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Poly-Si Devices and Applications, IEE Colloquium on

Date 23-24 Mar 1993

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Displaying Results 1 - 25 of 28
  • Polysilicon for bipolar technology and circuits

    Publication Year: 1993 , Page(s): 11/1 - 11/4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (284 KB)  

    The properties of polysilicon emitter contacts in bipolar transistors are discussed. Self-aligned processes using single and double polysilicon layer technology such as SICOS and trench isolated bipolar technology, and the implementation of vertical pnp polysilicon emitter transistors in complementary bipolar technology are reviewed. The performances of state of the art digital ECL bipolar circuits and of bipolar SRAMs and PROMs are presented View full abstract»

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  • In-situ phosphorous doped VLPCVD poly-Si layers for polysilicon thin film transistors

    Publication Year: 1993 , Page(s): 10/1 - 10/4
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (236 KB)  

    The authors have developed a Very Low Pressure Chemical Vapor Deposition process (VLPCVD) allowing in-situ phosphorous doping and have tried both to control the doping level in a large range and to get a related high conductivity. They show that controlling the deposition parameters allows one to optimize the film conductivity, free carrier mobility, and doping efficiency. This process has been used to fabricate source and drain regions of thin film transistors View full abstract»

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  • High field effects in polysilicon thin film transistors

    Publication Year: 1993 , Page(s): 35
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  • Stability of microdefects in poly-Si films grown by α-Si solid state crystallization

    Publication Year: 1993 , Page(s): 21/1 - 21/4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    For poly-Si thin film transistors (TFTs) in order to improve the electrical characteristics of the poly-Si films a better understanding of the structure of the films and the related defects versus grain size is needed. In this contribution the structure and the stability of defects of the α-Si films which are formed by low temperature solid state crystallization and subsequent annealing is discussed. Amorphous silicon films were deposited on glass by the LPCVD and annealed at 610°C for 8 h. Most of the crystallites exhibit a three dimensional ellipsoidal shape. The large axis of the ellipsoid coincides with the ⟨112⟩ crystallographic direction while the smallest one is along the ⟨111⟩ direction. In the core of the crystallites multiple (111) type twins are formed along the ⟨112⟩ direction View full abstract»

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  • Observation and modelling of the gate-source capacitance peak in polysilicon TFTs

    Publication Year: 1993 , Page(s): 8/1 - 8/4
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (124 KB)  

    Analysis and modelling of the terminal capacitances of polysilicon TFTs are of great interest in view of the design and fabrication of digital and analog circuits. The authors present for the first time measurements of the gate-source capacitance (Cgs) in a wide frequency range (20 Hz-10 kHz), and propose a new model to explain the observed behaviour View full abstract»

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  • Numerical simulations of poly-crystalline silicon thin film transistors including leakage effects

    Publication Year: 1993 , Page(s): 23/1 - 23/4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (176 KB)  

    The authors show good agreement between numerical simulations and experimental data of the electrical characteristics of poly-crystalline silicon (poly-Si) thin film transistors (TFTs). They focus on the field-effect mobility, threshold voltage, leakage current, and the so-called `kink' effect. They demonstrate how the `on-state' performance of these devices can be modeled by a uniform effective medium approach and show how their characteristics vary with fabrication process, which in turn determines the effective density of states (DOS) distribution. Leakage currents are modeled by adding a single grain boundary with a trap to band tunneling mechanism View full abstract»

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  • Low temperature (⩽600°C) poly-silicon thin film transistors

    Publication Year: 1993 , Page(s): 5/1 - 5/4
    Cited by:  Patents (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (172 KB)  

    The authors have fabricated thin film transistors using UHVCVD silicon layers and DECR PECVD gate oxides. With this combination of manufacturing processes, TFTs with an acceptable level of off-current have been obtained without the need to use lightly doped drain (LDD) or field plate structures. The results could probably be improved by the use of Si2H6 as parent gas for the UHV chemical vapour deposition of silicon since the deposition rate would increase, leading to lower levels of contamination in the films View full abstract»

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  • Design and operation of ploy-Si circuits on glass

    Publication Year: 1993 , Page(s): 97 - 102
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  • Comparison of the hydrogenation techniques on polysilicon TFTs

    Publication Year: 1993 , Page(s): 22/1 - 22/4
    Cited by:  Patents (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (160 KB)  

    Hydrogenation is a key technique to improve the electrical performances of the polysilicon thin film transistors (TFT). However, the modifications of the electrical properties strongly depend on the techniques of hydrogenation. Usually, hydrogen passivation of polysilicon films is performed using RF plasma of hydrogen (1) or by the use of silicon nitride films deposited by plasma enhanced chemical vapor deposition (PECVD) on the polysilicon TFT (2). However, a new technique of hydrogenation based on the electron-cyclotron resonance plasma (ECR) is under investigation in several laboratories (3). In this paper, early electrical results on the hydrogenation of polysilicon TFTs using a new microwave plasma technique which does not use a magnetic field as the ECR technique is presented and compared with those obtained with the silicon nitride passivation technique View full abstract»

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  • The current status and future prospects of poly-Si devices

    Publication Year: 1993 , Page(s): 1/1 - 1/4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (240 KB)  

    Over the past twenty years the use of thin-film transistors (TFTs) deposited onto glass substrates has developed into a new discipline, large-area microelectronics. This is now the subject of intensive industrial activity because of its applications, particularly the application to active-matrix addressing of LCDs. The transistors used in large-area microelectronics are insulated-gate FETs. Three thin-film semiconductors have received significant attention for use as the channel material, namely cadmium selenide, amorphous silicon, and polycrystalline silicon. It is becoming increasingly clear that polysilicon offers the best overall combination of properties. Salient points in this respect are: superior stability and lifetime; good performance at high ambient temperatures; no photo effect; CMOS compatibility; mobilities sufficient for useful circuitry; small, self-aligned, transistors; low parasitic capacitance; and use of intrastructure of silicon science and technology View full abstract»

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  • A study of the effect of in situ doping on the crystallinity of LPCVD polysilicon

    Publication Year: 1993 , Page(s): 19/1 - 19/4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    Results are presented for the degree of crystallinity, determined by Raman spectroscopy, of in situ B doped LPCVD polysilicon as a function of deposition temperature. The results are compared with those reported in the literature for P doped polysilicon and it is found that for B doping full crystallinity of the layer is achieved at a significantly lower deposition temperature than is required for P doping. An attempt to understand this effect is made in terms of a quantitative model which allows an estimation of values for silicon self-diffusivity and which is in accord with the experimental observations View full abstract»

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  • Poly-Si on glass technology for liquid crystal displays

    Publication Year: 1993 , Page(s): 4/1 - 4/5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    Since the initial demonstration of poly-Si addressed liquid crystal displays with integrated drive circuits, based on high temperature integrated circuit processes on quartz substrates, there has been considerable interest in developing a comparable low temperature process for implementation on inexpensive glass substrates. In this paper the basic operating principles of an active matrix addressed flat panel display are summarised and the material property requirement, principally carrier mobility, for integrated drive circuits discussed. The principle features and issues of the monolithic and laser based hybrid approaches are reviewed View full abstract»

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  • Large area shower implanter for thin film transistors

    Publication Year: 1993 , Page(s): 6/1 - 6/4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (168 KB)  

    Using a 30 cm diameter RIPE ion source, a large area low energy ion shower implanter has been developed for low cost TFT fabrication. The beam current density uniformity is ±3.5% over the centre 20 cm diameter. With magnetic field of 200 Gauss and RF power of 450 W, the extracted ion current density at 3×10-4 mbar hydrogen pressure and 3 KV screen voltage was 100 μA/cm2. For 3 KeV and five minute phosphorus implantation, dose and projected range are 2.48×1016 cm-2 and 83 Å, respectively. The fine rectifier characteristics of implanted diodes show that this shower implanter is suitable for TFT contact layer formation View full abstract»

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  • Poly-Si drive circuits for liquid crystal displays

    Publication Year: 1993 , Page(s): 109 - 112
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  • Design and operation of poly-Si analogue circuits

    Publication Year: 1993 , Page(s): 29/1 - 29/4
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    Describes the use of poly-Si thin film transistors (TFTs) to fabricate analogue circuits and in particular operational amplifiers (op amps). A brief description of the poly-Si technology peculiarities and their effects on the design of analogue circuits are given and some results obtained with low temperature processes on two designs discussed View full abstract»

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  • The stability of devices and circuits formed using various low temperature poly-Si TFT technologies

    Publication Year: 1993 , Page(s): 24/1 - 24/4
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    The author discusses instability due to hot carrier degradation. It has been shown that degradations to both the drive current and the leakage current of TFTs result at high drain biases. This occurs for both high and low temperature processed devices, and for both p and n channels. The evidence suggests that this is due to a combination of effects, the formation of interface acceptor and donor states, and to electron and hole trapping in the gate oxide. In view of the importance of hot carrier degradation effects in poly-Si TFTs the author concentrates on these effects, their dependencies on fabrication technology and device structure, and their control View full abstract»

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  • Process and device modelling of VLSI polysilicon components

    Publication Year: 1993 , Page(s): 14/1 - 14/4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (176 KB)  

    One of the universally used materials in key device components is polysilicon: used in bipolar VLSI for both emitter and contact regions of the bipolar transistor and resistor structures; and in CMOS VLSI for the gate contact and advanced isolation regions. Progress in simulation of some of these important structures using the 2D process simulator STORM and device simulator HFIELDS is presented. The polysilicon process model utilized in these simulators incorporates the influence of polysilicon materiel properties and processes on dopant and mechanical stress distributions as well as device characteristics. Examples demonstrate its application to simulation of processes and devices from current industrial VLSI technology View full abstract»

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  • Characterisation of trapping states in poly-Si thin film transistors

    Publication Year: 1993 , Page(s): 7/1 - 7/4
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    Polycrystalline-silicon thin film transistors have been assessed using current based deep level transient spectroscopy. A continuous distribution of states was observed through the bad gap with a high density of tail states near the conduction band edge. Hot carrier stressing was shown to produce a spatially non-uniform increase in the density of states at the drain end of the device View full abstract»

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  • Thermionic-diffusion of minority carriers in polysilicon emitters

    Publication Year: 1993 , Page(s): 12/1 - 12/4
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    A modified analysis has been developed to study the hole current through an n-type polysilicon emitter of a Bulk Unipolar (Barrier) Transistor BU(B)T. A serial mechanism of both the thermionic-emission at the poly-monosilicon interface and the diffusion at the BU(B) side of the structure, has been considered in developing the minority-carrier transport equation View full abstract»

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  • Small geometry effects on poly-Si gated MOSFET devices

    Publication Year: 1993
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    Summary form only given. The dependence of MOSFET threshold voltage VT on device length, L and width, W is described; V T is also a function of drain voltage, VDS and the slope of this function depends on the back surface bias, VBS. All these principal features of small geometry effects are explained in a non-mathematical fashion with diagrams of the fringing electrostatic field from the polysilicon gate electrode. Data on VT dependence on VDS and VBS are presented; even at an effective channel length as long as 3 microns a non-scaled device can have poor short channel performance with huge VT dependence on geometry and steep VT dependence on VDS View full abstract»

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  • Low temperature poly-Si technologies and comparison with high temperature poly-Si processes

    Publication Year: 1993 , Page(s): 16/1 - 16/4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (244 KB)  

    Polysilicon TFTs in combination with liquid crystals can be used for direct view LCDs as well as for projection displays. With glass substrates a low temperature process (T⩽630°C) has to be used. The authors discuss the formation poly-Si thin films, gate insulator, source and drain formation, and H passivation View full abstract»

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  • Hot carrier induced degradation in polycrystalline silicon TFTs: experimental and theoretical analysis

    Publication Year: 1993 , Page(s): 25/1 - 25/4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (244 KB)  

    The application of bias-stresses with high source-drain voltage and different gate voltages produces in polycrystalline silicon thin-film transistors marked modifications both in the off-current as well as in the device transconductance. These effects have been explained in terms of hot-carrier effects related to a combination of charge injection into the gate insulator and formation of interface states near the drain View full abstract»

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  • Polysilicon thin film transistors for isolated protection circuits within an insulated gate bipolar transistor process

    Publication Year: 1993 , Page(s): 13/1 - 13/4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (180 KB)  

    The authors investigate the processing of polysilicon thin film transistors of a type suitable for merging with silicon power devices such as DMOSTs and IGBTs. They find it is possible to make such devices with a performance about one tenth that of the equivalent single crystal device. Complementary field effect transistors can be made without undue process complication. They are confident that these possibilities create new opportunities for power devices with increased functionality View full abstract»

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  • A comparison of polysilicon produced by excimer laser and furnace crystallisation of hydrogenated amorphous silicon (a-Si:H)

    Publication Year: 1993 , Page(s): 17/1 - 17/4
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    The authors report on the electronic properties of polysilicon produced by furnace and excimer laser crystallisation of undoped hydrogenated amorphous silicon (a-Si:H). The degree of amorphisation and average grain size are determined by UV reflectivity and electron microscopy respectively. A maximum areal grain size of 0.4 μm2 is obtained for furnace crystallised polysilicon, a lower value of 0.1 μm2 is observed in excimer (ArF) laser crystallised polysilicon. Optical absorption, DC conductivity and transient photoconductivity (TPC) measurements are employed to investigate carrier transport mechanisms. These are found to exhibit many qualitative similarities to those observed in amorphous semiconductors. The authors present a brief overview of their main findings to date View full abstract»

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  • The design, fabrication and performance of digital poly-Si thin film transistor circuits on glass

    Publication Year: 1993 , Page(s): 27/1 - 27/5
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (196 KB)  

    The author presents results of some digital CMOS circuits which were fabricated using a low temperature process. All the results presented were obtained on devices and circuits fabricated on glass substrates. The active layer of the transistor was 1500 Å of undoped polysilicon, formed by deposition of a-Si (using a Rytrak LPCVD reactor) onto Hoya NA40 glass substrates, followed by a crystallisation anneal at 600°C. The gate and passivation insulators were SiO2 , deposited by APCVD. Phosphorus and boron implants were performed after patterning of the poly-Si gate so as to obtain self-aligned NMOS and PMOS TFTs. The TFTs were completed with aluminium metallisation. ITO was used for the pixel electrodes and columns. Plasma hydrogenation was not used. Circuit measurements were carried out on four batches, with average TFT parameters as follows: threshold voltages and mobilities were 11.5 V and 27 cm2/V/s for NMOS and -17.5 V and 29 cm2/V/s for PMOS devices. Transfer characteristics currently obtained on this process when optimised for on-current are shown View full abstract»

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