Raised Source/Drain (RSD) and Vertical Lightly Doped Drain (LDD) Poly-Si Thin-Film Transistor

The raised source/drain (RSD) structure is one of thin film transistor designs that is often used to improve device characteristics. Many studies have mentioned that the high impact ionization rate occurring at a drain side can be reduced, owing to a raised source/drain area that can disperse the drain electric field. In this study, we will discuss how the electric field at the drain side of an RSD device is reduced by a vertical lightly doped drain (LDD) scheme rather than a RSD structure. We used different raised source/drain forms to simulate the drain side electric field for each device, as well as their output characteristics, using Integrated Systems Engineering (ISE-TCAD) simulators. Different source and drain thicknesses and doping profiles were applied to verify the RSD mechanism. We found that the electric fields of a traditional device and uniform doping RSD structures are almost the same (similar to 2.9 x 10(5) V/cm). The maximum drain electric field could be reduced to similar to 2 x 10(5) V/cm if a vertical lightly doped drain RSD scheme was adopted. A pure raised source/drain structure did not benefit the device characteristics if a vertical lightly doped drain design was not included in the raised source/drain areas.

Automated summary

The study discussed how the electric field at the drain side of an RSD device can be reduced by adopting a vertical lightly doped drain (LDD) scheme instead of a pure raised source/drain structure. Different device structures were simulated to compare their impact on electric field and output characteristics, revealing that the vertical lightly doped drain RSD scheme can effectively reduce the drain electric field.