IEE Proceedings - Circuits, Devices and Systems
Volume 150, Issue 4, August 2003
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Volume 150, Issue 4
August 2003
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- Author(s): Safa Kasap
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 150, Issue 4, p. 233 –234
- DOI: 10.1049/ip-cds:20030826
- Type: Article
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- Author(s): J.A. Theil
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 150, Issue 4, p. 235 –249
- DOI: 10.1049/ip-cds:20030529
- Type: Article
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Integrated circuit manufacturing capabilities have reached the stage where it is technically and economically feasible to create new components that may be monolithically combined with them to create unique devices. One of the most elementary yet reliable of such monolithic components is the elevated diode. These diodes may be used to detect or generate light for parallel photodetection or photogeneration applications, such as imaging, chemical detection, or displays. Because new materials are required for all implementations, various process flows and integration challenges are discussed. In particular, focus on interconnection to the top and bottom of the junction is considered. In addition, since the elevated diode concept gives the designer control of such parameters as junction thickness, semiconductor bandgap, and light emission spectrum, the issues that drive junction design are presented for both the elevated photodiode and elevated OLED. Finally, because of the decoupling of diode size and pixel size, and the presence of new materials, novel pixel circuits are considered to achieve novel or greater pixel-level functionality, and because material behaviour may dictate the method to drive the junction. The new possibilities that these junctions present create a new realm of applications and are initial examples of a new class of devices called monolithic instruments. - Author(s): R.A. Street ; J.-P. Lu ; S.R. Ready
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 150, Issue 4, p. 250 –257
- DOI: 10.1049/ip-cds:20030555
- Type: Article
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Flat panel X-ray imagers using amorphous silicon active matrix addressing have been introduced to the medical imaging market at sizes up to 40×40 cm and with up to 10 million pixels. Some new technology developments, which can further increase the performance of these devices, are described. High atomic number polycrystalline X-ray photoconductors can operate near the theoretical sensitivity and at reasonably low bias voltages. The higher sensitivity obtained in HgI2 allows single-photon detection, which opens up new imaging opportunities. Another approach to improve sensitivity is to integrate an amplifier at the pixel level, which requires laser-recrystallised polysilicon transistors. A pixel-level source follower amplifier is shown to have enough gain to overcome other noise sources. A three-dimensional device structure is needed to accommodate the pixel electronics, and so the sensor is deposited on top of the electronics, separated by a thick passivation layer. Future possible detector technologies based on printing and organic semiconductors are discussed. - Author(s): M.Z. Kabir ; S.O. Kasap ; W. Zhao ; J.A. Rowlands
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 150, Issue 4, p. 258 –266
- DOI: 10.1049/ip-cds:20030663
- Type: Article
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Imaging characteristics of photoconductive flat panel X-ray image detectors, such as X-ray sensitivity, detective quantum efficiency (DQE), and resolution in terms of the modulation transfer function (MTF) are examined with applications to amorphous selenium (a-Se), polycrystalline HgI2 and CdZnTe detectors. A theoretical model has been developed for the calculation of X-ray sensitivity of a pixellated detector by using the Shockley–Ramo theorem, the weighting potential of the individual pixel and the final trapped charge distribution across the photoconductor. The X-ray sensitivity of pixellated X-ray detectors mostly depends on the mobility and lifetime product of charges that move towards the pixel electrodes, and the extent of dependence increases with decreasing pixel per unit detector thickness. A cascaded linear system model that includes incomplete charge collection and interaction depth dependent conversion gain and charge collection stages is considered for the calculation of the zero spatial frequency detective quantum efficiency DQE(0) of a direct conversion X-ray image detector. The DQE(0) performance of a-Se, HgI2 and CdZnTe detectors is examined for fluoroscopic applications. It is shown that, in addition to high quantum efficiency, both high conversion gain and high charge collection efficiency are required to improve the DQE performance of an X-ray image detector. The factors affecting the MTF of a-Se flat-panel detectors for digital mammography are investigated. Both theoretical and experimental methods are examined. A theoretical model has been developed based on cascaded linear system analysis with parallel processes to take into account the effect of K-fluorescence. This model has been used to understand the performance of a small-area prototype detector with 85 μm pixel size. The presampling MTF of the prototype has been measured and compared to a theoretical calculation based on the model. The calculation shows that K-fluorescence accounts for a 15% reduction in the MTF at the Nyquist frequency of the prototype detector. The measurement of presampling MTF of the prototype detector reveals an additional source of blurring, which is probably due to charge carrier trapping in the blocking layer at the interface between a-Se and the active matrix. This introduces a drop in presampling MTF at high spatial frequencies. - Author(s): K.S. Karim ; A. Nathan ; J.A. Rowlands ; S.O. Kasap
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 150, Issue 4, p. 267 –273
- DOI: 10.1049/ip-cds:20030602
- Type: Article
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The most widely used pixel architecture is a passive pixel sensor (PPS) where the pixel consists of a detector and an amorphous silicon (a-Si) thin-film transistor (TFT) readout switch. While the PPS has the advantage of being compact and amenable towards high-resolution imaging, the column charge amplifiers add a large noise component to the PPS that reduces the minimum readable sensor input signal. The authors investigate a prototype current-mediated, active pixel sensor (C-APS) X-ray detection array for diagnostic medical imaging applications. Preliminary tests indicate linear performance, and a programmable circuit gain via choice of supply voltage and sampling time. In addition, the performance of C-APS amplified pixels is examined from both a-Si TFT metastability and noise performance perspectives. Theory and measurements indicate that the C-APS pixel architecture is promising for diagnostic medical imaging modalities including low-noise, real-time fluoroscopy. - Author(s): T. Kosteski ; N.P. Kherani ; P. Stradins ; F. Gaspari ; W.T. Shmayda ; L.S. Sidhu ; S. Zukotynski
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 150, Issue 4, p. 274 –281
- DOI: 10.1049/ip-cds:20030628
- Type: Article
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The introduction of tritium into hydrogenated amorphous silicon has given rise to a novel material with interesting physical properties and potential applications. Tritium undergoes radioactive decay, transforming into 3He+ and emitting an electron with average energy 5.7 keV, at a rate equivalent to a half-life of 12.3 years. The decay of tritium results in the creation of electron–hole pairs and in the formation of dangling bonds. Infrared spectroscopy and effusion measurements were used to analyse tritium bonding in the silicon network. Electron spin resonance and photoluminescence of tritiated amorphous silicon were examined as a function of time to study the evolution of dangling bonds. Thermal annealing was used to study metastability of dangling bonds in the material. Electrical characteristics of pin diodes containing tritium in the intrinsic layer were investigated. The application of tritiated–hydrogenated amorphous silicon in betavoltaic devices is presented. - Author(s): U. Das ; S. Morrison ; E. Centurioni ; A. Madan
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 150, Issue 4, p. 282 –286
- DOI: 10.1049/ip-cds:20030627
- Type: Article
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Pulsed plasma enhanced chemical vapour deposition (PECVD) involves modulation of standard 13.56 MHz RF plasma in the kilohertz range. This allows an increase in the electron density during the ‘ON’ cycle, while in the ‘OFF’ cycle, neutralising the ions responsible for dust formation in the plasma. The authors report the development of state-of-the-art nanocrystalline Si (nc-Si:H) materials using a pulsed PECVD technique with 220 crystallite orientation, grain size of ∼200 Å, low O concentration and a minority carrier diffusion length Ld of ∼1.2 μm. The crucial effects of the p/i interface and the incubation layer have been investigated and an efficiency of ∼7.5% for a single junction nc-Si:H p-i-n device has been achieved for an i-layer thickness of 1.4 μm, using non-optimised textured substrates. - Author(s): C. Ornaghi ; M. Stöger ; G. Beaucarne ; J. Poortmans ; P. Schattschneider
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 150, Issue 4, p. 287 –292
- DOI: 10.1049/ip-cds:20030630
- Type: Article
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Thin film polycrystalline silicon solar cells on foreign substrates are viewed as one of the most promising approaches to cost reduction in photovoltaics. To enhance the quality of the film, the use of ‘seeding layers’ prior to deposition of active material is being investigated. It has been shown that a phenomenon suitable to create such a seeding layer is the aluminium-induced crystallisation of amorphous silicon. Previous work mainly considered glass as the substrate of choice, thereby introducing limitations on the deposition temperature. Results concerning the application of such a technique to ceramic substrates (allowing the use of high-temperature CVD) are described. Also, the first reported results of a solar cell made in silicon deposited on these seeding layers are presented. - Author(s): R. Bilyalov ; J. Poortmans ; R. Sharafutdinov ; S. Khmel ; V. Schukin ; O. Semenova ; L. Fedina
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 150, Issue 4, p. 293 –299
- DOI: 10.1049/ip-cds:20030665
- Type: Article
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A new gas-jet electron beam plasma enhanced chemical vapour deposition (GJEB PECVD) method for high-rate deposition of crystalline silicon films is presented. The method is based on the activation of initial gas molecules in an electron beam plasma and fast convective transfer of the radicals to a substrate by means of a supersonic free jet. Nanocrystalline, microcrystalline and polycrystalline Si film growth on different foreign substrates is investigated using morphological and optical analyses in dependence on the temperature of the substrate and its distance from the nozzle. It is shown that a middle range of substrate distance is required to avoid crystallinity damage by heavy ions while still keeping their effect on grain nucleation. In this case, well shaped crystalline grains embedded with a ‘highly ordered’ amorphous phase are found in Si films grown at a low temperature at the edge of crystalline growth. - Author(s): F. Finger ; R. Carius ; T. Dylla ; S. Klein ; S. Okur ; M. Günes
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 150, Issue 4, p. 300 –308
- DOI: 10.1049/ip-cds:20030636
- Type: Article
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The development of microcrystalline silicon (μc-Si:H) for solar cells has made good progress with efficiencies better than those of amorphous silicon (a-Si:H) devices. Of particular interest is the absence of light-induced degradation in highly crystalline μc-Si:H. However, the highest efficiencies are obtained with material which may still include a-Si:H regions and light-induced changes may be expected in such material. On the other hand, material of high crystallinity is susceptible to in-diffusion of atmospheric gases which, through adsorption or oxidation, affect the electronic transport. Investigations are presented of such effects concerning the stability of μc-Si:H films and solar cells prepared by plasma-enhanced chemical vapour deposition and hot wire chemical vapour deposition. - Author(s): K. Lips ; C. Boehme ; W. Fuhs
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 150, Issue 4, p. 309 –315
- DOI: 10.1049/ip-cds:20030578
- Type: Article
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A review of recombination in silicon thin-film solar cells studied by means of electrically detected magnetic resonance (EDMR) is presented. It is shown that the EDMR results in μc-Si:H p-i-n solar cells can be described by a simple diffusion model that was developed for crystalline silicon p-n junctions assuming that recombination is dominated by dangling bonds in the space charge region. The results are compared to a-Si:H p-i-n cells and discussed in a recombination model involving the excited states of charged dangling bonds. - Author(s): V.L. Dalal ; J.H. Zhu ; M. Welsh ; M. Noack
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 150, Issue 4, p. 316 –321
- DOI: 10.1049/ip-cds:20030629
- Type: Article
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The properties of microcrystalline Si:H materials and solar cells fabricated using remote, low pressure ECR (electron cyclotron resonance) plasma deposition are described. p+nn+ junction solar cells were deposited at 275–325°C on stainless steel substrates using mixtures of silane and hydrogen. Microcrystalline layers and solar cells could be produced even for low dilution ratio of hydrogen/silane of 8:1. It was found that once crystallisation started, one could decrease the hydrogen/silane ratio and still obtain microcrystalline Si:H solar cells. The voltage of the solar cells could be improved by tailoring the interface between p+ and n layers. An amorphous interfacial layer improved the voltage. A thin amorphous Si:H layer at the back, between n+ and n layers was used to significantly reduce the shunt resistance. Standard device analyses, including dark I(V) curves and capacitance measured at several frequencies, revealed that device characteristics could be understood in terms of a standard Si diode model. The doping densities in the n layer were found to be in the 1×1015 to 2×1016/cm3 range and could be adjusted by altering the amount of compensatory B doping of the layer. The influence of the addition of He dilution to the mixture was also studied, and it was found that He degraded the crystallinity, though it increased the growth rate and open-circuit voltage. - Author(s): A. Kumar ; K. Sakariya ; P. Servati ; S. Alexander ; D. Striakhilev ; K.S. Karim ; A. Nathan ; M. Hack ; E. Williams ; G.E. Jabbour
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 150, Issue 4, p. 322 –328
- DOI: 10.1049/ip-cds:20030730
- Type: Article
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Design considerations are presented for a-Si:H based AMOLED display backplanes, including 2-TFT voltage-programmed and 4-TFT threshold-voltage-shift-resistant current-programmed circuits. The RC equivalent models of voltage-programmed and current-programmed pixels are derived, based on which array simulations are performed. Array size scalability and optimal driving requirements for a-Si:H AMOLED pixels are also presented. The TFTs used were fabricated in-house and the array under consideration is a (320×240) QVGA operating at 60 frames/s. - Author(s): A. Nathan ; P. Servati ; K.S. Karim ; D. Striakhilev ; A. Sazonov
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 150, Issue 4, p. 329 –338
- DOI: 10.1049/ip-cds:20030554
- Type: Article
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The authors review amorphous silicon (a-Si:H) thin film transistor (TFT) integration and design considerations, including stability, and present examples of integration for two application areas: active matrix organic light emitting diode (AMOLED) displays and active matrix flat panel imagers (AMFPIs) for medical imaging. Pixel architectures and TFT circuit topologies are described that are amenable for vertically integrated, high aperture ratio or high fill factor pixels. Here, the OLED or detector layers are integrated directly above the TFT circuit layer to provide an active pixel area that is at least 80% of the total pixel area with an aperture ratio or fill factor that remains virtually independent of scaling. The design is based on physically-based compact TFT models, which accurately predict both static and dynamic behaviour. - Author(s): I-C. Cheng and S. Wagner
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 150, Issue 4, p. 339 –344
- DOI: 10.1049/ip-cds:20030573
- Type: Article
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P-channel and n-channel thin film transistors (TFTs) can be made from directly deposited nanocrystalline silicon (nc-Si:H) at temperatures as low as 150°C. A staggered top gate, bottom source/drain geometry, which is adapted to the structural evolution of nc-Si:H, ensures that the channel is the last-to-grow layer, avoids plasma etch damage, and opens a wide process window for source/drain patterning. The TFT structure is fabricated on top of a ∼50 nm thick intrinsic nc-Si:H seed layer, which serves to develop the crystalline structure of the channel layer. A hole mobility of ∼0.2 cm2 V−1 s−1 and an electron mobility of ∼40 cm2 V−1 s−1 are obtained in TFTs on glass substrates, at a maximum process temperature of 150°C. The processes have been integrated for p- and n-channel TFT fabrication on single glass or Kapton E polyimide substrates. The p-channel TFTs reach a hole mobility of ∼0.2 cm2 V−1 s−1 on glass and ∼0.17 cm2 V−1 s−1 on Kapton, and the n-channel TFTs have an electron mobility of ∼30 cm2 V−1 s−1 on glass and ∼23 cm2 V−1 s−1 on Kapton. These mobility values suggest that directly deposited nc-Si:H is an attractive channel material for realising CMOS on plastic. However, high gate leakage and shifts in the TFT characteristics indicate that the gate dielectric and the channel layer/dielectric interface are not yet ready for CMOS fabrication. - Author(s): R.E. Johanson ; M. Günes ; S.O. Kasap
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 150, Issue 4, p. 345 –349
- DOI: 10.1049/ip-cds:20030749
- Type: Article
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Measurements were made of conductance noise of a-Si:H and a-Si1−xGex:H in two different geometries: one where the current flow is transverse to the surface and the other where it is longitudinal to the surface. Because of the large change in sample resistance between the two geometries, it was not possible to measure both geometries at the same temperature. For both geometries, alloying with up to 40% Ge reduces the noise magnitude by several orders of magnitude over that found in a-Si:H. The decrease is incompatible with several popular noise models. Extrapolating the temperature trends for each geometry shows that it is possible that the noise observed in the transverse samples has the same origin as the higher frequency part of the double power law spectra observed in the longitudinal samples. - Author(s): F.G. Della Corte ; F. Pezzimenti ; F.G. Della Corte
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 150, Issue 4, p. 350 –354
- DOI: 10.1049/ip-cds:20030577
- Type: Article
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Results from a detailed simulation study are presented to help evaluate the pros and cons of a wide-gap hydrogenated amorphous silicon emitter (a-Si:H) introduced to improve the injection efficiency at the emitter–base junction of a GaAs bipolar transistor. For a set of devices withstanding the same maximum emitter–collector voltage, it is shown that the current gain, besides a net dependence on the defect state concentration at the emitter–base interface, is also strongly influenced by the base thickness and doping. The base thickness, however, has a weak impact on the cut-off frequency, which in turn shows a clear dependence on the emitter electron mobility. The study predicts that the current thin film silicon technology would allow the fabrication of a transistor performing a DC current gain close to 3000 and a cut-off frequency in excess of 15 GHz. Owing to the simplicity of fabrication, such a device could represent an effective way of adding a bipolar stage to a GaAs MESFET IC without resorting to AlGaAs/GaAs heterostructures. - Author(s): A. Tsargorodskaya ; A.V. Nabok ; A.K. Ray
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 150, Issue 4, p. 355 –360
- DOI: 10.1049/ip-cds:20030640
- Type: Article
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Electroluminescence (EL) of porous silicon (PS) samples was studied at anodic polarisation using neutral electrolyte contact. SEM and AFM morphology study of PS revealed its complex structure comprising features with micrometre and tens of nanometre dimensions. The observed features of EL, including its degradation during anodisation, were discussed in terms of a phenomenological model of a chemically modified silicon surface. The adsorption of polyelectrolytes polyallylamine (PAA) and polysterylsulphonate (PSS) demonstrated sufficient improvement of EL stability. The effect of adsorption of protein bovine serum albumin (BSA) on EL quenching was studied. - Author(s): K. Arshak and O. Korostynska
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 150, Issue 4, p. 361 –366
- DOI: 10.1049/ip-cds:20030664
- Type: Article
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Optical, electrical and structural properties of metal oxide thin films of tellurium dioxide (TeO2), indium oxide (In2O3) and silicon monoxide (SiO) and their mixtures were studied in terms of gamma radiation influence. These films were prepared using the thermal vacuum evaporation technique. 60Co and 137Cs sources were used to expose the samples to γ-radiation. It was found that the optical band gap values decreased with increasing radiation dose. The radiation induced changes in the electrical properties of these films. Devices with resistor-type structures and p-n junctions were studied. Irradiation resulted in the degradation of the device performance, e.g. current–voltage characteristics of these devices experienced significant alterations. It was observed that values of current were increased with increasing radiation dose. The response of these devices to radiation was found to be composition-dependent. Radiation-induced changes in the structure and surface morphology of In2O3/SiO films were examined by scanning electron microscopy and X-ray diffraction. The irradiation of these thin films with a dose of 8160 μSv led to a change in their phase from amorphous to partially crystallised. - Author(s): R. Çapan ; A.K. Hassan ; A.V. Nabok ; A.K. Ray ; T.H. Richardson ; M.C. Simmonds ; C. Sammon
- Source: IEE Proceedings - Circuits, Devices and Systems, Volume 150, Issue 4, p. 367 –371
- DOI: 10.1049/ip-cds:20030556
- Type: Article
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Non-centrosymmetric alternate-layer Langmuir–Blodgett (LB) films of stearic acid and eicosylamine molecules were treated with a twelve-hour-long exposure of hydrogen sulphide (H2S) gas. Surface plasmon resonance (SPR) experiments are carried out to monitor the change in optical properties of composite films. Structural analysis using atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy give a positive identification of the presence of cadmium sulphide (CdS) nanoparticles after the treatment. Quasistatic measurements give smaller pyroelectric activity in H2S-gas-treated LB films than untreated ones.
Editorial: Amorphous and microcrystalline semiconductors
Advances in elevated diode technologies for integrated circuits: progress towards monolithic instruments
New materials and processes for flat panel X-ray detectors
Direct conversion X-ray sensors: sensitivity, DQE and MTF
X-ray detector with on-pixel amplification for large area diagnostic medical imaging
Tritiated amorphous silicon betavoltaic devices
Thin film silicon materials and solar cells grown by pulsed PECVD technique
Thin film polycrystalline silicon solar cell on ceramics with a seeding layer formed via aluminium-induced crystallisation of amorphous silicon
Microcrystalline and polycrystalline silicon films for solar cells obtained by gas-jet electron-beam PECVD method
Stability of microcrystalline silicon for thin film solar cell applications
Recombination in silicon thin-film solar cells: a study of electrically detected magnetic resonance
Microcrystalline Si:H solar cells fabricated using ECR plasma deposition
Design considerations for active matrix organic light emitting diode arrays
Thin film transistor integration on glass and plastic substrates in amorphous silicon technology
Nanocrystalline silicon thin film transistors
1/f noise in hydrogenated amorphous silicon–germanium alloys
Design of a-Si:H/GaAs heterojunction bipolar transistors with improved DC and AC characteristics
Study of electroluminescence in porous silicon for sensing applications
Radiation-induced changes in thin film structures
Formation of nanocomposite Langmuir–Blodgett alternate multilayers
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