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2013
- K. Venta, G. Shemer, M. Puster, J. A. Rodriguez-Manzo, A. Balan, J. K. Rosenstein, K. L. Shepard, and M. Drndic, "Differentiation of short, single-stranded DNA homopolymers in solid-state nanopores," ACS Nano, Advanced On-Line Publication (April 26, 2013)
Abstract
In the last two decades, new techniques that monitor ionic current modulations as single molecules pass through a nanoscale pore have enabled numerous single-molecule studies. While biological nanopores have recently shown the ability to resolve single nucleotides within individual DNA molecules, similar developments with solid-state nanopores have lagged, due to challenges both in fabricating stable nanopores of similar dimensions as biological nanopores and in achieving sufficiently low-noise and high-bandwidth recordings. Here we show that small silicon nitride nanopores (0.8- to 2-nm diameter in 5- to 8-nm-thick membranes) can resolve differences between ionic current signals produced by short (30 base) ssDNA homopolymers (poly(dA), poly(dC), poly(dT)), when combined with measurement electronics that allow a signal-to-noise ratio of better than 10 to be achieved at 1-MHz bandwidth. While identifying intramolecular DNA sequences with silicon nitride nanopores will require further improvements in nanopore sensitivity and noise levels, homopolymer differentiation represents an important milestone in the development of solid-state nanopores.
- J. K. Rosenstein, S. Ramakrishnan, J. Roseman, and K. L. Shepard, "Single ion channel recordings with CMOS-anchored lipid membranes," Nano Letters, Advanced On Line publication (May 1, 2013)
Abstract
We present single-ion-channel recordings performed with
biomimetic lipid membranes which are directly attached to the surface of a
complementary metal−oxide−semiconductor (CMOS) preamplifier chip. With
this system we resolve single-channel currents from several types of bacterial ion
channels, including fluctuations of a single alamethicin channel at a bandwidth of
1 MHz which represent the fastest single-ion-channel recordings reported to
date. The platform is also used for high-resolution α-hemolysin nanopore
recordings. These results illustrate the high signal fidelity, fine temporal
resolution, small geometry, and multiplexed integration which can be achieved
by leveraging integrated semiconductor platforms for advanced ion channel interfaces.
- S. Realov and K. L. Shepard, "Analysis of random telegraph noise in 45-nm CMOS using on-chip characterization system," IEEE Transactions on Electron Devices 60, pp. 1716-1722 (May, 2013)
Abstract
An on-chip variability characterization system implemented in a 45-nm CMOS process is used for direct time-domain measurements of random telegraph noise (RTN) in small-area devices. A procedure for automated extraction of RTN parameters from large volumes of measured data is developed. Statistics for number of traps, NT, and single-trap amplitudes, ΔVth, are studied across device polarity, bias, and gate area. A Poisson distribution is used to model NT and a log-normal distribution is used to model ΔVth. The scaling of the two statistics across gate dimensions is discussed; the expected value of NT is shown to scale with (L −ΔL)−1, whereas the expected value of ΔVth is shown to scale with W−1(L −ΔL)−0.5. The two statistics are combined in a compact RTN probabilistic model representing the statistics of the overall ΔVth fluctuations because of RTN. This model is demonstrated to give accurate predictions of the tails of the measured RTN distributions at the 95th percentile level, which scale with W−1(L −ΔL)−1.5. A comparison between nMOS and pMOS devices shows that pMOS devices exhibit both a higher average number of traps and a larger average single-trap ΔVth amplitude, leading to a comparatively larger overall impact of RTN.
- C. Cheng, R. Davies, N. Sturcken, K. Shepard, and W. E. Bailey, "Optimization of ultra-soft CoZrTa/SiO2/CoZrTa trilayer elements for integrated inductor structures," Journal of Applied Physics 113, 17A343 (2013).
Abstract
We show the optimization of magnetic properties of ferromagnetic (FM)/SiO2/FM trilayer structures as potential candidates for the magnetic core in toroidal integrated inductors, with FM materials Co91.5Zr4.0Ta4.5 (CZT) and Ni80Fe20 (Py). In the single-layer parent films, we found a monotonic reduction of easy-axis coercivity (Hc down to 0.17 Oe in CZT, 0.4Oe in Py) with increasing dc magnetron sputtering voltage. In the trilayer rectangular structures, with induced easy-axis in the short lateral dimension, we found proof of dipolar coupling between the two FM layers from BH loop measurements in the CZT system, showing linear response with minimal hysteresis loss when the external field is applied in the long axis. Py elements did not show this optimized property. Further investigation of domain configurations using scanning transmission x-ray microscopy suggests an insufficient induced anisotropy in Py compared with the shape anisotropy to realize the antiparallel-coupled state.
- S. Realov and K. L. Shepard, "On-Chip Combined C-V/I-V Characterization System in 45-nm CMOS Technology," IEEE Journal of Solid-State Circuits, Vol. 48, No. 3, March 2013.
Abstract
An on-chip system for combined capacitance-voltage (C-V) and current-voltage (I-V) characterization of a large integrated transistor array implemented in a 45-nm bulk CMOS process is presented. On-chip I-V characterization is implemented using a four-point Kelvin measurement technique with 12-bit sub-10 nA current measurement resolution, 10-bit sub-1 mV voltage measurement resolution, and sampling speeds on the order of 100 kHz. C-V characterization is performed using a novel leakage- and parasitics-insensitive charge-based capacitance measurement (CBCM) technique with atto-Farad resolution. The on-chip system is employed in studying both random and systematic sources of quasi-static device variability. For the first time, combined C-V/I-V characterization of circuit-representative devices is demonstrated and used to extract variations in the underlying physical characteristics of the device, including line-edge-roughness (LER) parameters and systematic device length variations across the die.
- N. Petrone, I. Meric, J. Hone, and K. L. Shepard, "Graphene Field-Effect Transistors with Gigahertz-Frequency Power Gain on Flexible Substrates," Nano Letters, 12 (1), pp. 121-125. 2013.
Abstract
The development of flexible electronics operating at radiofrequencies
(RF) requires materials that combine excellent electronic
performance and the ability to withstand high levels of strain. In this work,
we fabricate graphene field-effect transistors (GFETs) on flexible substrates
from graphene grown by chemical vapor deposition (CVD). Our devices
demonstrate unity-current-gain frequencies, f T, and unity-power-gain frequencies,
f max, up to 10.7 GHz and 3.7 GHz, respectively, with strain limits of 1.75%.
These devices represent the only reported technology to achieve gigahertz-frequency power gain at strain levels above 0.5%. As such, they demonstrate the potential of CVD graphene to enable a broad range of flexible electronic technologies which require
both high flexibility and RF operation.
- Sturcken, N.; O'Sullivan, E. J.; Wang, N.; Herget, P.; Webb, B. C.; Romankiw, L. T.; Petracca, M.; Davies, R.; Fontana, R. E.; Decad, G. M.; Kymissis, I.; Peterchev, A. V.; Carloni, L. P.; Gallagher, W. J.; Shepard, K. L. , A 2.5D Integrated Voltage Regulator Using Coupled-Magnetic-Core Inductors on Silicon Interposer, IEEE Journal of Solid-State Circuits, January, 2013
Abstract
An integrated voltage regulator (IVR) is presented
that uses custom fabricated thin-film magnetic power inductors.
The inductors are fabricated on a silicon interposer and
integrated with a multi-phase buck converter IC by 2.5D chip
stacking. Several inductor design variations have been fabricated
and tested. The best performance has been achieved with a set
of eight coupled inductors that each occupies 0.245 mm2 and
provides 12.5 nH with 270 mΩ DC. With early inductor prototypes,
the IVR efficiency for a 1.8 V:1.0 V conversion ratio peaks
at 71% with FEOL current density of 10.8 A/mm2 and inductor
current density of 1.53 A/mm2 . At maximum load current, 69%
conversion efficiency and 1.8 V:1.2 V conversion ratio the FEOL
current density reaches 22.6 A/mm2 and inductor current
density reaches 3.21 A/mm2 .
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