Department of Electrical Engineering

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Solution processed n -channel organic field-effect transistors based on [6,6]-phenyl C61 butyric acid methyl ester with high mobility and low contact resistance are reported. Ca, Au, or Ca capped with Au (Ca/Au) was used as the top source/drain electrodes. The devices with Ca electrodes exhibit excellent n -channel behavior with electron mobility values of 0.12 cm2 /V s, low threshold voltages (∼2.2 V), high current on/off ratios (105- 106) and subthreshold slopes of 0.7 V/decade. By varying the channel lengths (25-200 μm) in devices with different metal/semiconductor interfaces, the effect of channel length scaling on mobility is studied and the contact resistance is extracted. The width-normalized contact resistance (RC W) for Au (12 k cm) is high in comparison to Ca (7.2 kcm) or Ca/Au (7.5 kcm) electrodes at low gate voltage (VGS =10 V). However, in the strong accumulation regime at high gate voltage (VGS =30 V), its value is nearly independent of the choice of metal electrodes and in a range of 2.2-2.6 kcm. These devices show stable electrical behavior under multiple scans and low threshold voltage instability under electrical bias stress (VDS = VGS =30 V, 1 h) in N2 atmosphere. © 2009 American Institute of Physics.

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Journal of Applied Physics

Study of electrical performance and stability of solution-processed n -channel organic field-effect transistors

In this paper, improved RF MEMS SP4T and SP6T switches using a new design and layout topology, having significant impact on the RF characteristics of the device are presented. The device takes advantage of the CPW transmission line with small width and spacing configured for 50Ω line impedance in ohmiccontact SPST switch. The results show significant improvement in insertion loss and isolation without any significant changes in other electromechanical and RF parameters. A systematic comparison of different configurations of CPW designs and SPST switch is performed. The simulated insertion loss and isolation are better than -0.238 dB and - 53.002 dB obtained for SP4T and - 0.2956 dB and -57.217 dB for SP6T switch at 8 GHz respectively. © 2009 IEEE.

Proceedings of the International Semiconductor Conference, CAS

Design optimization of RF MEMS SP4T and SP6T switch

Perfectly aligned arrays of single-crystalline silicon nanowires were fabricated using top-down CMOS-compatible techniques. We demonstrate that these nanowire devices are able to detect adipocytokines secreted by adipose cells with femtomolar sensitivity, high specificity, wide detection range, and ability for parallel monitoring. The nanowire sensors also provide a novel tool to reveal the poorly understood signaling mechanisms of these newly recognized signaling molecules, as well as their relevance in common diseases such as obesity and diabetes. © The Royal Society of Chemistry 2009.

Nanoscale

Ultra-sensitive detection of adipocytokines with CMOS-compatible silicon nanowire arrays

Three dimensional silicon integration technologies are gaining considerable attention as the traditional CMOS scaling becoming more challenging and less beneficial. The advanced packaging solutions based on thin silicon carrier are being developed to interconnect integrated circuits and other devices at high densities. A key enabling technology element of the silicon carrier is Through Silicon Via (TSV), which can provide vertical interconnects in stacked ICs. In this paper, we present vias-first process to realize vertical interconnects that is fully FEOL compatible. The vias are filled by doped polysilicon and wafers with such pre-fabricated vias can be used as the starting wafers for any CMOS device processing. The process details and their characterization are elaborated along with the physical and electrical analysis of such vias. ©2009 IEEE.

Proceedings of the Electronic Packaging Technology Conference, EPTC

Polysilicon interconnections (FEOL): Fabrication and characterization

The use of organic semiconducting material sensors as total dose radiation detectors is proposed, wherein the change in conductivity of an organic material is measured as a function of ionizing radiation dose. The simplest sensor is a resistor made using organic semiconductor. Furthermore, for achieving higher sensitivity, organic field effect transistor (OFET) is used as a sensor. A solution processed organic semiconductor resistor and an OFET were fabricated using poly 3-hexylthiophene (P3HT), a p -type organic semiconductor material. The devices are exposed to Cobalt-60 radiation for different total dose values. The changes in electrical characteristics indicate the potential of these devices as radiation sensors. © 2009 American Institute of Physics.

Applied Physics Letters

Determining ionizing radiation using sensors based on organic semiconducting material

This work establishes a novel circuit simulation methodology for organic thin film transistors (OTFTs). Because of a lack of well developed physical models for OTFTs and due to the limitations of conventional parameter extraction techniques, the approaches presented in this work come in handy for circuit designers. The first approach uses a Look-up Table (LUT) model, which is implemented in a general purpose public-domain circuit simulator SEQUEL (Solver for circuit EQuations with User-defined Elements). In the second approach, circuit simulation is performed using equivalent SPICE parameters, which are extracted using a global optimization technique namely particle swarm optimization (PSO) algorithm. A good match has been observed between LUT simulations and SPICE based circuit simulations for both DC and transient cases. ©2009 IEEE.

2009 2nd International Workshop on Electron Devices and Semiconductor Technology, IEDST '09

DC &amp; transient circuit simulation methodologies for organic electronics

The highly sensitive and sequence-specific detection of single-stranded oligonucleotides using nonoxidized silicon nanowires (SiNWs) is demonstrated. To maximize device sensitivity, the surface of the SiNWs was functionalized with a densely packed organic monolayer via hydrosilylation, subsequently immobilized with peptide nucleic acid (PNA) capable of recognizing the label-free complementary target DNA. Because of the selective functionalization of the SiNWs, binding competition between the nanowire and the underlying oxide is avoided. Transmission electron microscopy was conducted to clearly differentiate the SiNW surface before and after removal of SiO2. Fluorescence microscopy was used to further realize the selectivity of the oxide-etched chemistry on the SiNWs and sequence specificity of PNA-DNA hybridization. The concentration-dependent resistance change measurements upon hybridization of PNA-DNA show that detection limit down to 10 fM can be obtained. The SiNW devices also reveal the capability of an obvious discrimination against mismatched sequences. Among several efforts being made to improve detection sensitivity, this work addresses one significant issue regarding surface functionalization which enables highly sensitive biomolecular sensing with SiNWs. © 2008 Elsevier B.V. All rights reserved.

Biosensors and Bioelectronics

Highly sensitive measurements of PNA-DNA hybridization using oxide-etched silicon nanowire biosensors

In this paper a novel method is presented to design a sliding mode spatial control for a large Pressurized Heavy Water Reactor (PHWR) using a new formulation of Multirate Output Feedback (MROF). In the new formulation of MROF, the outputs of the system should be some of the states of the system or system should be in special form. The non-linear model of PHWR including xenon and iodine dynamics is characterized by 70 state variables and 14 inputs and outputs each. Linear nodal model is obtained by linearizing the non-linear dynamic equations of the reactor about the full power operating point. The 14 outputs of the PHWR are the power levels in 14 zones, also these are the 14 states of the system. The PHWR model is perfectly suitable for the application of this new formulation in which the states of the system can be computed using reduced system matrix inversion. The PHWR is an ill-conditioned system and the computation of the states of the system using existing MROF require the larger matrix inversions which sometimes may not possible. The proposed approach avoids this difficulty and produces the similar result as it is produced by the existing technique. The proposed control method does not require state information of the system for feedback purposes and hence may be easier to implement. From simulation of the non-linear model of the reactor in representative transients, the proposed control scheme is found to be superior to other methods. Copyright © 2007 International Federation of Automatic Control All Rights Reserved.

IFAC Proceedings Volumes (IFAC-PapersOnline)

Discrete time output feedback sliding mode control of a large pressurized heavy water reactor

A coupled neutronics-thermal hydraulics model of Advanced Heavy Water Reactor (AHWR) which can be used for control system studies, simulation etc. is presented in this paper. A nodal model is developed for core neutronics and a simple two-phase thermal hydraulics model is developed from first principles. Neutronics-thermal hydraulics coupling is achieved through the void reactivity feedback model. Selection of a suitable nodalization scheme through steady state analysis is discussed, and dynamic response of the model is also presented. © 2008 IEEE.

Proceedings of the INDICON 2008 IEEE Conference and Exhibition on Control, Communications and Automation

Coupled neutronics-thermal hydraulics model of advanced heavy water reactor for control system studies

The paper elaborates a technique to realize fully circular self-sealed channels with diameter varying from few micrometers to less than 100 nm using standard silicon processes like trench formation, doped silicon oxide filling and thermal cycle for its re-flow. The integration of the channels with the fluidic reservoirs, their packaging with input and output ports for fluids and external electrodes is also presented. Such a chip is used as lateral patch clamp to record the electrical activity of the cells. © 2007 Elsevier B.V. All rights reserved.