Kenichi Yanai

Threshold voltage shift of amorphous silicon thin‐film transistors by step doping

The threshold voltage (VT) shift of hydrogenated amorphous silicon thin‐film transistors (a‐Si:H TFTs) by boron doping has been investigated. In TFTs with a uniformly doped structure (SiN/B‐doped a‐Si:H), VT shifts to a positive voltage by boron doping, while the field‐effect mobility decreases markedly. By using a step‐doped structure (SiN/undoped a‐Si:H/B‐doped a‐Si:H), the degradation of the field‐effect mobility by boron doping becomes less than that of a uniformly doped TFT with the same VT shift, and a VT shift of 3.5 V was obtained without degradation of the field‐effect mobility.

Dependence of thermal stability of NiSi and Ni(Pt)Si /Si on crystal orientation

We report NiSi and Ni(Pt)Si films with excellent thermal stability showing a particular crystal orientation on Si(001). The Ni-silicide film with a deposition temperature of about 200 °C consists of a conformal domain structure. We examined detail crystallographic analysis of silicide and clarified the psudo-epitaxial growth of NiSi(202)//Si(220) [or NiSi(211)//Si(220)] was the key scheme of superior thermal stability. By using this optimized Ni-silicide formation process, we have fabricated Ni-silicide that is thermally stable up to 650 °C and shows low fluctuation in sheet resistance and low leakage current in electrical measurements. This process is a promising candidate for future silicidation technology.

Noncrossing TFT matrix with reduced dc level shift and crosstalk

— A noncrossing TFT matrix and drive scheme that eliminates dc level-shift differences among data and reduces crosstalk without a storage capacitor is proposed. To compensate for the dc level shift, an extra TFT is added to each pixel. By applying a compensation pulse to the TFT, the dc level-shift differences among data are reduced to less than 0.01 V. The compensating TFT also provides redundancy. The peak-to-peak data voltage amplitude is lowered by changing the reference voltage according to the LC cell voltage polarity. By using the lowered data voltage and the shielded reference bus structure, crosstalk is reduced sufficiently to allow for 64 gray levels.