Reduction In Processing Temperature Research Articles

Non-uniform microstructure evolution in transparent alumina during dwell stage of high-pressure spark plasma sintering

Applying pressure during sintering of ceramics is a common practice, allowing for significant reduction in processing temperature, and fabrication of dense specimens with fine-grained microstructures. However, sintering under relatively high pressure can accentuate stress-related phenomena that occur during the final stage of sintering. The present study describes transparent alumina microstructure evolution during the dwell period of high-pressure spark plasma sintering (HP-SPS) at 1100 °C under 500 MPa. It was observed that the grain size, pore morphology and transparency changed rapidly with dwell time and varied between the center and periphery of the samples. Microstructural evidence suggests that microstructure evolution is related to creep during the dwell period under relatively high pressure and low temperature. Temperature measurements in the HP-SPS setup revealed a small temperature gradient (ΔT=~10 °C) in the opposite direction to the grain size gradient. Based on grain growth kinetics at different regions, we propose that a stress gradient exists and the stress at the sample center is roughly twice as high than at the periphery. Thus, the applied pressure is the dominant factor governing densification and grain growth and is responsible for non-uniform microstructure evolution during HP-SPS. Furthermore, analysis of optical in-line transmittance allowed to decouple the scattering effects of porosity and birefringence. The analysis revealed significant pore growth between dwell time of 5 to 15 min, though, birefringence remained the main scattering source. Understanding these aspects of pressure-assisted sintering will help gain better control of final microstructures, which determine physical, mechanical, and optical properties of ceramics.

All ceramic cathode composite design and manufacturing towards low interfacial resistance for garnet-based solid-state lithium batteries

Solution-assisted all-oxide-cathode formation method allows reduction of processing temperature without using sintering additives, demonstrating the lowest interfacial impedance in garnet-based solid-state lithium batteries.

Practical modeling and optimization of ultrasound-assisted bleaching of olive oil using hybrid artificial neural network-genetic algorithm technique

Multi-objective modeling and optimization of ultrasound-assisted bleaching of olive oil were accomplished by a hybrid artificial neural network (ANN) and genetic algorithm (GA) method using an ultrasonic bath with a frequency of 25kHz. The influence of process parameters including ultrasonic power, bleaching clay dosage, process temperature and time (inputs) on final Lovibond red (Lr) and peroxide value (PV) (outputs) was modeled by a multilayer feed-forward back propagation ANN. The accurate 2-hidden layer model with 20 neurons in each, high R2 (up to 90%) and minimum mean square error (MSE) obtained by ANN was introduced to GA to find the best operation conditions to achieve minimum Lr and PV. The optimum treatment was found with ultrasonic power of 30%, bleaching clay of 1.2%, bleaching time of 13min and temperature of 65°C. Under optimal conditions, Lr and PV were 2.47 and 6.49 (meqO2/kg), respectively, that were consistent with predicted values.Optimally ultrasonic bleached olive oil and an industrially bleached olive oil were compared. In most cases, the results indicated no detrimental effects of ultrasound on oil structure. Thus, 40% reduction in bleaching clay dosage, 35% reduction in process temperature and 57% reduction in time over ultrasound-assisted bleaching which not only provided economic and environmental benefits, but also retained edible oil nutritional value in comparison to common bleaching procedure. The results of this study confirm the applicability of ultrasound-assisted bleaching by ultrasonic bath as an economic and feasible approach for bleaching of olive oil to reduce high bleaching costs.

Dramatic reduction in process temperature of InGaN-based light-emitting diodes by pulsed sputtering growth technique

P-type doping of GaN by pulsed sputtering deposition (PSD) at a low growth temperature of 480 °C and dramatic reduction in the growth process temperature for InGaN-based light-emitting diodes (LEDs) were achieved. Mg-doped GaN layers grown on semi-insulating GaN at 480 °C exhibited clear p-type conductivity with a hole concentration and mobility of 3.0 × 1017 cm−3 and 3.1 cm2 V−1 s−1, respectively. GaN/In0.33Ga0.67N/GaN LEDs fabricated at 480 °C showed clear rectifying characteristics and a bright electroluminescence emission near 640 nm. These results indicate that this low temperature PSD growth technique is quite promising for the production of nitride-based light-emitting devices on large-area glass substrates.

Tin Nanoparticle-Based Solder Paste for Low Temperature Processing

Materials have shown a tendency to modify their bulk properties depending on powder particle size. Nanoparticles' coalescence temperature tends to decrease as particle size decreases. Taking advantage of this behavior, a nanoparticle-based solder paste has been developed as a proof-of-concept and is described in this paper for attaching electronic components at a lower processing temperature to avoid thermally induced damage and reduce energy consumption. Tin nanoparticles were successfully synthesized via a wet chemistry route. The synthesis consists on the use tin (II) chloride dehydrated as the Sn precursor, 1,10-phenanthroline as the surfactant, and sodium borohydride as the reducing agent. A flux system was developed based on ethylene glycol. The solder paste based on the synthesized Sn nanoparticles showed good surface wetting, but not a sufficient metal volume to produce an attachment because the paste required high flux content, thus resulting in a poor metallic load paste. By using commercially procured Sn nanoparticles the results showed acceptable coalescence of the noncapped nanoparticles at temperatures as low as 200°C with a processing time of 20 min. A reduction in processing temperature of approximately 40°C has been found when comparing the developed solder paste with typical SAC lead-free solders. The mechanical and electrical properties of the resulting structure were characterized by means of lap-shear testing and a four-wire Kelvin test showing acceptable shear strength and electrical conductivity.

Effect of low-temperature processing on dry film photoresist properties for flexible electronics

This study presents the mechanical characterization of the dry film photoresist PerMX and its adhesion properties when laminated onto Kapton® E (PI) and Melinex® ST506 (PET). Additionally, the processing temperature, the adhesion strength, and the neutral plane position are investigated and optimized. A relatively low-temperature (85 °C) process is developed to protect the integrity of the polymers with low glass transition temperature and reduce the thermal mismatch stress. Reduction in processing temperature led to a decrement in the adhesion strength. To counteract this unwanted effect, surface treatments (oxygen plasma) are performed on the polymer surface before lamination. Using the latter techniques, adhesion of PerMX to PET (hard bake: 1 h at 85 °C) is increased from 0.07 to 0.26 N mm−1 (variation of 270%). Finally, the mechanical robustness is investigated and increased by tuning the position of the neutral plane, after 50,000 bending cycles and a radius of curvature of 2.5 mm. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013

Atomic Layer Deposition of SiN for spacer applications in high-end logic devices

Continuous down scaling of transistor size resulted in introduction of high-k material to replace the conventional gate oxide. High-k Metal Gate implementation brings new challenges to the subsequent processing steps of the device. Both oxide ingress and removal of the HKMG stack during later cleaning steps must strictly be avoided. We have developed and optimized an ALD SiN encapsulation liner which protects the HKMG stack and also serves as a robust spacer for subsequent ion implantation. SiN was chosen because of its oxide-blocking characteristics and its durability in diluted hydrofluoric acid. We developed sophisticated ALD processes using ionized ammonia radicals and dichloro-silane. This ALD process has several advantages compared to conventional LPCVD or PECVD processes: Superior thickness control and uniformity, excellent step coverage and no loading effects. In addition, process temperature could be reduced to 500°C, which is shown to be critical for protecting the HKMG stack. Further reduction in process temperature to 400°C is also demonstrated using a novel precursor.

Polyamide 6‐wheat straw composites: Degradation kinetics

AbstractDegradation kinetics of ground wheat straw (WS), polyamide 6, and a WS‐polyamide 6 composites obtained from extrusion were investigated. 15 wt% of ground WS was melt blended with other additives naming; lithium chloride salt (LiCl) and N‐butylbenzenesulfonamide plasticizer (N‐BBSA) as matrix treatments. The additives were added to reduce the melting point of polyamide 6 and ease of composite processing (reduction in processing temperature and time). Two commonly used non‐isothermal kinetic models were used to investigate the degradation kinetics of WS and the composite. Thermal gravimetric analysis was utilized to measure the thermal stability and degradation kinetics of different composite formulation. The activation energy of WS was identified by iso‐conversional Friedman kinetic method. Through this method, WS activation energy was found to be around 141.4 kJ/mol. Composite kinetic studies were based on the Coats and Redfern procedure. It was concluded that the composite activation energy was correlated to the residual weight percentage of the composite at the maximum thermal degradation temperature. The onset of degradation of WS was dictated by the thermal stability of its lignin content and was found to be around 188°C. WS, however, did not go through a major degradation up to 245°C at which drastic decomposition starts. This temperature range overlaps with processing temperature of Polyamide 6 and required matrix/WS treatments. Addition of salt and plasticizer individually or with each other at any level decreased the onset of degradation temperature. Addition of plasticizer at 4 wt% level, however, shifted the degradation peak to higher temperature representing a more thermally stable composite. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Initial studies into the use of ultrasound to reduce process temperatures and chemical usage in the PCB desmear process

PurposePrevious studies have proven that, under optimised ultrasonic conditions, a range of materials used in electronic manufacturing can be sonochemically surface modified using benign solutions at low temperature. The purpose of this paper is to focus on a specific process, namely, the desmearing of through holes in printed circuit boards (PCB). The objective was to determine whether the introduction of low frequency ultrasound (20 kHz) to the “etch” stage of a standard “swell and etch” desmear system could enable reduced temperature processing and the use of less chemistry in the permanganate solution.Design/methodology/approachThe study was divided into three main stages. In the first “screening” phase, the effect of ultrasound in the etch solution was studied by measuring the weight loss after desmear on a PCB laminate material (Isola 370HR). Factors such as etch temperature and concentration of permanganate (including permanganate‐free) were varied. In stage 2, confirmatory runs were carried out on the most promising conditions from the screening work and through holes in a four‐layer multi‐layer board (MLB) were assessed for smear removal using a scanning electron microscope (SEM). Finally, a four‐layer MLB was desmeared through the most promising ultrasonic process and then metallized at a PCB manufacturer. Thermal shock testing was subsequently carried out and sections from the board assessed for inter‐connection defects (ICDs).FindingsThe initial screening study indicated that, whenever ultrasound was used in the etch stage of the desmear process, significantly higher weight loss was achieved compared to a standard “silent” process. This effect was most pronounced when permanganate was removed from the etch solution and, in this situation, weight loss could be an order of magnitude higher than the silent equivalent. Further testing on through holes suggested that smear‐free inner‐layers could only be guaranteed if permanganate was present in the etch solution but that ultrasound again improved smear removal. Final testing under semi‐production conditions confirmed that, if ultrasound was employed in the etch part of the desmear process, then a reduction in processing temperature from 85°C to 60°C could be achieved and the permanganate concentration halved (65 to 33 g/L) whilst still achieving ICD‐free boards.Originality/valueThe paper indicates the feasibility of using ultrasound to reduce temperatures and chemical concentrations used in the permanganate etch solution, whilst still producing through holes with no ICDs.

Cereal‐based biorefinery development: Integrated enzyme production for cereal flour hydrolysis

Restructuring the traditional fermentation industry into viable biorefineries for the production of fuels, chemicals and plastics is essential in order to replace (petro)chemical processing. This work presents engineering aspects of Aspergillus awamori submerged fermentation for on-site production of an enzymatic consortium that contains glucoamylase, protease and phosphatase. The crude broth filtrate was used for the production of wheat flour hydrolysates. Improvements on traditional starch hydrolysis carried out in two stages (liquefaction and saccharification) were attempted through integration of unit operations and reduction of processing temperature and reaction duration. An initial increase of temperature to 68 degrees C and a subsequent decrease to 60 degrees C for the rest of the enzymatic hydrolysis resulted in a starch to glucose conversion yield of 94 and 92% when a wheat flour concentration and commercial starch concentration of 225 g L(-1) was used, respectively. The use of crude broth filtrates resulted in the simultaneous hydrolysis of wheat protein and phytic acid, as was indicated by the increase in free amino nitrogen and phosphorus concentration, respectively.

Absorption of CO 2 and subsequent viscosity reduction of an acrylonitrile copolymer

Acrylonitrile (AN) copolymers (AN content greater than about 85 mol%) are traditionally solution processed to avoid a cyclization and crosslinking reaction that takes place at temperatures where melt processing would be feasible. It is well known that carbon dioxide (CO 2) reduces the glass transition temperature ( T g) and consequently the viscosity of many glassy and some semi-crystalline thermoplastics. However, the ability of CO 2 to act as a processing aid and permit processing of thermally unstable polymers at temperatures below the onset of thermal degradation has not been explored. This study concentrates on the ability to plasticize an AN copolymer with CO 2, which may ultimately permit melt processing at reduced temperatures. To facilitate viscosity measurements and maximize the CO 2 absorption, a relatively thermally stable, commercially produced AN copolymer containing 65 mol% AN was investigated in this research. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) indicated that CO 2 significantly absorbs into and reduces the T g of the AN copolymer. Pressurized capillary rheometry indicated that the magnitude of the viscosity reduction is dependent on the amount of absorbed CO 2, which correlates directly to the T g reduction of the plasticized material. Up to a 60% viscosity reduction was obtained over the range of shear rates tested for the plasticized copolymer containing up to 6.7 wt% CO 2 (31 °C T g reduction), corresponding to as much as a 30 °C equivalent reduction in processing temperature. A Williams–Landel–Ferry (WLF) analysis was used to estimate the viscosity reduction based on the T g reduction (and corresponding amount of absorbed CO 2) in the plasticized AN copolymer, and the predicted viscosity reduction based on using the universal constants was 34–85% higher than measured, depending on the amount of absorbed CO 2. Van Krevelen's empirical solubility relationships were used to calculate the expected absorbance levels of CO 2, and found to be highly dependent on the choice of constants within the statistical ranges of error of the Van Krevelen relationships.

The First Wafer-fused AlGaAs-GaAs-GaN Heterojunction Bipolar Transistor

ABSTRACTWe describe the use of wafer fusion to form a heterojunction bipolar transistor (HBT), with an AlGaAs-GaAs emitter-base fused to a GaN collector. In this way, we hope to make use of both the high breakdown voltage of the GaN and the high mobility of the technologically more mature GaAs-based materials. This paper reports the first dc device characteristics of a wafer-fused transistor, and demonstrates the potential of wafer fusion for forming electronically active, lattice-mismatched heterojunctions. Devices utilized a thick base (0.15um) and exhibited limited common-emitter current gain (0.2–0.5) at an output current density of ∼100A/cm2. Devices were operated to VCE greater than 20V, with a low VCE offset (1V). Improvements in both device structure and wafer fusion conditions should provide further improvements in HBT performance. The HBT was wafer-fused at 750°C for one hour. Current-voltage characteristics of wafer-fused p-GaAs/n-GaN diodes suggest that the fusion temperature could be reduced to 500°C. Such a reduction in process temperature should mitigate detrimental diffusion effects in future HBTs.

21.4: Study on the Thermal Shrinkage of Annealed Corning Code 1737 Glass for Low‐Temperature Poly‐Si Application

AbstractThermal shrinkage of annealed Corning 1737 glass was measured following simulated thermal cycles for low temperature poly‐Si fabrication. If process temperature is reduced from 600 to 550°C, thermal shrinkage decreases by more than 50%. Reduction of process temperature as well as cycle time have a large impact on reducing thermal shrinkage.

Low-temperature and low thermal budget fabrication of polycrystalline silicon thin-film transistors

A top-gate self-aligned n-channel polycrystalline silicon (poly-Si) thin-film transistor (TFT) has been fabricated with low temperature (/spl les/550/spl deg/C) and low thermal budget process. The ultrahigh vacuum chemical vapor deposition (UHV/CVD) grown poly-Si was served as the channel film, the chemical mechanical polishing (CMP) technique was used to polish the channel surface, plasma-enhanced chemical vapor deposited (PECVD) tetraethylorthosilicate (TEOS) oxide was used as the gate dielectric, and NH/sub 3/ plasma was used to passive the device. In this process, the solid phase crystallization (SPC) step is not needed. A field effect mobility of 46 cm/sup 2//V-s, ON/OFF current ratio of over 10/sup 7/, and threshold voltage of 0.8 V are obtained. The significant reduction in process temperature and thermal budget make this process advantageous for larger-area-display peripheral driver circuits on glass substrate.

Low loss achieved in sol-gel based silica-on-silicon integrated optics using borophosphosilicate glass

Polarisation-independent propagation losses of 0.2 dB/cm are reported for near-infrared silica-on-silicon channel guides formed using sol-gel borophosphosilicate glass deposited by repetitive spin coating and rapid thermal annealing. The low loss is ascribed to a reduction in process temperature, which has allowed a total glass thickness of 30 µm. The use of two dopants allows the glass viscosity to be adjusted independently of its refractive index, simplifying reflow and burial.

Effects of dual spectral sources on the curing of polyimide films by rapid isothermal processing

There are fundamental differences between conventional furnace processing (CFP) and rapid isothermal processing (RIP). The radiation spectrum of a conventional furnace consists of photons in the infrared and longer wavelength regions, whereas the spectrum of the incoherent light sources used in RIP consists of some UV, visible, and infrared photons. As compared to CFP, the photophysical and photochemical effects associated with RIP provide the capability of lower temperature processing. However, a further reduction in processing temperature can be achieved by the use of vacuum ultraviolet (VUV) and UV light sources in conjunction with a single spectral source RIP. We provide experimental results for the dual spectral source curing of polyimide dielectric films. Our findings indicate that simultaneous exposure of polyimide samples to both VUV and conventional RIP sources during processing cured the polyimide more rapidly and at lower temperatures than did single spectral source RIP alone. These results may be of great importance for the RIP of the future generation of semiconductor devices.