Film Stack Research Articles

Improved energy storage properties through multilayer stacking of relaxor ferroelectric and antiferroelectric thin films

Abstract Multilayers of relaxor ferroelectric (Pb0.92La0.08Zr0.52Ti0.48O3) and antiferroelectric (Pb0.96La0.04Zr0.98Ti0.02O3) thin films were fabricated on Pt/Ti/SiO2/Si substrates by Chemical Solution Deposition (CSD) method. The properties of the independent relaxor ferroelectric (RFE denoted as R) and antiferroelectric (AFE denoted as A) thin films were compared with their various stack configurations made by alternatively coating the R and A layers in the patterns of R/A, R/A/R, R/A/R/A/R/A, A/R, A/R/A, and A/R/A/R/A/R. The crystallographic studies confirmed the coexistence of both RFE and AFE phases in the multilayer stacks which was further verified by electrical characterizations. The multilayer stack showed improved power density (PD), energy efficiency (η), and reduced dielectric loss compared to individual R and A films. Among all the multilayer configurations, the stack with A/R/A/R/A/R layer exhibited significant improvement in energy efficiency (94%) which is higher than the reported results so far on multilayer structures.

Robust ultrablack film deposited on large-curvature magnesium alloy by atomic layer deposition

A broadband absorber composed of a TiAlC/SiO2 film stack prepared by atomic layer deposition was presented, which could be uniformly coated on magnesium alloys with large curvature, achieving an average absorption as high as 99.4% within the wavelength range from 400 to 1000 nm. An Al2O3/TiO2 interlayer was deposited on magnesium alloys prior to the deposition of ultrablack films, which effectively prevented corrosion of magnesium caused by Al3+ and Cl− by-products in the TiAlC film. With the presence of this interlayer, the ultrablack film on the surface of the magnesium alloy exhibited good adhesion and abrasion resistance. Furthermore, after undergoing damp heat and thermal cycling tests, the absorptions of the ultrablack film-coated magnesium alloys remained at 99.1% and 99.0%, respectively, which indicated that the film is promising for application in precision optics under harsh environmental conditions.

Enhancing dielectric-silicon interfaces through surface electric fields during firing

Minimising charge losses at silicon interfaces is a major development area for highly efficient solar cells. Here we report on the interface improvements achieved by establishing a surface electric field during low-temperature firing of dielectric thin films. By inducing a corona electric field on the surface of a thin film stack, we observe significant modifications to the silicon-dielectric interface upon annealing, which correlate with the characteristics of interface defects. The passivation properties of the interfaces strongly depend on the polarity and strength of the electric field during firing, as well as the dielectric materials in the layer stack. We show that the surface electric fields not only influence surface carrier population but also affect the resulting chemical interface properties post-annealing. It is postulated that hydrogen migration plays a role in these observed effects. Leveraging the corona-induced electric field enables fine-tuning of both the chemical and field-effect passivation in thin film surface dielectrics, resulting in recombination current densities as low as 2.8 fA cm−2 in research-grade float zone silicon, and 14 fA cm−2 in industrial-grade textured silicon. The simplicity and versatility of the thin film electric polarisation enable a new strategy for controlling and exploiting the chemical enhancement of interfaces in solar cell devices, from current TOPCon and PERC devices to future multijunction silicon-based cells.

CuSbS2 thin films and solar cells produced from Cu/Sb/Cu stacks via sulfurization

Phase-pure crystalline chalcostibite (CuSbS2) thin films were prepared by depositing Cu/Sb/Cu metal stacks using a thermal evaporation method, followed by sulfurization at 400oC and 430oC for different durations. The investigation revealed the formation of a dominant orthorhombic CuSbS2 phase accompanied by a minor Sb2S3 phase in the film stacks sulfurized at 400oC for 10–60 min. Extending the reaction time to 90 min triggered a decrease in the Sb2S3 phase and the emergence of an additional famatinite (Cu3SbS4) phase alongside the dominant CuSbS2 phase. Sulfurization of the film stack at 430oC for 10 min similarly produced a Cu3SbS4 secondary phase. When sulfurization was maintained beyond 30 min at 430oC, it resulted in phase-pure CuSbS2 films, characterized by a crystalline grain size of 25.9 nm, direct bandgap of 1.41 eV, and hole mobility ranging from 0.6–1.0 cm2V−1s−1. Thin film solar cells fabricated using the CuSbS2 absorbers grown at 430oC for 30–90 min displayed exceptional device efficiency due to the formation of phase-pure and highly crystalline films. Specifically, solar cells fabricated using the CuSbS2 absorber sulfurized for 60 min demonstrated a peak device efficiency of 2.2%, featuring an open-circuit voltage of 546.6 mV, short-circuit current density of 12.8 mA/cm2, and a fill factor of 31.3%. This study provides a reference for preparing highly crystalline CuSbS2 thin films for efficient solar cells.

Study on the preparation of porous polyethylene glycol terephthalate film and the influencing factors of etching rate

AbstractPorous polyethylene glycol terephthalate (PET) film is a kind of mesopore structure template with pore size ranging from nanometer to micrometer by chemical etching after irradiation of heavy ions. The etching rate is an important factor affecting the pore morphology and quality of the membrane. In this paper, four stacked PET film were irradiated with 140 MeV 32S ions at room temperature and vacuum. During chemical etching of irradiated samples, the path etching rate Vt was determined by conduction method, and the bulk etching rate Vb was determined by weighing method. The relationship between etching temperature, concentration, sensitization time, and etching rate was studied. The results show that the etching rate is exponentially correlated with the etching temperature, and increases linearly with the increase of the etching solution concentration. When the concentration of NaOH is 3 mol·L−1 and the etching temperature is 75°C, the formation of cylindrical micropores is the most favorable. The pore size of porous PET film can be adjusted, and the relationship between pore size and etching time is . This is of great significance for the preparation of nanowires with uniform size and stable properties.Highlights We have obtained the optimal conditions for obtaining cylindrical holes. The relationship between the diameter of holes and etching time were determined.

Extreme Dewetting Resistance and Improved Visible Transmission of Ag Layers Using Sub-Nanometer Ti Capping Layers.

As technology development drives the thickness of thin film depositions down into the nano regime, understanding and controlling the dewetting of thin films has become essential for many applications. The dewetting of ultra-thin Ag (9 nm) films with Ti (0.5 nm) adhesion and capping layers on glass substrates was investigated in this work. Various thin film stacks were created using magnetron sputtering and were analyzed using scanning electron microscopy/energy dispersive X-rays, Vis/IR spectrometry, and four four-point probe resistivity measurements. Upon annealing for 5 h in air at 250 °C, the addition of a 0.5 nm thick Ti capping layer reduced the dewet area by an order of magnitude. This is reflected in film resistivity, which remained 2 orders of magnitude lower than uncapped variants. This Ti/Ag/Ti structure was then deployed in a typical low-emissivity window coating structure with additional antireflective layers of AZO, resulting in a superior performance upon annealing. These results demonstrate an easy, manufacturable process that improves the longevity of devices and products containing thin Ag films.

Fabrication of a piezoelectric micromachined ultrasonic transducer (PMUT) with dual heterogeneous piezoelectric thin film stacking

In this study, a piezoelectric micromachined ultrasonic transducer (pMUT) was developed using dual heterogeneous piezoelectric thin films stacked on top of each other. One piezoelectric layer is specialized for the actuation, while the other is specialized for the reception of the ultrasonic waves. This combined use of two materials promises to realize a pMUT transceiver array with an excellent transmitting and receiving performance and a high fill factor. Taking fabrication feasibility into consideration, AlN/Pb(Mg1/3, Nb2/3)O3-PbTiO3 (PMN-PT) and Pb(Zr, Ti)O3 (PZT)/AlN pMUTs were selected as two candidates for prototyping as the dual-layer pMUTs. The driving tests were performed by actuation of each piezoelectric layer and a resonance frequencies around 265 kHz and 203 kHz were confirmed for AlN/PMN-PT and PZT/AlN pMUT, respectively. The diaphragm of AlN/PMN-PT pMUT has a displacement sensitivity of 3538 nm V−1 and 306 nm V−1 when actuating PMN-PT layer and AlN layer at resonance frequency, respectively. While the diaphragm of PZT/AlN pMUT has a displacement sensitivity of 1036 nm V−1 and 744 nm V−1 when actuating the PZT layer and the AlN layer at the resonance frequency, respectively.

Optical properties study of a perovskite solar cell film stack by spectroscopic ellipsometry and spectrophotometry

Spectroscopic ellipsometry is a reproducible and non-invasive characterization technique that allows the evaluation of multilayered structures. However, it is an indirect technique and requires the use of well-calibrated models to correctly analyze the materials. In this work, we report a multilayer modeling approach to investigate the optical properties of the three layers of interest typically employed on an inverted perovskite solar cells structure, namely, indium-tin-oxide (ITO) as a transparent anode, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a hole transport layer, and methylammonium lead iodide (MAPbI3) as the perovskite layer. The parameterized optical constants based on oscillator models were simultaneously fitted to ellipsometry and intensity-transmission data and validated with ultraviolet–visible (UV–Vis) spectroscopy and profilometry. We propose this multilayer modeling approach as a method to be employed throughout the different stages of the fabrication process to study the distinct mechanisms that impact the final performance of a photovoltaic device.

Gallium‐Doped Zinc Oxide/Tungsten‐Doped Indium Oxide Stacks with Enhanced Lateral Transport Capability for Efficient and Low‐Cost Silicon Heterojunction Solar Cells

To decrease the series resistance in front gallium‐doped zinc oxide (GZO) silicon heterojunction (SHJ) solar cells caused by high‐resistivity GZO films, stack films including tungsten‐doped indium oxide (IWO) films which have better lateral transport properties are used as the front transparent conductive oxide (TCO) to improve charge transport. The crystal structure and electrical and optical characteristics of GZO/IWO stacks with different thickness ratios are investigated, and the current–voltage performance of SHJ solar cells with front GZO/IWO stacks and rear GZO film are analyzed. The effective transmittance of the stacks is greater than 98% in the visible region. When the thickness of GZO/IWO is 50 nm:50 nm, the resistivity reaches 8.59 × 10−4 Ω cm, which is a significantly 70% reduction compared with that of a single GZO film. Meanwhile, the power conversion efficiency is improved to 23.8%, effectively reducing the efficiency gap by approximately 0.12% compared to a single IWO transparent electrode. More effective lateral transport lowers the series resistance of SHJ solar cells. By employing stacks with lower indium content in the front TCO of SHJ solar cells, the cost can be reduced without significantly affecting the efficiency, which is important for the large‐scale development of SHJ solar cells.

Drastic enhancement of stable and fast domain wall motion in GdFe nanowires through laser-annealing treatment at wire edges

One of the key challenges in racetrack memory (RM) technology is achieving stable and high velocities for domain walls (DWs) while maintaining low power consumption. In our study, we propose a novel laser-annealing (LA) process to modify wire edges for a smoother DW movement along the nanowire. In this regard, a film stack of Pt (5 nm)/Gd26Fe74(20 nm)/SiN(10 nm) was deposited by magnetron sputtering. The DW velocity in the wire was measured by applying single voltage pulses and then observing the DW motion using a Kerr microscope. The current-induced domain walls motion measurements have shown that the LA process significantly enhances the velocity of DW motion. The LA of both edges of the nanowire results in a threefold increase in DW velocity compared to non-LA conditions. Further experiments illustrated that the DW velocity remains stable for the laser-annealed condition across a wide range of applied currents, spanning from 3 × 1011 to 7 × 1011 A/m2. Additionally, our investigation into the magnetic characteristics of laser-annealed nanowire regions exhibited a notable reduction of Hc at the laser-annealed edges. This decrease in Hc indicates greater ease in manipulating the material’s magnetization, which is essential for efficient DW motion. Furthermore, we explored the influence of LA on the Dzyaloshinskii–Moriya Interaction (DMI) field. The DMI finding underscores the strong correlation between DMI fields and DW speed. This achievement, i.e. the stability and consistency of the domain’s velocity (as the components of an RM) in a wide range of applied current, is significant progress in the field of operation and industrialization of RM.

Low friction behaviors of self-assembled GO/CMWCNTs composite films on high-speed steel

To reduce the energy loss of high-speed steel (HSS) rolls during the rolling process, coatings with effective friction reduction qualities were studied. In this paper, the magnetic stirring was used to prepare the composites of graphene oxide and carboxylated multi-walled carbon nanotubes (GO/CMWCNTs) with various mass ratios. By using 3-(aminopropyl)triethoxysilane (APTES) as a transition layer on hydroxylated-treated HSS, Si-O and C-N bonds were formed to obtain the assembled GO/CMWCNTs films. The results of the friction tests with Al2O3 ceramic balls indicate that the assembled GO/CMWCNTs-2 (1:2) films have an optimum friction reduction effect with the coefficient of friction of about 0.06 (about 83% lower than bare steel). Analysis of the wear mark surface reveals that the reason for the low friction behaviors is the formation of GO/CMWCNTs lubricating films with more sp2 content at the friction interface. The lubricating mechanism of the self-assembly films is to produce a stable multilayer film stacking system with layers joined by covalent bonds.

Enhancing pulse energy-storage performance via strategy of establishing sandwich heterostructure

The effects of sandwich heterostructure on the energy-storage property are still existing some “mess”, detailed and systematic investigation should be carried out. In this work, novel sandwich heterostructure ceramics composed of (Ba0.94Li0.02La0.04)(Mg0.04Ti0.96)O3 and 0.85(Ba0.94Li0.02La0.04)(Mg0.04Ti0.96)O3–0.15NaNbO3 were prepared by film stacking and laminating technology and traditional solid-state sintering, to reveal the relationship between sandwich heterostructure and energy-storage performance. Sandwich heterojunction significantly affects electron-injection, space-charge, build-in electric field (Ei) direction, interlayer-coupling, interface-blocking and clamping effect. Ei direction is adjusted and electric tree growth is restrained. Interface blocking effect mainly occurs when Ei direction is opposite to applied electric field. Comparatively high polarization and tilted polarization-electric field hysteresis loops are obtained. Outstanding recoverable energy-storage density of 5.81 J/cm3 and discharge energy density of 3.99 J/cm3 are gained with current density of 1016.71 A/cm2 and power density of 305.01 MW/cm3. Satisfactory frequency stability, temperature stability and anti-fatigue feature are also achieved. Such sandwich heterostructure design develops a convenient and effective method to enhance energy-storage performance, and related research guides the study of energy-storage performance in multilayer heterostructure.

Development and verification of interfacial fracture energy simulation methodology for porous stacked thin films

In view of the fracture failure mechanism induced by low interfacial strength in porous low-dielectric materials, this study establishes an approach based on fracture mechanics theory and finite element simulation to analyze different pore distribution scenarios and interfacial cracks. The study investigates the estimation method of energy release rate for the fracture tip on concerned interfaces with pores and cracks in porous stacked thin films. By incorporating the proposed finite element simulation into J-integral calculations for fracture energy release rate and comparing with previous research, the approach is reliably verified. Subsequently, using the developed simulation approach, cracks and pores in porous materials are analyzed to understand the variations of energy release rates under different structural parameters. Finally, a Monte Carlo method is considered to model porous materials and analyze the fracture energy between dissimilar material interfaces under varying porosity levels. The simulation methodology developed in this study can be applied to estimate the critical value of interfacial fracture energy for corresponding porous materials and heterogeneous material interfaces under external loads. It can serve as a criterion for structural failure assessment.

A high-resolution 3D radiochromic hydrogel photonic crystal dosimeter for clinical radiotherapy.

The precise, rapid and direct visualization of 3D topographical dose in the target tissue that is crucial for effective radiation therapy remains a challenge. Herein, by combining hydrogel photonic crystals with film stacking or 3D printing, a 3D radiochromic dosimeter with a dose sensitivity of up to 10 nm Gy-1, a spatial resolution <50 μm, and the ability to detect complex 3D topographical dose distribution was proposed for clinical radiation dose verification. The sensitivity and response range of the dosimeter by radiation-induced polymer cross-linking and consequent Bragg wavelength shift can be tuned via the solid content and extent of acrylate modification. The combination of rapid readout, low dose response, high spatial resolution, and great pre-irradiation and post-irradiation stability highlights the translational potential of this technology for topographical dose mapping in clinical radiotherapy applications.

Design, synthesis and characterization of hierarchical porous stacked thin films based on MOFs and ordered mesoporous oxides

Integration of mesoporous thin films and metal–organic frameworks as stacked bilayers, towards hierarchical porous 1D photonic crystals.

Ultrahigh output energy density of explosive-energy-conversion devices assembled from multilayer ferroelectric films

A multilayer PMN–PZT + 2Li film stack with a volume of 0.9 cm3 could generate a current of 3156 A, exceeding that of existing ferroelectric ceramics by 2 orders of magnitude.

Sputter-deposition of ultra-thin film stacks from EUROFER97 and tungsten: characterisation and interaction with low-energy D and He ions

Abstract We have sputter-deposited stacks of ultrathin layers from EUROFER97 and tungsten on silicon substrates. Ion beam analysis techniques are used for composition characterisation and microscopy methods are employed for structural examination. The films are subsequently studied by time-of-flight low-energy ion scattering (ToF-LEIS) for primary 10 keV He+ and 8 keV D+ ions to demonstrate an approach of providing accurate and precise experimental reference electronic stopping cross-sections for fusion-relevant steels. The energy-converted ToF-LEIS spectra are compared to Monte-Carlo simulations for quantitative analysis explicitly considering the influence of plural and multiple scattering. We discuss the deduced stopping cross-sections of EUROFER97 in comparison to predictions by SRIM using Bragg’s rule of stopping power additivity.

CO2 ultrathin film growth on a monolayer of CO2 adsorbed on the NaCl(100) surface: sticking coefficient and IR-optical signatures in the ν3 region.

CO2 ultrathin molecular films were grown onto a preadsorbed monolayer NaCl(100)/p(2 × 1)-CO2 at 40 K. Polarization infrared spectroscopy (PIRS) reveals that so-prepared films have better quality than directly grown films. A sticking probability of 0.74 ± 0.1 was deduced from the integrated IR absorption. The presence of the monolayer doublet in the film spectra suggests a Stranski-Krastanov film growth with locally varying film thicknesses on the surface. In the region of the ν3(12C16O2) band, fine structure was observed between the well-known transverse-optical (TO) and longitudinal optical (LO) bands. Two independent computational models were applied to analyze the nature of the observed fine structure. Both pair potential calculations in combination with a vibrational exciton model as well as plane-wave density functional theory (DFT) in combination with phonon calculations of IR intensities at the Γ-point reveal that a weak mode visible in s-polarization and p-polarization originates from a vibrational film excitation located near the substrate interface. A series of p-polarized weak bands appearing and partly disappearing upon film-growth is assigned to film stacks of unique local thickness.

Improvement of fluorine attack induced word-line leakage in 3D NAND flash memory

In this work, the influence of fluorine (F) erosion on tungsten (W) gate process is studied, and the measure to mitigate the word line (WL) leakage resulting from F erosion in 3D NAND flash memory is proposed. As the number of layers in 3D NAND increases, the tungsten (W) gate word line (WL) layer fill process becomes more challenging in the post-gate process. As the fill path length increases, the tungsten gates become more susceptible to voiding during deposition, resulting in the accumulation of fluorine (F) by-products, and causing fluorine attack issues. In particular, under the influence of subsequent high-temperature processes, the by-products containing fluorine can diffuse into the surrounding structure and corrode the surrounding oxide layer. This leads to WL leakage, thereby affecting device yield and reliability. This paper begins by analyzing the microscopic principles of fluorine erosion in 3D NAND. We also propose a low-pressure annealing method to address the issue of fluorine erosion. Then, we conduct the experiments on annealing planar thin film stacks and 3D filled structures under atmospheric condition and low-pressure condition. We use various methods to characterize the concentration and distribution of residual fluorine elements. The experimental results demonstrate that under appropriate conditions, the residual fluorine in the tungsten gate can be effectively released by low-pressure annealing, thus reducing the leakage index of the word line. Additionally, as the outer CH is closer to the fluorine discharge channel, the influence of low-pressure annealing on the outer CH is more pronounced than on the inner CH. The low-pressure annealing can significantly reduce the fluorine content in the tungsten gate. This method can also mitigate the issue of fluorine attack oxides and reducethe WL leakage. Using low-pressure annealing treatment can also enhance the quality of 3D NAND flash technology.

Mesoscopic Stacking Reconfigurations in Stacked van der Waals Film.

Mesoscopic-scale stacking reconfigurations are investigated when van der Waals (vdW)films are stacked. A method to visualize complicated stacking structures and mechanical distortions simultaneously in stacked atom-thick films using Raman spectroscopy is developed. In the rigid limit, it is found that the distortions originate from the transfer process, which can be understood through thin film mechanics with a large elastic property mismatch. In contrast, with atomic corrugations, the in-plane strain fields are more closely correlated with the stacking configuration, highlighting the impact of atomic reconstructions on the mesoscopic scale. It is discovered that the grain boundaries do not have a significant effect while the cracks are causing inhomogeneous strain in stacked polycrystalline films. This result contributes to understanding the local variation of emerging properties from moiré structures and advancing the reliability of stacked vdW material fabrication.