Compatibility 4.6 Manufacturing Cost Analysis Chapter 5 Conclusion References Abstract in Korean 162 감사의 글 166Docto