Noureddine Tayebi

Nanopencil as a wear-tolerant probe for ultrahigh density data storage

A dielectric-sheathed carbon nanotube probe, resembling a “nanopencil,” has been fabricated by conformal deposition of silicon-oxide on a carbon nanotube and subsequent “sharpening” to expose its tip. The high aspect-ratio nanopencil probe takes advantage of the small nanotube electrode size, while avoiding bending and buckling issues encountered with naked or polymer-coated carbon nanotube probes. Since the effective electrode diameter of the probe would not change even after significant wear, it is capable of long-lasting read/write operations in contact mode with a bit size of several nanometers.

An ultraclean tip-wear reduction scheme for ultrahigh density scanning probe-based data storage.

Probe-based memory devices using ferroelectric media have the potential to achieve ultrahigh data-storage densities under high write-read speeds. However, the high-speed scanning operations over a device lifetime of 5-10 years, which corresponds to a probe tip sliding distance of 5-10 km, can cause the probe tip to mechanically wear, critically affecting its write-read resolution. Here, we show that the long distance tip-wear endurance issue can be resolved by introducing a thin water layer at the tip-media interface-thin enough to form a liquid crystal. By modulating the force at the tip-surface contact, this water crystal layer can act as a viscoelastic material which reduces the stress level on atomic bonds taking part in the wear process. Under our optimized environment, a platinum-iridium probe tip can retain its write-read resolution over 5 km of sliding at a 5 mm/s velocity on a smooth ferroelectric film. We also demonstrate a 3.6 Tbit/inch(2) storage density over a 1 × 1 μm(2) area, which is the highest density ever written on ferroelectric films over such a large area.

Fully inverted single-digit nanometer domains in ferroelectric films

Achieving stable single-digit nanometer inverted domains in ferroelectric thin films is a fundamental issue that has remained a bottleneck for the development of ultrahigh density (>1 Tbit/in.^2) probe-based memory devices using ferroelectric media. Here, we demonstrate that such domains remain stable only if they are fully inverted through the entire ferroelectric film thickness, which is dependent on a critical ratio of electrode size to the film thickness. This understanding enables the formation of stable domains as small as 4 nm in diameter, corresponding to 10 unit cells in size. Such domain size corresponds to 40 Tbit/in.^2 data storage densities

Tuning the Built-in Electric Field in Ferroelectric Pb(Zr0.2Ti0.8)O3 Films for Long-Term Stability of Single-Digit Nanometer Inverted Domains

The emergence of new technologies, such as whole genome sequencing systems, which generate a large amount of data, is requiring ultrahigh storage capacities. Due to their compactness and low power consumption, probe-based memory devices using Pb(Zr(0.2)Ti(0.8))O(3) (PZT) ferroelectric films are the ideal candidate for such applications where portability is desired. To achieve ultrahigh (>1 Tbit/in(2)) storage densities, sub-10 nm inverted domains are required. However, such domains remain unstable and can invert back to their original polarization due to the effects of an antiparallel built-in electric field in the PZT film, domain-wall, and depolarization energies. Here, we show that the built-in electric-field can be tuned and suppressed by repetitive hydrogen and oxygen plasma treatments. Such treatments trigger reversible Pb reduction/oxidation activity, which alters the electrochemistry of the Pb overlayer and compensates for charges induced by the Pb vacancies. This tuning mechanism is used to demonstrate the writing of stable and equal size sub-4 nm domains in both up- and down-polarized PZT films, corresponding to eight inverted unit-cells. The bit sizes recorded here are the smallest ever achieved, which correspond to potential 60 Tbit/in(2) data storage densities.

Hard HfB2 tip-coatings for ultrahigh density probe-based storage

Probe-tip mechanical wear is a fundamental issue facing probe-based storage, which can cause serious degradation of the write-read resolution over the device lifetime. HfB2 conductive coatings grown at low temperatures using chemical vapor deposition possess high mechanical properties that are ideal for this technology. Here, we show that HfB2 coated probe-tips can potentially enhance a previously demonstrated 5 km wear endurance mechanism developed using PtIr coated probe-tips to beyond 8 km, thereby increasing the lifetime of probe-based memory devices. We foresee the extension of this coating technology to other scanning probe based systems and nanoelectromechanical devices.

Ultrahigh Density Probe-based Storage Using Ferroelectric Thin Films

The probe-based seek-and-scan data storage system is an ideal candidate for future ultrahigh-density (> 1 Tbit/ inch2) nonvolatile memory devices (Vettiger et al., 2002; Pantazi et al., 2008; Hamann et al., 2006; Ahn et al., 1997; Cho et al., 2003; Cho et al., 2005; Ahn et al., 2004; Cho et al., 2006; Heck et al., 2010). In such a system, an atomic force microscope (AFM) probe (or an array of AFM probes) is used to write and read data on a nonvolatile medium; the bit size depends mainly on the radius of the probe tip. Moreover, the storage area is not defined by lithography like in SSDs, but rather by the movement of the probes. Thus improving the probe motion control to the tenth of a distance can translate into two orders of magnitude higher density. Bit size as small as 5 nm and a storage density in the Tbit/ in2 regime with data rate comparable to flash technology have been achieved (Cho et al., 2005; Cho et al., 2006). Unlike SSD technology which requires new lithographic and fabrication tools for each new generation, manufacturing of the probe-based device can be achieved using existing low-cost semiconductor equipment, which can reduce the price of these devices considerably. Another advantage of probe-based memory is that the mechanism to move the probes is low power, which reduces power consumption and heat dissipation in comparison to HDD devices. While various writing mechanisms have been proposed for probe-based storage, e.g., thermomechanical and thermal writings on polymeric and phase-change media (Vettiger et al., 2002; Pantazi et al., 2008; Hamann et al., 2006), a great deal of attention has recently been devoted to the electrical pulse writing on ferroelectric films due to the non-structuredestructive nature of the write-erase mechanism (Ahn et al., 1997; Cho et al., 2003; Cho et al., 2005; Ahn et al., 2004; Cho et al., 2006; Heck et al., 2010). When a short electrical pulse is applied through a conductive probe on a ferroelectric film, the highly concentrated electric field can invert the polarization of a local film volume, resulting in a nonvolatile ferroelectric domain that is the basis of data recording. This mechanism allows for longer medium lifetime, i.e., larger number of write-erase cycles that is comparable to hard disk drives, faster write and read times (Forrester et al., 2009), smaller bit size (Cho et al. (2006) and higher storage densities (Cho et al. (2006). Although the probe-based storage technology based on ferroelectric media has shown great promise, no commercial product has yet reached the market. This is mainly due to

16.1 A nanogap transducer array on 32nm CMOS for electrochemical DNA sequencing

In this paper, we have demonstrated a highly scalable all-electronic approach towards DNA sequencing using CMOS readout electronics coupled with post-processed nanogap transducers. While this test chip demonstrated a small array of 8,192 pixels, a 25mm2 chip could theoretically contain over 12 million pixels including I/O pads. Through careful architectural design choices and selection of a novel transduction scheme, we demonstrate that biosensing, such as DNA sequencing, can be performed on advanced CMOS process nodes.

High frequency microwave on-chip inductors using increased ferromagnetic resonance frequency of magnetic films

The fabrication and characterization of high frequency on-chip inductors using sputtered magnetic films with an improved frequency range is presented. Reducing the sputtering power in the deposition process was found to result in smoother film surfaces and stronger uniaxial magnetic anisotropy and increased the FMR of CoZrTaB from 1.48 GHz to 2.13 GHz. A magnetic-core, on-chip inductor was fabricated using the CoZrTaB films. Results have shown 150% higher inductance and a larger Q-factor up to 1.2 GHz as compared to an air-core inductor.

Scalable Nanogap Sensors for Non-redox Enzyme Assays

Clinical diagnostic assays that monitor redox enzyme activity are widely used in small, low-cost readout devices for point-of-care monitoring (e.g., a glucometer); however, monitoring non-redox enzymes in real-time using compact electronic devices remains a challenge. We address this problem by using a highly scalable nanogap sensor array to observe electrochemical signals generated by a model non-redox enzyme system, the DNA polymerase-catalyzed incorporation of four modified, redox-tagged nucleotides. Using deoxynucleoside triphosphates (dNTPs) tagged with para-aminophenyl monophosphate (pAPP) to form pAP-deoxyribonucleoside tetra-phosphates (AP-dN4Ps), incorporation of the nucleotide analogs by DNA polymerase results in the release of redox inactive pAP-triphosphates (pAPP3) that are converted to redox active small molecules para-aminophenol (pAP) in the presence of phosphatase. In this work, cyclic enzymatic reactions that generated many copies of pAP at each base incorporation site of a DNA template in combination with the highly confined nature of the planar nanogap transducers ( z = 50 nm) produced electrochemical signals that were amplified up to 100,000×. We observed that the maximum signal level and amplification level were dependent on a combination of factors including the base structure of the incorporated nucleotide analogs, nanogap electrode materials, and electrode surface coating. In addition, electrochemical signal amplification by redox cycling in the nanogap is independent of the in-plane geometry of the transducer, thus allowing the nanogap sensors to be highly scalable. Finally, when the DNA template concentration was constrained, the DNA polymerase assay exhibited different zero-order reaction kinetics for each type of base incorporation reaction, resolving the closely related nucleotide analogs.

Sensitive and selective gas/VOC detection using MOS sensor array for wearable and mobile applications

We demonstrate a monolithic, micro-fabricated metal-oxide semiconductor (MOS) sensor array comprising of different metal oxides, allowing for independent temperature controls and readouts from individual pixels in a multiplexed fashion. The sensor pixels are designed on an ultrathin membrane to minimize heat dissipation, thereby significantly lowering the overall power consumption (<10μW). The use of such an array at varying temperatures results in multidimensional data, which we use to train neural network machine learning algorithms to determine unique fingerprints of individual gases within a homogenous mixture. Our findings indicate that a multiplicity of MOS elements together with the ability to vary and measure at various temperatures can identify individual gases or VOCs within mixtures. The small form-factor and microfabrication approach of our sensor array also lends itself to CMOS integration, paving the way for a sensitive and selective gas/VOC platform for wearable and portable applications.