Mustafa Pinarbasi

Demonstration of 35 Gbits/in/sup 2/ in media on glass substrates

A recording density of 35 Gbits/in/sup 2/ was achieved in longitudinal recording media with high-sensitivity GMR heads. The media displayed excellent thermal stability as a result of a CoPtCrB alloy with high magnetocrystalline anisotropy and relatively narrow grain size distribution. The degree of Co easy-axis orientation in the plane of the /spl mu/m was greatly improved and the grain size was reduced in the media on glass substrates. Estimates of the switching volume from dynamic coercivity and signal-to-noise measurements are larger than the physical grain size, suggesting that intergranular interactions improve stability. A potential path to further increases in recording density above 35 Gbits/in/sup 2/ is to use antiferromagnetically coupled magnetic layers in the media.

Antiparallel pinned NiO spin valve sensor for GMR head application (invited)

NiO antiferromagnetic material possesses certain advantages for spin valve applications and has attracted considerable attention. Some of the key advantages are its insulating properties, very high corrosion resistance, less sensitivity to composition, and its low reset temperature. This material, however, has a low blocking temperature which prevents its application to simple spin valve designs. The use of this material in spin valve structures required significant improvements in thermal stability, blocking temperature, and the spin valve design. In the present study, the blocking temperature and the blocking temperature distribution of the NiO films have been improved by depositing the films reactively using ion beam sputtering. A number of improvements in the processing method and deposition system had to be made to allow full NiO spin valve deposition for mass production. Another critical part was the use of antiparallel pinned design in place of the simple design to improve the thermal stability of the NiO spin valves as read elements at disk drive temperatures. The selection of the ferromagnetic pinned layers and the Ru spacer thickness in AP-pinned spin valves has significant impact on the behavior of the devices. These spin valves are all bottom type, NiO/PL1/Ru/PL2/Cu/Co/NiFe/Ta, where the metallic portion of the spin valve is deposited on top of the NiO AF layer. The PL1 and PL2 are ferromagnetic layers comprising NiFe and Co layers. Read elements have been made using these spin valves that delivered areal densities of 12 Gbit/in. These topics and other improvements which resulted in successful use of NiO spin valves as GMR heads in hard disk drives will be discussed.NiO antiferromagnetic material possesses certain advantages for spin valve applications and has attracted considerable attention. Some of the key advantages are its insulating properties, very high corrosion resistance, less sensitivity to composition, and its low reset temperature. This material, however, has a low blocking temperature which prevents its application to simple spin valve designs. The use of this material in spin valve structures required significant improvements in thermal stability, blocking temperature, and the spin valve design. In the present study, the blocking temperature and the blocking temperature distribution of the NiO films have been improved by depositing the films reactively using ion beam sputtering. A number of improvements in the processing method and deposition system had to be made to allow full NiO spin valve deposition for mass production. Another critical part was the use of antiparallel pinned design in place of the simple design to improve the thermal stability of ...

12 Gb/in/sup 2/ recording demonstration with SV read heads and conventional narrow pole-tip write heads

We have successfully demonstrated magnetic recording at areal densities as high as 12 Gb/in/sup 2/ at a data rate of 14/spl sim/15 MB/s using separate spin-valve read heads and narrow pole-tip inductive write heads on low noise Co alloy thin film disks. In this work, the nominal target densities were 350 Kbpi/spl times/34 Ktpi. To make these densities possible, large signal-to-noise gains were attained with the use of high performance spin-valve read heads and low noise thin film media. At the same time, very narrow track write heads were designed and fabricated by extending conventional photolithographic techniques. Finally, small magnetic spacings between the head and the disk were attained with low flying ABS designs and improved head and disk surfaces. Recording tests showed satisfactory writability and large readback signal of around 2 mV//spl mu/m. The 50% rolloff densities were as high as 10 Kfc/mm, while the write and read trackwidths were as narrow as 0.7 and 0.5 /spl mu/m respectively. An overall assessment of the parametric recording results indicated an areal density capability of at least 10 Gb/in/sup 2/. This projection was confirmed by error rate testing with an EPR-4 channel, where very low ontrack errors of 10/sup -10//spl sim/10/sup -9/ were achieved at 315/spl sim/380 Kbpi. Furthermore, squeeze measurements revealed well-defined 747 behavior with offtrack maxima at 0.7/spl sim/0.8 /spl mu/m trackpitch. The product of linear and track densities for the write and read head combinations tested indeed showed that an areal density of 11/spl sim/12 Gb/in/sup 2/ has been achieved.

Effect of hydrogen content on the light induced defect generation in direct current magnetron reactively sputtered hydrogenated amorphous silicon thin films

The kinetics of light induced defect generation or the Staebler–Wronski effect have been investigated on device quality hydrogenated amorphous silicon films which were deposited by dc magnetron reactive sputtering. The total hydrogen content (CH) of the films, which varied from ∼10 to 28 at. %, had a strong influence on the defect generation. Low CH (10%–15%) films had a high initial density of defect states (∼7 to 10×1015 cm−3 ) compared to the high CH (≥17 at. %) films with a density of ∼3×1015 cm−3. However, light exposure increased the defect density more slowly on the low CH films, such that after about 1 h of light exposure their defect density was lower. A high‐quality glow discharge produced film was also measured, and behaved similarly to the high CH sputtered films. The greater stability of the low CH films was also reflected in a slower decrease of the electron photoconductivity relative to the other samples. For exposure times (t) up to 1000 h, the total density of defect states of the films i...

Status of electroplating based CIGS technology development

CIGS is the leading thin film PV material in terms of it capability to yield high efficiency solar cells. Co-evaporation method already yielded solar cells with close to 20% efficiency. Despite this success, however, commercialization of CIGS has not been aggressive. One reason for this is the fact that CIGS is a complex material. The other reason is the difficulty of scaling up this technology while keeping the cost structure competitive. SoloPower has developed a low cost electrodeposition-based CIGS technology for large scale roll-to-roll manufacturing. The substrate is a flexible metallic foil. CIGS absorber layers are formed through annealing and thermal activation of electrodeposited precursor layers. Top and bottom contacts are formed by roll-to-roll sputtering approaches. The technique has excellent ability to control the composition of the deposited layers over large are substrates. After forming a roll of solar cells, devices are cut and then packaged in module structures. Flexible solar cells with an area of over 100 cm2 were fabricated with over 12% efficiency. Over 1 m2 area modules with an efficiency of 10% were also fabricated.

AP-pinned spin valve GMR and magnetization

We present a general analytical coherent rotation model for AP-pinned spin valve magnetoresistance (MR) and magnetization (M). The magnetic structure is determined by minimizing the sum of the Zeeman and the two interfacial exchange energies, σAF and σAP. We compare the model to M(H) and MR(H) taken from an experimental series of AP-pinned spin valves (NiO/AP1/Ru/AP2/Cu/free layer) measured in magnetic fields −5⩽H⩽5 kOe, and at temperatures 20⩽T⩽240 °C. The Ru thicknesses were 4.5 A⩽tRu⩽10.4 A. We fit the model to data by varying σAF and σAP. The fits reproduce the data quantitatively, and the resulting exchange strengths agree well with published studies of Co/Ru/Co multilayers and ferromagnet/NiO exchange couples.

Beyond 10 Gb/in/sup 2/: Using a merged notched head (FIB-defined writer and GMR reader) on advanced low noise media

We demonstrated recording performance at greater than 10 Gb/in/sup 2/ with data rates up to 25 MB/s, using a single combined write and read head (Merge Notched head).

Recent advances in electroplating based CIGS solar cell fabrication

Electrodeposition based CIGS technology developed by SoloPower is highly attractive route for preparation of precursor layers due to its low cost, efficient materials utilization and scalability to high-volume manufacturing. Several aqueous electroplating solutions both in acidic and alkaline regimes are formulated and optimized for achieving stable plating solutions for roll-to-roll electrodeposition that give adherent and high quality films with controllable molar compositions. An optimized rapid thermal annealing approach was developed to achieve device-quality CIGS absorber layers. In this paper, we discuss various electrodeposition approaches for CIGS precursor formation and present a summary of the recent results for SoloPowers flexible cells.

Reduced Staebler–Wronski effect in reactively sputtered hydrogenated amorphous silicon thin films

The kinetics of light‐induced defect generation or the Staebler–Wronski effect (SWE) have been measured on device quality hydrogenated amorphous silicon (a‐Si:H) films having hydrogen contents (CH) of ∼10–28 at. %. The films were deposited with direct current (dc) magnetron reactive sputtering. The low CH films have a density of defect states (DOS)∼7 to 10×1015 cm−3 which is three to five times higher than the high CH films. Under light exposure, the DOS for low CH films increases slower than that of the high CH or glow discharge produced films; in fact it is smaller after a few hours of light exposure. These measurements show that low CH dc magnetron reactively sputtered a‐Si:H appears to be more stable material for sensitive applications such as solar cells.

Electrodeposition methods and chemistries for deposition of CIGS precursor thin films

We studied the electroplating methods and chemistries for the deposition of several thin films including Cu-Ga, Cu-In, Cu-In-Ga, In-Se, Ga-Se and Cu-In-Ga-Se from alkaline plating solutions containing complexing agents. Our approach utilized the full potential of complexation by formulating aqueous electroplating solutions containing complexing agents in the alkaline regime instead of the commonly reported acidic regime. We found that a blend of complexing agents could be used to provide a complete chealation of all the Cu, In and Ga ions in these plating electrolytes. No appreciable complexation occurs between Se and the complexing agents. Therefore, the Se reduction potential could be independently controlled by the amount of dissolved Se in the In-Se, Ga-Se and Cu-In-Ga-Se solutions. We established that the current density applied during deposition had a pronounced effect on the composition and morphology of the films. Intentional grading of elemental species throughout the film thicknesses could be achieved in the plated layers by changing the applied current density or voltage during the electrodeposition steps. Various precursor formation techniques were developed utilizing these graded thin films for the preparation of CIGS absorber layers.