Matthew R. Gibbons

Voltage-induced barrier-layer damage in spin-dependent tunneling junctions

The effect of a dc stress voltage on the junction resistance and magnetoresistance (MR) of spin-dependent tunneling (SDT) junctions with naturally oxidized barriers was investigated. There is a threshold voltage at which irreversible resistance change begins. Beyond this threshold, device resistance decreases gradually over a transition period prior to breakdown of the tunneling barrier. The onset voltage of irreversible resistance change is much higher than the optimum operating voltage of SDT heads having the precursor aluminum thicknesses here investigated (5–11 A). The MR ratio decreased with increasing stress voltage in a pattern similar to that of the junction resistance.

Demonstration and characterization of greater than 60 Gb/in/sup 2/ recording systems

We have successfully demonstrated longitudinal recording at areal densities greater than 60 Gb/in/sup 2/ at data rates as high as 160 Mbps (20 MB/s) and at a Bit-Aspect-Ratio (BAR) of 5.7, using merged inductive-write/spin-valve-read heads with microactuators on low noise thin film disks. The heads were fabricated with standard photolithography and wafer pole trimming used in currently available commercial products. At track densities of 60 KTPI and higher, traditional servoing mechanisms are not adequate. With the use of a microactuator, we can further improve the track density by 15%, the linear density by 10% and the areal density by more than 20%. Thus, using a microactuator with the 50 Gb/in/sup 2/ head/media combination, we have increased our areal density achievement up to 63.2 Gb/in/sup 2/.

Demonstration and characterization of 36 Gb/in/sup 2/ recording systems

We have successfully demonstrated recording at areal densities as high as 36 Gb/in/sup 2/ at data rates as high as 173 Mbits/s (21.6 MB/s) and at a Bit-Aspect-Ratio (BAR) of 7.3, using merged inductive-write/spin-valve-read heads on low noise thin film disks. Recording at a data rate of 590 Mbits/s (73.8 MB/s) has also been achieved at the corresponding linear density of 231 KBPI. Comparisons with previous areal density demonstrations have also been summarized.

Thermal boundary resistance for gold and CoFe alloy on silicon nitride films

Advances in microelectronics technology strongly depend on the thermal optimization of metal/dielectric interfaces, which requires precise modeling and thermal characterization of metal/dielectric structures. This work experimentally investigated the influence of metallic layers on the thermal boundary resistance of silicon nitride dielectric material. The results reveal that the thermal boundary resistance of silicon nitride thin films depends on the metallic layers. The thermal boundary resistance at the interface between Au and SiNx is larger than that between Co0.9Fe0.1 and SiNx. The reasons to cause this difference are discussed with phonon transmission probability and the ratio of the Debye temperature between metals and dielectrics.

Spin-dependent tunneling junctions with parallel hard bias for read heads

We investigated the feasibility of a spin-dependent tunneling (SDT) read head with a parallel hard bias. In this scheme, the longitudinal biasing to the free layer is provided by fringe fields from a hard magnet which is fabricated over or under the free layer. A linear response to the applied field is achieved for a SDT junction biased with 400 A CoCrPt underneath. Thinner CoCrPt layers yield Barkhausen jumps in the free layer. Micromagnetic simulation indicates the bias field at the edge of the free layer is smaller than that which would result from an abutted magnet. The simulation results are similar to experimental data, and indicate that shielded devices with 400 A permanent magnet will provide stable transfer curves.

Comparison of semiclassical calculations to experiment for spin valve films grown on oxide surfaces

The physical properties of spin valve films grown on the surface of nano-oxide layers were studied as a function of Cu spacer layer thickness. In comparison to identical structures without the oxide surface, the films exhibited an increase in ΔR/R of 30% accompanied by a reduction of only 5% in resistance. Semiclassical calculations were preformed on these films with a close match to experiment. Assuming the oxide layer did not cause drastic changes in the properties of the other film layers, the specular reflection was changed to obtain a match with experiment. The increase in giant magnetoresistance response was achieved by increasing the specular reflection at the metal/oxide interfaces from 15% to 85%, indicating high efficiency for specular reflection at the nano-oxide interface.

A heating model including effects on magnetoresistance (MR) in MR and giant MR heads

An analytic model is presented that describes current induced heating effects in giant magnetoresistive (GMR) heads. Unlike previous transmission line models, the model includes temperature effects on the measured GMR response of the head in addition to changes in the temperature and the resistance. The response of the head will decrease with temperature in part due to the negative thermal coefficient for the GMR. The model predicts that the measured GMR response does not decrease as much as indicated by the thermal coefficient since the signal is enhanced by the change in temperature due to the GMR response to the applied field.

Lifetime of magnetic tunnel junctions under voltage stress

Summary form only given. Magnetic tunnel junctions (MTJ) are being investigated for possible application in magnetic sensors and memories. Due to the thin tunnel barrier, the junctions are very sensitive to electrical breakdown and degradation. This paper describes the lifetime of junctions under voltage stress with extrapolation to use conditions assuming an exponential acceleration factor. The tunneling films were deposited with a DC magnetron sputtering system. The aluminum layer is plasma oxidized in an oxidation module to form an Al/sub 2/O/sub 3/ tunneling barrier. Aluminum thickness, oxidation times, and plasma powers were used to create barriers of different thickness. The film structure is NiFe/PtMn/CoFe/Ru/CoFe/AlO/CoFe/NiFe/Ta. The TMR response of the junction decreases with voltage resulting in a peak for the TMR signal versus voltage. The acceleration factor calculated in stress testing can be used to estimate the junction lifetime at the optimum operating voltage.

Stability of dual synthetic spin valve devices

Magnetic field sensitivity of IrMn-based synthetically pinned dual spin valve structures was studied using quasi-static testing (QST). The dual synthetic spin valve structure was demonstrated to have inherent advantages in terms of high sensitivity to magnetic field and robust low asymmetry against changing bias current and elevated temperatures. In addition, the diamond like carbon coated devices demonstrate that there are no measurable changes in either resistance or QST amplitude after 3 days annealing at 120/spl deg/C.

Experimental study of playback giant magnetic resonance head nonlinearity in perpendicular recording

In this article, nonlinear distortions of the playback giant magnetic resonance (GMR) sensor in perpendicular recording are characterized in both time and frequency domains. We use three perpendicular media with different Mrt (0.46, 0.6, and 0.8 emu/cm2) and two groups of similar magnetic-read width (MRW) but different junction type [contiguous junction (CJ) and lead-over-lay (LOL)] GMR heads. Square-wave patterns at moderate densities are recorded to minimize NLTS, partial erasure, and transition broadening effects. Both time- and frequency-domain measurements indicate that the LOL-type GMR heads show playback nonlinearity (7%–23%), while the CJ-type GMR heads do not. Micromagnetic simulation is utilized to understand the hard bias field with different junction designs. The result indicates that the hard bias (HB) field in LOL type (HB field ∼6.9 Oe) at the air bearing surface (ABS) and stripe center is much lower than that in CJ type (HB field ∼54.0 Oe). Therefore, the free layer with large HB–HB distan...