F. Udrea

University of Cambridge, Cambridge, England, United Kingdom

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Publications (321)188.41 Total impact

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    ABSTRACT: In this paper we demonstrate the use of a CMOS infra-red emitter in a low power Non Dispersive Infra Red (NDIR) based carbon dioxide sensor for application in domestic boilers. Compared to conventional micro-bulbs as IR wideband sources, CMOS IR emitters offer several advantages: They are faster, smaller, have lower power consumption and can have integrated circuitry. The emitter is a 1.16 mm × 1.06 mm chip with an integrated FET drive and consists of a tungsten heater fabricated in a CMOS process followed by Deep Reactive Ion Etching (DRIE) to form a thin membrane to reduce power consumption. The NDIR sensor consists of the emitter and a commercial detector placed 5 mm apart in a simple tube. Operating the emitter at 10 Hz with a power consumption of only 40 mW, the sensor was measured in the range of 6-14% by volume of CO 2 , showing a resolution of 0.5%, a response time of 20 s, and low cross-sensitivity to humidity.
    IEEE Sensors; 11/2014
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    ABSTRACT: Abstract- This paper presents a multiphysic 3-D model of an SOI CMOS MEMS thermal wall shear stress sensor, considering all the physical domains involved and their interaction. After a brief introduction, the device is presented and its working principle explained. The numerical model and the validation process are then described.
    CAS; 10/2014
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    ABSTRACT: The aim of this work is to present a model capable to describe the behaviour of a thermal flow sensor under every physical aspect. Those devices contains a resistive element biased with an external current to locally increase the temperature, surrounded by one or more temperature sensing elements. The analysis involves three different and coupled physic domains: electric current, heat transfer in solids and laminar flow. Once the model was ready, it has been used to model an existing SOI CMOS MEMS wall shear stress sensor. The results shows a perfect agreement with the experimental data under every condition, proving the validity of the model.
    COMSOL Conference 2014; 09/2014
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    ABSTRACT: This abstract presents the development of a Silicon-on-Insulator (SOI) CMOS micro-electro-mechanical (MEMS) micro-hotplate based infra-red (IR) light source employing a vertically aligned multi-walled carbon nanotubes (VA-MWCNTs) emission layer. Chips were batch fabricated using a standard SOI CMOS process with tungsten metalization followed by a deep reactive ion etching (DRIE) post-CMOS process. VA-MWCNTs were grown at the chip level with a proven in-situ technique. The CNTs coated devices were compared with uncoated devices. Herein we discuss the device performance in terms of power dissipation, beam collimation, thermal transient times, integrated emitted radiation and emitted radiation spectral profile.
    EUROSENSORS 2014, Brescia; 09/2014
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    ABSTRACT: This work presents for the first time a 3-D model of an SOI CMOS MEMS thermal wall shear stress sensor using multiphysics approach. The model involves three different physical domains and, when compared with the experimental results, shows an excellent agreement in every condition. After the validation process, the model has been used to perform a transient analysis on the device to evaluate the electro-thermal transient time, defined as the time required from the device to change its temperature from 10 to 90% of the steady state value when a step is applied to the biasing current.
    EUROSENSORS 2014, Brescia; 09/2014
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    ABSTRACT: This paper describes the development of a novel low-cost Rayleigh Surface Acoustic Wave Resonator (SAWR) device coated with a graphene layer that is capable of detecting PPM levels of NO2 in air. The sensor comprises two 262 MHz ST-cut quartz based Rayleigh SAWRs arranged in a dual oscillator configuration; where one resonator is coated with gas-sensitive graphene, and the other left uncoated to act as a reference. An array of NMP-dispersed exfoliated reduced graphene oxide dots was deposited in the active area inside the SAWR IDTs by a non-contacting, micro ink-jet printing system. An automated Mass Flow Controller system has been developed that delivers gases to the SAWR sensors with circuitry for excitation, amplification, buffering and signal read-out. This SAW-based graphene sensor has sensitivity to NO2 of ca. 25 Hz/ppm and could be implemented in a low-power low-cost gas sensor.
    EUROSENSORS 2014, Brescia; 09/2014
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    ABSTRACT: In this paper, we describe an infrared thermopile sensor comprising of single crystal silicon p+ and n+ elements, with an integrated diode temperature sensor fabricated using a commercial SOI-CMOS process followed by Deep Reactive Ion Etching (DRIE). The chip area is 1.16 mm × 1.06 mm. The integrated diode, being on the same substrate, allows a more localized measurement of the cold junction temperature compared to a conventional external thermistor. The use of single crystal silicon allows good process control and reproducibility from device-to-device in terms of both Seebeck coefficient and sensor resistance. The device has a measured responsivity of 23 V/W, detectivity of 0.75 × 10 8 cm√Hz/W, a 50 % modulation depth of 60 Hz and shows enhanced responsivity in the 8 – 14 µm wavelength range, making it particularly suitable for thermometry applications.
    EUROSENSORS 2014, Brescia; 09/2014
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    ABSTRACT: An infra-red (IR) device comprising a dielectric membrane formed on a silicon substrate comprising an etched portion; and at least one patterned layer formed within or on the dielectric membrane for controlling IR emission or IR absorption of the IR device, wherein the at least one patterned layer comprises laterally spaced structures.
    Ref. No: US 20140291704 A1, Year: 06/2014
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    ABSTRACT: The model of interconnected numerical device segments can give a prediction on the dynamic performance of large area full wafer devices such as the Gate Commutated Thyristors (GCTs) and can be used as an optimisation tool for designing GCTs. In this study the authors evaluate the relative importance of the shallow p-base thickness, its peak concentration, the depth of the p-base and the buffer peak concentration.
    IET Circuits Devices & Systems 05/2014; 8(3):221-226. · 1.02 Impact Factor
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    ABSTRACT: A custom designed microelectromechanical systems (MEMS) micro-hotplate, capable of operating at high temperatures (up to 700 °C), was used to thermo-optically characterize fluorescent temperature-sensitive nanosensors. The nanosensors, 550 nm in diameter, are composed of temperature-sensitive rhodamine B (RhB) fluorophore which was conjugated to an inert silica sol–gel matrix. Temperature-sensitive nanosensors were dispersed and dried across the surface of the MEMS micro-hotplate, which was mounted in the slide holder of a fluorescence confocal microscope. Through electrical control of the MEMS micro-hotplate, temperature induced changes in fluorescence intensity of the nanosensors was measured over a wide temperature range. The fluorescence response of all nanosensors dispersed across the surface of the MEMS device was found to decrease in an exponential manner by 94%, when the temperature was increased from 25 °C to 145 °C. The fluorescence response of all dispersed nanosensors across the whole surface of the MEMS device and individual nanosensors, using line profile analysis, were not statistically different (p < 0.05). The MEMS device used for this study could prove to be a reliable, low cost, low power and high temperature micro-hotplate for the thermo-optical characterisation of sub-micron sized particles. The temperature-sensitive nanosensors could find potential application in the measurement of temperature in biological and micro-electrical systems.
    Sensors and Actuators B Chemical 03/2014; 192:126–133. · 3.84 Impact Factor
  • Power Semiconductor Devices & IC's (ISPSD), 2014 IEEE 26th International Symposium on; 01/2014
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    ABSTRACT: This letter demonstrates for the first time the effect of the incomplete ionization (I.I.) of the transparent p-anode layer on the static and dynamic characteristics of the field-stop insulated gate bipolar transistors (FS IGBTs). This effect needs to be considered in FS IGBTs TCAD modeling to match accurately the device characteristics across a wide range of temperatures. The acceptor ionization energy (EA) governing the I.I. mechanism for the p-anode is extracted via matching the experimental turn-off waveforms and the static performance with Medici simulator.
    IEEE Electron Device Letters 01/2014; 35(1):105-107. · 2.79 Impact Factor
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    ABSTRACT: As an important step in understanding trap-related mechanisms in AlGaN/GaN transistors, the physical properties of surface states have been analyzed through the study of the transfer characteristics of a MISFET. This letter focused initially on the relationship between donor parameters (concentration and energy level) and electron density in the channel in AlGaN/GaN heterostructures. This analysis was then correlated to dc and pulsed measurements of the transfer characteristics of a MISFET, where the gate bias was found to modulate either the channel density or the donor states. Traps-free and traps-frozen TCAD simulations were performed on an equivalent device to capture the donor behavior. A donor concentration of 1.14×1013 cm-2 with an energy level located 0.2 eV below the conduction band edge gave the best fit to measurements. With the approach described here, we were able to analyze the region of the MISFET that corresponds to the drift region of a conventional HEMT.
    IEEE Electron Device Letters 01/2014; 35(1):27-29. · 2.79 Impact Factor
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    ABSTRACT: Non-dispersive-infra-red (NDIR) sensors are believed to be one of the most selective and robust solutions for CO 2 detection, though cost prohibits their broader integration. In this paper we propose a commercially viable silicon-on-insulator (SOI) complementary metal-oxide (CMOS) micro-electro-mechanical (MEMS) technology for an IR thermal emitter. For the first time, vertically aligned multi walled carbon nanotubes (VA-MWCNTs) are suggested as a possible coating for the enhancement of the emission intensity of the optical source of a NDIR system. VA-MWCNTs have been grown in situ by chemical vapour deposition (CVD) exclusively on the heater area. Optical microscopy, scanning electron microscopy and Raman spectroscopy have been used to verify the quality of the VA-MWCNTs growth. The CNT-coated emitter demonstrated an increased response to CO 2 of approx. 60%. Furthermore, we show that the VA-MWCNTs are stable up to temperatures of 500 °C for up to 100 hours.
    IEEE Sensors 2013; 11/2013
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    ABSTRACT: In this paper we present for the first time, a novel silicon on insulator (SOI) complementary metal oxide semiconductor (CMOS) MEMS thermal wall shear stress sensor based on a tungsten hot-film and three thermopiles. These devices have been fabricated using a commercial 1 μm SOI-CMOS process followed by a deep reactive ion etch (DRIE) back-etch step to create silicon oxide membranes under the hot-film for effective thermal isolation. The sensors show an excellent repeatability of electro-thermal characteristics and can be used to measure wall shear stress in both constant current anemometric as well as calorimetric modes. The sensors have been calibrated for wall shear stress measurement of air in the range of 0 -0.48 Pa using a suction type, 2-D flow wind tunnel. The calibration results show that the sensors have a higher sensitivity (up to four times) in calorimetric mode compared to anemometric mode for wall shear stress lower than 0.3 Pa.
    CAS; 10/2013
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    ABSTRACT: Aerospace testing and monitoring systems are based nowadays on point-to-point wiring, which results in heavy cables, difficult installation and maintenance and a limited number of sensors. Switching to wireless communication will allow to respond to these constraints but will create new challenges due to transfer reliability requirements, high data rate and energy constraints. In this context, there is a strong need for energy efficient wireless sensor communications as each node is powered from a battery or from energy harvesting. This paper describes a wireless communications architecture tailored for this purpose, based on a low power Impulse Radio Ultra Wide Band (IR-UWB) physical layer and an energy efficient TDMA MAC layer. The whole measurement system for aircraft Structure Health Monitoring was implemented and tested on a G500 aircraft mock-up with good results. The complete system architecture from sensors to data collect is presented.
    9th International Workshop on Structural Health Monitoring 2013; 09/2013
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    ABSTRACT: There is considerable demand for sensors that are capable of detecting ultra-low concentrations (sub-PPM) of toxic gases in air. Of particular interest are NO 2 and CO that are exhaust products of internal combustion engines. Electrochemical (EC) sensors are widely used to detect these gases and offer the advantages of low power, good selectivity and temporal stability. However, EC sensors are large (∼1 cm 3), hand-made and thus expensive (∼$25). Consequently, they are unsuitable for the low-cost automotive market that demands units for less than $10. One alternative technology is SnO 2 or WO 3 resistive gas sensors that are fabricated in volume today using screen-printed films on alumina substrates and operate at ∼400°C. Unfortunately, they suffer from several disadvantages: power consumption is high ∼200 mW; reproducibility of the sensing element is poor; and cross-sensitivity is high.
    TRANSDUCER 2013, Barcelona; 06/2013
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    ABSTRACT: This paper presents for the first time the performance of a silicon-on-insulator (SOI) p+-n+ thermodiode, which can operate in an extremely wide temperature range of -200 °C to 700 °C while maintaining its linearity. The thermodiode is embedded in a thin dielectric membrane underneath a tungsten microheater, which allows the diode characterization at very high temperature (> 800 °C). The effect of the junction area (Aj) on the thermodiode linearity, sensitivity and self-heating is experimentally and theoretically investigated. Results on the long-term diode stability at high temperature are also reported.
    TRANSDUCER 2013, Barcelona; 06/2013
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    ABSTRACT: In this paper, we demonstrate a micro-inkjet printing technique as a reproducible post-process for the deposition of carbon nanoparticles and fullerene adlayers onto fully CMOS compatible micro-electro-mechanical silicon-on-insulator infrared (IR) light sources to enhance their infrared emission. We show experimentally a significant increase in the infrared emission efficiency of the coated emitters. We numerically validate these findings with models suggesting a dominant performance increase for wavelengths <5.5 lm. Here, the bimodal size distribution in the diameter of the carbon nanoparticles, relative to the fullerenes, is an effective mediator towards topologically enhanced emittance of our miniaturised emitters. A 90% improvement in IR emission power density has been shown which we have rationalised with an increase in the mean thickness of the deposited carbon nanoparticle adlayer. V C 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4809546]
    Journal of Applied Physics 06/2013; · 2.21 Impact Factor

Publication Stats

970 Citations
188.41 Total Impact Points

Institutions

  • 1994–2014
    • University of Cambridge
      • Department of Engineering
      Cambridge, England, United Kingdom
  • 2011
    • University of Electronic Science and Technology of China
      • State Key Laboratory of Electronic Thin Films and Integrated Devices
      Chengdu, Sichuan Sheng, China
  • 2010
    • Hiroshima University
      Hirosima, Hiroshima, Japan
    • De Montfort University
      Leiscester, England, United Kingdom
    • Massachusetts Institute of Technology
      • Department of Electrical Engineering and Computer Science
      Cambridge, MA, United States
  • 1996–2010
    • The University of Warwick
      • School of Engineering
      Warwick, ENG, United Kingdom
  • 2006–2008
    • University of Naples Federico II
      • Department of Electronical Engineering and Telecommunications
      Napoli, Campania, Italy
  • 2007
    • University of Bucharest
      Bucureşti, Bucureşti, Romania
    • University of Nottingham
      Nottigham, England, United Kingdom
  • 2004
    • Valahia University of Târgoviste
      Tîrgovişte, Dâmboviţa, Romania