Spatially resolved temperature measurement in microchannels

Non-intrusive local temperature measurement in convective microchannel flows using infrared (IR) thermography is presented. This technique can be used to determine local temperatures of the visualized channel wall or liquid temperature near this wall in IR-transparent heat sinks. The technique is demonstrated on water flow through a silicon (Si) microchannel. A high value of a combined liquid emissivity and substrate overall transmittance coupled with a low uncertainty in estimating this factor is important for quantitative temperature measurement using IR thermography. The test section design, and experimental and data analysis procedures that provide increased sensitivity of the detected intensity to the desired temperature are discussed. Experiments are performed on a 13-mm long, 50 μm wide by 135 μm deep Si microchannel at a constant heat input to the heat sink surface for flow rates between 0.6 and 1.2 g min⁻¹. Uncertainty in fluid temperature varies from a minimum of 0.60°C for a Reynolds number (Re) of 297 to a maximum of 1.33°C for a Re of 251.     

A numerical hydrodynamic and thermal characterization of an inter-strata liquid cooling solution for 3D ICs

A novel integrated thermal management solution is proposed to alleviate hot spots in a contemporary 3D IC architecture. The solution employs a series of integrated microchannels, interconnected through each stratum by through silicon fluidic vias (TSFVs), and permits the transfer of heat, via a coolant, from hot to cold zones. This microfluidic system is driven by an integrated AC electrokinetic pump embedded in the channel walls. Recent advancements in electrokinetic micropump technology have allowed greater increases in fluid velocity (mm/s) while operating within the voltage constraints of a 3D IC. This paper presents a 2D simulation of an electrokinetic micropump operating at V_pp = 1.5 V in a 40 μm channel and examines its velocity profile for six frequencies in the range 100 ≤ ω ≤ 100 MHz. An optimum frequency of 100 kHz was established within this range and this was further examined with a constant heat flux of 186 W/cm2 imposed on the wall for an inlet fluid temperature of 40°C. Temperature profiles are presented at the channel-silicon interface and compared with theory.     

Infrared thermography in the hands and feet of hand-arm vibration syndrome (HAVS) cases and controls

This study evaluated IR thermography during 15 min of re-warming after cold water immersion in accordance with ISO guidelines (12 °C for 5 min) in cases with the vascular component of HAVS and controls. The purposes of the study were: (1) To evaluate the performance of IR thermography as a diagnostic test for the vascular effects of HAVS in the fingers, (2) To determine if there were any temperature differences in the toes between cases and controls and, if so, to evaluate the IR thermography as a diagnostic test for toe vascular effects in HAVS. A total of 39 HAVS cases and 46 controls were included in the study. In the fingers, an ROC analysis indicated that the highest areas under the curve (AUC) were obtained at 7 min of re-warming for the fingertips, middle phalanges and proximal phalanges. However, at these locations and time period of re-warming the sensitivities and specificities were not sufficiently high. For example a sensitivity of 66.7% was associated with specificities of 60.9%–67.4%. In the toe analysis 33 (84.6%) cases but only 3 controls (6.5%) reported increased cold intolerance in the feet and this difference was statistically significant (p < 0.001). These 33 cases were then compared to the 46 controls. In the ROC analysis for the toes, the AUC's were lower than those for the fingers and the estimated sensitivities and specificities were worse for the toes than for the fingers. However some statistically significant colder temperatures were found in cases in comparison to controls towards the end of the re-warming period. IR thermography after the ISO recommended cold water stimulation conditions did not perform well as a diagnostic test in the hands or feet. The statistically significant colder temperatures in the toes towards the end of re-warming are relevant to our understanding of foot vascular effects associated with vibration. In industry there is recent interest in determining the effects of foot transmitted vibration (FTV). Many workers have mixed HAV and FTV and it is important to account for feet effects secondary to HAVS in the hands when evaluating the effects of FTV.     

A hybrid capacitive pressure and temperature sensor fabricated by adhesive bonding technique for harsh environment of kraft pulp digesters

We have developed a compensated capacitive pressure and temperature sensor for kraft pulp digesters (pH 13.5, temperatures 25–175°C reaching a local maximum of 180°C and pressures up to 2 MPa). The gauge capacitive pressure sensor was fabricated by bonding silicon and Pyrex chips using a high temperature, low viscosity UV (ultraviolent) adhesive as the gap-controlling layer and heat curing adhesive as the bonding agent. A simple chip bonding technique, involving insertion of the adhesive into the gap between two chips was developed. A platinum thin-film wire was patterned on top of a silicon chip to form a resistance temperature detector (RTD) with a nominal resistance of 1,500 Ω. A silicon dioxide layer and a thin layer of Parylene were deposited to passivate the pressure sensor diaphragm and the sensors were embedded into epoxy for protection against the caustic environment in kraft digesters. The sensors were tested up to 2 MPa and 170°C in an environment chamber. The maximum thermal error of ±1% (absolute value of ±20 kPa) full scale output (FSO) and an average sensitivity of 0.554 fF/kPa were measured. Parylene-coated silicon chips were tested for a full kraft pulping cycle with no signs of corrosion.     

Silicon tip sharpening based on thermal oxidation technology

Thermal oxidation at low temperatures (below 1050 °C) is widely used in the microfabrication of sharp silicon tips. However, the influences of the oxidation temperature on morphology of the tips have not been investigated in detail. This work systematically studied the dependence of tip profile on the oxidation temperature. Thermal oxidation were performed in four groups at 900, 950, 1000 and 1050 °C. The results show that a trade-off between the tip aspect ratio and diameter should be taken into account when choosing the oxidation temperature. The optimized oxidation temperature to make tips with small apex, high aspect ratio, and smooth surface is around 1000 °C. The tip with a diameter of 6.3 nm was realized through oxidation at 1000 °C.

     

Experimental and numerical investigation into the joule heating effect for electrokinetically driven microfluidic chips utilizing total internal reflection fluorescence microscopy

This paper presents a detection scheme for analyzing the temperature distribution nearby the channel wall in a microfluidic chip utilizing a temperature-dependent fluorescence dye. An advanced optical microscope system—total internal reflection fluorescence microscope (TIRFM) is used for measuring the temperature distribution on the channel wall at the point of electroosmotic flow in an electrokinetically driven microfluidic chip. In order to meet the short working distance of the objective type TIRFM scheme, microscope cover glass slits are used to fabricate the microfluidic chips. The short fluorescence excitation depth from a TIRFM system makes the intensity information obtained using TIRFM is not sensitive to the channel depth variation which ususally biases the measured results while using a conventional Epi-fluorescence microscope (EPI-FM). Therefore, a TIRFM can precisely describe the temperature profile of the distance within 100 nm of the channel wall where consists of the Stern layer and the diffusion layer for an electrokinetic microfluidic system. Results indicate the proposed TIRFM provides higher measurement sensitivity over the EPI-FM. Significant temperature gradient along the channel depth is experimentally observed. In addition, the measured wall temperature distributions can be the boundary conditions for numerical investigation into the joule heating effect. The proposed method gives a precise temperature profile of microfluidic channels and shows the substantial impact on developing a numerical simulation model for precisely predicting the joule heating effect in microfluidic chips.     

Single-cell-based measurement of supraphysiological thermal injury in human carcinoma cells utilizing a micropatterned hydrogel chip

Hyperthermia affects certain regulatory proteins, kinases or cyclins, resulting in alternations to the cell cycle and even to apoptosis. Damage to the cell plasma membrane is a key factor in the killing of a cell by hyperthermia. Analysis at the single-cell level is necessary for understanding the fundamental mechanisms of hyperthermia-induced cell death and the generation of thermotolerance in surviving cells. Engineering approaches achieving precise control of cellular micropatterning provide the potential for investigating the mechanisms of thermal injury to cells at the single-cell level. The main purpose of this study is to fabricate a hydrogel chip with microwells for cellular patterning and to demonstrate the feasibility of measurement of supraphysiological thermal injury in human carcinoma cells (HeLa cells) at the single-cell level. To accomplish this, measurement of membrane injury by dye leakage post-thermal insult was performed and reported in this work. A hydrogel chip with microwells with different diameters was fabricated. For cell concentrations at 0.5 × 10⁶ cells/mL, the occupancy of cells on the microchip with 40 μm microwells was up to 86.6%, a value far higher than that found on the 30 μm microwells (approximately 78.5%). Most microwells of 30 μm in diameter (about 70%) were occupied by a single cell; hence, the hydrogel chip with 30 μm microwells was suitable for the applications of single-cell-based analysis. The fluorescent images showed that calcein leakage occurred when cell membranes were damaged under supraphysiological temperatures between 43 and 50°C. The normalized intensity of calcein decreased to 32% under a supraphysiological temperature of 43°C for 20 min. The intensity of calcein in cells was less than 20% under a supraphysiological temperature of 50°C. The feasibility of the single-cell-based experiment of thermal injury in the microchip with hydrogel microwells was therefore successfully demonstrated.     

Micro-hotplate based temperature stabilization system for CMOS SAW resonators

Due to the sensitivity of the piezoelectric layer in surface acoustic wave (SAW) resonators to temperature, a method of achieving device stability as a function of temperature is required. This work presents two methods of temperature control for CMOS SAW resonators using embedded polysilicon heaters. The first approach employs the oven control temperature stabilization scheme. Using this approach, the device’s temperature is elevated using on-chip heaters to T_max = 42°C to maintain constant device temperature. Both DC and RF measurements of the heater together with the resonator were conducted. Experimental results have indicated that the TCF of the CMOS SAW resonator of −97.2 ppm/°C has been reduced to −23.19 ppm/°C when heated to 42°C. The second scheme uses a feedback control circuit to switch the on-chip heaters on and off depending on the ambient temperature. This method provided reduction of the TCF from −165.38 ppm/°C, to −93.33 ppm/°C. Comparison of both methods was also provided.     

A kinetic model for beer production under industrial operational conditions

A kinetic model for beer production is proposed. The model takes into account five responses: biomass, sugar, ethanol, diacetyl and ethyl acetate. In contrast with previously published models, this model segregates biomass into three components: lag, active and dead cells and considers the active cells as the only fermentation agent. Experiments were first performed at laboratory scale and isothermal runs were carried out at five temperatures (8°C, 12°C, 16°C, 20°C and 24°C). Fitting of experimental data was made by non-linear regression. Parameter values calculated were similar to those given in the literature. The kinetic model was able to fit experimental data with a very good agreement. Afterwards, experiments were conducted at pilot plant scale and runs were now carried out changing temperature with time, in the industrial way. The kinetic model, with the parameter values calculated as a function of temperature, was able to predict with a very high accuracy the non-isothermal experimental data achieved. This model can be used for simulation of the industrial process under different operational conditions and for faults detection. It can also be utilized for the optimization and even for the supervised control of the process and its automatization.     

Simulation of a high-power LED lamp for the evaluation and design of heat dissipation mechanisms

High-power LED lamps have been under intense development in recent years. However, issues related to heat dissipation on the LED chip continue to plague research efforts. Heat generation increases with the power of the LED chip and heat accumulation is exacerbated by the plastic casinge of the lamp. Accumulated heat can seriously shorten the lifespan of an LED device. Consequently, manufacturers are constantly seeking ways to improve heat dissipation via heat transfer mechanisms. Little analysis has been performed on coupling the fluid field and heat dissipation inside LED lamps. Using FLUENT software, this study developed a simulation method for LED lamps in order to investigate thermal and fluid fields inside a lamp. The simulation results of an 8 W LED lamp predicted a chip temperature of 75.1 °C and maximum air velocity of 97.3 mm/s within the lamp with two sets of air circulation. The proposed model facilitates new fin designs and the determination of the optimal inner-shell thickness with the proposed design of a LED lamp having 36 fins and an inner-shell thickness of 1 mm for increased heat dissipation.     

Application of wavelet neural network in signal processing of MEMS accelerometers

A new method with wavelet neural network is described to optimize MEMS accelerometers for temperature independent sensitivity. Linear accelerations are measured and compensated by a thermocouple the fast algorithm which is used to deal with the nonlinearity error. The simulation results show that MEMS accelerometers with compensation is characterized by an excellent temperature stability of the sensitivity with less than 0.1% variation for a temperature range −40–100°C, while the variation of acceleration without compensation is 8%. The proposed algorithm can be useful for realization of high accuracy miniature gyroscope systems based on MEMS technology.     

Characterisation of defects in very high deep-etch X-ray lithography microstructures

 In deep X-ray lithography synchrotron radiation is applied to pattern several hundred micrometer thick resist layers. This technique has been used to obtain micro structures with an aspect ratio up to 100 and dimensions in the micrometer range. The structures are characterised by straight walls and a typical sidewall roughness of approximately 50 nm. To be able to fabricate n-coherent structures with any lateral shape and to have the possibility to use these resist microstructures in an additional electroforming process the resist is usually mounted on a ceramic or metallic substrate. Due to the different thermal expansion coefficients of the resist material and the substrate a developing temperature of 37 °C produces cracks in the resist structures depending on the microstructure design. These defects are not observed if the developing temperature is reduced to 20 °C. Better structure quality is obtained using the GG-developer instead of MIBK/IPA, but the developing rate is decreased. Measurements of the developing rate of PMMA in GG-developer at different temperatures show that the contrast of the developer-resist system is increased at 20 °C compared to 37 °C. Received: 25 August 1997/Accepted: 3 September 1997     

Temperature effect on microchannel oil-in-water emulsification

Microchannel (MC) emulsification is a promising technique to produce monodisperse emulsions by spontaneous interfacial-tension-driven droplet generation. The purpose of this study was to systematically characterize the effect of temperature on droplet generation by MC emulsification, which is a major uncharted area. The temperature of an MC emulsification module was controlled between 10 and 70°C. Refined soybean oil was used as the dispersed phase and a Milli-Q water solution containing sodium dodecyl sulfate (1 wt%) as the continuous phase. Monodisperse oil-in-water (O/W) emulsions with a coefficient of variation below 4% were produced, and at all the operating temperatures, their average droplet diameter ranged from 32 to 38 μm. We also investigated the effect of flow velocity of the dispersed phase on droplet generation characteristics. The maximum droplet generation rate (frequency) from a channel at 70°C exceeded that at 10°C by 8.1 times, due to the remarkable decrease in viscosity of the two phases. Analysis using dimensionless numbers indicated that the flow of the dispersed phase during droplet generation could be explained using an adapted capillary number that includes the effect of the contact angle of the dispersed phase to the chip surface.     

A 0.6 V 117 nW high performance energy efficient system-on-chip (SoC) CMOS temperature sensor in 0.18 µm CMOS for aerospace applications

This research article presents and describes a novel design with improved performance low power consumption threshold voltage based CMOS thermal sensor for aerospace applications. The proposed temperature sensor utilizes the change in behavior of threshold voltage of MOSFET with variation in temperature. The challenge while designing the temperature sensor was to achieve the linearize output voltage with respect to change in temperature. Process corner analysis has been done to check the robustness of the circuit while performance analysis and sensitivity of the temperature sensor have been verified in the occurrence of parasitic. The proposed temperature sensor is featured with low power consumption, less power supply voltage utilization, high performance and sensitivity with inaccuracy as low as possible. The presented temperature sensor utilizes an active area of 18 µm × 9.85 µm with 117 nW power consumption. An improved linear performance with an inaccuracy of merely − 0.01 to + 0.47 °C over a wide temperature range of − 20 to + 120 °C is presented here. The sensitivity of proposed temperature sensor is found to be as high as 0.77 mV/°C. The proposed temperature sensor is realized and tested in Cadence virtuoso mixed signal design atmosphere using 0.18 µm CMOS technology and further investigated with support of tool from Mentor graphics. The engaged area of pad-limited chip is measured to be 0.96 mm².

     

Cyanate ester based resin systems for snap-cure applications

 Resin compositions comprising cyanate ester have been demonstrated to be useful as die attach adhesives, underfills and encapsulants, where the characteristics of the resins can be varied in a wide range by copolymerization with functionalized comonomers such as epoxies, phenols, rubbers, thermoplastics and others. To reach a combination of properties such as long pot life, short cure time and high glass transition temperature, we encapsulated small particles of effective hardeners to make them insoluble and non-reactive when mixed with the resin at room temperature. Pot lifes of more than 3 months could be reached, whereas the same cyanate ester gels and becomes solid within 30 min at room temperature, if the neat hardener is used instead of the capsules. At a certain elevated temperature, which mainly depends on the structure of the hardener, the capsules open and the curing reaction starts immediately. Low-temperature systems with cure times less than 5 min at 80 °C reach glass temperatures of about 140 °C, and a glass transition temperature of 220 °C after 10 s cure can be achieved with another combination. The developed snap cure resin systems can be easily mixed with a lot of common additives such as minerals, tougheners, metallic powders and others to cover a wide range of performance characteristics for use as adhesives, underfills, encapsulants and the like. Received: 15 May 2001/Accepted: 15 October 2001     

Characterisation of silicon carbide JFETs with respect to microsystems for high temperature applications

 In this work first commercially available SiC-transistor prototypes were tested with regard to their applicability in high temperature electronic circuits for sensor signal conditioning. The influence of the temperature on the device behaviour (drain-saturation current, gate leakage current, I–V-characteristics, long-term effects) was investigated. The devices showed reliable operation up to 450 °C. The maximum forward transconductance g _m and the short circuit drain source current I _DSS decreased to approximately 30% of the room temperature values. Also, a slight increase of the pinch-off voltage V _p was observed. The gate leakage current I _GSS rose with temperature, staying below 1 μA at 450 °C. A pre-ageing study was carried out to verify changes in the device characteristics with time. The devices were exposed to a 270 °C environment and it was observed that the DC parameters tend to stabilise after about 100 h. From the I–V-characteristics the SPICE parameters were extracted for a series of temperatures, allowing the design and optimisation of amplifier gain stages. The SPICE device simulation results are in good agreement with the measured characteristics. Received: 28 November 1996/Accepted: 2 December 1996     

MEMS-based microthruster with integrated platinum thin film resistance temperature detector (RTD), heater meander and thermal insulation for operation up to 1,000°C

We have fabricated microthruster chip pairs—one chip with microthruster structures such as injection capillaries, combustion chamber and converging/diverging nozzle machined using the deep reactive ion etching process, the other chip with sputtered platinum (Pt) thin film devices such as resistance temperature detectors (RTDs) and a heater. To our knowledge, this is the first microelectromechanical systems-based microthruster with fully integrated temperature sensors. The effects of anneal up to 1,050°C on the surface morphology of Pt thin films with varied geometry as well as with/without PECVD-SiO₂ coating were investigated in air and N₂ and results will also be presented. It was observed that by reducing the lateral scale of thin films the morphology change can be suppressed and their adhesion on the substrate can be enhanced. Chemical analysis with X-ray photoelectron spectroscopy showed that no diffusion took place between neighboring layers during annealing up to 1?h at 1,050°C in air. Electrical characterization of sensors was carried out between room temperature and 1,000°C with a ramp of ±5?Kmin^?1 in air and N₂. In N₂, the temperature-resistance characteristics of sensors had stabilized to a large extent after the first heating. After stabilization the sensors underwent up to eight further temperature cycles. The maximum drift of the sensor signal was observed for temperatures above 950°C and was less than 8.5?K in N₂. To reduce the loss of combustion heat, chip material around microthruster structures was partially removed with laser ablation. The effects of thermal insulation were investigated with microthruster chip pairs which were clamped together mechanically. The heater was operated with up to 20?W and the temperature distribution in the chip pairs with/without thermal insulation was monitored with seven integrated RTDs. The experiments showed that a thermal insulation allows the maximum temperature as well as the temperature gradient within the microthruster chip pairs to be increased.     

Pre-programmable polymer transformers as on-chip microfluidic vacuum generators

This paper develops novel polymer transformers using thermally actuated shape memory polymer (SMP) materials. This paper applies SMPs with thermally induced shape memory effect to the proposed novel polymer transformers as on-chip microfluidic vacuum generators. In this type of SMPs, the morphology of the materials changes when the temperature of materials reaches its glass transition temperature (T _g). The structure of the polymer transformer can be pre-programmed to define its functions, which the structure is reset to the temporary shape, using shape memory effects. When subjected to heat, the polymer transformer returns to its pre-memory morphology. The morphological change can produce a vacuum generation function in microfluidic channels. Vacuum pressure is generated to suck liquids into the microfluidic chip from fluidic inlets and drive liquids in the microchannel due to the morphological change of the polymer transformer. This study adopts a new smart polymer with high shape memory effects to achieve fluid movement using an on-chip vacuum generation source. Experimental measurements show that the polymer transformer, which uses SMP with a T _g of 40°C, can deform 310 μm (recover to the permanent shape from the temporary shape) within 40 s at 65°C. The polymer transformer with an effective cavity volume of 155 μl achieved negative pressures of −0.98 psi. The maximum negative up to −1.8 psi can be achieved with an effective cavity volume of 268 μl. A maximum flow rate of 24 μl/min was produced in the microfluidic chip with a 180 mm long channel using this technique. The response times of the polymer transformers presented here are within 36 s for driving liquids to the end of the detection chamber. The proposed design has the advantages of compact size, ease of fabrication and integration, ease of actuation, and on-demand negative pressure generation. Thus, this design is suitable for disposable biochips that need two liquid samples control. The polymer transformer presented in this study is applicable to numerous disposable microfluidic biochips.     

Optical loss of metal coated optical fibers at temperatures up to 800°C

Temperature band of ordinary telecommunication optical fibers is −60...85°C. The developing fiber optic sensors which can work at higher temperatures, required to develop metal coated optical fibers. The Purpose of the work is a researching additional optical loss of copper alloy coated optical fibers which were drawn from low hydroxyl group contamination preforms at temperatures 20...800°C. It is reached that metal coated optical fiber worked at temperature 700°C for 7 hours, while the optical losses changed from 2 to 3 dB/km at the wavelength of λ = 1300 nm. It is not observed intensive growth of optical losses on hydroxyl groups at 800°C, which was observed in metal coated optical fiber when it was heated at 700°C.     

SU-8 as resist material for deep X-ray lithography

 A new negative tone resist for deep X-ray lithography is presented. This resist is a nine parts to one mixture of the EPON SU-8 resin with 2,2-bis-(3,5-dichloro-4-hydroxyphenyl)propane (Tetrachlorobisphenol A, TCBA), the latter acting as the photoinitiator. The resist was irradiated at the synchrotron source of DCI at LURE. It was dried for 7 to 20 days beforehand over silica gel while under a light vacuum (20 mbar). Best results for a 150 μm high resist were obtained with a X-ray bottom dose of 3 kJ cm⁻³ and a post exposure bake at 33 °C. Differential Scanning Calorimetry measurements (DSC) determined the glass transition temperature of the resist. The glass transition for the undried, loose resist was 34.7 °C, and it was 28.7 °C when the resist was pressed on a silicon substrate. For a sample of the dried resist, the glass transition was 33.4 °C for the loose resist and 29.8 °C when it was pressed on a Silicon substrate. CD measurements were made on top surface of a set of 100 μm long columns structures, which were produced in 150 μm of this resist. These structures have a constant 100 μm pitch, and the structures themselves varied in width from 20 to 17 μm. For these structures, the CD was calculated to be 0.15 ± 0.03 μm. Received: 8 February 2000/Accepted: 3 March 2000