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In order to improve the efficiency of tunneling oxide passivated contact (TOPCon) cells, a p-type tunneling oxide passivation contact structure was fabricated on the front of N-type TOPCon cells through high-temperature diffusion, improving the emitter passivation performance and reducing front metal recombination. The effects of different deposition time, drive-in temperature, drive-in time and other process parameters on the passivation performance and doping curve of experimental samples were investigated. The experimental results show that when the deposition time is 1 500 s, the drive-in temperature is 920 °, and the drive-in time is 20 min, the boron doped polysilicon layer can achieve better passivation performance and boron doping concentration, with the doping concentration of sample polycrystalline silicon layer reaching 1.40 x 1020 cm-3. The implied open circuit voltage(iVoc) is greater than 720.0 mV. The photoelectric conversion efficiency of TOPCon cells prepared based on this parameter can reach 23.89%, corresponding to a short-circuit current density of 39.36 mA/cm², the open circuit voltage (Voc) is 726.4 mV, and the fill factor (FF) is 83.54% [ABSTRACT FROM AUTHOR]

In order to improve the photoelectric conversion efficiency of tunnel oxide passivated contact (TOPCon) solar cells, the selective emitter structure was prepared by boron diffusion and laser doping. The effects of sheet resistance of boron diffusion, power output ratio of laser and oxidation time on the passivation of the emitter were studied. The experimental results show that when the sheet resistance is 140 Ω/❏, the oxidation temperature is 1 020 °C, and the oxidation time is 30 min, the sheet resistance of light doping region (p+) reaches 320 Ω/❏, the corresponding implied open circuit voltage reaches 729 mV, and the dark saturation current density is 12 fA/ cm². The sheet resistance of heavily doping region (p++) reaches 113 Ω/❏, the corresponding implied open circuit voltage reaches 710 mV, and the dark saturation current density is 26 fA/ cm². Based on the selective emitter process, the highest conversion efficiency of 24. 75% was obtained with an open circuit voltage of 720 mV, and a short-circuit current improvement of 30 mA, leading to an absolute efficiency gain of 0. 26 percent point for the champion conversion efficiency. [ABSTRACT FROM AUTHOR]

Autodoping is a well-known phenomenon of unwanted dopant transfer in silicon epitaxy process. In this work, we discovered boron lateral autodoping in normal rapid thermal process (RTP) and used it to controllably form shallow junctions for device fabrication. The redeposition of boron from the gas phase to the solid surface was identified to be the limiting step of the boron incorporation into the undoped silicon area in the RTP process. At a given RTP temperature, boron autodoping could be increased by elevating the concentration of the boron source or enhancing the evaporation coefficient. Extending the annealing time can substantially improve the uniformity of the boron concentration in the gas phase, thus reducing the pattern dependence of the autodoping results. In addition, the autodoping process also avoids the traps and defects induced by ion implantation. Therefore, the described mechanism holds great promise for shallow junction formation in selectively patterned area with low cost. [ABSTRACT FROM AUTHOR]

This paper reviews the behaviour of fluorine in silicon and silicon-germanium devices. Fluorine is shown to have many beneficial effects in polysilicon emitter bipolar transistors, including higher values of gain, lower emitter resistance, lower 1/f noise and more ideal base characteristics. These results are explained by passivation of trapping states at the polysilicon/silicon interface and accelerated break-up of the interfacial oxide layer. Fluorine is also shown to be extremely effective at suppressing the diffusion of boron, completely suppressing boron transient enhanced diffusion and significantly reducing boron thermal diffusion. The boron thermal diffusion suppression correlates with the appearance of a fluorine peak on the SIMS profile at approximately half the projected range of the fluorine implant, which is attributed to vacancy- fluorine clusters. When applied to bipolar technology, fluorine implantation leads to a record fT of 110 GHz in a silicon bipolar transistor.

In order to improve the photoelectric conversion efficiency of n-type interdigitated back contact (IBC) solar cells, the selective emitter structure was prepared by screen printing boron paste and high temperature diffusion, the effects of boron diffusion and screen printing on the passivation and contact properties of the cells were studied. The experimental results show that when the deposition time and annealing time of boron diffusion remain unchanged, the BBr3 flow rate is 100 mL/min, the deposition temperature is 830 °C, and the annealing temperature is 920 °C, the implied open circuit voltage of light doping emitter (p+) reaches 710 mV, and the dark saturation current density reaches 12.2 fA/cm². When the consumption of the locally printed boron paste at the emitter is 220 mg, after high temperature annealing on boron diffusion, the implied open circuit voltage of heavily doping emitter (p++) remains at about 683 mV, the sheet resistance is only 46 Ω/*, and the metal contact resistance is 2.3 mΩ·cm². The highest photoelectric conversion efficiency and average photoelectric conversion efficiency of IBC cells prepared by this process are 24.40% and 24.32%, compared with the IBC cells before optimization, the conversion efficiency is improved by 0.28 percentage points. [ABSTRACT FROM AUTHOR]

During the preparation of boron-doped emitters for TOPCon solar cells, boron atoms accumulate, forming a boron-rich layer (BRL). Oxidation, during the boron diffusion process, can eliminate the BRL. Prolonged oxidation which forms a SiO 2 layer can remove the BRL, also act as a protective mask for the front surface. Nevertheless, during high-temperature thermal oxidation, boron will be redistributed. Boron reaches a higher equilibrium concentration in SiO 2 than in the silicon wafer, and the SiO 2 /Si interface shifts inward during SiO 2 formation. Simultaneously, the high temperature during oxidation prompts the boron inside the silicon wafer to diffuse deeper. The dual effects of oxidation and diffusion cause boron to be depleted near the surface of the silicon wafer. Boron depletion leads to a reverse bending of the energy band, which hampers carrier collection and impedes further enhancement of cell power conversion efficiency. In this paper, the oxidation process was mainly adjusted to reduce surface boron depletion, resulting in approximately 0.09% abs. increase in power conversion efficiency compared to pre-optimization. [Display omitted] • Proposed a process for preparing boron emitters to reduce surface boron depletion. • Oxidation temperature had a significant effect on boron depletion. • TOPCon solar cells showed an efficiency gain of approximately 0.09 % abs.. [ABSTRACT FROM AUTHOR]

In the present study, the substrates made of 34CrAlNi7 steel have been used for the powder pack boriding to harden their surfaces. The boriding agent Ekabor 1 ™ was employed in the experiments, with the treated samples being kept in the fluidized bed furnace between 1123 and 1323 K for 1 to 4 hours. The cross-sections of boronized samples were examined by a scanning electron microscope and revealed a less saw-tooth appearance for boride needles at the phase interfaces. The XRD analysis showed the presence of chromium borides as Cr2B and Cr5B3 besides the two iron borides (FeB and Fe2B). The diffusion coefficients of boron in the FeB and Fe2B layers have been evaluated with the integral method. Afterwards, the values of boron activation in both layers were deduced and compared with the literature results. [ABSTRACT FROM AUTHOR]

In this work, the spin Hall characteristics of W/CoFeB/MgO have been systematically studied to provide an in‐depth insight for the optimization of the SOT‐MRAM channel. The bcc and β phases of tungsten (W) are identified clearly from XRD and resistivity studies, which shows marked impact on the electrical characteristics. Moreover, the same is found have tremendous affect on W's spin Hall characteristics with a twelvefold increase of the spin Hall angle ΘSH. The evaluation of W/CoFeB interfacial spin mixing conductance geff↑↓ using ab initio studies shows good coherency with the same evaluated experimentally, which is used to estimate interfacial spin transparency T to accurately evaluate intrinsic spin Hall conductivity σSH of W. The findings equivocate for a strong claim on β‐W's σSH to be around −0.23 ∓ 0.03, addressing the ongoing discrepancy. Increasing boron concentration in (Co1Fe3)100−xBx and thermal annealing temperature are found to reduce ΘSH effectively which is inferred to boron diffusion toward W. Alloying of W with Ta does not necessarily enhance ΘSH, for which very optimized relative concentration and the alloy growth phase is critical. The findings can significantly contribute to the ongoing SOT‐MRAM development for achieving various means of control for improvement in the device characteristics. [ABSTRACT FROM AUTHOR]

Abstract In this work, the spin Hall characteristics of W/CoFeB/MgO have been systematically studied to provide an in‐depth insight for the optimization of the SOT‐MRAM channel. The bcc and β phases of tungsten (W) are identified clearly from XRD and resistivity studies, which shows marked impact on the electrical characteristics. Moreover, the same is found have tremendous affect on W's spin Hall characteristics with a twelvefold increase of the spin Hall angle ΘSH. The evaluation of W/CoFeB interfacial spin mixing conductance geff↑↓ using ab initio studies shows good coherency with the same evaluated experimentally, which is used to estimate interfacial spin transparency T to accurately evaluate intrinsic spin Hall conductivity σSH of W. The findings equivocate for a strong claim on β‐W's σSH to be around −0.23 ∓ 0.03, addressing the ongoing discrepancy. Increasing boron concentration in (Co1Fe3)100−xBx and thermal annealing temperature are found to reduce ΘSH effectively which is inferred to boron diffusion toward W. Alloying of W with Ta does not necessarily enhance ΘSH, for which very optimized relative concentration and the alloy growth phase is critical. The findings can significantly contribute to the ongoing SOT‐MRAM development for achieving various means of control for improvement in the device characteristics.

FeCoB/MgO bilayer is prepared to study the interface magnetism and its role in azimuthal angle-dependent magnetic properties. As observed in magneto-optic Kerr effect measurements, unusual hysteresis loops are understood precisely through interface resolved grazing incident nuclear resonance scattering (GINRS) measurements under x-ray standing wave (XSW) conditions. To excite XSW modes, the bilayer is deposited between a Pt waveguide structure, where the position of the anti-nodes is varied by changing incident angles. As GINRS is an isotope sensitive technique, the FeCoB layer is enriched with 57Fe isotope during deposition. The formation of a high-density 57FeCoB layer at the 57FeCoB/MgO interface with a hyperfine field ~34.25 T is found and attributed to the increasing volume of FeCo at the interface. Boron diffusion from 57FeCoB to the MgO layer is found to be responsible for FeCo rich FeCoB layer near the interface. The azimuthal angle-dependent unusual shape of hysteresis loops is described in terms of coupled magnetization reversal between the bulk and interface parts of FeCoB layer. In contrast to some studies in literature, no evidence of the formation of an oxide layer is observed at the interface. [ABSTRACT FROM AUTHOR]

The boriding process is a branch of materials heating treatments that studies the improvement of the mechanical properties in steels and alloys. Recently, the borided trends have been studied by a selected group of researchers around the world with an interest to divulge the new results on borided materials for different industrial and biomedical applications. The aim of this study is to provide an overview of the historical review of the boriding process using the Bibliometric analysis. In total, 1227 documents in the Scopus database have used the boriding process as keyword with a growth rate of 7.3% every year from 1962 to 2020. The papers were written by around 2434 authors, mainly from Mexico, Turkey, and Poland, representing 37.7% of the total publications analyzed. The data obtained show that the boriding process has been global and fast-growing in the scientific publications of the last ten years. [ABSTRACT FROM AUTHOR]

The present work investigates the influence of growth conditions on the magneto-structural properties of magnetron-sputtered CoFeB alloy thin films. Films grown at room temperature (RT) are soft magnetic (coercivity <9 Oe), show amorphous microstructure, and possess a distinct uniaxial magnetic anisotropy (UMA) in the film plane. The amorphous microstructure and UMA persist up to a growth temperature (Ts) of 300 °C. CoFeB film grown at Si (100) substrate shows amorphous to crystalline phase transformation at Ts = 500 °C. In contrast, under the same growth conditions, the CoFeB film prepared on the SiO 2 substrate maintains an amorphous structure up to Ts = 500 °C. The difference in the microstructures was explained in terms of the out-diffusion of B to the interfacial layer and segregation near the substrate for the films having crystalline and amorphous structure, respectively. On both the substrates Addition of W buffer layer facilitated the growth of smooth and nanocrystalline CoFeB films at Ts ∼300 °C. Upon crystallization, UMA evolution with a simultaneous increase in the coercive field is interpreted in terms of joint effect of random anisotropy model and surface/interface roughness-induced magnetization reversal mechanism. Unlike post-annealing, the CoFeB films prepared at high temperature shows superior thermal stability against crystallization. The relationship between the soft magnetic performance, UMA evolution, and thermal stability of CoFeB films with the growth conditions is established. The study reveals the role of growth condition engineering, to obtain CoFeB thin films with controlled microstructure and magnetic performance, which is crucial for designing the spintronics devices. • Growth conditions such as temperature, substrate and buffer layer were varied to deposit CoFeB thin films were successfully prepared. • On SiO 2 substrate films remained amorphous, soft magnetic and persist UMA up to Ts = 500 °C • In comparision to post annealing, gowth temperature variation results in thermally stable film structure. • At high temperature, B distribution dictates the final microstructure. • W buffer layer addition result in smooth CoFeB film with improved crystalline quality. [ABSTRACT FROM AUTHOR]

• A new boron diffusion model is proposed for the nuclear reactor core analysis. • The effect of turbulent diffusion is taken into consideration. • The model is implemented in the subchannel analysis code. • The CFD method is used to verify the new model. The diffusion characteristic of borated water in nuclear reactor core is important for the reactivity control during some possible reactivity transient scenarios. The non-uniform distributions of boron concentration increase the risk of reactor accidents and lead to some reactor safety problems. Hence it is necessary to develop an effective boron diffusion model into the reactor thermal-hydraulic analysis code. In this paper, a quasi-three dimensional boron tracking model, in which the turbulent diffusion effect was considered carefully, was proposed and successfully implemented in the subchannel analysis code. The reliable CFD method with k-omega turbulent model validated against International Standard Problem (ISP No. 43) experimental data was used to verify the feasibility of proposed boron tracking model. A typical Pressurized Water Reactor (PWR) 3 × 3 fuel bundle model was established and the borated water was injected into one specified channel and pure water into other channels. The distributions and variations of boron concentration along the flow direction were achieved and analyzed. Results indicate that the proposed boron tracking model could predict the boron diffusion process in the fuel rod bundles more accurately compared with the original model. This work provides an essential supplement for the nuclear reactor subchannel analysis method. [ABSTRACT FROM AUTHOR]

Silicon solar cells with a tunnel oxide passivating contact (TOPCon) structure are the new mainstream products; however, emitter recombination has become the bottleneck for further improvement. The introduction of selective emitter (SE) technology becomes imperative to address this issue. In this study, the appropriate range of sheet resistance in the light-doped region (230–280 Ω/sq)and the reasonable interval of the diffusion junction depth in the heavy-doped region (1.2–1.3 μm) are presented. The selective emitter with a suitable doping distribution is realized using the mask and etch-back method. Compared to the homogeneous emitter with a sheet resistance of 150 Ω/sq, J 0e of 16 fA/cm2, and J 0metal-front of 500 fA/cm2, the optimum selective emitter results in a J 0e-light doping of 8 fA/cm2, J 0e-heavy doping of 45 fA/cm2 and J 0metal-front of 213 fA/cm2. Finally, the boron SE-TOPCon cell samples U OC (726.5 mV), FF (84.01%), and efficiency (25.51%) are obtained, compared with the TOPCon cell with homogeneous emitter U oc (717.6 mV), FF (83.77%) and efficiency (25.17%) of the reference. In addition, the efficiency potential of the boron SE-TOPCon cell (26.02%) at the optimal process conditions is determined based on device simulations. This study provides a feasible technical path for mass-produced TOPCon cells to increase the efficiency to more than 26%. • The selective emitter with suitable doping distribution is realized by mask and etch method. • The boron SE-TOPCon cell sample with efficiency (25.51%) is obtained. • The efficiency potential of the boron SE-TOPCon cell is 26.02% in simulations. [ABSTRACT FROM AUTHOR]

Abstract A predictive simulation framework, combining process and device simulation, is developed in order to assist in BBr 3 boron tube furnace diffusion process optimization for n -type silicon wafer solar cells. After an appropriate calibration, the influence of the tube diffusion process parameters (drive-in temperature, oxidation temperature, etc) on the final solar cell efficiency can be predicted. The key process parameters of BBr 3 tube furnace diffusion are identified and their sensitivity on the final solar cell efficiency is calculated. An efficiency gain of 0.6% absolute to 20.0% is realized by optimizing only the front-side boron diffused layer of the front and back contacted cells. The efficiency is further improved to 20.9% by introduction of a local back-surface field design. A further optimization potential of up to 0.2% absolute is predicted by modifying the boron diffusion profile. Highlights • A predictive simulation framework supporting optimization of BBr 3 tube diffusion is developed. • Sensitivity analysis of boron tube diffusion process parameters are presented. • An efficiency gain of 0.6% absolute is realized by optimizing only the boron diffused layer. • The efficiency is further improved to 20.9% by introduction of a local back-surface field design. • A further optimization potential of up to 0.2% absolute is predicted. [ABSTRACT FROM AUTHOR]

Abstract Controlling the B diffusion in CoFeB-MgO based magnetic tunnel junctions (MTJs) is important to realize the large tunneling magnetoresistance (TMR) ratio, which is required to realize high density magnetic random access memories (MRAMs). Here we investigate the detailed microstructure of the MgO-CoFeB MTJs having W underlayer and overlayer in comparison with well-studied MTJs with Ta underlayer and overlayer. Detailed microstructure analysis based on transmission electron microscopy and electron energy loss spectroscopy revealed that B diffused into Ta under-/overlayers and crystallization of CoFeB to CoFe efficiently occurred upon annealing at 300 °C and 400 °C in MTJs with Ta underlayers. In contrast, B diffused into the [001] tilt grain boundaries of MgO barrier in the case of MTJs with W under-/overlayers. These structural differences well explain the difference in post annealing temperature dependence of TMR ratio and resistance area product (RA) of MTJs with Ta and W under-/overlayers. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

In this paper we have developed an algorithm of boron diffusion after thermal annealing in a highly doped polysilicon film. This algorithm takes into account electrically active point defects by associating some parameters such as boron solubility limit and diffusion coefficient. We have studied effect of annealing temperature in order to perform impact of this parameter on maximum depth diffusion of junction and maximum of concentration by analysis of Secondary Ion Mass Spectrometry (SIMS) profiles. In fact we have proposed numerical model based on Fick's equation, resolved by finite difference method under Matlab also we have simulated this phenomenon by Silvaco software. [ABSTRACT FROM PUBLISHER]

We present a detailed optimization of a hole selective rear contact for p –type crystalline silicon solar cells which relies on full-area processes and provides full-area passivation. The passivating hole-contact is based on a layer stack comprising a chemically grown thin silicon oxide, an intrinsic silicon interlayer, and an in-situ boron-doped non-stoichiometric silicon-rich silicon-carbide layer on top. After deposition, the structure is annealed at 775–900 °C to diffuse dopant impurities to the c-Si wafer and a hydrogenation step is carried out. It is shown that hydrogenation is essential to obtain high quality surface passivation. In particular, we compare the effect of annealing in forming gas and annealing with a silicon-nitride overlayer as hydrogen source. We present a systematic optimization of the hole-selective contact, for which we varied the doping concentration, annealing parameters and report the implied open circuit voltage ( iV oc ) and combined specific contact resistivity ( ρ c ). It is observed that for highly doped layers the optimum annealing temperature for high quality surface passivation is 800 °C while for lowly doped layers the optimum annealing condition shifts to 850 °C. Excellent surface passivation and efficient current transport is evidenced by an iV oc value of 718 mV which corresponds to a saturation current density ( J 0 ) of 11.5 fA/cm 2 and a ρ c of 17 mΩcm 2 on p −type wafers. Moreover, the evolution of the boron diffusion profiles with different annealing conditions is investigated. Finally, we demonstrate proof-of-concept p −type hybrid solar cells employing the full-area hole-selective rear contact presented here and standard heterojunction front electron contact. The excellent efficiency potential of our passivating rear contact is highlighted by conversion efficiencies up to of 21.9%, enabling V oc of 708 mV, FF of 79.9% and J sc of 38.7 mA/cm 2 . [ABSTRACT FROM AUTHOR]

To achieve p- n junctions for n-type solar cells, we have studied BBr diffusion in an open tube furnace, varying parameters of the BBr diffusion process such as temperature, gas flows, and duration of individual process steps, i.e., predeposition and drive-in. Then, output parameters such as carrier lifetime, sheet resistance, and diffusion profile were measured and statistically analyzed to optimize the emitter characteristics. Statistical analysis (factorial design) was finally employed to systematically explore the effects of the set of input variables on the outputs. The effect of the interactions between inputs was also evaluated for each output, quantified using a two-level factorial method. Temperature and BBr flow were found to have the most significant effect on different outputs such as carrier lifetime, junction depth, sheet resistance, and final surface concentration. [ABSTRACT FROM AUTHOR]

Boron (B) is known as a melting-point depressant for the middle interlayer to transient liquid phase (TLP) bonding of the nickel-based single crystal superalloys (Ni-SCS). However, the mechanisms for the effect of refractory elements M (=Re, W, Mo or Ta) on B diffusion in Ni-SCS remain unclear till now. Thus, the refractory elements M (=Re, W, Mo or Ta)'s effects on the diffusion of B in Ni-SCS is investigated using the density functional theory in this paper. It is found that Mo and Re atoms are mainly distributed in the γ-Ni phase, while majority of W and Ta atoms are mostly located in the Al site in γ′-Ni 3 Al phase. The octahedral interstices of γ-Ni and γ′-Ni 3 Al are preferentially occupied by B atoms. The results indicate that the M (=Re, W, Mo or Ta) atoms doped in the structures prevent B diffusion, and the change trend of B diffusion E(BFP) follows Re < Mo < W < Ta. Electronic structure analysis shows that the different atomic radiuses from Re to Ta and different hybrid orbitals between M d and B 2p from Re to Ta play important roles in the diffusion properties of B in the nickel-based single crystal superalloys. • A study of effect of refractory elements on B diffusion in Ni-SCS based on DFT. • The atomic occupancy of efractory elements and B in Ni-SCS have revealed. • The change trend of B diffusion E(BFP) follows Re < Mo < W < Ta. • The relevant electronic structure analysis are discussed. [ABSTRACT FROM AUTHOR]

This study aims at understanding the influence of the borosilicate glass (BSG) homogeneity obtained by BCl 3 diffusion on the passivation quality of the boron emitter. First, the diffusion process was optimized in order to improve the homogeneity along the tube. Average uniformities below 3% were reached on a full loaded furnace. It was showed that the non-homogeneity of the borosilicate glass layer (BSG) thickness has a limited influence on the emitter Rsheet homogeneity. Nevertheless the diffusion homogeneity is much more detrimental on the surface passivation quality when a thermal oxide SiO 2 / PECVD SiN stack is used. We showed that the replacement of the SiO 2 layer by an ALD deposited Al 2 O 3 layer leads to an improved passivation with no dependence on the BSG thickness. [ABSTRACT FROM AUTHOR]

This paper experimentally shows the reduction of anomalous narrow width effect (NWE) observed in gate-first high- $k$ metal-gate (HKMG) nMOS transistors by using pregate carbon implants. The experiments are performed with different carbon implant doses and energies, in collaboration with a semiconductor foundry. The 28-nm gate-first HKMG CMOS technology is used as the baseline flow. The physical mechanisms responsible for this improvement are identified and explained in detail. It is further shown that the pregate carbon implant used to suppress the NWE also increases junction leakage, improves the device electrostatics, and improves the universal curve. [ABSTRACT FROM PUBLISHER]

In this work, the influence of highly doped layers on the hydrogen in-diffusion into silicon from hydrogen-rich silicon nitride is investigated. Hydrogen in the crystalline silicon bulk of wafers with and without highly doped layers present was examined in solar cell-like structures by resistivity measurements for quantification of BH-pair dynamics. Hydrogen diffusion through phosphorus- and boron-doped Float-Zone samples without highly doped layers and with p+- respectively n+-layers was determined via secondary ion mass spectrometry. Therefore, deuterium concentration in an amorphous silicon layer on the backside was measured. This experiment shows an up to threefold increase of deuterium concentration in the amorphous layer for samples with highly doped layers present. A possible explanation of this observation is given by simulations. • Influence of highly doped layers on H in-diffusion. • BH-pair dynamics in samples with and without highly doped layers. • SIMS data of D diffusing through highly doped layers and bulk c-Si. • Simulations of H-species in samples with n+-p-n+ structure after firing. [ABSTRACT FROM AUTHOR]

Tunnel magnetoresistance (TMR) was measured in CoFeB–MgO-based double-barrier magnetic tunnel junctions. The variation of sputtering power density is used to control the relative B content of the middle electrode. MR ratios in both top and bottom junctions are suppressed with respect to the single-barrier case. While the bottom junction shows a saturation of the MR as a function of high-temperature annealing for all sputtering power densities, the top junction exhibits an increase in MR as a function of annealing temperature with higher values for higher sputtering power density. The suppression of high MR is attributed to a lack of strong crystallization in the middle electrode, which is confirmed by cross-sectional transmission electron microscopy. Slight crystallization of the middle electrode is achieved at the highest sputtering power density despite the fact that boron diffusion is suppressed due to the adjacent MgO tunnel barriers. Optimal deposition and postannealing conditions resulted in MR values of 140% and 80% for the top and bottom junctions, respectively. [ABSTRACT FROM AUTHOR]