Surface Of Silicon Chip Research Articles

A study on the effect of the geometric properties and surface defects on silicon chip flexibility for wearable electronics

A study on the effect of the geometric properties and surface defects on silicon chip flexibility for wearable electronics

Acoustofluidics-assisted strategy of zinc oxide nanoarrays for enhancement of phase-change chip cooling

Enhancing flow boiling in microchannel via surface modification is crucial for addressing the energy consumption challenges posed by high-power compact electronic devices. However, improving boiling heat transfer performance with well-defined nanostructured surfaces in a limited space remains a challenge. Herein, we present a simple and straightforward acoustofluidics strategy for stable, controllable, and efficient fabricates of functional Zinc oxide (ZnO) nanoarray silicon chip surface with excellent phase change cooling performance. The intentionally designed flower-like sharp-edge structure integrated acoustic has been experimentally and numerically verified for its enhanced mass transfer mixing. The resulting ZnO nanoarray-coated chip with customizable lengths, densities, and morphology is implemented by simple reactor parameter adjustment. Excellent boiling heat transfer performance is obtained on this surface, giving priority to nucleation (superheat≈ 4 °C), low energy consumption (≤3.2 kPa) and simultaneously enhancing the critical heat flux (CHF) and heat-transfer coefficient (HTC) by up to 70.8 % and 107.5 %, respectively, compared with a smooth chip surface. In situ observation and analysis of the wicking of the nanoarray and nucleation, growth, and departure of the bubbles reflect that ZnO nanoarray promotes the phase change heat exchange process by the large number of nucleation sites and ultrafast liquid re-wetting. These findings not only provide important guidelines for the precise control and rational design of functional nanomaterials, but also provide new insights for embedded cooling and significant energy savings on power devices.

Creation of micro-and nanochannels on the surface of silicon chips by lithography methods and investigation of ion transport in channel

We developed a technique for fabrication microfluidic silicon-glass chips with a system of nanochannels connecting two microchannel using traditional optical lithography and a focused ion beam. To investigate the transport phenomena in the nanochannels we experimentally studied their ion conductivity and using optical microscopy confirmed the existence of the diffusion flow through them. The developed method allows us to create systems of nanochannels with on-purpose geometry and controlled sizes. Devices with such nanochannels can be applied in the creation of biosensor devices and for genetic studies.

From magnetoresistor element to in-plane sensitive Hall device

This paper contributes to the development of in-plane sensitive Hall-effect configurations based on a new sensor concept. An original coupling of pairs of identical two-contact (2C) magnetoresistors transduce an in-plane magnetic field, i.e., parallel to the silicon chip surface into a Hall voltages by means of four-contact (4C) and eight-contact (8C) devices. Two different arrangements are accomplished – hybrid realization with a discrete resistor bridge and fully integrated implementation. The pair’s ohmic contacts of the magnetoresistors are cross-coupled and parallel connected. These configurations has linear and odd output signal as a function of the magnetic field and supply current. The quadratic and even magnetoresistance of innovative solutions is completely suppressed, which ensures high measurement accuracy alongside with identification of the magnetic field polarity. The experimental prototypes feature simplified technological fabrication, sensitivity about 100 V/AT, low output temperature drift and high linearity. The lowest detected magnetic induction at current of 3 mA over frequency range 5 Hz ÷ 500 Hz at a signal-to-noise ratio equal to unity is around 10–12 μT. A benchmarking of the characteristics was performed with both new configurations as well as with an in-plane sensitive four-contact Hall element with closed design. It is established that the new arrangements have advantage and confirms the innovativeness of the proposed concept. The complete electrical, temperature and technological matching of proposed Hall devices is very promising for many practical applications.

Inkjet-printed micro-calibration standards for ultraquantitative Raman spectral cytometry.

Herein we report the development of a cytometric analysis platform for measuring the contents of individual cells in absolute (picogram) scales; this study represents the first report of Raman-based quantitation of the absolute mass - or the total amount - of multiple endogenous biomolecules within single-cells. To enable ultraquantitative calibration, we engineered single-cell-sized micro-calibration standards of known composition by inkjet-printer deposition of biomolecular components in microarrays across the surface of silicon chips. We demonstrate clinical feasibility by characterizing the compositional phenotype of human skin fibroblast and porcine alveolar macrophage cell populations in the respective contexts of Niemann-Pick disease and drug-induced phospholipidosis: two types of lipid storage disorders. We envision this microanalytical platform as the foundation for many future biomedical applications, ranging from diagnostic assays to pathological analysis to advanced pharmaco/toxicokinetic research studies.

A low cross-axis sensitivity piezoresistive accelerometer fabricated by masked-maskless wet etching

The paper focuses on the design, simulation, fabrication and experiment of a low cross-axis sensitivity piezoresistive accelerometer fabricated by masked-maskless wet etching in iodine-supersaturated KOH solution. The piezoresistive accelerometer consists of a proof mass, eight supporting beams and four sensing beams. The sensing beams are located at the top surface of silicon chips in order to pattern piezoresistive resistors and metal lines. A boron-diffused piezoresistive Wheatstone bridge is located at the frame-side end of a sensing beam to detect the strain. The gravity center of the proof mass lies within the neutral plane of supporting beams to minimize the rotation of the proof mass under in-plane acceleration. Compared with accelerometer of which the supporting beams located at the surface of chips, the rotating angle of the newly designed sensor under in-plane acceleration is reduced by 98.91%. Preliminary experimental results show that the cross-axis sensitivity under X and Y acceleration is 1.67% and 0.82%, respectively.

Spontaneous Generation of Electromotive Force in Thin Film Al/Nanosilicon/Al Structures

Contemporary pursuits in electronics include the miniaturization as well as flexibilization of devices. Although there are a large number of different thin and flexible electrochemical batteries, only a few can boast the possibility of working in high humidity conditions. This paper reports on the fabrication of structures consisting of films of silicon nanoparticles encased between two aluminium electrodes. The value of electromotive force (emf) measured depends on the temperature of the sample and on the pressure of water vapor in the storage atmosphere and reaches approximately 1 V. Volt-ampere characteristics were investigated at different conditions to yield a model of emf generation in these structures. It was found that the reaction of water with silicon nanoparticles is the prime reason behind emf generation. Such a source may be introduced into electronic paper, and employed in the next generation of smart cards. The structure may also be manufactured directly on the surface of silicon chips, such as on the back of crystals in microschemes.

Stress Reduction of Solar Cell with Nanostructures on Silicon Chip Surface

Silicon chip has been widely used in solar cell recently. The thinning of silicon chip, easily inducing surface defects, becomes necessary to produce solar cells more efficiently. The surface defects resulting in stress concentration on the silicon chip surface would be the source of chip failure. In this study, the finite element analysis was used to investigate the stress distribution near the surface crack of a solar cell on which the nanostructures were introduced to alleviate the induced stress. For the solar cell model, positive silver and negative aluminum electrodes were added on the top and bottom sides of silicon chip. The solar cell under four-point bending was simulated in analysis with and without nanostructures. The results show that the stresses reduce more than 50 % for the solar cell model with nanostructures. When the crack depth is deeper enough, the stress at crack tip is higher than that at junction near the electrode and the crack leads to the failure of solar cell. The effect of different section length of nanostructures on the stress distribution caused by the surface crack was also discussed.

Boiling heat transfer enhancement of nanofluids on a smooth surface with agitation

The pool boiling heat transfer performance on a smooth silicon chip surface with agitation was experimentally investigated in this study. The nanofluids (Ag/alcohol) of 0.02 % volume concentration and ethyl alcohol with purification over 99.9 % were the two contrast working fluids. For each group, subcoolings of 40, 50 and 60 K were conducted under atmospheric pressure. To enhance the heat transfer performance, an agitating device was fixed above the top of the chip. The experimental results indicated that nanofluids could enhance the heat transfer performance especially in the nucleate boiling region. The heat transfer coefficient was significantly increased with nanofluids, while the critical heat flux (CHF) was nearly not changed. In the agitation Reynolds number of 20,300, the heat transfer performance of nanofluids was significantly enhanced in the convection region, and the CHF was increased by more than 25 % for all groups. This boiling phenomenon was observed for both nanofluids and alcohol groups. Meanwhile, the boiling curves of different liquid subcoolings in the nucleate region were quite similar to each other under agitation.

Stress distribution affected by nanostructures near a surface crack on a silicon chip

During the thinning and machining processes, surface defects or cracks are easily induced on a silicon chip. The defects or cracks may cause stress concentration and become one of the failure sources for silicon chips. One of our previous papers reported that the stress concentration at the crack tip on a silicon chip with nanostructure was greatly reduced for the case of four-point bending. In this paper, the finite element analysis was used to further study the effect of nanostructures on the stress distribution near the surface crack for a silicon chip. Since the stress distribution near the surface crack was our main concern for a chip under four-point bending, nanostructures were introduced in the area near the crack on the chip surface in the analysis for computational efficiency. The spacing and depth of the nanostructure, and the crack depth on the silicon chip surface were varied to access their effects on the stress distributions near the crack on the silicon chip.

The effects of Ni contents on hydrogen sensing response of closely spaced Pd–Ni alloy nanoparticle films

Pd–Ni alloy nanocrystals, with a controlled Ni atom content ranging from 0 to 60%, were synthesized with a gas aggregation process. The mean size of the alloy nanoparticles was found to decrease with Ni content. Quantum conductance-based hydrogen sensors were fabricated by depositing films of closely spaced Pd–Ni nanoparticles in gas phase with a well-controlled coverage, on the surface of silicon chips prefabricated with interdigital electrodes. Significant changes on the α- β phase transition behavior of PdHx and hence the hydrogen response characteristics of the nanoparticle-based sensors, induced by the incorporation of Ni into the Pd nanoparticles, were demonstrated. An optimal Ni content of 16% was suggested to make excellent H2 sensors with rapid response, high sensitivity as well as good linearity and reliability in a wide hydrogen pressure range.

Impedance characterization, degradation, and in vitro biocompatibility for platinum electrodes on BioMEMS.

Fine control of molecular transport through microfluidic systems can be obtained by modulation of an applied electrical field across channels with the use of electrodes. In BioMEMS designed for biological fluids and in vivo applications, electrodes must be biocompatible, biorobust and stable. In this work, the analysis and characterization of platinum (Pt) electrodes integrated on silicon substrates for biomedical applications are presented. Electrodes were incorporated on the surface of silicon chips by adhesion of laminated Pt foils or deposited at 30°, 45° or 90° angle by e-beam or physical vapor (sputtering) methods. Electrical and physical properties of the electrodes were quantified and evaluated using electrical impedance spectroscopy and modelling of the electrode-electrolyte interfaces. Electrode degradation in saline solution at pH 7.4 was tested at room temperature and under accelerated conditions (90 °C), both in the presence and absence of an applied electrical potential. Degradation was quantified using atomic force microscopy (AFM) and inductively coupled plasma mass spectroscopy (ICP-MS). Biocompatibility was assessed by MTT proliferation assay with human dermal fibroblasts. Results demonstrated that the deposited electrodes were biocompatible with negligible material degradation and exhibited electrochemical behavior similar to Pt foils, especially for e-beam deposited electrodes. Finally, Pt electrodes e-beam deposited on silicon nanofabricated nanochannel membranes were evaluated for controlled drug delivery applications. By tuning a low applied electrical potential (<1.5 VDC) to the electrodes, temporal modulation of the dendritic fullerene 1 (DF-1) release from a source reservoir was successfully achieved as a proof of concept, highlighting the potential of deposited electrodes in biomedical applications.

Superparamagnetic iron oxide nanoparticle attachment on array of micro test tubes and microbeakers formed on p-type silicon substrate for biosensor applications

A uniformly distributed array of micro test tubes and microbeakers is formed on a p-type silicon substrate with tunable cross-section and distance of separation by anodic etching of the silicon wafer in N, N-dimethylformamide and hydrofluoric acid, which essentially leads to the formation of macroporous silicon templates. A reasonable control over the dimensions of the structures could be achieved by tailoring the formation parameters, primarily the wafer resistivity. For a micro test tube, the cross-section (i.e., the pore size) as well as the distance of separation between two adjacent test tubes (i.e., inter-pore distance) is typically approximately 1 μm, whereas, for a microbeaker the pore size exceeds 1.5 μm and the inter-pore distance could be less than 100 nm. We successfully synthesized superparamagnetic iron oxide nanoparticles (SPIONs), with average particle size approximately 20 nm and attached them on the porous silicon chip surface as well as on the pore walls. Such SPION-coated arrays of micro test tubes and microbeakers are potential candidates for biosensors because of the biocompatibility of both silicon and SPIONs. As acquisition of data via microarray is an essential attribute of high throughput bio-sensing, the proposed nanostructured array may be a promising step in this direction.

Enhanced Boiling Heat Transfer by Using Micro-Pin-Finned Surface in Three Different Test Systems

For efficiently cooling electronic components, experiments were conducted to study heat transfer performance of FC-72 over a silicon chip with micro-pin-fins in three different test systems including pool boiling, natural circulation flow boiling, and forced flow boiling. A smooth chip (chip S) and a micro-pin-finned chip having fin thickness of 30 μm and fin height of 60 μm (chip PF30-60) were tested. The micro-pin-fins were fabricated on the surface of square silicon chip (10 × 10 × 0.5 mm3) by use of dry etching technique for enhancing boiling heat transfer. The experiments were conducted at fluid velocities of 0.5 and 1 m/s for the forced flow boiling and the liquid subcoolings of 25 and 35 K for all three test systems. With regard to the three test systems, the micro-pin-finned surface shows a considerable heat transfer enhancement compared to the smooth surface and shows a sharp increase in the critical heat flux (CHF). For the same chip, the boiling curves are almost the same for the pool boiling and the natural circulation flow boiling, while the boiling curves shift toward a smaller wall superheat for the forced flow boiling. The critical heat flux was the highest for the forced flow boiling at a fluid velocity of 1 m/s.

Compact Low-Power Impedance-to-Digital Converter for Sensor Array Microsystems

With the rapid progress in CMOS compatible microfabrication of biosensors, there is an emerging need to miniaturize biosensor arrays onto the surface of silicon chips that acquire and process sensor data, permitting improved sensitivity, cost and throughput. In this paper, a low power circuit that extracts and digitizes sensor impedance information is presented. Composed of a novel multiplying integrator and a unique bidirectional counter/shifter, the circuit shares resources for impedance extraction and digitization to maximize hardware efficiency. The extremely compact size of the circuit enables the implementation of sensor array microsystems with simultaneous multi-channel readout. Fabricated in 0.5 mum CMOS, the circuit consumes 6 muW at 3 V and occupies only 0.06 mm2, permitting over 100 readout channels within a 3 times 3 mm die. Circuit performance has been verified with a biosensor for gramicidin ion channel embedded in a tethered bilayer lipid membrane.

Seed bubbles trigger boiling heat transfer in silicon microchannels

The smooth channel surface of microsystems delays boiling incipience in heated microchannels. In this paper, we use seed bubbles to trigger boiling heat transfer and control thermal non-equilibrium of liquid and vapor phases in parallel microchannels. The test section consisted of a top glass cover and a silicon substrate. Microheater array was integrated at the top glass cover surface and driven by a pulse voltage signal to generate seed bubbles in time sequence. Each microheater corresponds to a specific microchannel and is located in the microchannel upstream. Five triangular microchannels with a hydraulic diameter of 100 μm and a length of 12.0 mm were etched in the silicon substrate. A thin platinum film was deposited at the back surface of silicon chip with an effective heating area of 4,500 × 1,366 μm, acting as the main heater for the heat transfer system. Acetone liquid was used. With the data range reported here, boiling incipience was not initiated if wall superheats are smaller than 15°C without seed bubbles assisted. Injection seed bubbles triggers boiling incipience and controls thermal non-equilibrium between liquid and vapor phases successfully. Four modes of flow and heat transfer are identified. Modes 1, 2, and 4 are the stable ones without apparent oscillations of pressure drops and heating surface temperatures, and mode 3 displays flow instabilities with apparent amplitudes and long periods of these parameters. The four modes are divided based on the four types of flow patterns observed in microchannels. Seed bubble frequency is a key factor to influence the heat transfer. The higher the seed bubble frequency, the more decreased non-equilibrium between two phases and heating surface temperatures are. The seed bubble frequency can reach a saturation value, at which heat transfer enhancement attains the maximum degree, inferring that a complete thermal equilibrium of two phases is approached. The saturation frequency is about a couple of thousand Hertz in this study.

Subcooled flow boiling heat transfer of FC-72 from silicon chips fabricated with micro-pin-fins

Experiments were conducted to study the subcooled flow boiling heat transfer performance of FC-72 over silicon chips. For boiling heat transfer enhancement, two kinds of micro-pin-fins having fin thickness of 50 μm and fin heights of 60 and 120 μm, respectively, were fabricated on the silicon chip surface with the dry etching technique. The fin pitch was twice the fin thickness. The experiments were conducted at the fluid velocities of 0.5, 1 and 2 m/s and the liquid subcoolings of 15, 25 and 35 K. The micro-pin-finned surfaces showed a sharp increase in heat flux with increasing wall superheat and a large heat transfer enhancement compared to a smooth surface. The nucleate flow boiling curves for the two micro-pin-finned surfaces collapsed to one line showing insensitivity to fluid velocity and subcooling, while the critical heat flux values increased with fluid velocity and subcooling. The micro-pin-finned surface with a larger fin height of 120 μm provided a better flow boiling heat transfer performance and a maximum critical heat flux of 145 W/cm 2. The wall temperature at the critical heat flux for the micro-pin-finned surfaces was less than 85 °C for the reliable operation of LSI chips.

Experimental study of boiling phenomena and heat transfer performances of FC-72 over micro-pin-finned silicon chips

Experiments were conducted to study the effects of micro-pin-fins on boiling phenomena and heat transfer from square simulated silicon chips immersed in a pool of FC-72. Two kinds of micro-pin-fins having fin thickness of 30 μm and fin heights of 60 and 200 μm, respectively, were fabricated on the silicon chip surface with the dry etching technique. The experiments were conducted at the liquid subcoolings of 3, 25, 35 and 45 K. The effects of dissolved air in FC-72 and chip orientation were also investigated. The boiling curve of the micro-pin-finned chips was characterized by a very small increase in wall superheat with increasing heat flux, and the wall temperatures at the CHF point for all the micro-pin-finned chips were less than the upper limit for the reliable operation of LSI chips (Tw=85°C). Liquid subcooling was very effective in elevating CHF for the micro-pin-finned chips compared to the smooth surface and other treated surfaces. The enhanced boiling heat transfer mechanisms for the micro-pin-finned chips were discussed.

Development of new no-flow underfill materials for both eutectic Sn-Pb solder and a high temperature melting lead-free solder

In recent years, no-flow underfill technology has drawn more attention due to its potential cost-savings advantages over conventional underfill technology, and as a result several no-flow underfill materials have been developed and reported. However, most of these materials are not suitable for lead-free solder, such as Sn/Ag (m.p. 225/spl deg/C), Sn/Ag/Cu (m.p. 217/spl deg/C), applications that usually have higher melting temperatures than the eutectic Sn-Pb solder (m.p. 183/spl deg/C). Due to the increasing environmental concern, the demand for friendly lead-free solders has become an apparent trend. This paper demonstrates a study on two new formulas of no-flow underfill developed for lead-free solders with a melting point around 220/spl deg/C. As compared to the G25, a no-flow underfill material developed in our research group, which uses a solid metal chelate curing catalyst to match the reflow profile of eutectic Sn-Pb solder, these novel formulas employ a liquid curing catalyst thus provides ease in preparation of the no-flow underfill materials. In this study, curing kinetics, glass transition temperature (Tg), thermal expansion coefficient (TCE), storage modulus (E') and loss modulus (E'') of these materials were studied with a differential scanning calorimetry (DSC), a thermo-mechanical analysis (TMA), and a dynamic-mechanical analysis (DMA), respectively. The pot-life in terms of viscosity of these materials was characterized with a stress rheometer. The adhesive strength of the materials on the surface of silicon chips were studied with a die-shear instrument. The influences of fluxing agents on the materials curing kinetics were studied with a DSC. The materials compatibility to the solder penetration and wetting on copper clad during solder reflow was investigated with both eutectic Sn-Pb and 95.9Sn/3.4Ag/0.7Cu solders on copper laminated FR-4 organic boards.

Microelectrode array sensor for water quality monitoring

A versatile microelectrode array sensor for water quality monitoring has been developed. The array fabrication, based on batch microelectronic processes, results in a highly stable passivation of the silicon chip surface and provides the possibility to use a backside contact. Packaging was optimized for on-line water operation at high pressures. Examples of applications include chlorine monitoring in drinking water, ozone monitoring in deionized water, dissolved oxygen in activated sludge and preliminary measurements of trace arsenic.