The Non-volatile Capacitorless Memory by Poly-Si Thin Film Transistors
Date Issued
2009
Date
2009
Author(s)
Chen, Yen-Ting
Abstract
In recent years, low temperature polycrystalline silicon thin film transistors (LTPS TFTs) have been widely used in flat panel display driving circuit. The a-Si film is recrystallized to the poly-Si film by excimer laser crystalline method and achieves the advanced display technology. First, we will discuss the basic model and current conduction mechanism of grain boundaries in the poly-Si film. Due to the influence of grain boundaries, the subthreshold characteristics are explained by the gate and drain induced barrier lowering. The leakage current is also investigated by trap generation and emission in the drain depletion region. A novel capacitor-less random access memory has been developed in recent years and used in the storage devices. This memory exhibits data remanence, but is still volatile in the conventional sense that data is eventually lost when the memory is not powered. The nonvolatile memory is utilized extensively in the electronic systems because of its long retention time and low power consumption. Therefore, we constructed a new memory device which is compatible with TFT fabrication processes. The new operation mode is to realize the memory characteristics by operating the poly-Si TFTs in the accumulation region. The application of capacitorless non-volatile memory based on poly-Si TFTs shows more advantages, such as low operation current, long retention time, low power consumption, and excellent endurance characteristics. Finally, drain avalanche hot carrier stress of n-channel TFTs is investigated. This degradation depends with the drain stress voltage, channel length and stress temperature. The stress-induced degradation in the on-state current may be attributed to the hot carriers inject into the grain boundaries to create amount defect states. The threshold voltage shift can be explained that the hot carriers inject to the interface and create the negative interface states. The reliability issue must be taken into consideration for process and circuit design.
Subjects
thin film transistors
grain boundary
capacitorless memory
non-volatile memory
avalanche effect
Type
thesis
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