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ABSTRACT: The thermal dynamic behaviors of terahertz quantum cascade lasers are investigated using a spectrally matching terahertz quantum-well photodetector. The THz output power of a lasing device under a pulse excitation is found to decrease with time, which is attributed to the increase of active-region temperature. The measurements show that the duration of output lasing pulse ranges from a few microseconds up to 77 ¿s, depending on device bias and heat-sink temperature. A theoretical analysis based on a two-dimensional heat diffusion model is presented. The model calculates lasing quenching time based on an ¿average active-region temperature¿ criterion as well as a ¿reserve of gain¿ criterion. The best fit for quenching time is found when the vertical thermal conductivity in the quantum well region is two orders of magnitude lower than that of substrate. The measured lasing quenching time is in very good agreement with theoretical modeling calculated using both criteria.
IEEE Journal of Quantum Electronics 04/2010; · 1.88 Impact Factor
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ABSTRACT: In this letter, we report a near-infrared (NIR) optical upconverter consisting of an integrated InGaAs-InP heterojunction phototransistor (HPT) with an organic light-emitting diode (OLED), which converts 1.5-mum IR light to visible light with a built-in electrical gain. The device was fabricated through direct tandem integration of an OLED with an inorganic InGaAs-InP HPT. Incoming 1.5-mum optical radiation is absorbed by the HPT, generating an amplified photocurrent. The resultant photocurrent drives the OLED that emits at 545 nm. Upconversion is demonstrated at room temperature with a gain of 15 from the HPT and an overall external upconversion efficiency of 0.15 W/W.
IEEE Photonics Technology Letters 11/2009; · 2.19 Impact Factor
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ABSTRACT: An all photonic terahertz communication link operating at 3.8 THz using a quantum cascade laser and quantum well photodetector has been demonstrated. The link consists of a quantum cascade laser transmitter and a quantum well photodetector receiver. The link was used to transmit audio through 2 m of room air. Carrier strength at the photodetector was 100 times greater than the noise level measured.
Electronics Letters 09/2009; · 0.96 Impact Factor
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F.R. Giorgetta,
E. Baumann, M. Graf,
Quankui Yang,
C. Manz,
K. Kohler,
H.E. Beere,
D.A. Ritchie,
E. Linfield,
A.G. Davies,
Y. Fedoryshyn,
H. Jackel,
M. Fischer,
J. Faist,
D. Hofstetter
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ABSTRACT: This paper gives an overview on the design, fabrication, and characterization of quantum cascade detectors. They are tailorable infrared photodetectors based on intersubband transitions in semiconductor quantum wells that do not require an external bias voltage due to their asymmetric conduction band profile. They thus profit from favorable noise behavior, reduced thermal load, and simpler readout circuits. This was demonstrated at wavelengths from the near infrared at 2 mum to THz radiation at 87 mum using different semiconductor material systems.
IEEE Journal of Quantum Electronics 09/2009; · 1.88 Impact Factor
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ABSTRACT: A near-infrared to visible light optical upconverter by the integration of an i-In<sub>0.53</sub>Ga<sub>0.47</sub>As/C<sub>60</sub> junction and an organic light emitting diode is reported. This device shows the photovoltaic effect of an i-In<sub>0.53</sub>Ga<sub>0.47</sub>As/C<sub>60</sub> heterojunction and potential application in a pixelless upconversion imaging device.
Electronics Letters 08/2009; · 0.96 Impact Factor
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ABSTRACT: Actuated car doors are a promising way to increase the convenience of access to cars. In this paper, an advanced door concept which can easily be integrated into conventional car doors is presented. Using a linear, non-backdrivable actuator and various sensors, both automatic and manual door operations can be realized. The principal part is the realization of a high-quality haptic interaction of the car door for the manual operation. We implemented and tested four different impedance control schemes, of which impedance control with actuator force feedback performed best. This control scheme was subsequently used to haptically render different supportive dynamics and effects. An experimental evaluation with 16 participants revealed a predominant approval of the haptic sensation of the actuated car door.
EuroHaptics conference, 2009 and Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems. World Haptics 2009. Third Joint; 04/2009
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ABSTRACT: A monolithic gas sensor array fabricated in industrial CMOS technology combined with post-CMOS micromachining is presented. The device comprises an array of three metal-oxide-coated micro-hotplates with integrated MOS transistor heaters and the needed driving and signal-conditioning circuitry. Three digital PID controllers enable individual temperature regulation for each hotplate. The operating temperature of the SnO<sub>2</sub> metal-oxide sensors may amount up to 350degC. A serial interface and the temperature control units have been implemented digitally. The mainly digital implementation offers the advantage to apply a power-saving mode and temperature modulation techniques to enhance the analyte discrimination capability.
Sensors, 2008 IEEE; 11/2008
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IRS2, Nuernberg; 04/2008
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ABSTRACT: In this paper, measurements of environmentally relevant gases (CO, CH<sub>4</sub> and NO<sub>2</sub>) with a novel single-chip digital microhotplate array are presented. The array consists of three tin-oxide-coated microhotplates with integrated MOS-transistor heaters and specifically designed circuitry. The programmable digital temperature controllers enable individual regulation of the microhotplate temperatures in continuous or dynamic mode. Nanocrystalline tin-oxide thick films with different Pd dopings (undoped, 0.2 wt% and 3 wt%) were tested. Excellent discrimination between the three gases was achieved with detection limits of less than 1 ppm for CO, 100 ppm for CH<sub>4</sub> (40% RH) and 10 ppb of NO<sub>2</sub> (30%/70% RH).
Sensors, 2004. Proceedings of IEEE; 11/2004
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ABSTRACT: For a Smart-Power-Technology on SOI new concepts for suitable ESD protection elements are investigated. It is shown that variations of the maximum failure current correlate with undue thickness variations of the active silicon layer whereas the DC-characteristics in the low current regime are not influenced.
Electrical Overstress/Electrostatic Discharge Symposium, 2003. EOS/ESD '03.; 10/2003
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D. Hofstetter, M. Graf,
G. Scalari,
L. Ajili,
M. Beck,
D. Ritchie,
E. Linfield,
H. Beere,
H. Wu,
W.J. Schaff,
L.F. Eastman,
J. Faist
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ABSTRACT: During the last ten years, opto-electronic devices based on intersubband transitions have seen a development at a very fast pace. As an example, quantum cascade lasers have become reliable sources for the various applications in the mid-infrared, and most recently also in the far-infrared. Likewise, quantum well infrared photodetectors are now important building blocks of thermal imaging systems in the mid-infrared. In the first half of this presentation, we report on room temperature continuous wave operation of an InP-based 9.1 µm quantum cascade laser, as well as on a 77 K operated continuous wave far-infrared quantum cascade laser built from GaAs/AlGaAs. The second part will be devoted to photodetectors. We recently demonstrated such devices in the far-infrared and in the near-infrared wavelength region. While the former device is contains a chirped AlGaAs/GaAs-superlattice, the latter is based on a regular GaN/AlN superlattice with a period of 40 Å.
TDLS 2003, Zermatt; 07/2003
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ABSTRACT: Micro-photodiode arrays have been developed which are intended to eventually replace the function of degenerated photoreceptor cells in the retina. Electric current generated by tiny micro-photodiodes is delivered to the neuronal network in the retina via micro-electrodes. Since the coupling between electrode and tissue is capacitive of nature, only transient signals may be used for stimulation. Therefore, high capacitance of the interface between electrodes and tissue is an important prerequisite for efficient charge transfer. In addition, the electrical properties of the micro-photodiodes as are reflected in current/voltage traces have a profound influence on the charge delivery. For the first time the electrical properties of the entire system consisting of micro-photodiode array, electrode/electrolyte interface and tissue were studied. Our results indicate charged balanced operation of the device and the presence of a non-zero electrode polarization. The latter may be avoided, if an active current sink is employed in order to draw current to discharge the electrode capacitance.
Biomedical Microdevices 05/2001; 3(2):133-142. · 3.03 Impact Factor
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E Zrenner,
F Gekeler,
V P Gabel,
H G Graf, M Graf,
E Guenther,
H Haemmerle,
B Hoefflinger,
K Kobuch,
K Kohler,
W Nisch,
H Sachs,
B Schlosshauer,
M Schubert,
H Schwahn,
M Stelzle,
A Stett,
B Troeger,
S Weiss
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ABSTRACT: A survey is given on the status of developments, concerning a subretinal electronic microphotodiode array that aims at replacing degenerated photoreceptors. Various prototypes have been developed, tested, and implanted in various experimental animals up to 18 months. The fact that electrical responses were recorded from the visual cortex of pigs after electrical stimulation by subretinal electrodes and the fact that responses are also recorded in-vitro in degenerated rat retinae, shows the feasibility of this approach. However, there are a number of open questions concerning the biocompatibility, the long-time stability, and the type of transmitted image to be solved before application in patients can be considered.
Der Ophthalmologe 05/2001; 98(4):357-63. · 0.62 Impact Factor
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E. Zrenner,
F. Gekeler,
V.P. Gabel,
H.G. Graf, M. Graf,
E. Guenther,
H. Haemmerle,
B. Hoefflinger,
K. Kobuch,
K. Kohler,
W. Nisch,
H. Sachs,
B. Schloßhauer,
M. Schubert,
H. Schwahn,
M. Stelzle,
A. Stett,
B. Troeger,
S. Weiss
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ABSTRACT: Es wird eine Übersicht über den Stand der Entwicklungen eines subretinalen, elektronischen Mikrophotodioden-Arrays gegeben,
mit dem degenerierte Photorezeptoren ersetzt werden können. Verschiedene Prototypen wurden entwickelt, getestet und bei verschiedenen
Versuchstieren bis zur Dauer von 18 Monaten implantiert. Die Tatsache, dass mit subretinalen Elektroden elektrische Antworten
vom visuellen Kortex von Schweinen abgeleitet werden können und Antworten auch in vitro in Netzhäuten von Ratten mit Netzhautdegenerationen
nachweisbar sind, zeigt die Sinnhaftigkeit dieses Ansatzes. Allerdings sind noch wichtige Fragen der Biokompatibilität, der
Langzeitstabilität und der Art des vermittelbaren Bildeindrucks zu bearbeiten, bevor an einen Einsatz beim Menschen zu denken
ist.
A survey is given on the status of developments, concerning a subretinal electronic microphotodiode array that aims at replacing
degenerated photoreceptors. Various prototypes have been developed, tested, and implanted in various experimental animals
up to 18 months. The fact that electrical responses were recorded from the visual cortex of pigs after electrical stimulation
by subretinal electrodes and the fact that responses are also recorded in-vitro in degenerated rat retinae, shows the feasibility of this approach. However, there are a number of open questions concerning
the biocompatibility, the long-time stability, and the type of transmitted image to be solved before application in patients
can be considered.
Der Ophthalmologe 03/2001; 98(4):357-363. · 0.62 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Micro-photodiode arrays have been developed and are intended to
serve as a replacement for degenerated photoreceptor cells in the
retina. The chips are implanted into the sub-retinal space. Electric
current generated in tiny micro-photodiodes is delivered to the neuronal
network in the retina via micro-electrodes. Since the coupling between
electrode and tissue is capacitive of nature, only transient signals may
be used for stimulation. Accordingly, a high capacitance of the
interface between electrodes and tissue is an important prerequisite for
efficient charge transfer. In addition, the electric properties of the
micro-photodiodes as are reflected in current/voltage traces have a
profound influence on the overall charge delivery. Therefore, the entire
system made up of micro-photodiode array, electrode/electrolyte
interface and tissue has to be taken into consideration. Current
delivery has been both calculated and measured based on current/voltage
traces and electrode capacitance data. The authors' results indicate
charged balanced operation of the device and a non-zero electrode
polarization. The latter may be avoided, if an active current sink is
employed in order to draw backward current
Engineering in Medicine and Biology Society, 2000. Proceedings of the 22nd Annual International Conference of the IEEE; 02/2000
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ABSTRACT: The German `SubRet' consortium has fabricated various types of
microphotodiode arrays, the photovoltaic response of which will induce a
retina response after implantation in the subretinal space. Ultrathin
and flexible devices have been designed as well as CMOS-based chips with
different pixel sizes and electrode configurations. From in-vitro
electrostimulation studies, it becomes clear that a purely photovoltaic
mode of operation will not be feasible, but an additional energy input
by near-infrared radiation or radio frequency power transmission needs
to be incorporated. Implantation experiments on pigs and rabbits prove
the biocompatibility, general function and local stability of the
implants. The inner retina architecture is well preserved, and literally
no glia proliferation is found from long-term monitoring and
histological examination. In conclusion, the subretinal approach is very
promising and our results are encouraging, although major obstacles
cannot be excluded concerning the application in human
Systems, Man, and Cybernetics, 1999. IEEE SMC '99 Conference Proceedings. 1999 IEEE International Conference on; 02/1999
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E. Zrenner,
S. Weiss,
A. Stett,
B. Brunner,
V. R. Gabel, M. Graf,
H. G. Graf,
H. Haemmerle,
B. Hoefflinger,
K. Kobuch,
K. -D. Miliczek,
W. Nisch,
H. Sachs,
M. Stelzle
[show abstract]
[hide abstract]
ABSTRACT: The feasibility of a retinal prosthesis for the blind has been discussed since the 1950s. Early attempts to realize a subretinal
implantable prosthesis suffered from technical and microsurgical limitations at that time. Nowadays these problems can be
solved because of the amazing progress that has been made in the fields of intraocular surgery, silicon microfabrication and
our knowledge of the silicon/neuron junction. Therefore, a new attempt to develop a retinal prosthesis seems justified. While
other research groups1–3 have concentrated their efforts on the development of an epiretinal visual prosthesis, which receives energy and preprocessed
visual information via a relatively complex telemetric system, Chow and coworkers4–7 published the concept of a retinal implant consisting of thousands of microphotodiodes. The principle of this concept is
based on an implant that is placed in subretinal space and stimulates the underlying retinal cells with the photocurrents
generated solely from the incident light (Fig. 1).
12/1998: pages 497-505;
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Solid-State Device Research Conference, 1997. Proceeding of the 27th European; 10/1997
