F. Udrea

University of Cambridge, Cambridge, England, United Kingdom

Are you F. Udrea?

Claim your profile

Publications (328)217.73 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents the performance of a silicon-on-insulator (SOI) p+/p-well/n+ diode temperature sen-sor, which can operate in an extremely wide temperature range of 80 K to 1050 K. The thermodiode is placed underneath a tungsten micro-heater which is embedded in a thin dielectric membrane, obtained with a post-CMOS deep reactive ion etching process. Analytical and numerical models are used to sup-port experimental findings. Non-linearity, sensitivity and methods for their reduction and enhancement, respectively, are investigated in detail.
    Sensors and Actuators A Physical 02/2015; 222:31-38. · 1.94 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Gas sensors have a wide range of applications such as in environmental monitoring, biomedical, and security. Presently, commercially available gas sensors are power hungry (>100 mW) and expensive (>$20). Both academia and industry are thus striving to develop low power, low cost, gas sensing devices. Different technological approaches (e.g. sensors on low cost flexible platform [1], sensors on CMOS platform with on-board electronics [2]) are being investigated to make new smart sensors. In this paper we demonstrate the integration of zinc oxide nanowires (ZnONWs) onto a SOI (Silicon on Insulator) CMOS MEMS (micro-electromechanical system) substrate for low power ethanol sensing. The SOI CMOS MEMS devices were entirely fabricated in a commercial foundry. The device consists of a tungsten micro-heater and gold interdigitated electrodes (IDEs) separated by a silicon oxide layer. The micro-heater is used to heat up the membrane and the IDEs are used for measuring the sensing layer's resistance. The devices were back-etched at wafer level using a deep reactive ion etching technique. This membrane structure was formed to reduce considerably the power consumption. A typical power vs temperature curve is shown in Figure 1. These devices can reach very high operating temperatures (e.g. 600°C) with only 65 mW DC power consumption. ZnONWs powder was grown hydrothermally. The nanowires were then sonicated for eight hours in terpineol to make a viscous solution. The zinc oxide slurry was next in-house deposited on the devices using a commercial dip pen nanolithography system (NPL 2000). A scanning electron microscopy image of ZnONWs on the IDEs is shown in Figure 2(a). An enlargement of the nanowires region is shown in Figure 2 (b). The zinc oxide nanowires devices were tested in the presence of ethanol vapour in air. The optimum operating temperature of the NW sensor was found to be at 350°C. The devices were tested at four concentrations of ethanol (100 – 750 ppm range) in the presence of 10% and 40% humid air as shown in Figure 3. The sensor response is defined here as the ratio of baseline resistance to resistance in ethanol. The response was found to be 3.5 times (in presence of 750 ppm ethanol with 10% humidity), and increases with an increase of ethanol concentration. It was found that as we increase the humidity the response of zinc oxide in presence of ethanol decreases. This could be due to the fact that at high temperature water vapour dissociates to H + which interact with ZnO active sites. This eventually decreases the number of active sites for ethanol to interact with. We believe that the development of low power ethanol sensors using zinc oxide nanowires on SOI CMOS substrate will be useful for future generation sensor development.
    NanoFIS, Graz, Austria; 12/2014
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Micro-hotplates are MEMS structures of interest for low-power gas sensing, lab-on-chips and space applications, such as micro-thrusters. Micro-hotplates usually consist in a Joule heater suspended on a thin-film membrane while thermopiles or thermodiodes are added as temperature sensors and for feedback control. The implementation of micro-hotplates using a Silicon-On-Insulator technology makes them suited for co-integration with analog integrated circuits and operation at elevated environmental temperatures in a range from 200 to 300 °C, while the heater allows thermal cycling in the kHz regime up to 700 °C, e.g. necessary for the activation of gas sensitive metal-oxide on top of the membrane, with mWrange electrical power. The demonstrated resistance of micro-hotplates to gamma radiations can extend their use in nuclear plants, biomedical sterilization and space applications. In this work, we present results from electrical tests on micro-hotplates during their irradiation by Cobalt-60 gamma rays with total doses up to 18.90 kGy. The micro-hotplates are fabricated using a commercial 1.0 μm Silicon-On-Insulator technology with a tungsten Joule heater, which allows power-controlled operation above 600 °C with less than 60 mW, and temperature sensing silicon diodes located on the membrane and on the bulk. We show the immunity of the sensing platform to the harsh radiation environment. Beside the good tolerance of the thermodiodes and the membrane materials to the total radiation dose, the thermodiode located on the heating membrane is constantly annealed during irradiation and keeps a constant sensitivity while post-irradiation annealing can restore the thermodiode.
    SPIE Sensing Technology + Applications; 06/2014
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper is concerned with design considerations for enabling the operation of Field-Stop Insulated Gate Bipolar Transistors (FS IGBTs) at 200 C. It is found that through a careful optimization of the Field-Stop layer doping profile the device has a low leakage current and delivers a favorable tradeoff between the on-state voltage (Von) and turn-off loss (Eoff). An investigation of the adverse effects of increasing the junction temperature on the temperature-dependent properties of the FS IGBTs is also discussed herein.
    2014 IEEE 26th International Symposium on Power Semiconductor Devices & IC's (ISPSD); 06/2014
  • Source
    [Show abstract] [Hide abstract]
    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. · 0.91 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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
  • [Show abstract] [Hide abstract]
    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. · 3.02 Impact Factor
  • [Show abstract] [Hide abstract]
    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. · 3.02 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The effect of the bandgap narrowing (BGN) on performance of power devices is investigated in detail in this paper. The analysis reveals that the change in the energy band structure caused by BGN can strongly affect the conductivity modulation of the bipolar devices resulting in a completely different performance. This is due to the modified injection efficiency under high-level injection conditions. Using a comprehensive analysis of the injection efficiency in a p-n junction, an analytical model for this phenomenon is developed. BGN model tuning has been proved to be essential in accurately predicting the performance of a lateral insulated-gate bipolar transistor (IGBT). Other devices such as p-i-n diodes or punch-through IGBTs are significantly affected by the BGN, while others, such as field-stop IGBTs or power MOSFETs, are only marginally affected.
    IEEE Transactions on Electron Devices 12/2013; 60(12):4185-4190. · 2.36 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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

Publication Stats

1k Citations
217.73 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