Probe-based Data Storage Research Articles

Scanning probe-type data storage beyond hard disk drive and flash memory

Abstract

Model detection with application to probe based data storage

Detection of a model from a set of models that best describes the behavior of a system is of primary importance in many applications. In this article two discriminating signals are derived from measurements for a plant that switches between two model behaviors, where the transfer functions from inputs to the two signals are identical when one model is effective while they are negative of each other when the other model is effective. The developed detection algorithm called the innovation squared mismatch is utilized for the read operation of probe based data storage. The innovations squared mismatch method offers better detection performance with significantly less computational complexity compared to prevalently used maximum a posteriori probability based methods in current data storage systems. The article further proposes employing maximum likelihood sequence detection based methods where the plant behavior can switch from one model to another at high rates and the transients from a previous behavior affect the current behavior causing inter-symbol interference. Exhaustive simulation and experimental results corroborate the efficiency of the proposed methods.

The Route for Ultra-High Recording Density Using Probe-Based Data Storage Device

Phase-change probe memory using Ge2Sb2Te5 has been considered as one of the promising candidates as next-generation data storage device due to its ultra-high density, low energy consumption, short access time and long retention time. In order to utmostly mimic the practical setup, and thus fully explore the potential of phase-change probe memory for 10 Tbit/in2 target, some advanced modeling techniques that include threshold-switching, electrical contact resistance, thermal boundary resistance and crystal nucleation-growth, are introduced into the already-established electrothermal model to simulate the write and read performance of phase-change probe memory using an optimal media stack design. The resulting predictions clearly demonstrate the capability of phase-change probe memory to record 10 Tbit/in2 density under pico Joule energy within micro second period.

Probe-based Data Storage Technology: Thermomechanical Storage –State of the Art

Ultra high density data storage imposes an ever increasing demand on the capacity and speed of data storage systems becoming an essential issue in this digital age. Secondary storage has been indispensable constituent of any computer system for storing data at high speed with ultra-high density. AFM (Atomic Force Microscopy) based data storage is a promising alternative to conventional magnetic data storage because it offers great potential for considerable storage density improvements, which has become very popular. Significant challenges, salient features and associated benefits of the nano tip based data storage devices were discussed briefly in this case study. This study addresses the following: (i) a brief discussion on emerging research directions broadly in the areas of thermomechanical data storage and storage intersecting low-dimensional polymer materials; (ii) advancing experimental methods to fabricate microcantilever with nano tip that can sustain with pulse gradient, thermo mechanically stable under large thermal cycles which can be electrically interrogated with negligible parasitic loss.

Influence of Material Properties on Major Tribological Factors at a Nanoscale Sliding Electric Contact of Probe Devices

Precise processes or devices utilizing scanning nanoprobes, e.g., probe-based nanolithography and probe-based data storage, are state-of-the-art technologies that can handle nm-sized tiny patterns. To transfer these technologies from the research and development stage to practical implementation, a significant improvement in the wear resistance of the probe tip is required for reliable and long-term operation of the system. On the other hand, to remove the unevenness of the size of drawn patterns or recorded bits, the electric contact resistance at the nanoscale sliding contact area of the probe tip must be stable even when the scanning speed of the probe increases to achieve higher throughput. To solve these dilemmatic problems, tribological investigation of the probe tip is very important.In this study, the influence of the material properties on the relations among electric contact resistance, friction force, and wear durability of nanoprobe tips was examined in detail to clarify the tribological phenomena that occur at the nanoscale contact area of the probe tips. From the results, the authors discussed the key material properties that are dominant for the abovementioned three tribological factors. In conclusion, management of the surface oxide thickness of metal electrodes was the key among all the three factors.

Investigation of Mechanical and Tribological Properties of Polyaniline Brush by Atomic Force Microscopy for Scanning Probe-Based Data Storage

Investigation of Mechanical and Tribological Properties of Polyaniline Brush by Atomic Force Microscopy for Scanning Probe-Based Data Storage

Cantilever arrays with self-aligned nanotips of uniform height

Cantilever arrays are employed to increase the throughput of imaging and manipulation at the nanoscale. We present a fabrication process to construct cantilever arrays with nanotips that show a uniform tip–sample distance. Such uniformity is crucial, because in many applications the cantilevers do not feature individual tip–sample spacing control. Uniform cantilever arrays lead to very similar tip–sample interaction within an array, enable non-contact modes for arrays and give better control over the load force in contact modes. The developed process flow uses a single mask to define both tips and cantilevers. An additional mask is required for the back side etch. The tips are self-aligned in the convex corner at the free end of each cantilever. Although we use standard optical contact lithography, we show that the convex corner can be sharpened to a nanometre scale radius by an isotropic underetch step. The process is robust and wafer-scale. The resonance frequencies of the cantilevers within an array are shown to be highly uniform with a relative standard error of 0.26% or lower. The tip–sample distance within an array of up to ten cantilevers is measured to have a standard error around 10 nm. An imaging demonstration using the AFM shows that all cantilevers in the array have a sharp tip with a radius below 10 nm. The process flow for the cantilever arrays finds application in probe-based nanolithography, probe-based data storage, nanomanufacturing and parallel scanning probe microscopy.

Nanopositioning With Multiple Sensors: A Case Study in Data Storage

The use of multiple sensors for nanopositioning is well motivated in high-density data-storage devices, such as probe-based data storage devices. In these devices, ultra-high positioning accuracies are desired over their lifetime in the presence of external disturbances. In addition to meeting the stringent requirements for nanopositioning, the use of multiple sensors lends itself for performing sensor fusion and obtaining reliable estimates of position and velocity. These estimates can be used for the detection of shocks and vibrations and the calibration of sensors. The objective of this work is to provide a comprehensive overview of the problem of nanopositioning using multiple sensors in the context of probe-based data storage. We present the control of a micro-scanner used in a probe-based data-storage device with two sensors, a global thermal position sensor and medium-derived positional information. In one approach, Kalman and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> filtering are employed to perform sensor fusion, and the resulting state estimates in turn serve to design feedback controllers. An alternate approach is to design a multiple-input single-output controller using either the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> or <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> control paradigm. These controllers are investigated in detail to reveal the underlying structure and the inherent sensor fusion that takes place. Comparisons are made between the two approaches.

A Discrete-Time Single-Parameter Combined Feedforward/Feedback Adaptive-Delay Algorithm With Applications to Piezo-Based Raster Tracking

We evaluate the performance of a combined feedforward/feedback control architecture applied to the raster scan of a piezo-based positioning system. Proper design of feedforward filters for minimum and nonminimum-phase plants is discussed. Further, empirical work suggests that a nontraditional variation upon the feedforward plant-injection architecture allows our system to track a raster pattern at a greater performance level than previously achieved in our research. This variation is manifested as additional delay inserted in the feedforward control system rather than a unity-gain filter constructed from plant parameters. An online adaptive technique is used to determine the required amount of additional delay. The key benefit of the algorithm is an adaptation calculation that does not require knowledge of plant parameters. This method can be applied to piezo-based positioning systems including atomic force microscopes, other scanning probe microscopes, probe-based data storage systems or other systems in which raster tracking is a critical control objective.

Force modulation for enhanced nanoscale electrical sensing

Scanning probe microscopy employing conductive probes is a powerful tool for theinvestigation and modification of electrical properties at the nanoscale. Application areasinclude semiconductor metrology, probe-based data storage and materials research.Conductive probes can also be used to emulate nanoscale electrical contacts. However,unreliable electrical contact and tip wear have severely hampered the widespread usage ofconductive probes for these applications. In this paper we introduce a force modulationtechnique for enhanced nanoscale electrical sensing using conductive probes. This techniqueresults in lower friction, reduced tip wear and enhanced electrical contact quality.Experimental results using phase-change material stacks and platinum silicide conductiveprobes clearly demonstrate the efficacy of the proposed technique. Furthermore,conductive-mode imaging experiments on specially prepared platinum/carbonsamples are presented to demonstrate the widespread applicability of this technique.

High-speed spiral nanopositioning

AbstractNanometer-precise positioning at ultra-high velocities is a major challenge for rapidly emerging applications that use scanning probes in order to observe and alter the properties of materials down to the nanoscale. Typical examples include surface imaging, nanolithography and data storage. For example in probe-based data storage, constant linear velocity along the scan trajectory is required, in order for storage operations to be feasible. In this paper, a spiral-enhanced tracking control architecture is presented for the constant linear velocity spiral case. The proposed controller exploits the spire-wise narrowband frequency content of the reference signal, enabling very high speed and accurate positioning. The tracking performance and high-frequency operation are corroborated with experimental results from a piezo-actuated nanopositioner with magneto-resistance-based position sensors.

Multivariable Control Designs for Piezoelectric tubes

AbstractMost AFMs use piezoelectric tube nanopositioners for scanning. Fast actuation of piezoelectric tubes are restricted due to the presence of low mechanical resonant modes. These resonances, when excited, set off vibrations that cause loss of precision and repeatability of the scans. Thereby restricting the scanning frequencies to less than 1% of the first resonance frequency. Here, an innovative multivariable control design methodology for damping the resonant modes of the tube is presented. This methodology exploits the symmetry present in transfer-functions relating the input and output, and converts the multivariable control design problem into independent SISO designs. This methodology in conjunction with Integral Resonant control is used for damping the first resonant mode of the tube, and enables scans upto 10% of the first resonant mode. The proposed methodology can be applied to a large class of parallel kinematics nanopositioners used in scanning probe microscopes and probe-based data storage systems.

Nanopositioning with multiple sensors: MISO control and inherent sensor fusion

AbstractThere is a strong motivation for using multiple sensors for feedback control in ultrahigh accuracy data storage devices such as a probe-based data storage device. One elegant way to design such controllers using multiple sensors is to design a direct multi-input-single-output (MISO) controller using either the H2 or H∞ control design paradigm. In this paper we discuss the control of a micro-scanner used in a probe-based data storage device. Two sensors, a global position sensor and medium derived positional information, are employed simultaneously. MISO controllers are designed to obtain the desired frequency separation in closed loop performance. These controllers are investigated in detail to understand their underlying structure and the inherent sensor fusion that takes place during the control. Comparisons are made with conventional Kalman filtering and H∞ filtering problems.

Parallel optical readout of cantilever arrays in dynamic mode

Parallel frequency readout of an array of cantilevers is demonstrated using optical beamdeflection with a single laser–diode pair. Multi-frequency addressing makes the individualnanomechanical response of each cantilever distinguishable within the received signal.Addressing is accomplished by exciting the array with the sum of all cantilever resonantfrequencies. This technique requires considerably less hardware compared to other paralleloptical readout techniques. Readout is demonstrated in beam deflection mode andinterference mode. Many cantilevers can be readout in parallel, limited by the oscillators’quality factor and available bandwidth. The proposed technique facilitates parallelism inapplications at the nano-scale, including probe-based data storage and biological sensing.

Low Fatigue in Epitaxial Pb(Zr0.2Ti0.8)O3 on Si Substrates with LaNiO3 Electrodes by RF Sputtering

Epitaxial PZT (001) thin films with a LaNiO3 bottom electrode were deposited by radio-frequency (RF) sputtering onto Si(001) single-crystal substrates with SrTiO3/TiN buffer layers. Pb(Zr0.2Ti0.8)O3 (PZT) samples were shown to consist of a single perovskite phase and to have an (001) orientation. The orientation relationship was determined to be PZT(001)[110]∥LaNiO3(001)[110]∥SrTiO3 (001)[110]∥TiN(001)[110]∥Si(001)[110]. Atomic force microscope (AFM) measurements showed the PZT films to have smooth surfaces with a roughness of 1.15 nm. The microstructure of the multilayer was studied using transmission electron microscopy (TEM). Electrical measurements were conducted using both Pt and LaNiO3 as top electrodes. The measured remanent polarization P r and coercive field E c of the PZT thin film with Pt top electrodes were 23 μC/cm2 and 75 kV/cm, and were 25 μC/cm2 and 60 kV/cm for the PZT film with LaNiO3 top electrodes. No obvious fatigue after 1010 switching cycles indicated good electrical endurance of the PZT films using LaNiO3 electrodes, compared with the PZT film with Pt top electrodes showing a significant polarization loss after 108 cycles. These PZT films with LaNiO3 electrodes could be potential recording media for probe-based high-density data storage.

Regular arrays of highly ordered ferroelectric polymer nanostructures for non-volatile low-voltage memories

Ferroelectric nanostructures are attracting tremendous interest because they offer a promising route to novel integrated electronic devices such as non-volatile memories and probe-based mass data storage. Here, we demonstrate that high-density arrays of nanostructures of a ferroelectric polymer can be easily fabricated by a simple nano-embossing protocol, with integration densities larger than 33 Gbits inch(-2). The orientation of the polarization axis, about which the dipole moment rotates, is simultaneously aligned in plane over the whole patterned region. Internal structural defects are significantly eliminated in the nanostructures. The improved crystal orientation and quality enable well-defined uniform switching behaviour from cell to cell. Each nanocell shows a narrow and almost ideal square-shaped hysteresis curve, with low energy losses and a coercive field of approximately 10 MV m(-1), well below previously reported bulk values. These results pave the way to the fabrication of soft plastic memories compatible with all-organic electronics and low-power information technology.

Achieving Subnanometer Precision in a MEMS-Based Storage Device During Self-Servo Write Process

In probe-based data storage devices, microelectromechanical system-based microscanners are typically used to position the storage medium relative to the read/write probes. Global position sensors are employed to provide position information across the full scan range of these microscanners. However, to achieve repeatable positioning, it is also necessary to have medium-derived position information. Dedicated storage fields known as servo fields are employed to obtain this medium-derived position information. The servo-patterns on these servo fields have to be written using the global position sensors prior to the regular operation of the storage device by employing a scheme known as ldquoself-servo writerdquo process. During this process, subnanometer positioning resolutions, well below that provided by the global position sensors, are desirable. Such precise positioning at acceptable bandwidth requires the directed design of the closed-loop noise sensitivity transfer function so as to minimize the impact of sensing noise. This paper describes control architectures in which the impact of measurement noise on positioning is minimal while providing satisfactory tracking performance. It is estimated that the positioning error due to sensing noise is a remarkably low 0.25 nm. Experimental results are also presented that show error-free operation of the device at high densities.

Modeling and Experimental Identification of Silicon Microheater Dynamics: A Systems Approach

Microfabricated silicon cantilevers with integrated heating elements are powerful tools for manipulation and interrogation at the nanoscale. They can be used for highly localized heating of surfaces and also serve as electrothermal probes such as topography and position sensors. A thorough understanding of the dynamics of these heating elements is essential for an effective design and operation of such devices. In this paper, we present a tractable feedback model that captures the dynamics of these microheaters. The operator model separates the thermal and the electrical response of the microheater into two operators, with a linear dynamic operator mapping the applied electrical power to the heater temperature and a second nonlinear but memoryless operator mapping the heater temperature to the electrical resistance. We present experimental results that show the identification of a write heater used in probe-based thermomechanical data storage and the accurate synthesis of arbitrary temperature profiles. In the application of microheaters as electrothermal probes, the signals being measured are believed to perturb the thermal system. Therefore, an extension of our model is presented to analyze the response to this perturbation. The extended model is used to identify and forecast the performance of electrothermal sensors, such as the read heater in probe-based data storage. Also presented are results on thermal position sensors, in which microheaters are employed as nanoscale position sensors for a MEMS-based microscanner.

Nanopositioning for probe-based data storage [Applications of Control

Probe-based data-storage devices are being considered as an ultra-high-density, small- form-factor alternative to conventional data storage. The probe-based data-storage concept is derived from scanning-probe microscopy, where nanometer-sharp tips are used to interrogate and manipulate matter down to the atomic scale. One implementation of this concept is based on a thermomechanical principle for storing and retrieving data encoded as nanometer-scale indentations in thin polymer films. Ultra-high densities of more than 1 Tb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> have been achieved with this scheme. A small-scaleprototype system comprising all of the elements of a probe- based data storage device has been developed. One of the key challenges is the positioning of the storage medium relative to the read/write probes with nanometer-scale accuracy. A microscanner with X/Y motion capability is used to position the storage medium. Position information along both scan directions is provided by a pair of thermal position sensors. In addition, medium-derived position information provides a measure of the cross-track deviations in the Y-scan direction. Control architectures for both scan directions are presented. The X control architecture relies on thermal position sensors alone, whereas the Y control architecture relies on both the thermal position sensors and the medium-derived PES. Nanometer-scale positioning accuracies are achieved over a bandwidth of a few hundred hertz. Read/write demonstrations with sufficiently low error rates demonstrate the efficacy of the nanopositioning schemes employed.

Heat conduction analysis of nano-tip and storage medium in thermal-assisted data storage using molecular dynamics simulation

In the thermal-assisted data storage technologies, the behavior of heat transfer between the nano-tips and the storage medium during thermo-mechanical data bit formation process is a critical factor affecting the areal storage density, data bit writing/reading speed and system reliability. In this paper, the thermal properties of a nano-tip are analyzed using the non-equilibrium molecular dynamics simulation. The simulated results show that the effects of the nano-structural configuration and boundary conditions on the thermal transport are remarkable, which can be attributed to the phonon boundary-scattering and possible phonon spectrum modification. Furthermore, the heat transfer between the nano-tip and the silicon medium film is simulated. The results show that the medium film can be efficiently heated locally with no pressure force. For a tip-medium contact area of 5.31 nm2, an area of about 95.5 nm2 on the medium surface can be heated with a temporal resolution of 0.11 ns. This time period is much smaller than the conduction timescale ( ≈ 2 μs) on the nano-tip in the heat-assisted scanning probe-based data storage technology during data bit writing process.