Electrical Engineering

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Shiv Nadar University

Barrier to the commercial implementation of optical interconnects between integrated circuits (ICs) center around the fabrication of optical elements on wafers through conventional Si processes. Most other approaches for optical interconnects use direct bandgap emitters that require drastic changes in conventional fabrication processes. In this work, we demonstrate the ability to transmit electrical signals using Si-based components, i.e., the light was generated by biasing a p-n junction at avalanche breakdown voltage, light was coupled through a fiber cable made of SiO2, and detected by an Si-based avalanche photodiode. Results presented demonstrate the switching behavior of light emitter, transmission of signal across the fiber, and measurement of signal limited by the bandwidth of the receiver amplifier.

(SoE) School of Engineering

World University root node

IEEE Photonics Technology Letters

All Si-based optical interconnect for interchip signal transmission

In the present work, we have demonstrated a novel process for fabricating suspended P+ silicon micromechanical structures such as cantilever beam, microbridge etc. which are recessed in the substrate. The recessed structures formed inside anisotropically etched rectangular cavity, can be further secured by a low temperature planar wafer-bonding process, which also provides the "pull down electrode" for electrostatic actuation of the beam, if required. It is visualized that the recessed structures can be advantageously adapted for many applications such as accelerometer, IR detector, pressure sensors and micro-relay. Since the delicate moving parts are recessed in the substrate, these can be handled and packaged more easily compared to non-recessed structures. We have used standard spin coating process for photoresist application instead of electrodeposition process reported elsewhere which requires an electroplating base. The issues related to photolithography and subsequent etching process on silicon substrate with sharp topographic features are addressed. © 2003 IEEE.

DTIP 2003 - Design, Test, Integration and Packaging of MEMS/MOEMS 2003

P+ silicon recessed micromechanical structures for MEMS applications

A series of helical ceramic springs were manufactured from MgO partially stabilized zirconia to investigate their mechanical properties. Nine springs were machined from zirconia tubing, initially one inch in length, with a rectangular pitch of 16, 14, or 12 turns per inch. An experimental apparatus that both supports and equalizes the applied loads on springs was developed. The spring deflection versus applied load was measured using an optical sight mounted on a micrometer. Deflection data on each spring were collected, plotted and successfully modeled using Hooke's Law. A more extensive model was used to calculate the shear modulus of rigidity and shear stress. This model incorporates the spring dimensions, pitch, applied load, and deflection and provides insight into the effects of the materials of construction and manufacturing technique on the effective shear modulus of spring. A specific manufacturing effect was observed in the initial deflection resulting from the mass of the spring as the pitch was increased. © 2003 Kluwer Academic Publishers.

Journal of Materials Science

Experimental investigation on the mechanical performance of helical ceramic springs

With ever-increasing applications of microelectromechanical systems (MEMS), techniques to measure their micro-movements have become important. This paper presents a new method for amplitude measurement of a vibrating silicon diaphragm using Talbot interferometry. A silicon wafer glued to a speaker diaphragm was initially used as a periodically vibrating test sample. A sinusoidal voltage was applied to the speaker to induce vibrations whose amplitude was measured as a function of frequency. The same technique has further been extended for amplitude measurement of vibration of mechanically excited silicon diaphragm, fabricated using well known "bulk micromachining technology".

Proceedings of SPIE - The International Society for Optical Engineering

Amplitude measurement of vibrating silicon using talbot interferometry

The barrier to the industrial implementation of optical interconnects on an IC, center around the fabrication of optical elements on wafers through conventional Si processes. It has been shown previously that Si-based p+-n+ diodes operating in avalanche breakdown mode emit light in the 400-900 nm range. This paper focuses on demonstrating that these Si-based light emitters can operate in the GHz range and provide reliable operation. The modulation of the light emitter was verified using a Hamamatsu streak camera for operation up to 50 psec of pulse width signals. The reliability of these emitters was verified through accelerated AC, DC, and temperature stressing. None of the stressing methods altered the total junction light emission. Low current DC stressing, however, did cause reversible light coalescence. A model has been developed to explain this phenomena. © 2002 IEEE.

Proceedings of the IEEE 2002 International Interconnect Technology Conference, IITC 2002

High speed, high reliability Si-based light emitters for optical interconnects

Silicon, apart from conventional integrated circuits, is also the basis for fabricating miniaturized 3-dimensional (3-D) mechanical structures. This paper presents a technique for the optimization of time duration of heat pulse required for transient thermography in silicon wafers. In the present work, a silicon diaphragm fabricated on one surface of a silicon wafer has been electro-thermally modeled as a 3-D Resistance Capacitance (RC) network. The region below the diaphragm was treated as a defect. Heat transfer by all three modes: conduction, convection and radiation has been taken into account. A C++ program generates the equivalent electrical circuit of the given sample, which was then directly simulated by SPICE (Simulation Program with Integrated Circuit Emphasis), a popular electrical circuit simulator. Experimental verification was performed on the silicon diaphragm sample. Prediction of a time duration in which temperature contrast of the sample reaches its maximum (saturation) value with minimum rise of sample temperature, is experimentally verified. This could be very useful in thermography situations where temperature rise should be no more than necessary to avoid potentially dangerous thermal stresses. Another possible use of the technique is for finding the heat flux of very short-pulsed heat sources.

Heat pulse optimization by SPICE simulation for transient thermography in silicon

The speed of operation of a reverse biased pn junction is evaluated using a streak camera. As such, power requirement for optical interconnects is calculated using the experimental value of quantum efficiency. It is shown from the results of the experiments that Si-based diodes are capable of operating in minimum of 10's of GHz and that is requires power less than conventional global metal interconnects on an IC.

High speed CMOS - Si light emitters for on-chip optical interconnect

This paper presents computationally efficient artificial neural network technique for assessing the security of the power system against line outages. Performance index (PI), which accounts for various line limit violations per contingency, is defined. The basic purpose of ANN is to assess the severity of line outages in terms of PI, based on training examples from off-line analysis. The selection of input signals for ANN is influenced by the operating state of the system and the contingency in question which determines the extent of line power limit violations. In an attempt to attain perfection in PI prediction, suitable architecture and topology for the network is investigated. To expedite learning process, saturating linear coupled neuron model (sl-CONE) is also tried out. The effectiveness of proposed technique is demonstrated on 5-bus (7-line) and IEEE 14-bus (21-line) test systems. Computation efficiency of the method makes it potential candidate for inclusion in on-line comprehensive security analysis package. © 2002 Elsevier Science Ltd. All rights reserved.

International Journal of Electrical Power and Energy Systems

ANN for transmission system static security assessment

This paper presents modeling of transient thermography in terms of equivalent electrical parameters, its simulation using a popular circuit simulator SPICE (Simulation Program with Integrated Circuit Emphasis), followed by experimental verification. A novel current source based electro-thermal modeling of radiative heat sources is introduced. Analytic comparison of thermal and electrical circuits forms the basis for modeling and simulation of transient thermography experiments, in which the current source (modeling rate of incident radiative energy) drives a 3- dimensional (3-D) Resistance-Capacitance (RC) network (modeling heat conduction in the material). The current source value was derived from pyranometer-based measurements of the heat flux from the source. A mild-steel sample with a blind hole below the front surface, irradiated by a heat pulse, has been modeled by the proposed technique. SPICE then simulates the absolute thermal contrast of the surface as a function of time, in moderate computing time (seconds). The simulations compare well with experimental observations and similar to generally reported results. Current source approach, allows estimation of radiative heat flux necessary, to view sub-surface defects in a given material, at different depths, in general, and to predict time and magnitude of surface temperature over the defect and non-defect region in particular.

Current source modeling of radiative heat source in transient thermography simulation by SPICE

A non-contact, non-destructive technique for sensing the temperature of metal lines carrying alternating current is presented. The technique uses heterodyne laser probing, followed by measurements using lock-in amplifier. Predictions based on a developed theoretical model are in good agreement with experimental results.