Nominanda, Helinda (2008-08). Amorphous silicon thin film transistor as nonvolatile device.. Doctoral Dissertation. Thesis uri icon

abstract

  • n-channel and p-channel amorphous-silicon thin-film transistors (a-Si:H TFTs) with copper electrodes prepared by a novel plasma etching process have been fabricated and studied. Their characteristics are similar to those of TFTs with molybdenum electrodes. The reliability was examined by extended high-temperature annealing and gate-bias stress. High-performance CMOS-type a-Si:H TFTs can be fabricated with this plasma etching method. Electrical characteristics of a-Si:H TFTs after Co-60 irradiation and at different experimental stages have been measured. The gamma-ray irradiation damaged bulk films and interfaces and caused the shift of the transfer characteristics to the positive voltage direction. The field effect mobility, on/off current ratio, and interface state density of the TFTs were deteriorated by the irradiation process. Thermal annealing almost restored the original state's characteristics. Floating gate n-channel a-Si:H TFT nonvolatile memory device with a thin a- Si:H layer embedded in the SiNx gate dielectric layer has been prepared and studied. The hysteresis of the TFT's transfer characteristics has been used to demonstrate its memory function. A steady threshold voltage change between the "0" and "1" states and a large charge retention time of > 3600 s with the "write" and "erase" gap of 0.5 V have been detected. Charge storage is related to properties of the embedded a-Si:H layer and its interfaces in the gate dielectric structure. Discharge efficiencies with various methods, i.e., thermal annealing, negative gate bias, and light exposure, separately, were investigated. The charge storage and discharge efficiency decrease with the increase of the drain voltage under a dynamic operation condition. Optimum operating temperatures are low temperature for storage and higher temperature for discharge. a-Si:H metal insulator semiconductor (MIS) capacitor with a thin a-Si:H film embedded in the silicon nitride gate dielectric stack has been characterized for memory functions. The hysteresis of the capacitor's current-voltage and capacitance-voltage curves showed strong charge trapping and detrapping phenomena. The 9 nm embedded a-Si:H layer had a charge storage capacity six times that of the capacitor without the embedded layer. The nonvolatile memory device has potential for low temperature circuit applications.
  • n-channel and p-channel amorphous-silicon thin-film transistors (a-Si:H TFTs)

    with copper electrodes prepared by a novel plasma etching process have been fabricated

    and studied. Their characteristics are similar to those of TFTs with molybdenum

    electrodes. The reliability was examined by extended high-temperature annealing and

    gate-bias stress. High-performance CMOS-type a-Si:H TFTs can be fabricated with this

    plasma etching method.

    Electrical characteristics of a-Si:H TFTs after Co-60 irradiation and at different

    experimental stages have been measured. The gamma-ray irradiation damaged bulk

    films and interfaces and caused the shift of the transfer characteristics to the positive

    voltage direction. The field effect mobility, on/off current ratio, and interface state

    density of the TFTs were deteriorated by the irradiation process. Thermal annealing

    almost restored the original state's characteristics.

    Floating gate n-channel a-Si:H TFT nonvolatile memory device with a thin a-

    Si:H layer embedded in the SiNx gate dielectric layer has been prepared and studied. The

    hysteresis of the TFT's transfer characteristics has been used to demonstrate its memory function. A steady threshold voltage change between the "0" and "1" states and a large

    charge retention time of > 3600 s with the "write" and "erase" gap of 0.5 V have been

    detected. Charge storage is related to properties of the embedded a-Si:H layer and its

    interfaces in the gate dielectric structure. Discharge efficiencies with various methods,

    i.e., thermal annealing, negative gate bias, and light exposure, separately, were

    investigated. The charge storage and discharge efficiency decrease with the increase of

    the drain voltage under a dynamic operation condition. Optimum operating temperatures

    are low temperature for storage and higher temperature for discharge.

    a-Si:H metal insulator semiconductor (MIS) capacitor with a thin a-Si:H film

    embedded in the silicon nitride gate dielectric stack has been characterized for memory

    functions. The hysteresis of the capacitor's current-voltage and capacitance-voltage

    curves showed strong charge trapping and detrapping phenomena. The 9 nm embedded

    a-Si:H layer had a charge storage capacity six times that of the capacitor without the

    embedded layer. The nonvolatile memory device has potential for low temperature

    circuit applications.

publication date

  • August 2008