Dorothea Wiesmann

Probe-based ultrahigh-density storage technology

Ultrahigh storage densities can be achieved by using a thermomechanical scanning-probe-based data-storage approach to write, read back, and erase data in very thin polymer films. High data rates are achieved by parallel operation of large two-dimensional arrays of cantilevers that can be batch fabricated by silicon-surface micromachining techniques. The very high precision required to navigate the storage medium relative to the array of probes is achieved by microelectromechanical system (MEMS)- based x and y actuators. The ultrahigh storage densities offered by probe-storage devices pose a significant challenge in terms of both control design for nanoscale positioning and read-channel design for reliable signal detection. Moreover, the high parallelism necessitates new dataflow architectures to ensure high performance and reliability of the system. In this paper, we present a small-scale prototype system of a storage device that we built based on scanning-probe technology. Experimental results of multiple sectors, recorded using multiple levers at 840 Gb/in2 and read back without errors, demonstrate the functionality of the prototype system. This is the first time a scanning-probe recording technology has reached this level of technical maturity, demonstrating the joint operation of all building blocks of a storage device.

Demonstration of thermomechanical recording at 641 Gbit/in/sup 2/

Ultrahigh storage areal densities can be achieved by using thermomechanical local-probe techniques to write, read back, and erase data in the form of nanometer-scale indentations in thin polymer films. This paper presents single-probe experimental results in which large data sets were recorded at 641 Gbit/in/sup 2/ and read back with raw bit-error rates better than 10/sup -4/. (d,k) modulation coding is used to mitigate the effect of partial erasing, occurring when subsequent indentations are spaced too closely together, and to increase the effective areal density. The physical indentation profile, the sensitivity of the probe in readback mode, and noise sources that affect data detection are also discussed. Quantitative measurements of the partial erasing effect in both the on-track and cross-track directions are reported.

Apodized surface-corrugated gratings with varying duty cycles

We present the first realization of a Bragg grating apodization based on a concatenation of different duty cycles. The gratings were fabricated in SiON planar waveguides. The reflected signal exhibits a sidelobe suppression better than -20 dB outside a bandwidth of 1.36 nm. At the same time the reflection is stronger than 99.9%, i.e., the resonant light is suppressed better than -30 dB in transmission over 0.22 nm. The gratings are perfectly suited to serve as the wavelength-selective element of a Mach-Zehnder add/drop filter.

Dynamic superlubricity and the elimination of wear on the nanoscale

One approach to ultrahigh-density data storage involves the use of arrays of atomic force microscope probes to read and write data on a thin polymer film, but damage to the ultrasharp silicon probe tips caused by mechanical wear has proved problematic. Here, we demonstrate the effective elimination of wear on a tip sliding on a polymer surface over a distance of 750 m by modulating the force acting on the tip-sample contact. Friction measurements as a function of modulation frequency and amplitude indicate that a reduction of friction is responsible for the reduction in wear to below our detection limit. In addition to its relevance to data storage, this approach could also reduce wear in micro- and nanoelectromechanical systems and other applications of scanning probe microscopes.

Functionalized Fluorinated Hyperbranched Polymers for Optical Waveguide Applications

Fluorinated dendritic or hyperbranched polymers are demonstrated for the first time to be potentially useful for optical waveguide applications, for example in telecommunications. The required materials properties include the control of the refractive index over a wide range and UV-crosslinking for ease of processing and stable long-term mechanical properties. The authors report the synthesis of suitable functionalized fluorinated hyperbranched polymers and how the above requirements can be met by functionalization at the periphery of the polymers.

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.

Add–drop filter based on apodized surface-corrugated gratings

We report on the fabrication of a grating-based add–drop filter in SiON planar waveguide technology. We achieved apodization of the Bragg grating by concatenating subgratings with various duty cycles. We present the theoretical and experimental dependence of the coupling coefficient on the duty cycle, which leads to a minimum coupling coefficient of 30%. With a breeder genetic algorithm we were able to find optimal apodization profiles within this limited coupling coefficient range. The final device is compatible with a 100-GHz channel spacing and has a bandwidth utilization factor of 36%.

Failure Analysis of Virtual and Physical Machines: Patterns, Causes and Characteristics

In todays commercial data centers, the computation density grows continuously as the number of hardware components and workloads in units of virtual machines increase. The service availability guaranteed by data centers heavily depends on the reliability of the physical and virtual servers. In this study, we conduct an analysis on 10K virtual and physical machines hosted on five commercial data centers over an observation period of one year. Our objective is to establish a sound understanding of the differences and similarities between failures of physical and virtual machines. We first capture their failure patterns, i.e., the failure rates, the distributions of times between failures and of repair times, as well as, the time and space dependency of failures. Moreover, we correlate failures with the resource capacity and run-time usage to identify the characteristics of failing servers. Finally, we discuss how virtual machine management actions, i.e., consolidation and on/off frequency, impact virtual machine failures.

Modeling, Design, and Verification for the Analog Front-End of a MEMS-Based Parallel Scanning-Probe Storage Device

We present an integrated analog front-end (AFE) for the read-channel of a parallel scanning-probe storage device. The read/write element is based on an array of microfabricated silicon cantilevers equipped with heating elements to form nanometer-sized indentations in a polymer surface using integral atomic-force microscope (AFM) tips. An accurate cantilever model based on the combination of a thermal/electrical lumped-element model and a behavioral model of the electrostatic/mechanical part are introduced. The behavioral model of the electrostatic/mechanical part is automatically generated from a full finite-element model (FEM). The model is completely implemented in Verilog-A and was used to co-develop the integrated analog front-end circuitry together with the read/write cantilever. The cantilever model and the analog front-end were simulated together and the results were experimentally verified. The approach chosen is well suited for system-level simulation and verification/extraction in a design environment based on standard EDA tools.

Compact tunable FIR dispersion compensator in SiON technology

We present a tunable dispersion compensator, based on a sixth-order finite impulse response lattice filter. The filter has a free spectral range of 100 GHz and can be tuned for linear group delay slopes between -100 and 100 ps/nm with less than 1-ps ripple over a usable bandwidth of more than 60 GHz. Within this usable bandwidth, the average polarization-mode dispersion is low, reaching 2.4 ps only for extreme group delay slopes. The filter can also generate higher order group delay curves, for example for dispersion slope compensation.