Publications – 2009

M.L. Johnston, I. Kymissis, and K.L. Shepard, “An array of monolithic FBAR-CMOS oscillators for mass-Sensing applications,” Proc. of 15th International Conference on Solid-State Sensors, Actuators & Microsystems (Transducers ’09), June 2009.

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T.D Huang, S. Sorgenfrei, P. Gong, R. Levicky, K.L. Shepard, “A 0.18-um CMOS Array Sensor for Integrated Time-Resolved Fluorescence Detection,” IEEE Journal of Solid-State Circuits, 44, 5, (May 2009), pp. 1644-1654.

This paper describes the design of an active, integrated CMOS sensor array for fluorescence applications which enables time-gated, time-resolved fluorescence spectroscopy. The 64-by-64 array is sensitive to photon densities as low as 8×8 x 106 photons/cm with 64-point averaging and, through a differential pixel design, has a measured impulse response of better than 800 ps. Applications include both active microarrays and high-frame-rate imagers for fluorescence lifetime imaging microscopy.

P.M. Levine, P. Gong, R. Levicky, K.L. Shepard, “Real-time, multiplexed electrochemical DNA detection using an active complementary metal-oxide-semiconductor biosensor array with integrated sensor electronics,” Biosensors and Bioelectronics 24 (2009), pp. 1995-2001.

Optical biosensing based on fluorescence detection has arguably become the standard technique for quantifying extents of hybridization between surface-immobilized probes and fluorophore-labeled analyte targets in DNA microarrays. However, electrochemical detection techniques are emerging which could eliminate the need for physically bulky optical instrumentation, enabling the design of portable devices for point-of-care applications. Unlike fluorescence detection, which can function well using a passive substrate (one without integrated electronics), multiplexed electrochemical detection requires an electronically active substrate to analyze each array site and benefits fromthe addition of integrated electronic instrumentation to further reduce platform size and eliminate the electromagnetic interference that can result from bringing non-amplified signals off chip. We report on an active electrochemical biosensor array, constructed with a standard complementary metal-oxide-semiconductor (CMOS) technology, to perform quantitative DNA hybridization detection on chip using targets conjugated with ferrocene redox labels. A 4°ø4 array of gold working electrodes and integrated potentiostat electronics, consisting of control amplifiers and current-input analog-to-digital converters, on a custom-designed 5mm°ø3mmCMOS chip drive redox reactions using cyclic voltammetry, sense DNA binding, and transmit digital data off chip for analysis.We demonstrate multiplexed and specific detection of DNA targets as well as real-time monitoring of hybridization, a task that is difficult, if not impossible, with traditional fluorescence based microarrays.

S. Realov, W. McLaughlin, K. L. Shepard, “On-chip transistor characterization arrays with digital interfaces for variability characterization,” Proceedings of the International Symposium on Quality Electronic Design, 2009.

An on-chip test-and-measurement system with digital interfaces that can perform device-level characterization of large-dense arrays of transistors is demonstrated in 90- and 65-nm technologies. The collected variability data from the 90-nm run is used to create a statistical device model based on BSIM4.3 to capture random variability. Principal component analysis (PCA) is used to extract a reduced set of purely random variables from a set of correlated BSIM4.3 parameters. Different layout-dependent systematic effects, related to poly- and active-flares, STI-stress, and lithography limitations, are examined in both technologies. These layout-dependent effects are mapped to systematic shifts in BSIM4.3 and BSIM4.4 model parameters in 90- and 65-nm, respectively.

S. Sorgenfrei, I. Meric, S. Banerjee, A. Akey, S. Rosenblatt, I. P. Herman, K. L. Shepard, “Controlled dielectrophoretic assembly of carbon nanotubes using real-time electrical detection,” Applied Physics Letters, 94, 5, (February 2009).

We investigate dielectrophoretic deposition of single-walled carbon nanotubes using an in situ detection system. Pairs of electrodes are stimulated with a small-amplitude, low-frequency voltage superimposed on a large-amplitude, high-frequency dielectrophoretic voltage. Measuring the magnitude of the current both at dc Idc and at the low frequency Iac through a digital lock-in technique allows us to determine when a nanotube has made electrical contact and to halt the dielectrophoretic process. Because Idc is determined by nonlinearities in the device current-voltage characteristic, measurement of the Idc / Iac ratio allows the real-time determination of whether the deposited nanotube is metallic or semiconducting.

Z. Xu, K. L. Shepard, “Design and Analysis of Actively-Deskewed Resonant Clock Networks,” IEEE Journal of Solid-State Circuits, 44, 2, (February 2009), pp. 558-568.

Active deskewing is an important technique for managing variability in clock distributions but introduces latency and power-supply-noise sensitivity into the resulting networks. In this paper, an adaptively deskewed resonant clock network, based on an injection-locked distributed differential oscillator, is described, in which the delay lines required for deskewing are incorporated into the injection-lock source, dramatically improving jitter immunity. A power management system based on automatic amplitude control of the resonant grid further enhances energy efficiency. A prototype system operates at a nominal 2-GHz frequency in a 0.18 m technology with on-chip jitter and skew measurement circuits and with more than 25 pF/mm???? of clock loading.