Interlayer Film Research Articles

Polyimide for silicon solar cells with double-sided textured pyramids

Silicon solar cells incorporating double-sided pyramidal texture are capable of superior light trapping over cells with front-side only texture. However, increased surface area, roughness and exposed <111> crystal planes of textured surfaces not only causes increased recombination, but also makes cells susceptible to shunting through pinholes in the dielectric at the sharp peaks and valleys of the textured pyramids. A polyimide film as an insulating interlayer film is investigated to circumvent the tradeoff between improved light trapping, increased recombination and increased shunt paths. When applied at the rear of the interdigitated back contact silicon solar cell structure, the polyimide film provides an excellent electrical insulation (> 1000 MΩ of insulation resistance) and increases photocurrent (~ 1.1 mA/cm2) owing to an increased rear internal reflectance. The polyimide is also compatible with metal annealing of passivating dielectrics such as silicon nitride. Optical simulation and experimental results are combined in a 3D semiconductor simulation (Quokka) to quantify the possible gain of implementing the double-sided texture in high efficiency silicon solar cells.

Exceptional power density and stability at intermediate temperatures in protonic ceramic fuel cells

Over the past several years, important strides have been made in demonstrating protonic ceramic fuel cells (PCFCs). Such fuel cells offer the potential of environmentally sustainable and cost-effective electric power generation. However, their power outputs have lagged behind predictions based on their high electrolyte conductivities. Here we overcome PCFC performance and stability challenges by employing a high-activity cathode, PrBa_(0.5)Sr_(0.5)Co_(1.5)Fe_(0.5)O_(5+δ) (PBSCF), in combination with a chemically stable electrolyte, BaZr_(0.4)Ce_(0.4)Y_(0.1)Yb_(0.1)O_3 (BZCYYb4411). We deposit a thin dense interlayer film of the cathode material onto the electrolyte surface to mitigate contact resistance, an approach which is made possible by the proton permeability of PBSCF. The peak power densities of the resulting fuel cells exceed 500 mW cm^(−2) at 500 °C, while also offering exceptional, long-term stability under CO_2.

Mechanical enhancement effect of the interlayer hybrid CNT film/carbon fiber/epoxy composite

Floating catalyst chemical vapor deposition carbon nanotube (CNT) film was intercalated into carbon fiber (CF) prepregs to fabricate hybrid composites. The effect of CNT film thickness was studied by using a 25 μm thick film and an ultrathin 2 μm film respectively. The results showed that the ultrathin CNT film interlayer had dramatically improved the compression strength of hybrid composite by 34% compared with CF/epoxy control composite owing to the altered failure modes. The damping ratio of ultrathin CNT film hybridized composite was substantially increased by two orders of magnitude, due to the energy dissipation of numerous nanoscale interconnections and interfaces. Moreover, the interlaminar properties and water resistance of the hybrid composites were all improved. Since a small amount of CNT film can significantly enhance the mechanical properties of CF/epoxy composite, this type of hybrid composite has potential application in multifunctional lightweight structures.

Novel perovskite/TiO2/Si trilayer heterojunctions for high-performance self-powered ultraviolet-visible-near infrared (UV-Vis-NIR) photodetectors

Methylammonium lead halide perovskites have been reported to be promising candidates for high-performance photodetectors. However, self-powered broadband ultraviolet-visible-near infrared (UV-Vis-NIR) photodetection with high responsivity is difficult to achieve in these materials. Here, we demonstrate, for the first time, a novel trilayer hybrid photodetector made by combining an n-type Si wafer, TiO2 interlayer and perovskite film. By precisely controlling the thickness of the TiO2 layer, enhanced separation and reduced recombination of carriers at the Si–perovskite interface are obtained. As a result, perovskite film, when combined with a low-bandgap Si, extends the wavelength range of photo response to 1,150 nm, along with improved on/off ratio, responsivity, and specific detectivity, when compared to pristine perovskite. Results obtained in this work are comparable or even better than those reported for perovskite-based UV-Vis-NIR photodetectors. In particular, the hybrid photodetectors can operate in a self-powered mode. The mechanism of enhancement has been explored and it is found that the increased separation and reduced recombination of photogenerated carriers at the junction interface leads to the improved performance.

Production and evaluation the properties of laminated oat protein film and electrospun nylon

Electrospun synthetic fiber was used to reinforce protein-based composite. Two monolayer and laminated films based on either made from just isolated oat protein or a composite containing an interlayer of nylon-6 nanofiber was developed. It was revealed that monolayer film has relatively weak barrier and mechanical properties compared to other proteinous films. To improve film characteristics, 0.5, 1, and 1.5% (wt/wt) of the nanofiber were incorporated into the film. According to the results, film solubility in water decreased while its oxygen and water vapor permeability and mechanical properties were significantly improved. Due to the presence of 1.5% (wt/wt) of nanofiber, the elastic modulus increased significantly and, therefore, glass transition temperature (TG) of laminated film was also increased. Addition of nanofibers did not significantly affect optical properties. The results show that incorporation of electrospun nylon nanofibers into a film obtained from a natural polymer may show promise and improves its properties. Practical applications Laminating of different films and combination of their features are one of the popular methods to improve properties of biodegradable films. In this study, electrospun nylon nanofiber was incorporated as interlayer of film based on oat protein. By this way, effect of interlayer nylon nanofiber mat (NNM) on physical and mechanical properties of oat protein–NNM was investigated. The results showed that water vapor and oxygen permeability, mechanical properties, and its resistance to soluble in water improved, while interlayer did not have significant effect on optical properties of laminated film.

Influence of the interlayer film thickness on the mechanical performance of AA2024-T3/CF-PPS hybrid joints produced by friction spot joining

Friction Spot Joining (FSpJ) is an innovative friction-based joining technique for metal-polymer hybrid structures. Friction spot joints of aluminium alloy 2024-T3 and carbon fibre-reinforced poly(phenylene sulphide) composite laminate (CF-PPS) were produced with an additional PPS film interlayer. Two different film thicknesses were investigated in this study: 100 and 500 μm. Lap shear testing demonstrated that the joints produced with 100-μm film (2093 ± 180 N) were stronger than the joints with 500 μm (708 ± 69 N). Additionally, the fracture surface analysis revealed a larger bonding area for the joints with 100-μm film (53 ± 2 mm2) as compared to the joints with 500-μm film (40 ± 1 mm2). Considering the low thermal conductivity of PPS, the thinnest film is more likely to soften by the frictional heat during the joining process. Hence, the low viscosity of the molten PPS favours the wettability of the parts’ surfaces. Microstructural analyses proved that the metallic nub formation and the interdiffusion of PPS chains between film and composite matrix are also favoured for thinner film use. Thus, superior adhesion between the partners is achieved. Therefore, it was concluded that the addition of the thinnest film interlayer leads to stronger joints.

Two-Dimensional Magnetic Semiconductor in Feroxyhyte.

A few years ago, it was claimed that the two-dimensional (2D) feroxyhyte (δ-FeOOH) layer could possess a net magnetic moment and it could be applied for potential spintronics applications because it showed a band gap. However, the exact crystal structure is still unknown. Hereby, we investigate the crystal structure, electronic band structure, and magnetic and optical properties of 2D δ-FeOOH using density functional calculations. On the basis of the experimental observation and dynamical stability calculations, we propose that the 2D δ-FeOOH originates from bulk Fe(OH)2 via oxidation. A perfect antiferromagnetic ground state was observed in the monolayer structure with an indirect band gap of 2.4 eV. On the other hand, the bilayer structure displayed a direct band gap of 0.87 eV, and we obtained a ferrimagnetic state. The net magnetic moment in the bilayer was 1.49 μB per cell. The interlayer distance and film thickness in bilayer δ-FeOOH were 1.68 and 7.37 Å, respectively. This interlayer distance was suppressed to 1.47 Å in a trilayer system, and the band gap of 1.6 eV was found. The trilayer δ-FeOOH had a film thickness of 11.57 Å, and this is comparable to the experimental thickness of 12 Å. To compare with the experimental band gap of 2.2 eV obtained from a UV-visible optical spectrum measurement, we also calculated the absorption spectra, and the onset of the absorption peak in the monolayer, bilayer, and trilayer appeared at 3.2, 2.8, and 2.2 eV, respectively. Overall, considering the magnetic state, optical absorption, and film thickness, we propose that the trilayer structure agrees with the experimentally synthesized structure.

Optimization of charge transfer and transport processes at the CdSe quantum dots/TiO2 nanorod interface by TiO2 interlayer passivation

Surface trap states hinder charge transfer and transport properties in TiO2 nanorods (NRs), limiting its application on optoelectronic devices. Here, we study the interfacial processes between rutile TiO2 NR and CdSe quantum dots (QDs) using TiO2 interlayer passivation treatments. Anatase or rutile TiO2 thin layers were deposited on an NR surface by two wet-chemical deposition treatments. Reduced interfacial charge recombination between NRs and CdSe QDs was observed by electrochemical impedance spectroscopy with the introduction of TiO2 thin film interlayers compared to bare TiO2 NRs. These results can be ascribed to in-gap trap state passivation of the TiO2 NR surface, which led to an increase in open circuit voltage. Moreover, the rutile thin layer was more efficient than anatase to promote a higher photo-excited electron transfer from CdSe QDs to TiO2 NRs due to a large driving force for charge injection, as confirmed by surface photovoltage spectroscopy.

Microstructure-Dependent Charge Carrier Transport of Poly(3-hexylthiophene) Ultrathin Films with Different Thicknesses.

Since the interfacial order of conjugated polymers plays an essential role for the performance of field-effect transistors, comprehensive understanding on the charge carrier transport in ultrathin semiconducting films below thicknesses of 10 nm is required for the development of transparent and flexible organic electronics. In this study, ultrathin films based on poly(3-hexylthiophene) as conjugated polymer model system with a thickness range from single monolayer up to several multilayers are investigated in terms of microstructure evolution and electrical properties of different molecular weights. Interestingly, a characteristic leap in field-effect mobility is observed for films with thickness greater than four layers. This threshold mobility regarding film thickness is attributed to the transition from 2D to 3D charge carrier transport along with an increased size of the P3HT aggregates in the upper layers of the film. These results disclose key aspects on the role of the film interlayer on the charge carrier transport through conjugated polymers in transistors.

(Invited) Hot Carrier Reliability of High Voltage HVMOSFETs in BCD (Bipolar-CMOS-DMOS) Technology

This paper discusses three important issues in hot carrier (HC) reliability of LDMOSFET ((Laterally Diffused MOSFETs) in BCD technology. One of the main reliability issues encountered during development of the LDMOSFET is optimizing the trade-offs between specific on-resistance (Rdson) and hot carrier (HC) degradation [2]. For instance, Rdson can be reduced by increasing the drift region doping concentration or shrinking the drift region length. Both of these changes result in higher lateral electric field in the drift region which lead to increased HC degradation. The second issue is how to reduce HC degradation in LDMOS due to Back-End-Of-Line (BEOL). It has been reported for CMOS devices that HC performance can be degraded by BEOL processes such as interlayer dielectric film deposition, etch, metal deposition and etch process [3, 4]. The BEOL processes in BCD technology may have a worse impact on LDMOS HC performance than on CMOS’s since it has such as higher energy implants and thicker metal deposition and etch. The third issue is the influence of self heating on the measurement of HC degradation in high gate voltages stress for HC SOA (safe-operating-area) in high voltage LDMOS [5, 6]. To address the first issue, we have compared the thin gate oxide (11.5nm) and thick gate oxide (60nm) LNDMOS hot carrier degradation results as shown in Fig.1 (b). The HC degradation has been significantly reduced in thick gate oxide LNDMOS. The main reason for the reduction may be due to drift region oxide thickness. Based on the results, we proposed a new LDMOS structure in a BCD technology that improves HC degradation without sacrificing the device breakdown voltage or Rdson [1]. The process to form the thick oxide in drift region-I in the LNDMOS is the same as to form thick gate oxide MOSFET, so only a layout change is required. The 11.5nm gate oxide thickness in the channel region remains the same for both LNDMOS structures. The maximum lateral electric field Emax in drift region-I would be reduced by over 94% if the oxide thickness increased to 60nm from 11.5nm based on our calculation. TCAD simulations clearly show that impact ionization rate for the 30V LNDMOS with the thick oxide in drift region-I has been significantly reduced, and also its peak location has been pushed away from the surface into the bulk of the silicon within drift region-I as shown in Fig.2(b). For the second issue, we demonstrated a modified SiN barrier layer which can improve device hot carrier performance in the LDMOSFET. We show experimentally that using a barrier layer of SiN or SiON which is engineered to have a relatively high refractive index (RI) and electrical conductivity can reduce the BEOL effect on hot carrier performance. Increasing the SiH4 flow rate during deposition increases the film’s RI and also its electrical conductivity [9]. The increased electrical conductivity of the SiN barrier layer allows charge from plasma processing to be dissipated into the silicon. At 4000C, a typical BEOL dielectric deposition temperature, the conductivity of the SiN barrier layer is much higher. Thus, the SiN barrier layer can reduce the PPID for the oxide in drift region resulting in reduced HC degradation. The HC Idlin degradation for the LNDMOS device with thick oxide in drift region and high RI SiN or SiON barrier layer has been significantly reduced to less than 1/3 the degradation observed in the standard LNDMOS as shown in Fig.2 (a). The reduced HC Idlin degradation is about 68% due to the thick oxide in drift region-I, and about 32% from the high RI SiN barrier layer. The HC Vth (threshold voltage) degradation exhibited very small degradation after the HC stress. Our data shows self heating, caused by HC stress in the thick gate oxide HV LNDMOS, significantly affected Idlin/Rdson electrical parameter and HC degradation characteristic. The change in delay time between the removal of the HC stress after each stress cycle and the parameter measurement resulted in a significant difference in HC Idlin/Rdson degradation [6]. For a longer delay time, lower Idlin degradation was observed, see Fig.3 (a). The difference or recovery of degradation was mainly due to the self heating effect from Idlin degradation vs junction temperature change (Fig3.(b)) and temperature monitor data. The Idlin degradation from self heating effect seems to be more than from HC effect in packaged HV LNDMOS. In the final paper, we will include some methods to eliminate the self heating effect, and to separate the self heating and local HC injection effect. Figure 1

Sandblasting induced stress release and enhanced adhesion strength of diamond films deposited on austenite stainless steel

We firstly used sandblasting to treat austenite stainless steel and then deposited a Cr/CrN interlayer by close field unbalanced magnetron sputtering on it. After that, diamond films were prepared on the interlayer. It is found that the sandblasting process induces phase transition from austenite to martensite in the surface region of the stainless steel, which decreases thermal stress in diamond films due to lower thermal expansion coefficient of martensite phase compared with that of austenite phase. The sandblasting also makes stainless steel’s surface rough and the Cr/CrN interlayer film inherits the rough surface. This decreases the carburization extent of the interlayer, increases nucleation density and modifies the stress distribution. Due to lower residual stress and small extent of the interlayer’s carburization, the diamond film on sandblast treated austenite stainless steel shows enhanced adhesion strength.

Photoluminescence enhancement of ZnO via coupling with surface plasmons on Al thin films

We present that the ultra-violet emission of ZnO can be enhanced, as much as six-times its integral intensity, using an Al thin interlayer film between the Si substrate and ZnO thin film and a post-fabrication laser annealing process. The laser annealing is a cold process that preserves the chemical state and integrity of the underlying aluminum layer, while it is essential for the improvement of the ZnO performance as a light emitter and leads to enhanced emission in the visible and in the ultraviolet spectral ranges. In all cases, the metal interlayer enhances the intensity of the emitted light, either through coupling of the surface plasmon that is excited at the Al/ZnO interface, in the case of light-emitting ZnO in the ultraviolet region, or by the increased back reflection from the Al layer, in the case of the visible emission. In order to evaluate the process and develop a solid understanding of the relevant physical phenomena, we investigated the effects of various metals as interlayers (Al, Ag, and Au), the metal interlayer thickness, and the incorporation of a dielectric spacer layer between Al and ZnO. Based on these experiments, Al emerged as the undisputable best choice of metal interlayers because of its compatibility with the laser annealing process, as well as due to its high optical reflectivity at 380 and 248 nm, which leads to the effective coupling with surface plasmons at the Al/ZnO interfaces at 380 nm and the secondary annealing of ZnO by the back-reflected 248 nm laser beam.

Modification of Schottky barrier properties of Al/p-type Si Schottky rectifiers with graphene-oxide-doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) interlayer

The effects of graphene-oxide (GO) doping in the poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) interlayer on the electrical and chemical properties of Al/p-type Si Schottky diodes were demonstrated. GO concentrations of 0.05 and 0.1 wt. % were used in the interlayer. The barrier height of the Al/p-type Si Schottky diode with a GO-doped PEDOT:PSS interlayer was higher than that of the diode with the pristine PEDOT:PSS interlayer; ultraviolet photoelectron spectroscopy measurements indicated that this could be well correlated with variations in the hole-injection barrier between the PEDOT:PSS interlayer and Al film caused by GO doping. The addition of 0.05 wt. % GO to the PEDOT:PSS interlayer increased the PEDOT to PSS ratio, resulting in an increase in conductivity. However, the conductivity of the PEDOT:PSS doped with 0.1 wt. % GO decreased; x-ray photoelectron spectroscopy results indicated that this could be attributed to the increased insulating GO content in PEDOT:PSS. At higher forward bias, an analysis of the forward log I–log V plot of the Al/p-type Si Schottky diodes with pristine and GO-doped PEDOT:PSS interlayers revealed different space-charge-limited current-transport mechanisms, which could be associated with additional traps originating from the GO.

FEM thermal analysis of Cu/diamond/Cu and diamond/SiC heat spreaders

The effects of thermal stress resulting from thermal cooling in copper/diamond/copper heat spreader is investigated using finite element method. A similar model of diamond/SiC heat spreader is compared without addition of interlayer. The effect of carbide interlayer in reduction of interfacial thermal stress is investigated. The results show that the carbide interlayer film thickness is critical in stress reduction for a copper/diamond/copper heat spreader device. Diamond/SiC device has lower interfacial stress without interlayer. The study of mechanical and thermal property of diamond heat spreader is useful for optimal designs of efficient heat spreader for electronic components.

Consecutive deposition of amorphous SiO2 interlayer and diamond film on graphite by chemical vapor deposition

Chemical vapor deposition (CVD) diamond films can be used as effective protective coatings on graphite components, while the film-substrate adhesion is poor probably due to the graphite etching caused by the atomic hydrogen. It is supposed as a useful way to pre-deposit an amorphous SiO2 (a-SiO2) layer for solving this problem. In this study, by interposing a-SiO2 interlayers, four types of diamond films are deposited on common commercial graphite substrates, and noteworthy is that such the a-SiO2 layer and CVD diamond film are consecutively synthesized in the same hot filament CVD apparatus. It is proved that as-deposited a-SiO2 layer has typical amorphous features, provides sufficient protections on the substrate, and avoids the natural removal of the diamond film when growing. Micro-crystalline diamond, nano-crystalline diamond, boron-doped micro-crystalline diamond (BDMCD) and boron-doped nano-crystalline diamond films deposited on a-SiO2 coated graphite substrates present typical features in consistent with micro- or nano-sized diamond films on other substrates. Among the four diamond films, mainly facing to some application requirements for the electrical conductivity, the BDMCD film shows relatively better comprehensive performance, including high diamond purity, high nano hardness (74.21 GPa) and elastic modulus (890.93 GPa), favorable adhesion and low electrical resistivity (29 μΩ m).

The sound absorption of sisal fiber and sisal fiber/polyethylene film sheets: Morphology and structure

Sisal fiber (SF) and waterborne polyurethane adhesive were used to prepare SF‐based sound absorption material through hot press molding. SF with elastic polyethylene (PE) film interlayers was also fabricated as a new type of sound absorbing composite. The effects of SF treatment methods and PE film on sound absorption coefficient were evaluated. The alkaline‐treated SF composite had higher sound absorption as compared with the untreated SF composite when the sound wave was below 5500 Hz. The sound absorption peak of alkaline/oxidation‐treated SF composite moved towards low‐ and middle‐frequency regions. The SF/PE film composite showed that at low‐frequency the more layers of PE film inserted the better sound absorption property. The mass‐temperature relationship and FTIR of the composites were discussed. The SF surface and the cross section of the composites were observed by SEM, which showed the void structure and microfiber contributed to enhancing sound absorbing property. POLYM. COMPOS., 39:2812–2818, 2018. © 2016 Society of Plastics Engineers

Correlation between Numerical and Experimental Tests of Laminated Glass Panels with Visco-elastic Interlayer

Present research is focused on numerical and experimental investigation of glass laminate structure consolidated with ethylene vinyl acetate film. The European wide industry standard for laminate glass panels is considered polyvinyl butyral interlayer film where ethylene vinyl acetate layer is particular out of autoclave manufacturing process related. Conducted numerical and experimental research worldwide rarely consider this type of polymer in lamination process even though in Baltic‘s this is industry standard. So far such glass laminate products are not mechanically characterised to the level that experimental results correlation with numerical predictions to give an engineers required confidence. Therefore current research initially characterise post cured ethylene vinyl acetate film then integration of viscoelastic material properties in numerical four point bending analysis and finally verification with non-contact measurements of natural frequencies to assess mechanical response of laminate glass panels. It was shown that by introducing non-linear viscoelastic behaviour of ethylene vinyl acetate film for depicting mechanical behaviour in 4-point bending the discrepancy between numerical and experimental results was less than 5% whereas assuming the interlayer as isotropic material only obtained discrepancy reached up to 50%.

Electrode–electrolyte interface stability in solid state electrolyte systems: influence of coating thickness under varying residual stresses

We introduce a model of electrode–electrolyte interfacial growth which focuses on the effect of thin coating layers on the interfacial stability in prestressed systems. We take into account transport resulting from deposition from the electrolyte, from capillarity driven surface diffusion, and from changes of the chemical potential due to the elastic energy associated with the interface profile. As model system, we use metallic lithium as electrode, LLZO as electrolyte and Al2O3 as a thin film interlayer, which is a highly relevant interfacial system in state of the art all-solid-electrolyte batteries. We consider the stability of the electrode-coating-electrolyte interface depending on the thickness of the thin film interlayer and the magnitude of the elastic prestresses. Our central approach is a linear stability analysis based on the mass conservation at the planar interface, employing approximations which are appropriate for solid state electrolytes (SSEs) like LLZ, a thin Li metal electrode and a thin coating layer with a thickness in the range of nanometres.

Formation of Defects in Solid-Liquid Reaction-Diffusion Bonding of Copper Using a Tin Film Interlayer

Formation of Defects in Solid-Liquid Reaction-Diffusion Bonding of Copper Using a Tin Film Interlayer

Growth of single crystalline germanium thin film on (100) silicon substrate

Epitaxial growth of germanium thin films (GeTFs) on Si (111) and Si (100) substrates was investigated, and the prepared films were compared with the films grown on SiO2 substrates. Ge films were prepared in three steps. Initially, a Ge interlayer film with thickness of ∼ 10 nm was deposited on the substrate followed by annealing and recrystallization of the film. A Ge film with a thickness of 500 nm was then deposited. A single crystalline Ge film was grown on Si (100) whereas polycrystalline films were grown on the other substrates. The growth rate of the films depends on the type of the substrates used, which in turn determines the crystallinity of the films. Highly crystalline films were obtained with slow growth rates. The single crystalline epitaxial layer of GeTFs formed on Si (100) exhibited a lower threading dislocation density as compared with those grown on Si (111) and SiO2.