Wireless Microfluidic Systems for Programmed,Functional Transformation of Transient Electronic Devices

Electronic systems that enable programmable transformation of functional behaviors by remote control or by autonomous responses to user‐defined circumstances create unusual engineering opportunities, where physical changes in the hardware induce desired changes in operation. This paper presents materials and device architectures for technologies of this type, in which localized microfluidic chemical etching of targeted constituent components in the electronics occurs in a sequential, selective manner. Custom circuits that include reconfigurable radio‐powered thermal actuators with analog amplifiers and square waveform generators illustrate the concepts.     

Materials and Fabrication Processes for Transient and Bioresorbable High‐Performance Electronics

Materials and fabrication procedures are described for bioresorbable transistors and simple integrated circuits, in which the key processing steps occur on silicon wafer substrates, in schemes compatible with methods used in conventional microelectronics. The approach relies on an unusual type of silicon on insulator wafer to yield devices that exploit ultrathin sheets of monocrystalline silicon for the semiconductor, thin films of magnesium for the electrodes and interconnects, silicon dioxide and magnesium oxide for the dielectrics, and silk for the substrates. A range of component examples with detailed measurements of their electrical characteristics and dissolution properties illustrate the capabilities. In vivo toxicity tests demonstrate biocompatibility in sub‐dermal implants. The results have significance for broad classes of water‐soluble, “transient” electronic devices.     

Test Planning and Test Resource Optimization for Droplet-Based Microfluidic Systems

Recent years have seen the emergence of droplet-based microfluidic systems for safety-critical biomedical applications. In order to ensure reliability, microsystems incorporating microfluidic components must be tested adequately. In this paper, we investigate test planning and test resource optimization for droplet-based microfluidic arrays. We first formulate the test planning problem and prove that it is NP-hard. We then describe an optimization method based on integer linear programming (ILP) that yields optimal solutions. Due to the NP-hard nature of the problem, we develop heuristic approaches for optimization. Experimental results indicate that for large array sizes, the heuristic methods yield solutions that are close to provable lower bounds. These heuristics ensure scalability and low computation cost. This research was supported in part by the National Science Foundation under grant number IIS-0312352. A preliminary version of this paper appeared in Proc. European Test Symposium. pp. 72–77, 2004 Fei Su received the B.E. and the M.S. degrees in automation from Tsinghua University, Beijing, China, in 1999 and 2001, respectively, and the M.S. degree in electrical and computer engineering from Duke University, Durham, NC, in 2003. He is now a Ph.D. candidate in electrical and computer engineering at Duke University. His research interests include design and testing of mixed-technology microsystems, electronic design automation, mixed-signal VLSI design, MEMS modeling and simulation. Sule Ozev received her B.S. degree in Electrical Engineering at Bogazici University in 1995, and her M.S. and Ph.D. degrees in Computer Science and Engineering at University of California, San Diego in 1998 and 2002 respectively. Since 2002, she has been a faculty member at Duke University, Electrical and Computer Engineering Department. Her research interests include RF circuit analysis and testing, process variability analysis, and mixed-signal testing. Krishnendu Chakrabarty received the B. Tech. degree from the Indian Institute of Technology, Kharagpur, in 1990, and the M.S.E. and Ph.D. degrees from the University of Michigan, Ann Arbor, in 1992 and 1995, respectively, all in Computer Science and Engineering. He is now Associate Professor of Electrical and Computer Engineering at Duke University. Dr Chakrabarty is a recipient of the National Science Foundation Early Faculty (CAREER) award and the Office of Naval Research Young Investigator award. His current research projects include: design and testing of system-on-chip integrated circuits; design automation of microfluidics-based biochips; microfluidics-based chip cooling; distributed sensor networks. Dr Chakrabarty has authored three books Microelectrofluidic Systems: Modeling and Simulation (CRC Press, 2002), Test Resource Partitioning for System-on-a-Chip (Kluwer, 2002), and Scalable Infrastructure for Distributed Sensor Networks (Springer, 2005) 3/4 and edited the book volume SOC (System-on-a-Chip) Testing for Plug and Play Test Automation (Kluwer 2002). He has published over 200 papers in journals and refereed conference proceedings, and he holds a US patent in built-in self-test. He is a recipient of best paper awards at the 2005 IEEE International Conference on Computer Design and 2001 IEEE Design, Automation and Test in Europe (DATE) Conference. He is also a recipient of the Humboldt Research Fellowship, awarded by the Alexander von Humboldt Foundation, Germany. Dr Chakrabarty is an Associate Editor of IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, IEEE Transactions on VLSI Systems, IEEE Transactions on Circuits and System I, ACM Journal on Emerging Technologies in Computing Systems, and an Editor of Journal of Electronic Testing: Theory and Applications (JETTA). He a member of the editorial board for Sensor Letters and Journal of Embedded Computing and he serves as a subject area editor for the International Journal of Distributed Sensor Networks. He has also served as an Associate Editor of IEEE Transactions on Circuits and Systems II: Analog and Digital Signal Processing. He is a senior member of IEEE, a member of ACM and ACM SIGDA, and a member of Sigma Xi. He serves as Vice Chair of Technical Activities in IEEE’s Test Technology Technical Council, and is a member of the program committees of several IEEE/ACM conferences and workshops. He served as the Program Co-Chair for the 2005 IEEE Asian Test Symposium.     

Dissolution Behaviors and Applications of Silicon Oxides and Nitrides in Transient Electronics

Silicon oxides and nitrides are key materials for dielectrics and encapsulation layers in a class of silicon‐based high performance electronics that has ability to completely dissolve in a controlled fashion with programmable rates, when submerged in bio‐fluids and/or relevant solutions. This type of technology, referred to as “transient electronics”, has potential applications in biomedical implants, environmental sensors, and other envisioned areas. The results presented here provide comprehensive studies of transient behaviors of thin films of silicon oxides and nitrides in diverse aqueous solutions at different pH scales and temperatures. The kinetics of hydrolysis of these materials depends not only on pH levels/ion concentrations of solutions and temperatures, but also on the morphology and chemistry of the films, as determined by the deposition methods and conditions. Encapsulation strategies with a combination of layers demonstrate enhancement of the lifetime of transient electronic devices, by reducing water/vapor permeation through the defects.     

微流控芯片硅阳模的加工

研究了单晶硅阳模的制作工艺。考察了光刻胶前烘和后烘的温度、刻蚀剂浓度、组成及刻蚀温度等因素对单晶硅阳模质量的影响。得出了单晶硅阳模制作的最佳条件，用AZA620光刻胶转移图形及二氧化硅为硅片刻蚀的牺牲层，前烘温度为90℃，后烘温度为120℃，刻蚀温度为60℃；刻蚀液组成为氢氧化钾23．4％，异丙醇14．9％，水61．7％。在该条件下制作的单晶硅阳模表面光亮，通道侧壁较光滑。用热压法可快速地将此阳模上的微通道复制于聚碳酸酯基片上，每片约需时5min。已成功地复制了200多片。     

Dry Transient Electronic Systems by Use of Materials that Sublime

The recent emergence of materials for electronic systems that are capable of programmable self‐destruction and/or bio/eco‐resorption creates the potential for important classes of devices that cannot be easily addressed using conventional technologies, ranging from temporary biomedical implants to enviromentally benign environmental monitors to hardware secure data systems. Although most previous demonstrations rely on wet chemistry to initiate transient processes of degradation/decomposition, options in “dry transient electronic systems” could expand the range of possible uses. The work presented here introduces materials and composite systems in which sublimation under ambient conditions leads to mechanical fragmentation and disintegration of active devices upon disappearance of a supporting substrate, encapsulation layer, interlayer dielectric and/or gate dielectric. Examples span arrays of transistors based on silicon nanomembranes with specialized device designs to solar cells adapted from commercial components.     

Study of Physically Transient Insulating Materials as a Potential Platform for Transient Electronics and Bioelectronics

Controlled degradation and transiency of materials is of significant importance in the design and fabrication of degradable and transient biomedical and electronic devices and platforms. Here, the synthesis of programmable biodegradable and transient insulating polymer films is reported, which have sufficient physical and chemical properties to be used as substrates for the construction of transient electronics. The composite structure can be used as a means to control the dissolution and transiency rate of the polymer composite film. Experimental and computational studies demonstrate that the addition of gelatin or sucrose to a PVA polymer matrix can be used as a means to program and either slow or enhance the transiency of the composite. The dissolution of the polymer composites are fitted with inverse exponential functions of different time constants; the lower time constants are an indication of faster transiency of the polymer composite. The addition of gelatin results in larger time constants, whereas the addition of sucrose generally results in smaller time constants.     

微流控通道加工技术的研究进展

在微流控芯片中,微通道是进行微分析的重要保证,其成型质量直接影响芯片的分析性能.从加工机理、技术特点以及适用范围等方面对激光直写加工、光刻加工、热压印技术、微细铣削加工和3D打印等微流控通道主要加工方法进行了阐述,并总结了这几种加工技术的优缺点,这为实际生产提供了一定参考.最后,对微流控通道加工技术的发展进行了展望,未...     

基于专业需求的“电工电子技术”课程内容的优化

为了解决“电工电子技术”课程内容多、学时少和专业针对性差的问题。笔者将课程教学内容划分为基础内容与专业内容两部分。基础内容是各非电专业共同的学习内容,专业内容则是根据各专业人才培养计划的实际需求设置的学习内容,贯穿在理论教学和实验环节之中。实践结果表明,基于专业需求的电工学教学内容对提高学生学习兴趣,改善课程教学质量、...     

An Analytical Model of Reactive Diffusion for Transient Electronics

Transient electronics is a class of technology that involves components which physically disappear, in whole or in part, at prescribed rates and at programmed times. Enabled devices include medical monitors that fully resorb when implanted into the human body (“bio‐resorbable”) to avoid long‐term adverse effects, or environmental monitors that dissolve when exposed to water (“eco‐resorbable”) to eliminate the need for collection and recovery. Analytical models for dissolution of the constituent materials represent important design tools for transient electronic systems that are configured to disappear in water or biofluids. Here, solutions for reactive‐diffusion are presented in single‐ and double‐layered structures, in which the remaining thicknesses and electrical resistances are obtained analytically. The dissolution time and rate are defined in terms of the reaction constants and diffusivities of the materials, the thicknesses of the layer, and other properties of materials and solution. These models agree well with the experiments for single layers of Mg and SiO₂, and double layers of Mg/MgO. The underlying physical constants extracted from analysis fall within a broad range previously reported in other studies; these constants can be extremely sensitive to the morphologies of the materials, temperature, and the PH value, concentration, and properties of the surrounding liquid.     

Biodegradable Thin Metal Foils and Spin‐On Glass Materials for Transient Electronics

Biodegradable substrates and encapsulating materials play critical roles in the development of an emerging class of semiconductor technology, generally referred as “transient electronics”, whose key characteristic is an ability to dissolve completely, in a controlled manner, upon immersion in ground water or biofluids. The results presented here introduce the use of thin foils of Mo, Fe, W, or Zn as biodegradable substrates and silicate spin‐on‐glass (SOG) materials as insulating and encapsulating layers, with demonstrations of transient active (diode and transistor) and passive (capacitor and inductor) electronic components. Complete measurements of electrical characteristics demonstrate that the device performance can reach levels comparable to those possible with conventional, nontransient materials. Dissolution kinetics of the foils and cytotoxicity tests of the SOG yield information relevant to use in transient electronics for temporary biomedical implants, resorbable environmental monitors, and reduced waste consumer electronics.     

Liquid Metal‐Based Transient Circuits for Flexible and Recyclable Electronics

Transient electronics, arising electronic devices with dissolvable or degradable features on demand, is still at an early stage of development due to the limited choices of materials and strategies. Herein, a facile fabrication method for transient circuits by the combination of room‐temperature liquid metals (RTLMs) as the electronic circuit and water‐soluble poly(vinyl alcohol) (PVA) as the packaging material is reported. The as‐made transient circuits exhibit remarkable durability and stable electric performance upon bending and twisting, while possessing short transience times, owing to the excellent solubility of PVA substrates and the intrinsic flexibility of RTLM patterns. Moreover, the RTLM‐based transient circuit shows an extremely high recycling efficiency, up to 96% of the employed RTLM can be recovered. As such, the economic and environmental viability of transient electronics increases substantially. To validate this concept, the surface patterning of RTLMs with complicated shapes is demonstrated, and a transient antenna is subsequently applied for passive near‐field communication tag and a transient capacitive touch sensor. The application of the RTLM‐based transient circuit for sequentially turning off an array of light‐emitting‐diode lamps is also demonstrated. The present RTLM‐based PVA‐encapsulated circuits substantially expand the scope of transient electronics toward flexible and recyclable transient systems.     

Advanced Materials in Wireless,Implantable Electrical Stimulators that Offer Rapid Rates of Bioresorption for Peripheral Axon Regeneration

Injured peripheral nerves typically exhibit unsatisfactory and incomplete functional outcomes, and there are no clinically approved therapies for improving regeneration. Post-operative electrical stimulation (ES) increases axon regrowth, but practical challenges, from the cost of extended operating room time to the risks and pitfalls associated with transcutaneous wire placement, have prevented broad clinical adoption. This study presents a possible solution in the form of advanced bioresorbable materials for a type of thin, flexible, wireless implant that provides precisely controlled ES of the injured nerve for a brief time in the immediate post-operative period. Afterward, rapid, complete, and safe modes of bioresorption naturally and quickly eliminate all of the constituent materials in their entirety, without the need for surgical extraction. The unusually high rate of bioresorption follows from the use of a unique, bilayer enclosure that combines two distinct formulations of a biocompatible form of polyanhydride as an encapsulating structure, to accelerate the resorption of active components and confine fragments until complete resorption. Results from mouse models of tibial nerve transection with re-anastomosis indicate that this system offers levels of performance and efficacy that match those of conventional wired stimulators, but without the need to extend the operative period or to extract the device hardware.     

Chemical Sensing Systems that Utilize Soft Electronics on Thin Elastomeric Substrates with Open Cellular Designs

A collection of materials and device architectures are introduced for thin, stretchable arrays of ion sensors that mount on open cellular substrates to facilitate solution exchange for use in biointegrated electronics. The results include integration strategies and studies of fundamental characteristics in chemical sensing and mechanical response. The latter involves experimental measurements and theoretical simulations that establish important considerations in the design of low modulus, stretchable properties in cellular substrates, and in the realization of advanced capabilities in spatiotemporal mapping of chemicals' gradients. As the chemical composition of extracellular fluids contains valuable information related to biological function, the concepts introduced here have potential utility across a range of skin‐ and internal‐organ‐integrated electronics where soft mechanics, fluidic permeability, and advanced chemical sensing capabilities are key requirements.     

阵列式芯片特定区域内微流体加热研究

提出了阵列式芯片特定区域内微流体的加热方法,研制了4×4阵列式聚二甲基硅氧烷芯片及其特定区域的加热组件。在128°YX-LiNbO3基片上光刻16个叉指换能器,其激发的SAW驱动压电基片上油相流体,使其输运到待加热区的传热柱上,在油相流体两侧的叉指换能器上加电信号,激发SAW加热油相流体,并通过传热柱加热阵列式芯片受热区内微流体。以石蜡油微流体为实验对象进行阵列式芯片特定区域微流体加热实验,结果表明,SAW可有效加热阵列式芯片特定区域内石蜡油微流体,在30.0dBm电信号功率作用下,使7.5μL石蜡油温度从22.3℃上升到33.5℃。