Optically triggered surface channel MESFETs were fabricated on commercial polycrystalline diamond to be tested as
fast UV activated switches. Devices with an opaque-gate and asymmetric structure were designed in order to improve
charges photogeneration within gate-drain region. The sensitivity to UV light was demonstrated by using both modulated
over gap radiation and laser pulses at 193 nm, well over the diamond band gap. Linearity with the power light was
demonstrated as well as the parabolic dependence of the photogenerated current on the gate-source voltage when the
transistor is in saturation. The transient response to 193 nm laser pulses in the nanosecond regime shows as the
photogeneration process and charges collection to the drain contact are completed in a time scale of few nanoseconds.
Laser beam profiling technology in the UV spectrum of light is evolving with the increase of excimer lasers and lamps
applications, that span from lithography for VLSI circuits to eye surgery. The development of a beam-profiler, able to
capture the excimer laser single pulse and process the acquired pixel current signals in the time period between each
pulse, is mandatory for such applications. 1D and 2D array detectors have been realized on polycrystalline CVD
diamond specimens. The fast diamond photoresponse, in the ns time regime, suggests the suitability of such devices for
fine tuning feedback of high-power pulsed-laser cavities, whereas solar-blindness guarantees high performance in UV
beam diagnostics, also under high intensity background illumination. Offering unique properties in terms of thermal
conductivity and visible-light transparency, diamond represents one of the most suitable candidate for the detection of
high-power UV laser emission. The relatively high resistivity of diamond in the dark has allowed the fabrication of
photoconductive vertical pixel-detectors. A semitransparent light-receiving back-side contact has been used for detector
biasing. Each pixel signal has been conditioned by a multi-channel read-out electronics made up of a high-sensitive
integrator and a Σ-Δ A/D converter. The 500 μs conversion time has allowed a data acquisition rate up to 2 kSPS
(Sample Per Second).
Polycrystalline diamond detector prototypes suitable for x-ray spectroscopy were realized and tested. Thick diamond specimens, mechanically polished to reduce the surface roughness, were selected for prototypes development. Noble metal contacts were deposited on both faces, whereas multistrip structures were defined by photolithography on the growth face only with the aim of reducing the coupling capacitances and to allow characterization tests either in
planar or sandwich configuration. Leakage currents as low as 20 pA at 500 V were measured on a 270μm thick device. The x-ray sensitivity was tested monitoring the photocurrent as a function of the applied voltage under continuous 8.05 keV Cu Kα irradiation. Studies in pulsed mode were also performed by using a commercial miniature x-ray source. Pulse height distributions were carried out with a system composed of a charge-sensitive preamplifier and a digital pulse processor multi-channel analyzer. Analysis was carried out around Ta Lα and Cu Kα characteristic lines. Realized prototypes were able to resolve such two characteristic lines only 90 eV apart. Energy resolutions better than 3% have been evaluated for one of the prototype at 8.14 keV. Such features address very good energy resolving capabilities and the suitability of polished polycrystalline diamond in x-ray spectroscopy.
Conference Committee Involvement (1)
Independent Component Analyses, Wavelets, Neural Networks, Biosystems, and Nanoengineering VIII
7 April 2010 | Orlando, Florida, United States
SC715: Independent Component Analysis and Beyond: Blind Signal Processing and its Applications
Blind Signal Processing (BSP) is an emerging area of research and technology with solid theoretical foundations and many potential applications. The problems of separating or extracting of the source signals from sensor arrays, without knowledge of the transmission channel characteristics and the real sources, can be expressed briefly as a number of blind source separation (BSS) or related generalized component analysis (GCA) methods: Independent Component Analysis (ICA) (and its extensions), Sparse Component Analysis (SCA), Sparse Principal Component Analysis (SPCA), Non-negative Matrix Factorization (NMF), Time-Frequency Component Analyzer (TFCA) and Multichannel Blind Deconvolution (MBD). BSP is not limited to ICA or BSS. With BSP we aim to discover and validate principles or laws which govern relationships between inputs (hidden components) and outputs (observations) when the information about the propagation Multi-Input Multi-Output (MIMO) system and its inputs are limited or hindered. BSP incorporates many problems, like blind identification of channels of unknown systems or a problem of suitable decomposition of signals into basic latent (hidden) components which do not necessary represent true sources but rather some of their features or sub-components.
This four-hour course presents the fundamentals of blind signal processing, especially blind source separation and extraction, and in the remaining time discusses their applications in several important signal processing areas including estimation of sources, novel enhancement, denoising, artifact removal, filtering, detection, classification of multi-sensory signals and data, especially in biomedical applications and Brain Computer Interface (BCI).