Won-Kyu Park

A new charge pumping model considering bulk trap states in polysilicon thin film transistor

Abstract This paper proposes a new charge pumping model (bulk state model) in a polysilicon thin film transistor. The charge pumping current is calculated both from the bulk state model and the conventional model (interface state model) and each of them is compared with the measured data. In the bulk state model, the threshold voltage is defined as the gate voltage when the trapping time constant, which is a function of free electron concentration, is equal to the applied gate-pulse width. By applying this definition to each depth, the threshold voltage can be calculated as a function of depth. The threshold voltage shift is also taken into account to calculate the threshold voltage. From the threshold voltage, two associated emission energy levels are calculated. On the basis of the data from the field-effect conductance method, we assume that the trap distribution function is composed of two tails and two Gaussian functions. For each depth, the charge pumping current density is calculated by integrating the trap distribution function between two emission energy levels in silicon band gap. The charge pumping current is calculated by integrating the charge pumping current density with respect to depth. It shows that the calculated current of the bulk state model is more consistent with that of the measured rather than that of the interface state model.

High temperature cracking of tungsten polycide films on quartz substrate

Abstract Investigation of high temperature cracking of tungsten polycide films on quartz reveals that the average thermal expansion mismatch stress and process-related local stress due to the interfacial roughening and voids may be major factors generating cracks in tungsten silicide. The silicide reaction and silicon crystallization at high temperature are responsible for interfacial roughening in silicon-rich silicide (WSix>2.3)and local voids in tungsten-rich silicide (WSix

Ge nanopillar solar cells epitaxially grown by metalorganic chemical vapor deposition

Radial junction solar cells with vertically aligned wire arrays have been widely studied to improve the power conversion efficiency. In this work, we report the first Ge nanopillar solar cell. Nanopillar arrays are selectively patterned on p-type Ge (100) substrates using nanosphere lithography and deep reactive ion etching processes. Nanoscale radial and planar junctions are realized by an n-type Ge emitter layer which is epitaxially grown by MOCVD using isobutylgermane. In situ epitaxial surface passivation is employed using an InGaP layer to avoid high surface recombination rates and Fermi level pinning. High quality n-ohmic contact is realized by protecting the top contact area during the nanopillar patterning. The short circuit current density and the power conversion efficiency of the Ge nanopillar solar cell are demonstrated to be improved up to 18 and 30%, respectively, compared to those of the Ge solar cell with a planar surface.

A new charge pumping model for polysilicon thin film transistors

A charge pumping model considering bulk states in polysilicon thin film transistors has been developed. Here, we define the threshold voltage as a minimum voltage to fill the untrapped states within an applied pulse width. And the threshold voltage including the emission energy level was obtained as a function of depth. It shows that the calculated current of this model is more consistent with the measured one rather than the current or interface state model.