Thermal Control Layer Research Articles

Simulation of Outgassing Breakdown Induced by Electromagnetic Radiation on a Thermal Control Layer

Simulation of Outgassing Breakdown Induced by Electromagnetic Radiation on a Thermal Control Layer

Study on the Electromagnetic Radiation Effect of a Thermal Control Layer

To study the electromagnetic radiation effect of a thermal control layer (TCL) on the surface of general spacecraft in a space environment, a model of thermal control material irradiated with microwaves was established, a particle-in-cell (PIC)-Monte Carlo collisions (MCC) simulation was used, and the processes of field emission, multipacting, outgassing, and impact ionization on the surface of thermal control materials were simulated. By comparing the primary electrons, secondary electrons, and impact ionization electrons produced under different field intensities and frequencies of electromagnetic waves, different compositions of outgassing, and different thermal control materials, the influencing factors and critical thresholds of avalanche ionization were obtained. The simulation results show that whether avalanche ionization occurs in outgassing on the surface of the TCL is affected by the electromagnetic wave amplitude, electromagnetic wave frequency, outgassing composition, and the material of the TCL. This provides a theoretical reference for the safe operation of spacecraft.

Design of thermal stress control layers in the selective deposition technology of hot axle forging dies

The hardfacing process can effectively overcome surface softening of dies and improve the service life in hot forging operations; however, thermal cracks are frequently generated on deposited areas due to thermal stress from different material properties. A thermal stress control layer (TSCL) is applied to reduce thermal stress and increase fatigue life as a buffer in the vicinity of the joining region between the hardfacing layer and the base metal. The TSCL and hardfacing layer are deposited through layer-by-layer deposition on the surfacing of the substrate using a 3D printing process. The TSCL, which is produced by mixing of Stellite 21 and SKD61, is designed with thicknesses of 0 mm, 1 mm, 1.5 mm, and 2 mm respectively. The study aims to estimate the effect of a TSCL focused on thermal stress in the deposition region via two-dimensional finite element analysis. In addition, the optimal volume of transition regions and composition proportions are also predicted for the hot forging die of an axle shaft.

Optically Immersed Bolometer IR Detectors Based on V2O5 Thin Films with Polyimide Thermal Impedance Control Layer for Space Applications

Optically immersed bolometer IR detectors were fabricated using electron beam evaporated vanadium oxide as the sensing material. Spin-coated polyimide was used as medium to optically immerse the sensing element to the flat surface of a hemispherical germanium lens. This optical immersion layer also serves as the thermal impedance control layer and decides the performance of the devices in terms of responsivity and noise parameters. The devices were packaged in suitable electro-optical packages and the detector parameters were studied in detail. Thermal time constant varies from 0.57 to 6.0 ms and responsivity from 75 to 757 V W−1 corresponding to polyimide thickness in the range 2 to 70 μm for a detector bias of 9 V in the wavelength region of 14–16 μm. Highest D* obtained was 1.2×108 cmHz1/2 W−1. Noise equivalent temperature difference (NETD) of 20 mK was achieved for devices with polyimide thickness more than 32 μm. The figure of merit, NETD × τ product which describes trade-off between thermal time constant and sensitivity is also extensively studied for devices having different thickness of thermal impedance layers.

Investigation of the proposed solar-driven moisture phenomenon in asphalt shingle roofs

Unvented attics are an energy-efficiency measure to reduce the thermal load of the conditioned space and decrease the space conditioning energy consumption by about 10%. This retrofit is usually done by spraying polyurethane foam underneath the roof sheathing, and on the gables and soffits of an attic to provide an air barrier and a thermal control layer. Unvented attics perform well from this perspective, but from a moisture perspective sometimes homes with unvented attics have high interior humidity or moisture damage to the roof. As homes become more air tight and energy efficient, a better understanding of the hygrothermal dynamics of homes with energy-efficient envelopes becomes more important. One proposed reason for high unvented attic humidity has been that moisture can come through the asphalt shingle roof system and increase the moisture content of the roof sheathing and attic air. This has been called “solar-driven moisture.” Oak Ridge National Laboratory investigated this proposed phenomenon by examining the physical properties of a roof and the physics required for the phenomenon. Results showed that there are not favorable conditions for solar-driven moisture to occur. Oak Ridge National Laboratory also conducted an experimental study in a home with an unvented attic and compared the humidity below the roof sheathing before and after a vapor impermeable underlayment was installed. There was no statistically significant difference in absolute humidity before and after the impermeable underlayment was installed. The outcomes of the theoretical and experimental studies suggest that solar-driven moisture does not occur in any significant amount.

A study on the Effects of Geometrical Parameters of Overlay Coated Layer on the Thermal Stress-strain Distributions of Co-based Super-alloy Deposited Layer on Hot-working Tool Steel

Interests in an overlay coating technology, so called hardfacing technology, have steadily increased to improve the service life of hot-working tools through the reduction of the wear of tool surfaces. Characteristics of the overlay coated layer are dependent on geometrical parameters and material properties of sub-layers. The aims of the paper is to examine the effects of geometrical parameters of the overlay coated layer on thermal stress-strain distributions of Co-based super-alloy deposited layer on hot-working tool steel using finite element analysis (FEA). The overlay coated layer is designed as two sub-layers including the wear resistance layer with Co-based super-alloy and the thermal stress control layer (TSCL). The material of the TSCL is composed of 50 % of Co-based super-alloy and 50 % of hot-working tool steel. The protruded height and the inclined angle are chosen as geometrical parameters. The influence of the protruded height and the inclined angle on thermal stress-strain distributions in the vicinity of the overlay coated layer and the strain deviation in joined regions is quantitatively investigated. From the results of the investigation, an appropriate design methodology of the overlay coated layer is discussed.

3 차원 유한요소해석을 이용한 Stellite21 초합금으로 하드페이싱된 STD 61 열간금형강의 열응력제어층 재료조합 및 두께 예측

하드페이싱층과 기저부의 결합부에서 발생하는 잔류 응력/변형률을 감소시키기 위하여 열응력제어층에 대한 연구가 시작되고 있다. 이 연구에서는 3 차원 유한요소해석을 이용하여 Stellite21 초합금으로 하드페이싱된 STD61 열간금형강의 중간층으로 형성된 열응력제어층의 재료조합과 두께를 예측하고자 한다. 열응력제어층은 Stellite21 과 STD61 의 조합으로 생성하였다. 열응력제어층의 두께범위는 0.5-1.5 mm 로 선정하였다. 유한요소해석 결과를 이용하여 열응력제어층을 구성하는 Stellite21 과 STD61 의 혼합율 및 열응력제어층 두께에 따른 시편 내부 온도/열응력/열변형률분포를 정량적으로 분석하였다. 이 결과로부터 적합한 열응력제어층의 재료혼합비는 Stellite21 50 % 와 STD61 50 % 이며, 적절한 열응력제어층의 두께는 1.0 mm 임을 알 수 있었다.

8-${\rm Tb/in}^{2}$-Class Bit-Patterned Medium for Thermally Assisted Magnetic Recording

Three-dimensional optical/thermal spot profiles obtained by thermally assisted magnetic recording (TAMR) on bit-patterned media (BPM) with dot densities of 6 to 15 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> were numerically analyzed. Introduction of a spacing layer with higher thermal conductivity than that of the recording dots leads to narrow temperature distribution (i.e., steep temperature profile) in the dots. A temperature profile with FWHM of less than 5 nm was obtained on a patterned dot array under areal densities of 6 to 15 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . In addition, introduction of a thermal-control layer beneath the recording layer decreased vertical temperature difference within a recording bit while keeping a narrow temperature distribution. Feasibility of 8-Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> -class TAMR on a BPM was verified by LLG simulation with a triangular antenna-type near-field optical element.

Random Signal Characteristics of Super Resolution Near Field Structure Read-Only Memory Disc

We report the random pattern signal characteristics of the super resolution near field structure (Super-RENS) disk in a red laser optical system. (Laser wavelength 659 nm, numerical aperture 0.6) We improved the carrier to noise ratio (CNR) characteristics and the low frequency noise by optimizing the layer design and the pit structure, which results in 53 dB CNR at 173 nm pit length. It is equivalent to 50 GB capacity if it is converted by Blu-ray Disc (BD) specification according to the ratio of beam size. We also improved the readout power margin and the stability greatly by introducing the thermal control layer. The eye pattern under phase locked loop (PLL) state could be obtained through equalization adjustment (EQ). Through above improvements, we obtain the bER of 4.6×10-4 at 50 GB level by using partial response maximum likelihood (PRML) method.

A general consideration of incident impact energy accumulation in molecular dynamics thin film simulations—a new approach using thermal control layer marching algorithms

This paper investigates several highly accurate algorithms which can be used to calculate the morphology in a wide range of thin film process simulations, and which require minimum computational effort. Three different algorithms are considered, namely the kinetic energy corrector (KEC) algorithm, the thermal control layer marching (TLM) algorithm, and the thermal control layer marching algorithm with an incorporated KEC function (TLMC). A common characteristic of these algorithms is that they all address the recovery of the impact incident energy within the free reaction layer. However, they differ in their treatment of the thermal control layer. The TLM and TLMC algorithms consider this layer to be moveable, whereas the KEC algorithm regards it as being fixed. The advantage of employing a moveable thermal control layer is that the computational effort required to carry out simulation is reduced since the atoms lying below this layer are excluded. The relative accuracy and efficiency of the proposed algorithms are evaluated by considering their use in the simulation of the trench-filling problem associated with the damascene process. The results of the present investigation indicate that the TLM algorithm has the ability to provide an accurate morphology calculation for low and medium energy incident atoms. However, for higher incident energy impacts, the TLMC algorithm is found to be a more appropriate choice because the incorporated energy corrector function is required to remove the higher energy accumulation which occurs within the deposited atoms. Furthermore, for all three algorithms, it is noted that a suitable specification of the free reaction layer thickness is essential in determining the accuracy and efficiency of the simulation. Finally, this paper discusses the relationship between the energy absorption rate and the thickness of the free reaction layer, and presents the optimal free reaction layer thickness for different incident energy intensities.

Analysis on a new type magneto-optical disk for blue lasers

The conventional TbFeCo magneto-optical (MO) medium has a relatively smaller Kerr rotation angle in the blue region than in the red. With the recording wavelength gradually moving to the short wavelength, if TbFeCo is still used as recording medium, the conventional MO disk structure must be optimized to get a larger carrier to noise ratio (CNR). Sabi et al. have found that adding a metal layer attached to the TbFeCo film as thermal control layer is a useful way to get a high CNR. In this paper, we proved this through calculation, and carried out optimization of the new type of disk. Calculation results showed that the new structure is useful in preventing an excessive temperature increase, and has a better thermal response.

A Thermally Tunable GaAlAs–GaAs Micromachined Optical Filter With Submillisecond Tuning Speed

We fabricated a GaAlAs-GaAs thermally tunable vertical-cavity filter with a thermal strain control layer and heating element on a micromachined cantilever structure. We achieved a large negative temperature dependence of -0.79 nm/K for the vertical-cavity filter by loading a GaAs strain control layer. The tuning voltage is as low as 4.9 V for wavelength tuning of 18.1 nm. We examined the dynamic response of the thermally tunable micromachined GaAlAs-GaAs filter, exhibiting both rise time and fall time of below 100 μs.

Dual Damascene Simulation for Ionized Physical Vapor Deposition Process: Investigation on Incident Energy and Via Geometry Effects

This paper employs a dual damascene simulation to study the filling mechanisms of a dual via for the ionized physical vapor deposition (IPVD) process. The study focuses principally upon the influence of incident atom energy and via geometry upon the final dual via coverage. Additionally, the improvement in coverage which results from the use of beveled edges within the via is also considered. The molecular dynamics (MD) method is employed to simulate the filling process. The simulation is based upon three MD models, namely the dual via model, the deposition model and the potential model. Furthermore, the simulation incorporates the thermal control layer marching algorithm in order to increase the accuracy of the solution and to reduce the computational time. The results of the study show that in general, the coverage of both vias improves as the incident energy of the deposited atom increases, i.e. the filling pattern changes from anti-conformal to conformal, and then finally to super-filling as the incident energy increases. Typically, the optimum coverage of the upper via is obtained for a large via-radius ratio. However, it is found that coverage of the lower via is not only dependent upon the via-ratio, but that it is also strongly influenced by the incident energy of the deposited atoms. At lower incident energy levels, the via geometry effect governs the coverage results. However, as the incident energy increases, the incident energy effect becomes the dominant factor in determining the final coverage. It is determined that the interaction of these two effects influences the nature of the relationship between the coverage percentage and incident energy for different ranges of the via-radius ratio.

Study of beveled angle effect on morphology of dual damascene via filling using ionized physical vapor deposition

This article employs a molecular dynamics (MD) simulation approach to investigate the influence of beveled angles on the filling mechanisms of a dual damascene process. The objective of the present study is to propose a method that overcomes the problem of incomplete via filling associated with the traditional dual damascene process. The simulation incorporates three separate MD models, namely the dual via model, the deposition model, and the potential model. Furthermore, the simulation adopts the thermal control layer marching algorithm to increase the accuracy of the solution and to reduce the computational time. The present results indicate that the introduction of beveled angles at the upper via corners has a detrimental impact upon the filling of the lower via at moderately low via-radius ratios (1.75, 2.0). At a via-radius ratio of 1.75, the filling morphology changes from one of complete filling to one with trapped voids within the via when beveled angles are introduced, while at the slightly larger via-radius ratios of 2.0 and 2.5, the voids in the lower via are observed to grow in size. It is noted that the influence of beveled angles at the upper via corners on the lower via filling becomes less significant as the via-radius ratio increases (2.5, 3.0). In general, it is found that the introduction of beveled angles at the lower via corners is beneficial to the filling coverage of the lower via, but has no impact upon the filling of the upper via.

Microstructure evolution analysis in Co/Cu layers during the annealing process

By means of molecular dynamics simulation, this article investigates the annealing process of a Co/Cu two-layer structure used for giant magnetoresistance applications. The many-body, tight-binding potential method is used to model the interatomic force which acts between the atoms, and the Langevin technique is incorporated into the motion equation such that the thermal control layer is maintained at a constant equilibrium temperature. The issues considered within this article include the annealing Cu surface roughness and Co/Cu interfacial roughness, the annealing morphology, the annealing microstructure, a comparison of Co and Cu migration abilities, and the extent of Co and Cu interdiffusion. The results of the present study indicate that the annealing temperature required to cause Co atom migration is greater than that which is required for Cu atoms. Consequently, once the annealing temperature exceeds a certain threshold value, a significant change in the Cu surface roughness will be observed before there is any obvious change in the Co/Cu interfacial roughness. It is also noted that the Cu film microstructure adopts a disordered state earlier in the annealing process when the annealing temperature is higher. Finally, it is determined that Co/Cu interdiffusion occurs at elevated annealing temperatures. The degree of interdiffusion becomes more pronounced as the annealing temperature increases, and in extreme cases, it is observed that Co atoms may diffuse to such an extent that they even appear on the Cu film surface.

Design and fabrication of GaAs-GaAlAs micromachined tunable filter with thermal strain control

In this paper, we present the design and fabrication of a novel GaAlAs-GaAs micromachined vertical cavity filter with a thermal strain control layer for wide wavelength tuning. The integration of a thermal strain control layer and heating element enables wavelength tuning induced by heating. The proposed tunable filter under thermal tuning operation provides us large tuning range over conventional micromachined tunable filters using electrostatic force. The calculated result shows a possibility of large continuous tuning range of over 100 nm. We fabricated a micromachined GaAlAs-GaAs vertical cavity filter with a strain control layer. The temperature dependence of the filter can be freely controlled either with temperature insensitive operation or with an enhanced temperature dependence, which depends on the thickness of the thermal strain control layer. We demonstrate a thermal wavelength tuning of 53 nm with a low tuning voltage of 6.1 V for the first time.

GaAlAs/GaAs micromachined thermally tunable vertical cavity filter with low tuning voltage

A GaAlAs/GaAs micromachined thermally tunable vertical cavity filter with a low tuning voltage is proposed and its fabrication described. The integration of a thermal strain control layer and heating element enables wavelength tuning induced by heating. Wavelength tuning of 23.2 nm with a low tuning voltage of 4.7 V is demonstrated experimentally.

20 Gbit/inch2 Recording on Magneto-Optical Disk Using NA 0.85 and 405 nm Optics.

Various technique to reproduce magneto optical signals from high-density recorded patterns are reported, for example DWDD, MAMMOS, CAD, etc. In this paper we propose a method with NA 0.85 lens and a 405 nm laser. We search the feasibility of conventional MO media by laser-pulsed magnetic field modulation (LP-MFM) method having a target of high-density 20Gbit/inch2. We had the method of UV irradiation to suppress the media noise, thermal control layer to prevent the decay of the Kerr rotation angle, and optical phase shift method to reduce the cross-talk. And we could be making sure the feasibility of 20Gbit/inch2 observing a low error rate of less than 10-5 at the bit length of 0.13 μm.

Thermal Response Design for High Recording Density Magnetooptical Media

For the light intensity modulation recording process of magnetooptical (MO) disks, we have investigated the thermal response of the recording layer for high linear density recording. By means of a computer simulation, we found that the thermal response is improved by using a 6-layer structure which has an extra thermal flow control layer composed of a thermal buffer and an extra heat sink layer, unlike the conventional 4-layer structure. The thermal response improvement was also confirmed experimentally. It is possible to optimize both the thermal response and the optical requirements separately using our 6-layer structure which will be useful when designing higher density recording MO disks.

DIRECT OVERWRITE USING MAGNETO-STATICALLY COUPLED MULTILAYERS

The concept and some experimental results for single beam laser power modulation overwrite using magneto-statically coupled multilayers are described. The auxiliary magnetic layer(s) is coupled to the storage layer via the non-magnetic thermal control layer. The leakage field from the auxiliary magnetic layer(s) is modulated by the laser power level. The effective field direction is changed by leakage field modulation. Three methods for leakage field generation are reviewed. Experimental results for the method using a perpendicular thermo-magnetic biasing layer are described. The present status and the capability in the future development of magneto-statically coupled multilayer overwriting are clarified.