Showing papers by "Philippe M. Fauchet published in 2005"

Macroporous Silicon Microcavities for Macromolecule Detection

Abstract: Macroporous silicon microcavities for detection of large biological molecules have been fabricated from highly doped n-type silicon. Well-defined controllable pore sizes up to 120 nm have been obtained by systematically optimizing the etching parameters. The dependence of the sensor sensitivity on pore size is discussed. Excellent infiltration inside these macroporous silicon microcavities is demonstrated using 60 nm diameter latex spheres and rabbit IgG (150 kDa; 1Da = 1 g mol–1). The sensing performance of the device is tested using a biotin/streptavidin couple, and protein concentration down to 1–2 μM (equivalent to 0.3 ng mm–2) could be detected. Simulations show that the sensitivity of the technique is currently approximately 1–2 % of a protein monolayer.

Predictions of CMOS compatible on-chip optical interconnect

Abstract: Interconnect has become a primary bottleneck in integrated circuit design As CMOS technology is scaled, it will become increasingly difficult for conventional copper interconnect to satisfy the design requirements of delay, power, bandwidth, and noise On-chip optical interconnect has been considered as a potential substitute for electrical interconnect in the past two decades In this paper, predictions of the performance of CMOS compatible optical devices are made based on current state-of-art optical technologies Electrical and optical interconnects are compared for various design criteria based on these predictions The critical dimensions beyond which optical interconnect becomes advantageous over electrical interconnect are shown to be approximately one tenth of the chip edge length at the 22 nm technology node

On-chip optical interconnect roadmap: challenges and critical directions

Abstract: Intrachip optical interconnects can outperform electrical wires but the required parameters for optical components are yet unknown. Here the ITRS is used as a reference point to derive the requirements that optical components must meet.

A Three‐Dimensional Porous Silicon p–n Diode for Betavoltaics and Photovoltaics

Abstract: Modern society is experiencing an ever-increasing demand for energy to power a vast array of electrical and mechanical devices. As hydrocarbon resources dwindle, utilization of ample nuclear energy and abundant solar energy becomes more and more attractive. For 50 years, since the invention of the transistor, semiconductor devices that convert the energy of nuclear particles [1±5] or solar photons [6,7] to electric current have been investigated. However, conventional two-dimensional (2D) planar diode structures exhibit a number of inherent deficiencies that result in relatively low energy-conversion efficiencies. A unique three-dimensional (3D) porous silicon p±n diode has been developed to form the basis of a novel be-tavoltaic battery. Using tritium to demonstrate the proof-of-concept, the 3D diode geometry demonstrated a tenfold enhancement of efficiency compared to that of the usual 2D be-tavoltaic device geometry. Given the similarity of the energy-conversion physics for betavoltaic and photovoltaic devices, significant efficiency gains due to this 3D geometry might be expected for many types of photo detectors and solar cells. The 3D diode was constructed on porous silicon (PS), which consists of a network of pores formed by electrochemical an-odization of silicon substrates. According to the pore size, PS is classified as microporous (£ 2 nm), mesoporous (2±50 nm), or macroporous (> 50 nm). Such porous morphologies define a very large internal surface area, [8,9] which retains most of the characteristics associated with planar surface geometries, particularly for macropores. [10,11] Numerous investigations have been done on the physical and chemical properties of this complex material. [8,9,12] Moreover, it has been demonstrated that PS components can be integrated into microelectronic circuits in order to construct practical devices. [13] To date, however, PS has only been used as an antireflection and surface -passivation layer [14,15] in photovoltaic devices. It is believed that this work reports the first construction of confor-mal p±n junctions in PS. PS diodes with a 3D p±n junction structure were created as illustrated schematically in Figure 1 (see Experimental for details). The continuous p±n junction can be visualized as a 2D ªsheetº that is deformed to produce a uniform p±n junction layer on every accessible surface of the pore space. The built-in voltage [16] of the diodes was estimated to be ~ 0.8 V, assuming an n-dopant concentration of ~ 5 ” 10 18 cm ±3 and an abrupt p±n junction doping profile. The metallurgical junction was about 200 nm below the surface, and the …

Electrical and thermal modulation of silicon photonic bandgap microcavities containing liquid crystals.

Abstract: Electrical and thermal modulation of porous silicon microcavities is demonstrated based on a change in the refractive index of liquid crystals infiltrated in the porous silicon matrix. Positive and negative anisotropy liquid crystals are investigated, leading to controllable tuning to both longer and shorter wavelengths. Extinction ratios greater than 10 dB have been demonstrated. Larger attenuation can be achieved by increasing the Q-factor of the microcavities.

Electrical porous silicon chemical sensor for detection of organic solvents

Abstract: A novel electrical sensor platform containing a porous silicon (PSi) layer on a crystalline silicon substrate has been developed in which the electrical contacts are made exclusively on the backside of the substrate allowing complete exposure of the surface to the sensing molecules. The PSi layers were 20 μm thick with an average pore diameter of 1 μm. Real-time measurements of capacitance (C) and conductance (G) were performed and the response produced by the addition of different organic solvents was evaluated. The observed response is attributed to the combined effect of a change in dielectric constant inside the porous matrix and a modification in the depletion layer width in the crystalline silicon structure. A space charge region modulation model was used to explain the effect induced by molecules of different dipole moments, dielectric constants, polarizabilities and water solubilities.

Optical sensor based on resonant porous silicon structures.

Abstract: We propose a new design for an optical sensor based on porous silicon structures. We present an analysis based on a pole expansion, which allows for the easy identification of the parameters important for the operation of the sensor, and the phenomenological inclusion of scattering losses. The predicted sensitivity of the sensor is much greater than detectors utilizing surface plasmon resonance.

Enhanced control of porous silicon morphology from macropore to mesopore formation

Abstract: Porous silicon (PSi) is a versatile material that possesses a wide range of morphologies. There are two main types of microstructures that are widely used and well studied: branchy mesoporous silicon with pore sizes from 10 nm to 50 nm and classical macroporous silicon with pore sizes from 500 nm to 20 μm. Much less work has been done on structures with intermediate pore sizes from 100 nm to 300 nm. Applications such as immunoassays biosensing can greatly benefit from the intermediate morphology due to the larger pore openings compared to mesopores, and increased internal surface compared to classical macropores. In this work we demonstrate well-defined macropore of 150 nm diameter in average and precise control of the porous silicon morphology transition from smooth macropores to branchy mesopores on one substrate with one electrolyte. A multilayer structure (microcavity) consisting of both mesopores and macropores is presented.

Biosensing using porous silicon photonic bandgap structures

Abstract: Photonic bandgap (PBG) structures have remarkable optical properties that can be exploited for biosensing applications. We describe the fabrication of 1-D PBG biosensors using porous silicon. The optical properties of porous silicon PBGs are sensitive to small changes of refractive index in the porous layers, which makes them a good sensing platform capable of detecting binding of the target molecules to the bioreceptors. The material nanostructure and device configuration that lead to optimum performance of the devices are investigated in detail by modeling the optical response. It is shown that porous silicon based PBG sensors are useful for detecting biological matter, from small molecules to larger proteins.

Optical sensor based on resonant porous silicon structures

Abstract: We propose a new geometry for an optical sensor that is based on porous silicon structures. The sensitivity of the sensor is enhanced compared to the conventional surface plasmon resonance based sensors.

Electrical and optical on-chip interconnects in scaled microprocessors

Abstract: The interconnect has become a primary bottleneck in integrated circuit design. As CMOS technology is scaled, it will become increasingly difficult for conventional copper interconnect to satisfy the design requirements of delay, power, bandwidth, and noise. On-chip optical interconnect is therefore being considered as a potential substitute for electrical interconnect. Based on predictions of optical device development, electrical and optical interconnects are compared for various design criteria. The critical dimensions beyond which optical interconnect becomes advantageous over electrical interconnect at the 22 nm technology node are approximately one tenth of the chip edge length.

Methods of making energy conversion devices with substantially contiguous depletion regions

Abstract: A method of making an energy conversion device includes forming a plurality of pores within a substrate and forming a junction region within each of the plurality of pores. Each of the junction regions has a depletion region and each of the plurality of pores defines an opening size in the substrate and a spacing from adjacent pores so that the depletion regions of each of the pores is at least substantially in contact with the depletion region of the pores which are adjacent.

Optical properties and tunability of macroporous silicon 2-D photonic bandgap structures

Abstract: Photonic bandgap (PBG) materials offer an attractive and compact way of integrating the building blocks for optical interconnects and optoelectronic circuits. In this work we demonstrate 2-D macroporous silicon PBG structures fabricated using interferometric lithography and electrochemical etching of silicon. Optical measurements match well with simulations. We achieve tuning of the PBG using liquid crystals (LCs) infiltrated inside the porous silicon. Surface treatment methods for controlling the initial LC molecule orientation inside the pores are also demonstrated. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Direct energy conversion devices with a substantially contiguous depletion region and methods thereof

Abstract: An energy conversion device (10) includes a plurality of pores (14) formed within a substrate (12) and a junction region disposed within each of the plurality of pores (14) where each of the junction regions has a depletion region (20) Each of the plurality of pores (14) defines an opening size in the substrate (12) and a spacing from adjacent pores so that the depletion regions of each of the pores are at least substantially in contact with the depletion region of the pores which are adjacent.

Macroporous Silicon Sensor Arrays for Chemical and Biological Detection

Abstract: A new class of silicon-based chemical and biological sensors that offer an electrical response to a variety of substances is described. The devices utilize silicon flow-through sensing membranes with deep trench structures formed to depths up to 100μm, fabricated by electrochemical etching which transforms the silicon into macro-porous silicon (MPS). The sensors have demonstrated the ability to detect the presence of certain chemical and biological materials. Although the principle of operation of the devices is fairly complex, the transduction mechanisms can be compared to chemiresistors and chemically sensitive field-effect transistors (chemFETs). The electrical responses that have shown the most sensitivity are AC conductance and capacitance. Previous work has demonstrated that upon exposure to organic solvents (i.e. ethanol, acetone, benzene) the devices exhibit a characteristic impedance signature. The devices have also shown the ability to detect the hybridization of complementary DNA. The incorporation of other materials that have demonstrated sensitivity to low ambient levels of contaminants is also under investigation. The sensors have been designed and fabricated in linear array configurations; a microfluidic transport chip/package co-design is currently in progress.

Thermal tuning of silicon-based one-dimensional photonic bandgap structures

Abstract: Thermal tuning of silicon-based one-dimensional photonic bandgap microcavities is demonstrated. Thermally induced spectral shifts are caused by both the host silicon matrix and the optically active material infiltrated inside the photonic bandgap structures. The active material leads to the dominant thermal tuning contribution but the effect of the silicon matrix cannot be neglected. The interaction of the temperature dependence of the host matrix with that of the active material is explored. The general trends revealed by the characterization should be relevant for two-dimensional silicon-based photonic bandgap structures as well as other photonic bandgap materials systems. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Silicon photonic bandgap biosensors

Abstract: The sensitivity of photonic bandgap (PBG) structures to the environment makes them suitable for sensing applications. In this study, we describe how 1-D and 2-D PBG devices can be used for sensing biological matter, from small DNA segments to larger proteins. Our work focuses on using the tunability of silicon PBGs upon binding of the desired target on the internal surface of the air holes. Modeling of the optical response is performed to identify the material nanostructure and device configuration that lead to optimum performance (e.g., sensitivity).

Electrical tuning of the silicon-based 2-D photonic bandgap structures

Abstract: Silicon-based 2-D photonic bandgap (PBG) structures have an unmatched potential for integration with well-established microelectronic devices and circuits. They can allow for compact optical devices with enhanced functionality and performance. While a number of passive PBG silicon-based devices have already been demonstrated, electrical tuning of their properties has yet to be implemented. PBG tuning can be achieved by replacing the air inside the device with active optical material, for example liquid crystals (LCs) or an electro-optic polymer. The two main requirements necessary for tuning in PBG structures are (i) the electric field of the control signal should be present inside the active optical material to modify its properties, and (ii) the energy of the optical mode of interest should be distributed inside the active material. While the latter condition can be satisfied by proper optical design, the former requirement is difficult to satisfy due to external electric field screening by the conductive silicon walls. In this work, an analysis of this effect is conducted and guidelines to overcome screening and thus allow for switching are suggested. Further, by using LCs as an active optical material, electric field switching in 2-D silicon-based PBG structures is demonstrated for the first time. Results of this work can lead to the development of silicon-based switches, active routers and filters for future optical interconnects.

Active Building Blocks for Silicon Photonic Devices

Abstract: The need for alternative interconnect technologies that can efficiently deal with large bandwidths of information has led to the investigation of photonic devices suitable for integration into an optical interconnect platform. Active modulation of the optical properties of silicon-based photonic crystals provides the foundation for a variety of tunable components. One promising platform for active silicon photonics building blocks are porous silicon one-dimensional photonic bandgap microcavity structures infiltrated with optically active species. The porous silicon microcavities are fabricated by electrochemical etching, which allows flexibility in the design wavelength. As a first demonstration, electrical and thermal modulation of porous silicon microcavities is shown based on a change in the refractive index of liquid crystals infiltrated in the porous silicon matrix. Controllable tuning to both longer and shorter wavelengths is achieved based on the choice of liquid crystals. Extinction ratios greater than 10 dB have been demonstrated and larger attenuation can be realized by increasing the Q-factor of the microcavities. The porous silicon microcavities can also serve as a template for faster response time active devices based on the infiltration of quantum dots or electro-optic polymers. The relationships between microcavity Q-factor, extinction ratio, active species refractive index change, and device switching speed will be discussed.

A macroporous silicon field effect sensing system for liquid phase solvent detection

Abstract: Integration of electrical and fluidic systems for the design and fabrication of a system-on-chip (SOC) capable of sensing various liquid phase solvents is reported. A monolithic integration strategy makes use of macroporous silicon (MPS) as a gateway to interface the electrical and fluidic domains. In doing this, the MPS material, acting as a sensing membrane, is used in a flow-through structure to transport an analyte, or fluidic sample under investigation, from fluidic channels on one side of the chip to sensing electrodes on the other. A fluid/oxide/semiconductor interface results in the modulation of a space charge region in the semiconductor where real-time measurements are used to detect and distinguish between various solvents. To date, the fluidic system has delivered liquid sample sizes as small as 2 mul. Selected test solvents, i.e. acetone, ethanol, isopropyl alcohol, methanol, and toluene have generated a measured change in capacitance up to 11% and have been detected with specificity. The sensing device has a high degree of reusability and does not require heating or other solvent drive-out methods often necessitated in other sensing devices

Silicon-based building blocks for VLSI on-chip optical interconnects

Abstract: An all silicon-based on-chip optical interconnect is a promising candidate to overcome the electrical interconnect bottleneck. In this study, we focus on two missing optical building blocks: light sources and modulators. One- and two-dimensional photonic bandgap modulators are demonstrated. Light amplification is achieved in silicon nanocrystals and a distributed Bragg reflector is fabricated and tested to explore the possibility of a silicon laser.

Optical amplification in silicon quantum dot superlattices

Abstract: We report results on optical gain in superlattices containing nm-thick Si quantum dot layers. Using VSL method a fast (nsec) ASE component appears above a threshold under intense pulsed pumping. Gain up to 100 cm/sup -1/ is measured.

Label-free optical sensing of proteins with porous silicon microcavities

Abstract: We demonstrate a label free optical biosensor based on macroporous silicon microcavity. The biosensor is tested and characterized by using the streptavidin-biotin couple as a model system.

Direct energy conversion devices with substantially contiguous depletion region

Abstract: An energy conversion device (10) includes a plurality of pores (14) formed within a substrate (12) and a junction region disposed within each of the plurality of pores (14) where each of the junction regions has a depletion region (20) Each of the plurality of pores (14) defines an opening size in the substrate (12) and a spacing from adjacent pores so that the depletion regions of each of the pores are at least substantially in contact with the depletion region of the pores which are adjacent.