Nitride Thickness Research Articles

Langmuir Films of Layered Nanomaterials: Edge Interactions and Cell Culture Applications.

The application of nanomaterials in technology is limited by challenges in their processing into macroscopic structures with reliable and scalable methods. Herein, it is demonstrated that using scalable fabrication methods such as liquid-phase exfoliation, it is possible to produce dispersions of a wide variety of layered nanomaterials, including the first demonstration of boron nitride, with controllable and standardized size and thickness scaling. These can be used, as-produced, for Langmuir deposition, to create single layer films with tuneable density. Of particular importance, we show that the difference in edge chemistry of these materials dictates the film formation process, and therefore can be used to provide a generic fabrication methodology that is demonstrated for various layered nanomaterials, including graphene, boron nitride, and transition metal dichalcogenides. We show that this leads to controllable cancer cell growth on graphene substrates with different edge densities but comparable surface coverage, which can be produced on a statistically relevant cell study amount. This opens pathways for the generic fabrication of a range of layered nanomaterial films for various applications toward a commercially viable film fabrication technology.

Tfbar Sensors for Detection of Explosives Substances

Tfbar Sensors for Detection of Explosives Substances

Laser nitriding of titanium surfaces for biomedical applications

In this paper, titanium nitrides were produced on commercially pure titanium samples by laser nitriding processes, with the goal of improving bio-compatibility and corrosion resistance. To identify the critical set of laser nitriding processing parameters (a combination of both laser scanning parameters and the N2 content processing gas), mouse MLO-Y4 cells were utilized for bio-compatibility evaluation, and simulated body fluid was used for electrochemical behavior examination to characterize corrosion performance. The modified surfaces were also characterized with scanning electron microscope, X-ray diffraction, and nano-indentation techniques to reveal the connections between the bio-compatibility/corrosion resistance performance and the nitrided layer composition, thickness, and surface roughness. For improved bio-compatibility and corrosion resistance performance, a dense and thick titanium-nitride dendritic layer is desirable, which can be formed in a pure N2 environment, together with a high laser energy density.

Ionizing radiation tolerance of stacked Si3N4-SiO2 gate insulators for power MOSFETs

The total ionizing dose radiation response of metal-nitride-oxide-semiconductor capacitors are examined. Capacitors with different oxide and nitride thickness combinations are fabricated and irradiated using a Co-60 gamma source. Electrical characterization showed all samples with oxide/nitride stack gate insulators exhibited significantly higher tolerance to irradiation when compared to metal-oxide-semiconductor capacitors. Thick oxide-nitride layers can be used as gate insulators in power metal-oxide-semiconductor field effect transistors. Technology computer-aided design simulations are performed to characterize the radiation effects mechanisms. Spatially distributed interface traps at shallow energy level were present in all the oxide/nitride stacks. These interface traps decrease as total dose increases. This result may be due to radiation induced hydrogen passivation.

A Novel Structure for Improving Erase Performance of Vertical Channel NAND Flash With an Indium-Gallium-Zinc-Oxide Channel

We propose a novel structure to solve the hole erase problem of Indium-Gallium-Zinc-Oxide (IGZO) channels. The proposed structures are an IGZO-nitride-P filler (INP) structure and an IGZO-P filler (IP) structure. In the simulations using both structures, stable operation and erase efficiency can be achieved in an INP structure when the nitride barrier thickness is 7 nm. The erase performance achieved exceeds that of the polysilicon channel under the same conditions. Conversely, if the nitride thickness exceeds 8 nm, the read operation becomes unstable. Therefore, nitride thickness is an important parameter in the operation of an INP structure, and its maximum value is 7 nm. For improving upon this INP structure, the nitride was removed to create an IP structure, in which, leakage currents could be limited by reducing doping concentration. In particular, such an IP structure showed that the maximum erase performance (2 ms) of the polysilicon channel can only be achieved at $2.3~\mu \text{s}$ , and then the erase operation can continue. This result is due to lack of electron accumulation in the channel and their ability to move quickly through the filler directly connected to the IGZO channel. As a result, both proposed structures have shown that low erase performance can be overcome without sacrificing the excellent leakage current blocking characteristics of IGZO material.

Investigation of Low-Temperature Liquid Nitriding Conditions for 316 Stainless Steel for Improved Mechanical and Corrosion Response

Combined influence of liquid nitriding time and liquid nitriding temperature on the properties of nitrided region developed on 316 stainless steel was investigated. Studies were restricted to low temperatures of 425 °C and 475 °C while the nitriding time was varied from 4 to 16 h. Developed nitrided layers were characterized by optical microscopy, scanning electron microscopy and X-ray diffraction. Mechanical and electrochemical properties of the nitrided layers were characterized, respectively, by Vickers micro-hardness measurements and cyclic polarization studies in 3.5 wt% NaCl solution. After 4-h nitriding at 425 °C or at 475 °C, the developed expanded austenite started to contract with simultaneous decrease in nitrided layer thickness, hardness and corrosion resistance. These prolonged nitriding time effects have been attributed to the decreased chemical potential of nitrogen in salt bath leading to the outward diffusion of N (from sample to salt bath). However, the 4-h nitriding at 475 °C resulted in larger expansion of austenite as compared to 4-h nitriding at 425 °C. Due to this, better mechanical and electrochemical property was realized after 4-h nitriding at 475 °C suggesting that the increased amount of N solubility in sample led to simultaneous increase in hardness and corrosion resistance of stainless steels.

High-Efficiency Grating Coupler in 400 nm and 500 nm PECVD Silicon Nitride With Bottom Reflector

We design and experimentally demonstrate highly efficient Silicon Nitride based grating couplers with bottom distributed Bragg reflectors. All the layers were deposited using plasma enhanced chemical vapor deposition processing. We present gratings on two Silicon Nitride thickness (400 nm and 500 nm) platforms. On a 500 nm thick Silicon Nitride, we show a peak coupling efficiency of -2.29 dB/coupler at a wavelength of 1573 nm with a 1 dB bandwidth of 49 nm. On a 400 nm thick platform, we demonstrate a coupling efficiency of -2.58 dB/coupler at 1576 nm with a 1 dB bandwidth of 52 nm. The demonstrated coupling efficiency is the best reported as yet, for both 400 nm and 500 nm thick, plasma deposited Silicon Nitride platforms.

Surface Hardening of Massive Steel Products in the Low-pressure Glow Discharge Plasma

A process vacuum chamber is filled with a homogeneous plasma of glow discharge with electrostatic electron confinement, which is used for surface hardening of massive products. At the current of 2–20 A and the gas pressure ranging from 0.1 to 1 Pa the discharge voltage amounts to 350–500 V. When a bias voltage of 2 kV is applied to an immersed in the plasma hollow cylinder with a mass of 15 kg, electrical power spent on heating it by accelerated ions exceeds by an order of magnitude the power spent on the discharge maintenance. The massive cylinder is heated up to 700 °C for 15 min. When argon mixture with nitrogen (30%) is used, the nitriding for 3h results in an increase in the surface hardness from 400 up to 1000 HV50 and the nitrided layer thickness grows to ~100 μm. The nitriding rate is enhanced by a high degree of nitrogen dissociation due to decomposition by fast electrons and surface structural defects due to bombardment by high-energy ions.

Effect of Quench Polish Quench Nitriding Temperature on the Microstructure and Wear Resistance of SAF2906 Duplex Stainless Steel

The effect of quench polish quench (QPQ) nitriding temperature on the microstructure and wear resistance of SAF2906 duplex stainless steel was investigated. Results showed the surface of the nitrided samples was composed of an oxidized layer, a loose compound layer, a compact compound layer, and a diffusion layer. The oxidized layer was composed of Fe3O4. The main phases of the loose compound layer were CrN, αN, Fe2–3N, and Fe3O4. The compact compound layer was composed of CrN, αN, and Fe2–3N. In the diffusion layer, CrN and expanded austenite (S) were the main phases. The nitrided layer thickness increased from 20 to 41 μm with an increasing temperature of 570 to 610 °C. When the nitriding temperature was above 590 °C, the precipitates in the diffusion layer became coarsened, and their morphologies gradually changed from spherical particulate to rod-like and flocculent-like. Tribotests showed the cumulative mass loss of QPQ-treated samples was much lower than that of the substrate. The cumulative mass loss of the samples nitrided at 610 °C was higher than that at 570 °C during the first 29 h. When the test time was over 29 h, the former was lower than the latter.

Application of Laser Radiation for Intensification of Chemical Heat Treatment

The processes of chemical heat treatment were analyzed. The areas of their application, productivity, energy intensity, advantages and disadvantages are highlighted. The surface nitrided layers with hardness up to 800–900 HV were obtained. In this case, nitriding thickness does not exceed 0.15–0.2 mm, which is insufficient, especially if the value of residual deformations exceeds the thickness of the diffusion layer. It is shown that to increase the efficiency of nitriding, it is advisable to pre-modify the microstructure of the layer of the sample by laser irradiation. Modeling of thermal processes occurring in steels under irradiation and experimental studies have determined the conditions under which highly dispersed, with a high dislocation density, disoriented in space structures are formed in the surface layers. Dislocations, located on the grain boundaries and having a complex configuration, form paths along which nitrogen atoms can move, forming nitrides with alloy elements. It was shown that in U8 tool carbon steel (AISI M2) after laser treatment and subsequent nitriding in ammonia at a temperature of 780–800 °К for 12 h, a nitrided layer is formed. The depth of the nitrided layer without prior laser treatment is 0.115 mm, on laser-treated it varies within 0.12–0.46 mm depending on the processing speed. The results of the combined nitriding of 40Cr13 stainless steels (AISI 420 Stainless Steel) and 12Cr18Ni10Ti (AISI 321 Stainless Steel), in which the thickness of the hardened layer with a hardness of 815.7–917.7 HV is 0.4–0.5 mm, with a significantly shorter (by 3–5 times) process time and its cost, are presented. The expediency of manufacturing discretely located nitrided zones on the working surfaces of products is discussed.

Study of in Situ Silver Migration in Amorphous Boron Nitride CBRAM Device.

We report the dependence of the thickness of amorphous boron nitride (a-BN) on the characteristics of conductive bridge random access memory (CBRAM) structured with the Ag/a-BN/Pt stacking sequence. The a-BN thin film layers of three different thicknesses of 5.5, 11, and 21.5 nm were prepared by the sputtering deposition. Depending on the thickness of the a-BN layer, the devices are found to be in either low-resistance state (LRS) or high-resistance state (HRS) prior to any consecutive switching cycle. All devices with 5.5 nm thick a-BN switching layer are in LRS as the pristine state, while devices with 21.5 nm thick a-BN layer are found to be in HRS as the pristine state. To attain reliable switching cycles, initial RESET and electroforming process are necessarily required for the devices with 5.5 and 21.5 nm thick a-BN layer, respectively. However, the devices with the a-BN layer of thickness between 5.5 and 21.5 nm in pristine states are in either HRS or LRS. This dependence of the a-BN thickness on different resistance states in the pristine state can be explained by in situ Ag diffusion during its sputter deposition to form a top electrode on the a-BN layer. Our finding shows a detailed investigation and a deep understanding of the switching mechanism of Ag/a-BN/Pt CBRAM devices with respect to different a-BN thicknesses for the future computing system.

Fowler-Nordheim tunneling characteristics of graphene/hBN/metal heterojunctions

The heterostructures of low-dimensional materials are considered promising candidates for future electronic devices. In this work, we manifest the interlayer hexagonal boron nitride (hBN) thickness dependent tunneling characteristics of graphene/hBN/metal heterojunction back-gated field effect transistors (FETs). Direct tunneling of charge carriers through the ultrathin hBN layer is noticed at low bias voltages. Besides, Fowler-Nordheim tunneling takes place at high bias voltages revealing an increase in the barrier height with an interlayer film thickness. In addition, the back-gate dependent tunneling properties of graphene/hBN/metal heterojunction back-gated FETs are investigated. Furthermore, the Fermi level of graphene is tuned via back-gate voltages that results in the modification of the tunneling current, threshold voltage, and barrier height of the device. This could be an effective approach to modify the tunneling features of vertical heterostructures for their prospective role in next generation high performance electronic devices.

Experimental-numerical Technique to Evaluate the Thickness of TiN Thin Film

In this study, the numerical analysis of instrumented indentation testing was combined with the experimental procedure to evaluate the mechanical properties and thickness of a titanium nitride (TiN) film deposited on titanium substrate (Ti) by plasma processing. TiN film thickness is an important parameter for the surface treatment industry. In numerical analysis, the finite elements method (FEM) was applied using Marc™ commercial software. Initially, the mechanical properties of the film and substrate were determined using a numerical-experimental methodology, combining the results of indentation testing with a Berkovich indenter and the same numerical simulation for both the film and substrate. Next, the behavior of instrumented Vickers hardness as a function of maximum indenter penetration depth (hmax) was compared with the numerical results of this hardness as a function of the ratio between penetration depth and film thickness (hmax/t). Both curves were fitted using power law equations, which calculated film thickness applying a new convergence algorithm. Finally, it also was shown that the film thickness obtained agrees with the experimental range reported in the literature.

Mechanical and microstructural aspects of C20-steel blades subjected to gas nitriding

The paper presents the investigation of conical blades made of unalloyed steel C20 gas-nitrided by the Nitreg method. On the surface of steel blades (with tip angles in the range of 20–170°) an approx. 15mm-thick nitride layer of was fabricated, which had a bizonal structure of: ɛ (Fe2–3N and Fe3(N,C)1–x) and ɛ+γ′(Fe4N) with a hardness of 1310HV and 910HV, respectively. Hardness tests carried out on blade cross-section showed that a 0.7–1mm thick diffusion layer occurred under the nitride layer. By applying the criterion of effective nitrided layer thickness, gc+50, it was demonstrated that blades with a tip angle of 20° and 30° had been through-nitrided (i.e. nitrided through and through). A static compression test showed that, as a result of nitriding, the compressive strength of the blades had increased by a factor of two.

Homogeneous and heterogeneous micro-structuring of austenitic stainless steels by the low temperature plasma nitriding

The austenitic stainless steels have been widely utilized as a structural component and member as well as a die and mold substrate for stamping. AISI316 dies and molds require for the surface treatment to accommodate the sufficient hardness and wear resistance to them. In addition, the candidate treatment methods must be free from toxicity, energy consumption and inefficiency. The low temperature plasma nitriding process has become one of the most promising methods to make solid-solution hardening by the nitrogen super-saturation. In the present paper, the high density RF/DC plasma nitriding process was applied to form the uniform nitrided layer in the AISI316 matrix and to describe the essential mechanism of inner nitriding in this low temperature nitriding process. In case of the nitrided AISI316 at 673 K for 14.4ks, the nitrided layer thickness became 60 μm with the surface hardness of 1700 HV and the surface nitrogen content of 7 mass %. This inner nitriding process is governed by the synergetic interrelation among the nitrogen super-saturation, the lattice expansion, the phase transformation, the plastic straining, the microstructure refinement and the acceleration of nitrogen diffusion. As far as this interrelation is sustained during the nitriding process, the original austenitic microstructure is homogeneously nitrided to have fine grains with the average size of 0.1 μm and the high crystallographic misorientation angles and to have two phase (γ + α’) structures with the plateau of nitrogen content by 5 mass%. Once this interrelation does not work anymore, the homogeneous microstructure changed itself to the heterogeneous one. The plastic straining took place in the selected coarse grains; they were partially refined into subgrains. This plastic localization accompanied the localized phase transformation.

(Invited) Process Monitoring of 100 GaN-on-Diamond Wafers

The introduction of chemical vapor deposition (CVD) diamond as a viable substrate for GaN HEMTs [1], [2] makes GaN-on-diamond an attractive means to run higher power densities through the GaN HEMT compared to traditional GaN on host substrates. While power densities of 20 and 40W/mm have been demonstrated for pulsed devices on silicon carbide (SiC) [3], continuous powers exceeding 10W/mm will reduce the lifetime of the GaN HEMTs due to self-heating. GaN-on-diamond holds a promise of reducing the problems associated with self-heating and allows for increases in the power density of HEMT devices. To date, GaN-on-diamond has been shown to allow for higher areal power densities than GaN-on-SiC [4], [5]. The process of making GaN-on-diamond was first demonstrated more than 10 years ago [1], [2] has evolved and improved over the years from broken samples 1cm on a side with a 25 micron (800 W/mK thermal conductivity) diamond substrate to a 4” process with a 100 micron (1500 W/mK) diamond substrate. In this paper we will look at wafer level electrical comparisons of GaN-on-diamond to GaN on host substrates and at process monitoring for the 100 GaN-on-diamond wafers. The process we use to make GaN-on-diamond is to transfer an epitaxial layer of GaN from a silicon substrate to diamond. In this process we flip the GaN grown on silicon onto a sacrificial substrate and remove the growth silicon. At this point the AlGaN transition layers (TLs) which are necessary to grow low defect density GaN on silicon are etched away. The TLs while critical to the growth of low defect GaN are themselves highly defective and have poor thermal properties [6]. It is therefore advantageous both electrically and thermally to remove these layers. Once the TLs are removed we protect the GaN back side with a nucleation/adhesion layer and we grow the CVD diamond. The standard metric for GaN-on-diamond is the thermal boundary resistance (TBR) which measures how efficiently the heat can be transferred from the GaN to the diamond. With collaborators we have been able to demonstrate a drop from 135 m2K/GW to as low as 10 m2K/GW by removing the TLs and maintaining a consistent adhesion layer thickness of silicon nitride between the GaN and the diamond [7]. Process monitoring shows that we can consistently maintain a 35 +/- 5nm SiN adhesion layer between the GaN and the diamond. In this paper we will present process monitoring data of this and other parameters for the last 100 GaN wafers. Less well established are the electrical metrics for comparing GaN-on-diamond to GaN on host substrates. One important metric of electrical performance for GaN-HEMTs is the flat capacitance at high reverse bias. It allows us to characterize the presence of traps and/or doping at the GaN to host interface [8]. In our case the GaN to diamond interface. We measure this flat capacitance by taking the capacitance voltage (C-V) profile. Results show that we can take GaN-on-silicon which has a flat band capacitance of 25pF and turn it into GaN-on-diamond with a flat band capacitance of ~ 2pF Figure[1a]. This low capacitance is indicative of negligible GaN buffer and epi interface charge/doping. The capacitance of the GaN-on-diamond is now comparable to GaN-on-silicon carbide Figure [1b]. Figure 1

Structural Strength and Service Life of the Extrusion Forming Die for Agricultural Engine Piston Heads

Three-tier high-strength prestressed combination concave dies are designed to manufacture highpower corn combine harvester engine piston heads. This design integrates the advantages of traditional casting or hot die forging and warm extrusion. The following key parameters, viz radial dimensions of each mating layer, axial bonding and radial contact interaction, are obtained by theoretical calculation. Nonlinear analysis of the contact interaction was carried out, and the die contact condition was studied at no-load and full-load. Based on the Archard wear theory, thermomechanical bonding was studied in operation of the die. Through numerical simulation of the die wear in each operation cycle, the univariate linear regression equation of the die service life was derived, and the reliability of this equation was verified. The results show that the die contact is both stable and reliable if the radial contact interaction of the inner and outer layers is δ2 = 1.9716 mm and δ3 = 1.3870 mm, respectively. With the nitriding layer thickness of 0.24 mm, the extrusion die service life in the production of piston heads corresponds to 6357 pieces.

Reduction of Thermal Stress - Part III: UBM and Passivation Thickness Optimization

Abstract Integration of Back End Of Line (BEOL) CMOS technologies with Wafer Level Packaging (WLP) is challenging, as mismatch of Coefficient of Thermal Expansion (CTE) between materials can result in thermo-mechanical induced cracking. This is especially true during reflow cooling of wafers after the solder ball attach process. Factors that contribute towards cracking can be from both the BEOL as well the WLP process steps. Finite Element Analysis (FEA) of such designs can help identify possible root causes early in the design process and i.e. before actual fabrication. This would help save valuable prototyping & testing costs. In Part III of this series of FEA studies, two factors i.e. silicon nitride thickness (from the BEOL process), and the Under Bump Metalization (UBM) thickness (from the WLP process) were identified as significant factors in changing the maximum first principal stress levels in the passivation layer.

Gas inlet and input power modulated sputtering molybdenum nitride thin films

The molybdenum nitride films were fabricated by RF magnetron sputtering with various structural features by input power and gas flow ratio modulation. With Ar/N2 gas flow ratios from 10/10 to 18/2 and RF input powers from 150 to 300W, the molybdenum nitride films evolved from significant crystalline to amorphous features. The coating deposited at an Ar/N2 ratio of 16/4 and an input power of 300W showed an intensified Mo2N microstructure with preferred (111) orientation. In comparison, the crystalline phase of the coating was suppressed when an Ar/N2 ratio of 10/10 and an input power of 150W were applied. The thickness, deposition rate and crystallinity of the molybdenum nitride increased with Ar/N2 ratio and power input. The crystalline and amorphous monolayers were alternately stacked to form multilayered films. The correlation between structural evolution and mechanical behavior, such as hardness, Young's modulus, and scratch characteristics of the molybdenum nitride multilayer films was discussed.

Characterization of simultaneous aged and plasma nitrided 17-4 PH stainless steel

Microstructural characteristics (using TEM, SIMS, SEM, optical profilometry and XRD) and residual stress (using nanoindentation and XRD) of simultaneously aged and plasma nitrided martensitic 17-4 PH stainless steel were investigated. It was observed that morphology and microstructure produced during plasma nitriding of 17-4 PH stainless steel were very dependent on the treatment temperature and time. An unetchable nitrided layer formed on specimen surface nitrided at 400°C which contained expanded martensite, whereas nitrided layers at 450 and 500°C contained dark phases of nitrides in addition to expanded martensite. Nitride precipitates and expanded martensite laths were observed in TEM images and their corresponding diffraction patterns. Lack of incoherent copper rich precipitates in TEM confirmed that aging and plasma nitriding were performed simultaneously. SIMS profiles revealed that the total diffusion depth of nitrogen is 3–4 times thicker than the nitrided case. The lowest and highest surface residual stresses were contributed to PN400C5h and PN400C10h, respectively. Although hardness values increased by increasing temperature/time of plasma nitriding process, i.e. increasing nitrided layer thickness, residual stress was a function of residual stress relaxation at high temperature in addition to thickness of nitrided layer. Residual stress depth profile showed that maximum compressive residual stress at the surface, dropped to zero just below the nitrided case, then increased to a maximum value of tensile residual stress; then decreased gradually to zero. Hardness depth profile measurements revealed that hardness was very dependent on residual stress induced by nitrogen atoms diffused interstitially during plasma nitriding. Core hardness of specimens made it evident that aging took place during plasma nitriding.