F. Udrea

University of Cambridge, Cambridge, England, United Kingdom

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Publications (346)238.05 Total impact

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    DESCRIPTION: Abstract—In this paper we present a novel Silicon-on-Insulator (SOI) complementary metal oxide semiconductor (CMOS) micro-electro-mechanical-system (MEMS) thermal wall shear stress sensor based on a tungsten hot-wire and a single thermopile. Devices were fabricated using a commercial 1 μm SOI-CMOS process followed by a deep reactive ion etching (DRIE) back-etch step to release a silicon dioxide membrane, which mechanically support and thermally isolates heating and sensing elements. The sensors show an electro-thermal transduction efficiency of 50 µW/°C, and very small zero flow off-set. Calibration for wall shear stress measurement in air in the range of 0 - 0.48 Pa was performed using a suction type, 2-D flow wind tunnel. The sensors were found to be extremely sensitive, up to 4 V/Pa for low wall shear stress values. Furthermore, we demonstrate the superior signal to noise ratio (up to five times higher) of a single thermopile readout configuration compared with a double thermopile readout configuration (embedded for comparison purposes within the same device). Finally, we verify that the output of the sensor is proportional to the cube root of the wall shear stress and we propose an accurate semi-empirical formula for its modelling.
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    ABSTRACT: In this paper we present a novel Silicon-on-Insulator (SOI) complementary metal oxide semiconductor (CMOS) micro-electro-mechanical-system (MEMS) thermal wall shear stress sensor based on a tungsten hot-wire and a single thermopile. Devices were fabricated using a commercial 1 μm SOI-CMOS process followed by a deep reactive ion etching (DRIE) back-etch step to release a silicon dioxide membrane, which mechanically support and thermally isolates heating and sensing elements. The sensors show an electro-thermal transduction efficiency of 50 µW/°C, and very small zero flow off-set. Calibration for wall shear stress measurement in air in the range of 0 - 0.48 Pa was performed using a suction type, 2-D flow wind tunnel. The sensors were found to be extremely sensitive, up to 4 V/Pa for low wall shear stress values. Furthermore, we demonstrate the superior signal to noise ratio (up to five times higher) of a single thermopile readout configuration compared with a double thermopile readout configuration (embedded for comparison purposes within the same device). Finally, we verify that the output of the sensor is proportional to the cube root of the wall shear stress and we propose an accurate semi-empirical formula for its modelling.
    IEEE Sensors Journal 06/2015; DOI:10.1109/JSEN.2015.2444798 · 1.85 Impact Factor
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    ABSTRACT: This paper reports on the novel deposition of zinc oxide (ZnO) nanorods using dip pen nanolithographic (DPN) technique on SOI (silicon on insulator) CMOS MEMS (micro electro mechanical system) micro-hotplates (MHP) and their characaterisation as a low-cost, low-power ethanol sensor. The ZnO nanorods were synthesized hydrothermally and deposited on the MHP that comprises a tungsten micro-heater embedded in a dielectric membrane with gold interdigitated electrodes (IDEs) on top of an oxide passivation layer. The micro-heater and IDEs were used to heat up the sensing layer and measure its resistance, respectively. The sensor device is extremely power efficient because of the thin SOI membrane. The electro-thermal efficiency of the MHP was found to be 8.2°C/mW, which results in only 42.7 mW power at an operating temperature of 350°C. The CMOS MHP devices with ZnO nanorods were exposed to PPM levels of ethanol in humid air. The sensitivity achieved from the sensor was found to be 5.8%/ppm to 0.39%/ppm for the ethanol concentration range 25 – 1000 ppm. The ZnO nanorods showed optimum response at 350°C. The CMOS sensor was found to have a humidity dependence that needs consideration in realworld application. The sensors were also found to be selective towards ethanol when tested in presence of toluene and acetone. We believe that the integration of ZnO nanorods using DPN lithography with a CMOS MEMS substrate offers a low cost, low power, smart ethanol sensor that could be exploited in consumer electronics.
    RSC Advances 05/2015; DOI:10.1039/C5RA04584C · 3.71 Impact Factor
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    ABSTRACT: In this letter, we present a fully complementary-metal-oxide-semiconductor (CMOS) compatible microelectromechanical system thermopile infrared (IR) detector employing vertically aligned multi-walled carbon nanotubes (CNT) as an advanced nano-engineered radiation absorbing material. The detector was fabricated using a commercial silicon-on-insulator (SOI) process with tungsten metallization, comprising a silicon thermopile and a tungsten resistive micro-heater, both embedded within a dielectric membrane formed by a deep-reactive ion etch following CMOS processing. In-situ CNT growth on the device was achieved by direct thermal chemical vapour deposition using the integrated micro-heater as a micro-reactor. The growth of the CNT absorption layer was verified through scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The functional effects of the nanostructured ad-layer were assessed by comparing CNT-coated thermopiles to uncoated thermopiles. Fourier transform IR spectroscopy showed that the radiation absorbing properties of the CNT adlayer significantly enhanced the absorptivity, compared with the uncoated thermopile, across the IR spectrum (3 μm–15.5 μm). This led to a four-fold amplification of the detected infrared signal (4.26 μm) in a CO2 non-dispersive-IR gas sensor system. The presence of the CNT layer was shown not to degrade the robustness of the uncoated devices, whilst the 50% modulation depth of the detector was only marginally reduced by 1.5 Hz. Moreover, we find that the 50% normalized absorption angular profile is subsequently more collimated by 8°. Our results demonstrate the viability of a CNT-based SOI CMOS IR sensor for low cost air quality monitoring.
    Applied Physics Letters 05/2015; 106:194101. · 3.52 Impact Factor
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    ABSTRACT: In this letter, we present a fully complementary-metal-oxide-semiconductor (CMOS) compatible microelectromechanical system thermopile infrared (IR) detector employing vertically aligned multi-walled carbon nanotubes (CNT) as an advanced nano-engineered radiation absorbing material. The detector was fabricated using a commercial silicon-on-insulator (SOI) process with tungsten metallization, comprising a silicon thermopile and a tungsten resistive micro-heater, both embedded within a dielectric membrane formed by a deep-reactive ion etch following CMOS processing. In-situ CNT growth on the device was achieved by direct thermal chemical vapour deposition using the integrated micro-heater as a micro-reactor. The growth of the CNT absorption layer was verified through scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The functional effects of the nanostructured ad-layer were assessed by comparing CNT-coated thermopiles to uncoated thermopiles. Fourier transform IR spectroscopy showed that the radiation absorbing properties of the CNT adlayer significantly enhanced the absorptivity, compared with the uncoated thermopile, across the IR spectrum (3 μm–15.5 μm). This led to a four-fold amplification of the detected infrared signal (4.26 μm) in a CO2 non-dispersive-IR gas sensor system. The presence of the CNT layer was shown not to degrade the robustness of the uncoated devices, whilst the 50% modulation depth of the detector was only marginally reduced by 1.5 Hz. Moreover, we find that the 50% normalized absorption angular profile is subsequently more collimated by 8°. Our results demonstrate the viability of a CNT-based SOI CMOS IR sensor for low cost air quality monitoring.
    Applied Physics Letters 05/2015; 106(194101). DOI:10.1063/1.4921170 · 3.52 Impact Factor
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    ABSTRACT: Most of the variables measured in scientific investigations or engineering applications depend, by varying degrees, on temperature. This necessitates the simultaneous measurement of temperature along with the variable of interest in order to perform high fidelity temperature compensated measurements. Silicon diode based temperature sensors (or silicon thermodiodes) have the advantages of being low cost, having an absolute temperature measurement capability as well as providing the option of on-chip integration with electronics circuits and a wide temperature measurement range. Leveraging these advantages, engineers and scientists have used silicon thermodiodes in numerous and diverse applications. This paper identifies the common temperature measuring techniques, and focuses on the use and advantages offered by silicon diodes operated as temperature sensors in different drive modes. Finally it explores the published literature for summarizing the application areas where such sensors have been utilized successfully in recent years.
    Sensors and Actuators A Physical 05/2015; DOI:10.1016/j.sna.2015.04.022 · 1.94 Impact Factor
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    ABSTRACT: High doses of fast neutrons is detrimental to the performance of most common solid-state devices such as diodes and transistors. The ionizing effect is observed in particular for diodes used as simple integrated temperature sensors, or thermodiodes, when their junction voltage is measured at constant current bias. In this work, we present a low-power and in situ mitigation technique based on Silicon-on-Insulator (SOI) microhotplates to recover thermodiodes. The basic operating principle consists in annealing the temperature-sensitive diodes integrated on the membrane during or after their irradiation in order to restore similar sensing characteristics over time. We measured thermodiodes integrated to microhotplates during their irradiation by fast neutrons (23 MeV peak) with total doses about 2.97±0.08 kGy. The membrane annealing is taking place at 450 °C using 40 mW of electrical power. Thanks to the annealing, the diode keeps a total measurement error below 0.5 °C. In this harsh radiation environment and beside the good tolerance of the thermodiodes and the membrane materials to the total ionizing dose, the thermodiode located on the heating membrane keeps a constant sensitivity. The demonstrated resistance of microhotplates and the integrated thermodiodes to fast neutron radiations can extend their use in nuclear plants and for radiation detectors.
    ANIMMA 2015 - Advancements in Nuclear Instrumentation, Measurement Methods and Their Applications, Lisbon, Portugal; 04/2015
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    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. DOI:10.1016/j.sna.2014.11.023 · 1.94 Impact Factor
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    ABSTRACT: We report here the development of a resistive single wall carbon nanotubes (SWCNTs) sensor, based on a CMOS substrate that responds at ambient temperature to ppm levels of ammonia. The power efficient CMOS micro-hotplate is a thin membrane structure and comprises metal heater with an interdigitated electrode. The SWCNTs film was prepared first by treatment with aqua regia solution, followed by washing with distilled water, and then treated with ascorbic acid at 95 °C. The film was deposited by simply dipping the chip into the solution. The SWCNTs showed good response to ammonia in a humid nitrogen atmosphere.
    Procedia Engineering 12/2014; 87:224-227. DOI:10.1016/j.proeng.2014.11.627
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    ABSTRACT: This paper presents an experimentally verified 3D FEM model to understand heat transfer mechanisms in membrane based thermal conductivity sensors developed using SOI CMOS MEMS technology. It aims to provide a structured methodology to design micro thermal conductivity sensors for gas detection. The reported model takes in to account heat transfer by conduction and convection in conjunction with device geometry and is based on a sensor fabricated at a commercial CMOS foundry using a 1 μm process that measures only 1x1 mm2.
    Procedia Engineering 12/2014; 87:476-479. DOI:10.1016/j.proeng.2014.11.395
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    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
  • Maria-Alexandra Paun, Florin Udrea
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    ABSTRACT: The main characteristics of Hall Effect Sensors, based on “silicon-on-insulator” (SOI) structure in the ideal design features, are evaluated by performing three-dimensional physical simulations. A particular Hall shape reproducing an XFAB SOI XI10 integration process is analyzed in details. In order to assess the performance of the considered Hall cell, the Hall voltage, absolute sensitivity and input resistance were extracted through simulations. Electrostatic potential distribution and Hall mobility were also produced through simulations for the considered SOI Hall Basic cell. A comparison between the performance of the same Hall cell manufactured in regular bulk and SOI CMOS technology respectively is given.
    Journal of Magnetism and Magnetic Materials 11/2014; 372. DOI:10.1016/j.jmmm.2014.07.062 · 2.00 Impact Factor
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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: 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: 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

Publication Stats

2k Citations
238.05 Total Impact Points

Institutions

  • 1994–2015
    • University of Cambridge
      • Department of Engineering
      Cambridge, England, United Kingdom
  • 2010
    • Hiroshima University
      Hirosima, Hiroshima, Japan
    • De Montfort University
      • Faculty of Technology
      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
      Coventry, England, United Kingdom
  • 2007
    • University of Nottingham
      • Department of Electrical and Electronic Engineering
      Nottigham, England, United Kingdom
    • University of Bucharest
      Bucureşti, Bucureşti, Romania
  • 2006
    • University of Naples Federico II
      • Department of Electronical Engineering and Telecommunications
      Napoli, Campania, Italy
  • 2004
    • Valahia University of Târgoviste
      Tîrgovişte, Dâmboviţa, Romania
    • University of Toronto
      • Department of Electrical and Computer Engineering
      Toronto, Ontario, Canada
  • 2002
    • Coventry University
      Coventry, England, United Kingdom
  • 2000
    • Polytechnic University of Bucharest
      Bucureşti, Bucureşti, Romania