Alien Registration- Tibbitts, Mercha J. (Millinocket, Penobscot County)

https://digitalmaine.com/alien_docs/7237/thumbnail.jp

Amorphous and Polycrystalline Photoconductors for Direct Conversion Flat Panel X-Ray Image Sensors

In the last ten to fifteen years there has been much research in using amorphous and polycrystalline semiconductors as x-ray photoconductors in various x-ray image sensor applications, most notably in flat panel x-ray imagers (FPXIs). We first outline the essential requirements for an ideal large area photoconductor for use in a FPXI, and discuss how some of the current amorphous and polycrystalline semiconductors fulfill these requirements. At present, only stabilized amorphous selenium (doped and alloyed a-Se) has been commercialized, and FPXIs based on a-Se are particularly suitable for mammography, operating at the ideal limit of high detective quantum efficiency (DQE). Further, these FPXIs can also be used in real-time, and have already been used in such applications as tomosynthesis. We discuss some of the important attributes of amorphous and polycrystalline x-ray photoconductors such as their large area deposition ability, charge collection efficiency, x-ray sensitivity, DQE, modulation transfer function (MTF) and the importance of the dark current. We show the importance of charge trapping in limiting not only the sensitivity but also the resolution of these detectors. Limitations on the maximum acceptable dark current and the corresponding charge collection efficiency jointly impose a practical constraint that many photoconductors fail to satisfy. We discuss the case of a-Se in which the dark current was brought down by three orders of magnitude by the use of special blocking layers to satisfy the dark current constraint. There are also a number of polycrystalline photoconductors, HgI2 and PbO being good examples, that show potential for commercialization in the same way that multilayer stabilized a-Se x-ray photoconductors were developed for commercial applications. We highlight the unique nature of avalanche multiplication in a-Se and how it has led to the development of the commercial HARP video-tube. An all solid state version of the HARP has been recently demonstrated with excellent avalanche gains; the latter is expected to lead to a number of novel imaging device applications that would be quantum noise limited. While passive pixel sensors use one TFT (thin film transistor) as a switch at the pixel, active pixel sensors (APSs) have two or more transistors and provide gain at the pixel level. The advantages of APS based x-ray imagers are also discussed with examples

Low frequency noise in thin film transistors: effect of the laser annealing of the active layer

International audienc

Alien Registration- Tibbitts, Mercha J. (Millinocket, Penobscot County)

https://digitalmaine.com/alien_docs/7237/thumbnail.jp

ANALYSE DES MECANISMES DE CONDUCTION ET DE BRUIT EN 1/F DANS LES TRANSISTORS EN COUCHES MINCES DE SILICIUM POLYCRISTALLIN

NOTRE ANALYSE DES PROPRIETES ELECTRIQUES DES TRANSISTORS EN COUCHES MINCES DE SILICIUM POLYCRISTALLIN (POLY-SI TFTS) MET L'ACCENT SUR LE ROLE PRIMORDIAL, DANS LES MECANISMES DE TRANSPORT DE CHARGES ET DE BRUIT EXCEDENTAIRE EN 1/F, DES DISCONTINUITES ELECTRIQUES (BARRIERES DE POTENTIEL) INDUITES PAR LES ETATS CHARGES AUX JOINTS DE GRAINS. UNE ETUDE COMPAREE DE LA CONDUCTION ET DU BRUIT BASSE FREQUENCE MET EN EVIDENCE DEUX REGIMES L'UN CORRESPONDANT A UNE CONDUCTION THERMOIONIQUE ET L'AUTRE A UNE CONDUCTION LIMITEE PAR LA DIFFUSION AUX INTERFACES. DANS LE PREMIER REGIME, QUI SE DEMARQUE LE PLUS DE LA SITUATION DES TRANSISTORS MOS, NOUS AVONS EXPERIMENTALEMENT MONTRE QUE LE COURANT OBEIT A LA LOI EMPIRIQUE DE COMPENSATION (MEYER-NELDEL) DECRIVANT UNE ACTIVATION THERMIQUE NON IDEALE. LE FACTEUR D'IDEALITE DE L'ENERGIE D'ACTIVATION EST ATTRIBUE A LA VARIATION DU QUASI NIVEAU DE FERMI DANS LA ZONE DE DEPLETION DE PART ET D'AUTRE DES JOINTS DE GRAINS. IL PEUT ETRE UTILISE POUR QUALIFIER LA DISTRIBUTION SPATIALE DES DEFAUTS DANS LA COUCHE ACTIVE POLYCRISTALLINE. DANS CE MEME REGIME, LES VALEURS IMPORTANTES (JUSQU'A 2.10 - 1) DU PARAMETRE DE NORMALISATION DU BRUIT EN 1/F TRADUISENT L'EFFET DE LA DENSIFICATION DES LIGNES DE COURANT DANS LE CANAL HETEROGENE. UNE MODELISATION PAR LES METHODES DU CHAMP D'IMPEDANCE ET DU COURANT ADJOINT, AINSI QUE DES MESURES DE BRUIT EN FONCTION DE LA TEMPERATURE MONTRENT QUE LA VALEUR DU PARAMETRE DE BRUIT EST RELIEE A LA HAUTEUR DES BARRIERES DE POTENTIEL ET QUE LE BRUIT EN 1/F EST THERMIQUEMENT DESACTIVE. CES ENERGIES DE DESACTIVATION DU BRUIT ET D'ACTIVATION DU COURANT PEUVENT PERMETTRE DE CARACTERISER L'ECART TYPE DE LA HAUTEUR MOYENNE DES BARRIERES DE POTENTIEL. CES INTERPRETATIONS CONDUISENT A PROPOSER UNE METHODE EXPERIMENTALE PERMETTANT, EN S'AFFRANCHISSANT DE L'INCIDENCE DES BARRIERES DE POTENTIEL, D'ACCEDER A UN PARAMETRE DE BRUIT CARACTERISTIQUE DU COUPLE MATERIAU SEMI-CONDUCTEUR ET INTERFACE AVEC L'OXYDE DE GRILLE.CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

Comment on comparison of excess 1/f noise spectra in trimmed and untrimmed thick film resistors

The paper by Peled et al. (2000, International Journal of Electronics, 87, 1-9) reports a quantitative comparison between the low frequency excess 1/fnoise obtained on trimmed and untrimmed bismuth ruthenate thickfilm resistors (TFRs). The empirical relation of Hooge was used to quantify and compare the 1/fnoise level. Peled et al. concluded that the Hooge parameter aH increases for trimmed TFRs. In this comment it will be shown that misusing the Hooge relation for nonhomogeneous materials can lead to misleading high apparent a values describing not the 1/fproperties of the material but the current crowding in the material