Hard Disk Drive

An improved proximate time-optimal (PTO) positioning control approach with discrete-time sliding-mode control theory for a Hard Disk Drive (HDD) servo is presented. A third order velocity reference profile is introduced to improve the second order ones in the conventional proximate time-optimal servomechanism (PTOS). The proposed approach eliminates the mode-switching mechanism and dramatically reduces the seek time by 5-50%. Moreover, it is robust to unmodelled dynamics and parameter variations. Its effectiveness is verified in a simulation.

Position sensors other than the R/W heads are not embedded into current hard-disk drives (HDDs) due to cost, resolution, and signal-to-noise ratio (SNR) issues. Moreover, the "optimal" location for placing these sensors is still unknown. In this paper, the Pb-Zr-Ti (PZT) elements in the PZT suspension-based microactuator are used as a secondary actuator and a displacement sensor simultaneously with self-sensing actuation. The proposed displacement estimation circuit produces an estimated PZT microactuator's displacement with high SNR and nanometer resolution comparable to that measured from the laser doppler vibrometer (LDV). A robust active mode damping controller is then designed to damp the PZT microactuator suspension's torsion modes and sway mode, as well as decoupling the HDD dual-stage servo into two distinct loops for individual sensitivity optimization. Our results show attenuation of PZT microactuator's suspension modes by 5 dB and sway mode by 30 dB with low sensitivity. A reduction of up to 20% in 3σ position error signal is also observed.

In this paper, self-sensing control of a micro-actuator for the hard disk drive is presented. The micro-actuator is a suspension driving type. The micro-actuator uses a PZT actuator pair, installed on the assembly of the suspension. The self-sensing micro actuator can be used to form a combined actuation and sensing mechanism. Direct velocity feedback control and positive position feedback control of a self-sensing micro-actuator for an HDD is presented. The experimental results show that the direct velocity feedback controller and the positive position feedback controller are effective in suppressing the vibration modes. Experiments successfully demonstrate that the self-sensing actuator can be used for active feedback control of the HDD suspension assembly vibration.

Bit patterned media (BPM) is a promising technology for magnetic recording at densities beyond 1 Tbit/in 2. To be viable, bit patterns must be reliably fabricated over large areas with few defects. One potential route is to employ nanoimprint lithography and direct media etching using templates generated by electron beam mastering tools. In this work, we experimentally demonstrate the merits of rotary stage electron beam mastering and the effects of direct pattern transfer on BPM arrays patterned into 2.5" disks at a density of 366 Gbit/in 2. The fully circumferential staggered BPM and integrated servo arrays were patterned into CoCrPt media with 42nm down track pitch and 42-84nm cross-track pitch using rotary stage electron beam lithography, liftoff, reactive ion etching, and ion milling processes. Pattern quality is verified via contact recording methods. These results and advanced patterning and etching techniques for 4Tbit/in 2 BPM will be discussed in detail.

Flash memory solid-state disks (SSDs) are replacing hard disk drives (HDDs) in mobile computing systems because of their lower power consumption, faster random access, and greater shock resistance. We describe Hydra, a high-performance flash memory SSD architecture that translates the parallelism inherent in multiple flash memory chips into improved performance, by means of both bus-level and chip-level interleaving. Hydra has a prioritized structure of memory controllers, consisting of a single high-priority foreground unit, to deal with read requests, and multiple background units, all capable of autonomous execution of sequences of highlevel flash memory operations. Hydra also employs an aggressive write buffering mechanism based on block mapping to ensure that multiple flash memory chips are used effectively, and also to expedite the processing of write requests. Performance evaluation of an FPGA implementation of the Hydra SSD architecture shows that its performance is more than 80 percent better than the best of the comparable HDDs and SSDs that we considered.

Abstruct-While the performance of flash memory exceeds hard disk drives in almost every category, the cost of flash memory must come down in order to gain wider acceptance in mass storage applications. This paper describes a 3.3 Vonly 32 Mb NAND flash memory that achieves not only high performance but also low cost with a 94.9 mm2 die size, improved yields, and a simple process With 0.5 pm CMOS technology. Die size is reduced by eliminating high voltage operation on the bitlines through a self boosted program inhibit voltage generation scheme. Incremental-step-pulse programming results in a 2.3 MB/s program data rate as well as improved process variation tolerance. Interleaved data paths and a boosted wordline results in a 25 ns burst cycle time and a 24 MB/s read data rate. Maximum operating current is less than 8 mA.

The paper proposes a control scheme for detecting and compensating the low-frequency vibrations in hard disk drive systems. A vibration detector is proposed, utilizing the down-sampled position error signal (PES). Due to the performance limitation in loop shaping, attenuating low-frequency vibration is usually penalized by high frequency disturbance amplification. This paper proposes an adaptive scheme to intelligently adjust a vibration reduction factor, such that when vibration level is low, the servo loop maintains its normal operation mode, and little or no compensation is carried out. Experiments on hard disk drives on a vibration shaker validated the effectiveness of the proposed compensation scheme.

This paper presents a tutorial on iterative learning control (ILC) and repetitive control (RC) techniques in hard disk drive (HDD) industry for compensation of repeatable runouts (RRO). After each tutorial, an application example is given. For ILC, a simple filtering-free implementation for written-in RRO compensation is presented. For the RC part, a new application of RC in dual-stage HDD servo is presented.

This paper is to study how stray magnetic forces encountered in a long seeking process affect position errors of a hard disk drive after it finishes the seek and settles. The study consists of three parts: analysis of stray magnetic forces, numerical modeling, and analysis of numerical results. In the analysis of stray magnetic forces, we lump the stray magnetic forces into three components D1, D2 and D4. Specifically, D1 is a pair of stray magnetic forces in the plane of the voice coil. The two forces act on the two equal legs of the voice coil. In addition, the two forces point to and away from the pivot center, respectively. D2 is a pair of stray magnetic forces out of the plane of the voice coil. The two forces are equal in magnitudes but opposite in directions. The two force components also act on the two equal legs of the voice coil. D4 is identical to D2, except that the two force components in D4 act in the same direction. In the numerical study, we adopt a numerical model that includes a spinning spindle motor, a spinning disk pack with multiple disks, a stationary base plate with a top cover, and a slewing head-stack assembly. Moreover, multiple bearings are present in the model to connect the multiple components. In particular, fluiddynamic bearings connect the rotating spindle and disk pack with the base plate, pivot bearings connect the base plate with the head-stack assembly, and air bearings connect the spinning disk pack with head sliders located at the tip of the slewing head-stack assembly. Also, the numerical model assumes that the head-stack assembly seeks according to a user-specified seeking profile. Numerical simulations show two major conclusions. First, stray magnetic force component D1 does not lead to significant position errors when the head-stack assembly settles. Stray magnetic force components D2 and D4, however, can affect the position errors by significantly exciting torsion and bending modes of the head-stack assembly. Second, a flex cable can significantly increase position errors below 1 kHz during settling.

A hard disk drive is a non-volatile storage device that stores digitally encoded data on rapidly rotating rigid platters with magnetic surfaces. HDD is the mechanism that reads and writes data on a hard disk. Hard disk drives for PCs generally have seek times of about 12 milliseconds or less.

Abstruct-While the performance of flash memory exceeds hard disk drives in almost every category, the cost of flash memory must come down in order to gain wider acceptance in mass storage applications. This paper describes a 3.3 Vonly 32 Mb NAND flash memory that achieves not only high performance but also low cost with a 94.9 mm2 die size, improved yields, and a simple process With 0.5 pm CMOS technology. Die size is reduced by eliminating high voltage operation on the bitlines through a self boosted program inhibit voltage generation scheme. Incremental-step-pulse programming results in a 2.3 MB/s program data rate as well as improved process variation tolerance. Interleaved data paths and a boosted wordline results in a 25 ns burst cycle time and a 24 MB/s read data rate. Maximum operating current is less than 8 mA.

1. Jelaskan, mengapa setiap perangkat I/O yang baru pertama kali terpasang di komputer selalu didahului dengan instalasi driver?
2. Berikan 3 alasan mengapa sebuah laptop menggunakan SSD dan HDD?
3. Salah satu jenis cara pengelolaan I/O adalah DMA. Berikan alasan mengapa DMA memberikan performa lebih baik. Berikan juga 5 contoh perangkat I/O yang menggunakan DMA!

In this paper, we present a method of identifying the transfer function model of a linear time-invariant (LTI) dynamic system from its frequency response data. The presented algorithm is based on the principle of least-square fit on the complex plane. It fits the frequency response data to the response of a transfer function model, minimizing the sum of square of residual errors. Thus a transfer function model is extracted from the measurement of the frequency response at a discrete set of frequencies. We select the order of the transfer function model through the interpretation of the cost functions obtained from least-square estimation (LSE) for different orders of the transfer function.The effectiveness of the proposed technique is verified by estimating the transfer function model of a hard disk drive actuator. Ó

The aim of this paper is to put forward a novel design of a nonlinear PID controller type based on carefully choosing nonlinear gains to enable reducing the settling time, minimizing the overshoot and improving the required control effort during the functions of the read/write (R/W) head positioning servomechanism in hard disk drives. The controller is capable of adjusting a driving force, a damping effect and an integral action according to the position of the actual system output with respect to the desired output. This is carried out by utilizing the three actions of the PID controller which are tuned by different nonlinear functions to provide the system with the needed level of a driving force, a damping and a steady-state error correction action. Simulation results, including step function response, control signal history, and a disturbance rejection capability are presented to show the efficiency of the proposed controller.

Optical disk (OD) and drive (ODD) are important interfaces used for recording digital streams of bits that represent multimedia with analog nature or discrete data. Enhancing the ODDs in terms of reading/writing (operation) speed is vital as multi-layer (ML) ODs with high capacities are available in the market. This paper presents a simple strategy to enhance operation speed in ODDs by multi optical pickup unit (MOPU) 1 that leads to surprisingly higher transfer rates. The main considerations with different working modes plus theoretical and physical upper bounds are studied. To keep compatibility, the MOPU method is independent of the OD types or optical lens (OL) designs and based on the ODD hardware placement, so all ODs will be also readable at higher rates. Paper also discusses improvements achieved in experimental results based on prototypes.

Tunneling magnetoresistive (TMR) reading heads at an areal density of 80-100 Gbit/in 2 in a longitudinal magnetic recording mode have for the first time been commercialized for both laptop and desktop Seagate hard disk drive products. The first generation TMR products utilized a bottom TMR stack and an abutted hard bias design. These TMR heads have demonstrated three times the amplitude of comparable giant magnetoresistive (GMR) devices, resulting in a 0.6 decade bit error rate gain over GMR. This has enabled high component and drive yields. Due to the improved thermal dissipation of current-perpendicular-to-plane geometry, TMR runs cooler and has better lifetime performance, and has demonstrated the similar electrical static discharge robustness as GMR. TMR has demonstrated equivalent or better process and wafer yields compared to GMR. The TMR heads is proven to be a mature and capable reader technology. Using the same TMR head design in conjunction with perpendicular recording, 274 Gbit/in 2 has been demonstrated. Advanced design can reach 311 Gbit/in 2 .

Electrostatic stepper motors, also known as synchronous variable-capacitance motors, operate by utilizing the electrical energy stored in the variable capacitances formed between the poles of their rotor and stator. We present the design, modeling, and experimental characterization of a three-phase rotary stepper micromotor that employs a flexural suspension of the rotor to avoid any frictional contact during operation, providing precise, repeatable, and reliable bidirectional stepping motion without feedback control. A monolithic micromotor with high-aspect-ratio poles and an integrated three-phase electrical network was fabricated in a standard single-crystal silicon wafer by combining vertical trench isolation and bulk micromachining. The experimental characterization of a prototype having a diameter of 1.4 mm has demonstrated a rotational range of 26 • (±13 • ) at 75 V and a maximum speed of 1.67 • /ms. Half-stepping and microstepping operation modes were demonstrated with step sizes of 1/6 • and 1/48 • , respectively. The exceptional performance of the motor makes it suitable for use in hard-disk drives as a secondary stage actuator to maintain a constant orientation between the READ/WRITE head and the recording tracks. [2009-0150] Index Terms-Electrostatic rotary stepper micromotor, flexural pivot, skew angle, variable-capacitance micromotor, vertical trench isolation, virtual pivot. Manuscript , provided by the authors. This material consists of two MPEG videos, one demonstrating the operation of the rotary stepper motor (jmems-2009-0150-File025; size 4.99 MB) and one demonstrating the operation of the rotary stepper motor at high speed (jmems-2009-0150-File028; size 2.89 MB). E. Sarajlic was with Edin Sarajlic received the M.S. degree (cum laude) in mechanical engineering and the Ph.D. degree in electrical engineering from the

Intel® X25-E and X25-M SATA Solid-State Drives have been designed to provide high performance and capacity density for use in applications which were limited by traditional hard disk drives (HDD), input/output (I/O) performance bottlenecks, or performance density (as defined by bandwidth and I/Os/sec per gigabyte, per Rack Unit (RU), per Watt required to power, and per thermal unit waste heat. Solid State Drives (SSDs) have also found a place to assist in capacity density, which is the total gigabytes/terabytes per RU, per Watt, and per thermal unit waste heat. Enterprise, Web 2.0, and digital media system designers are looking at SSDs to lower power requirements and increase performance and capacity density. First as a replacement for high end SAS or Fiber Channel drives, but longer term for hybrid SSD + Hard Disk Drive (HDD) designs that are extremely low power, high performance density, and are highly reliable. This article provides an overview of the fundamentals of Intel’s Sing...

The recording performance of data-storage devices, in which write/read elements move relative to a storage medium to reliably store and retrieve information, depends on the capability of servo mechanisms to provide the necessary positioning accuracy. The desired characteristics of servo mechanisms for datastorage systems include robustness against variations of environmental parameters, high resolution, accuracy, stability, and fast response. This paper presents a comprehensive overview of advanced servo-control methods for data storage. The applications are to well-established recording technologies, including magnetic tape and magnetic disk systems as well as CD/DVD/Blue-Ray optical data-storage systems. Moreover, newer holographic and nearfield optical systems and the emerging probe-storage technology are also addressed. Emphasis is given to the potential exhibited by the technologies considered for achieving ultra-high storage capacity, as required by the exploding demand in data-storage capacity for archival systems and massive multimedia data storage.

The exponential increase in areal density of magnetic hard disk drives during the last years has led to incredibly tighter manufacturing tolerances. For the lithography process that is being used to make the principal component in a hard disk drive, the read-write head, this means that improved process control is required with respect to imaging and positioning performance. Beside the overlay performance from layer to layer, the relative placement of images in a single critical layer is being looked at as an important performance requirement on state-of-the-art DUV and I-line steppers. The terms stitching and collinearity [1] characterize the relative placement of images in a single layer. In this paper verification tests for stitching and collinear imaging are presented, as they are developed by ASML. Since these tests require an understanding of the terms stitching and collinearity, the definitions of these terms are outlined. The results for the two tests on an ASML PAS 5500/300 DUV stepper are presented and discussed. Also the effects of certain error sources and some ideas for future optimization are shown.

This paper deals with the problem of a servo system design for a conventional hard disk drive with a single voice-coil-motor (VCM) actuator using a so-called robust and perfect tracking (RPT) approach. We will first model the physical system and then formulate it into a robust and perfect tracking problem, in which a measurement feedback controller can be obtained to achieve a robust and perfect tracking for any step reference, i.e., the -norm of the resulting tracking error with 1 can be made arbitrarily small in the presence of external disturbances and initial conditions. Some tradeoffs are then made in order for the RPT controller to be implementable using the existing hardware setup. The implementation results of the RPT controller are compared with those of a proportional integral derivative (PID) controller. The results show that the servo system with our RPT controller has much better performance than the PID one has. Our servo system has faster settling time, lower overshoot and higher accuracy.

Magnetic tunnel junctions (MTJs) have received much attention because of their potential use as non-volatile memory storage cells in magnetic random access memory and as advanced read sensors in hard disk drives. These applications necessitate stringent requirements on the materials and structure of the magnetic tunnel junctions. This paper briefly describes one aspect of the numerous recent developments in MTJ materials. In particular, we discuss structures with improved magnetic properties via insertion of ultra-thin non-magnetic nano-layers within the MTJ. r

Magnetoresistive sensors using spin valves and magnetic tunnel junctions are reviewed, considering applications as readers in hard disk drives, as well as applications where the ultimate field detection limits are required (from nT down to pT). The sensor noise level in quasi-DC or high-frequency applications is described, leading to sensor design considerations concerning biomedical and read head applications. Magnetic tunnel junction based sensors using MgO barriers appear as the best candidates for ultra-low field (pT) detection, either in the high-frequency regime, or for quasi-DC applications.

A two-sample per cycle, programmable 5-tap, area efficient, FIR filter for hard-disk drive read-channels is presented. The design is optimised for low-power, achieving a figure of 5.16uW/Mhz[4] with a gate density of 2.3K, by a combination of algorithmic, architectural, circuit-level and layout techniques.

A HDD template is designed and developed for modeling and simulation for final assembly of hard disk drive (HDD) manufacturing using Arena. The designed HDD template is a high flexibility and good performance at an internal supply chain level and self-development and improves the system performance significantly. It is developed the intelligent based dynamic machine knowledge, which can capture dynamic based activities with fuzzy system. The study shows how modeling and simulation tools can be used and integrated to implement highly automated systems for industrial processes and deal with flexible products. In such context we designed and developed a prototype for the final assembly of hard disk drive with dynamic and static behavior.

In a typical disk drive servo system, two or more types of controllers are used for track seeking, track following, and track settling modes. This leads to the problem of mode switching among these controllers. We present in this paper a unified control scheme, the discrete-time composite nonlinear feedback control, which can perform all the above functions in hard disk drive (HDD) servo systems with actuator saturation. The proposed scheme is composed by combining a linear feedback law and a nonlinear feedback law. The linear feedback law is designed to yield a fast response, while the nonlinear feedback law is used to increase the damping ratio of the closed-loop system as the system output approaches the command input. In the face of actuator saturation, this control law not only increases the speed of closed-loop response, but also improves the settling performance. Implementation results show that the proposed method outperforms the conventional proximate time-optimal servomechanism by about 30% in settling time.

This paper provides a comprehensive review of various methods suggested over the past few years to design controller for dual-actuated servomechanism in hard disk drives. Main challenges in the design are explained, and different methods are compared based on these factors.

The pressure distribution in a squeeze film air bearing depends on the water vapor pressure and the saturation vapor pressure of water
at ambient temperature. When the water vapor pressure is compressed beyond the saturation vapor pressure, a portion of the water
vapor condenses, thus reducing the total gas pressure in the air bearing. This condensation mechanism thus reduces the flying height of
the slider. Using a magnetic recording system for experiments, we quantified the effect of condensation on flying height by measuring the
dependence of magnetic spacing on relative humidity.We developed a numerical model based on the proposed mechanism that matches
the experimental data and provides a detailed view of the air-bearing response to humidity.

The thermal flying height (FH) control technology had been applied to adjust FH in hard disk drive (HDD) during read/write processes. The readback signal-based in-situ FH testing technology is the feasible way to monitor and control the FH of heads in HDD. For perpendicular recording, the soft magnetic underlayer has the effects on readback signal and change the Wallace equation into a hyperbolic formula with no explicit solution to the spacing change versus the signal amplitude. Fortunately, the hyperbolic formula can be reduced to the traditional Wallace spacing loss equation at short wavelength. In the actual application, there is a need to compare the FH change or modulation at different disk locations and the harmonic ratio method is preferred to cancel media magnetic fluctuations and a certain level of off-track. This work proposed a new code pattern (11110000) to generate three major harmonic signals: the first, the third, and the fourth harmonics. With zero of the second harmonic signal, the harmonic energies are able to concentrate to the third and the fourth harmonics with strong signal intensity. The most important feature is that both the third and the fourth harmonics can meet the short wavelength requirement with enough signal intensity. This allows the new triple harmonic method to measure FH by the ratio of the fourth over the third harmonics. With the both harmonics in the range of short wavelength, it guarantees the accuracy of FH measurement during the touchdown process.

It is estimated that over 90% of all new information produced in the world is being stored on magnetic media, most of it on hard disk drives. Despite their importance, there is relatively little published work on the failure patterns of disk drives, and the key factors that affect their lifetime. Most available data are either based on extrapolation from accelerated aging experiments or from relatively modest sized field studies. Moreover, larger population studies rarely have the infrastructure in place to collect health signals from components in operation, which is critical information for detailed failure analysis.

Vapor corrosion inhibitor can improve the reliability of heads and disks in a hard disk drive by forming a protective film over exposed metal. Diffusion channels from a source and to a drain are designed to control the steady state relative partial pressure of the desirable species below saturation. Extended accelerated life tests and repeated condensing humidity cycle tests demonstrate the improved reliability.

NAND Flash memory-based Solid-State Disks (SSDs) are becoming popular as the storage media in domains ranging from mobile laptops to enterprise-scale storage systems due to a number of benefits (e.g., lighter weights, faster access times, lower power consumption, higher resistance to vibrations) they offer over the conventionally popular Hard Disk Drives (HDDs). While a number of well-regarded simulation environments exist for HDDs, the same is not yet true for SSDs. This is due to SSDs having been in the storage market for relatively less time as well as the lack of information (hardware configuration and software methods) about state-of-the-art SSDs that is publicly available. We describe the design and implementation of FlashSim, a simulator aimed at filling this void in performance evaluation of emerging storage systems that employ SSDs. FlashSim is an event-driven simulator that follows the objected-oriented programming paradigm for modularity. We have validated the performance of FlashSim against a number of commercial SSDs for behavioral similarity. We have also used FlashSim to compare the performance of SSD devices employing different Flash Translation Layer (FTL) schemes, and analyzed the energy consumption of different FTL schemes in the SSD. FlashSim has been written to be inter-operable with the well-regarded DiskSim simulator, thus enabling the simulation of a variety of "hybrid" storage systems employing combinations of SSDs and HDDs. Given the current interest in such hybrid systems as opposed to systems with SSDs replacing HDDs (due to higher price), we believe this to be an especially useful feature of FlashSim. We have made FlashSim freely available for download with the hope that it would be of use to researchers exploring the design of SSD-based systems.

Trends in the main application area of rare earth permanent magnets, data storage, are presented with the focus on miniaturization. Three examples of magnet applications, a CD-lens actuator, two spindle motors and the voice coil motor of hard disk drives, are discussed in detail and a brief sketch of other application areas is given. With respect to material properties we will focus on magnetization, high temperature use, shaping and shape integrity.

The complex flow features inside hard disk drive models are investigated in an axisymmetric and a semi-open shroud configurations. For the axisymmetric case, we have employed both experimental and computational approaches. The experiment focuses on both flow dynamics and the disk vibration, where measurements of the fluctuating pressure and velocity are undertaken at some representative points. The correlation between the disk vibration and the fluctuating pressure in the turbulent flow between disks is evident from the spectral analysis. The experimentally observed fluctuating pressure and velocity are partly due to the disk vibration and its contribution could be estimated by comparing the experiment with the results of a large eddy simulation. For the semi-open shroud case, although the characteristic peaks attributable to the large-scale vortical structure are still observed in the power spectra, the pressure fluctuation and the disk vibration are suppressed when the arm is inserted.

We report on large eddy simulations of the turbulent flow of air in hard disk drives (HDDs) using a commercial CFD code. In particular, we focus on HDD casings in which flow-induced vibrations are reportedly reduced by small geometrical modifications. The modifications investigated are M1: a blocking plate situated between the disks, M2: a spoiler (or deflector) located behind (downstream of) the actuator arm, and M3: a similar deflector upstream of the arm. We observed that M1, M2, and M3 significantly modify the mean flow patterns in the drives. M1 reduces velocity magnitudes in most parts of the drive, the modification of M2 causes flow reversal in regions close to the hub, while M3 causes the shedding of vortices upstream of the actuator arm. Our analysis points to M1 as the best candidate for mitigating the effects of turbulent airflow. This is because M1 is more effective in reducing the root-mean-square velocity fluctuations near the suspension. M1 is also more effective in reducing the pressure fluctuations near the base-plate and suspension region. This reduction, however, is at the cost of approximately 20% higher windage. Finally, we note that M3 has the adverse effects of increasing velocity and pressure fluctuations and hence is not the ideal candidate for mitigating airflow effects, among the modifications considered here.

Figure 1: A few snapshots of our interactive out-of-core walkthrough scene editing on The City Model (consisting of 110M triangles). The first image from left shows part of the original scene; the second one shows the scene after selecting an object (the house shown in green in the first image is chosen and shown in blue in the second image); the third image shows the scene after duplication of the same object and the last one after removing the original copy of the object.

Magnetic tunnel junctions (MTJs) have received much attention because of their potential use as non-volatile memory storage cells in magnetic random access memory and as advanced read sensors in hard disk drives. These applications necessitate stringent requirements on the materials and structure of the magnetic tunnel junctions. This paper briefly describes one aspect of the numerous recent developments in MTJ materials. In particular, we discuss structures with improved magnetic properties via insertion of ultra-thin non-magnetic nano-layers within the MTJ.