SiO2 Underlayer Research Articles

Low-temperature crystallization of BeO-assisted polycrystalline germanium layer for monolithic 3D integration

We demonstrated a new method for the low-temperature solid-phase crystallization (SPC) of germanium on beryllium oxide (BeO) films for monolithic 3D (M3D) integration. Using a wurtzite crystal BeO film, known for its high thermal conductivity of 370 W/m-k at 300 K and covalent bonding characteristics, as the underlying layer, we crystallized Ge at a reduced temperature of 410 °C. For the Ge-on-BeO, the formation of larger grains was consistently promoted at annealing temperatures of 410–500 °C, with a notable 125 % increase in the grain size at 500 °C compared to that at the SiO2 underlayer. The polycrystalline Ge layers crystallized on the BeO retained their tensile strain, as confirmed by the Raman spectra. Furthermore, its optical bandgap of ∼ 1.36 eV and average roughness of 0.847 nm at an annealing temperature of 450 °C make it more suitable for an M3D upper channel layer than Ge-on-SiO2. A comprehensive experimental analysis confirmed the enhanced crystallinity, stability, and channel properties of poly-Ge layers crystallized on BeO. Hence, this study developed a new method for the low-temperature SPC process and highlighted the potential of BeO as a crystallization-assistance thermal-management material for next-generation 3D integrated technology.

Investigation on PECVD-deposited SiO2 underlayer in permalloy-based magnetoelectronic devices

This study presents a comprehensive investigation into the dependence among processing conditions, surface properties of the PECVD-deposited SiO2 underlayer, and their consequential impact on the magnetic and film properties of permalloy. The key exploration parameters involve variations in deposition temperature and annealing temperature. By varying the parameters, microstructure changes within SiO2 were firstly analyzed. A thorough characterization of in-plane magnetic features of the Ni81Fe19/SiO2 multilayer film was then undertaken. The results reveal a significant reliance of magnetic anisotropy and coercivity on PECVD SiO2 deposition temperatures, particularly evident for deposition temperatures below 350°C. This effect is attributed to the formation of a suboxide SiOx film at a lower deposition temperature, which typically possesses more dangling bond and lattice defects, resulting in the formation of surface granular structures after annealing. These characterizations may lead to the identification of optimized processing conditions, which may be used for enhancing the performance of anisotropic magnetoresistance devices with SiO2 as an underlayer. Furthermore, the research findings extend beyond anisotropic magnetoresistance systems, with implications for a broad utilization of magnetoelectronic devices. Overall, the study provides a foundation for informed decision-making in the design and optimization of magnetoelectronic devices, in particular for integrated circuit incorporated devices, highlighting the potential for enhanced functionality through manipulation of processing conditions.

Effects of underlayer on the reduction of graphene oxide through atomic hydrogen annealing and soft X-ray irradiation

The reduction of graphene oxide (GO) through atomic hydrogen annealing (AHA) and soft X-ray irradiation is investigated using microwell substrates with μm-sized holes with and without Ni underlayers. The GO film is reduced through AHA at 170 °C and soft X-ray irradiation at 150 °C. In contrast, some GO films are not only reduced but also amorphized through soft X-ray irradiation. The effect of the Ni underlayer on GO reduction differs between AHA and soft X-ray irradiation. In AHA, the difference in GO reduction between SiO2 and Ni underlayer originates from the atomic hydrogen density on the sample surface. On the other hand, in soft X-ray irradiation, the difference in GO reduction between SiO2 and the Ni underlayer originates from the excited electrons generated by soft X-ray irradiation. Reduction without damage is more likely to occur in the suspended GO than in the supported GO.

Effects of the SiO2 underlayer on magnetic properties of the Pr-Fe-B thin film

Si3N4/Pr-Fe-B/SiO2 thin films were deposited by magnetron sputtering on Si (100) substrate with in-situ annealing at 650 °C. The magnetic properties of these thin films showed significant changes at the various thicknesses of the SiO2 underlayer. This resulted from various growth and orientations of the Pr2Fe14B hard-magnetic phase, and a new Fe3Si underlayer was differently formed at the interface of the Pr-Fe-B layer/SiO2 underlayer. It also led to changes in surface morphology and microstructure of thin films. Coercivity showed a considerable increment at the 75 nm thickness. A better perpendicular anisotropy was found at 20 and 50 nm thicknesses, although coercivities were lower at these thicknesses. Oxygen composition showed an insignificant effect on the magnetic properties of Pr-Fe-B thin film.

(Digital Presentation) Fabrication of Microbridges Based on Ge-on-SOI and Observation of Strong Resonant Light Emission

Introduction Ge is one of the most attractive material for silicon-based optoelectronics because it can be epitaxially grown on a Si substrate, allowing us to integrate Ge based light emitters and photodetectors monolithically on the Si platform. Although Ge is an indirect band gap semiconductor like Si, by epitaxially growing Ge on the Si substrate, tensile strain is introduced into Ge, resultantly leading to the Γ-valley shifts and increase in the light emission efficiency via the direct transition. The amount of the strain induced in Ge-on-Si, however, is not sufficiently large, demanding other methods of applying large tensile strain to Ge. Fabrication of Ge microbridge structure is expected to induce the larger strain and further improve light emission efficiency [1]. In general, microbridges reported so far have been fabricated by the electron beam lithography process, which is not appropriate for mass production. In this study, we fabricate Ge microbridge by simple photolithography process based on Ge-on-Si and Ge-on-SOI structures and very strong room temperature photoluminescence is obtained and strong resonant peaks can be observed. Experimental Method Ge layers were grown on a Si (110) wafer (Ge-on-Si) or a SOI (100) wafer (Ge-on-SOI) using a two-step growth method by solid source MBE. Firstly, a 40nm thick buffer layer at a low temperature of 350 ~ 400℃. Secondly, a 500 nm thick Ge layer was grown at a high temperature of 550 ~ 650℃. Post-growth-annealing was carried out at 800℃ for 10 minutes. The microbridge structures were defined by the standard photolithography process and mesa etching was performed by the reactive ion etching. Subsequently, the Si under the bridge and pads was selectively removed by KOH etchant, leading to free-standing Ge microbridge. For the Ge-on-SOI, the underlying SiO2 layer (buried oxide) was additionally removed by HF. Results and Discussion It was observed by SEM measurements that the Ge microbridges fabricated from Ge-on-Si were slightly warped from both ends to the center of the bridges. Hydrogen gases generated due to the reaction of Si and KOH during the selective etching are considered to be responsible for the warping of the microbridges, which makes it difficult to control the strain of the Ge. The selective etching time, therefore, has to be minimized to reduce the effects of the gas generation. For this purpose, the microbridges were fabricated from Ge-on-SOI, where the floating structure can be easily formed by the etching of the buried SiO2 layer with HF and the etching time of Si with KOH was reduced by a factor of four. As a result, the warping was completely suppressed and very flat microbridges were fabricated without any warping.Photoluminescence measurements at the center of the microbridge on Ge-on-SOI were performed at room temperature. Strong PL emissions were obtained in the wavelength range of 1630-2000 nm, where several strong resonant peaks appear. This resonance is considered to occur due to reflection at the side wall of the bridge and the peaks can be well fitted with the cavity length of the bridge width. Also, we carried out PL measurements from one end to another end of the bridge, and investigated the bridge position dependence of the PL emission. It was found that the light emission intensity increased toward the center of the bridge, and the highest intensity was obtained at the center. Moreover, the strain amounts were measured by micro Raman line scan along the bridge and strain dependence of PL emission was investigated. It was also shown that the strain amount increased toward the center of the bridge and became the highest at it. It was demonstrated that the higher PL intensity can be obtained due to the higher tensile strain at the center of the microbridge. In summary, we fabricated Ge microbridge structures by photolithography process and obtained strong room temperature resonant light emission from the Ge microbridges formed from Ge-on-SOI where bridge-warping was completely suppressed by shortening the etching time. From this result, we can say that the Ge microbridge light emitting devices are very promising for applications to the light sources on the Si platform.This work was partially supported by JSPS KAKENHI (Nos. 19H02175, 19H05616 and 20K21009).[1] M. J. Suess et al, Nat. Photonics 7: 466, 2013 Figure 1

DNA Origami for Silicon Patterning.

Desoxyribonucleic acid (DNA) origami architectures are a promising tool for ultimate lithography because of their ability to generate nanostructures with a minimum feature size down to 2 nm. In this paper, we developed a method for silicon (Si) nanopatterning to face up current limitations for high-resolution patterning with standard microelectronic processes. For the first time, a 2 nm-thick 2D DNA origami mask, with specific design composed of three different square holes (with a size of 10 and 20 nm), is used for positive pattern transfer into a Si substrate using a 15 nm-thick silicon dioxide (SiO2) layer as an intermediate hard mask. First, the origami mask is transferred onto the SiO2 underlayer, by an HF vapor-etching process. Then, the Si underlayer is etched using an HBr/O2 plasma. Each hole is transferred in the SiO2 layer and the 20 nm-sized holes are transferred into the final stack (Si). The resulting patterns exhibited a lateral resolution in the range of 20 nm and a depth of 40 nm. Patterns are fully characterized by atomic force microscopy, scanning electron microscopy, focused ion beam-transmission electron microscopy, and ellipsometry measurements.

Etching of sub-10 nm half-pitch high chi block copolymers for directed self-assembly (DSA) application

Directed Self-Assembly of block copolymers is a lithographic technique being developed to reach sub-10 nm technological nodes. Recently, high chi block copolymers have been developed to achieve higher resolution. In this paper, the high chi system investigated is a modified polystyrene-b-poly(methyl methacrylate)(PS-b-PMMA) presenting a pitch of 18 nm. One critical step for its integration is the PMMA removal selectively to the PS. Two approaches to remove the PMMA phase are presented, highlighting the challenges encountered due to its smaller dimensions. The first one is a full dry approach based on a CH4/N2 chemistry, which presents some bridge formation due to intensive sidewalls passivation and to a species confinement effect accentuated by the small 9-nm critical dimension of the lines. Therefore, the main high chi PS-b-PMMA dry etching difficulties come from the trade-off between obtaining high selectivity and avoiding bridge formation. The second approach is a mixed wet and dry PMMA removal process based on UV exposure followed by solvent rinse. An Ar/O2 dry brush layer opening was developed and the pattern transfer into the SiO2 and Si underlayers is demonstrated for the high chi PS-b-PMMA.

Correlation between SiO2 growth rate and difference in electronegativity of metal–oxide underlayers for plasma enhanced atomic layer deposition using tris(dimethylamino)silane precursor

The growth rate of an SiO2 film on various metal–oxide (M–O) underlayers by plasma-enhanced atomic layer deposition (ALD) using tris(dimethylamino)silane precursor and O2 plasma gas is systematically investigated, and the effect of the difference in the electronegativity of the M–O underlayer on the ALD-SiO2 growth mechanism is also discussed. All data for the ALD-SiO2 film thickness on HfO2, TiO2, Al2O3, and SiO2 underlayers satisfied a linear relationship as a function of the ALD cycle. The growth per cycle (GPC) value of the ALD-SiO2 film increased in the following order: SiO2 (0.043 nm/cycle) < Al2O3 (0.14) < TiO2 (0.17) < HfO2 (0.22). On the other hand, the negative charge concentration of oxygen atoms in the M–O underlayer becomes higher in the following order: Si–O (1.76 eV) < Al–O (2.03) < Ti–O (2.18) < Hf–O (2.27) due to the electronegativity difference between the Si, Al, Ti, Hf, and O elements of the M–O underlayer. A correlation between the GPC of the ALD-SiO2 film and the difference in the electronegativity of the M–O underlayer was also determined.

Atomic diffusion bonding using oxide underlayers for optical applications

Atomic diffusion bonding of quartz glass wafers using thin Ti films, with SiO2 underlayers on wafer surfaces, provides 100% light transmittance at the bonded interface along with strong bonding energy, after post-bonded low-temperature annealing. Cross-section images obtained using transmission electron microscopy show that the bonded interface after annealing at 350 °C consists of amorphous structure including nanocrystalline grains. Structural analysis using electron energy loss spectroscopy shows that post-bonded annealing enhances oxidation of Ti with oxygen dissociated from SiO2 underlayers, and that Ti oxides form close to TiO2 or Ti4O7. This oxidation provides 100% light transmittance with high bonding strength attributable to the annealing. Moreover, we applied this technique for bonding glass and sapphire wafers using SiO2–Nb2O5 underlayers, demonstrating that 100% light transmittance and control of refractive index matching are achieved simultaneously at the bonded interface.

High-responsivity turbostratic stacked graphene photodetectors using enhanced photogating

High-responsivity graphene photodetectors were fabricated using turbostratic stacked graphene, which provided enhanced photogating. Photogating is a promising means of increasing the responsivity of graphene photodetectors, and this effect is proportional to carrier mobility. Turbostratic stacked graphene exhibits higher carrier mobility than conventional monolayer graphene because it has the same band structure as monolayer graphene while preventing scattering by the underlying SiO2 layer. The photoresponse of these devices at a wavelength of 642 nm was approximately twice that obtained for a conventional monolayer graphene photodetector. The results reported show the feasibility of producing high-responsivity graphene-based photodetectors using a simple fabrication technique.

Development of Superconducting Nanostrip X-Ray Detector for High-Resolution Resonant Inelastic Soft X-Ray Scattering (RIXS)

To achieve a resolving power greater than 100 000, we are developing a superconducting nanostrip single photon detector (SSPD) for an ultrahigh-resolution RIXS spectrometer in the Taiwan Photon Source. To achieve the target resolving power, the SSPD, combined with a microstripline (MSL) structure, which acts as a delay line, should have a line pitch of 0.5 μm. This study uses numerical simulations to design SSPD. It consists of a meander of a 50-nm-thick Nb nanostrip and a 45-nm-thick SiO2 underlayer. The width of the line and the gap of the meander are 400 and 100 nm, respectively. The estimated velocity of the transmitted pulses due to X-ray absorption in the Nb nanostrip of the above SSPD is ~5% of the speed of light in free space. A detection area of 16 mm × 5 mm is sufficient to allow a time difference of ~1 ns between neighboring nanostrips to be distinguishable using conventional time to digital converters (TDCs). We fabricated a trial SSPD imager with dimensions of 4 mm × 0.1215 mm, and measured signal pulse characteristics for ions simulating soft X-ray photons. During an experiment, the maximum time difference of 7.5 ns between output pulses from both ends of the nanostrip successfully exhibited the proper imaging operation.

Atomic Diffusion Bonding for Optical Devices with High Optical Density

In recent years, high-brightness projector products equipped with laser light sources are widely used for digital cinema, projection mapping, and simulation. Their increased luminance enhances the optical energy density of the optical system, and the strong photon and thermal energies degrade the organic adhesive used in the optical interface. This has come to pose a severe shortcoming affecting the reliability and durability of optical elements used in optical systems. A new bonding method that provides high light transmittance with high bonding strength is necessary for the optical interface of high optical density devices. Atomic diffusion bonding (ADB) of wafers is a promising process to achieve room-temperature wafer bonding: Thin metal films are fabricated using sputter deposition on two flat wafers’ surfaces, with subsequent bonding of the two films on the wafers in vacuum (1,2). Bonding can be done even with film thickness of a few angstroms on each side. Incident light can be transmitted through such thin bonded films without any marked reduction in intensity. The use of thin Ti films is effective to achieve high light transmittance while maintaining high bonding strength to bond oxide wafers such as synthetic quartz crystal (2). However, optical energy absorption of 2% remains at the bonded interface even when the wafers are bonded using 0.2 nm thick Ti film on each side. A reduction of Ti film thickness below 0.2 nm enhances the transmittance further, but it reduces the bonding strength considerably. To enhance the light transmittance at the bonded interface, we propose atomic diffusion bonding using oxide underlayers: After oxide films are deposited on two flat wafers’ surfaces, the wafers are bonded as usual using thin metal films at room temperature using atomic diffusion bonding as shown in figure (A). Oxygen dissociated from oxide layers enhances the formation of Ti oxide; 100% light transmittance at the bonded interface can be achieved by post-bonded annealing in air at low temperatures. Table (B) presents the light transmittance at wavelength λ of 500 nm at the bonded interface for wafers bonded using Ti(0.5 nm) on each side. In the ADB process with oxide underlayer, SiO2 films deposited using ion-assisted vapor deposition were used. The SiO2 layer surface roughness was less than 0.5 nm. In ADB process with SiO2 underlayer, light transmittance at the bonded interface was enhanced considerably from 90% for as-bonded wafers to 100% for wafers annealed at 300 °C. It is noteworthy that this marked enhancement of the light transmittance is applicable to any material wafer. Without an oxide underlayer, enhancement of the light transmittance by annealing is slight: The enhancement for bonded quartz glass wafers, for instance, was from 90% for as-bonded to 91% for annealed even at 500 °C. Moreover, the surface free energy at the bonded interface for quartz glass wafers bonded using SiO2 underlayers was greater than that of wafers without the underlayers, indicating another important merit for ADB processing with an oxide underlayer. This bonding technique is applicable to almost all optical interfaces between mirror-polished surfaces of any material, and is expected to be useful to fabricate optical devices with high optical density such as high-brightness projectors with laser light sources. (1) T. Shimatsu and M. Uomoto, “Atomic diffusion bonding of wafers with thin nanocrystalline metal films,” J. Vac. Sci. Technol., B 28, 706-714 (2010). (2) T. Shimatsu, M. Uomoto, and H. Kon, “Invited: Room Temperature Bonding Using Thin Metal Films (Bonding Energy and Technical Potential),” ECS Transactions, 64(5), 317-328 (2014). Figure 1

Hydrogen passivation of silicon/silicon oxide interface by atomic layer deposited hafnium oxide and impact of silicon oxide underlayer

HfO2 synthesized by atomic layer deposition (ALD) can be used as a passivation material for photodetectors. This paper shows a significant reduction of density of interface traps at the Si/SiO2 interface using ALD HfO2. This is explained by a chemical passivation effect due to presence of hydrogen from water used in the ALD process. Furthermore, ALD HfO2 layers appear negatively charged which generate an additional field effect passivation. The impact of the SiO2 underlayer is also discussed by comparing a chemical silicon oxide to a standard thermal silicon oxide. It is shown that chemical silicon oxide can act as a reservoir of hydrogen atoms which helps to reduce the density of defects close to the Si/SiO2 interface. This result demonstrates the importance of the surface preparation before the ALD of HfO2 in the passivation scheme. Finally, this work shows the correlation between negatively charged defects and Si–O–Hf bonds at the SiO2/HfO2 interface. A passivation stack composed of chemical oxide permits to reach both a low density of interface traps (∼1.0 × 1011 cm−2 eV−1) and a negative charge density (∼−1.0 × 1011 cm−2). This stack provides both chemical and field effect passivation of the silicon surface.

(Invited) Internal Photoemission of Electrons from 2-Dimensional Semiconductors

Few monolayer (ML) thin transition metal dichalcogenide (TMD) semiconductors attract considerable interest because of their tunable properties relevant to a broad range of device applications. In particular, few-layer MoS2 has already been shown to deliver significant advantages in terms of transistor channel downscaling. The performance of the MoS2-based devices critically depends on the band alignment with other materials since the alignment determines the electrostatics of the stack, height of the tunneling barriers, contact resistance, etc. However, barrier characterization at interfaces of few-layer two-dimensional (2D) materials represents an experimental challenge: The electronic transport across these interfaces is strongly affected by hydrocarbon residues of the flake transfer process, non-homogeneities (e.g., domain boundaries), and defects in the material itself. Therefore, it is important to find a technique allowing one to reliably determine the 2D-semiconductor bandgap edge energies with respect to the bands of other materials. In the present work we will show that this goal can be achieved using the spectroscopy of Internal PhotoEmission (IPE) of electrons from MoS2 and WS2 into an insulating layer. By using 2- and 4-ML thick films of these TMDs grown on top of a SiO2 layer as the prototype interfaces, we observe electron IPE from the 2D photo-emitters and determine the corresponding energy barriers. The studied samples were prepared by thermal evaporation of a thin Mo or W film on SiO2/Si or HfO2(2 nm)/SiO2/Si substrates. Next, the samples were transferred to a furnace and sulfurized in pure H2S(10 or 100 mbar) at 800 °C resulting in the formation of a large-area (in the range of cm2) poly-crystalline MoS2 or WS2 films with crystallites of 50 nm size [1]. Cross-sectional TEM images reveal the characteristic layered structure. The Raman spectrum exhibits two distinct peaks corresponding to the in-plane (E2g) and the out-of-plane (A1g) vibrations in TMD layer, respectively. This observation reveals conversion of the metal film into 2H-MoS2 or 2H-WS2 hexagonal polytypes. By varying the thickness of the initially deposited metal, it appears possible to produce samples with 4 or 2 ML thick MoS2 and WS2 films without contamination of the sulfide/oxide interfaces. Electrical contacts were fabricated by evaporation of 100-nm thick Au or Al pads on top of the TMD films [2]. Fabrication of large area laterally uniform MoS2 and WS2 few-ML thin films enabled us to perform IPE experiments which address one of the fundamental issues concerning energy band alignment between different TMD materials. By observing electron photoemission from the valence band (VB) of MoS2 or WS2 into the conduction band (CB) of SiO2 underlayer, one can find the energy barriers. These correspond to the VB top energies of the two photo-emitting TMD materials referenced to the same energy level of the oxide CB bottom edge [3]. The IPE quantum yield spectra reveal the same field-dependent energy onset of the IPE current in the energy range 3.5-4.0 eV for both MoS2 and WS2 as well as in their stacked heterojenctions. Since the same photocurrent spectra were also obtained when using Al as the contact pad material instead of Au, the TMD layer can be identified as the sole source of photoelectrons [2]. This conclusion is independently affirmed by the observed significant decrease of the quantum yield if reducing the thickness of MoS2 electrode from 4 ML to 2 ML. The observed field dependence of the IPE spectra agrees well with the image-force barrier lowering at the TMD/SiO2 interface. The energy barrier of Fe =4.2±0.1 eV between the top of the MoS2 VB and the bottom of the SiO2 CB can be found by extrapolating this dependence to zero field. No significant difference between spectral thresholds from MoS2 and WS2 is found suggesting that the VBs of of these TMDs are nearly aligned. The same conclusion can be reached if analyzing the IPE yield spectra from MoS2/WS2 and WS2/MoS2 heterostructures. This result would suggest the validity of the “common anion rule” for sulfides of metals similarly to the earlier studied case of insulating metal oxides [3]. Recent IPE experiments addressing the effects of TMD layer transfer on top of insulating substrate will also be discussed. D. Chiappe et al., Adv. Mater. Interfaces 1500635 (2015).V. V. Afanasev et al. Microelectron. Eng. 147 294 (2015).V. V. Afanas’ev, Adv. Condens. Matter Phys. 301302 (2014).

On the use of (3-trimethoxysilylpropyl)diethylenetriamine self-assembled monolayers as seed layers for the growth of Mn based copper diffusion barrier layers

In this work x-ray photoelectron spectroscopy is used to investigate in-vacuo, the interaction of metallic manganese with a (3-trimethoxysilylpropyl)diethylenetriamine (DETA) self-assembled monolayer (SAM) on SiO2 and non-porous low-k dielectric materials. Subsequent deposition of a ∼0.5nm thick Mn, followed by a 200°C anneal results in the Mn diffusing through the SAM to interact with the underlying SiO2 layer to form a Mn-silicate layer. Furthermore, there is evidence that the Mn interacts with the carbon and nitrogen within the SAM to form Mn-carbide and Mn-nitride, respectively. When deposited on low-k materials the Mn is found to diffuse through to the SAM on deposition and interact both with the SAM and the underlying substrate in a similar fashion.

Physical, chemical and electrical characterisation of the diffusion of copper in silicon dioxide and prevention via a CuAl alloy barrier layer system

Cu and CuAl alloy (90%:10% wt) films deposited on thermally grown SiO2 were studied using thermal stress testing in vacuum, N2 flow and atmosphere ambient all at a temperature of 500°C, in order to rigorously test the effectiveness of the incorporation of Al into a Cu film at preventing degradation of the metal layer and diffusion of Cu into the underlying SiO2 dielectric. Capacitance voltage testing of metal-oxide-semiconductor (MOS) devices, using the Cu and the CuAl alloy as the gate metal show the failure of the Cu reference set via diffusion of Cu at the metal / SiO2 interface in contrast to the stability of the CuAl alloy devices, even following a 500°C anneal in atmosphere ambient. The flatband voltage of the Cu reference MOS structures were altered by the application of an external applied voltage bias, consistent with the diffusion and mobility of Cu+ ions into the underlying SiO2 layer. Optical and scanning electron microscopies of the surface metal layers show the degradation and delamination of the pure Cu films throughout the experimental anneal stages, in contrast to the stability of the CuAl alloy. X-ray photoelectron spectroscopy shows the growth of Al oxide at the surface of the CuAl alloy following thermal anneal which acts to passivate the film, preventing Cu oxide formation which was identified in the pure Cu reference sample set. Transmission electron microscopy analysis shows the inter-diffusion of Cu at the Cu / SiO2 interface following anneal, in contrast to the CuAl alloy which shows the growth of a continuous barrier layer interface. Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) was used to profile the entire metal / SiO2 / Si stack via 3 dimensional reconstructions, showing the inward diffusion of Cu within the Cu control samples and containment of Cu within the metal layer of the CuAl alloy samples.

Flatband Voltage Shift Depending on SiO<sub>2</sub>/SiC Interface Charges in 4H-SiC MOS Capacitors with AlON/SiO<sub>2</sub> Stacked Gate Dielectrics

The mechanism of flatband voltage shift in SiC metal-oxide-semiconductor (MOS) capacitors with stacked gate dielectrics consisting of aluminum oxynitride (AlON) layers and SiO2 underlayers was investigated by varying the AlON and SiO2 thicknesses. The flatband voltages of the fabricated capacitors with fixed SiO2 underlayer thicknesses were almost independent of the AlON thickness, indicating the negligible charges in AlON layer. On the other hand, when varying SiO2 underlayer thickness, the flatband voltage decreased with an increase in capacitance equivalent thickness (CET), and the slope of their linear fit was comparable to that for SiC MOS capacitors without AlON layer. These observations can be well explained by assuming interface charges at AlON/SiO2 interface with an amount comparable, but a polarity opposite to, those at SiO2/SiC interface.

Highly polarized emission from a GaN-based ultraviolet light-emitting diode using a Si-subwavelength grating on a SiO2 underlayer

The polarization characteristics of a 370nm GaN-based ultraviolet light-emitting diode (UV-LED) were controlled by a subwavelength grating (SWG) on a low-refractive-index SiO2 underlayer inserted between the SWG and LED surface. Highly polarized UV emission was demonstrated by utilizing the Bloch eigenmode resonance in the SWG structure for the two orthogonal polarization states. The polarization ratio of the emission reached 16:1, which is the highest reported to date for direct emission from a GaN-based UV-LED. The decrease in UV emission was also prevented by suppressing the diffracted plane wave and by increasing the amplitude of the wave incident onto the SWG structure; this increase was achieved by taking advantage of the low refractive index of SiO2.

Identification of Domain Boundary Defects in Crystalline Self-Assembled Monolayers.

One of the major challenges to the fabrication of functionalized templates using self-assembled monolayers (SAMs) is the characterization of nanoscale defects, particularly SAM domain boundaries (DBs). In this study, an etchant was used to chemically amplify the DBs in a SAM by forming microscale pits in the underlying SiO2 layer. This approach revealed that the naturally occurring DBs acted as structural defects in the SAMs. The DB structures were characterized by systematically varying the octadecyltrichlorosilane (ODTS) monolayer domain size from the nanoscale to the microscale by varying the preparation temperature. These approaches showed that the SAM DBs, which were visualized as having round- and line-shaped nanoscale structures, provided potentially chemical and mechanical surface defect sites. Our principal findings open up exciting new possibilities for understanding the structural defects in SAMs on the molecular level and suggest an approach for optimizing the conditions used to generate defect-free SAM templates.

Deposition of high permeability FeCoN films on mica substrates

In this study, sheet mica was explored as an alternative substrate for thin film deposition due to its unique layered structure and atomically flat surface. Static magnetic properties and microwave permeability of sputtered FeCoN films on mica with and without SiO2 under-layer were examined. In-plane isotropy and a large coercivity of 70 Oe were observed for the film directly deposited on mica substrate. With the insertion of 40 nm SiO2 under-layer between the film and mica substrate, well-defined in-plane anisotropy is formed due to the significant reduce in film residual stress, associated with a 3 Oe coercive force along easy axis. As a result, excellent microwave properties have been achieved and are comparable with the same film on Si substrate. Moreover, the permeability spectra are surprisingly stable from room temperature up to 390 K. Mica is proved as a promising substrate for magnetic films with high microwave performance, which is a great advantage for practical applications. Furthermore, our r...