Mutsuko Hatano

Daiwa House Central Research Laboratory, Edo, Tōkyō, Japan

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Publications (29)27.28 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We have developed bottom-gate amorphous-oxide TFTs with ZTO/ITO channel layers. The fabricated ZTO/ITO-TFTs demonstrated that threshold voltage (Vth) dispersion for TFTs with channel thickness dispersion was smaller one order of magnitude than that of conventional TFTs. Afield effect mobility of 52 cm2/Vs was obtained.
    SID Symposium Digest of Technical Papers. 05/2010; 41(1).
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    ABSTRACT: The degradation characteristics of n- and p-channel polysilicon thin-film transistors (TFTs) under circuit operation were investigated by using CMOS inverter circuits consisting of n-channel TFTs with a lightly doped drain (LDD) structure and p-channel TFTs with a single-drain (SD) structure. A new test element made it possible to separately evaluate the degradation characteristics of each type of TFT during CMOS inverter operation. In regard to n-channel LDD TFTs, the device degradation is mainly caused by accumulated dc stress under the condition that the gate voltage is near the threshold voltage and the high drain voltage, i.e., the drain-avalanche hot-carrier (DAHC) stress condition. In p-channel SD TFTs, the device degradation is caused by the mutual interaction between DAHC stress and negative-bias-temperature (NBT) stress. Hole injection due to NBT stress is accelerated by DAHC-stress-induced trapped electrons under inverter-circuit operation. The effect is thus enhanced not only by the increase in the number of hole injections but also by the increase in the number of electron injections. It was found that the device characteristics of p-channel TFTs are more rapidly degraded as the rising time of the input pulse becomes shorter. This degradation is caused by the transient increase in the number of hot electrons, which are generated when holes are emitted from the trap states when the p-channel TFTs are turned off.
    IEEE Transactions on Electron Devices 03/2010; · 2.06 Impact Factor
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    ABSTRACT: The temperature dependence of the performance and hot-carrier instability of excimer-laser-crystallized low-temperature polycrystalline silicon thin-film transistors (TFTs) is described. The dependence of the TFT's performance on temperature indicates three characteristics: 1) electron mobility decreases with decreasing temperature, whereas the hole mobility is temperature independent; 2) off-leakage current decreases with decreasing temperature; and 3) threshold voltage increases with decreasing temperature. To consider the origin of the temperature dependence of the threshold voltage, estimation using the trap state density obtained by capacitance-voltage analysis is carried out. The main origin is concluded to be the change in the density of occupied defect states owing to the temperature dependence of the Fermi level. Contrary to the mobility, current under the drain-avalanche hot-carrier stress is found to be higher in a cold environment. The more serious current degradation after the stress in a cold environment is attributable to the reduced scattering of hot carriers owing to less lattice vibration.
    Japanese Journal of Applied Physics 01/2010; 49(8). · 1.07 Impact Factor
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    ABSTRACT: — A flexible-printed-cable (FPC) free liquid-crystal-display (LCD) panel by using a capacitive-coupling technique has been developed. A QQVGAeight-color image was successfully displayed for the first time without attaching any signal or power cables to the panel. The receiving circuitry and capacitive-coupling electrodes were integrated on the LCD panel using a low-temperature polysilicon (LTPS) fabrication process. In the proposed digital coding method, the receiving circuit converts derivative waveform signals via the capacitive coupling to conventional logic-level signals. The maximum data rate of 2.4-Mbps × 3ch (RGB) was achieved. In addition, LTPS low-capacitance diode bridge and regulator enabled us to obtain stable DC power of 2.4 mW on the panel from the AC-power signal. This study is the first step towards integrating the wireless-communication function on the display panel to achieve a high-value-added flat-panel display (FPD).
    Journal of The Society for Information Display - J SOC INF DISP. 01/2010; 18(6).
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    ABSTRACT: A model for predicting on-current degradation caused by drain-avalanche hot carriers in NMOS low-temperature polysilicon thin-film transistors (TFTs) is described. The amount of trapped charge caused by hot-carrier stress was estimated by using a model describing the lightly doped drain region as an imaginary TFT, and it was found that the amount of trapped charge saturates as voltage-stress time passes. Moreover, the on-resistance increase caused by the trapped charge could be expressed as a function of voltage-stress time (t) , stress drain current (I<sub>d_str</sub>), and stress drain voltage (V<sub>d_str</sub>), i.e., DeltaR<sub>on</sub> = I<sub>d_str</sub> exp(-beta/ V<sub>d_str</sub>) At<sup>B</sup>. This function can be used to predict the on-current degradation of TFTs after a long time for various gate lengths, operation voltages, and crystallinities of polysilicon.
    IEEE Transactions on Electron Devices 02/2009; · 2.06 Impact Factor
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    ABSTRACT: A polysrystalline silicon (poly-Si) layer prepared by selectively enlarging laser crystallization (SELAX) was post-annealed by excimer laser irradiation. The average grain width increased 26% because of partly merged grains, while the morphological trace of the laterally grown poly-Si layer was maintained. The difference in field-effect mobility resulting from thin-film-transistor (TFT) configuration was reduced by post-annealing. The field-effect mobility of TFTs parallel to the lateral growth direction decreased slightly (within 4.5% for n-type and 11.5% for p-type). On the other hand, TFTs configured perpendicular to the lateral growth direction increased as the energy density during post-annealing increased (up to 200% for both types). For n-type TFTs these results were attributed to the increase of the effective width of the grain and the reduction of the density of trapping states at grain boundaries.
    Japanese Journal of Applied Physics 08/2008; 47(8):6217-. · 1.07 Impact Factor
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    ABSTRACT: We have developed a FPC-free LTPS-LCD panel with capacitive coupling and displayed a QQVGA-eight color static image for the first time, by utilizing our proposed digital coding architecture and LTPS low capacitance diode-bridge. The maximum data-rate of 2.4 Mbps × 3ch(RGB) and the power of 2.5 mW on the panel were obtained.
    SID Symposium Digest of Technical Papers 01/2008; 39(1).
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    ABSTRACT: The degradation mechanism in p-channel polysilicon thin-film transistors under negative-bias temperature (NBT) stress and pulse stress, which alternates NBT stress and drain-avalanche hot carrier (DAHC) stress, was investigated. An analysis of recovery effects and activation energy suggests that the device degradation under dc-NBT stress is explained by a reaction-diffusion model and limited by hydrogen diffusion. These features are also observed in the case of the device degradation under pulse stress. Pronounced degradation occurs not after DAHC stress application (electron injection) but after NBT stress application (hole injection). NBT stress degradation is locally accelerated after DAHC stress application because the effective gate voltage negatively increases due to trapped electrons during DAHC stress. The trap states and positive charges that were generated by this accelerated NBT stress are considered to be the main cause of device degradation under pulse stress.
    IEEE Transactions on Electron Devices 10/2007; · 2.06 Impact Factor
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    ABSTRACT: A unified model and a prediction technique for on-current degradation in NMOS low-temperature poly-Silicon thin-film transistors are presented. The resistance increase is expressed as a function of the stress-drain current and stress-drain voltage. This function is independent of the size, crystallinity, or initial characterization of the transistors. The turnaround time for circuit design can be shortened by using this technique.
    SID Symposium Digest of Technical Papers 01/2007; 38(1).
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    ABSTRACT: Pronounced device degradation and temperature dependence of p-channel polycrystalline silicon thin-film transistors (polysilicon TFTs) under pulse stress were investigated. This device degradation is due to the trap states produced by repetition between electron injection and hole injection. The analysis of activation energy affirms that the rapid degradation at high temperature is caused by an increase in the number of trapped holes, to which the negative-bias-temperature stress significantly contributes. The degradation is strongly dependent on the duration of hole injection and the location of the hole-injection region. To produce highly reliable TFT circuits, it is thus important to shorten the duration of hole injection and separate the region of hole injection from that of electron injection
    IEEE Transactions on Electron Devices 10/2006; · 2.06 Impact Factor
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    ABSTRACT: Trap-density analysis of laterally grown polysilicon films formed by continuous-wave laser revealed the main factor that controls the subthreshold property of low-temperature polysilicon thin-film transistors. In the low-current region, traps at the gate oxide/polysilicon interface are charged and the consequent insensitiveness of polysilicon surface potential to gate bias dominates the subthreshold property. In the higher current region, that is, close to the threshold voltage, a transport mechanism in which carriers are scattered at the grain boundaries becomes the dominant factor governing the subthreshold property.
    IEEE Electron Device Letters 05/2006; · 2.79 Impact Factor
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    ABSTRACT: High-resolution (>300 ppi) system-in-displays have been developed by using mixed low-voltage/high-voltage poly-silicon TFTs. That is, ELC TFTs are used for the display circuits with high-voltage endurance, and SELAX TFTs are used for the low-power, high-performance display circuits. In this hybrid TFT, the SELAX TFTs successfully integrate reliability with high current drivability.
    SID Symposium Digest of Technical Papers 01/2005; 36(1).
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    ABSTRACT: Selectively enlarging laser crystallization (SELAX) has been proposed as a new crystallization process for use in the fabrication of thin-film transistors (TFTs). This method is capable of producing a large-grained and flat film of poly-Si. The average grain size is 0.3×5 μm, and the surface roughness of the poly-Si layer is less than 5 nm. The TFTs fabricated with this method have better performance and are more uniform than those produced with the conventional excimer laser crystallization (ELC) method. The average values of field-effect mobility are 440 cm<sup>2</sup>/Vs (n-type), and 130 cm<sup>2</sup>/Vs (p-type). The subthreshold slope for both types is 0.20 V/dec. Values for standard deviation of threshold voltage are 0.03 V (n-type) and 0.20 V (p-type). The delay time of the CMOS-inverter of SELAX TFTs is less than half that of ELC TFTs.
    IEEE Transactions on Electron Devices 07/2004; · 2.06 Impact Factor
  • Solid State Phenomena. 01/2003; 93:185-190.
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    ABSTRACT: We have developed a new crystallization technique using the EO-modulated CW-laser (LD-pumped Nd:YVO4 SHG lambda=532nm). Enlarging of lateral crystallization is attained by rapid laser-scanning on Si surface where the large (4mum × 0.5mum in average) columnar grains are uniformly obtained. Sequential and step-by-step scanning makes large crystallization areas. During the each scanning, the irradiation is frequently suspended by pulse-like modulation. By using this technique, in-plane tensile strain in the irradiated areas is relieved. The size and the crystal orientation ({110} normal to the substrate and {100} normal to the growth direction) of obtained grains are, therefore, rather homogeneous. We have developed the crystallization technique, which can obtain high crystal quality as well as large grains in the selected areas. We have fabricated TFTs (typically W/L=4mum/2-4mum, tox=100nm, tSi=50nm) in the irradiation areas on the glass-substrate. The field-effect mobility is 480 cm2/Vs for n-channel devices and 130 cm2/Vs for p-channel devices, respectively. The sub-threshold swing (S-value) is less than 0.2 V/dec for both types. This technology gives possibility to integrate electronic systems on the glass.
    Proc SPIE 01/2003;
  • Hyomen Kagaku 01/2003; 24(6):375-382.
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    ABSTRACT: The thermal conductivity of amorphous silicon thin films is determined by using the non-intrusive, in situ optical transmission measurement as well as by the 3ω method. The temperature dependence of the film complex refractive index is determined by spectroscopic ellipsometry. The acquired transmission signal is fitted with predictions obtained by coupling conductive heat transfer with multi-layer thin film optics in the optical transmission measurement. The results of the two independent methods are in close agreement.
    International Journal of Heat and Mass Transfer 06/2002; 45(12):2439-2447. · 2.52 Impact Factor
  • Mutsuko Hatano, Takeo Shiba, Makoto Ohkura
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    ABSTRACT: A novel method for laser-recrystallized poly-Si layer formation is proposed. The pulse-duration-controlled solid-state laser is utilized to enhance the lateral crystal growth, and an excimer- laser-crystallized poly-Si layer is used as a precursor. The validity of the method is confirmed by superior TFT characteristics of high field-effect mobility (n-ch TIT:μ > 460 cm2/Vs, p-ch TFT: μ > 150 cm2/Vs) with low threshold voltage deviation (Vth: 3 σ < 0.25 V).
    SID Symposium Digest of Technical Papers 01/2002; 33(1).
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    ABSTRACT: A new double laser recrystallization technique that can produce lateral grains of tens of micrometers is presented. A nanosecond laser (excimer or Nd:YLF laser) and a pulse modulated ArPLU laser are used in the experiment. The effect of different parameters on lateral grain growth is investigated. These parameters include the time delay between the two lasers, the excimer laser fluence, the ArPLU laser power and the pulse duration. This process has wide process window and is insensitive to both the excimer laser fluence and the ArPLU laser power fluctuations. Preheating and melting of the a-Si film with the ArPLU laser before firing the excimer laser is found to be necessary for inducting lateral grain growth. The transient excimer laser irradiation is believed to generate nucleation sites for initiating the subsequent lateral grain growth. The solidification dynamics of the process is probed by high spatial and temporal resolution laser flash photography. A lateral solidification velocity of about 10m/s observed.
    Proc SPIE 01/2002;
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    ABSTRACT: Summary form only given. The pulsed laser-induced recrystallization of thin semiconductor films on amorphous substrates can have major potential applications in the fabrication of thin film transistors (TFTs) for high-definition active matrix liquid displays. For nanosecond pulses, the process is driven by rapid melting and resolidification. The associated heat transfer and phase-change thermodynamics have been studied by a variety of in situ diagnostics of nanosecond temporal resolution, including time-resolved optical transmission, reflection, multi-wavelength emission, and transient electrical conductance measurements. It was found that the recrystallized material structure critically depends upon the laser fluence (i.e. the pulse energy per unit surface area) and the melt quench rate which is determined by the heat loss to the substrate.The objective of the present work is to identify and investigate the fundamental mechanisms of phase-transformations at extremely fast rates. To accomplish this, 100 nm-thick amorphous silicon (a-Si) films deposited by low-pressure chemical-vapor deposition
    Lasers and Electro-Optics, 2001. CLEO '01. Technical Digest. Summaries of papers presented at the Conference on; 02/2001

Publication Stats

134 Citations
27.28 Total Impact Points


  • 2002–2010
    • Daiwa House Central Research Laboratory
      Edo, Tōkyō, Japan
  • 2000–2009
    • Hitachi, Ltd.
      • Central Research Laboratory
      Tokyo, Tokyo-to, Japan
  • 1999–2002
    • University of California, Berkeley
      • Department of Mechanical Engineering
      Berkeley, CA, United States