Department of Electrical Engineering

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We report the formation of defect-free SiGe vertical heterostructures using Ge condensation on vertical SiGe structures. To evaluate the effectiveness of substrate compliance in vertical structures, SiGe fins of various widths were subjected to Ge condensation. This formed vertical fin heterostructures comprising a SiGe core region sandwiched by Ge-rich regions. Using cross-sectional transmission electron microscopy (TEM), wide fins were found to contain more dislocations than narrower fins, in which we observed few or no dislocations. Lattice strain analysis using high-resolution TEM image analysis was used to confirm that strain relaxation has occurred. In the wide fins (noncompliant substrate), strain relaxation was dislocation mediated. In the narrow fins, substrate compliance enabled strain relaxation in the Ge-rich layer with reduced dislocation formation. Hence, we also demonstrated the formation of a strain-relaxed homogeneous SiGe fin (∼90% Ge concentration) with no observable dislocations. © 2005 American Institute of Physics.

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Applied Physics Letters

Investigation of silicon-germanium fins fabricated using germanium condensation on vertical compliant structures

Lanthanide-incorporated tantalum nitride (TaN) is studied as a potential metal gate candidate for n -channel metal-oxide-semiconductor field-effect transistors (n -MOSFETs). Lanthanides such as terbium (Tb), erbium (Er), and ytterbium (Yb) are introduced into TaN to form Ta1-x Tbx Ny, Ta1-x Erx Ny, and Ta1-x Ybx Ny metal gates, respectively, on Si O2 dielectric. The resistivity, crystallinity, film composition, and work function of Ta1-x Tbx Ny, Ta1-x Erx Ny, and Ta1-x Ybx Ny films were investigated at different post-metal-anneal temperatures and for different lanthanide concentrations. It was found that the work function of lanthanide-incorporated TaN can be effectively tuned by increasing the concentration of lanthanide. Work functions of about 4.2-4.3 eV can be achieved even after a 1000 °C rapid thermal anneal, making lanthanide-incorporated TaN a promising metal gate candidate for n -MOSFETs. The enhanced nitrogen concentration and the possible presence of lanthanide-N or Ta-N-lanthanide compounds in lanthanide-incorporated TaN film could be responsible for its chemical-thermal stability on Si O2. © 2005 American Institute of Physics.

Physical and electrical properties of lanthanide-incorporated tantalum nitride for n -channel metal-oxide-semiconductor field-effect transistors

This paper presents the design and optimization of the X-band microelectromechanical system (MEMS) capacitive switch using an electrical model and a mechanical model. The electrical model can accurately extract the resistance, capacitance and inductance of the switch. Based on the electrical model, a single-bridge switch and double-bridge switch with serpentine folded suspensions are proposed to achieve higher isolation compared to a typical MEMS capacitive switch at X-band frequencies. The measurement results show an isolation of 16.5-28 dB for single-bridge switch and 25-35 dB for double-bridge switch, both at 10-13 GHz. The mechanical performance is measured using an optoelectronic laser interferometric system. Due to the low effective spring constant of the serpentine folded suspensions, only 20.4 V of pull-down voltage is required. An improved fabrication process using surface and bulk micromachining techniques is also described. © 2004 Elsevier B.V. All rights reserved.

Sensors and Actuators, A: Physical

High isolation X-band MEMS capacitive switches

A new single-pole-double-throw (SPDT) switch circuit using high-aspect-ratio lateral RF microelectromechanics system (MEMS) switches has been designed to operate from DC to 20 GHz. By using lateral switches and coplanar waveguide configuration, compactness and low-loss can be obtained. The circuit provides greater than 22 dB isolation and less than 0.9 dB insertion loss up to 20 GHz. A low-cost high-yield silicon-on-glass (SOG) fabrication process has been developed to fabricate this SPDT switch circuit. The size of the whole circuit is only 1.64 mm × 1.3 mm in area. © 2005 IEEE.

Asia-Pacific Microwave Conference Proceedings, APMC

A compact DC - 20 GHz SPDT switch circuit using lateral RF MEMS switches

A dc 6 GHz single-pole double-throw (SPDT) switching circuit that employs lateral metal-contact micromachined switches is investigated. The lateral metal-contact switch consists of a set of quasi-finite ground coplanar waveguide (FGCPW) transmission lines and a high-aspect-ratio cantilever beam. A single-pole single-throw (SPST) lateral micromachined switch has an insertion loss of 0.08 dB and a return loss of 32 dB at 5 GHz. The isolation is 32 dB at 5 GHz. The measured insertion loss of the SPDT switching circuit is below 0.75 dB, whereas the return loss is higher than 19 dB at 5 GHz. The isolation at 5 GHz is 33 dB. Pull-in voltage of the switch is 23.3 V and switching time is 35 μs. The size of the SPDT switching circuit is 1.2 mm × 1.5 mm. A main advantage of this circuit structure is simple fabrication process with high yield (>90%) based on the deep reactive ion etching (DRIE) technique of silicon-on-insulator (SOI) wafer and shadow mask technology. © 2004 Elsevier B.V. All rights reserved.

A single-pole double-throw (SPDT) circuit using lateral metal-contact micromachined switches

In this paper, we present a new type of rf MEMS switch with low actuation voltage and high isolation, for high rf power and reliability applications in telecommunication. 'Symmetric toggle switch' (STS) is based on push-pull mechanism and utilizes torsion springs and levers, placed symmetrically and transverse to CPW line. The switches designed for 8-14 GHz applications have analytically calculated and FEM simulated actuation voltages in the range of 8-10 V. The simulated insertion loss and isolation for the devices are 0.25 and 35 dB, respectively, at 10 GHz. The fabrication process and preliminary experimental results are also presented. © 2005 Elsevier B.V. All rights reserved.

Symmetric toggle switch - A new type of rf MEMS switch for telecommunication applications: Design and fabrication

Active vibration control is an important problem in structures. One of the ways to tackle this problem is to make the structure smart, adaptive and self-controlling. The main objective of active vibration control is to reduce the vibration of a system by automatic modification of the system's structural response. This work features the modeling and design of a robust decentralized controller for a smart flexible system using a periodic output feedback control technique when there is a failure of a system component to function (say, an actuator). The entire structure is modeled in state space form using the finite element method and Euler-Bernoulli theory principles by dividing the master structure into eight finite elements and placing the piezoelectric sensor/actuators as collocated pairs at finite element positions 2, 4, 6 and 8, thus giving rise to a multi-input multi-output plant. Robust decentralized periodic output feedback controllers are designed for the various models of the plant, retaining the first two vibratory modes and considering one actuator failure at a time. The effect of failure of one of the piezopatches on the system is observed. In this control law, the control input to each actuator of the multimodel flexible system is a function of the output of that corresponding sensor only and the gain matrix has all off-diagonal terms zero. The designed robust decentralized periodic output feedback controller provides satisfactory stabilization of the multimodel smart structure system. © 2005 IOP Publishing Ltd.

Smart Materials and Structures

Fault tolerant control of flexible smart structures using robust decentralized periodic output feedback technique

The paper presents a new method for design of power system stabilizer (PSS) using discrete time power rate reaching law based sliding mode control technique. The control objective is to enhance the stability and to improve the dynamic response of a single machine infinite bus (SMIB) system, operating in different conditions. The control rules are constructed using discrete time power rate reaching law based sliding mode control. We apply this controller to design power system stabilizer for demonstrating the efficacy of the proposed approach.

7th International Power Engineering Conference, IPEC2005

Design of power system stabilizer using power rate reaching law based sliding mode control technique

Modern switched adaptive predictors such as Gradient Adjusted Predictor (GAP) estimates the slope of pixels from the prediction context of a unknown pixel. Based on this slope, the unknown pixels is predicted. But slope alone can not characterize some of the more complex relationship between the predicted pixel and its prediction context. In this work, this complex relationship is found in terms of a statistically valid sixth order predictor, which is used for predicting pixels under various slope conditions in the GAP frame work. It is seen through simulations, that the average entropy of the residual images is reduced significantly, when applied on high resolution images. The computational cost of the proposed method is almost of the same order as that of the GAP and requires the same previous two line buffering while coding. © 2005 IEEE.

IEEE International Conference on Communications

A switched adaptive predictor for lossless compression of high resolution images

This paper presents a new approach for sliding-mode control of discrete-time systems using the reaching law approach together with periodic output feedback technique. This method does not need the system states for feedback as it makes use of only the output samples for designing the controller. Thus, this methodology is more practical and easy to implement. A numerical example is presented to illustrate the design technique.